Fatigue Failure Analysis Research Articles

Bayesian analysis of low-cycle fatigue failure in printed wiring boards

In this study, a low-cycle fatigue experiment was conducted on printed wiring boards (PWB). The Weibull regression model and computational Bayesian analysis method were applied to analyze failure time data and to identify important factors that influence the PWB lifetime. The analysis shows that both shape parameter and scale parameter of Weibull distribution are affected by the supplier factor and preconditioning methods Based on the energy equivalence approach, a 6-cycle reflow precondition can be replaced by a 5-cycle IST precondition, thus the total testing time can be greatly reduced. This conclusion was validated by the likelihood ratio test of two datasets collected under two different preconditioning methods Therefore, the Weibull regression modeling approach is an effective approach for accounting for the variation of experimental setting in the PWB lifetime prediction.

The Biomechanical Relevance of Stress Range and Mean Stress in the Analysis of Variable Loading on Musculoskeletal Tissues

Musculoskeletal tissues usually experience loading referred to in the fatigue failure literature as “repeated stress” or “fluctuating stress” during the performance of occupational tasks. In addition, loads experienced during occupational work often involve highly stress variability. Under these types of loading conditions, the development of cumulative damage is highly influenced by the stress range and the mean stress associated with the loading regimen. This paper describes fatigue failure analysis techniques associated with variable loading situations, including cycle counting techniques, Goodman and Gerber equations for estimation of fatigue life, and the relevance of stress range and mean stress on damage accrual.

Musculoskeletal disorders as a fatigue failure process: evidence, implications and research needs

Mounting evidence suggests that musculoskeletal disorders (MSDs) may be the result of a fatigue failure process in musculoskeletal tissues. Evaluations of MSD risk in epidemiological studies and current MSD risk assessment tools, however, have not yet incorporated important principles of fatigue failure analysis in their appraisals of MSD risk. This article examines the evidence suggesting that fatigue failure may play an important role in the aetiology of MSDs, assesses important implications with respect to MSD risk assessment and discusses research needs that may be required to advance the scientific community’s ability to more effectively prevent the development of MSDs.Practitioner Summary: Evidence suggests that musculoskeletal disorders (MSDs) may result from a fatigue failure process. This article proposes a unifying framework that aims to explain why exposure to physical risk factors contributes to the development of work-related MSDs. Implications of that framework are discussed.

The analysis of choice influence in fatigue failure criteria on integrity assessment of wagon structure

This paper presents the S-N approach to fatigue failure analysis of welded joints that integrates well with finite element modelling. Goodman's criterion and fatigue criterion based on the equivalent stress range were used for the analysis of the fatigue failure. Goodman's criterion and fatigue criterion based on the equivalent stress range, for determining fatigue safety factor, are implemented in the software package for finite element analysis PAK. Numerical calculation of fatigue safety factor was determined to assess the integrity of wagon structure parts according to the most commonly used European standards for wagon analysis. According to failure safety factors obtained by Goodman's criterion and fatigue criterion based on the equivalent stress range it should be noticed that both methods give good results. Both criteria give us adequate identification causes of cracking on the underframe of wagon for containers transportation. The obtained results and their well matching prove reliability of both fatigue failure criteria and that they can be used for integrity assessment of wagon structure parts.

Fatigue failure analysis of rotor compressor blades concerning the effect of rotating stall and surge

Abstract Detailed investigation was performed on the effect of the rotating stall and surge on the fatigue failure mechanisms of the axial compressor first stage rotor blades. The static stress distribution of the blades was analysed using three dimensional (3D) finite element method (FEM). The critical fracture stress was calculated using the linear elastic fracture mechanics. Fractographic observation revealed different fatigue fracture modes corresponding to the different fatigue loads. Results demonstrated that during operation two kinds of fatigue loads can occur which are tension-torsion fatigue and bending fatigue. The tension-torsion fatigue stems from the periodic tension-torsion stress induced by the surge, while the bending fatigue load is caused by the rotating stall.

Estimation of Suitable Methodology for Determining Weibull Parameters for the Vortex Shedding Analysis of Synovial Fluid

Weibull distribution with two parameters, shape (k) and scale (s) parameters are used to model the fatigue failure analysis due to periodic vortex shedding of the synovial fluid in knee joints. In order to determine the later parameter, a suitable statistical model is required for velocity distribution of synovial fluid flow. Hence, wide applicability of Weibull distribution in life testing and reliability analysis can be applied to describe the probability distribution of synovial fluid flow velocity. In this work, comparisons of three most widely used methods for estimating Weibull parameters are carried out; i.e. the least square estimation method (LSEM), maximum likelihood estimator (MLE) and the method of moment (MOM), to study fatigue failure of bone joint due to periodic vortex shedding of synovial fluid. The performances of these methods are compared through the analysis of computer generated synovial fluidflow velocity distribution in the physiological range. Significant values for the (k) and (s) parameters are obtained by comparing these methods. The criterions such as root mean square error (RMSE), coefficient of determination (), maximum error between the cumulative distribution functions (CDFs) or Kolmogorov-Smirnov (K-S) and the chi square tests are used for the comparison of the suitability of these methods. The results show that maximum likelihood method performs well for most of the cases studied and hence recommended.

Assessment of Bending Fatigue Strength of Crankshaft Sections with Consideration of Quenching Residual Stress

High-cycle bending fatigue is the primary failure mode of crankshafts in engines. Compressive residual stresses are often introduced by induction quenching to improve the fatigue strength of crankshafts. The residual stresses, which are commonly obtained by numerical methods, such as the finite element method (FEM), should be included in fatigue failure analysis to predict the fatigue strength of crankshafts accurately. In this study, the simulation method and theory of quenching process are presented and applied to investigate the residual stresses of a diesel engine crankshaft. The coupling calculation of temperature, microstructure, and stress fields of the crankshaft section is conducted by FEM. Then, the fatigue strength of the crankshaft section is analytically assessed by Susmel and Lazzarin’s criterion based on the critical plane approach that superimposes the residual stresses onto the bending stresses. The resonant bending fatigue tests of the crankshaft sections are conducted, and the tests and analytical assessments yield consistent results.

Three dimensional analysis of low cycle fatigue failure in engine part subjected to multi-axial variable amplitude thermo-mechanical load

During the E5 engine durability test, the failure happens in cast iron cylinder head. This is characterized as low cycle fatigue. The macro-scale cracks initiate and propagate in valve bridge region. The present investigation focuses on simulating durability test and evaluating low cycle fatigue life of the failed part. The simulation includes one pre-step as a determination of material grid and three steps as fluid, structural and fatigue analyses. In order to cover the durability test, the analysis steps are repeated at five crack speeds, 750, 1650, 2075, 2350, and 2600rpm. The cylinder head is subjected to cyclic multi-axial variable amplitude loads. In fatigue analysis, critical plane and cumulative damage theories are utilized in order to predict fatigue life. A general script is developed and validated so as to calculate fatigue life in the whole model. The numerical results also show that the failure of critical cylinder head can be characterized as low cycle fatigue. The valve bridge region, in which high temperature exists during engine operation, is the critical area in fatigue analysis approach. The simulation results are in a good agreement with the durability test observations.

Fatigue Failure Analysis for Bolt-Nut Connections having Slight Pitch

Fatigue Failure Analysis for Bolt-Nut Connections having Slight Pitch

Fatigue failure analysis of pin-loaded lugs

In the present paper, mathematical models are proposed in order to analyze the strength of pinloaded lugs with semi-elliptical crack and through-the-thickness crack. The crack growth investigation of considered crack configurations tackles the fatigue life evaluation and the crack path simulation of semi-elliptical crack. The residual strength is estimated by applying the two-parameter driving force model. The numerical and analytical approaches are employed for the stress intensity factor calculation. Experimental fatigue crack growth data are used in order to verify efficiency of the developed models. A good correlation between fatigue crack growth estimations and experimental observations is obtained.

Very High Cycle Fatigue Failure Analysis and Life Prediction of Cr-Ni-W Gear Steel Based on Crack Initiation and Growth Behaviors.

The unexpected failures of structural materials in very high cycle fatigue (VHCF) regime have been a critical issue in modern engineering design. In this study, the VHCF property of a Cr-Ni-W gear steel was experimentally investigated under axial loading with the stress ratio of R = −1, and a life prediction model associated with crack initiation and growth behaviors was proposed. Results show that the Cr-Ni-W gear steel exhibits the constantly decreasing S-N property without traditional fatigue limit, and the fatigue strength corresponding to 109 cycles is around 485 MPa. The inclusion-fine granular area (FGA)-fisheye induced failure becomes the main failure mechanism in the VHCF regime, and the local stress around the inclusion play a key role. By using the finite element analysis of representative volume element, the local stress tends to increase with the increase of elastic modulus difference between inclusion and matrix. The predicted crack initiation life occupies the majority of total fatigue life, while the predicted crack growth life is only accounts for a tiny fraction. In view of the good agreement between the predicted and experimental results, the proposed VHCF life prediction model involving crack initiation and growth can be acceptable for inclusion-FGA-fisheye induced failure.

Analysis of flexural fatigue failure of concrete made with 100% Coarse Recycled Concrete Aggregates

The paper presents results of an investigation carried out to analyze the flexural fatigue performance of concrete beams made with 100% Coarse Recycled Concrete Aggregates (RCA) and its comparison with that of concrete made with 100% Coarse Natural Aggregates (NA). The fatigue performance of concrete beams made with RCA as well as NA has been assessed in terms flexural fatigue life distributions and two-million cycle endurance limit. Experiments were conducted to obtain the flexural fatigue lives of concrete beam specimens made with 100% RCA as well as 100% NA under different stress levels and further compared with literature available on NA. Specimens of size 100mm×100mm×500mm were tested under four point flexural fatigue loads applied at a frequency of 10Hz. It has been shown that the fatigue life distributions of concrete mixes made with 100% RCA and 100% NA can be modeled by the two-parameter Weibull distribution. The values of the shape parameters of the Weibull distribution obtained for concrete made with RCA have been found to be smaller than that of concrete made with NA in present investigation and previous studies on NA, thus indicating higher variability in the distribution of flexural fatigue life of concrete made with RCA viz. a viz. concrete made with NA. The two-million cycles endurance limit for concrete made with 100% RCA has been found to be 50%, which is about 8% and 7% lower than that of concrete made with NA in present and previous studies respectively.

A physical–statistical model of overload retardation for crack propagation and application in reliability estimation

ABSTRACTCrack propagation subjected to fatigue loading has been widely studied under the assumption that loads are ideally cyclic with a constant amplitude. In the real world, loads are not exactly cyclic, due to either environmental randomness or artificial designs. Loads with amplitudes higher than a threshold limit are referred to as overloads. Researchers have revealed that for some materials, overloads decelerate rather than accelerate the crack propagation process. This effect is called overload retardation. Ignoring overload retardation in reliability analysis can result in a biased estimation of product life. In the literature, however, research on overload retardation mainly focuses on studying its mechanical properties without modeling the effect quantitatively and, therefore, it cannot be incorporated into the reliability analysis of fatigue failures. In this article, we propose a physical–statistical model to quantitatively describe overload retardation considering random errors. A maximum likelihood estimation approach is developed to estimate the model parameters. In addition, a likelihood ratio test is developed to determine whether the tested material has either an overload retardation effect or an overload acceleration effect. The proposed model is further applied to reliability estimation of crack failures when a material has the overload retardation effect. Specifically, two algorithms are developed to calculate the failure time cumulative distribution function and the corresponding pointwise confidence intervals. Finally, designed experiments are conducted to verify and illustrate the developed methods along with simulation studies.

Corrosion Fatigue Failure Analysis of a Supporting Pipe Weld in Deaerization Plant

The aim of this work is to reveal the failure mechanism of a supporting pipe weld after 20 years of service in a deaerization plant. The characterization methods included inductively coupled plasma, optical microscopy, scanning electron microscope, X-ray energy dispersive spectrometer, mechanical tests, and finite element analysis (FEA). The results showed that the supporting pipe weld failed by corrosion fatigue cracking. Cracks initiated from the surface pits which were due to corrosion. FEA analysis revealed that stress concentration occurred in the failed weld. This paper brings out the details of the investigation and suggests remedial measures to improve performance of such pipe welds in deaerization plants.

Fatigue Failure Analysis on Key Components of Bladder Accumulators

Fatigue failure analysis on key components of bladder accumulators was conducted. Failure fracture of the key components, which included the shell, the support ring and the oil inlet valve body in the accumulators, was investigated by optical microscope (OM) scanning electron microscope (SEM). According to the metallographic analysis and micro-hardness determination at the crack profile, crack initiation and propagation direction was confirmed. By simulation using the finite element method, it was detected that the peak stress of the key components applied on the contact surfaces. Obvious plastic deformation was observed at the region with high stress. However, the fatigue crack did not initiate at the contact surface, but occurred on the second high stress area without contact.

Contact and Joint Forces Modeling and Simulation of Crawler-formation Interactions

Cable shovels are used in surface mining operations to achieve economic bulk production capacities. The service life of the rawlers and their shoes define shovel reliability, maintainability, availability and efficiency. The crawler track-terrain interaction generates high time-fluctuating contact forces that result in stress buildup, crack and fatigue failure of wler shoes. In addition, the link pins that connect two crawler shoes can exert large fluctuating pin loads on shoe lugding to shoe breakage. This paper addresses fundamental research into contact forces acting on crawler shoes, joint forces generated in the link pin and total deformation of the formation during shovel propel. During propel, the crawler track is controlled by two drive constraints that cause the crawler to follow straight or turning motions. A virtual prototype simulator of the crawler-terrain interaction dynamics is developed and simulated within the MSC ADAMS environment. The simulation results show that the average penetration depth for different crawler shoes is within the range of 5.9 and 6.7 cm for both types of driving constraints. During translation, the maximum magnitude of contact forces along vertical, longitudinal and lateral directions have respective values of 5.9 × 105 N, 5.5 × 105 N and 1.7 × 105 N. During turning, the crawler track experiences varying bouncing and rolling motions causing maximum magnitude of vertical and lateral contact forces on the crawler shoes to increase 1.15 and 1.42 times the maximum translation values. The total deformation of oil sand terrain for the two motions fluctuates between -0.24 and 0.26 cm and between -1.03 and 1.33 cm, respectively. This study provides solid foundation for further studies on dynamic stress and fatigue failure analysis of crawler shoes during shovel propel and loading operations.

Fatigue Life Prediction of Composite Laminates Based on Progressive Damage Analysis

A three dimensional analysis model is developed on the fatigue life prediction of composite laminates based on a progressive damage analysis. This model consists of stress analysis, fatigue failure analysis and material property degradation. Teserpe’s failure criteria is used to fatigue damage analysis. Fiber tensile/compressive breakage, matrix tensile/compressive cracking, matrix/fiber shear failure and tension/compression delamination are considered in fatigue damage analysis. The methodologies of sudden degradation and gradual degradation are both applied in the material property degradation. The stiffness and strength gradual degradation is based on the Shokrieh fatigue model, which is based on fatigue test for unidirectional laminates. In order to consider the scatter of the material in the practical structures, the stiffness and strength of the material are randomly distributed using normal distribution in the numerical model. The progressive fatigue damage model is developed in finite element code ABAQUS through user subroutine UMAT, which can simulate the fatigue damage process. Fatigue life of different ply stacking sequences and geometries composite laminates under different cycle loading are predicted. The predicted fatigue life is in good agreement with the experimental results.

Fatigue life prediction under variable amplitude loading using a non-linear damage accumulation model

Most of engineering components in service are usually subjected to variable cyclic loading. It is important to predict fatigue life and deal with the issue about fatigue damage accumulation for these components. One of the largest difficulties in fatigue failure analysis is to find a representative ‘damage criterion’ which can be easily connected with the Wöhler curve taken as the known material data. The most commonly used model is the Miner’s rule which ignores the loading history effect, under the same loading conditions the experimental results are higher than the Miner expectations for low-to-high load sequence and are lower than the Miner expectations for high-to-low load sequence. The fatigue driving stress that causes fatigue damage is presented to predict residual fatigue life under variable amplitude loading. It increases with loading cycles until equals the fatigue strength when fracture occurs. By determining the equivalent number of cycles that yields the same fatigue driving stress as the previous loads, the remaining life can be predicted. The proposed damage criterion is connected cycle by cycle to the Wöhler curve and the experimental results are in a good agreement with the model predictions.

Influence of Material Structure and its Properties on Predicting Life of Pressure Pipelines

Pressure pipelines belong to the group of technological carrying structures that are designed in accordance with Standard Eurocode 3: STN EN 1993: Design of steel structures. These standards are used also later in the stage for assessment of failure states and fatigue life. Standard Eurocode 3: STN EN 1993-4-3 establishes the requirements for material properties of pipes and welds, associated with mechanical properties. A serious problem in estimating fatigue life of structure is the consideration of gradual degradation. The article also discusses the analysis of fatigue failure of the pressure pipeline, where it was found that the initiation of fatigue failure occurred in the area of poor weld. The further spread of the crack then occurred in the base material of the pipeline.

Fatigue failure analysis of stay cables with initial defects: Ewijk bridge case study

A failure assessment method of stay cables containing fractured wires is presented through an example of an existing bridge. The wires constituting the stay cables of the bridge contained many initial defects that were formed during the rolling process of these wires. Despite moderate loading, fatigue cracks started to grow from these defects, increasing their size, and finally resulting in fracture of the remaining ligament of the wires. A probabilistic model is put forward for assessing the resistance of the stay cable based on a fracture mechanics model of the individual wires. A Bayesian update method is presented for estimating the distribution of initial defects based on the inspection of fractured wires. The calculated reliability of the stay cables of the examined bridge was lower than acceptable.