Fatigue Failure Analysis Research Articles

Fatigue failure analysis on the 2nd bulkhead beam of the Portuguese Air Force Epsilon TB-30 aircraft

Military aircraft perform demanding maneuvers with a wide range of load factor levels, allowing the growth of fatigue cracks that shall be duly monitored to prevent unexpected failures. In order to monitor the operation of the Portuguese Air Force Epsilon TB-30 fleet that performs basic and elementary piloting training, two systems were installed in these aircraft, allowing the recording of load factor data in the aircraft center of gravity and strain data in two critical locations.This study aims to evaluate and compare the growth of fatigue cracks on the 2nd bulkhead beam, one of the aircraft critical locations, through experimental tests and computational simulations. The methodology used in this work comprised the application of real flight load sequences to a 2024-T351 aluminum specimen that is representative of this critical location.Main results from these fatigue crack growth tests and simulations showed that NASGRO model is the one that comes closest to experimental data with maximum deviations of approximately 8%, presenting a deviation of 18% between the representative and real structures at the final rupture of the specimen. Additionally, experimental results provided knowledge about the component behavior regarding fatigue of materials, namely the evolution of the local strain as a function of the crack length.This study can be used by the Portuguese Air Force engineers to adjust the aircraft maintenance program according to the actual operation regime and consider a possible life extension of this fleet.

Fatigue Failure Analysis and Microstructural Characterizations on Flash Butt Welded Joint of Automotive Steel Wheel Rim

Fatigue Failure Analysis and Microstructural Characterizations on Flash Butt Welded Joint of Automotive Steel Wheel Rim

Fatigue life evaluation of different hip implant designs using finite element analysis

Fatigue failure is one of the causes of the failure of hip implants. The main objective of this work is to carry out fatigue failure analysis on different hip profiles and compare the outcomes for various combinations of materials. Three profiles each for circular, oval, elliptical, and trapezoidal stems are utilized for this study with four different material combinations consisting of materials like Ti-6Al-4V, CoCr Alloy and UHMWPE. CATIA V-6 is used for the modelling of these implants and the fatigue analysis using Goodman's mean stress theory is simulated using ANSYS 2022 R1. ISO 7206-4 and ASTM F2996-13 standards are used to define the boundary conditions. A total of 48 combinations were studied across four different shapes, three different profiles and four different material combinations to deduce the best possible combination for a hip implant for static and fatigue loading. Comparison of the implants is based on the factors like equivalent von Mises stress, displacement, equivalent elastic strain, fatigue life, safety factor and equivalent alternating stress. Profile 2 of the trapezoidal-shaped hip implant with a Ti-6Al-4V stem exhibited superior results both under static and fatigue loading conditions. Compared to displacements obtained for profiles one and three, profile 2 trapezoidal stem with Ti-6Al-4V and other parts as CoCr Alloy has about 72% lower displacement. Based on the findings, profile 2 with a trapezoidal stem made of Ti-6Al-4V and an acetabular cup made of CoCr shows the enhanced results over the other combinations considered.

Reliability study for diesel engine cylinder head through fatigue failure analysis and structural optimization

Crack and failure are often captured in the cylinder head of diesel engine during high cycle fatigue test. In order to study the cause and improve the fatigue resistance, tensile test, metallographic observation and fracture analysis were carried out. In addition, the finite element method was applied to simulate the stress distribution and fatigue strength of the cylinder head. Meanwhile, the influence of load factors on the fatigue strength was analyzed. The structure was optimized on the finite element analysis. The results show that the material properties are not the main cause of cylinder head failure. High cycle fatigue failure of cylinder head is identified by the reason of working loads. Among the causes affect fatigue strength, gas force was determined as the dominant factor by changing stress amplitude, while thermal load as the secondary factor by changing mean stress. Additionally, the structural optimization measures for the cylinder head were put forward according to the failure causes, and the safety coefficient of the vulnerable parts was increased from 0.88 to 1.04, meeting the design requirements. This study can provide a reference for the engine reliability analysis.

Fatigue Failure Analysis of Shaft in As-developed Wind Turbine with Reinforced-welding Elbow

This paper reports the fatigue analysis for a failure of a shaft in a wind turbine in which reinforced-welding elbow to support the shaft load. The shaft was broken near the reinforcing elbow. When designing mechanical and structural components, the diameter and the characteristics of materials have been considered not to exceed the permissible limit. However, after 40 days of the cycle operation, the shaft was broken at the accepted loading conditions within reasonable limits at a wind speed of 6-10 m/s. The crack initiate fatigue in the shaft is influenced by many variables that may due to uniaxial, bending, torsion, the shape of loading curve, part size, part finish, operating temperature, and atmosphere. For these reasons, it is important to investigate the fatigue behavior on the failure of the shaft. The main goal is to investigate and analyze the fatigue behavior on a broken shaft of the wind turbine gearbox to determine the features that cause the failure. A microscopic investigation of the fatigue-fracture surface was done. The microscopic analysis was carried out in terms of the chemical composition using ARL Spark Spectrometer, energy dispersive spectroscopy (EDS), the morphology of the fatigue by using scanning electron microscopy (SEM) and hardness test. Moreover, a theoretical analysis was made to illustrate the results and comparison between these results and the corresponding stress distribution data from a finite element method (FEM) simulation to know how the fatigue fracture began and propagated along the shaft. The result of the analysis shows that the fatigue occurred due to the unbalanced of the bending and torsion stress in the junction of the reinforced-welding elbow with hardness testing at the extreme cracking area is 435 HV. It is emphasized that the microstructure of fatigue surface structure shows sensitization to facilitate intergranular cracking and fatigue corrosion.

Experimental and numerical study of contact fatigue for 18CrNiMo7-6 and 20MnCr5 carburized gear tooth

Gear manufacturers must make decisions about the manufacturing materials and superficial treatments. The best performance as to a type of failure should be evaluated. However, it is a time-demanding and costly process. The present work proposes a methodology for a comprehensive assessment (experimental and computational) of contact fatigue of gears in FZG test rig. The materials investigated were 18CrNiMo7-6 and 20MnCr5 alloy steels, widely used in industrial and automotive transmission systems, but with very different raw material costs, which can exceed twice the first compared to the second. The study evaluated the contact analysis between gears from the macroscopic point of view and the microscopic (inclusion of roughness). At the same time, the evolution of roughness and pit-damaged area after each test stage was monitored. The approach determined the stress field after each loading cycle and thus correlating the regions of higher stresses with surface and subsurface fatigue (micropitting and pitting). In addition, Weibull’s statistical analysis and SEM-EDS observations were executed. In many cases, the methodology correlated the increased roughness and pitting affected area with the regions submitted to the higher contact stress. Observations by SEM-EDS revealed that the occurrence of plastic deformation as a mechanism of wear should be considered in the equations of microscopic stress analysis. The similar fatigue life of such different materials may be correlated to the competitive mechanisms of higher mechanical strength of 18CrNiMo7-6 and better crack propagation characteristics of 20MnCr5. The methodology proved to be consistent for fatigue failure analysis of gears in FZG test rig.

Validated Analytical Modeling of Eccentricity and Dynamic Displacement in Diesel Engines with Flexible Crankshaft

In spite of the fact that the flexibility of the crankshaft of diesel engines exhibits notable nonlinearities, analytical modeling of such nonlinearities is not yet realized. The present study thus analytically models the effect of eccentricity on flexible crankshaft and piston secondary motion. The eccentricity of the crankshaft is modeled as the summation of the hydrodynamic eccentricity and the dynamic mass eccentricity of the crankshaft. The study also models the absolute value of the vibrational dynamic displacement of the center of the crankshaft. The paper proves that such dynamic displacement of the center of the crankshaft is sensitive to the changes in its independent variables. It was found that the most influential parameters on the dynamic displacement of the center of the crankshaft due to vibration are the natural frequency and the eccentricity of the crankshaft. The modeling of the dynamic displacement in a flexible crankshaft was validated using a case study based on the eccentricity of the crankshaft showing a relative error of 4%, which is less than the relative error in the CMEM and GT-Power. Furthermore, the analytical modeling of the dynamic displacement in the flexible crankshaft was validated using another case study based on fatigue analysis of the crankshaft showing a relative error of 9%, which is less than that the relative error in Newman’s model of diesel engine fuel consumption and Lansky’s model of diesel engine cylinders. The paper also presents a proposed approach of fatigue failure analysis for vehicular dynamic components and presents a proposed nanostructure of crankshafts for improving such fatigue performance. The developed models would help develop efficient diesel engines and help prolong their service life.

Fatigue failure analysis of spur gear under moving load

This paper is prepared to analyze the crack propagation by developing a pointed moving load condition. The moving load from lower point tooth contact (LPTC) to high point tooth contact (HPTC) is applied on the gear flank, where the maximum load is acted on the pitch-point of the tooth flank. Different models of gear, taking a three teeth sector model (TTSM), are developed for different backup ratio (BR) of 0.3, 0.5, 0.8, 1.5 & 3.3 and initiating the initial crack (IC) length of 0.1 mm, 0.25 mm & 0.5 mm at orientation of critical planes for shear model oriented at 180° at the root region of the tooth. The finite element analysis (FEA) software - ANSYS is used to study the problem statement. The arbitrary crack method is used to initiate the crack presence in gear flank. The Paris law method is applied in separating morphing and adaptive remeshing technology (SMART) crack growth setup in static structural module of ANSYS, which helps in evaluation of number of cycles with crack extension length. The number of life cycles, crack extension length and crack propagation path are analyzed and their graphs are plotted to analyze the situation. From current study, the effect of rim thickness on the life cycle is studied when the point load is applied movable from LPTC to HPTC. It is observed that by having thin rims, the number of cycles of gear increases, but its failure is catastrophic that it can fracture other parts, mounted with gear. Although, higher backup ratios or larger rims have lower number of life cycles, but it will never lead to the catastrophic failure of the gear.

Macro-meso fatigue failure of bimrocks with various block content subjected to multistage fatigue triaxial loads

The non-linear mechanical behaviors of bimrock under static loading conditions have been widely studied currently. To data, however, the fatigue responses of bimrock with various rock block percentage (RBP) under multi-level cyclic loads were not well understood. The cyclic triaxial tests combined with post-test computed tomography scanning were employed to investigate the damage-cracking and volumetric dilatancy characteristics of a slope bimrock. The results reveal that multiple block-matric damage and volumetric dilatancy were strongly impacted by the block content. Bimrock strength and stiffness increase but volumetric deformation decreases with increasing block content. The occurrence of critical instability for bimrock with RBP is earlier than those with high RBP by the proposed volumetric strain rate. In addition, damage is larger for bimrock with low RBP and damage growth rate decreases accordingly. A two-stage damage evolution model was proposed to describe the damage propagation and the mode fits the testing data well. Moreover, the mesoscopic interface damage-cracking and volumetric dilatancy were visualized from CT images, two indices of interface damage ratio (IDR) and failed volumetric rock proportion (FVBP) reveal that the matrix expansion and interface cracking play a dominant role in volumetric dilatancy for bimrock with low block content. However, the block interlocking and occlusion contribute a lot to volumetric expansion of bimrock with high RBP, and their instability was limited at the confined condition.Through a series of macro-meso fatigue failure analysis, the effect of block proportion on bimrock under triaxial fatigue failure have been presented first. This study is in favor of predication the long-term stability of the bimrock slope under complex disturbed stress.

Artificial intelligence‐assisted fatigue fracture recognition based on morphing and fully convolutional networks

AbstractFatigue fracture is one of the most common metallic component failure cases in manufacturing industries. The observation on fractography can provide direct evidence for failure analysis. In this study, an image semantic segmentation method based on fully convolutional networks (FCNs) was proposed to figure out the boundary between fatigue crack propagation and fast fracture regions from optical microscope (OM) fractography images. Furthermore, a novel morphing‐based data augmentation method was adopted to enable few‐shot learning of sample images. The proposed framework can successfully segment two categories, namely, the crack propagation and fast fracture regions, thus differentiating the boundary of two regions in one image. This artificial intelligence (AI)‐assisted fatigue analysis architecture can complete the failure analysis procedure in 0.5 s and prove the feasibility of fatigue failure analysis. The segmentation accuracy of self‐developed network achieves 95.4% for the fatigue crack propagation region, as well as 97.2% for the fast fracture region. Not only for semantic segmentation DNN, we also prove that our novel data augmentation method can applied at the instance segmentation DNN, such as mask regional convolutional neural network (mask R‐CNN), one state‐of‐the‐art deep learning network for instance segmentation, to achieve similar accuracy.

Fatigue failure analysis of steel crane beams with variable-section supports

The service safety problem of steel crane beams in metallurgical industrial buildings has been attracting increasing attention recently. The fatigue failure problem of the steel crane beam with variable-section supports becomes particularly severe. Therefore, the present study focuses on exploring the reason for such fatigue failure in terms of the design method, actual service load, and reliability of existing structural components of the steel crane beams. First, the study clarifies the “Z class” of various variable-section supports based on fracture mechanics theory to design fatigue strength parameters for steel crane beams. Then, it explores the indeterminant design parameters of fatigue load through numerous load tests and analyses, discussing the applicability of current approaches on selecting appropriate parameters. At last, this paper carries out a statistical analysis of fatigue reliability of existing steel crane beams with variable-section supports. This study concludes the main reasons for frequent fatigue failures of steel crane beams with variable-section supports, which provides a basis for solving such fatigue failure problems in practice.

Computational fatigue failure analysis of magnesium alloy core structure inside the metal sandwich panels under constant spectrum loadings

This paper presents the delamination effect on the metal sandwich panel of AR500 with magnesium alloy of AZ31B as main core under constant spectrum loading. Recent sandwich panel mostly dealt with static loading, with least research under constant cyclic loading while also having cavity element on its structure, which made them exposed to the catastrophic failure under consistent loading. The metal sandwich panel were simulated using three types of core design for Magnesium alloy; smooth surface, rounded dimple and hemispherical dimple smooth under static and constant cyclic loading. Two types of conditions are applied to the simulation model; with and without pre-stress loads with varying load ratios. Gerber and Goodman stress life fatigue theory was used as a corrective model. Result shows that sandwich panel with dimple core design obtained up to 5% better fatigue life value compared to solid core panel, with and without pre-stress. This study is important as it can improve sandwich panel’s bonding strength and reduces the risk of early delamination, especially when it is use for real world application such as protection panel for military purposes.

Strain energy-based fatigue failure analyses of LB-PBF Inconel 718: Effect of build orientation

Additively manufactured Inconel 718 parts fabricated in three build orientations (horizontal, vertical, and angled at 45 degrees) are tested in fully-reversed bending fatigue mode. Damping measurements via the Impulse Excitation technique are used to assess the defects content in the microstructure and fractography analysis is performed to detect the root cause of failure. Two micro- and macro-scale methodologies of fatigue damage estimation based on the dissipated heat per cycle and the statistical estimation of micro-plastic strain energies are used to assess fatigue damage. It is shown that at a given stress level, the vertically built specimens endure the most fatigue damage before failure while the diagonally built ones sustain the least. The fatigue life is estimated for arbitrary load amplitudes via a microstructure-sensitive algorithm with acceptable accuracy as compared to the experiments.

Experimental Analysis of Fatigue Failure in Cruciform Welded Joint

Experimental Analysis of Fatigue Failure in Cruciform Welded Joint

Subsurface stresses analysis of flexible ball bearing with bendable races in a harmonic reducer by superimposition method

The bending of races of the flexible ball bearing in a harmonic reducer inevitably results in significant hoop stresses, which leads to the bearing working under a complex stress state. Studies show that hoop stresses can affect bearing life considerably, and subsurface stresses are the fundamental nature of the bearing failure mechanism. This paper established a simplified theoretical model of subsurface stresses for flexible ball bearing by considering bending deformation and contact deformation. First, the plane curved bar theory was used to solve the hoop stresses of the races caused by bending deformation. Second, the hoop stresses were superimposed on the Hertzian principal stresses generated by the contact load to calculate the maximum shearing stress of the raceway. Then, the influence of hoop stresses on subsurface stresses of both the inner and outer races was analyzed based on the proposed model. The results indicated that the subsurface stresses of the inner race calculated by the model were in good agreement with that of the cam-inner race-single ball contact finite element model. In addition, hoop stresses of the inner race increase the maximum shearing stress but decrease its depth to the contact surface, making the inner race more prone to spalling failure, while the outer race is the opposite. At last, the influence of the design parameters of flexible ball bearing on the subsurface stresses of races was studied to provide a theoretical basis for the optimization design of flexible ball bearing and its fatigue failure analysis.

Analysis of Compressive Fatigue Failure of Recycled Aggregate Concrete.

Using recycled aggregate in concrete is effective in recycling construction and demolition waste. It is of critical significance to understand the fatigue properties of recycled aggregate concrete (RAC) to implement it safely in structures subjected to repeated or fatigue load. In this study, a series of fatigue tests was performed to investigate the compressive fatigue behavior of RAC. The performance of interfacial transition zones (ITZs) was analyzed by nanoindentation. Moreover, the influence of ITZs on the fatigue life of RAC was discussed. The results showed that the fatigue life of RAC obeyed the Weibull distribution, and the S-N-p equation could be obtained based on the fitting of Weibull parameters. In the high cycle fatigue zone (), the fatigue life of RAC was lower than that of natural aggregate concrete (NAC) under the same stress level. The fatigue deformation of RAC presented a three-stage deformation regularity, and the maximum deformation at the point of fatigue failure closely matched the monotonic stress-strain envelope. The multiple ITZs matched the weak areas of RAC, and the negative effect of ITZs on the fatigue life of RAC in the high cycle fatigue zone was found to be greater than that of NAC.

4D microstructural characterization of corrosion and corrosion-fatigue in a Ti–6Al–4V / AA 7075-T651 joint in saltwater environment

Dissimilar alloy couples are susceptible to environmentally assisted damage owing to the presence of crevices and potential difference between the constituent alloys. In this study, x-ray computed tomography has been employed to non-destructively study the corrosion behavior of a dissimilar alloy fastener-plate couple (AA7075-T651/Ti–6Al–4V) in a 3.5 wt% NaCl environment. Following this, the specimen was subjected to corrosion fatigue and post fracture failure analysis was performed. The precise locations of corrosion pitting damage in the specimen were studied with respect to corrosion time. Microstructural factors that contribute to crack initiation were identified using a correlative microscopy-based approach and are discussed.

Experimental and computational analysis of bending fatigue failure in chopped carbon fiber chip reinforced composites

With a better balance among good mechanical performance, high freedom of design, and low material and manufacturing cost, chopped carbon fiber chip reinforced sheet molding compound (SMC) composites show great potential in different engineering applications. In this paper, bending fatigue behaviors of SMC composites considering the heterogeneous fiber orientation distributions have been thoroughly investigated utilizing both experimental and computational methods. First, four-point bending fatigue tests are performed with designed SMC composites, and the local modulus is adopted as a metric to represent the local fiber orientation of two opposing sides. Interestingly, SMC composites with and without large discrepancy in local modulus of opposing sides show different fatigue behaviors. Interrupted tests are conducted to explore the bending fatigue failure mechanism, and the damage processes of valid specimens are also closely examined. We find that the fatigue failure of SMC composites under four-point bending is governed by crack propagation instead of crack initiation. Because of this, the heterogeneous local fiber orientations of both sides of the specimen influence fatigue life. The microstructure of the lower side shows a direct influence while that of the upper side also exhibiting influence which becomes more prominent for high cycle fatigue cases. Furthermore, a hybrid micro–macro computational model is proposed to efficiently study the cyclic bending behavior of SMC composites. The region of interest is reconstructed with a modified random sequential absorption algorithm to conserve all the microstructural details including the heterogeneous fiber orientation, while the rest of the regions are modeled as homogenized macro-scale continua. Combined with a framework to capture the progressive fatigue damage under cyclic bending, the bending fatigue behaviors of SMC composites are accurately captured by the hybrid computational model comparing with our experimental analysis.

Mechanical behavior and fatigue failure analysis of standing seam aluminum alloy roof system under temperature effect

Standing seam metal roof systems with universal high-strength, lightweight, and thin-walled characteristics have been applied worldwide in massive large-span landmark buildings, such as gymnasiums, airports, and railway stations. The existing research focuses on the wind uplift design, but there are few studies on the mechanical properties under the temperature effect. In this paper, the temperature effect of the standing seam aluminum alloy roof (SSAAR) system was studied. To be familiar with the mechanical and deformation characteristics of the SSAAR system, the static loading tests under different temperatures and boundary constraints were carried out. Two specimens, one with anti-wind clips and the other without anti-wind clips, were further tested under cyclic loading to evaluate and quantify the fatigue failure characteristics of the roof system. The testing results indicate that the stress concentration, thermal expansion displacement, and wear of the SSAAR system are significant. The slab rib stress is the largest, accounting for about 83.7% of the yield strength, followed by the slab surface stress, and the slab bottom stress is the smallest. The horizontal displacement is greater than the vertical displacement, and the maximum is about 20.42 mm. The boundary constraint mainly affects the support stress and vertical displacement to increase by 47.2% and 79.3% respectively. The anti-wind clips mainly increase the wear thickness of the roof slab, which is increased by 67.5%.

High-cycle fatigue failure analysis of cast Al-Si alloy engine cylinder head

Due to the premature fracture of several cast Al-Si alloy cylinder heads at the same position during high-cycle fatigue (HCF) bench test, the HCF failure analysis including finite element simulation, microscopic observation and fatigue tests were conducted to determine the root cause of the failure. The results show that the external load was not the main cause of the fracture. The large defects with complex shapes and low compactness near the surface, and the poor surface finish of the water jacket surface are the main causes for the quick initiation of cracks. Furthermore, the alloy at the failure location exhibits relatively high porosity and secondary dendrite arm spacing, accelerating the crack propagation rate. Compared with the alloy at the non-failure locations, the yield strength, ultimate tensile strength and elongation of the alloy at the failure location are reduced by 9.3%, 25.8% and 65.3%, respectively. The fatigue life of the alloy at the non-failure location is several times the alloy at the failure location, verifying that the local large defects and poor microstructure characteristics are the main causes for the low HCF strength of the cylinder head.