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Damage in gas turbine engines can accumulate from multiple damage mechanisms including creep, fatigue, and oxidation. Each damage mechanism is influenced by various parameters which typically occur during different portions of engine operation. For instance, fatigue is influenced by large stress/strain ranges that occur during startup and shutdown transient conditions while creep is affected by sustained stress and temperature at dwell conditions. In some cases, the maximum damage location for one mechanism could experience negligible contribution in damage from any other mechanism, but in most cases, there is some degree of influence from two or three mechanisms. In those instances, damage will accumulate at various rates during separate portions of operation under different damage mechanisms. Since some applications require engines to dwell for long periods of time while other applications favor more frequent cycling, every engine will accumulate damage differently at each location. Therefore, it is difficult to estimate which location is critical to durability, rendering it necessary to capture all possible critical locations so that damage can be estimated for each application. This paper suggests a method by which to visualize and select critical locations based on all possible customer use scenarios. Once critical locations are identified, a Reduced Order Model (ROM) can be generated for each point of interest and damage can be estimated and monitored using data collection. Damage mechanisms can be combined if micromechanistic affects are additive, the material response compounds, or the material properties evolve with time. Examples of each case are demonstrated. In addition, the visual representation of damage interaction allows for uncertainty to be visualized and implemented to rank location criticality.

To increase fuel efficiency and reduce emission, aluminium alloys have been increasingly used in automotive body-in-white structures for lightweighting. Due to its advantages over some of the more traditional joining technologies, self-piercing riveting (SPR) has been widely used for these lightweight structures. Research has showed that friction is a very important factor that influences both the riveting process and joint strength for SPR, but these influences have not been fully understood. In this paper, an innovative method was used to modify the local surface of the top sheet around the rivet piercing location with different impression tools (the central pin, the small ring, the medium ring and the large ring) and garnet particles to study the influence of local frictions on rivet inserting process, joint features and static lap shear strength. The results showed that the local surface textures on the aluminium sheet did not have significant influence on the rivet inserting process based on displacement-force curve analysis. The local surface textures could slightly change the joint features, especially the rivet head height, but overall this influence was not significant. The lap shear tests showed that ring impressions with garnet particles and central pin impressions on the bottom surface of the top sheet increased the static lap shear strength of the SPR joints. The results confirmed that the critical location for local friction influence on the lap shear strength was around the rivet leg piercing location.

Many engineering structures are exposed to non-proportional fatigue loading. However, at the critical location of crack initiation, often only one of the load sequences dominates – the individual load cases result in different crack initiation sites. Based on engineering judgment a simplified local uniaxial or proportional loading situation may be assessed. In general, the critical location must be identified by calculating fatigue lives for a variety of locations. The position of the critical location depends on the hypothesis applied for life calculation – besides loading, geometry, material and many other influence factors. For sharp three-dimensional notches the region for the search of the critical location may be restricted considerably. Weld start and stop points are an industrial example for such sharp notches. They are the object of the present investigation. They are exposed to nominal normal and shear loading. The individual hot spots for crack initiation lie necessarily close together. A strong interaction of the loading cases for both proportional and non-proportional loading was experimentally observed. In the numerical investigation notch stresses were calculated using an idealised weld end model. Based on the critical plane approach according to Findley, numerical interaction lines were produced.

In the present paper, fatigue life of a steel box girder bridge has been evaluated by two approaches and the influencing parameters on fatigue life have been studied. In the first approach, the box girder bridge has been idealized as a Euler–Bernoulli beam and the coupled bridge–vehicle equations are developed. In the second approach, vehicle equations are first solved taking bridge as rigid. The pavement force found from the vehicle response and road roughness has been given as input in 3-D FEM model created in CSI Bridge. Fatigue life of the bridge component at the critical location has been found out using Miner approach and the stress time history from coupled and uncoupled schemes has been used for comparison purpose. The parameters which affect the fatigue life, i.e., velocity of the vehicle and road surface roughness are varied to observe the effect on fatigue life.

Scatter of structural fatigue life is mainly caused by the variability in structures and load-time histories. To study the scatter of structural load-time history of aircrafts in a fleet, this research is focused on analysis of operational load spectra at four typical structure details, of which representative coupon fatigue tests have been carried out. First, operational load-time histories at critical locations in question of each aircraft are obtained according to the flight-data based load equation and transfer function relating the monitored load to the critical location stresses. Then, the fatigue notch coefficient in local stress-strain method is calibrated and validated by representative coupon test data and then used to calculate fatigue damage under different structural load-time histories of each aircraft. Finally, statistical analysis of the fatigue damages is conducted on the assumption of log-normal distribution and scatter factor are obtained. It has indicated that there are significant differences in the scatter factor of different structural load-time histories. It may be advisable to fully consider the differences of scatter factor among different structures in structure fatigue life assessment.

For RC columns exposed to blast loads, fibre reinforced polymer (FRP) is employed to examine its effectiveness in strengthening the concrete structure against blast load. It should be noted that no systematic studies could be found in the literature to derive pressure and impulse (P-I) diagram for FRP retrofitted RC columns. Therefore, the objective of this research is to develop finite element model to provide data for use in the development of P-I diagram that can be used to mitigate blast hazards and predict damage in RC columns retrofitted with FRP. In this study, various strengthening scheme performed against blast loads numerically by running computer simulations using the commercial software LS-DYNA. Validation of the models is performed based on the blast field test to investigate the accuracy of model simulations to present the behaviour of the models. The research compared the structural behaviour of an un-strengthened RC column with various column strengthened with different FRP wrap thickness, strength and arrangement. The results of the simulations showed that strengthening with FRP is an effective way to increase the blast resistance capacity of columns. This information would allow the designer to identify the critical location for placing blast barriers for protection purpose.

In trolleybuses in service, fatigue cracks were frequently encountered in a welded structural detail in their rear axle housing. Sufficiently representative stress-time histories for the critical cross section through this part were obtained by measurement during rides with empty as well as fully-loaded vehicles. The fatigue characteristics of the critical location had to be established by estimation. This information was used as the basis for parametric calculations of fatigue life. The main purpose of these calculations was to ascertain whether these in-service failures could have been predicted (and prevented) during the design stage, and what their main cause had been. Furthermore, this investigation explored the feasibility of verifying this structural detail's service life using the fatigue life distribution function.

The wing leading edge is one of the aircraft structures which are vulnerable to birdstrike. Therefore, Federal Aviation Regulation has clear requirements of anti-birdstrike performance for wing leading edge. However, the impact location is not specified in aviation regulation. The forefront of the wing leading edge is selected as a critical location for the birdstrike in most researches. But the rationality of the selection is not given. This paper proposes an analytical method for determining the critical location that causes the most severe damage under impact due to birdstrike. The analysis is based on the concept of effective impact, i.e. the component of the bird velocity perpendicular to the surface of wing leading edge. A birdstrike model is established using Pam-crash and used to validate the analytical prediction. The numerical model proves its effectiveness compared to the birdstrike test. The residual compressive strength of the spar when the birdstrike is at the critical impact location determined by the proposed method is 44.5% of that at the traditional impact location. Moreover, the critical penetrating velocity of the traditional impact location is not the lowest. In other words, the traditional impact location is not the weakest. Airworthiness verification experiment of birdstrike on wing structure should pay attention to this aspect.

In the past few decades, effect of natural hazards such as earthquake, wind etc. on existing structures has attracted the attention of designers. Progressive collapse is nothing but a condition of indigenous failure of prime structural element which in turn leads to the collapse of connecting members and then it leads to the additional collapse. For the case of progressive collapse, damage is included in the model through the elimination of important structural component like column. The progressive collapse design guidelines primarily suggest the simplified analysis actions occurred due to the sudden removal of specific columns in a building. The study of analytical approaches for evaluating progressive collapse is carried out by linear static analysis using Alternate Path Method (APM) recommended in General Service Administration (GSA) guidelines and the same is presented in this study. This study involves the use of various general methods of progressive collapse design & evaluation based on numerical mock up and experimental information. For this study, a multistoried composite building (i.e. G+7) is considered. The prime objective of this study is to analyze the composite building by removing columns at different locations and finding out critical location of column vulnerable to progressive collapse and also prevention of progressive collapse of structure using linear static analysis. Location of removed column, Number of floors, vertical irregularity were studied and their influence was also carried out in this research.

The inner vessel of FBR-1&2 separates the hot pool sodium from the cold pool and permits the passage for the standpipes. Stress analysis of the inner vessel, which is designed based on this requirement has been performed under mechanical loadings for normal operating, operation basis earthquake and safe shutdown earthquake conditions. Thermal stress analysis has been carried out on the optimized geometry thus obtained. Progressive deformation and creep-fatigue damage have been estimated for normal operating condition by using elastic analysis method as per the RCC-MR code. The critical location is the maximum thermal stress region where the creep damage is greater than one. On considering stress relaxation at this location and anticipating the presence of weld at the critical location, the creep and fatigue damages are found to be 0.7 and 3.89E−08 respectively. Hence the optimized geometry with the proposed thickness and loading conditions meets all the limits as per RCC-MR.

A series of 3D soil–fluid coupled finite element analyses was conducted to examine the long-term tunnel behaviour of an old cast-iron cross passage in stiff London clay. In the proposed geotechnical FE model, an advanced critical state constitutive model was employed to simulate complex soil behaviour, whereas the details of the tunnel linings was simplified using shell elements. The computed time-dependent soil load derived from the geotechnical model was then applied to a structural finite element model where the details of the cross passage structure such as bolted-joints and tunnel segments were explicitly modelled. This proposed semi-coupled soil-structure model shows agreement against field observations and it was found in this particular case that the structural condition evaluated from the FE model is more critical than that of the conventional bedded ring method. Results show that the surface ground settlement is governed mainly by the twin tunnel construction and the presence of the cross passage does not increase the settlement. On the other hand, the construction of a cross passage affects the structural performance of the adjacent running tunnel in both short term (undrained) and long term (soil consolidation). In particular, the critical location is identified to be the tunnel segment adjacent to the opening at the axis level and its stresses and deformation increase with consolidation time.

Prostheses products must undergo simulation and physical testing, before clinical testing. Finite element method is a preliminary simulation for in vivo test. The method visualizes the magnitude of the compressive force and the critical location of the Total Knee Replacement (TKR) prostheses design. In vitro testing is classified as physical testing for prostheses product. The test is conducted to evaluate the potential failure of the product and the characteristics of the prostheses TKR material. Friction and wear testing are part of the in vivo test. Motion of knee joints, which results in the phenomena of extension and deflection in the femoral and tibia insert, is represented by friction and wear testing. Friction and wear tests aim to obtain an approximate lifetime in normal and extreme load patterns as characterized by the shape of the friction surface area. The lifetime estimation requires friction and wear full-scale testing equipments for TKR prostheses products. These are necessary in obtaining ...

Certain surface defects of significant depth with maximum linear indication of 20 mm at the weld area have been observed during Liquid Penetrant Inspection (LPI) of the Inclined Fuel Transfer Machine (IFTM) welded chain. The same has been subjected to fatigue and break load testing to ascertain its structural integrity under service conditions. Two specimens have been subjected for testing to get repeatable experimental observations. Both the specimens tested for the required number of fatigue cycles (97000 cycles as per ASME, Mandatory Appendix 6) towards the structural integrity demonstration. At the end of fatigue testing, the maximum linear indication of the surface defect of the weld area increased from 20 mm to 25 mm without any loss of integrity. Individual links of both the chains were able to articulate freely after completing the fatigue test. After completing the required fatigue cycle both the specimens were subjected to break load testing. The lowest break load obtained from both the specimen was 27.1t and the respective collapse load obtained as per the ASME double slope method was 22 t. The above results indicated that, IFTM chain assembly qualifies for the safety with very high margins. Also, these experimental results give confidence that, collapse load obtained by the ASME double slope method is having a very high margin (∼ 18%) with the actual break load. Finite element analysis has also been performed before conducting the experiment to understand the overall stress distribution of the chain under load condition and also to identify the critical location. The critical location predicted by FE analysis was in good agreement with the experimental results.

Fatigue analysis of main landing gear of typical fighter aircraft was carried out using MSC Fatigue software considering the strain spectra measured at critical location during the flight starting from taxiing, take-off to landing. In the absence of load information on the landing gear, a methodology was proposed to calculate the equivalent load system from measured strains and verified. Fatigue life of landing gear was obtained using various stress spectra based on stress-life approach and was compared with the fatigue life calculated using constant life diagram (CLD) approach. Fatigue life estimation using Gerber mean stress correction was found to be in good agreement with the fatigue life estimation using CLD approach. Fatigue analysis using maximum absolute principal stress criterion and linear damage rule give the conservative fatigue life, and hence, these criteria may be used as fatigue life estimation criteria for design.

To investigate the potential of using dynamic distributed fibre optic sensing (DDFOS), a series of slender and deep reinforced concrete beams were tested. The beams were loaded cyclically using combinations of three and four-point bending and then tested to ultimate while DDFOS was used to measure the reinforcement strains. The DDFOS data was used to assess the increase in deflections due to cyclic loading as well as the change from beam action to arching action in some specimens. The strain profiles were able to capture the moment of failure including critical location in terms of peak reinforcement strains.

Laboratory fatigue testing is widely used to evaluate fatigue characteristics of asphalt mixtures in the pavement design. The fatigue results based on the classical fatigue analysis is influenced by the test types and specimen size. The goal of the research in this paper is to develop a new fatigue analysis method, which enables comparison of the fatigue relations obtained from different types of fatigue test and using different specimen sizes. The yield surface at the critical location of the specimen was determined in the I1 − √J2 space based on monotonic tension and compression test results. Then a new parameter RΔ was introduced as an indicator of the “safety against failure” at a certain stress state. A straight line was found by plotting RΔ at the critical location and the fatigue life on log–log scale. The results show that this new fatigue analysis method provides a possibility to compare the fatigue results obtained from different test types and specimen sizes.

PURPOSES: The objective of this study is to analyze and evaluate the behavior of orthotropic steel bridge deck pavement using three-dimensional finite element analysis and full-scale wheel load testing. METHODS: Since the layer thickness and material properties used in the bridge deck pavement are different from its condition, it is very difficult to measure and access the behavior of bridge deck pavement in the field. To solve this problem, the full-scale wheel load testing was conducted on the PSMA/Mastic bridge deck pavement and the deflection of bridge deck and horizontal tensile strain on top of pavement were measured under the loading condition. Three-dimensional finite element analysis was conducted to predict the behavior of bridge deck pavement and the predicted deflection and tensile strain values are compared with measured values from the wheel loading testing. RESULTS: Test results showed that the predicted deflections are 10% lower than measured ones and the error between predicted and measured horizontal tensile strain values is less than 2% in the critical location. CONCLUSIONS: The fact indicates that the proposed the analysis is found to be accurate for estimating the behavior of bridge deck pavements.

Modern 9-12%Cr steels are widely used for steam turbine components. For the design optimization and lifetime estimation of steam turbines, it is very important to investigate and describe the deformation as well as crack initiation behavior at critical location of steam turbine components under multiaxial service-type loading conditions. In this paper a phenomenological lifetime estimation method was validated by multiaxial loading. The applicability and reliability of this lifetime estimation model was confirmed by a recalculation of biaxial creep fatigue tests performed on cruciform specimens of rotor steel X12CrMoWVNbN10-1-1 successfully.

For the fatigue failure mode of turbine of turbocharger for vehicle application, the method for fatigue reliability analysis and fatigue life prediction of turbine is studied based on the endurance test profile of engine. Firstly, the critical location of turbocharger turbine with fatigue failure mode is determined. Then, the fatigue stress process of turbine is calculated according to the main operating modes consisted of the endurance test profile of engine. The fatigue strength of critical location of turbine with fatigue failure mode is studied through the fatigue test of imitation specimen, and the relationship between the fatigue life of turbine and stress is developed. Further, according to the endurance test profile of engine, the reliability model of turbine with fatigue failure mode is developed, and the rule that the reliability of turbine with fatigue failure mode changes as the cycle number of endurance test of engine is studied. Finally, the method for determining the reliable fatigue life of turbine is proposed.

At present the highway horizontal curve section of Anti-glare panels with a uniform height, through investigation and analysis, the arrangement of the glare effect is not very good ,under mixed traffic, to analyze the reasonableness of the highway glare plate height,the ighway glare plate heigh of the road sightline safety model is set up , the design speed of 60km / h, 80km / h,anti-glare plate height of model is proven。Concluded，In the combinations of different vehicles，anti-glare plate height ranges between 1.15 and 1.65；By contrasting static line of sight and moving-horizon，in thedifferent velocity, when vehicles travel a critical location, vehicle traffic safety start to receive greater impact. Conclusions can be got,first,vehicles travel in the flat curve sections, according to different traffic, adopt different glare height; When the design speed is 60km / h, if central angle is less than 15 °, vehicles which is traveling on the section is safe; When the design speed is 80km / h, if central angle is less than 30°, vehicles which is traveling on the section is safe.

Accurate determination of critical structure responses plays a vital role in the ability of the Mechanistic-Empirical Pavement Design Guide (MEPDG) to achieve a reliable pavement design. In the MEPDG, the responses generated by a single axle are evaluated at a series of predefined locations, and responses under multiple axle gears are determined using the responses from a single axle following the principle of superposition. This research indicates that the approach currently employed in the MEPDG is able to identify the critical location and obtain the critical response for a tandem axle, while it is inadequate for a tridem or quad axle. The primary reason for the inadequacy is that the response along the outside axle of a tridem or quad gear is not computed and compared to responses at other locations. The erroneous critical location identified by the MEPDG for a tridem or quad axle will lead to an underestimated critical response and consequently an overpredicted pavement life. The results show...

Fatigue failure has become a major concern in the automobile and aircraft industry, heavy machinery etc. Failures by fatigue are especially dangerous because they are unpredictable; giving no prior notification of the imminent failure they occur suddenly. Front axle of tractor is one of the major and very important components that undergo severe load conditions and it fails unexpectedly causes unrecoverable losses. The objective of this study is to analyze the existing design of the front axle of the tractor for service load conditions and redesign to its functional requirements and to increase its life expectations. Finite element simulation is carried out for the existing front axle using ANSYS. The critical location of the front axle has to be identified and redesigned to ensure the safety. The existing geometry of the front axle is modified to the optimum size which suits for functional requirements with increased life and minimum cost. In this analysis, the geometry of the front axle is modified and a new design is proposed. The life expectancy of the front axle was predicted for the dynamic load using ANSYS fatigue design module.

Currently, structures are designed without structural health monitoring (SHM) in mind. It is proposed that SHM should be addressed at the design stage of new structures. This paper explores the benefit which can be gained from such considerations. The scope encompasses Lamb-wave-based SHM and a given fatigue critical location (FCL). Optimization is performed using specialised ray tracing. A case study is carried out using a specimen that simulates a hard-to-inspect region in a fuel vent hole in wings structures of aircraft. This work will report on the potential use of the focussing of stress wave to improve detectability of defect in this hard-to-inspect location. Following optimization, results are produced numerically and experimentally. The results revealed sensitivity to damage is nearly doubled while minimum detectable damage size is significantly decreased. As a result, this study brings together an assortment of specialised tools to form a workflow ready for implementation.

A globe valve is a linear motion valve used to shut off and regulate fluid flow in pipelines. Depending on the number of process connections, they are produced as two‑ or three-way valves. The main valve component carrying the internal pressure is the valve body. For safe exploitation, the valves are designed with the allowable internal pressure taken into consideration. The aim of this paper is to investigate the influence of the wall thickness on the allowable and failure pressures of two- and tree-way globe valve bodies, DN50 and DN100 respectively. Twice-elastic-slope (TES) and the tangent‑intersection (TI) methods are used to obtain the plastic collapse pressures at the critical location which was determined (Fig. 1a and 1b) at the location where maximum equivalent plastic strain throughout the valve body thickness reaches the outer surface. Obtained values are used afterwards to calculate corresponding allowable pressures according to the limit design method, while the failure pressure at the same location was determined as the highest point from the load-maximal principal strain curve. Calculated allowable pressure values, for both valve bodies, are compared with the corresponding ones obtained using the EN standard.

This paper was presented the finite element modeling, analysis and fatigue life prediction of lower suspension arm using the strain-life approach. Aluminum alloys are selected as a suspension arm materials. The structural model of the suspension arm was utilizing the Solid works. The finite element model and analysis were performed utilizing the finite element analysis code. TET10 mesh and maximum principal stress were considered in the linear static stress analysis and the critical location was considered at node (6017). From the fatigue analysis, Smith-Watson- Topper mean stress correction was conservative method when subjected to SAETRN loading, while Coffin-Manson model is applicable when subjected to SAESUS and SAEBRKT loading. From the material optimization, 7075-T6 aluminum alloy is suitable material of the suspension arm.

The high temperature notched fatigue strength of the CMSX-4 single crystal superalloy has been experimentally investigated. Notched specimens with orientation have been tested at 950°C in load control in the LCF life regime. SEM observations of the failed specimens has been made in order to associate the actual crack initiation location in the notch to the crystallographic orientation and to the critical location in the notch as given by suitable multiaxial fatigue parameters. In order to model the material behavior in the notch, stress-strain analysis of the notched specimens was performed by an elastic-plastic FEM procedure; the parameters describing the material behavior of the single crystal superalloy have been identified by comparison with experimentally determined stress-strain fatigue behavior of smooth specimens. A suitable model for the assessment of the fatigue life of single crystal materials is proposed for the purpose of application to the design of turbine engines components.

This paper discusses the development of a procedure for computing creep and stress relaxation at the critical location in a through-hole structure. A high-speed methodology was developed for calculating cyclic creep and stress relaxation at critical locations of a pile on elastic foundation subjected to cyclic thermomechanical loading. This simplified analysis was exercised for two cases involving a pile on elastic foundation problem with different thermomechanical loading. The simplified analysis exhibited no computational problems and gave a stable solution for the full dwell times. Comparisons made with experimental results for these cases gave an excellent agreement at a much faster computing time. This simplified procedure is expected to be even much faster when an entire pile on elastic foundation assembly is analyzed.

The effect of the size and location of spherical pores on the transverse rupture strength of WC-10Co cemented carbides was investigated. Based on the observations of fractographies of the transverse rupture test specimens, it was found that the cracks in WC-10Co cemented carbides initiate from the spherical closed pores near the surface, not from the open pores at the surface. The relationship between the transverse rupture strength and the size and location of the spherical pores was analyzed considering the stress field near the spherical shaped pores. In this analysis, for one spherical pore, a critical location exists within the specimen where the transverse rupture strength is minimized, but not on the surface of the specimen. By considering the various sizes and locations of pores, a map showing the transverse rupture strength according to the location and size of pores was obtained. © 2007 Elsevier B.V. All rights reserved.

In this chapter, factors affecting S–N curves will be discussed, and the determination of the stress range at the critical location (hot spot) of the joint is discussed as well. Methods for determining stress concentration factors will be presented. In part III, tubular joints and plated connections, termed “critical details” or simply “details,” are discussed. For the sake of consistency, discussions of fatigue criteria in this chapter will be mainly based on NORSOK. However, it is recommended that readers refer to the codes relevant to their projects such as IIW, Eurocode 3, IACS, ABS, and DNV, among others. In general, a thickness correction to the design equation for the S–N curve is required when plate thickness is thicker than reference thickness. In general, the fatigue life in seawater under free corrosion is 33% of the life in air at high-stress ranges. The classification societies define fatigue criteria in their rules and guidance/guidelines. The most efficient methods involve possible improvement of the design, such as reducing geometric stress concentration factors. The fatigue analysis procedure is based on ranges of cyclic principal stresses. To determine the stress range, two approaches have been developed, the “nominal stress” approach and the “hot-spot stress” approach. A stress concentration factor may be defined as the ratio of the hot-spot stress range over the nominal-stress range.

The interest of the fatigue life for rubber components was increasing according to the extension of warranty period of the automotive components. In this study, the fatigue lifetime prediction methodology of the vulcanized natural rubber was proposed by incorporating the finite element analysis and fatigue damage parameter determined from fatigue tests. Finite element analysis of 3D dumbbell specimen and rubber component was performed based on a hyper-elastic material model determined from the mechanical tests. The Green-Lagrange strain at the critical location determined from the finite element analysis was used for evaluating the fatigue damage parameter of the natural rubber. Fatigue tests were performed using the 3D dumbbell specimens and rubber component with different levels of maximum strain and various load. Fatigue life curves can be effectively represented by a following single function using the maximum Green-Lagrange strain. Fatigue lives of the natural rubber are predicted by using the fatigue damage parameters at the critical location. Predicted fatigue lives of the rubber component for automobile vehicle agreed fairly with the experimental fatigue lives.

Fatigue lifetime prediction methodology of the vulcanized natural rubber was proposed by incorporating the finite element analysis and fatigue damage parameter determined from fatigue test. Finite element analysis of 3D dumbbell specimen of natural rubber was performed based on a hyper-elastic material model determined from the tension, compression and shear tests. Stroke controlled fatigue tests were conducted using fatigue specimens at different levels of mean strain. The Green-Lagrange strain at the critical location determined from the FEM was used for evaluating the fatigue damaged parameter of the natural rubber. It was shown that the maximum Green-Lagrange strain was proper damage parameter, taking the mean strain effects into account. Fatigue lives of the natural rubber are predicted by using the fatigue damage parameters at the critical location. Predicted fatigue lives of the natural rubber agreed fairly well the experimental fatigue lives a factor of two.

Fatigue lives obtained from complex testing and monitoring of different components often involve some degree of discrepancy in results due to geometrical variations, even when they are tested under controlled conditions and have a similar surface cyclic strain range at the critical location. Recently, several fatigue models have been developed to improve the correlation of specimen lives using a critical ‘process zone’ that surrounds the damaged material. A review of such an approach is presented. The approach is based on critical subsurface strains and consists of a fatigue damage summation procedure in the affected area. The fatigue life-prediction model is applied to two structural materials using three geometries subjected to biaxial cyclic stresses. These include notched bars, rhombic plates and car components. The subsurface strains are evaluated by using a detailed elastic–plastic finite element analysis, and by considering critical subsurface fatigue strain paths. It is shown that in the several cases investigated, the subsurface approach appears to improve life predictions.

The residual stresses that occur as a result of nonhomogeneous heating and cooling during welding may have a significant effect on the accumulation of fatigue damage in a welded joint. The problem is complicated not because of the complex spatial distribution of the residual stress fields, but because those fields typically change under an applied load. The present study considers the effect of residual stresses on fatigue damage accumulation in a welded joint subjected to stochastic loading. The influence of residual stresses on stochastic fatigue damage accumulation is accounted for by a simple approach based on an elastic–perfectly-plastic material model and the Gerber correction factor. The model assumes that the residual stress remaining at the critical location depends on the largest nominal stress ever endured by a welded joint. The model predicts that the residual stresses during stochastic loading randomly decay to zero. The effect of material yielding is additionally investigated by considering an elastic–plastic material model with linear kinematic hardening. The residual stresses in this case are computed through Monte Carlo simulations. It is demonstrated that the effect of material hardening is to reduce the rate of residual stress decay and thus to accelerate the rate of fatigue damage accumulation.

This paper provides a comprehensive description of the analysis and fatigue testing performed by Southwest Research Institute (SwRI) in support of Phase II of the AlphaSTAR Corporation’s USAF STTR project entitled, “Hybrid Structures for Improved Damage Tolerance of Unitized Structures.” These analysis and fatigue tests explored the effect of a fiber metal laminate (FML) material used as structural reinforcement of a test coupon representative of a fatigue critical location on a USAF fighter/trainer airframe. The analysis, testing objectives, test setup, test procedure, and the results will all be detailed for the coupon. The tests included fatigue testing of the baseline geometry and testing a new FML material. In Phase I of the STTR AlphaSTAR developed methods and tools to analyze FMLs. The technology was transferred to SwRI as part of the Phase II effort. SwRI performed a damage tolerance analysis of the FML coupon using analysis routines MCQComposites, MCQ-Metals and GENOA to predict the FML crack growth life. The analytical results accurately predicted the FML test. This paper will discuss the coupon testing and analytical techniques validation of the analysis with the test data. The purpose of this paper is not to document the development of new analytical method but rather to demonstrate the maturity of an analytical method and its transition to use by industry.

A simplified analysis of cyclic elastoplastic creep responses in structures subjected to cyclic mechanical loads with a holding time at high temperature is presented in this paper. The main feature of this method is to transform the complicated response analysis to another approximately equivalent problem—the elastoplastic analysis of a structure subjected to a cyclic loading with variant load amplitude, while the load amplitude variation in each loading branch is determined by the amount of stress relaxation during the holding time before the subsequent load reversal. Then two methods which are used in simulating cyclic elastoplastic responses and creep stress redistribution respectively as well as a load equivalence technique to deal with their interaction are combined to track the response evolution of cyclic elastoplastic creep at a critical location concerned in a structure.

In this paper, analysis of an aircraft crash upon an outer containment of a nuclear power plant is presented. The effect of target yielding is considered simultaneously by calculating the reaction time in a time marching scheme. The concrete model employed is capable of predicting the cracking and yielding. The response for different cracking strains and different locations of aircraft strike for different aircraft has been studied. Critical location of aircraft strike for the containment has been investigated. The analytical procedure and the material model used are found to be capable of representing the aircraft impact response of the containment structure.

Random-amplitude fatigue situations are studied to determine the possible effects of residual stresses induced by the welding of the specimens. Experimental results show that large-amplitude precycling of a welded specimen can significantly extend its fatigue life under small constant-amplitude loadings, and that this effect is consistent with the results of the Gerber formula for the effect of mean stress, along with an assumption of elastoplastic stress-strain behavior of the specimen. This model predicts that the remaining residual stress at the critical location in the specimen is a function of the largest load that has ever been applied to the specimen. For a stochastic loading this implies that the mean stress gradually decays in a random manner throughout the fatigue life of the specimen. Numerical results show that the stochastic fatigue life may be significantly extended beyond that predicted by neglecting the decay of residual stress.

Rubber components have been widely used in automotive industry as anti-vibration components for many years. These subjected to fluctuating loads, often fail due to the nucleation and growth of defects or cracks. To prevent such failures, it is necessary to understand the fatigue failure mechanism for rubber materials and evaluate the fatigue life for rubber components. Fatigue lifetime prediction and evaluation are the key technologies to assure the safety and reliability of automotive rubber components. The objective of this study is to develop the durability analysis process for vulcanized rubber components, which is applicable to predict fatigue lifetime at initial product design step. Fatigue lifetime prediction methodology of vulcanized natural rubber was proposed by incorporating the finite element analysis and fatigue damage parameter of maximum Green-Lagrange strains appearing at the critical location determined from fatigue test. In order to develop an appropriate fatigue damage parameter of the rubber material, a series of displacement controlled fatigue tests was conducted using 3-dimensional dumbbell specimens with different levels of mean displacement. It was shown that the maximum Green-Lagrange strain was a proper damage parameter, taking the mean displacement effects into account. Nonlinear finite element analyses of the engine mount insulator and 3-dimensional dumbbell specimens were performed based on a hyper-elastic material model determined from the simple tension, equi-biaxial tension and planar test. Fatigue lifetime prediction of engine mount insulator was made by incorporating the maximum Green-Lagrange strain values, which was evaluated from the finite element analysis and fatigue tests, respectively. Predicted fatigue lives of the rubber component showed a fairly good agreement with the experimental fatigue lives. Fatigue analysis procedure employed in this study could be used approximately for the fatigue design.

A proposed new IAEA regulation describes a procedure for proving a container to be safe against brittle fracture. A very important aspect is the definition of a reference flaw. In non-destructive testing (in this case 100% volumetric US testing) the probability of non-detection of any flaw must be on the order of 1 in 100. In combination with statistics the reference flaw depth will be about 5 times the minimum detectable flaw size. Additional requirements concern the sizes of rejection flaws and critical flaws. Once the reference flaw has been established, it must be shown that even for its most critical location and orientation, the applied stress intensity is smaller than the fracture toughness divided by a safety factor. The most critical location was found to be a subsurface flaw close to the surface. The relevant loading for the MOSAIK 80T (an 80 ton heavy-section ductile iron shipping vessel) investigated in this paper is the deceleration of 120g resulting from a 9 m side drop into an unyielding target. It was found that this container is indeed safe against brittle fracture.

Osseointegrated transfemoral implants have been introduced as a prosthetic solution for above knee amputees. They have shown great promise, providing an alternative for individuals who could not be accommodated by conventional, socket-based prostheses; however, the occurrence of device failures is of concern. In an effort to improve the strength and longevity of the device, a new design has been proposed. This study investigates the mechanical behavior of the new taper-based assembly in comparison to the current hex-based connection for osseointegrated transfemoral implant systems. This was done to better understand the behavior of components under loading, in order to optimize the assembly specifications and improve the useful life of the system. Digital image correlation was used to measure surface strains on two assemblies during static loading in bending. This provided a means to measure deformation over the entire sample and identify critical locations as the assembly was subjected to a series of loading conditions. It provided a means to determine the effects of tightening specifications and connection geometry on the material response and mechanical behavior of the assemblies. Both osseoinegrated assemblies exhibited improved strength and mechanical performance when tightened to a level beyond the current specified tightening torque of 12 N m. This was shown by decreased strain concentration values and improved distribution of tensile strain. Increased tightening torque provides an improved connection between components regardless of design, leading to increased torque retention, decreased peak tensile strain values, and a more gradual, primarily compressive distribution of strains throughout the assembly. © 2011 American Society of Mechanical Engineers.

In this work, a method is proposed for rolling contact fatigue crack propagation analysis using contact and fracture theories in conjunction with fatigue laws. The proposed method is used in the fatigue analysis of rocker and roller-rocker bearings of a railway open web girder bridge which is instrumented with strain gages. Using a contact algorithm based on the minimum energy principle for bodies in rolling contact with dry friction, the normal and tangential pressure distribution are computed. It is seen that the most critical location of a crack in bearings is at a point very close to the contact region, as expected. (C) 2010 Elsevier Ltd. All rights reserved.

A detailed experimental plan was developed with the goal of transitioning the DARPA/Northrop Grumman Structural Integrity Prognosis System (SIPS) onto a DoD platform. This plan consisted of a series of experiments conducted for the purposes of calibration and validation of the SIPS system. The objective of the first level of experimentation was to develop a detailed understanding of the sequence of events involved in the creation of microstructurally long fatigue cracks in a commercial aluminum alloy. Thus, these experiments involved constant amplitude fatigue tests of notched specimens with periodic interruptions of the fatigue cycling in order to make microstructural observations for use in calibrating the various fatigue models. The next level of experimentation was laboratory testing of coupons with a specimen geometry representative of the fatigue critical location on the aircraft with various fatigue sensors gathering damage data for validation of SIPS deterministic fatigue models. Subsequently, the probabilistic models were validated by subjecting the coupons to two different flight spectra and comparing the laboratory generated crack size distributions to those obtain with probabilistic predictions. Ultimately, the entire prognosis system was validated with three full-scale fatigue tests performed on retired wing panels. Procedures, observations, results, etc. will be reported on for each of the test phases, and the description of how these experiments led to a flight demonstration of SIPS on an active vehicle in the U.S. Navy fleet.

The overall objective of this paper is to compare and evaluate the fatigue performance of two competing manufacturing technologies for automotive component, namely forged steel and cast iron steering knuckle. The paper details the different experimental evaluation, mechanical properties and performance of two materials and components, their results for the steering Knuckle. Fatigue is the primary cause of failure of component due to the cyclic loading and presence of stress concentrations at the fillets and critical areas. The steering knuckle consisted of mainly sections namely spindle, strut mounting holes and hub mounting attachments. The masses of both steering knuckle were similar with the forged steel at 4.8 kg and the cast iron at 4.5 kgs. Also, the failure location of the steering knuckle used in this study was in the first step and second step fillet, which agrees with the typical failure location for an automotive steering knuckle. The paper concludes that the crack growth life for both steering knuckle was a significant portion of the fatigue life during the steering knuckle testing. The crack growth rate of the forged steel steering knuckle was slower than the cast iron steering knuckle. During steering knuckle fatigue tests, circumferential cracks developed in the first step and second step fillet of both forged steel and cast iron steering knuckles which was identified as the critical location from FEA.Copyright © 2010 by ASME

Fatigue crack initiation tests were carried out on notched specimens, with K t values ranging from 1.4 to 4.2, made of a large variety of steels. The paper describes the application of the critical location approach to these tests on the basis of low-cycle fatigue data obtained on smooth specimens under Neuber control straining or under conventional reverse straining (R, = (∈ m i n /∈ m a x ) = -1).

For the present work high pressure turbine stage is studied for various casing recess and tip clearance configurations. For the present work a linear casing (G = 6%) and variants of casing recess have been studied. For the later configuration three tip clearance gaps (G = 0, 3, and6%), three casing recess locations (dx = 32%, 36.8%, 42%) and three casing recess depths (R/H = 8.8%, 11.4% and 14%) have been simulated. For the linear casing case efficiency is (84%). The maximum efficiency is 89.219% for which G =3%, R/H = 11.4% and dx = 36.8%. For the three set of calculations the maximum efficiency is achieved for G=3%. For all tip clearance heights the relative maximum efficiencies are achieved for dx = 36.8%, which illustrates that there is one critical location of casing recess for a particular geometry for which maximum efficiency exist. The overall gain in efficiency is 6.21% as compared to original configuration (linear or sloped casing). For G = 6% the efficiency improvement is 5.44% (dx = 36.8%) as compared to linear casing, this is due to the correct matching of NGV and rotor flow. It also shown in this work that subject high pressure turbine has achieved its desired performance by these modifications and there is major improvement due to casing recess.

An automobile suspension link has been made from SAE 1055 steel and the nominal strain history when the wheel strikes a pot hole has been measured on a test track, Figure I. The critical location for fatigue crack initiation has a fatigue strength reduction factor of 3. How many times can the test track history be repeated before a detectable crack is formed?

This paper presents the results of a study to quantify the effect of defects on drilled shafts under axial loading. These results represent the efforts of the first phase of a multi-phase project with the goal of delivering a validated computation tool that will permit the direct assessment of the load carrying capacity and performance of drilled shaiLs that have been rejected due to the detection of defects by non-destructive evaluation (NDE) methods. Current and historical industry practices for considering defects have been investigated and commonly occurring defects have been characterized in terms of shape, size, and location. A two-dimensional model for assessing drilled shaft behavior has been developed using the commercial finite element program PLAXIS and verified by reproducing existing axial load test data of "near perfect" drilled shatts. The validated model was then used to analyze weak layer and neck-in type defects in three cohesive soil profiles. A parametric study of the size, strength, and position of the defects was been performed and their effect on the load carrying capacity of an idealized shaft is presented. The results of this analysis show that under axial loading, the effect of a defect is highly dependent upon the geotechnical capacity of a drilled shaft. A shaft in stronger soil will experience greater loads and will therefore be more affected by presence of a defect than a shaft in weaker soil. The position of a defect is also critical in determining its effect on shaft capacity. Under axial loading, the top of the shaft is the critical location. Defects located at the midpoint and toe of the shaft were found to have a greatly reduced effect on shaft capacity compared to those located at the top of the shaft.

Publisher Summary The smart patch approach, which is based on self-monitoring, would considerably alleviate the certification concerns for implementing bonded composite repairs to primary aircraft structures. This approach relies on the ability to automatically detect disbonding in the patch, i.e., the smart patch approach is basically a continuous safety-by-inspection approach for the bonded repair. However, this approach brings its own problem of reliability assurance. Currently, the approach appears technically feasible but, in the short term, only economically viable for repairs to very significant and costly primary structure. Studies on laboratory coupon specimens at Defense Science Technology Organization (DSTO) have shown that the concept of the smart approach using autonomous patch health monitoring systems appears to be viable. These systems establish, store, and allow the operator (at their convenience) to upload patch health values (i.e., ratios of patch strain at a critical location to far-field strain). This ratio gives an indication of the level of load transfer into the patch. Any decrease in this ratio is an indication of disbonding of the patch in this critical region. In this approach there is no requirement for measurement of the actual loading: disbonding is indicated by the reduction in relative strain.

Fatigue in concrete is very difficult to analytically quantify owing to the intricacies of several factors that affect concrete performance. As a result, it has been a subject of much experimental research. Fatigue effects have been incorporated into concrete design procedures including airport pavement design. This research effort studied the factors that affect concrete fatigue life in relation to an airport pavement scenario. Analysis of preliminary test results from the National Airport Pavement Test Facility (NAPTF) test site reveal that pavements experience more stress reversals and more load cycles than anticipated when a dual tandem or a tridem gear is used for loading. Stress patterns were observed at the longitudinal edge, a critical location for pavement response. Test results were supported with finite element simulations. The NAPTF was a scaled model and hence effects of gear type on stress ranges were analytically simulated for an actual airport pavement at the Denver International Airport (DIA) with B777 loads. It is concluded that the NAPTF sections are subjected to more severe loads than anticipated and might fail earlier than expected. It is recommended that effects of axle spacing be accounted for when results from these tests are related to real life airport pavements.