Fatigue, Durability, and Fracture Mechanics

Airborne structural parts are designed for critical operating flight and landing load conditions following the certification guidelines for enough strength and rigidity. But in the development test environments they will be subjected to loads differently than expected in the operating life unexpectedly leading to premature fatigue failures. Instances like fastener loosening due to loss of positive lock in primary attachments will trigger vibratory dynamic loads and fail the structural attachments. It is essential to avoid these unsafe situations by considering such events in the design. This paper aims at dealing one such instance practically observed during flight testing of helicopter. Redesign and analysis is carried out that show simulation of critical stress levels for dynamic vibration loads for fastener loosing effects and design accomplishment to avoid such premature structural failures and maintain original damage-tolerant behavior with better strength and fatigue life levels to meet operation life requirements.

The objective of this study is to design optimized frame under fatigue condition through finite element analysis (FEA) for the off-highway electric drive dump truck. In today’s globalization world, the off-highway sectors started adopting advance technologies to get the optimized and reliable products. Nowadays, the off-highway vehicles have to be cost-effective and must have high power-to-weight ratio for the better fuel efficiency and to increase life of the critical components such as powertrain aggregate engine, alternator, etc. In the mining sector, desirability depends on the economics of operation in terms of ‘cost per ton’ of material transported. The cost per ton can be achieved only through the higher payload equipment and lower cost per ton approach. In case of open cast mine, the lower cost per ton can be achieved by adopting higher capacity dump truck with optimized weight and ease of maintenance of the electric drive dump truck. Therefore, this study has made an attempt to design the optimized frame rail size under fatigue condition through FEA method for the electric dumper. It covers how and when to adopt the optimization approach while designing frame structure. Also, it has emphasized that the fatigue load is one of worst load conditions for the frame design, where the complete frame will be twisted under left and right ramp conditions. Under these conditions, the optimum frame rail was designed with optimum plate thickness to meet the design criteria. The frame rail with different sizes and plate thickness were considered and analysed under the same alternate load conditions. Based on the historical data of frame with respect to the frame life, the optimized frame rail size and required plate thickness of frame were determined at the initial stage of design. This approach results in optimized frame and meets targeted power to weight ratio. Finally, this optimized design enhances the life of powertrain aggregates and improves fuel efficiency of vehicle.

Today, many ageing aircrafts in air forces of many countries are in service beyond their designed total technical and calendar service life. In general, typical military fighter and trainer aircraft airframe structure is designed for a service life of 20–30 years. The life extension programmes are being undertaken today for ageing aircraft considering the non-utilization of aircraft to its full potential, high acquisition cost of an aircraft limited by defence budget. This paper presents on the total technical life extension of an IAF (operator) trainer aircraft with initial Total Technical Life (TTL) of 8000 h. TTL extension programme has been carried out with operator formed task team including HAL and certifying agencies to extend the TTL of airframe beyond 8000 flight hours. Life extension studies consisted of full airframe (viz. fuselage, wing, tail plane and engine mounts, etc.) with respect to strength and fatigue life analysis margins, full scale fatigue test results, post-test inspection reports, histories of earlier overhaul data, material ageing aspects (considering environmental degradation, corrosion prevention and protective coating, wear and tear), ‘g’ exceedance and hard landing data, incident histories and repair scheme implemented on service aircraft. Additionally, TTL attained two lead aircrafts were strip opened, thorough inspections suggested and results were studied. After these extensive studies, the task force concluded that TTL of trainer airframe can be increased by 500 flight hours. Hence, as per recommendation, TTL of the aircraft extended to 8500 flight hours. Considering the present usage rate in fleet, the extension will ensure availability of trainer aircraft for training in another 4 years, thereby benefitting the operator for performing the intended tasks.

Reactor pressure vessel (RPV) of a pressurized water reactor (PWR) is an important pressure retaining equipment which decides the life of a nuclear power plant. RPV is constructed of special quality nuclear grade low-alloy steel having sufficient fracture toughness at the beginning of life and a good resistance to neutron embrittlement. However, the steel is not completely free from embrittlement phenomenon due to the presence of small amounts of impurities like copper, phosphorus, and sulfur. RPV houses the nuclear fuel core and thereby it is subjected to neutron flux which causes irradiation embrittlement of the material over a period of operation time. This results in loss of fracture toughness of the pressure boundary material leading to a possibility of brittle fracture toward the end of life. This governs the safe operating life of the RPV. In this paper, the strategy for life estimation of a RPV using LEFM approach is described and a sample calculation for a typical RPV is presented. A semi-elliptical surface crack is postulated as per ASME B & PV code, Section-III, Appendix-G, at critical locations like core belt region and nozzle-vessel junction, and the flawed structure is analyzed under the severe most loading, i.e., a rapid cooldown transient, using the finite element method. 3D FEM model of the respective portions of the RPV is made using brick elements for analyzing the behavior of the postulated cracks under the load. The model includes the 3D crack geometry as an unconstrained boundary within the structure, with quarter-point elements near the crack front for simulation of square root singularity. Fracture calculations are done to evaluate the stress intensity factors for the postulated cracks. The extent of irradiation embrittlement of the material (measured as the shift in nil-ductility-transition temperature) with respect to neutron fluence (and hence total operation time) is assessed by using the empirical correlations as per the USNRC regulatory guide. The safe operating life of the RPV is estimated from the criticality condition of the postulated cracks.

Study on life extension was undertaken for actuating cylinder of main and nose landing gear (MLG and NLG) of fighter aircraft. Activities involved for life extension are load estimation on landing gear (using MIL-A-8862) and actuating cylinder, stress analysis of actuating cylinder, fatigue load spectrum generation (using MIL-A-8866C), theoretical fatigue life estimation, and fatigue testing of actuating cylinders. Fatigue testing was carried out on one specimen each of actuating cylinder of MLG and NLG, for load spectrum of 4000 landings, considering scatter factor of 4. Crack was observed on MLG actuating cylinder eye end, one of the major load-carrying member. Therefore, it was decided to carry out fatigue crack growth analysis of eye end to decide the inspection interval in life extended period. Fatigue crack growth analysis is carried out using Paris equation. Suitable stress intensity factor (SIF) for crack geometry and material constants for Paris equation are selected from available literature. It is concluded that, assuming an initial crack of 0.5 mm in eye end at threaded region, it will become critical after minimum 1500 landings. This was practically seen during fatigue test. Crack length reached during fatigue test was around 7 mm; however, unstable crack growth was not observed. This study recommends the thorough inspection of eye end to be carried out at every 400 landings after initial assigned life in number of landings to ensure absence of cracks.

Indian pressurised heavy water reactors are pressure tube type reactors using natural uranium as fuel. Primary heat transport system consists of heavy water as coolant at high temperature and pressure flowing on the fuel bundles to remove the fission heat generated. The primary heat transport system consists of 306 Zr–2.5% NB tubes, feeders, headers and steam generators as important pressure boundary components. Breach of any of these components/equipment results in impaired cooling to fuel bundles containing fission products and thus possibility of fuel failure. It becomes mandatory to provide assurance that structural integrity of these components is intact and balance life remains in accordance with the design criteria. A detailed in-service inspection and surveillance programme is in place to monitor the health of systems, Components and structures important to nuclear safety. In service inspection programme on these critical components are devised such that the inspection results do not only demonstrate the healthiness of these components for further safe reactor operation but also predict the balance life of the component is being examined. This in achieved by conducting specialized non-destructive techniques developed of individual critical component. Since these components are located at high radiation field, robotic system is in use to deploy the NDT inspection system probe/sensors to the required area for inspection. The life assessment of critical components like coolant channel, primary piping and stream generator are elaborated in this paper.

Ferritic stainless steel (FSS) is general considered to have poor weldability in comparison to austenitic stainless steel but it has many industrial applications due to their low cost and better corrosion resistance and magnetic nature. In this work a single sided butt-joint (60o V groove) of FSS (430 grade) was selected for welding by using a specific filler wire (ER409Nb Grade) contents Ta + Nb during TIG welding. The optical micrograph studies revealed grain coarsening and martensite and carbide precipitates especially on the grain boundary regions in the WZ. But this feature of micrographs changed gradually if PWHT increases from 500 to 700 °C for 2 h after welding. The PWHT at 700 °C for 2 h decomposed the martensite into ferrite and carbides, eliminated segregation, sensitization and residual stresses, and improved corrosion resistance and tensile properties. The tensile properties was evaluated after TIG welding then PWHT at 500–700 °C for 2 h and subsequently weldments analysed by SEM with EDAX. It has been clearly indicated stabilizer Ta + Nb contents about 1.22 wt% Ta + trace Nb after PWHT. The tensile properties was performed through UTM as per ASTM E8 standard and notable properties observed after PWHT at 700 °C likely to YS of 296 MPa, UTS of 348 MPa, ductility of 8.46%, and RA of 33.47% and YS to UTS ratio of 0.80, respectively. It can be concluded that tensile properties and toughness of weldments increased by using Ta + Nb stabilizers during TIG welding of FSS plate.

Compressor rotor blades of Gas Turbine Engines are critical components in the flow path. Their durability is determined by Life and integrity at different operating conditions. These blades experience stresses due to body loads and complex bending stresses due to the aerodynamic work done. While it is essential to establish adequate safety margins in the rotor blade during the design phase, it is equally important to monitor the life that is being consumed in actual operation at different combinations of mass flow rate, pressure and speeds depending on the aero-thermodynamics at various altitudes and manoeuvre conditions. A Meta model is developed with strain as the response surface in terms of mass flow rate and rotational speed as the controlling parameters. Design of Experiments using FEM is conducted for nine combinations of these parameters from which a generic strain model is constructed. This model is capable of predicting the strain in the rotor blade for any engine operating point which in this case is essentially a function of the mass flow and rotational speed of the rotor blade. At the same time, few of these rotor blades have been strain gauged during developmental engine tests for strain/health monitoring. Strain data obtained from engine testing at various operating points is utilized to correlate the aforementioned response model developed wherein good correlation is observed and the error is within 5%. Strain responses predicted from the meta model at respective engine operating points are then used to arrive at the strain ranges the blade would encounter during operation. Rain flow cycle counting method in conjunction with life models are used to arrive at the damage fraction in the rotor blade during each engine test cycle. Damage is cumulated over repeated usages in the engine to arrive at residual life of the rotor blade.

The experimental and analytical study on calculation of ultimate strength and deformation of plain cement concrete strengthened by wrapping with fiber reinforced polymer (FRP) for circular short column is presented. The study emphasizes on comparison of analytical strength obtained by Abaqus® (finite element tool) with theoretical mathematical equations formulated by researchers Mander et al., Girgin and Richart et al. This paper focuses on the validation of deformation and strength by experimental, analytical and mathematical results. The validation assessment is made with virgin and fractured specimen strengthened with carbon FRP (CFRP) and incorporating the similar boundary conditions in analytical tool (Abaqus®). The study highlights on good agreement between analytical model with experimental deformation results and strength that are validated with proposed models proposed by researchers Mander et al. [1], Girgin [2] and Richart et al. [3] The study has helped in evaluating the confinement value (k) for PCC for the development of confined compressive strength using the empirical formula.

In present study, the notch geometry, constraint conditions, loading conditions and peak equivalent strains have been accounted to review classical hypotheses for estimation of localized stress/strain values. Two dimensional and three dimensional FE analyses have been performed on planner and tube geometry for validation of classical schemes based on strain energy conservation on maximum principal stress/strain plane and von-Mises equivalent stress/strain. These geometries (plane 2D and tube) have single central circular hole subjected to three different equivalent peak strain levels. The hypotheses based on conservation of strain energy on equivalent stress and strain values results in better predictions of localized stress for plane stress, plane strain and tube geometries. The hole diameter was also varied to study the effect of strain gradient. It has been brought out that for given equivalent peak strain, the percentage difference between predicted and FE localized stress results is nearly similar for various hole diameters. Further, a three dimensional tube geometry with intermediate constraint level was also analyzed and the suitability of classical hypotheses have been brought out w.r.t. FE outcome.

Several metal alloys demonstrate a cyclic plasticity hardening behavior that is higher than the monotonic hardening behavior seen in a uniaxial test. This increased hardening with increase in strain range is known as non-masing behavior. This influences the shape of the stress–strain hysteresis curve and has a direct impact on the failure life for that strain range. This paper numerically models this non-masing behavior and its memory effect by tracking the current strain range hardening region in the plastic strain space. This model dynamically modifies plasticity parameters as the strain range changes as well as captures the memory effect of strain range seen in such materials. The impact of modeling this behavior is then showed by comparing with experimental stress–strain hysteresis curves as well as life numbers available in literature for 316L(N) stainless steel.

As a part of the stringent safety requirement in the case of the operation of Fast Breeder Reactor, it is necessary to demonstrate that the postulated part-through-crack on the pipe surface shall not become the through-thickness crack during the period between two successive in-service inspection/repair schedules. A fast and accurate estimate of through-thickness crack growth studies plays an important role in demonstrating the structural integrity of the power plant components more effectively. Deployment of an advanced computational technique plays an important role in this direction. 3D numerical estimate on the Fatigue Crack Growth (FCG) behaviour of the prototype piping products is relatively slow and computationally expensive. Towards this end, it is necessary to develop simple computational models without compromising the accuracy. Accordingly, the FCG simulation has been carried out for a full-scale pipe bend, and the results are compared with an equivalent plate type geometry. The salient features adopted in identifying the equivalent plate concept and its comparative performance in the simulation of FCG behaviour are brought out in this paper.

Optomechanical systems include a set of optical lens mounted in mechanical housing which will be exposed to the external environment. It is cumbersome to hold this mechanism in adverse thermal and vibrational conditions, unlike other metallic materials. However, it is inevitable to make sure this optomechanical combination to withstand fatigue loads. This paper presents Finite Element Analysis (FEA) and analytical calculation for the thermal, vibrational effects, and performance characteristics of optical lens while it is bonded with elastomer in a metallic cell to withstand such stringent conditions without any fracture of optical lens. FEA has been carried out to verify these effects on optical parameters, viz. wavefront errors using Zernike surface deformations polynomials. Both analytical calculations and FEA were carried out to achieve optimal design as well as to ensure for design validation. This paper also determines the fatigue design strength of optical lens for a specified lifetime.

Tires are the complex composite product of filled-rubber, steel, and fiber cords, made of as many as 20 components. Filled-rubber used for each component has a different formulation, characteristic, and physical property. Each component of tire is designed to have a set of properties to perform a unique functionality. These different components of tire are adhered together by chemical bonding, van der Waals force, or electrostatic attraction. During the motion of the tire, each rubber component is under continuous fatigue loading, which may cause failure at some critical location in the tire. This research study mainly focuses on establishing the experimental framework for failure in rubber components due to crack generation. An experimental study was carried out on machine fatigue to failure testing (FTFT) for evaluating the life of rubber samples. Further surfaces of failed samples have been studied and compared through advanced microscopy.

Welded steel joints are widely used for the structural components in the on/off-highway industry. Due to increasing regulations around CO2 emissions and competitive demand for improved fuel economy, there is a significant focus on the lightweighting of structures in the machinery components deriving the use of higher strength steel grades. It’s given that the lightweighting objectives should be achieved without compromising on functional performance, life-long durability, and safety among many others. HSLA (high-strength low alloy steel) and UHSS (ultra high-strength steel) grades are of specific interest considering their favorable mechanical properties along with excellent weldability. During this study, 345-MPa HSLA and 690-MPa UHSS steel grades were selected. Understanding the fatigue behavior of high-strength steel welded joints is of specific interest because fatigue properties for some of the steel grades can degrade from the thermal effects of welding. Keeping this objective in mind, an extensive and systematic experimental fatigue test study was performed on the double fillet T-joints welded from HSLA and UHSS steel grades. The experimental investigation included detailed metallurgical analysis such as microstructure and hardness variations across three distinct zones of welded joints, residual stress measurements using X-ray diffraction, and weld toe geometry measurements using dental molds. Further, detailed numerical finite element and fatigue analysis were carried out to predict the total fatigue life (crack initiation plus propagation) of the welded joints, based on the total fatigue life approach. The total fatigue life approach is an advanced fatigue analysis method which allows estimating the total life of the structure without the need to divide into arbitrary crack initiation and propagation phases, making this an attractive method for engineering practice. Finally, the outcome from the numerical analysis has been compared with the experimental fatigue test results for the welded joints made from HSLA and UHSS steel grades, showing good correlations.

The present study is aimed at assessment of stabilized cyclic elastic–plastic stress/strain response of low C–Mn steel used as the primary piping material of Indian PHWRs. The material model considers von Mises yield criterion, three decomposed non-linear kinematic hardening-based Chaboche model and associative flow rule. Three-dimensional tubular geometry (as tested) has been analysed using in-house developed finite element code. The Chaboche’s parameters have been calibrated using the stabilized low-cycle fatigue test loop for a given pure axial strain amplitude. These calibrated parameters have been used to predict cyclic plastic material response for pure axial, pure torsion, in-phase axial–torsion and out-of-phase axial–torsion strain paths. The predicted cyclic stress–strain response under pure axial, pure torsion and in-phase axial–torsion conditions is nearly comparable to test response. However, the material stress response is underestimated in axial and shear directions for non-proportional axial–torsion conditions.

This work involves stress analysis of bolted structures using Finite Element Analysis (FEA) with High-Strength Carbon Fiber Reinforced Polymer (CFRP) composite material such as AS4/8552 R134 AW196 which can be replaceable with the steel for the construction of footbridges and railway bridges though it costs more than ancient steel but strength wise most strong approximately four times than steel. Two CFRP-steel models have been created. One with 16 layered CFRP-steel combination with [02/452/602/902]s ply orientation, and other is 8 layered CFRP-steel combination with [0/45/60/90]s ply orientation. Here, considering the pretension of HSFG bolts and tensile load which was applied to the connected plates, the stress and deformation behaviors and shear failure of bolts were studied. According to macro mechanical analysis of lamina, failure of lamina in terms of strength ratio is studied. Strength ratio versus Layers of graphs are plotted in order to determine the safe and unsafe laminae or order of failure of laminae from safe to unsafe. From the analysis, it can be concluded that weight reduction and hence material and cost saving of CFRP is possible by testing with the half of the thickness of the cover plates and with regular dimensions. From this study, it can be suggested that lesser material of CFRP can be used when compared with steel for the same application of the construction of bridges.

Reliability and durability of aeronautical components and systems are directly influenced by fatigue, which is perhaps the most prominent mode of their failure. Quality aspects like surface integrity affect component reliability, and in turn determine system safety. Quality–reliability–risk–safety paradigm is thus self-reinforcing, either as a vicious or a virtuous cycle. System safety principles, originally proposed by Joseph H. Saleh, are high-level, domain-independent and technologically agnostic principles built on the notion of level of safety hazard and its escalation to accident sequence. They include (i) fail-safe safety principle, (ii) safety margin principle, (iii) ungraduated-response principle, (iv) defence-in-depth principle, (v) observability-in-depth principle; to which (vi) human factors principle and (vii) integration-in-totality principle can be added. Reliability of the component, and safety of the system, can be effectively examined by applying these cardinal principles. The technical article brings out a few case studies related to fatigue failure of aero-engine and aircraft components, analyzing the progression of failure in light of the system safety principles. Suitable remedial measures are recommended to obviate the destructive manifestation of fatigue damage, like improving stiffness and fatigue strength, enhancing attenuation/damping, monitoring fatigue life consumption, isolating contributory factors, etc. so that crack initiation and propagation can be controlled by early anticipation, regular monitoring and timely actions. Fatigue fracture failure of airborne systems can be effectively analyzed using Functional Resonance Analysis Method (FRAM) propounded by Erik Hollnagel. The paper demonstrates the use of ‘FRAMED-IN-FRAM® Diagram’ developed by the authors, an improved version of the ‘FRAM Diagram’, for understanding the combinational, resonant and temporal aspects related to the emergence of a safety hazard consequent to fatigue deterioration of the component. The authors also introduce a new concept of ‘Reflexive Resonance’ using FRAMED-IN-FRAM® Diagram for analyzing and depicting the vulnerability/durability of fatigue-damage-prone components and systems.

Crack is an unavoidable flaw in structures with time, this crack increases and leads to failure of the structure. In this paper, numerical analysis was performed on RCC beam having a particular depth of crack for assessing the damage in the beam. Width as a parameter was used to check the variation in the damage. Variations in Stress Intensity Factor (SIF) for different beam widths were evaluated for opening and closing forces. The force transmitted by the reinforcement bars to the concrete element with the change in cover was evaluated. Additionally analytical studies were carried out on RCC beam strengthened by Fiber Reinforced Polymer (FRP) using ANSYS software. The effect of width of the beam and thickness of FRP laminate were the parameters used to study the behavior of the beam. From the study, it can be concluded that the geometry of the member plays a significant role in deciding the crack properties.

The manufacturing processes such as shaping, forming, cutting, heat treatment and joining processes are being adopted in engineering applications, and various types of tools are necessarily being deployed during these operations to produce components. In this context, the failure of HSS counter punch tool used in cold forging is reported from an industry, as cold forging is a part of forming processes. The problem has been entrusted to investigate the cause of failure taking into account the selection of input parameters considered during cold forging and also the steps involved in the tool making. The material M35 HSS tool had developed a long crack along the periphery passing through the central axis of the counter punch tool. The mechanical and metallurgical investigations were done involving hardness, microstructure, retained austenite measurement, fractography as well as the non-destructive tests, viz., visual inspection, dye penetrant test and ultrasonic detection as a part of this study. The investigation revealed fatigue-induced damage due to the application of one-time load during forging caused by the microstructural changes observed during the post processes. The root cause of failure of the tool is established based on the analysis and interpretation of the experimental data. Further, the reason of failure is communicated to the industry along with the possible solutions from the point of avoiding failure occurrence in future.

Nuclear pressure vessels are generally made of butt weld joints which are larger in size. Since it is difficult to perform experimental investigation on large structures with weld defects, a ring specimen of simpler geometry is considered for investigation. An experimental setup was fabricated to apply repeated loading on ring specimen, and the fatigue life of ring specimen with various weld defects like lack of penetration, lack of fusion, porosity, and undercut was recorded. Also, finite element models of ring specimen incorporated with weld defects are used to predict the fatigue life, and the same is compared with experimental results. The methodology adopted in the present work can be extended to investigate the influence of weld defects on fatigue life of roof slab.

Air Disc Brake is a safety critical system in a heavy commercial vehicle, and its components are subjected to various types of loads during braking. Fatigue damage of brake components due to cyclic loading is the most critical and common component failure among other failures. Fatigue is the most widely recognized reason for failure in metal components/structures, and the main aim of this study is to predict fatigue life of casting components with Finite Element Method (FEM) simulation and correlate/validate with experimental results. Fatigue analysis of Brake Caliper of Air Disc Brake which is manufactured by sand casting is carried out using strain-life method. This study considers only mechanical fatigue of strain-life theory with plastic stress and strain. Softwares, ANSYS 18.2 and nCodeDesignLife, are used to calculate component fatigue life under static loading condition. The influence of the various parameters like Surface Roughness, different Mean Stress Correction Theories, Stress Combination Method, and Stress Gradient on the simulated results were studied in detail to correlate/validate with experimental results. It is observed that fatigue life by nCode DesignLife strain base method gives good result in comparison with experimental result.

A numerical simulation was performed to study the fatigue behavior of a center pre-cracked thin panel of an aluminum alloy 6061-T6 repaired with a polymer composite patch. The patch consists of a thin separating woven GFRP (glass-fiber-reinforced plastics) ply and load-bearing UD-CFRP (carbon-fiber-reinforced plastics) plies. The model was simulated using the finite element package ANSYS 15.0. The cohesive zone material model (CZM) was employed to simulate the behavior of the interface between the skin and the patch. The numerical model evaluated J-integral for different crack lengths (2a = 20 mm, 22 mm, …., 32 mm). The value of stress intensity factor ( $$K_{I}$$ ) was evaluated for each crack length using equivalence relation between the J-integral and $$K_{I}$$ . A second-order polynomial curve was fitted to obtain the algebraic relationship between $$\Delta K_{I}$$ and crack length. The Paris law was invoked to get the relation between the crack growth and the number of cycles. The relationship, predicted by the numerical simulation, matched well with those obtained from experimental studies.

Constant amplitude fatigue crack growth rate tests were conducted on a nickel base superalloy IN718 at various stress ratios, R ranging from R = 0.1 to 0.7. Tests were conducted at room temperature and in lab air atmosphere. Tests were performed in a 100 KN computer-controlled servo-hydraulic test machine using compact tension specimens with sinusoidal waveform at 10 Hz. Crack length was monitored by compliance technique using COD gage. Increasing stress ratio was observed to increase crack growth rates and also decrease threshold stress intensity factor range, ∆Kth. Stress ratio effects on crack growth rates were correlated by using a two-parameter crack driving force, $$\Delta K*$$ . This approach was observed to provide a reasonably good correlation which can further be employed in modeling crack growth behavior under service loads.

Fatigue failure in dynamic structures occurs because of continuous cyclic loading; especially bending fatigue often takes place depending upon the loading under yield and ultimate strength of the material. Generally, fatigue data of material is not commonly accessible because of lengthy experimentation and unavailability of testing machines. There are some fatigue testing machines that are available with complex mechanism and data acquisition system at high operating cost. The research work presents design and development of a plane bending fatigue testing machine with simple operating mechanism and data acquisition unit to obtain fatigue life of isotropic and orthotropic material at comparatively low operating and manufacturing cost. The machine is designed with the application of DFMA principles, manufactured, assembled, and tested for design specifications and performance which includes measurement of angular displacement, speed setting, load measurement, and vibrations generated. At the end, the performance of the machine is tested with the experimental work on fatigue testing of Al alloy for plane bending. The testing performance is considered satisfactory, and an economical and accurate testing setup is developed.

Fatigue load is the most major type of load acting on the structural components. About 90% of the components fail due to fatigue. Hence, determining the fatigue life of a material is an important aspect of engineering applications. The fatigue life is estimated as number of cycles to failure. In this paper, fatigue life of polymer matrix composite material is determined using rotating bending fatigue test machine. Here, the composition of composite material is bidirectional fiberglass as a fiber and epoxy resin in the form of matrix. The volume fraction for epoxy is 40% and fiber is 60%. Hand layup technique is used as a method to assemble fiber and matrix. This sandwich material is cut in the form of dog bone shape, and specimens are tested on the machine. In this present work, experimental and simulation tests were carried out. Results obtained are within the acceptable limits. The bending moment applied to the specimen varied from 50 to 80 kg-cm. The experimental results have been compared with the simulation results. The maximum stress or bending stress obtained by manual calculation for 75 kg-cm bending moment is 377.1 MPa, and by simulation it is 381.41 MPa with an error of 1.13%. The number of cycles to failure for 55 kg-cm bending moment obtained by experiment is 7856 cycles, and by simulation it is 7950.5 cycles with an error of 1.19%. The range of values obtained by experiment and simulation are plotted as stress(S) versus number of cycles to failure (N) (S-N) graph.

The structural integrity of the rotor generator and turbine shafts of a 60 MW hydro plant has been carried out through the application of advanced Phased Array Ultrasonic Technique (PAUT) and crack growth rate analysis. The size and orientation of the crack-like defects were evaluated by the PAUT technique. The multi-array ultrasonic sensor was scanned all over the accessible surfaces of the shaft through manual scanning. The scanning was performed in different diameter sections of the shaft. The complete volume of the shaft was evaluated through scanning in different patches made from the top to bottom portion of the shaft. The critical defects identified by this technique with their locations and orientation inside the rotor have been presented. The stress and fatigue life of the shaft under defect-free condition have been carried out by finite element analysis using the commercial code ANSYS Mechanical®. The calculation of the remaining life of the rotor shaft was carried out based on the principle of fracture mechanics using the code FRANC3DTM. The residual life of the shaft was calculated based on the crack growth rate data of critical cracks close to the surface.

In aircraft turbine disc, cracks are originated at the trailing edge of the blades during operations. The literature review on microstructural studies revealed that the fatigue cracks are initiated due to high operating temperatures of turbine which led to failure of the disc and blades by stress rapture followed by fatigue crack propagation at the hub of the turbine. It is recommended that incorporation of functionally graded material (FGM) in the hub section of the turbine will impede the initiation and growth of crack at the hub of the turbine blades. A literature review on characterizing the effect of induction and laser hardening processes for fatigue life of steel alloy is systematically presented. The suggestion toward the improvement of fatigue life of an aircraft turbine disc and blades is addressed.

In today’s world, the elastomer is making an immense presence in many engineering applications like tires, etc. During service, the elastomeric component experiences complex loading cycles with varying amplitudes. Therefore, fatigue failure is a prime concern in their end-use application. The available effective techniques to predict fatigue life under complex loading is very crucial for designing the elastomeric component. The failure behavior of the elastomer depends on the various phenomena (Crack precursor size, crack growth rate, strain induce crystallization, fatigue threshold, load path) that governs the durability of the elastomeric component. In order to characterize the durability of the elastomer, several fatigue equivalence parameter-based studies have been introduced for multiaxial loading conditions. These fatigue life evaluation parameters include maximum principal strain, strain energy density (scalar parameter, independent of plane orientation), and crack energy density (plane-specific or critical plane parameter). This paper cites a comprehensive review of literature on fatigue behavior with prime focus on available methodology and models for crack initiation and growth prediction on the elastomer-based components. Different effective methods for fatigue failure prediction are reviewed and discussed.

Rubber materials are used in many pneumatic applications. Rubber has excellent damping characteristics and it experiences large reversible elastic deformation. For the safety and reliability of rubber components, it is important to predict the behaviour of rubber. In this research, fatigue life of rubber components is predicted by finite element analysis and developed fatigue life equation. Mechanical tests such as uniaxial tension, uniaxial compression and pure shear test were performed on NBR material for the material characterisation in ANSYS. A hyperelastic model was selected by performing the curve fitting in ANSYS. Fatigue tests on a standard dumbbell specimen of NBR material were performed at different strains, and fatigue life equation was derived with least square fit method and fatigue test data. Then the maximum principal elastic strain obtained through FEA was used as the fatigue damage parameter as mentioned in the literature. Maximum principal elastic strain was substituted in the obtained fatigue life equation and fatigue life of rubber spring was predicted. The results were validated by performing the fatigue test on rubber spring.

The objective of this paper is to present experimental work on fatigue life and fatigue strength of adhesively bonded teakwood filled circular hollow tube. Adhesively bonded teakwood filled circular hollow sectioned steel tube was subjected to 4-point rotating bending fatigue to determine the fatigue strength and fatigue life. S-N curve was drawn and relations have been built to predict the number of cycles for the applied stress or vice versa. The relations built in this paper can safely be applied for design of the fatigue life or fatigue strength of adhesively bonded teakwood filled circular hollow steel tubes. Experimental results were validated by static strength in bending by Euro code (EC4).

Due to an increasing need for sustainability, durability of concrete structures has become a matter of prime importance. And as far as durability of concrete is concerned, it is inversely proportional to its tendency to allow the ingress of water. It is thus quite instrumental in relating the measure of concrete’s resistance to exposure in aggressive conditions. This paper presents the effect of adding steel fibers in concrete on the surface water absorption using sorptivity test. The variation in the sorptivity with varying percentage of steel fibers in concrete is determined by measuring the increase in the mass of specimens resulting from absorption of water as a function of time when only one surface of the specimen is exposed to water as per ASTM C1585. Test results indicate that the presence of steel fibers in concrete reduces the surface water absorption significantly as compared to the plain concrete indicating increased resistance to the uptake of water and hence increased durability.

Many failures in aircraft structures are due to fatigue cracks initiating and developing from fastener holes at which there are large stress concentrations. In a typical wing skin, in the zone of riveted joint of rib/skin, the combination of high stress concentration could potentially lead to the appearance of the crack initiation and then crack growth under cyclic loading. Stress Intensity Factor (SIF) solutions are required for the assessment of fracture strength and residual fatigue life for defects in structures. In this context, many research works focused on evaluating the residual life of various cracked aircraft structures but only a few works have been done on light transport aircraft wing skin. The material used for wing skin is AL 2024-T351. A computational model for estimating the residual fatigue life of cracked wing skin is proposed. The complete computation procedure for the crack propagation analysis using low-cycle fatigue material properties is illustrated with the damaged wing skin. Initially, stress concentration effects at the cracked wing skin rivet holes are determined by applying analytical and numerical methods. Further, residual life and the failure mechanism in the cracked rivet holes of the wing skin are estimated. The wing skin with two cracked rivet holes for a pitch of 26 mm was analyzed using MSC NASTRAN/PATRAN for different crack lengths using MVCCI (Modified Virtual Crack Closure Integral) method by which strain energy release rate as well as stress intensity factors are calculated for different crack lengths, and fatigue crack growth life for progressive cracks for different R ratios is computed using a MATLAB program. Comparisons of the stress intensity factors estimated by FE analysis were in good agreement with the analytical solutions. Further, using SIF solutions, the residual life was estimated for the cracks emanating from the two rivet holes using crack growth models. The work also investigates the first failure mechanism out of two competing mechanisms of failure; Failure due to fracture or Failure due to plastic collapse at the net section between two advancing crack tips of the rivet holes of the wing skin. It was observed that the wing skin with crack rivet holes would fail by plastic collapse due to net section yielding. Further, the study can be extended to a multi-axial stress condition.

The cryogenic treatments improve fatigue life of tool and die steels. This work involves heating the H13 steel specimens to 1020 °C, quenching in oil thereafter double tempering at 520 °C for 2 h. Thereafter these specimens are subjected to minus 185 °C in a cryobath for 16 h and 1 h soft tempering at 100 °C. The nitriding was performed at 550 °C in the atmosphere of atomic nitrogen for 2 h to get the effective case depth of 200 μm. These specimens were subjected to rotating bending fatigue at constant amplitude with room temperature conditions at a speed of 3000 rpm. The H13 specimens were characterised for hardness, surface roughness and analysis of fractured specimens to investigate the improved fatigue life for cryogenically treated specimens. It was established that improved hardness, reduced surface roughness and moderate distribution of alloy carbides were accountable for the increased fatigue life for 16 h cryo-treated steel.

In elastic fracture analysis, stress intensity factors (K) and T-stress (T) are the two-important stress field characterizing parameters ahead at the crack-tip/front. In this paper, 3D finite element analyses were carried on Compact Tension Shear (CTS) mixed mode (I/II) fracture specimen with various thickness to width (B/W) ratios and loading angle (β) to evaluate the effect of loading angle on K and elastic T. For assort B/W ratios and β of the CTS mixed mode (I/II) specimen, the effective stress intensity factors (Keff) and T results predominantly vary from center to surface along the crack-front. The Keff and T results obtained in the present analyses were used to characterize the constraint effects in CTS mixed mode (I/II) fracture specimen.

Most of the household articles and devices which we use in everyday life are made of natural polymers and synthetic polymers. Existing research also reports that polymer nanocomposites show far better performance versus micro-fillers. Premature failure, of the machine components, occurs well within the endurance limit of the material. This failure due to fatigue is a common phenomenon on many of the applications across industries and hence the prediction and prevention of fatigue failures is critical for safe and economic operation of machines. This work reviews various methods of fatigue characterization of polymer composites. Stress–life and strain–life approaches have been applied by many researchers in this domain. The fatigue characterization leads to the development of life estimation curves by both these methods. There are also works done on other methods to arrive at Stress–life curves. This paper addresses these different methods of characterization and compares them. The analysis of these data for evaluation of various fatigue parameters is also covered in this work.

In the present era, life assessment of building is of paramount importance. In this paper, an attempt has been made in using the concept of fracture mechanics using steel fibers using software such as ANSYS, E-TABS, etc. Before that experimental investigation is carried out using steel fibers, and parameters such as fibers type, aspect ratio, and optimum dosages are covered. In general, fiber-reinforced concrete structures are more durable than normal RCC structures.

This paper aims at developing (LM13) a composite made of LM13 reinforced with varying percentage of fused SiO2 (3, 6, 9, 12%). Also the Fracture Toughness was evaluated both by experimental and FEA. Various metallic and Non-metallic chills were used during the casting process to ensure uniform heat dissipation. The effect of chilling on fracture toughness was also studied. ASTM (E399 1990) standards were used to carry out fracture toughness test. The presence of clusters of particles leads to premature fracture. Upto 9wt% there was increase in fracture toughness, beyond this limit decrease in trend was noticed. Highest fracture toughness was observed at 9 wt% with copper chill and was about 17% higher in comparison to unreinforced matrix alloy. The fracture toughness values as obtained by experimental and FEA are in close agreement with each other and marginal variation of 3–4% has been seen. This is a clear indication of uniform distribution of reinforcement particles in the matrix A- alloy (LM13).

Forming limit curves is one of the important parameters to know the formability of a material. In the present work, forming limit diagram of Al-6063 was obtained by using analytical software PAM-STAMP and it is compared by conducting out-of-plane test or Nakazima test. The experimental procedure for determining the forming limit curve requires expensive equipment. Forming limit diagram of Al-6063 is found by conducting out-of-plane test or Nakazima test in PAM-STAMP software. Trials are conducted to obtain actual FLD in terms of major and minor strains with respect to the velocity of the punch. Obtained results are compared with experimental values, there is a good agreement value between numerical and experimental solution.

Every machine with the relative motion of parts produces sound and vibration. All the gear boxes usually generate vibrations and respective vibration signatures may be taken as referable characteristics if the condition of the gear is good. During working condition, whenever fault occurs, it may result in serious damage of the gear box. The change in the gear pair meshing could result in changes in vibration signals. The accelerometer mounting on the gear box system is the accurate task for assessment of pair of gear. So the technique of monitoring the condition is very essential to prevent and diagnose the vibration of gear box. Nowadays damage identification and condition monitoring of gear boxes in the industrial machinery have received more attention from the researchers. To analyze the various fault and problems related with gear box failure in a working environment efficiently and accurately, few technologies like material technology, information technology, and processing of signals, etc. bring latest solutions. For the assessment of industrial gear boxes, many investigations are carried out for monitoring the condition of machinery. Signal processing and vibration analysis techniques are well known and much suitable for industrial practices. Since, the signals of vibrations from the gear box are transient and non-stationary in nature. Every technique has some disadvantages and may not be used in all condition, i.e., few failure detection is not possible by simple vibration method. At an early stage, simple analysis by spectral is not very successful to find the injury of gear.

Aluminium (Al)-based metal matrix composites have their own applications in automotive components, aerospace structure and many other structural applications because of their low density, good plasticity, high strength, good machinability, excellent resistance to corrosion and sensible thermal and electrical conduction, etc. Many of those applications need higher fracture toughness that is the ability to resist failure because of crack propagation. Fracture properties of composites are essential in assessing the flaw tolerance of the structures. The Characteristics of base metal and the reinforcing materials play an important role in dominant the toughness of composites. The various reinforcements utilized in the processing of metallic-based composites are Silicon Carbide, Aluminium Oxide, Titanium carbide, titanium dioxide and Boron Carbide, etc. Mechanical properties of metal-based composites are greatly affected by the properties of matrix and reinforcement materials, their geometry, composition and also the technique of process these composites. The present paper reviews the early investigation methods and recent methods and practices followed to gauge fracture mechanics parameters like stress intensity factor, J-integral, crack tip opening displacement, etc., for aluminium alloys and aluminium-based composite materials.

The mechanical properties of the materials depend on strain rate. The mechanical properties of material respond variously at quasi static conditions as well as high strain rate conditions. The Split-Hopkinson Pressure Bar is mostly used for high strain rate testing in range of 102–104 s−1 of strain rate. The SHPB is used to perform dynamic three-point bend test to measure fracture toughness. The strain rate of the pre-cracked specimen is measured using the strain gauges attached to the incident bar and transmitted bar. Additionally, a simulation study is carried out in which three dimensional models of a modified SHPB and a specimen are prepared and analysed using ANSYS©. The transient dynamic analysis technique is used for simulating the high strain-rate condition for the pre-cracked specimen. The results obtained through the simulation are compared with those obtained through the experiments. From the output of the simulation, the values of load and displacement are obtained. These values from the simulation are substituted to the analytical formula for calculation of the fracture toughness of pre-cracked specimen.

The objective of the work was to well understanding of the impact of exterior treatment on the bio reinforcement and optimization of mechanical strengths of the Bio fibril composites. Reseacher during this research provides better viewpoint over outcome of chemical treatment on the surface of Luffa-Tamarind fibrils by the NaOH and benzene diazonium chloride treatment for the tractile, flexural and compressive properties of crossover composites. The outcome of % of raw and chemically treated fiber content with and without presence of moisture, unwanted materials/impurities on mechanical properties was studied. The mechanical properties were ideally expanded at 40% wt. of surface customized Luffa-Tamarind fibers loading and underneath or above 40% wt. it exhibited a poorer mechanical properties. The alkali and benzene diazonium chloride treatment consumes the voids spaces of fiber, diminishes the unwanted materials, aligns uneven fibers, provides rough surface topography, improves the aspect ratio and strengthening efficiency.

The effort of instigator in this recent work was to investigate the effect and impact of fiber length and surface treatment on the mechanical properties of biofibers fortified composites. Biofibers are hydrophilic and resin is aquaphobic, which does the fibers and resin contrary and effects in deprived interfacial binding among the resin blend and fibers. Fundamental inspiration driving this chemical action was to shrink their wetness retention property of the fibers and, further more, to expand the compatibility with matrix blend. In the current research work, hybrid biofibers composites were fabricated by blending 10% vinyl ester matrix with 90% epoxy with the reinforcement of Bagasse–Luffa fibers into the resins blend. The superiority and optimal values of tensile, compressive, and flexural properties were observed for 2-cm fiber length, benzene diazonium chloride-processed composites than the unprocessed fiber composites, 5% NaOH-treated, 10% NaOH-treated hybrid biofibers composites, and other chemically customized composites.

In structural integrity analysis of components operating at high temperature, it is important to understand whether the presence of residual stresses lead to failure [1]. Accurate prediction of the creep crack initiation is needed in structural integrity assessments of components. General assessment of structures uses the experimental data obtained from laboratory test specimens subjected to either displacement or load tests but in actual operating condition, components are subjected to both inherent residual stresses and applied load. In the current research work, two test rigs are designed and tests are performed to understand the effects of EFU, long-range residual stress and external applied load on creep behaviour of 316H stainless steel. Results obtained show that, for the same total initial reference stress, the time for crack to grow is lower in the case of mixed loading conditions compared to load-controlled tests. The longer crack growth times are a consequence of the relaxation and redistribution of the residual loads in the structure. The initiation time is also a function of the elastic follow-up.

In the original version of the book, the Volume Editor “Ravindra R. Malagi's” affiliation has been corrected from “Mechanical Department, KLS Gogte Institute of Technology, Belagavi, Karnataka, India” to “Product Design and Manufacturing, Visvesvaraya Technological University, Belagavi, Karnataka, India”. The book has been updated with the change.