Fatigue Failure Behavior Research Articles

Misalignment effect on the fatigue failure behavior of load-carrying cruciform welded joints

This paper presents an analytical model based on the Strain Energy Density (SED) method to predict the high cycle fatigue failure behavior of load-carrying cruciform welded joints (LCWJ) weakened by axial and angular misalignments. Compared with the Hot Spot Stress (HSS) and Effective Notch Stress (ENS) methods recommended in standard codes, the SED values at weld toe and weld root were carried out systematically considering the welded details and the types of misalignments. Moreover, the analytical model was applied to estimate the magnitudes of fatigue indicators and illustrated the effects of misalignment on the fatigue failure transition region in LCWJ. It is validated effectively as a supplementary analysis method for fatigue life prediction and fatigue design of welded joints compared with the experimental data and published reports.

Fatigue failure behavior and strength prediction of nickel-based superalloy for turbine blade at elevated temperature

The fatigue failure behavior and fatigue strength prediction were performed on a Ni-based superalloy for the turbine blade in 750 °C elevated temperature environment. The asymmetric load tests with the stress ratios R = -1 and 0.1 were tested, followed by microstructure characterization and fracture mode analysis via two & three-dimensional microscopic observation and electron-backscattering diffraction, etc. Results show that as stress level decreases, fatigue failure is less likely to be induced by pore, while the possibility of grain cracking induced failure increases. The larger roughness of the fracture surface is attributed to the geometric incompatibility of grains and the plastic deformation at the crack tip. For the grain related failure, crack nucleation is mainly in Goss grain along the direction of the maximum Schmid factor. Moreover, the threshold values of small & long cracks, the transition crack size from small to long, are all lower for interior failure due to the effect of vacuum environment. Finally, based on El-Haddad model, a new fatigue strength prediction model is proposed, and the predicted results are in good agreement with the experimental ones.

Influence of graphite on the low-frequency fatigue behavior of zirconium diboride ceramics

The fatigue behavior of a ZrB2-based ceramic containing SiC and graphite was compared to a ZrB2-SiC reference material based on bending testing, quantitative calculations as well as crack growth and fracture characterization. The addition of graphite flake makes ZrB2-SiC-Graphite ceramics exhibit fatigue failure behavior at very high stress level (93% of the characteristic strength, σ0), owing to the increased KIc promoted by crack deflection, bridging, bifurcation and pull-out of graphite, while the fatigue behavior of ZrB2-SiC appears when the maximum stress is below ~86%σ0. However, both the slow crack growth exponents of the graphite containing ceramic, n and nc values, which reflect the fatigue resistance in static and cyclic fatigue conditions, respectively, are only 1/4 as compared to the reference graphite-free ceramic. This may be due to the weak boride/graphite interfaces, which lead to the decrease of the initial critical stress intensity factor (Kc-initial) value from 2.6 to 2.0 MPa m1/2.

Experimental evaluation of sandstone under cyclic coupled compression-shear loading: fatigue mechanical response and failure behavior

Experimental evaluation of sandstone under cyclic coupled compression-shear loading: fatigue mechanical response and failure behavior

Misalignment effect on the fatigue failure behaviour of steel cruciform welded joints

This study investigates the displacement and angular misalignment of steel load-carrying cruciform welded joints and its effect on fatigue curves. The misalignment states of the welded joints were statistic and examined by optical equipment. The high cycle fatigue experiments on the misalignment load-carrying cruciform welded joints were carried out to obtain the S-N curves, which was compared to the IIW nominal reference curves. Finite element analysis was conducted to obtain the related fatigue indicators considering the effect of the displacement and angular misalignment on the basis of the SED method, hot spot method, and effective notch stress method. The related analytical solutions for the misalignment cases were proposed to for the fatigue strength estimations.

The fatigue failure behaviors of ferroelectric materials

In the fields of some major equipment technology such as aerospace and nuclear power generation, as the sensitive elements of high-temperature transforming/actuating/energy harvesting devices, the fatigue failure of bismuth layered ferroelectric (BLSF) ceramics seriously restrict the improvement in the life and reliability of devices. This paper is set in the urgent demand of BLSF ceramics, sticking to the fatigue crack growth, domain polarization switching, and interaction mechanisms. It reviewed the progress in the fatigue failure behaviors of ferroelectric materials subjected to three kinds of loadings, including heat, stress, electricity, and their coupled effects. This paper also discusses the research directions of ferroelectric materials in the future according to their new developments and applications. This work aims at providing references for the design of ferroelectric/piezoelectric devices with long life and high performance.

Corrosion mechanism and fatigue behavior of 2A70-T6 aluminum alloy under alternating corrosion and fatigue

PurposeMost supersonic aircraft were manufactured using 2A70 aluminum alloy. The purpose of this paper is to study the corrosion mechanism and fatigue behavior of an aircraft in a semi-industrial atmospheric corrosive environment, alternating effects of corrosion and fatigue were used to simulate the aircraft’s ground parking corrosion and air flight fatigue.Design/methodology/approachFor this purpose, the aluminum alloy samples were subjected to pre-corrosion and alternating corrosion-fatigue experiments. The failure mechanisms of corrosion and corrosion fatigue were analyzed using microscopic characterization methods of electrochemical testing, X-ray diffraction and scanning electron microscopy. Miner’s linear cumulative damage rule was used to predict the fatigue life of aluminum alloy and to obtain its safe fatigue life.FindingsThe results showed that the corrosion damage caused by the corrosive environment was gradually connected by pitting pits to form denudation pits along grain boundaries. The deep excavation of chloride ions and the presence of intergranular copper-rich phases result in severe intergranular corrosion morphology. During cyclic loading, alternating hardening and softening occurred. The stress concentration caused by surface pitting pits and denudation pits initiated fatigue cracks at intergranular corrosion products. At the same time, the initiation of multiple fatigue crack sources was caused by the corrosion environment and the morphology of the transient fracture zone was also changed, but the crack propagation rate was not basically affected. The polarization curve and impedance analysis results showed that the corrosion rate increases first, decreases and then increases. Fatigue failure behavior was directly related to micro characteristics such as corrosion pits and microcracks.Originality/valueIn this research, alternating effects of corrosion and fatigue were used to simulate the aircraft’s ground parking corrosion and air flight fatigue. To study the corrosion mechanism and fatigue behavior of an aircraft in a semi-industrial atmospheric corrosive environment, the Miner’s linear cumulative damage rule was used to predict the fatigue life of aluminum alloy and to obtain its safe fatigue life.

Research on the fatigue failure behavior of 1Cr17Ni2 blades ground by abrasive belt with passivation treatment

As precision machining process of aero-engine blades, the surface integrity after abrasive belt grinding closely related to its fatigue resistance. In order to explore new anti-fatigue abrasive belt grinding methods, reveal the influence mechanism of blade surface integrity on anti-fatigue performance, and provide guidance for the anti-fatigue grinding, vibration fatigue tests were carried out on blades processed by different grinding process, and the effects of abrasive belt passivation treatment and feed speed on blade surface integrity and fatigue life were studied. Fatigue failure behavior of blades processed by different processes were also discussed from the fracture morphology and cross-section analysis. Results showed that blades processed by blunt grinding have different fatigue failure mechanisms, and the passivation treatment of abrasive belt and low feed speed can improve the surface integrity and fatigue life of aero-engine blades. The combination process of abrasive belt passivation treatment and slow feed speed were proposed for anti-fatigue grinding processing of aero-engine blades. In this research, compared with blades processed by new abrasive belt with feed speed 1000 mm/min, the fatigue life of blades processed by passivated abrasive belt at feed speed 100 mm/min was increased by 3.1 times.

An Anti-Fatigue Design Strategy for 3D Ribbon-Shaped Flexible Electronics.

Three-dimensional (3D) flexible electronics represent an emerging area of intensive attention in recent years, owing to their broad-ranging applications in wearable electronics, flexible robots, tissue/cell scaffolds, among others. The widely adopted 3D conductive mesostructures in the functional device systems would inevitably undergo repetitive out-of-plane compressions during practical operations, and thus, anti-fatigue design strategies are of great significance to improve the reliability of 3D flexible electronics. Previous studies mainly focused on the fatigue failure behavior of planar ribbon-shaped geometries, while anti-fatigue design strategies and predictive failure criteria addressing 3D ribbon-shaped mesostructures are still lacking. This work demonstrates an anti-fatigue strategy to significantly prolong the fatigue life of 3D ribbon-shaped flexible electronics by switching the metal-dominated failure to desired polymer-dominated failure. Combined in situ measurements and computational studies allow the establishment of a failure criterion capable of accurately predicting fatigue lives under out-of-plane compressions, thereby providing useful guidelines for the design of anti-fatigue mesostructures with diverse 3D geometries. Two mechanically reliable 3D devices, including a resistance-type vibration sensor and a janus sensor capable of decoupled temperature measurements, serve as two demonstrative examples to highlight potential applications in long-term health monitoring and human-like robotic perception, respectively.

A mesoscale fatigue progressive damage model for 3D woven composites

A mesoscale fatigue progressive damage model (FPDM) is proposed for fatigue life prediction and failure behavior assessment of 3D woven composites (3DWC). The Hashin's fatigue criteria and the maximum tensile/shear stress criteria are used as damage activation criteria for the yarn and resin-rich matrix, respectively. A fatigue damage evolution model is developed based on Fang's static-load damage evolution model, where the damage irreversibility and compressive crack closure effect are considered. The UserMat subroutine and APDL language in ANSYS are employed to implement the fatigue process of 3DWC. The results show that all predicted fatigue lives are within two-fold error band.

Fatigue Resistance and Failure Behavior of Penetration and Non-Penetration Laser Welded Lap Joints

Penetration and non-penetration lap laser welding is the joining method for assembling side facade panels of railway passenger cars, while their fatigue performances and the difference between them are not completely understood. In this study, the fatigue resistance and failure behavior of penetration 1.5+0.8-P and non-penetration 0.8+1.5-N laser welded lap joints prepared with 0.8 mm and 1.5 mm cold-rolled 301L plates were investigated. The weld beads showed a solidification microstructure of primary ferrite with good thermal cracking resistance, and their hardness was lower than that of the plates. The 1.5+0.8-P joint exhibited better fatigue resistance to low stress amplitudes, whereas the 0.8+1.5-N joint showed greater resistance to high stress amplitudes. The failure modes of 0.8+1.5-N and 1.5+0.8-P joints were 1.5 mm and 0.8 mm lower lap plate fracture, respectively, and the primary cracks were initiated at welding fusion lines on the lap surface. There were long plastic ribs on the penetration plate fracture, but not on the non-penetration plate fracture. The fatigue resistance stresses in the crack initiation area of the penetration and non-penetration plates calculated based on the mean fatigue limits are 408 MPa and 326 MPa, respectively, which can be used as reference stress for the fatigue design of the laser welded structures. The main reason for the difference in fatigue performance between the two laser welded joints was that the asymmetrical heating in the non-penetration plate thickness resulted in higher residual stress near the welding fusion line.

Investigation of tensile and high cycle fatigue failure behavior on a TIG welded titanium alloy

The fracture behaviors of tungsten inert gas (TIG) welded titanium alloy TA15 subjected to tensile and fatigue loadings were investigated. Using the staircase test method, the fatigue probabilistic S-N (P-S-N) curves of the titanium alloy were obtained. Electron back scattered diffraction (EBSD) and Scanning electron microscope (SEM) were utilized to study fracture mechanism. The results showed that the weldment had different microstructure sensitivity when it was subjected to different loading conditions. The tensile failure of TIG welded TA15 was mainly dominated by the geometry and plasticity deformation ability of the weldment. The grain boundary mismatch in the connection region of the base metal and heat-affected zone increased the grain boundary energy and hindered the dislocation movement in the fatigue test. The texture transformation between the base metal and the connection of base metal and heat-affected zone caused a slip mismatch region in which the material has weak fatigue strength. In short, the reason for the tensile and fatigue failure of TIG welded TA15 was discussed systematically in this study.

Effect of surface roughness on the fatigue failure and evaluation of TC17 titanium alloy

This paper is focused on the investigation of fatigue failure mechanism for TC17 with surface roughness, which is the quantitative expression of surface micro-scratch. First, the designed fatigue tests for TC17 with different surface conditions are carried out to investigate the mechanism of fatigue failure behavior for TC17 with surface roughness. A modified formula is developed to evaluate the fatigue limit of TC17. Then, with the comprehensive application of S–N curve models and test results, the new finding of model parameters is adopted, leading to a fatigue life model of TC17 with surface roughness. Study of fatigue evaluation model of TC17 with surface roughness is significant in theoretical and engineering fatigue study.

Extremely Low Cycle Fatigue Failure Behavior of Box-column to I-beam Welded Joints

In this paper, cyclic loading tests are carried out to study the extremely-low-cycle fatigue (ELCF) failure behavior of the beam-to-column welded joints of steel structures subjected to severe seismic excitation. Firstly, the fatigue crack evolution and local strain of the weld zone obtained from experiments are adopted to investigate ELCF failure behavior for steel structures. In these experiments, three large scale specimens of box-column to I-beam connection are controlled by different cycle displacement ranges greater than the yield displacement. Secondly, the crack initiation and propagation law as well as the damage and deterioration mechanism are examined; then, the preliminary criterion for crack initiation for the box-column joint is proposed. Finally, failure characteristics and strain distribution of the box-column joint are analyzed. This study shows that the ELCF failure of the box-column to the I-beam joint is multiaxial and nonproportional. Based on the crack initiation and propagation along the thickness direction of the beam flange, the crack macro-penetration mode can be divided into two categories, i.e., standard failure mode and mixed failure mode. Moreover, load drop, change rate of load drop, and loading amplitude are key factors of the damage mechanism.

Fatigue failure behaviour of horn mounting bracket using finite element analysis

The aim of this present work is to find natural frequency for both existing and proposed horn mounting bracket designs to avoid the possibility of resonance. Next is to find out the dynamic behavior of existing bracket assembly from 5 to 17.3 Hz at the peak to peak distance of 10 mm by means of harmonic response analysis and then to find out the fatigue life using Goodman curve by vibrating the bracket assembly at first resonance frequency at 1.5 G acceleration. Finite element analysis (FEA) is carried to analysis the horn mounting bracket using ANSYS workbench software.

Fatigue behavior of dissimilar friction stir welded T-lap joints between AA5083 and AA7075

This study clarified the fatigue failure behavior of Friction Stir Welded T-lap joints between AA7075-T651 and AA5083-H116. The results showed that the fatigue life of the T-lap joints was significantly depended on interface morphology. The geometry and orientation of kissing bonds (KBs) kept an important role in the fatigue failure behavior of the joints. The fatigue crack predominantly initiated at the weld toe under the skin-directional loading test. Regarding the stringer-directional loading test, however, the fatigue crack dominantly originated at the KBs. Furthermore, the role of the KBs geometry and orientation in enhancing stress intensity factors was simulated and discussed.

The mean stress and phase angle effect on multiaxial fatigue behavior of a TiAl alloy: Failure analysis and life modeling

In the presence of multiaxial fatigue loadings with multiple loading variables, fatigue behavior of material differs from those under in-phase (IP) multiaxial fatigue loadings. The co-existence of non-zero mean stress and phase angle could be extremely harmful to fatigue resistance of material. In this case, it is vital for researchers engaging in relative fields to put forward capable life prediction methods. In this study, the mechanical property of a TiAl alloy under combined tension-torsion (CTT) fatigue loadings is investigated through experiments. The applied fatigue load contains non-zero mean stress components as well as phase angle components. The fracture of specimen is observed by scanning electron microscope (SEM) to investigate the correspondence between multiaxial fatigue life and failure behavior. Susmel and Lazzarin's (S-L) fatigue criterion is critically reviewed to put forward a modification on its intrinsic drawback. In parallel, a correction factor is introduced to make the modified Wӧhler curve method (MWCM) feasible for multiaxial fatigue life prediction with multiple loading variables. Verified by experimental results of present work, the proposed method is of good accuracy compared with Matake method and McDiarmid method.

Fatigue Behavior of Welded API 5L X70 Steel Used in Pipelines

In this study, fatigue failure behavior of welded X70 pipeline steel was investigated by rotating bar bending fatigue tests performed at room temperature. S–N curves of base metal, weld and heat-affected zone (HAZ) were plotted. Tension tests, hardness measurements and Charpy V-notched impact tests were carried out for mechanical characterization. Samples were examined with optical microscope and scanning electron microscope (SEM) microstructurally. Fracture surfaces were examined with SEM. In addition to fractographic analysis, striation counting method was used to estimate the crack growth rate of base metal, weld and HAZ. Stress intensity factor (∆K) ranges were also calculated. Tensile properties and hardness values of base metal and weld were found to be almost the same. Charpy impact test results show that base material has approximately twice impact energy than weld and HAZ at room temperature. However, Charpy impact energies of HAZ and weld decreased noticeably at − 30 °C, while very slight decrease was observed for base metal. The comparison of high-cycle fatigue and crack growth behaviors shows that base metal has better fatigue behavior of all from the point of crack initiation and propagation. Moreover, our findings also support the idea that striation counting can be used as a fractographic approach to estimate the crack growth behavior of materials.

Biaxial fatigue crack growth in proton exchange membrane of fuel cells based on cyclic cohesive finite element method

During the operation of proton exchange membrane in fuel cells, cyclic mechanical loads are introduced due to the humidity cycles. The resulting fatigue crack is known to be the main source for its mechanical degradation. In this paper, we use a relation between damage evolution of the cohesive elements and Paris law to simulate the biaxial fatigue crack growth. The effects of various loading conditions are investigated. The predicted crack growth is in a good agreement with experimental studies. Both the transverse stress and the tensile overload have retardation effects. It is also found that the fatigue crack growth rate associated with a shorter pre-crack depends more on the load waveform. Moreover, fatigue crack grows faster under the low-high loading history than the high-low one. These simulation results have provided significant insights into the fatigue failure behavior of membranes during operation conditions and can help improve their durability.

Revealing the competitive fatigue failure behaviour of CFRP-aluminum two-bolt, double-lap joints

The fatigue failure behaviour of CFRP-metal fastened joints in highly-loaded structures differs from that of CFRP-CFRP or metal-metal fastened joints because of the significant dissimilarity between fatigue damage mechanisms of CFRP and metal materials. In this paper, the competitive fatigue failure behaviour of a CFRP-aluminum two-bolt, double-lap joint was revealed via experiments and a novel numerical prediction method. In the proposed method, fatigue failures of the CFRP and aluminum joined plates were predicted by a novel progressive fatigue damage model and the nominal stress method, respectively. The predicted competitive fatigue life and failure mode of the joint were consistent with the experimental results, which validated the efficiency of the proposed method. It was found that, the collapse failure of the joint is caused by the failure of the CFRP laminate at high loading levels, whereas caused by the failure of the aluminum plate at low loading levels. Furthermore, influences of the thickness ratio of the joined plates on the competing fatigue failure of the joint were determined. Based on the critical thickness ratios corresponding to the transition of failure mode, the fatigue failure mode diagram of the joint was established, which is helpful for the design of the CFRP-aluminum bolted joint.