Fatigue Properties Research Articles

Mechanical responses of chemically corroded sandstone under cyclic disturbance: Insights from fatigue properties and macro-micro fracturing mechanism

Engineering rock masses are likely to be subjected to coupled chemical corrosion and cyclic load disturbance, deteriorating the internal structure of rocks and further threatening the long-term stability of engineering structures. In this study, to investigate the combined effect of cyclic loading and chemical corrosion, the cyclic uniaxial compression tests are conducted on sandstone specimens chemically corroded by different corrosion times (0, 20, 40, 60 days) and pH values (1, 3, 7, 11, 13). Our results indicate that chemically corroded sandstone specimens featured by an increase in irreversible strain and hysteresis energy density compared with natural rocks. A coupling damage variable is proposed to reflect the initial damage induced by chemical corrosion and the mechanical damage induced by cyclic disturbance, and the accumulation rate of coupled chemical-fatigue damage variables significantly increases with increasing corrosion time or enhancing acidity and alkalinity. Fatigue failure modes of tested specimens transform from splitting failure to unidirectional shear failure as corrosion time increases, and chemically corroded specimens are featured by ductile failure characteristics compared to natural state. Moreover, X-ray diffraction (XRD) and Scanning Electron Microscope (SEM) are employed to analyze the micro-fracturing mechanism of sandstone. Cement minerals dominate the reactions in acidic solutions, whereas quartz takes the lead in alkaline conditions. Due to pronounced influence of cement minerals on the macroscopic mechanical properties of sandstone, acid corrosion specimens tend to experience more severe damage. Micro-cracks inside rocks under cyclic loading have sufficient time to pass through weakly bonded particles, and chemical reactions markedly weaken inter-particle bonding degree, and thus the fatigue fracture of chemically corroded specimens predominantly exhibits intergranular (IG) fracture.

Bending Fatigue Properties of Ultra-High Toughness Cementitious Composite (UHTCC).

Ultra-High Toughness Cementitious Composite (UHTCC) represents a composite material meticulously engineered on the foundation of micromechanical principles. The multi-crack cracking and strain-hardening characteristics of UHTCC enable it to be applied to orthotropic steel decks to control the crack width. Different from most studies which only focus on hybrid fiber or fatigue characteristics, this paper studies the influence of hybrid fiber content on static mechanical properties, flexural toughness, and flexural fatigue characteristics of UHTCC under different stress levels. The compressive and flexural strength, bending toughness, and fatigue damage of UHTCC under different fiber ratios were compared, and the fatigue properties of hybrid fiber UHTCC were verified. The results reveal that hybrid fiber exerts a more pronounced effect on toughness, augmenting the maximum folding ratio by 23.7%. Single-doped steel fiber UHTCC exhibits a characteristic strain-softening phenomenon attributable to inadequate fiber content, whereas the bending toughness index of hybrid fiber UHTCC surpasses that of SF1.5P0 by 18.6%. Under low-stress conditions, UHTCC demonstrates a nearly threefold increase in bending fatigue life with a mere 1% steel fiber content, while the influence of polyvinyl alcohol (PVA) fiber on fatigue life is more significant: with an increase of only 1/5 volume content, the fatigue life increased by 29.8%, reaching a maximum increase of 43.2% at 1/4 volume content. Furthermore, the fatigue damage accumulation curve of UHTCC follows a three-stage inverted S-shaped trajectory. The inclusion of PVA fiber facilitates early initiation of stable cracking during the fatigue failure process, thereby advancing the entire strain stability development stage and mitigating external load forces through the proliferation of micro-cracks. Consequently, compared to SF1P0, the ε0 of SF1P5 experiences a significant increase, reaching 143.43%.

Effect of Coherent Twin Boundary on the Low-Cycle Fatigue Property of 321 Austenitic Stainless Steel

Effect of Coherent Twin Boundary on the Low-Cycle Fatigue Property of 321 Austenitic Stainless Steel

Fatigue and Corrosion Fatigue Properties of Mg–Zn–Zr–Nd Alloys in Glucose-Containing Simulated Body Fluids

Fatigue and Corrosion Fatigue Properties of Mg–Zn–Zr–Nd Alloys in Glucose-Containing Simulated Body Fluids

Evaluation of Fatigue Behavior of Asphalt Field Cores Using Discrete Element Modeling.

Fatigue cracking is one of the primary distresses of asphalt pavements, which significantly affects the asphalt pavement performance. The fatigue behavior of the asphalt mixture observed in the laboratory test can vary depending on the type of fatigue test and the dimension and shape of the test specimen. The variations can make it difficult to accurately evaluate the fatigue properties of the field asphalt concrete. Accordingly, this study proposed a reliable method to evaluate the fatigue behavior of the asphalt field cores based on discrete element modeling (DEM). The mesoscopic geometric model was built using discrete element software PFC (Particle Flow Code) and CT scan images of the asphalt field cores. The virtual fatigue test was simulated in accordance with the semi-circular bending (SCB) test. The mesoscopic parameters of the contacting model in the virtual test were determined through the uniaxial compression dynamic modulus test and SCB test. Based on the virtual SCB test, the displacement, contact forces, and crack growth were analyzed. The test results show that the fatigue life simulated in the virtual test was consistent with that of the SCB fatigue test. The fatigue cracks in the asphalt mixture were observed in three stages, i.e., crack initiation, crack propagation, and failure. It was found that the crack propagation stage consumes a significant portion of the fatigue life since the tensile contact forces mainly increase in this stage.

Fatigue properties of SiC graded ceramic lattice structures with a triply periodic minimal surface manufactured by laser powder bed fusion

SiC graded ceramic lattice structure (GCLS) offers superior mechanical strength and its impact on fatigue warrants investigation. In this work, SiC triply periodic minimal surface (TPMS) GCLSs were prepared via laser powder bed fusion technology and liquid silicon infiltration process, alongside SiC TPMS uniform ceramic lattice structure (UCLS) as a reference. Fatigue properties, fatigue failure, and strengthening mechanisms were systematically investigated through compression fatigue tests, finite element (FE) simulations, and theoretical analysis. Fatigue failures of SiC UCLSs and GCLSs are influenced by cyclic ratcheting and fatigue damage, with cyclic ratcheting dominance. The fatigue strength ratios of UCLS and GCLS are 0.7 and 0.74, indicating that GCLSs exhibit stronger deformation resistance and superior fatigue performance. FE results show that surface tensile stress level in GCLS is lower than in UCLS, resulting in slower fatigue crack initiation. Stress redistribution and higher crack thresholds contribute to enhanced fatigue resistance in SiC TPMS GCLSs.

High‐Cycle‐Fatigue Anisotropy of an Aluminum Alloy Superthick Plate

The effect of anisotropy on high‐cycle fatigue (HCF) property along the rolling direction (RD) and the transverse direction (TD) of a 7××× aluminum alloy super thick plate is mainly investigated in this study. The results show a similar microstructure at different thicknesses, and the HCF properties are close as well. The fatigue fracture morphologies show that the fatigue crack sources are all located on the surfaces of the RD and TD specimens. By considering the differences in the HCF properties, there is only a slight anisotropy effect at the center thickness of the plate, which can be attributed to the tensile anisotropy caused by textures. Besides, the fatigue damage degree along the TD is slightly higher than that along the RD at the center thickness. The reason can be explained by two aspects: one is the higher probability of defect occurrence along the TD compared with that along the RD which is analyzed by the previously proposed Yield strength‐Tensile strength‐Fatigue strength model, and the other is the influence of the textures. The combination of hard and soft orientations may cause fatigue damage localization easily in the soft‐oriented grains which accelerates the fatigue failure.

Understanding the fatigue behaviour of Ti–6Al–4V manufactured via various additive processes

Additive Manufacturing (AM) is receiving widespread attention from both industry and academia who are looking to benefit from the numerous advantageous possibilities that AM processes have to offer, such as the potential to design and produce highly complex bespoke geometries with minimal material wastage. Yet, despite this, AM also has some drawbacks. Some of the most significant include the presence of process-induced defects and the inherent surface roughness of an AM built component, both of which can have a considerable influence on the mechanical properties of the final product. This research will investigate the role of an as-built surface on the fatigue properties of AM Ti–6Al–4V manufactured by electron beam melting (EBM), laser powder bed fusion (L-PBF) and laser metal deposition with wire (LMD-w). Fatigue results have been generated alongside advanced surface profilometry, microstructural, defect and fractographic analyses that have revealed that whilst the surface roughness in the majority of instances is the primary factor impacting the fatigue performance on AM material, it cannot be considered alone. It was found that the inherent as-built (AB) surface finish was significantly different across the various AM processes, inducing a range of effective stress concentrations and thus, a contrasting impact on the resulting fatigue performance. Results from each variant have been compared against a machined and polished equivalent, to provide a further consideration as to whether the as-built surface would be suffice from a time and economical viewpoint. Statistical analysis of the generated results also allowed for an extrapolation of predicted fatigue lives in the very high cycle regime for the alternative AM Ti–6Al–4V variants.

Experimental Investigation of Stress Concentration and Fatigue Behavior in 9% Ni Steel Welded Joints under Cryogenic Conditions

This experimental study delves into the intricate mechanics of stress concentration and fatigue behavior exhibited by 9% Ni steel welded joints under cryogenic conditions. The study specifically examines butt-welded, fillet longitudinal, and fillet transverse specimens, comparing their fatigue properties under room and cryogenic temperatures. Notably, determining hot-spot stress presents a challenge, as it cannot be directly obtained through traditional means. To overcome this limitation, a method for predicting hot-spot stress is introduced, which considers the effects of misalignments and weld bead characteristics. The study also highlights the impact of grip-clamping-induced specimen deformation and the reduced middle section on stress concentration resulting from misalignments. Furthermore, it proposes separate consideration of the effects of the weld bead on the axial nominal stress and on the bending stress of the specimen. The accuracy of strain gauge measurements in cryogenic environments is addressed by suggesting a method to correct the output of 2-wire strain gauges using a fixed ratio derived from 2-wire and 3-wire strain gauges. By comparing predicted hot-spot stress with actual measurements, the study validates the reliability of the proposed predictive method. These findings contribute to a deeper understanding of the behavior of 9% Ni steel welded joints under cryogenic conditions and provide valuable insights for design and engineering in similar applications.

Improvement of the fatigue life of an electron-beam welded Ti2AlNb joint subjected to an electromagnetic coupling treatment

The local stress concentration created by the seam welding process often reduces the fatigue life of the material along and around the seam. Post-welding heat treatment is usually used to improve the weld performance, but the improvement effect on fatigue life may not be obvious. In this study, a new treatment method of electromagnetic coupling was applied to regulate the Ti2AlNb electron beam weld after heat treatment, so as to improve the fatigue properties of the welded joint. The results show that after electromagnetic coupling treatment, the fatigue limit of the welded joint is increased by 10.4 %, the residual compressive stress is increased, and the fatigue crack propagation rate is decreased. The microstructure analysis shows that after electromagnetic coupling treatment, the fatigue crack source starts in the subsurface layer, the substructural crystals in the fusion zone and the heat affected zone decrease, the recrystallization content and the large angle grain boundary increase, and the dislocation density increases and tends to be homogenized. An increase of at least 2.3 % in hardness of the welded joints also indicates the increase in the dislocation density. Local high density dislocation is found in the grain, which causes dislocation entanglement and hinders crack initiation and propagation and this provides an important basis for improving fatigue properties. This study provides a new method for improving the fatigue properties of Ti2AlNb electron beam welds which can also be used to study the properties of other welded joints.

High cycle fatigue behavior of bulk 6061Al prepared by cold spray-friction stir processing composite additive manufacturing

In this work, the high cycle fatigue behavior of bulk 6061Al prepared by cold spray-friction stir processing composite additive manufacturing (CFAM) was studied for the first time. The microstructure and fatigue fracture morphology of CFAM sample were characterized by scanning electron microscopy equipped with electron backscattering diffraction. The stress versus number of cycles of failure (S-N) curve for CFAM sample was established, and the fatigue crack growth behavior of CFAM sample was analyzed. The results showed that the microstructure of CFAM sample was denser and more homogeneous compared with cold spray (CS) sample, and the average grain size was refined to 3.3 μm due to dynamic recrystallisation. The dense, homogeneous and fine microstructure delayed the initiation and growth of fatigue cracks, and thus resulted in a 178% increase in fatigue strength in the CFAM sample over CS sample. The fatigue surface of the CFAM sample could be divided into fatigue source zone, crack growth zone, and transient fracture zone, showing typical fatigue fracture characteristics. The fatigue crack growth rate in the CFAM sample was significantly lower than that of CS sample for the same stress intensity factor range (ΔK). This was because the fine grains uniformly distributed in CFAM sample increased the proportion of grain boundaries and hindered the fatigue cracks growth. Therefore, CFAM is a promising technology for preparing bulk 6061 Al with excellent fatigue properties.

The effect of various treatment parameters in duplex plasma nitrided and diamond-like carbon coating on high-cycle fatigue and fretting fatigue lifetimes of piston pin 16MnCr5 steel

This paper investigates the impact of duplex plasma nitriding and diamond-like carbon (DLC) coatings on the pure fatigue and fretting fatigue properties of 16MnCr5 steel extracted from industrial piston pins used in combustion engines. Two different nitriding and DLC coating processes were performed: "DLC-A" and "DLC-B". The Raman spectrometry and microhardness tests were utilized to evaluate the formation of DLC coating on the sample. Subsequently, the pure and fretting fatigue tests (at 350 MPa and under 100 Hz of the frequency) were performed on as-cast and DLC-coated specimens to obtain the effect of coatings on the fatigue behaviors of the 16MnCr5 steel. Finally, the formation of the DLC layer and the fracture mechanisms were also briefly investigated using field-emission scanning electron microscopy. Then, the obtained results demonstrated that DLC coating ("DLC-B") increased the fatigue lifetime of 16MnCr5 steel by 47.7 % and 85.3 % in pure and fretting fatigue conditions, respectively. This layer can improve the surface properties of engineering materials and components, which can enhance the fatigue lifetime by increasing microhardness and compressive residual stress, reducing wear and friction, and improving adhesion between the substrate and coating. However, due to the white layer, the “DLC-A” improperly enhanced the material performance.

Fatigue response of wire-arc additive manufactured nickel-aluminum bronze (NAB) in the post-annealed condition

Nickel-aluminum bronze (NAB) is chosen for critical applications like marine propellers, pump components, and offshore structures due to its exceptional mechanical properties and corrosion resistance. Considering the utmost importance of the fatigue performance of NAB in such applications, this study investigates the fatigue performance of wire arc additive manufactured (WAAM) NAB in the annealed (675 °C for 6 h then furnace cooling) condition. To this end, static mechanical properties were evaluated using uniaxial tensile testing, while fatigue properties were assessed through fully reversed tests conducted at ambient temperature. Electron backscatter diffraction (EBSD) was utilized for the examination of the texture, and grain size distribution in annealed WAAM NAB. Additionally, scanning electron microscopy was employed to inspect fatigue-fractured specimens, while the analysis of EBSD was conducted to examine the deformation behavior beneath the crack initiation zone. The results provide insights into the fatigue life, crack initiation, and propagation characteristics of WAAM NAB relative to the cast counter material. The findings of this research provide valuable insights into the mechanical properties, microstructural characteristics, and fatigue response of WAAM NAB, informing the design of fatigue-resistant components and supporting the reliable utilization of WAAM NAB in demanding applications such as the marine and naval industries.

Fatigue performance analysis of fine aggregate matrix using a newly designed experimental strategy and viscoelastic continuum damage theory

Fine aggregate matrix (FAM), as the matrix phase in asphalt concrete (AC), significantly affects the fatigue behavior of AC. To accurately assess the mechanical properties of FAM, a newly designed experimental strategy for FAM testing was developed, and the viscoelastic continuum damage theory (VECD) theory was applied to analyze FAM’s fatigue cracking characteristics. In this study, a dumbbell-shaped geometry for dynamic shear rheometer testing was designed and verified through the FE-aided method. Subsequently, three AC mixtures’ FAM specimens with this special geometry were fabricated for the frequency sweep and linear amplitude sweep tests. Results showed that the specially designed specimens effectively capture the viscoelastic and fatigue properties of FAM with high replicability. Analyses based on the VECD theory indicated that FAM of porous asphalt (FAM(PA13)), featuring a higher asphalt content, exhibits a significant reduction in pseudo stiffness with increasing damage at the initial stage, but the reduction rate diminishes as damage progresses when compared to the other two FAMs. It was speculated that the higher aggregate content in FAM of dense-graded AC mixture (FAM(AC20) induces stress concentrations in the asphalt mastic near the protrusion areas of aggregates, thereby rendering the sample more susceptible to damage. The proposed methods will be readily extended to characterize other mechanical properties of FAM.

High-temperature thermal fatigue of Ni3Al-based single crystal alloy affected by wall thickness and peak temperature

Complex thin-walled structures are commonly employed in turbine components to improve cooling efficiency. However, thin-walled blades are prone to thermal fatigue failure due to the high thermal stress induced by frequent and abrupt temperature fluctuations during duty cycles. The thermal fatigue behavior of Ni3Al-based single crystal alloy with thin-walled structure during 25 °C ↔ 1000 °C/1100 °C was investigated by combining thermal fatigue tests and finite element simulation. The thermal fatigue demonstrated a significant thickness debit effect, with thermal fatigue property dropping as peak temperature and wall thickness increased. Wall thickness had a more pronounced effect than peak temperature. Visible slip traces were found on the wall thickness surface, and their density was positively correlated with wall thickness. Further investigation revealed that thermal fatigue is primarily driven by the octahedral slip system ({111}<110>), with significant contributions from (111)[101‾] and (1‾1‾1)[101]. Simulations of thermal stress distribution and J-integral at the crack tip during crack initiation and propagation stages indicated that wall thickness influences thermal fatigue properties by affecting thermal stress concentration at the notch and crack tip. Higher peak temperatures increased thermal stress and reduced yield strength, thus diminishing thermal fatigue performance. A thermal fatigue crack propagation prediction model was constructed incorporating Paris' law and the J-integral. The model revealed an unfavorable correlation between material Cj/ nj and both peak temperature/wall thickness, indicating that both factors adversely affect thermal fatigue resistance.

Fatigue Life Data Fusion Method of Different Stress Ratios Based on Strain Energy Density.

To accurately evaluate the probabilistic characteristics of the fatigue properties of materials with small sample data under different stress ratios, a data fusion method for torsional fatigue life under different stress ratios is proposed based on the energy method. A finite element numerical modeling method is used to calculate the fatigue strain energy density during fatigue damage. Torsional fatigue tests under different stresses and stress ratios are carried out to obtain a database for research. Based on the test data, the Wt-Nf curves under a single stress ratio and different stress ratios are calculated. The reliability of the models is illustrated by the scatter band diagram. More than 85% of points are within ±2 scatter bands, indicating that the fatigue life under different stress ratios can be represented by the same Wt-Nf curve. Furthermore, P-Wt-Nf prediction models are established to consider the probability characteristics. According to the homogeneity of the Wt-Nf model under different stress ratios, we can fuse the fatigue life data under different stress ratios and different strain energy densities. This data fusion method can expand the small sample test data and reduce the dispersion of the test data between different stress ratios. Compared with the pre-fusion data, the standard deviations of the post-fusion data are reduced by a maximum of 21.5% for the smooth specimens and 38.5% for the notched specimens. And more accurate P-Wt-Nf curves can be obtained to respond to the probabilistic properties of the data.

Fatigue properties of titanium-clad bimetallic steel butt-welded joints

Titanium-clad (TC) bimetallic steel is a high-performance constructional material that yields promising application potential in future ocean and coastal civil engineering. However, the understanding on the mechanical behaviors of the corresponding weld joints is still limited. In this paper, a tensile-tensile fatigue experimental study was conducted on two types of butt-weld joints fabricated of hot-rolled TA2 +Q355B TC bimetallic steel. Based on the test results, the fatigue stress-life curves (S-N curve) of the two types of weld joints were obtained and subsequently compared with that of TC parent materials, other representative structural metals, that of butt-weld on other metals and the codified S-N curves provided by six structural/fatigue design standards. Most specimens of the two types of TC weld joints are initially cracked at the clad-to-cap weld. The bonding strength between clad and substrate layers exhibit a promising reliability under fatigue loadings. The fatigue resistance of the two types of TC weld joints is considerably less than the different TC parent materials studied. The fatigue lives of clad material (TA2) and substrate material (Q345/Q355B) are greater than that of TC weld joints. The S-N curves of two TC weld joints are considerably lower than that of high-strength steel series but higher than that of aluminum alloy 6061-T6. The design S-N curves of EC3 (Class 36) and IIW (Class 36) are too conservative for the two TC weld joints.

Effect of trace element arsenic on the high cycle fatigue properties and the carbide uniformity in high carbon chromium bearing steel

AbstractIn this paper, the mechanical properties and microstructures of bearing steels with arsenic contents of 30, 40, and 120 ppm have been investigated. The results show that As‐40 steel has the highest tensile strength but lower fatigue strength than As‐120 steel. The fatigue crack propagation rate of As‐120 steel is relatively low, mainly due to the increase in ΔKth. After quenching and tempering, As‐120 steel has larger prior austenite grains and more undecomposed, elongated carbides appear, reducing the uniformity of the steel. For carbides with an aspect ratio greater than 2, they cannot grow by the Oswald mechanism of spontaneous migration but are spheroidized by self‐cracking. The undissolved elongated carbides have a lower chemical potential, which increases the diffusion tendency of arsenic in the matrix. SIMS and EPMA analyses show that there is no significant distortion of the trace element arsenic.

Investigating the influence of infill patterns and mesh modifiers on fatigue properties of 3D printed polymers

This research examines the structural performance of Tough Polylactic Acid (PLA) components made through material extrusion, focusing on tensile and fatigue behaviors. Tough PLA, similar to regular PLA, exhibits improved toughness comparable to acrylonitrile butadiene styrene (ABS). As the application of 3D printed parts for functional use expands, understanding the mechanical attributes of materials under both static and dynamic loading conditions is crucial. This study investigates the impact of infill pattern/density and localized reinforcement on the tensile and fatigue strength of Tough PLA samples. Digital image correlation (DIC) and optical micrographs were used to acquire surface-strain data. The findings highlight the influence of localized reinforcement and infill density. Increased infill density is associated with higher tensile strength and Young’s modulus, with specimens at 90 % infill achieving a tensile strength of 28 MPa and Young’s modulus of 0.46 GPa. Incorporating mesh modifiers can enhance tensile properties by up to 20 %. An Analysis of Variance (ANOVA) confirmed the significant effects of these factors on tensile strength. Fatigue test results show a grid pattern without modifiers exhibits the best fatigue life, with specimens enduring up to forty-two thousand cycles at 45 % UTS, while a line modifier balances fatigue strength and tensile properties.

Comparative investigation of fatigue properties between additively and conventionally manufactured Invar 36 alloy

The mechanical properties of ASTM F1684 (Invar 36) alloy manufactured via laser beam powder-bed-fusion (PBF-LB) technique are strongly influenced by the non-equilibrium solidification microstructure. Due to the complexity of printed microstructure, e.g., the presence of melted pools, nano-precipitates, and high-density dislocations, it is very challenging to disentangle the specific mechanisms responsible for the fatigue properties. Here, a comparative investigation of the fatigue properties between PBF-LB and conventionally manufactured (CM) samples was conducted. Dedicated characterizations, including electron channeling contrast imaging (ECCI), and high-angular resolution EBSD (HR-EBSD), were performed. The mid-cycle (104–105 cycles) fatigue behaviors of both samples are comparable, while the fatigue resistance of PBF-LB sample becomes inferior at high-cycle range (≥106 cycles). This disparity can be ascribed to the competing effect between crack nucleation and propagation. PBF-LB samples are more susceptible to fatigue crack initiation due to the printed macro-defects. Whereas, the homogeneous plastic deformation and the grain fragmentation, both triggered by the ultrafine cellular structure, efficiently mitigate crack propagation rates. Based on these findings, the current understanding of the underlying mechanisms governing the fatigue performance of PBF-LB Invar 36 alloy is deepened, emphasizing the significant advantages of non-equilibrium solidification microstructure in retarding fatigue crack propagation.