Fatigue Failure Characteristics Research Articles

Low amplitude fatigue performance of sandstone, marble, and granite under high static stress

Fatigue tests under high static pre-stress loads can provide meaningful results to better understand the time-dependent failure characteristics of rock and rock-like materials. However, fatigue tests under high static pre-stress loads are rarely reported in previous literature. In this study, the rock specimens were loaded with a high static pre-stress representing 70% and 80% of the uniaxial compressive strength (UCS), and cyclic fatigue loads with a low amplitude (i.e., 5%, 7.5% and 10% of the UCS) were applied. The results demonstrate that the fatigue life decreased as the static pre-stress level or amplitude of fatigue loads increased for different rock types. The high static pre-stress affected the fatigue life greatly when the static pre-stress was larger than the damage stress of rocks in uniaxial compression tests. The accumulative fatigue damage exhibited three stages during the fatigue failure process, i.e., crack initiation, uniform velocity, and acceleration, and the fatigue modulus showed an “S-type” change trend. The lateral and volumetric strains had a much higher sensitivity to the cyclic loading and could be used to predict fatigue failure characteristics. It was observed that volumetric strain $$\varepsilon _{{\text{v}}}$$ = 0 is a threshold for microcracks coalescence and is an important value for estimating the fatigue life.

The effects of joint design, bolting procedure and load eccentricity on fatigue failure characteristics of high-strength steel bolts

A detailed failure analysis was applied to a set of broken high-strength steel bolts originally fitted on a heavy fuel oil meter. The investigation included both experimental and numerical analysis. Experimental analysis confirmed failure of the bolts by a premature fatigue fracture process with failure being predominantly at thread runout. The present failure was prompted by the presence of relatively high stresses within the bolts – sometimes exceeding the material's yield strength. A two-stage finite element modelling (FEM) was used to model loading patterns within the overall meter assembly and also on individual bolts. FEM results have shown that loading patterns and the associated tensile stresses within bolts are the result of varying degrees of loading eccentricity, which itself was found to be the result of a neglectful bolting procedure. Furthermore, failure location is confirmed to be the result of a major design weakness where thread runout was found to coincide with flange interface. Contrary to some published results, fatigue crack front curvature was shown by experimental evidence to be related to the degree of axial misalignment between crack front ends rather than mean stress level. FEM results indicated that stress concentration factor is inversely related to the degree of load eccentricity and to a much lesser degree to the applied load. Finally, some operating and design recommendations are made in the light of present results as preventive measure of such failures in the future.

Fatigue Test Research on Improved T-Stub Specimen of Welded Beam-to-Column Connections

The current T-stub specimen of welded beam-to-column connections in steel structures was improved by adding clamping ends at both sides for convenience of fatigue tests. Uniaxial fatigue tests of the T-stub specimens were conducted. The fatigue properties and failure characteristics of the T-stub specimens were summarized and compared with those of two other standard welded joint configurations. Based on finite element analysis, various fatigue assessment approaches were used to predict the fatigue life of the specimens and the assessment results were compared with the test results. Previously developed unified design curves suitable to high-cycle and low-cycle fatigue assessment of standard welded joint configurations were extended to welded joints in beam-to-column connections. The results show that accurate experimental results can be obtained using the improved T-stub specimens with clamping ends; Under cyclic loading, the welded joint in beam-to-column connections has satisfying energy dissipation capacity, but the fatigue strength is relatively poor; the unified design curves are well applicable to the fatigue life assessment and design of welded beam-to-column connections in steel structures.

Experimental investigations on mechanical performance of rocks under fatigue loads and biaxial confinements

In this research, a series of biaxial compression and biaxial fatigue tests were conducted to investigate the mechanical behaviors of marble and sandstone under biaxial confinements. Experimental results demonstrate that the biaxial compressive strength of rocks under biaxial compression increases firstly, and subsequently decreases with increase of the intermediate principal stress. The fatigue failure characteristics of the rocks in biaxial fatigue tests are functions of the peak value of fatigue loads, the intermediate principal stress and the rock lithology. With the increase of the peak values of fatigue loads, the fatigue lives of rocks decrease. The intermediate principal stress strengthens the resistance ability of rocks to fatigue loads except considering the strength increasing under biaxial confinements. The fatigue lives of rocks increase with the increase of the intermediate principal stress under the same ratio of the fatigue load and their biaxial compressive strength. The acoustic emission (AE) and fragments studies showed that the sandstone has higher ability to resist the fatigue loads compared to the marble, and the marble generated a greater number of smaller fragments after fatigue failure compared to the sandstone. So, it can be inferred that the rock breaking efficiency and rock burst is higher or severer induced by fatigue loading than that induced by monotonous quasi-static loading, especially for hard rocks.

Failure analysis of rear axle shaft of a heavy vehicle

Failure of the rear axle shaft of a heavy vehicle was thoroughly investigated. It was noticed that the axle shaft had failed during service and broken into two pieces. Different types of investigations were carried out on the failed axle shaft which includes visual examination, chemical analysis, Mechanical testing, Fractography and ultrasonic testing. Several cleavages were noticed in the Fractography, which depicted a sign of brittle fracture. Fatigue striations were observed in scanning electron microscopic analysis of the as received failed axle, which a typical indispensible characteristics of fatigue failure. The tensile fracture surface revealed mixed component of dimple as well as cleavage facet. Results indicated that failure occurred due to sudden loading on the axle shaft. The shear stress in the weak portion of the axle was not sufficient to counter the stress imposed by sudden loading.

Fatigue Reliability Analysis of a Compressor Disk Based on Probability Cumulative Damage Criterion.

The reliability of aero engine has a direct impact on the flight safety of the whole plane. With the continuous improvement of performance requirements of aero engines, the related fatigue and reliability problems also appear. For the fatigue failure characteristics of the typical component (compressor disk) in an aero engine, the fatigue reliability of its multi-site damage structure in service is analyzed by using probability cumulative damage criterion in this paper. The probability distribution definitions of life, damage and damage threshold are discussed and the relationship among them is also introduced by the new proposed criterion. Meanwhile, a method to determine the probability distribution of cumulative damage threshold and probability life prediction is carried out, based on which a hierarchical index system of statistical analysis and reliability modeling principle on the system level is further constructed for compressor disk. At the end of the paper, a certain cruise of fighter plane is analyzed to verify the validity of the new model. Emphasizing the difference between the compressor disk and traditional component, the new reliability analysis model developed in this study is basically reasonable for most of the load histories for the compressor disk, other than the traditional one, especially for the changeable and complex cruise missions.

Effect of indenter material on reliability of all-ceramic crowns.

ObjectivesControversy exists about whether the elastic modulus (E) mismatch between the loading indenter and ceramic materials influences fatigue testing results. The research hypotheses were that for porcelain veneered Y-TZP crowns 1) A low modulus Steatite indenter (SB) leads to higher fatigue reliability compared to a high modulus tungsten carbide indenter (WC); 2) Different surface damage patterns are expected between low and high modulus indenters after sliding contact fatigue testing. All ceramic crowns will exhibit similar step-stress accelerated life testing (SSALT) contact fatigue reliability (hypothesis 1) and failure characteristics (hypothesis 2) when using high stiffness tungsten carbide (WC, E = 600 GPa) vs. enamel like steatite (SB, E = 90 GPa) indenters. MethodsManufacturer (3M Oral Care) prepared Y-TZP-veneered all-ceramic molar crowns were bonded to aged resin composite reproductions of a standard tooth preparation and subjected to mouth-motion SSALT fatigue (n = 18 per indenter type). Failure was defined either as initial inner cone crack (IC), or final fracture (FF) when porcelain fractured (chipping). Selected IC specimens that did not progress to FF were embedded in epoxy resin and sectioned for fractographic analysis. ResultsThe distribution of failures across the load and cycle profiles lead to similar calculated Weibull Use Level Probability Plots with overlap of the 2-sided 90% confidence bounds. The calculated reliability for IC and FF was equivalent at a mission of 300 N or 700 N load and 50,000 cycles, although the WC indenter had a trend for lower reliability for IC at 700 N. Both indenters produced similar patterns of wear and cracking on crown surfaces. Fractographic landmarks showed competing failure modes, but sliding contact partial inner cone cracks were the most dominant for both groups. SignificanceThe more compliant Steatite indenter had similar veneered crown fatigue reliability and failure modes to those found with use of a high stiffness tungsten carbide indenter (hypotheses 1 and 2 rejected).

Fatigue damage of PBH shear connector of steel-concrete composite structure

Perfobond Leiste (PBL) shear connector is a widely-applied shear connector that rely on the concrete tenons and penetrating steel bars in the open hole steel ribs to resist slipping. Perfobond Hoop (PBH) shear connector uses the stirrups in the concrete structure to replace the independent penetrating straight reinforcement in the PBL shear connector, which has better spatial rigidness, and shear performance. In this paper, the static and fatigue tests of PBH shear connector are designed to analyze the static and fatigue failure characteristics and study the fatigue damage mechanism and fatigue damage evolution model of PBH shear connector. The study found that PBH shear connector has higher shear stiffness and fatigue properties than PBL shear connector. The concrete tenon in the open-hole steel rib plate is the key part of the PBH shear connector, and its failure form is different during static and fatigue failure. The fatigue shear stiffness of the PBH shear connector is shown as a jump reduction, which is different from the static shear stiffness as a smooth decline. The fatigue damage process of PBH shear connector is divided into three stages according to the failure mechanism: the bond failure stage of the steel-concrete composite interface, the crushing and migration stage of the concrete tenon, and the bending and failure stages of the penetrating steel bar. The three stages take up 10%, 80% and 10% of the fatigue life in turn. With the damage degree as the fatigue process variable, a two-line fatigue damage evolution model of the PBH shear connector is established, which can be used to predict the final interface slip value and fatigue life.

Real world application of angular scan pulse-echo ultrasonic propagation imager for damage tolerance evaluation of full-scale composite fuselage

Composite structures are assertively used for new airframe designs and manufacturing in military aircrafts because of superior strength-to-weight ratios and fatigue resistance. Because the composites have different fatigue failure characteristics compared with metals, it is necessary to develop different approaches for the composite fatigue design and testing. In this study, we propose an in situ damage evaluation technology with high spatial resolution during full-scale fatigue testing of composite aircraft structures. For real composite structure development considering composite fatigue characteristics, full-scale fatigue and damage tolerance tests of the composite fuselage structure were conducted to evaluate the structural characteristics. In the meantime, the laser ultrasonic nondestructive inspection method, called an angular scan pulse-echo ultrasonic propagation imager, which is fully noncontact, real-time, and portable to position it in between the complex test rigs, is used to observe in situ damage growth of the composite. Finally, the verification procedure assisted by the angular scan pulse-echo ultrasonic propagation imager assures no growth of the initial impact damages after lifetime operation and proves the damage tolerance capability of the developed composite fuselage structure.

Research on multidisciplinary fatigue optimization design method in structural design of high speed train

Aiming at the shortcomings of single-discipline fatigue design and life prediction optimization design method for high-speed trains, considering the characteristics of structural design integrity, a durability analysis method for key structural components based on multi-disciplinary fatigue optimization design is proposed. According to the characteristics of vibration fatigue and structural failure of key structural components of high-speed trains, the multi-disciplinary fatigue design of carbody components is carried out from the perspectives of materials, loads and structural design. In the research process, qualitative and quantitative analysis and comparison of multi-objective optimization analysis (MOO) and multi-disciplinary optimization (MDO) processes were carried out. At the same time, considering the actual example, considering the vibration characteristics of the vehicle structure, the typical load spectrum and the complex material characteristics, the failure characteristics of the structural components are analyzed in detail. The research results are shown that there are certain limitations in single-disciplinary fatigue design and analysis. In order to effectively solve the complex engineering structure failure problem, it is necessary to fully consider the vibration characteristics of the entire vehicle structure. Through the multi-disciplinary fatigue design and optimization method of high-speed train structural components, the safety and structural integrity of key structural components of rail transit can be better guaranteed.

The Fractal Characteristics of Coal Sample’s Fragments Subjected to Cyclic Loading

A series of test were performed to study the fractal characteristics of fatigue failure of coal samples. The research revealed the difference of fractal characteristics in conventional compression test and cyclic loading test, and obtained the relationship among the fractal dimension, size, mass and quantity of fragments. In cyclic loading test, three levels of confining pressure (0, 5 and 10 MPa) were applied during axial cyclic loading at 0.25 and 0.5 Hz frequency. These tests showed that: (1) The size and mass distribution of the debris are affected by the confining pressure, frequency, and loading mode. Compared to conventional compression experiments, fatigue failure from coal samples produces more debris and smaller dimensions. (2) The size of the pieces is less affected by the experimental method. However, as the size range of the fragments decreases, the shape of the fragments changes from a long thin strip to a rectangular parallelepiped. (3) The fractal dimension of the cyclic load test is larger than the traditional compression experiment. In the cyclic load test, the fractal characteristics are more obvious as the confining pressure increases.

Fatigue characteristics of in-service cold recycling mixture with asphalt emulsion and HMA mixture

Cold central-plant recycling (CCPR) mixture with asphalt emulsion has been successfully used in heavy-duty pavement rehabilitation for 11 years in China. The fatigue performance of CCPR mixture attracts the engineer’s and researcher’s attention. However, few studies have aimed at investigating the fatigue characteristics of the in-service CCPR mixture that had been placed in pavement for many years and its fatigue properties have not been well understood till now. Thus the main objective of this study was investigating the fatigue characteristics of in-service CCPR mixtures cored from the field pavement using laboratory Indirect Tensile Fatigue Test (ITFT). In addition, one hot mix asphalt (HMA) mixture from the same pavement was evaluated for comparison. Based on the laboratory fatigue test results, the fatigue failure characteristics and fatigue lives for in-service CCPR and HMA mixtures were determined and discussed. In addition, a method was proposed in this study to calculate the shift factors of CCPR and HMA mixtures based on the laboratory fatigue test results and field traffic loadings. The findings of this study hope to provide recommendations for improving the design and construction method of the CCPR mixture.

The Fatigue Strength and Failure Mode of Coal Sample Subjected to Cyclic Loading

In order to study the fatigue strength and failure characteristics of coal samples, a series of multilevel cyclic loading tests were carried out. The test results show that: (1) When the confining pressure corresponds to 0, 5 and 10 MPa, the fatigue strength of coal samples at a frequency of 0.5 Hz is slightly larger than that with a frequency of 0.25 Hz. (2) For fatigue failure, the circumferential strain is more sensitive than that of axial strain. (3) In the condition of conventional compression test, it is favorable for larger scale cracks to growth and rapid development when the broken degree of coal samples is low. In the long-term cyclic loading test, it is beneficial to produce small cracks. The coal sample is more broken in this case.

Stress, Deformation and Failure Analysis of Parabolic Leaf Spring by Finite Element Analysis with Material Optimization

A leaf spring is a simple form of spring commonly used for the suspension system in heavy duty vehicles which is originally called laminated or carriage spring. It performs the isolation task in transferring the vibration due to road irregularities to the passenger’s body or goods transported on it. The advantage of leaf spring over helical spring is that the ends of the spring have been guided along a definite path as it deflect to act as a structural member in addition to an energy absorbing device. Increasing competition and innovations in the automobile sector, tends to modify the existing products with new or advanced material products. To improve the performance of the suspension system, many modifications have been taken place overtime but the recent innovations imply parabolic leaf spring and application of composite materials, as the composite materials have high strength-to-weight ratio compared to the conventional steels. The present work attempts to analyze the comparison between the conventional steel (AISI1030) leaf spring and the composite (Carbon/Epoxy) leaf spring with respect to static and fatigue analysis. Here static analysis determines the safe stress, deformation and corresponding pay load and also studies the behavior of structures under practical conditions. The research also focuses on fatigue analysis to determine its life cycle and also to observe its fatigue failure characteristics. The model of the leaf spring has been carried out into the CAD software. The analysis of the steel leaf spring has been divided into theoretical, experimental and simulation sections. The simulation of steel leaf spring has been validated with the theoretical and the experimental results. Further simulation has been done for composite leaf spring by FEA software. Finally, the result shows that the composite leaf spring has better load carrying capacity in reduced weight, and better fatigue behavior rather than the conventional steel material for the leaf spring.

Experimental investigation on fatigue failure characteristics of QP-16 type ball-eye under bending load

Abstract In order to ensure the safety and reliability of power delivery systems, the fatigue characteristics and mechanical properties of ball-eyes (BE) are studied by proprietary equipment: bending fatigue test equipment (BFTE), scanning electron microscope (SEM), stereomicroscope, energy dispersive spectrometer (EDS), hardness display equipment. It was found that, compared with the BEs of the annealing process and quenching and tempering process (QTP), the mechanical properties of BE treated by normalizing process are the best under the three different bending fatigue loads, which are 200, 300, 400 MPa. The three kinds of BE with different processes have their own characteristics, in which, the fatigue fracture of BE treated by normalizing process has obvious cowrie pattern and multi fatigue origins. The fatigue extension region is relatively smaller, but the appearance are more smooth and delicate, whose color are black and dark. In final fracture region, there is obvious rust, coarse, a granular surface. The microstructure is fine uniform ferrite and pearlite. The fracture morphology are characterised by transgranular and quasi-cleavage fracture with a few intergranular cracks and the fracture surface contains more impurities. Fatigue fractures of BE from the other two processes of the characteristics of inhomogeneous microstructure, large difference of micromorphology, rough fracture surface and different impurity elements. Under the same stress amplitude, the life of the BE under bending load is lower than that of the BE under tensile load.

Energy‐based fatigue failure characteristics of materials under random bending loading in elastic‐plastic range

AbstractThis article presents selected aspects connected to the methods of identification of strain energy density that are used to calculate the fatigue strength of materials. The authors focus on selected methods for determination of energy‐based (stress‐strain) characteristics of the fatigue life of materials (Wa − Nf), including a new approach for the determination of strain energy density parameter Wa. The paper also contains description and evaluation of models for determining the stress amplitudes σa in the elastic‐plastic range, for bending. The developed procedure should give new capabilities in fatigue life calculations.

Comparison of the fatigue failure behaviour for asphalt binder using both cyclic and monotonic loading modes

The objective of this paper is to investigate and compare the fatigue failure characteristics of neat and modified asphalt binders using both cyclic and monotonic loading modes, and further discuss the potential possibility of using the monotonic test for binder fatigue resistance ranking of purchase specification. The cyclic linear amplitude sweep (LAS) test (AASHTO TP 101) has been introduced to quantify the strain at peak stress, and also to predict the strain-controlled binder fatigue life from applying the simplified-viscoelastic continuum damage modeling (S-VECD) approach. Although the LAS is getting acceptance, the mathematical fitting approach is very complicated and require advanced curve fitting and analysis procedure. A simple alternative for characterizing binder failure properties is the use of monotonic loading as described in the binder yield energy test (BYET) and dynamic shear rheometer-elastic recovery (DSR-ER) test (AASHTO TP 123). In this study the BYET based failure strain is found to most efficiently correlate to the LAS based failure strain and predicted fatigue life. However, the multiple-peak phenomenon observed in the BYET stress-strain curves of some of the complex modified binders makes it very difficult to clearly identify the failure parameters. Results collected in this study show that using the DSR-ER test results can be a good addition to the BYET to predict fatigue life of a number of highly modified binders as estimated from the complex LAS mathematical procedure. Therefore, the combined use of the monotonic BYET and DSR-ER tests is recommended as an alternative to the cyclic LAS test for ranking the fatigue resistance of modified asphalt binders in routine practice.

Investigating the fatigue failure characteristics of A283 Grade C steel using magnetic flux detection

The Metal Magnetic Memory (MMM) method is a non-destructive testing method based on an analysis of the self-magnetic leakage field distribution on the surface of a component. It is used for determining the stress concentration zones or any irregularities on the surface or inside the components fabricated from ferrous-based materials. Thus, this paper presents the MMM signal behaviour due to the application of fatigue loading. A series of MMM data measurements were performed to obtain the magnetic leakage signal characteristics at the elastic, pre-crack and crack propagation regions that might be caused by residual stresses when cyclic loadings were applied onto the A283 Grade C steel specimens. It was found that the MMM method was able to detect the defects that occurred in the specimens. In addition, a justification of the Self Magnetic Flux Leakage patterns is discussed for demonstrating the effectiveness of this method in assessing the A283 Grade C steel under cyclic loadings.

Experimental and analytical verification of the characteristics of shear fatigue failure in the adhesive interface of porous foam materials

In the past, many studies have been conducted to examine the effect of static load and fatigue load on the adhesive interface between two different materials or the same materials, but little research has been done on porous materials. Thus, this study was carried out to examine the effect of fatigue load on the adhesive interface formed by aluminum foam, which exhibits porous characteristics. For the experiment, five specimens were fabricated with the thicknesses varied in increments of 10 mm from 25 mm to 65 mm. The aluminum foam was bonded using the single-lap method, and MTS landmark was used to conduct the fatigue experiment. Based on the initial static experiment, the maximum reaction force at which total failure occurred in the adhesive interface was obtained, and fatigue load was applied on the lower load cell in the 10 Hz sine graph form. The results of the experiment showed that for all five of the specimens, the adhesive strength of the adhesive agent was maintained in the adhesive interface during the 5000 cycle of the fatigue load. Also, based on the correlation between displacement and repeated load cycles, it was discovered that the adhesive interface underwent total failure after a sharp displacement in the interface in all five cases when the load was repeated for more than 5000 cycles In addition, a numerical analysis was performed based on the experimental results, and the stress distribution was visualized. The numerical analysis results showed similar tendencies as the experimental results, which confirmed the reliability of the analysis results. Thus, it was deemed that it would be possible to analyze the fatigue failure behavior of actual, bonded structures made of a porous material based on the experimental and numerical analysis results obtained through this study.

Ultrasonic quantification of high temperature cyclic damage in an advanced nickel based superalloy

Abstract Present paper discusses about a new methodology to quantify cyclic damage through ultrasonic measurement. Based on experimental results, correlations have been made between damage accumulated inside the material due to strain excursions and corresponding ultrasonic parameters. It has been proposed that based on the existing correlation between attenuation coefficient and number of cycles to failure, fatigue failure characteristics can be partitioned into two regimes (a) failures due to early nucleation and rapid propagation of cracks and (b) failures due to delayed propagation and crack coalescence. Plastic strain accumulation and surface crack density have been chosen as two physical parameters directly influencing attenuation coefficient and it has been observed that with increasing plastic strain accumulation, ultrasonic attenuation increases. Between two primary echoes of ultrasonic spectra, some secondary defect echoes have been found. A damage descriptor has been introduced by taking difference between the bandwidth of defect echo and backwall echo normalized by overall amplitude frequency distributions of backwall echo. It has been found to bear sensitivity towards surface crack density. This quantitative estimation differentiates between the classical descriptions of damage due to dislocation mediated plasticity, micro crack generation and coalescence.