Recent Trends in Computational Mechanics and Simulation

Table of Contents

1. Frontmatter

2. On Effects of the Fringing Field on Static Pull-in Instability Parameters of Electrostatically Actuated Thick Timoshenko Microbeams

   Kedar S. Pakhare, P. Punith, P. J. Guruprasad, Rameshchandra P. Shimpi

   Abstract

   Micro-electro-mechanical-systems (MEMS) prefer electrostatics as their actuation technique. In the literature, MEMS have been generally analysed as a combination of a Bernoulli-Euler microbeam-type deformable electrode, stationary ground electrode and an electrostatic potential difference applied between them. There exists a microbeam configuration-dependent inherent upper threshold on the amount of voltage that can be applied between electrodes. If the applied voltage is increased beyond this value, the deformable electrode shifts from a stable to an unstable configuration, thereby snapping on the ground electrode. This critical value of the applied voltage is termed as the pull-in voltage and the corresponding maximum microbeam displacement is termed as the pull-in displacement. The beam lateral shear starts to play significant role as the beam thickness-to-length ratio increases. In this paper, details with regard to the Timoshenko beam theory-based spectral finite element (TBT-SFE) for the determination of static pull-in instability parameters of narrow shear deformable microbeams, thereby taking non-linearity associated with forcing terms as well as beam lateral shear of the first-order into account, are presented. The authors have investigated an appropriate combination of number of nodes per element and total number of elements of the proposed TBT-SFE to carry out the aforementioned study. The authors have also presented effects of the electrostatic fringing field on static pull-in instability parameters of microbeams having different values of the beam thickness-to-length ratio. This paper highlights the importance of the electrostatic fringing field and beam lateral shear on static pull-in instability parameters of narrow shear deformable microbeams.

3. Influence of Inclusion Volume Fraction, Shape, Distribution, and Orientation on the Mechanical Behavior of Composites

   Kshitiz Kshitiz, Ratna Kumar Annabattula, Shantanu Shashikant Mulay

   Abstract

   Composites are a class of heterogeneous materials with randomly distributed second phase material (with varying volume fractions) in the form of particles or fibers in a parent matrix phase. The influence of heterogeneities on composites’ macroscopic response can be studied by performing experiments on large samples with different physical and geometrical properties (time-consuming). It can also be carried out by computationally simulating the entire body, including all heterogeneities that require enormous computing power and data storage. One of the less expensive solutions is to develop models based on microstructure physics while predicting the macroscopic response of composite for different geometric parameters. Finite element (FE) modeling, using representative volume elements (RVE) subjected to periodic boundary conditions (BCs) for various loading conditions, can be used to estimate the homogenized properties of the composite. In this work, the transverse homogenized properties, like transverse elastic and shear moduli as well as transverse Poisson’s ratio of Epoxy (LY556) resin matrix mixed with E-glass inclusions (different shapes), are computed. The sensitivity analysis is then performed to analyze the effect of volume fraction, shape, and distribution of inclusion particles on the macroscopic properties of the composite. The effect of orientation and number of inclusions is studied, at different volume fractions, for elliptic inclusions. Finally, the FE modeling results are compared appropriately with results from various well-known analytical micromechanics methods.

4. Transient Thermo-Elastic Analysis of a Thin Composite Plate Using Three Phase Lag Heat Conduction

   N. Satish, S. Gunabal, K. Brahma Raju, S. Narendar

   Abstract

   Transient thermo-elastic analysis of a thin composite plate, made up of a dominating matrix (region-1) and an insert (region-2), is studied because of the widespread use of composite structures in heat environments. The linked heat conduction equations for the two locations are derived using a three-phase lag heat conduction model. The composite plate's region-1 receives its heat from a step function-shaped heating source. The composite plate is expected to have lumped thermal behavior along the thickness axis. The governing heat conduction equations are solved using Laplace transformation and Riemann-sum approximation techniques. Transient impacts of thermally generated strains (found to be compressive) and deformations in the composite plate are analyzed based on the history of temperature distribution in region-1. Thermal stresses in the composite plate have been seen to mimic the behavior of the regional temperature distribution. Composite plates’ transient thermoelastic responses are investigated, along with the effects of heat source intensity, heat pulse length, region-2 volume proportion, and convection coefficients.

5. Artificial Neural Network-Based Frequency Predictions of FG-GPL-Reinforced Porous Plates

   Mohammed Shakir, Mohammad Talha, A. D. Dileep

   Abstract

   In the present study, the natural frequency of functionally graded graphene nanoplatelets (FG-GPL)-reinforced porous plate is predicted using an artificial neural network (ANN)-based model. The plate is reinforced with GPL and is modeled in a functionally graded fashion by varying the size and density of pores in the thickness direction. The effective property such as modulus of elasticity is obtained using the Halpin–Tsai model while mass density, and Poisson’s ratio are estimated by the Voigt model. Governing equations and finite element model are developed in the framework of higher-order shear deformation theory (HSDT). The data is generated for the selective features keeping natural frequencies of FG-GPL porous plates as the desired output. The database is split into a training set with 70% of the data and 30% of the data is considered for testing and validation purposes. A regression-based ANN model is employed to train the existing data and the trained model is further utilized to predict natural frequencies for the unseen values of the features, i.e., thickness ratio, porosity coefficient, and weight fraction of GPL. It is observed that the ANN-based algorithm predicts the natural frequencies with a significant low error (<1%). It can be concluded that the ANN-based model is quite efficient to handle large databases, various features, and function complexity associated with material modeling.

6. On the Influence of the Van Der Waals Force on the Static Pull-In Instability of Electrostatically Actuated Timoshenko Nanobeams

   Kedar S. Pakhare, P. Punith, P. J. Guruprasad, Rameshchandra P. Shimpi

   Abstract

   Just like micro-electro-mechanical-systems (MEMS), nano-electro-mechanical-systems (NEMS) are also generally analyzed as a combination of deformable beam-type electrode and stationary ground electrode with an electrostatic potential difference applied between them. In case of NEMS, the gap between these electrodes is of the order of few nanometers and these systems most often employ electrostatics as their actuation technique. Hence, similar to MEMS, NEMS also undergo the pull-in phenomenon when the applied voltage between electrodes exceeds nanobeam configuration-dependent inherent upper threshold. The van der Waals (vdW) force also comes into effect when the gap between electrodes is less than 20 nm. However, this force is absent in case of MEMS as the gap between electrodes in their case is of the order of few micrometers. Additionally, the beam lateral shear starts to play significant role as the beam thickness-to-length ratio increases. In this paper, details with regard to the Timoshenko beam theory-based spectral finite element (TBT-SFE) for the determination of static pull-in instability parameters of narrow shear deformable nanobeams, thereby taking non-linearity associated with forcing terms as well as beam lateral shear of the first-order into account, are presented. The authors have investigated an appropriate combination of number of nodes per element and total number of elements of the proposed TBT-SFE to carry out the aforementioned study. This paper highlights the importance of the vdW force and of the beam lateral shear on pull-in instability parameters of narrow shear deformable nanobeams.

7. Fatigue Crack Growth in RCC T Beam Under Cyclic Load: A Numerical Study

   Devjit Acharjee, Dibya Jyoti Basu, Debasish Bandyopadhyay

   Abstract

   Failures of RCC bridges are quite common these days which are important to be studied. It is often associated with the failure of RCC girders subjected to repetitive wheel loads. The present study aims to develop a computational FE model of a simply supported RCC T-beam subjected to various repetitive loadings to assess its modal properties and crack consequences, which may be extended to determine the expected remaining fatigue life. The considered T-beam models with periodic loading resemble the real-life bridge girders subjected to repetitive axle loading and subsequent distress. A parametric numerical study is performed considering changes in amplitude and frequency of the load cycles, material properties. The eXtended Finite Element Method (XFEM) is adopted for the enriched crack region to evaluate the remaining life of the RCC T-beam considered. The entire study is divided into two parts: the first part is performed using a dynamic explicit analysis where the flexural damage and crack patterns are evaluated. In the second part of analysis, crack propagation is studied using XFEM method to evaluate the stress intensity factor (SIF) and location of crack tip. The entire Finite Element Analysis has been carried out using Abaqus/CAE 6.14-5. Finally, the remaining life of the RCC T-beam to withstand the same kind of repetitive loading is predicted using the Linear Elastic Fracture Mechanics (LEFM) approach for quasi-brittle materials like RCC. It seems that the remaining life of the flexural member depends on the loading as well as material properties, particularly on the stress intensity factor and fracture toughness. The present study seems to be important for the remaining life assessment of the RCC bridge girders with respect to their safety and durability.

8. Polygonal Finite Element Method for Displacement Based Elasto-Plastic Analysis

   Shalvi Singh, Pritam Chakraborty

   Abstract

   Polygonal elements provide more flexibility in biased mesh generation of complex domains with a lesser number of elements in comparison to available unstructured triangular and quadrilateral elements. Furthermore, polygonal elements can provide more accurate solutions with larger element sizes. Polygonal elements are also used as transition elements to connect two dissimilar elements and to perform coarsening and refinement of structured meshes. In polygonal elements, the Wachspress shape functions based on rational polynomial are comparatively easy to develop and fulfill the partition of unity and Kronecker delta properties of conventional Finite Element Method (FEM) shape functions. While, a large number of studies using linear Wachspress shape functions can be found in the literature for linear elasticity, elastic fracture mechanics, and elasto-plasticity, works in literature on higher-order Wachspress shape functions are scarce. The higher-order functions fulfill the C¹ continuity in a domain and can reduce the error in solution with a lesser number of elements more effectively. Based on this understanding, we have tried to develop the quadratic Wachspress shape function in this work. The higher-order interpolation is achieved by inserting middle nodes on each polygonal edge and then applying the same procedure as constructing rational polynomials for the linear Wachspress shape functions. For numerical integration of the weak form, we have applied the Gaussian quadrature rule on the triangulated polygons. The efficiency of the developed higher-order polygonal elements has been tested using patch test and beam bending problem in elastic and elasto-plastic analysis. The solutions have been compared with the conventional quadrilateral elements for elastic plane stress analysis, which demonstrate the workability of the higher-order polygonal elements.

9. Thermomechanical Homogenization of Integrated Thermal Protection System for Reusable Launch Vehicles

   Nazim Khan, Pritam Chakraborty

   Abstract

   The Integrated Thermal Protection System (ITPS) is designed to endure both structural and severe thermal loads acting on the external surfaces of the Reusable Launch Vehicles (RLV). The corrugated core sandwich structures are being considered for ITPS applications due to their superior insulative and structural properties. It can experience significantly varying thermal loads during different phases of flight from ascent to re-entry, resulting in spatially varying temperature-dependent properties and thermal stresses depending on its location on vehicle and operating conditions. Thermomechanical analysis of components such as wing and fuselage along with ITPS panel subjected to varying thermomechanical load is a formidable task as the length-scale of such structures is significantly larger than core geometry of ITPS panel. Thus, analysis becomes infeasible due to exorbitant computational cost. To address this problem, ITPS panel is idealized as an orthotropic plate to enable thermomechanical analysis by homogenizing the response of corrugated core sandwich structure. In this work, homogenization method has been developed to obtain the thermomechanical properties of plate representation of the ITPS panel. The novelty of this approach is the incorporation of through-thickness temperature field in the derivation of the homogenized thermomechanical properties using shear-deformable plate theory. The formulation incorporates the effect of temperature gradient in generic polynomial form and represents the homogenized properties in terms of unknown constants that can be calibrated with unit-cell and beam analyses depending upon the order of polynomial. This formulation can be extended to any higher-order temperature polynomial with additional constants to be calibrated. For demonstration purpose, linear thickness-wise temperature distribution varying along the length is considered for both homogenized plate model and ITPS panel. The efficacy of the proposed method is demonstrated by comparing the homogenized model with full-scale model of ITPS panel subjected to spatially varying temperature field and pressure load. The comparison shows that the derived homogenized plate provides a reasonably accurate and efficient representation of ITPS panel.

10. Response of Shear Wall to Material and Geometric Nonlinearity

    Vikram S. Singh, Keshav K. Sangle

    Abstract

    Reinforced concrete walls can fracture quickly at lower ductility levels, causing catastrophic damage. As a result, accurate modelling of shear-dominant concrete walls is required in order to provide a solution strategy for nonlinear analysis. To predict the behaviour of thin-walled structures, the concrete damage plasticity model was considered in this article, which is computationally very efficient. Concrete and steel were treated as independent components until they were integrated at the section level to characterize the elemental behaviour. The predictions of the finite element model are validated by comparing them to existing experimental data. The load–displacement relationships of walls are then analysed under various stress situations to ensure that the suggested model is sound. The model was then utilized to undertake a series of numerical simulations to assess the impact of different nonlinearities on the response of vertically oriented rectangular wall. This investigation revealed some key insights about wall response.

11. A Diffused Material Interface-Based Analytical Method for Elastic Analysis of Composites with In-Plane Inhomogeneity

    Ayyappan Unnikrishna Pillai, Mohammad Masiur Rahaman

    Abstract

    The development of high-performance bio-inspired composites is one of the contemporary topics of research interest. Experiments on composites made of constituents with contrasting material properties and thus possessing a distinct material interface have shown very promising results in terms of having high strength and high toughness. To the best of the knowledge of the authors, although several analytical studies on the functionally graded in-homogeneous plates with material properties varying in exponential or power series manner are available in the literature, there is no analytical method to find a closed-form solution for composites with a distinct material interface. Because of no availability of analytical methods, finite element solutions are extensively used for the analysis of these problems. However, validation of the finite element solution for composites with material interface against benchmark problems will increase the confidence. In this work, we propose a diffused material interface-based novel method for finding analytical solutions of elastic deformation in composites with in-plane inhomogeneity that can be used as benchmark problems for the validation of the finite element solutions. In the proposed analytical method, we have diffused the material interface by using a Gaussian kernel function and derived expressions for the material properties that are smooth, i.e., functions and their derivatives are continuous, in the entire domain. We have then used the Galerkin method to solve the governing partial differential equations for the derived smooth material properties. We have demonstrated the efficacy of the proposed analytical approach through illustrative examples of the composite bar, beam, and plates with in-plane inhomogeneities.

12. Julia Implementation of a Phase-Field Model for Studying the Effect of Interlocking Angle on the Mechanical Behavior of Geometrically Interlocked Composites

    Mohammad Masiur Rahaman, Ved Prakash

    Abstract

    Energy absorbed during damage depends on the toughness of solids. Material with high toughness can dissipate more energy for the same damage compared to a lower-toughness material. Hence the use of high-toughness material can add to the energy dissipation mechanism of structures. Bio-inspired composites that combine a soft phase with the majority of a hard phase referred to as brick and mortar (BM) structure, show an enhanced fracture toughness compared to the constituent materials. Recent experimental studies show that topologically interlocked composites possess even superior properties than conventional bio-inspired composites with BM-type structures. In this study, we examined how different interlocking angles influence the mechanical behavior of topologically interlocked composites. Specifically, we developed open-source codes by implementing a phase-field model (PFM) using a Julia-based new finite element (FE) library, Gridap. These codes serve as a numerical aid to investigate the influence of interlocking angles on fracture toughness. Gridap enables a compact and user-friendly implementation, requiring minimal memory usage and offering users significant flexibility in writing weak forms of partial differential equations. In addition, Gridap provides a very convenient way to impose displacement continuity at the material interface.

13. A Two-Scale Particle-Based Model for Hot Isostatic Pressing (HIP)

    V. Chandra, M. Aasiba Nisrin, B. Srivathsa, R. Sankarasubramanian, P. Chakraborty

    Abstract

    Hot Isostatic Pressing (HIP) is a manufacturing process that consolidates powders of metallic materials to produce near-net-shape components with theoretical density. In this process, the material powder is enclosed in a die which is then subjected to high temperature and pressure in a closed container filled with inert gas such as argon. In the initial stages of the process, when both the pressure and temperature are increased, the particles undergo plasticity driven deformation and neck formation leading to significant pore closure. Subsequently, temperature and pressure are held constant during which further pore closure is attained through diffusion mediated mechanisms. While this process has found widespread use to manufacture defect free high-end components such as turbine discs precise control of process parameters is necessary to avoid localized porosity and deviation from desired final geometry. Thus, various thermo-elasto-viscoplastic-densification continuum models have been developed to perform optimization of HIP process parameters. However, these models are chiefly phenomenological and are weakly connected to particle scale behavior through some material constants. In order to address this shortcoming, development of particle scale model of HIP is necessary. Though a wide range of phase-field-based models of sintering can be found in the literature, similar attempts to capture the behavior of particle aggregates during HIP is lacking. A key limitation being the initial large deformation and instantaneous plasticity in this process, as well as the exceedingly large computational cost associated with 3D phase-field simulations. In this work, a 3D thermo-mechanical Finite Element Method (FEM) micro-model of particle interaction has been developed to obtain accurate macroscale constitutive behavior during HIP. In the micro-model a body-centered cubic arrangement of particles has been considered assuming average size and initial packing factor of 0.68, which is close to the typical packing density after initial compaction. The particles in the Representative Volume Element (RVE) have been assumed to have an isotropic elastic plastic creep (both dislocation and diffusional) behavior. Since, the diffusivities are higher on the surfaces and at the particle contact regions, a thin layer of elements at the particle surfaces have been assigned larger diffusivities in the creep model. The RVE has been subjected to various macroscopic deformation gradients histories in addition to periodic boundary conditions to perform microscale FEM simulations. The macroscopic stress–strain and density evolution has been obtained using the temperature dependent properties for Inconel 718 and compared with a macroscopic model based on Abouf and Downey. The comparisons show that the microscale RVE analysis provides similar volume averaged responses as the macro-constitutive model, demonstrating the usability of the multi-scale approach to derive physics-based microstructure dependent constitutive models of HIP.

14. Structural Health Monitoring of Steel Truss Bridges Subjected to Environmental Variability

    Akash Yadav, Ananth Ramaswamy

    Abstract

    Structural engineering defines damage as changes in material property, boundary conditions, or geometry. The changes in these parameters lead to a change in the measured response. The difference in measurements can be due to actual damage in the member due to crack or corrosion, or it might be due to environmental variability. Environmental variability, such as variation in temperature while making measurements, significantly influences the ability to quantify structural damage in structural health monitoring programs. Performing damage detection without isolating these variations can lead to false damage detection. Hence, a method is required to isolate the effect of these variabilities while detecting damage. Various methods have been developed and analyzed to separate environmental-based effects from damage-induced changes in the measures. Generally, two main approaches have emerged from research activity in this field: (a) statistics-based tools analyzing patterns in the data or computed parameters and (b) methods utilizing the structural model of the system considering environmental as well as damage-based changes of stiffness values. This paper addresses the problem of detecting damage under environmental variability. The proposed method uses the Approximate Bayesian Computation Nested Sampling (ABC-NS) algorithm to detect damage under temperature variations. The paper introduces a new damage index for identifying potentially damaged members. After performing damage localization, we estimate the parameters’ posterior distribution for potentially damaged members using ABC-NS to quantify damage. All the relevant data and codes used in this study will be available at https://github.com/akashyadav0210/ABC_SHM.

15. Simulation of a Dislocation Near Semiconductor Bi-Material Interface with Misfit Strain

    Neha Duhan, Anjali Jha, B. K. Mishra, I. V. Singh

    Abstract

    The semiconductor materials from group III–V form compound semiconductors which are used in quantum dot (QD) systems. As a representation of a QD system, a square semiconductor bi-material made of Indium Arsenide (InAs) for the QD and Gallium Arsenide (GaAs) for the substrate is considered with an edge dislocation present in InAs. The lattice parameter of InAs is greater than the lattice parameter of GaAs. This lattice mismatch results in the compressive strain in InAs, known as misfit strain. An edge type dislocation is considered near the material interface, which has an inclination of 15° with the horizontal. The numerical simulations of dislocation are performed using the extended finite element method (XFEM). For solving the force equilibrium equation, the traction field is applied at the outer boundary. The heat equation is solved for different heat boundary conditions (heat flux in the x-direction and y-direction, isothermal temperature). The temperature variation is taken from 300 to 500 K. The Peach-Koehler (P-K) force of the dislocation is computed after obtaining the strains, stresses and temperature gradients in the domain. The P-K force increases with temperature for the heat flux boundary conditions when misfit strain is not considered. With the consideration of misfit strain, the trend of the P-K curve corresponding to heat flux in the y-direction changes a bit. Moreover, the P-K curves for the isothermal boundary condition have the same trend with and without misfit strain.

16. Machine Learning Models for Stress Recovery in Finite Element Method

    Bedanta B. Saikia, Dipjyoti Nath, Sachin S. Gautam

    Abstract

    The rise in computational power has encouraged researchers to use concepts like machine learning in the field of computational mechanics. In this work, artificial neural networks (ANNs) are applied in the field of stress recovery. Stress recovery is a widely studied topic since the day finite element method (FEM) began. Machine learning models are trained using stresses from finer meshes. The trained model is then used to calculate stresses at any point over the domain. These stresses are compared with stresses calculated in a coarse mesh, from the popular stress recovery technique, the superconvergent patch recovery (SPR) technique. Errors are calculated by considering stresses from a very fine mesh as reference stress. Three separate models are created for the three components of stress in a plane stress problem. Using the developed ANN models, the Cook’s skew beam problem is solved.

17. A Volume-to-Volume Interaction-Based FE Model for Large Deformation Planar Adhesive Contacts

    Suprateek Roy, Narayan K. Sundaram

    Abstract

    A volume-to-volume interaction-based Finite Element framework is developed for large deformation planar adhesive contacts. A three-fold scheme consisting of a careful selection of cut-off radius, k-d tree-based fast selection of contact pairs and ultra-fine graded mesh generation technique for interaction calculations is designed and used to reduce the huge computation cost of the volume-to-volume interaction-based models. An arc-length solver is specially designed to tackle the intrinsic ‘snap-back’ and ‘snap-through’ instabilities associated with the adhesive contact problems. The efficacy of the newly developed framework is shown with two numerical examples consisting of adhesive contacts of two planar elastic bodies interacting through 6–12 Lennard-Jones interaction potential. Realistic material and interaction parameters are used for the demonstrations. This new framework will be useful in simulating adhesive contact behaviors of various mechanical, micro-electro-mechanical and biological systems.

18. A Micromechanical Study to Investigate the Elasto-Plastic Behaviour of Carbon Fibre Reinforced Composites

    Sanjay Singh Tomar, C. S. Upadhyay

    Abstract

    The article presents a micromechanical study to investigate the effective response of carbon fibre reinforced plastics (CFRP). A Representative Volume Element (RVE) approach has been used to model the material microstructure. Monte Carlo method-based Random Sequential adsorption algorithm (RSA) has been used to imitate the random microstructure of the CFRPs. A thorough comparison between the random and uniform microstructures has been shown to account the effect of randomness in the material. Fibres have been modelled as elastic and transversely isotropic, whereas the inelastic nature of the matrix has been modelled using classical J2 plasticity criterion. A three-dimensional boundary value problem with six (three normal and three shear) standard cases have been solved using finite element methodology. The computation has been performed using ABAQUS/CAE software. A UMAT material subroutine in FORTRAN has been used to include the different material models for fibre and matrix. Parametric studies have been performed to demonstrate the effect of fibre volume fraction and RVE size on the effective response of the materials.

19. Pavement and Road Health Monitoring Using Random Forest Technique

    Revanth Dugalam, Simma Sai Ram, Guru Prakash

    Abstract

    Detecting road anomalies is crucial for preventing road accidents, yet the challenges in achieving efficient detection persist. Traditional visual inspections are costly, cumbersome, and often unreliable, making them impractical for comprehensive road network monitoring. To overcome these issues, this study leverages machine learning (ML) techniques to develop an algorithm for road anomaly detection using acceleration data. The proposed algorithm employs the random forest (RF) technique for anomaly detection and classification, and its performance is compared with other models, including decision tree (DT), K-nearest neighbors (KNN), and support vector machine (SVM). The results highlight the superiority of the random forest (RF) classifier, achieving an impressive accuracy rate of 90.6%. Additionally, the SVM model emerges as a significant contender with an accuracy rate of 89.43%. This research underscores the potential of ML in enhancing road safety by efficiently and accurately identifying road anomalies, thereby reducing accident risks.

20. Theoretical Model for Assessing the Spatiotemporal Temperature Inside a Building Compartment

    Umang Pulkit, Satadru Das Adhikary

    Abstract

    In order to guarantee that the structure and its members can withstand a realistic fire exposure that is expected in some building compartments, which are contemporary office buildings, hospitals, libraries, etc., this paper presents a new framework for assessing the spatiotemporal temperature which can occur inside a building compartment. Achieving a fair balance between the complexity and variety of such fires and the practicability and simplicity required by a structural engineer in properly defining fire as a load, served as the main guiding concept in designing the proposed model for building compartments.

21. GCFEM Using Generalized Fitting of Boundary Curves

    Pranjal Saxena, Aalok Kumar Jha, Chandra Shekhar Upadhyay

    Abstract

    Domains with curvature and sharp corners (cusps) are prone to geometric approximation errors, due to which they are sensitive to the order and type of fitting polynomials. Approximating such geometries using lower-order polynomials can lead to errors in the solutions. In this article, we present a methodology to approximate complex boundaries. This method uses various types and orders of shape functions (Lagrange, B-Splines, and NURBS) along with the associated adaptive mesh size to optimise and approximate a boundary within the desired tolerance. We have adopted projection based curve fitting by minimizing of H¹-norm and solving a system of linear equations to get the desired fit. A comparative study has been presented on curve fitting by projection using different basis functions.

22. Finite Element Simulations of Deformation and Material Removal of Polycrystalline IN718

    Srihari Dodla

    Abstract

    This paper presents the microstructure-based polycrystalline model to simulate the micromachining of polycrystalline Inconel 718. A crystal plasticity material model was used to investigate the deformation behavior. The microstructure feature, such as crystallographic orientation, is considered in the constitutive model. A shear strain-based criterion described the material removal during the chip formation. The ABAQUS finite element solver with a user-defined subroutine is used for the model. The material parameters have been identified with the experimental data. From the proposed model, the effect of microstructure on the cutting forces and the chip formation process is investigated.

23. A New Hydrostatic Stress-Dependent Yield Criterion with Coupled Growth of Inelasticity and Damage in Polymer Matrix Materials

    Yenike Sharath Chandra Mouli, C. S. Upadhyay, P. M. Mohite

    Abstract

    The present study proposes a new hydrostatic stress-dependent yield criterion and discusses coupled evolution of inelasticity and damage in polymer matrix materials. In addition, the study presents a constitutive model that simultaneously incorporates the evolution of inelasticity and damage. An associative flow rule is used for the evolution of inelastic strains. The damage growth model is coupled with the evolution of accumulated inelastic strain. Model predictions are compared with the experimental data in the literature. Further, attention is given to the growth and saturation of inelastic strain and damage before rupture. It is noted that the damage saturates at different values under tension, compression, and shear. Also, the damage saturation happens at lower strains, and then the inelastic strain evolution continues until rupture.

24. Numerical Investigation of a Concrete Stress Block at the Post-Heating Stage of a Parametric Fire Curve

    Mahesh Gaikwad, Harpal Singh, Suvir Singh, N. Gopalakrishnan

    Abstract

    The paper presents a robust approach for concrete stress blocks to evaluate accumulated internal damage during the post-heating phase of the fire. In this study, computational efforts have been made to get insight into the phenomena that occur during gradual cooling by predicting heat propagation, thermal response, material constitutive behavior, and transformation in stress blocks of concrete at different time intervals of a fire. The methodology includes heat transfer analysis to anticipate temperature profile at various time intervals, followed by stress analysis for the predicted thermal profile using a simplified mechanics-based sectional analysis method. The average layer temperature distribution is used in the stress analysis. The heating and post-heating analyses used the Euro code 4 theoretical stress-strain model as an input parameter. The modelled stress analysis tool is then employed to conduct a parametric study incorporating different strain profile and neutral axis depth combinations. The stress capacity of individual concrete fibers is presented by non-dimentionalising with the corresponding strength value. The findings of the study include a thermal evolution and stress block behavior in different fire time intervals. Even after the fire is extinguished, the surface concrete layers cool while the inner concrete layers heat, resulting in a differential thermal gradient occurred over the depth. Concrete fibers exhibit significant stress loss in the post-heating phase of fire due to the very high fire temperature encountered during the heating stage. Despite the recovery, the stress reduction becomes stable over the post-heating phase.

25. Estimation of Shrinkage Strain Considering the Effect of Reinforcing Steel for a Thick RCC Vault of a Nuclear Structure

    Chapparam Sai Bharath, Srijan Kumar, Praveen Kumar, Leni Ranjith, Girish V. Shenai

    Abstract

    Nuclear safety structures are designed for loads arising due to shrinkage of concrete based on the formulations given in AERB/SS/CSE-1 [AERB/SS/CSE-1.: Design of Concrete Structures Important to Safety of Nuclear Facilities. Atomic Energy Regulatory Board, Niyamak Bhavan, Mumbai (2002)]. In these formulations, the effect of reinforcement on concrete shrinkage is not considered as empirical equations were derived considering plain cement concrete samples. Presence of reinforcement in a structural concrete member, restraints the induced shrinkage strains in concrete. In the present study, effect of reinforcing steel on concrete shrinkage is estimated by modeling concrete and reinforcement in FEM software. In first part of the study, structural members like beams and walls are modeled separately along with their reinforcement. Shrinkage strain is calculated as per the provisions of AERB/SS/CSE-1 [AERB/SS/CSE-1.: Design of Concrete Structures Important to Safety of Nuclear Facilities. Atomic Energy Regulatory Board, Niyamak Bhavan, Mumbai (2002)] and incorporated as temperature change for the respective structural member. Concrete shrinkage strain without and with reinforcement (for different percentages) is calculated using FE analysis. Variation of shrinkage strain in concrete with and without reinforcement % is recorded. The effect of shrinkage is studied by varying the parameters of structural members like their size and grade of concrete. In second part of the study, a thick Reinforced Cement Concrete (RCC) vault of a nuclear structure is considered and similar analysis as first part of the study is carried out. Based on the study for M30, M40, M50, and M60 concrete, it is observed that reduction in shrinkage strain increases with reinforcement but it increases marginally with compressive strength. If RCC vault is designed for M30 concrete, it is observed that there is a reduction of approximately 2.4–13.71% of shrinkage strain in the RCC vault when the reinforcement is around 0.5–2.46%. Hence, in the case of heavily reinforced structures considering the effect of reinforcement on the shrinkage strain in concrete can lead to more realistic and economical design.