Advances in Structural Integrity for Mechanical, Civil, and Aerospace Applications

This paper deals with the modelling of load bearing capacity of bored-pile groups under the vertical eccentric load using Python. In many practical problems, the pile foundations of civil engineering structures (such as bridges, retaining walls, offshore structures) are frequently subjected to eccentric loads. There are two main tasks considered in the present work: (1) a group of equally spaced, identical piles subjected to an external moment vector, and (2) general case of a group of unevenly distributed and dissimilar piles. It is observed that the pile group subjected to vertical eccentric load failed by a cap rotation about the head of a pile and all piles within the group achieve the ultimate axial capacity in compression under the collapse mechanism. Finally, a wind turbine (with 95 m height) having a circular raft (with 16 bored piles, 22 m long, 0.8 m diameter) is modelled in the present work considering typical sub-soil profile (consisting of a deep layer of over consolidated, inorganic silty clay of high plasticity up to a depth of about 15 m with the ground water table 2.0 m from the ground level) and estimated the undrained shear strength in the intermediate layer and in the lower stiff clay. The authors will optimise the pile group under eccentric loading for the cost–benefit analysis.

Concrete is widely used as a construction material; due to its heterogeneous behavior, the service life of the structures becomes crucial so as to avoid the sudden brittle failures. Fracture in concrete is accompanied by emergence and evolution of an inelastic zone, fracture process zone (FPZ), around the crack tip. Inside this FPZ, many mechanisms occur: crack blunting, aggregate bridging, and microcracking, which prevent brittle failure. The softening of stress–strain curve in post-peak region and the size-effect phenomena is attributed due to the existence of this FPZ. As the size of FPZ influences the toughness of concrete—larger the FPZ, higher will be toughness; it becomes necessary to quantify the length and width of FPZ. Till now, the research was primarily focused on the length of fully developed FPZ. However, for better insight into the crack growth, an accurate prediction of FPZ size is necessary. Hence, precise quantification of width is also important. In this work, an attempt has been made to estimate the width of fracture process zone using v-displacement data of digital image correlation (DIC). The study aims to propose a methodology to find the FPZ width in plain concrete members. The maximum FPZ width for monotonic loading is estimated for geometrically similar beam samples. The proposed methodology has been verified against the existing literature on other non-contact techniques, and a good agreement has been found between them.

Composite stiffened panels are widely used in numerous components of aircraft. Stiffeners can recover stability and stiffness efficiently with less gain in the structure’s weight when compared to increasing plate thickness. In this paper, finite element analysis of stiffened panels made of composite is carried out using ABAQUS. Damage analysis within the plies is performed by implementing progressive damage modelling based on Hashin’s criteria. The initiation and evolution of the adhesive layer damage are modelled using cohesive zone modelling. A convergence study is conducted to find the optimal mesh size. Next, a parametric study is carried out by varying stiffener sections such as T, I, and C. The failure load and the post-buckling stiffness of the structure are taken as performance examiners to evaluate the concert of each stiffener. In this work, optimization of the stiffened panel is carried out by using Rao-1 Algorithm. The optimal dimensions of the stiffener height, the distance between the stiffeners, the thickness of the stiffener, the height of the stiffener, and the thickness of the panel are estimated for the given specified panel size.

Beam definitions are used to simplify complex structures like bridges or skyscrapers. This study highlights the importance of monitoring beams as they are often the critical components and damage in them can result in changes in their dynamic characteristics. This study proposes a substructure-based approach for damage estimation in structural beams, that can later be extended for monitoring high-dimensional structures. The traditional approach of full structure monitoring mandates heavy instrumentation and computational costs. To avoid that, the existing subdomain estimation approaches need to deal with the quasi-static displacement at subdomain boundaries making the estimation a coupled problem. Instead, the proposed approach focuses on only monitoring a subdomain of interest, independently, making it computationally cheaper. The study employs an interacting filtering algorithm with Particle and Ensemble Kalman filters, circumventing the complexities of quasi-static displacement. The proposed approach has been tested numerically and the results are promising for further investigation and improvement.

Biological composite materials found in nature like nacre, shells of cephalopods, and woodpecker beaks possess superior mechanical properties compared to their simple constituents having weak mechanical properties. The weak suture interfaces present in these biological composite materials play a significant role in achieving excellent mechanical properties since they govern the deformation and fracture mechanisms. These non-adhesive suture interfaces possess non-linear behaviour depending on friction and the geometrical interlocking. Bio-inspired sutured materials are developed by mimicking the excellent properties of biological materials. The geometry of a curved suture can be developed using the two-dimensional (2D) shape descriptor approach. In the present study, an elliptical geometry of the suture interface is proposed, and the analytical equations and finite element results are developed to capture the non-linear pullout response of the suture.

Carbon fiber-reinforced polymer (CFRP) composites have gained popularity in various fields owing to their strength, durability, and lightweight nature. CFRP is a fiber-reinforced composite material that employs carbon fiber as the primary structural component, making it suitable for aircraft components that require high strength, anisotropy, and thermal conductivity. For the components made from composite laminate, drilling is a crucial machining technique that requires particular attention. During drilling, maintaining processing quality is challenging due to the influence of drilling force, which can lead to delamination, tearing, and other defects. In this paper, we present a finite element analysis of the drilling process in carbon fiber composite and study its mechanical behavior. We developed a three-dimensional model of an M21/T700 carbon fiber-reinforced polymer and simulated the drilling process using Abaqus software. The various force components during drilling are analyzed and compared the stress and plastic equivalent strain incurred during the drilling process with the spindle speed and feed rate. This study can aid in selecting a spindle speed and feed rate combination that reduces the thrust force induced during drilling, preventing interlaminar and intralaminar failure modes at critical thrust forces. This, in turn, can assist in reducing the degradation and development of drilling tools and designing carbon fiber composite materials.

The optimization problem of the design of orthogrid-stiffened cylinder under combined axial force and external pressure is a complex problem. It involves finding the optimal layout of stiffening rings and stringers (number of rings and stringers which are discrete variables) and sizing of members and skin (continuous variables) while minimizing the mass of the stiffened cylinder and satisfying the buckling constraints. Also, the presence of multiple modes of buckling adds to the complexity of the optimization problem. Further, the design space is nonconvex with multiple local minima, and steps must be taken to avoid sub-optimal solutions. In this paper, a methodology for carrying out systematic optimization for the stiffened cylinder is presented. The optimization problem statement is defined as the minimization of mass with buckling load factor as the constraint, and two methods are presented to evaluate the buckling load. The first method is a simplified analytical method for evaluating individual buckling modes, and the second method is a high-fidelity method where buckling load is calculated using FEM. The optimization problem is solved using both methods. A comparison is made between the optimal solutions by the two fidelity models in terms of accuracy and cost. It is observed that the low-fidelity method is suited for preliminary calculations and screening the design space. The high-fidelity method gives an optimal solution which is having significant mass savings (28.13%) compared to results in the literature.

“Functionally graded materials” (FGMs) are becoming more popular owing to merits in their thermos-mechanical behaviour and performance. However, designing the systems made of FGM, considering the practical conditions such as thermal conditions, corrosive environments, manufacturing difficulties and manufacturing defects are still evolving. Present work is aimed at reviewing different design and modelling approaches suitable specifically to rotor systems made of “functionally graded” materials. Though research is picking up in this area, limited studies have been reported on FG rotors. A step-by-step concise information has been provided on every aspect of FGM related to rotor systems, which includes brief history of FGM, literature review of fabrication methods, applications of FGM, material modelling due to gradation of materials over the cross section of rotor, temperature variant material properties because of temperature distribution, analytical and finite element methods available to analyse rotor systems subjected dynamic loads, modelling and analysis of defects such as effect of corrosion, porosity and cracks in dynamic behaviour of rotor systems.

Brackets, crucial components in aerospace structures, serve the dual purpose of load transfer and mounting packages onto airframe shells. Achieving the delicate balance between minimizing mass and meeting stringent strength and stiffness requirements is a perennial design challenge. This paper details the optimization of brackets, employing solid modeling software for intricate design and ANSYS packages for rigorous analysis and optimization. The process integrates finite element analysis to assess structural integrity, topology optimization to refine material distribution, and parametric optimization to fine-tune geometric parameters. The resulting design achieves optimal efficiency within the constraints of confined space and attachment requirements dictated by various subsystems. Beyond optimization, the design undergoes thorough manufacturability scrutiny, considering material properties and fabrication processes. The successful realization of a prototype hardware validates the proposed methodology, showcasing a seamless transition from conceptualization to a technically robust and functional bracket design.

The innovations and advancements in composite materials have significantly been backed by the design of biological composites such as spider silk, nacre, bone, antler, and bamboo, owing to their magnificent mechanical properties. Even though the constituents at their basic level are weak, biological composites are characterized by superior mechanical properties like high toughness and strength which makes them unique. Bio-inspired composites, inspired by biological composites, are engineered by mimicking the essential features of the biological composites, which are responsible for their superior mechanical properties. These include geometric and material properties such as the aspect ratio of platelet, Young’s moduli ratio of platelet to the matrix, and the staggering and hierarchical arrangement of platelets. This study deals with the comparison of stress distribution in a multi-scale finite element model of a two hierarchical (2H) non-self-similar bio-inspired composite. The results of non-self similar composite which is a 2H Stairwise staggered composite with Regular staggered composite as platelets (SR) are compared with that of the models without hierarchy.

In past years, sensor-based health diagnostics have shown significant potential for electromechanical impedance (EMI) techniques with many practical implementations. In order to enhance the effectiveness of health monitoring systems, it is crucial to examine the bonding interface between the piezoelectric sensor (PZT) and the host structure. A promising approach to achieve this goal is the utilization of Sn–Ag bonding, which offers improved resistance to moisture, chemicals, and temperature compared to traditional epoxy adhesive bonding. The Sn–Ag bond layer presents a novel attachment method to the structural design, which may ultimately enhance the sensitivity of the health monitoring system. This study used EMI techniques to instrument a unique Sn–Ag alloy-based bond and compared it against an epoxy adhesive bond for better sensing and actuation. Later, both the bonds were cured, and the bond performances were analyzed through conductance and susceptance signatures. Moreover, three different bond layer damage conditions, i.e., incipient, moderate, and severe, were chosen to check the performance of the bond layer through admittance signatures. The EMI techniques rely on pristine data, which presents significant constraints when applied to pre-existing structures. Furthermore, the experimental results were used to predict baseline data through deep learning classifications, i.e., convolutional neural network (CNN), long short-term memory (LSTM), and CNN-LSTM hybrid model for all the bond layer damage conditions. The experimental results were compared against the chosen deep learning model for futuristic prediction. The efficiency of all the deep learning models is quantified using performance metrics like accuracy and R2 score. The present study demonstrates that the hybrid model yields superior performance compared to the other two models for predicting Sn–Ag and adhesive bond layer damage. The proposed framework aims to replace traditional optimization algorithms to achieve a more simplified effective prototype for the futuristic prediction of EMI signals.

Deep groove bearing is widely used in rotating machines as it can operate at a wide range of load and speed combinations. This article presents two simulation models for deep groove ball bearings. The first model of bearing is a 5-DOF system block diagram model developed using MATLAB Simulink environment and the second model of bearing is a detailed three-dimensional multi-body dynamic model of bearing where contact between races, slip and effects due to friction are taken into consideration and it is developed using multi-body simulation (MBS) software ADAMS. Different geometrical faults are given to the different parts of the bearing. Envelope analysis is done to the simulated signal and the result are than interpreted to find out the condition of bearing. These models of deep groove ball bearing elements can be integrated to different machine components to find the condition of industrial rotating machines.

Bulging instability is a mechanical failure that happens when a thin tube undergoes excessive localized deformation before ultimately failing. Understanding this process is crucial in ensuring the stability of various mechanical and biological systems, such as fluid-carrying rubber tubes and aneurysms in the human brains. In this numerical study, we used the finite element method and a hyperelastic material to simulate bulging instability in a closed-end tube. Our findings reveal that inflation only occurs when the internal pressure in the tube reaches a critical value, which depends on the tube's thickness but not its length. Further analysis of the poro-hyperelastic tube demonstrates that the presence of porosity lowers the critical pressure required for inflation by reducing the stresses in the tube material.

The deterioration of bone cartilage in hip joints caused by osteoarthritis and rheumatoid arthritis is the most prevalent cause of total hip replacement. The femoral stem in the implant is fixed to the bone at the time of surgery. It is coated with biocompatible ceramics such as hydroxyapatite (HAp) to enable faster bone growth. The coating experiences relative motion during the initial period, before sufficient bone growth occurs, and loosens in many cases. Suspension plasma-sprayed hydroxyapatite (HAp)-based coatings such as HAp/Titania on titanium substrates have been proven suitable for both mechanical properties and biocompatibility. Slip occurs primarily at the coating and metallic implant interface (the bonded interface), accelerating the coating damage due to fretting. The current investigation is directed at understanding the influence of assembly load, coating property, and delamination length on the interface strength between coating and implant. A two-dimensional finite element model of a 170 mm-long femoral stem coated with HAp/Titania coating is analyzed using commercial software. The geometrical model is like the original joint condition of the human hip implant. The numerical analysis showed that the first contact edge is where the most stress and contact slip happen because that is where the stress is concentrated during an assembly loading condition. The variation in load and contact slip conditions will result in coating failure in the implant.

Comparing other possible actuators for compliant mechanisms, shape memory alloy has an advantage in terms of compactness and the specific actuation energy. In this work, actuation capacity of an SMA wire under different prestressed condition has been studied. To perform this study, due to the elastic nature of the compliant mechanism, the mechanism has been modeled as a spring and considered the entire system to be a spring and SMA wire assembled in series. With a suitable constitutive model for SMA, the displacement of spring has been simulated for cyclic thermal loading. This analysis has been repeated for different prestressed condition. The simulation results show the strong dependence of prestressed value with the actuator displacement.

Fibre metal laminates (FMLs) are advanced multilayered composite materials. In recent days, the demand of using these materials increased rapidly in aerospace, structural and automotive industries due to their high strength and lightweight attributes. These FMLs may be subjected to various vibratory loads and prone to damages during their working condition; in the present work, a numerical comparative study between Glass-Aluminium-reinforced Laminates (GLARE) and Carbon-Aluminium-reinforced Laminates (CARALL) with 5 mm, 10 mm, 15 mm, 20 mm length cracks and without cracks is conducted under free vibration analysis; the effect of boundary condition on natural frequency is also studied. From the results, it is clearly noticed that CARALL exhibited higher natural frequency values when compared to GLARE. It may be due to high strength and stiffness nature of the carbon fibre. It is also depicted that, as the crack length increases at the fixed position the natural frequency for different modes decreases, which may be due to decrease in stiffness of the FML.

Finite element (FE) model updating is a framework for identification of FE model and its parameters consistent with the system measurements. For updating FE model with uncertain model parameters, the Bayesian model updating approach is widely adopted which uses probability logic for uncertainty quantification. This approach using modal data is conducted by mode matching or without mode matching approaches. Mode matching approach requires solving the eigenvalue problem and relative weighting factors for modal frequencies and mode shapes. Whereas, without mode matching approach adopts the eigenvalue equation instead of solving it and does not require weighting factors. Due to limitations in gathering data from the structure in a single setup, model updating can be performed using data from multiple setups. Sampling techniques are commonly adopted for generating samples from posterior distribution of model parameters and its statistics. Among various sampling techniques, Gibbs sampling is appropriate for multi-dimensional problems when conditional distributions are possible for the parameters. The present work aims to perform FE model updating using modal data from multiple setups. The effectiveness and efficiency of a modified Gibbs sampling method in Bayesian model updating are illustrated by 10 degrees of freedom (DOF) numerically simulated freedom (DOF) numerically simulated example.

The internal fluid pressure holding capacity of the isotropic toroidal pressure vessel (TPV) with a circular cross-section can be enhanced by the external wrapping of fiber-reinforced polymer (FRP) composites. An analytical solution for this metal-FRP hybrid TPV is not readily available. This study presents an approximate analytical solution to predict strains and stresses in the base metal and FRP layer in the metal-FRP TPV. The solution is derived based on modified-linear membrane theory (MLMT). This energy-based approach overcomes the deficiency of singular displacements commonly observed in a pure linear membrane theory. The solution considers an equivalent metal thickness for the FRP layer. The proposed solution is cross-verified with results of finite element analysis. Three-dimensional FE models were created and analyzed. Comparison of FE results with analytical predictions shows that the assumption of FRP as an equivalent isotropic material results in a more straightforward solution besides providing the better prediction of strains and stresses in the metal-FRP TPV.

Focused ultrasound (FUS) is an exciting and emerging technology that can ablate or fractionate tissues and is used to treat solid tumors alone or in combination with other therapies. FUS waves at the focus can produce shear waves that can be used to understand the stiffness of the tissue or track treatment progression or completion. Herein, using finite element model (FEM)-based simulations, we test multiple ultrasound frequencies at different focal pressures, producing shear waves in a nonlinear medium. We quantified the displacements and shear stress produced by the shear wave propagation. We observed that for the 0.75 MPa FUS transducer surface pressure, the peak shear stress production was substantially different between 250 and 500 kHz. Furthermore, the time to peak for shear stress waves was lower for the 250 kHz and 0.75 MPa conditions than the 1 MPa condition at 250 kHz and the 1 MPa condition at 500 kHz. In summary, we have developed a framework to evaluate the effect of different FUS transducers in producing shear waves in nonlinear media.

This work addresses the problem of identification of modal properties, namely partial modeshapes, damping ratios, and natural frequencies, of a non-classically damped system under ambient excitation using a Bayesian probabilistic method. Ambient vibration tests eliminate the need for expensive dynamic experiments which take a lot of time, require permission, and cause problems to people who avail the benefits of the structure. Under operating conditions, naturally occurring vibrations can be measured and subsequent modal identification can be performed. For a Multiple Degree of Freedom (MDOF) system, the first few modes make the greatest contribution to the structural response. The operational excitation is assumed to be broadband enough to excite the most important modes of the structure so that the response can be effectively used for modal identification. In this work, a probabilistic approach based on Bayesian inference is presented to identify the complex modal parameters of a linear MDOF structure using output-only response data in the time domain. Computational obstacles in the estimation of probabilities are also overcome by using an approximate expansion for the likelihood function. The effectiveness of the approach is tested on simulated response data from a 2-DOF system.

The existence of submerged components can significantly influence the seismic response of a liquid storage tank. Consequently, due to the modification of dynamic properties, the seismic behavior of liquid tank systems with internal components can be significantly benefited. In this research, a potential-based finite element technique has been adopted to study the slosh dynamics of a partially filled rigid rectangular container with a bottom-mounted submerged block under harmonic excitation. The liquid domain is governed by the Laplace equation where a velocity potential-based Galerkin’s approach is adopted for the liquid domain formulation. The obtained results of the developed finite element model are validated with the published results with a decent agreement. The phenomenal sloshing behavior of the base-isolated tank for different widths and depths of the block is emphasized in the present analysis by the application of the laminated rubber bearing. The parametric research of tank-liquid-block-isolation systems demonstrates the significance of varying dimensions of the submerged structural component.

A fundamental problem in mechanics of materials is homogenization which involves the calculation of the effective response of heterogenous materials. Mean field homogenization (MFH) methods are easy to setup, computationally cheap, and reasonably accurate making them quite attractive. However, there are persistent questions about their accuracy, physically admissibility, and versatility. In this paper, the experience of the co-authors over past 3 years is presented. MFH methods are studied from a wide range of perspectives from predictive abilities to confirming physically admissibility for a range of composites with varied fiber architectures. Algorithms are developed for microstructure generation with complex fiber architectures and finite element (FE) models are created by automation using python scripts. The MFH methods are benchmarked against the full FE solutions with comparisons at several length scales—effective modulus, stresses in individual inclusions and stresses in the interphase. Using this modus operandi, a wide range of MFH schemes is studied from full Mori–Tanaka (MT) formulation to pseudo-grain discretized version of MT to various multi-step MT formulations. It is concluded that each of the MFH variants is approximate with reasonable predictions for some microstructure and large errors for some microstructures. The accuracy of these methods decrease as the length scale of comparison is reduced. MFH methods are extended to model composites with discontinuous curved fibers which involve transformation of fibers to equivalent assembly of inclusions. An unbiased comparison formulation methodology is developed to validate the MFH methods involving transformation of fibers to equivalent assembly of inclusions.

Composite materials have been heavily used in major industrial applications like defence, automobiles and wind turbine blades for the past few decades due to their tailorability to meet specific design needs. The high-cost left-over prepreg (3–5% waste) during composite manufacturing is usually land-filled. These left-overs can be chopped into rectangular chips and, through random spatial distribution in the mould, can be compression moulded into flat, curved plates or any other complex structural part. These randomly oriented strands (ROS) reinforced transversely isotropic composite can replace conventional metals and unidirectional composite for aircraft’s secondary and tertiary loading components. In the present work, the stochastic spatial distribution of chips in compression moulded ROS reinforced composite is modelled through Representative Volume Element (RVE). The behaviour of ROS composite is analysed by performing finite element analysis. A continuum mechanics-based linear-elastic damage model is developed involving damage parameters to degrade the effective property of individual constituents of composite for constitutive material modelling through user material, UMAT in commercial finite element solver Abaqus/Standard. This work mainly focuses on failure in the constituents of the ROS composite. The four failure modes in the chip are longitudinal breakage, transverse splitting, in-plane and out-plane shear failure, and the failure mode in the matrix is isotropic. The uni-axial tensile loaded ROS reinforced composite shows transverse chip splitting and matrix failure as dominant modes of failure, which were in good agreement with the in-house experimental results.

Interconnected arches are conceived by fusing two or more planar arches at their centres; like the ribs of an umbrella. They offer three-dimensional structural robustness of shells and analytical simplicity of planar arches. Furthermore, just as an umbrella flips upside down in strong winds, interconnected arches are observed to be bistable. In this paper, a shallow interconnected bistable arch with pinned boundary conditions is subjected to a transverse load at the centre. We analytically model the resulting post-buckling behaviour and describe it by obtaining the force–displacement characteristics. The analytical model accounts for bending, compression, and torsional energies developed in the interconnected arch as it switches between its stable states. The bistable behaviour and dependence of the geometric parameters of the connected arch predicted by the analytical model are validated with the results from nonlinear finite element analysis and table-top experiments.

The computational cost in analyzing a dynamical system increases with the dimension of the model. This cost further increases where repeated solutions for different parameter values of the system are required, such as uncertainty quantification and optimization. In recent years, a proper orthogonal decomposition (POD)-based reduced order model (ROM) has been developed that reduces the cost significantly. This ROM is intrusive in nature, that is, it requires access to the computer codes used for solving the high-dimensional model. However, for many complex problems such as soil-structure interaction (SSI), such access is not available, which poses a limitation to the ROM. To address this issue, a non-intrusive ROM is developed in this work that does not require access to the source codes. The objective of this paper is to develop a non-intrusive ROM for SSI problems considering uncertainty in the excitations that can be further used for the uncertainty quantification of SSI under earthquake load or random excitations. This ROM is developed using deep neural networks. The application of neural networks makes the model learn features of an earthquake excitation efficiently. Finally, the accuracy of the proposed ROM is tested numerically on a beam on Winkler foundation.

The problem of random vibration analysis of gravity dam reservoir system subjected to spatially varying multi-component ground motion is considered. The work is done in two parts. First part deals with seismic wave propagation modelling in a three-dimensional elastic medium caused due to a seismic disturbance at a specified location in the interior. The disturbance is modelled as an effective point source of slip characterised by an impulsive double couple varying in time as a spatially localised infinite duration ramp function on the fault plane. A frequency domain wave propagation model that incorporates damping behaviour via a complex modulus representation is employed. The time domain representation is obtained further using Fourier integral. An ensemble of ground motions is simulated by treating various source parameters and properties of the intervening medium as uncertain. In the second part of work, governing equations for the dam reservoir system are formulated in which the ground motions derived in the previous step appear as boundary conditions. This set of equations is subsequently analysed using the finite element method to characterise the dynamic response of the system considering fluid structure interaction. This, in turn, forms the basis for investigating reliability of the dam structure with respect to a set of limit states. Furthermore, the analysis also leads to the determination of seismic fragility curves. While the problem of seismic response of dam reservoir system has been widely studied in the existing literature, present study permits us to examine the role played by spatial variability of support motion and their non-stationary and non-Gaussian features.

Hydrogels are three-dimensional network structures consisting of crosslinked polymer chains. When immersed in a solvent, hydrogels swell such that they retain the structural integrity due to presence of crosslinks. The elastic properties of hydrogels depend on the density of crosslinks: the higher the crosslink density, the stiffer the gel. They derive elastic properties from the polymer network and swelling properties from the migration of solvent molecules through the network. Due to high swellability and deformability, hydrogels have found applications in various engineering fields, such as drug delivery systems, tissue engineering, wound dressing, and soft actuators. We present here a continuum framework to describe the elastic responses of hydrogels undergoing finite deformations. An expression for free energy density of hydrogels has been utilised. Constitutive equations of hydrogels subjected to swelling are derived in a finite deformation framework. The model is calibrated by fitting the stress-strain curve of Polyrotaxane (PR) hydrogels in uniaxial tension. The results are verified with the available experimental results.

Permitting multiple materials within a topology optimization setting increases the search space of the technique, which facilitates obtaining relatively high-performing and efficient optimized designs. Structures with multiple materials involving fluidic pressure loads find various applications. However, dealing with the design-dependent pressure loads is challenging in topology optimization, which gets even more pronounced with a multi-material framework. This paper provides a density-based topology optimization method to design fluidic pressure loadbearing multi-material structures. The design domain is parameterized using hexagonal elements as they ensure nonsingular connectivity. Pressure modeling is performed using the Darcy law with a conceptualized drainage term. The flow coefficient of each element is determined using a smooth Heaviside function considering its solid and void states. The consistent nodal loads are determined using the standard finite element methods. Multiple materials are modeled using the extended SIMP scheme. Compliance minimization with volume constraints is performed to achieve optimized loadbearing structures. A few examples are presented to demonstrate the efficacy and versatility of the proposed approach. The optimized results contain the prescribed volume of different materials.

Present study reports the theoretically supported wind tunnel experimental investigations on the load distribution in a flapping wing under low amplitude flapping. Wind tunnel experiments are performed at 2, 4 and 6 m/s wind speed for hummingbird inspired nanocomposite wing. The spatial deformations fields are obtained from Digital image correlation (DIC). Modified Theodorsen lift theory is implemented to obtain load distribution from the local chord deformations to obtain aerodynamic loads. Three spatial locations at 25, 50 and 75% wing-span are considered for deformation data. The theoretical formulation was used to separate out the inertial and aerodynamic components of loads. Results reveal that the mid-stroke deformation mostly contributes for the aerodynamic lift, while all other deformation instants represent the dominance of inertial loads.

In recent years, the automotive and aerospace industries have accelerated interest in the use of advanced carbon fibre-reinforced composites as a primary structural material because of their great potential. However, unidirectional fibre-reinforced laminates have limitations such as low inter-laminar crack propagation resistance, low delamination resistance, low impact damage resistance, and poor post-impact damage tolerance due to the lack of through-thickness reinforcement. Z-pinning can overcome these problems as it is the only technique suitable for reinforcing prepreg laminates in the through-thickness direction. In the present study, the realistic RVE was generated from the idealization of the micro-structure. The finite element model was developed by considering a pure resin-rich region, an in-plane fibre waviness for 0.28 mm diameter, 2–5% volume fraction, and 90 $$^{\circ }$$ ∘ inclination angle of a Z-pin. A Continuum Damage Mechanics (CDM)-based damage model was developed to predict the micro-damage initiation based on the von Mises criterion for isotropic material failure and the Tsai–Wu criterion for transversely isotropic material failure. Further, a CDM-based isotropic hardening plasticity damage model for matrix material was developed to predict damage progression based on elasticity and plasticity governing equations (yield function, equivalent plastic strain, plastic flow law, plastic dissipation). The backward Euler and Newton’s methods are used to simplify the iteration algorithm. In addition to the theories and criteria that derive the damage process, the material properties/stiffness degradation method (MPDM) was carried out throughout the finite element analysis.

The spectral analysis of the structural waveguide leads to the dispersion relation, which shows the behavior of the different wave modes with frequency. It helps in ultrasonic-guided wave-based non-destructive inspection to choose an excitation frequency based on the choice of the excitation wave mode(s). The dispersion curves for a waveguide with simple defect-free geometry work well for their inspection. However, it’s important to note that the presence of defects within the structure can significantly affect the wave dispersion behavior used for diagnostics. Therefore, the use of the dispersion curves of the defect-free waveguide for the inspection of the defective ones can yield less accurate inspection results. This emphasizes the need to conduct the spectral analysis of the structural waveguide with defects and investigate the sensitivity of dispersion curves to various defect parameters such as shape, size, depth, and orientation. The dispersion curves can be obtained analytically or numerically, but they have inherent limitations. The analytical methods are limited to simple geometry; however, using the numerical methods for complex geometry will require a substantial computational cost. Therefore, this paper presents the spectral analysis of the three-dimensional structural waveguide with defects using the Semi-Analytical Finite Element Method, which uses the advantages of both analytical and numerical methods. We have performed the spectral analysis of the simple geometry without and with defects (such as cracks or delamination) of varying sizes. It is observed that the finite element discretization of the cross-section affects the number and accuracy of wave modes obtained in the dispersion curves. The validity of the SAFE framework has been initially established by comparing the dispersion curves obtained from our SAFE formulation with those generated by GUIGUW (Bocchini et al. 2011), an open-source dispersion computation software, for a defect-free structural waveguide. Subsequently, we applied our SAFE formulation to compute dispersion curves for waveguides with defects. As the defects reduce the structure’s stiffness, we observed a significant reduction in the cutoff frequencies of the higher-order wave modes in the dispersion curves for defective waveguides compared to the defect-free waveguide.

This paper deals with the modeling of beam–column connections in reinforced concrete (RC) buildings subjected to various seismic loadings based on a fracture mechanics approach using Python. A numerical approach framed within the fracture mechanics formulation is presented for evaluating crack initiation and propagation (fatigue life) at beam–column joints in a six-story MDOF building frame subjected to lateral cyclic loads. The performance of RC frames is significantly influenced by the response of beam–column joints, which cause partial or complete collapse of buildings during ground motion. High shear stresses are concentrated at beam–column joints; thus the present work deals with the modeling of RC beam–column connections for determining the number of loading cycles required for the nucleation of cracks leading to subsequent failure or fracture of reinforcing bars. The cross-sectional area, geometrical features, material characteristic strengths, stress–strain life parameters, and equivalent lateral forces due to earthquakes are used to determine the number of cycles for an initial crack of 1 mm. The Ramberg–Osgood relationship has been used to determine the true stress–strain curve by providing fatigue test data such as elasticity modulus (E), failure cycles, stress, and strain parameters of the material. The number of loading cycles for crack initiation and fracture is computed for joint members at every floor of the considered six-story MDOF frame building. The critical crack length and the number of cycles after which bars fractures is computed for all six floor beam–column joints with varying diameter steel bars. From the numerical model developed in Python, it was found that the cracks initiated in the joint rebars at 335.39 ≈ 336 cycles at the fifth floor where there are maximum lateral forces and 5030 cycles at the fourth floor. The critical crack length of different bar diameters (8–20 mm) for the 5th were found to be 0.62, 0.97, 1.37, 1.84, 2.35, 2.9, and 3.49 mm.

The corrugated core sandwich structure is a promising candidate for the Integrated Thermal Protection System (ITPS) of Reusable Launch Vehicles (RLVs) due to its multi-functionality of load-bearing and thermal insulation capabilities. It is incorporated on the exterior of RLVs to protect the underlying structure from the severe aerodynamic and thermal loads during ascent to re-entry. ITPS can be exposed to drastically varying thermal loads during flight operations depending on its position on the vehicle, resulting in spatially varying thickness-wise temperature-dependent properties and thermal stresses. Thermomechanical analysis of RLVs components such as wing, fuselage, etc., along with actual geometry of ITPS panel makes it computationally infeasible due to their disparate length scales. This issue can be addressed by idealizing the ITPS panel as a homogeneous thick plate. In this work, a homogenization method is proposed to model the ITPS panel as a homogeneous plate to perform thermomechanical analysis. The methodology has been developed based on First Order Shear and Normal Deformation Theory (FSNDT) to incorporate the effect of out-of-plane normal strain in addition to transverse shear in the homogeneous plate model. The finite element computation of homogenized stiffness properties and sectional thermal forces and moments are presented in this paper. The efficacy of this method is verified with the comparison of the plate model and full-scale model of an ITPS panel with a thickness-wise temperature field. The comparison shows that derived plate representation is capable to encapsulate the response of the full-scale model efficiently.

With recent advances in science and technology, there is a worldwide demand for lightweight, environmentally friendly, low-cost polymer composites. Basalt fiber-reinforced composites have received a lot of interest since they are less expensive, have good chemical stability, and have better mechanical properties than glass fiber. The present study is concerned with the effect of hydroxyl functionalized multi-walled carbon nanotubes (MWCNTs) on the mode I fracture behavior of basalt fiber-reinforced epoxy composites. The composites are fabricated by conventional hand layup with vacuum bagging technique and the mode I energy released rate $$G_{{{\text{IC}}}}$$ G IC is evaluated using a double cantilever beam test with three different MWCNTs contents of $$0.125,$$ 0.125 , $$0.25,$$ 0.25 , and $$0.5\%$$ 0.5 % per weight of epoxy/hardener. It is observed that the fracture toughness increased proportionally with the addition of MWCNTs till $$0.25\% .$$ 0.25 % . The enhancement is primarily due to improved dispersion and interfacial adhesion between the epoxy resin and the MWCNTs. However, the interfacial characteristics for $$0.5\%$$ 0.5 % of MWCNT might be diminished due to the agglomeration of MWCNTs in the epoxy resin. The finite element modeling (cohesive zone) correlates well with the experimental results and confirms the enhancement of interlaminar fracture toughness by adding MWCNTs.

Typically, floor diaphragms of RC buildings with a long and narrow plan or poor plan geometry, large openings, and inadequate vertical lateral load-resisting elements exhibit huge in-plane flexibility; which leads to unforeseen drift patterns and force distribution among structural elements. Building code provisions independently define rigid diaphragm by placing upper limits on (i) the plan aspect ratio, (ii) the percentage area of openings, and (iii) the relative diaphragm displacements, with additional remarks on plan geometry. Therefore, this study aims to understand the combined effects of these parameters and check the applicability of these provisions given in building codes. Thus, parameters influencing floor flexibility are identified based on relative diaphragm displacements. Equivalent Static Analysis ESA is conducted on the spectrum of rectangular building configurations consisting of RC Moment Frame and RC Structural Wall buildings having: (a) rectangular plan geometry, (b) slab with openings, (c) structural walls located at the periphery, and (d) varying height, respectively. Results agree with Linear Time History Analysis THA. Floor diaphragms of buildings with RC Frames are always rigid and those with RC structural walls (located especially at edges) show significant in-plane floor deformation under earthquake shaking. Also, defining rigid floor diaphragm solely based on plan aspect ratio, the percentage area of openings and relative diaphragm displacements may not ensure diaphragm to behave rigidly; the relative diaphragm displacements exceed the prescribed limits even if the plan aspect ratio or percentage area of opening is within the limits, especially in buildings with structural walls located at the periphery. Building code provisions (like India) must revise the criteria by satisfying all three conditions collectively. For a fixed relative diaphragm displacement, upper limits are placed on the plan aspect ratio and percentage area of the opening.

This work highlights the existing contradictions in satisfying boundary conditions while modeling nanobeams in cantilevered configurations. Various analytical and numerical models can analyze it. Depending on the configuration, these models behave differently. Hence, it is difficult for an engineer to select the method to design the component/structure. Cantilevered nanobeams under point and uniformly distributed load (UDL) are investigated. Different methods’ results are contrasted. Inconsistencies found while satisfying essential and natural boundary criteria are examined. The nonlocal moment-curvature relationship and its effect on the solution are also discussed. All fundamental quantities are compared. While some methods anticipate cantilever hardening, others predict softening. The results show technique flaws. A unified and consistent approach to problem-solving is needed.

The fire-damaged properties of concrete are one of the concerns for the structural application that may affect structural stability and integrity against collapse. Nowadays, infrastructure industries prefer to use high-strength concrete (HSC) or high-performance concrete (HPC) over normal strength concrete (NSC) due to structural sustainability and serviceability aspects, and such HSC/HPC is observed to be highly susceptible to temperature than NSC. Knowledge of thermal-induced properties, i.e., conductivity, specific heat, and diffusivity, is essential for evaluating heat transfer phenomenon that not only helps in the selection of appropriate materials but also helps to obtain HSC/HPC structural member’ desired fire resistance rating and behaviour. Hence, a comprehensive set of experimentally measured data of thermally induced properties of HSC/HPC have been collected from different literature, and this reveals that the type of aggregates, cementitious content with water, and the chemico-physico-hygro-thermo process of the mix design can significantly influence thermally induced properties. Also, it is observed that their behavioural response to temperature and relationship with each other is still not very well established. Therefore, this paper aims to review and discuss the influence of elevated temperature on the type of concrete properties, i.e., mechanical, chemical, and physical properties, and its suitability for structural application.

Past seismic events have shown that high-rise Reinforced Concrete Moment Resisting Frames (RC-MRFs) designed according to current building codes often experience significant inelastic deformations. Predicting and controlling these deformations has proven challenging, as there is no precise method available. This study aims to introduce a performance-based plastic design (PBPD) approach for analyzing and designing high-rise RC-MRF frames while accounting for the inelastic behavior of the structure. In this study, a 24-story RC-MRF frame is selected for analysis and design, utilizing both the force-based design (FBD) method and the PBPD method for seismic loads. The PBPD approach considers three performance levels: immediate occupancy (IO), life safety (LS), and collapse prevention (CP). Indian standard code guidelines and principles are applied in the analysis and design of the frame. The performance assessment of the frame is conducted through nonlinear static pushover analysis. The results obtained indicate that the PBPD-LS frame outperforms the other frames. It is noteworthy that design sections in the PBPD-LS frame are found to be the most efficient, and the displacements remain within defined limits. On the other hand, the PBPD-IO frame is found to be highly uneconomical among the frames. Additionally, secondary moment effects (P-delta) appear to dominate in the PBPD-CP frame. Based on these observations, it can be concluded that, among all the frames, the PBPD-LS frame meets the desired PBPD outcomes and performs exceptionally well within the specified limits.

The microstructure of material strongly influences its mechanical properties and the microstructure itself is influenced by the processing conditions. Thus, establishing a Process-Structure-Property relationship is a crucial task in material design and is of interest in many engineering applications. We develop a GAN (Generative Adversarial Network) to synthesize microstructures based on given processing conditions. This approach is devoid of feature engineering, needs little domain awareness, and can be applied to a wide variety of material systems. Results show that our GAN model can produce high-fidelity multiphase microstructures that have a good correlation with the given processing conditions.

Cracks are the most common types of damage in beams that need to be detected early so that remedial measures can be taken on time otherwise it leads to complete structural failure. Hence, the damage detection in beam like element is important for structural integrity, long service life, and operational cost minimization. In the last few years, several damage detection and quantification methods have been developed using vibration measurements. However, most of them fail to detect the damage, quantify its magnitude and localize it accurately. In this study, an integrated approach has been proposed that will address these issues in a single framework. The proposed approach utilizes the concept of modal analysis to detect any damage in beams. Both the numerical and experimental analyses were used to determine the modal frequencies and results were compared. Moreover, the proposed approach has been utilized to localize and quantify the damage in a steel beam. The developed integrated approach demonstrated superior results on a test specimen of a cantilever beam and successfully approximated the location and magnitude of the damage.

This work investigates the numerical simulation of the sub-interface crack in the limited permeable piezoelectric bi-material. The mechanical and dielectric equilibrium is satisfied by incorporating electrostatic tractions on the crack surface. A crack opening model is used to incorporate the crack face tractions in the framework of the extended finite element method (XFEM). The level-set method is used in association with XFEM to track the discontinuity in the discretized domain. The sixfold electro-mechanical enrichment functions are adopted to get the effect of arbitrary poling direction in the context of XFEM. The electric displacement intensity factor (EDIF) is obtained using the electro-mechanical interaction integral in conjunction with asymptotic crack tip variables. The effect of poling direction and permittivity of the medium are studied to understand the behavior of EDIF.

The present work describes the usefulness of artificial neural networks (ANN) for predicting residual stresses in a butt-welded plate joint. The motivation for the present work is driven by the recently emerging usage of machine learning techniques to reduce computational cost of finite element (FE) analysis. A sample specimen with unequal plate thickness, often used in aircraft panels and shipyards, is investigated here, in order to consider the effects of plate thickness variation in the prediction process. Datasets for building ANNs are generated from sequentially coupled thermal and elasto-plastic FE analysis of the welded specimens using varying inputs like length, width, thickness of plates, weld power, and welding speed. The longitudinal and transverse residual stresses in the domain are obtained as outputs for every set of inputs. ANN models comprising of different activation functions and hidden layers are trained and tested using inputs of three-dimensional coordinate points of the specimens along with the inputs–outputs of FE simulations. The ANN models are then used to predict residual stresses using new input data, and their validity is investigated through FE simulations. It was observed that predictions of ANN models agree well with the simulations, thereby establishing the ANNs as powerful alternatives to FE analysis of welding. For the welding process and material investigated in the present work, the ANN scheme can be used to predict the residual stresses at a considerably faster speed than the conventional FE computations for varying weld-process parameters and geometric parameters.

Ordinary Portland cement is a versatile material in the construction industry. The production of cement is identified to be the major greenhouse emitter, ejecting about 5–7% of total carbon dioxide (CO2) released into the environment. Cement industry analysis report—2022 advocates, ‘in 2021, the post-COVID-19 pandemic, the hopeful prospect about the growth in Infrastructure and real estate sector is probably increasing the demand for cement, which is expected to rise 8 million tons per annum additionally in the production of cement.’ Addressing the above issue, Geopolymers are identified to be an environmentally friendly construction material that alternates ordinary Portland cement. Geopolymers are produced by alkali activation of alumino-silicates, obtained from sources rich in silica and alumina. Geopolymer concrete utilizes supplementary cementing materials (SCM) both natural pozzolans like metakaolin, calcined shale, volcanic tuffs, and industrial by-products such as Fly ash (FA), ground granulated blast furnace slag (GGBS), rice husk ash (RHA), and silica fume (SF) as the sources. Geopolymers have undergone notable development in the research and application field from the day the material stepped into the construction industry. This paper aims to comprehend the different factors such as characteristics of raw materials, the need for blending and proportion of blending, the effect of alkali activator solution, and the effects of proportionately blending raw materials. Furthermore, the review advocates that more research should be done on both material and structural levels to enhance Geopolymer, a potential material in the construction industry.

Torsional effects are prominent in buildings having poor: (i) plan geometry in plan and elevation, (ii) distribution of vertical structural elements, and (iii) distribution of mass, respectively. It causes torsional eccentricity and torsional flexibility (whose fundamental mode is torsional) in buildings. Hence, building code provisions like India design for torsion using torsional eccentricity and define torsional irregularity using ratio of edge element displacements and natural period ratios (which defines torsional flexibility). Additionally, limits are placed on plan geometry using projection plan dimensions or area, and aspect ratio. Effect of plan shape on lateral-torsional response of building is studied on different H-shaped plan geometries using equivalent static approach (ESA) and response spectrum approach (RSA), based on local or global response parameters, like displacement and rotation about the centre of mass CM, force distribution among structural elements, base shear and torsional moment, and torsional irregularity criteria. Comparison of normalized responses of rectangular and H-shaped buildings showed that unsymmetrical buildings show more translation in ESA and more rotation in RSA, but the overall variation is marginal, i.e. 1.1–1.3 irrespective of level of torsional eccentricity. Alternately, the normalized force demand imposed on each structural element based on ESA is more than RSA. Hence, it is required to provide a dynamic amplification factor (DAF) for torsion in both ESA and RSA. Also, it is preferred to avoid re-entrant corners in H-shaped buildings by dividing them into individual blocks. Amplification in normalized shear forces of structural elements of H-shaped buildings and their corresponding individual blocks varies from 1.1 to 3.1; thus, it is preferred to limit building projections. Otherwise, design the structural elements by providing with adequate stiffness, strength, and deformability to ensure better performance.

In the health monitoring of steel structures, the acoustic emission (AE) testing method is the most eminent method as it can identify the micro-level cracks in inaccessible places. AE waves are a quick release of energy inside any material that can be recorded using piezoelectric sensors. It is furthermore possible while capturing the AE signals that the sensors can record the noise signals which can result in an error. So the true information about the structure is restrained. Hence it is important to discriminate the actual AE signal from the other signals captured by the sensors. The employment of artificial intelligence will reduce human involvement and increase the accuracy of any AE testing-related applications such as damage detection or source localization in any structure. Therefore, this paper proposes a discriminating method of separating different signals captured by the sensors from the actual AE crack signals with the help of the support vector machine (SVM) algorithm. The AE crack data are collected on a 1.5 mm thick steel plate, which implements an R6∝ sensor using a pencil lead break-up test. Other noisy signals, i.e., rubbing and impact signals are generated by rubbing a small metal block and dropping it on the steel plate, respectively. The generated AE signals, sensed by the sensors are amplified since AE waves release a very small amount of energy, and then they are sent to the data acquisition system for further processing.

Since it only requires a small surveillance sample, small punch creep test (SPCT) analysis has been used to estimate the lifespan of power stations and nuclear reactors. As the specifications in uniaxial creep test (UCT) and SPCT differ, numerous correlations have been proposed for calculation of conventional tensile characteristics for elastic plastic behavior of metallic materials. Due to the high operating temperatures in nuclear power plants and highly developed ultra-super critical plants, many of the components experience creep deformation. In order to determine how long a component will last, it is crucial to understand the correlations between creep properties calculated through SPCT. Thin disk specimens subjected to SPCT can be thought of as a helpful method for identifying the creep characteristics of components exposed to high temperatures. The challenge is to estimate the conventional bulk creep properties from a small punch sample. Finite element analysis (FEA) of SPCT of a metallic material can help in estimation of bulk properties and therefore FEA of a metallic material having $$E/Y_{{\text{S}}} = 277$$ E / Y S = 277 with a power law creep behavior is carried out using ABAQUS software. This particular paper focuses on the influence of specimen thickness on the site of maximum stress, sometimes known as the weakest section, when the punch travel time was varied.

Lattice structures find applications in many structural areas where the weight to strength ratio needs to be minimum, for example: in space and aerospace applications. With the proper choice of lattice and selection of their geometric features functionally graded structures are designed. Lattice structures are non-homogeneous periodic structures at macroscopic level and the distribution of load, stress and strain will not be as uniform as in a continuous and homogeneous solid metal structures and components. For example, a plate made of lattice structure with face sheets will exhibit a different distribution of the stress and strain compared to a solid plate. This poses a different challenge and opportunity to study and understand the end effects of structural components made with lattice structures. In this article Saint Venant’s end effect of a lattice plate is analyzed using finite element analysis. End effects of a solid plate are analyzed and considered as base line. The end effect of a plate made with simple lattice structures like square, triangular and honeycomb are analyzed and its relationship with volume fraction of the lattice is studied.

Vibration characteristics of a machine change with the operating conditions (speed, load, fault, and etc.). Gears are widely used as power transmission device due to its flexibility to operate at wide range of speed and load. Any faults in the gear can lead to complete failure or even seizure of machine. Therefore, predictive maintenance strategy is adopted where the monitoring of condition of gear is done by analyzing the signal (vibration, acoustics, current, and etc.) of gear. Modeling of a physical system is economical due to the cost involves in experiments. Moreover, the models are scalable and several types of faults can be introduced into it. In the present study, a gear kinematics based 9-degrees of freedom (DOFs) model is considered to find the response of the gear in healthy as well as in faulty (broken or may be missing tooth) conditions. A higher contact ratio spur gear system is considered for analysis. The model consists of a gear-pinion pair, a loader and a driver. The equations of motion of planer block diagram model of gear-pinion system are solved in Matlab-Simulink environment to study the response of the healthy and faulty gear. This study can be extended for different gear systems to find out the fault symptoms under missing/broken tooth.

In this study, the elastic properties of carbon/carbon (C/C) composite are computed by incorporating the presence of pores. Microstructure of C/C composites is analysed using scanning electron microscope (SEM) images. The pores inside the C/C composite are characterized based on area, shape and dimensions. Thirty-six SEM images are analysed. Based on this analysis, a three-dimensional RVE of C/C composite is constructed. The number of pores, their size and spatial distribution in the RVE is given by the analysis. Carbon fibres inside the representative volume element (RVE) are generated using the random sequential adsorption algorithm (RSA). Once the model is generated, periodic boundary conditions are imposed on the RVE model using Python script in Abaqus CAE. Effective elastic properties of C/C composites are computed using the finite element analysis (FEA)-based homogenization method. The effect of pore size distribution on the elastic properties of C/C composite can be understood from this study.