High Cycle Fatigue Tests Research Articles

Experimental and numerical investigation on mechanical and fatigue performance of corroded Q690D high-strength steel

As a prevalent environmental factor in the service process of steel structures, corrosion have a significant impact on the mechanical and fatigue properties of steel, thus deteriorating service safety. In this article, focused on corroded Q690D high-strength steel, experimental and numerical investigations have been performed. Electrolytic accelerated corrosion experiments were conducted, and 3D surface morphology measurements were employed to analyse the surface properties of specimens with various corrosion degrees. Mechanical and high-cycle fatigue tests were carried out on the corroded specimens, then degradation models between the mechanical behaviours and corrosion characteristics were established. Furthermore, the fatigue damage evolution model of Q690D high-strength steel was calibrated based on continuum damage mechanisms (CDM), and numerical simulations of the corroded specimen corresponding to the monotonic tensile tests and high cycle fatigue tests were conducted. The results show that with the increase of corrosion degree, the elastic modulus, yield stress, and tensile stress would decrease, and the fatigue performance would deteriorate. Corrosion has a greater effect on the fatigue life of long-life range and the slopes of the S-N curves after corrosion are more uniform. With the CDM parameters of non-corroded Q690D and the numerical model with consideration of surface roughness, the fatigue life of corroded Q690D could be well simulated.

Effect of Isothermal Annealing on Residual Stresses and Fatigue Properties of LPBF 316L Steel

This study aims to investigate the influence of isothermal annealing on the residual stresses and fatigue properties of a 316L austenitic stainless steel, manufactured by the laser powder-bed fusion (LPBF), possessing a high density of 99.98%. Residual stresses were evaluated using the X-ray diffraction techniques. High-cycle fatigue tests were performed on cylindrical samples manufactured in both horizontal and vertical orientations, subjected to force-controlled axial fully reversed loading. Following fabrication, the samples underwent isothermal annealing in a furnace either at 600 °C for 120 minutes or at 900 °C for 30 minutes. Subsequently, the samples were machined to their final dimensions and electropolished to a mirror surface finish. Preliminary findings revealed that increasing the annealing temperature effectively reduced the surface residual stresses. However, this reduction did not lead to an improvement in the fatigue resistance of this nearly fully dense material in the high-cycle fatigue regime. Interestingly, the structure annealed at 600 °C exhibited a higher fatigue strength compared to the structure annealed at 900 °C, with no discernible difference between the printing directions. Fracture surfaces and microstructural features examined using light and electron microscopy revealed that cracking was primarily initiated at surface defects or slip bands. These results highlight the complex interplay between residual stresses, microstructure, strength, and fatigue behaviour of LPBF 316L austenitic stainless steel. Further analysis and investigations are required to fully understand the underlying mechanisms and develop strategies for enhancing the fatigue performance of additive manufactured components.

A Study on the Microstructure, Tensile and Fatigue Properties of Martensitic Stainless Steel Plate

The microstructure, tensile and fatigue properties of a martensitic stainless steel (MSS) plate with a thickness of 0.152 mm are investigated in this study. The microstructural properties were initially studied using electron backscatter diffraction microscopy. High dislocation densities were observed in the microstructure, along with the rolling texture revealed by the pole figure, following an initial cold rolling process of the as-received MSS plate. Tensile tests were conducted in both the rolling and transverse directions to compare the strength of the material in both directions. The results showed that the tensile strength was relatively low in the rolling direction. This can be attributed to the microstructure and crystallographic orientation of the material along that direction. Additional tensile tests were performed at various temperatures within the operating temperature range in the rolling direction. The results indicate that the highest tensile strength and elastic modulus are observed at room temperature. A high-cycle fatigue test was performed to determine the fatigue limit of the MSS plate. Furthermore, the microstructure was analyzed by controlling the fatigue cycles within the same stress range. The results revealed a proportional relationship between the accumulated deformation within the grains and the fatigue cycles. This can be helpful in understanding the fatigue damage mechanisms of the MSS plate.

High Cycle Fatigue Testing of Silicon IGBT Devices Under Application-Close Conditions

High Cycle Fatigue Testing of Silicon IGBT Devices Under Application-Close Conditions

Fatigue resistance of rib-to-bimetallic steel deck welded joints in orthotropic steel bridge decks

The stainless-cladding techniques have been applied in the top plate of the orthotropic steel decks in the high-speed railway steel bridges to improve the corrosion and wear resistance. The rib-to-deck (RD) welded joint with the stainless-clad bimetallic steel deck plate becomes a new critical fatigue detail. This study firstly examines the fatigue performance of this full-scale new RD joint through six high-cycle constant-amplitude fatigue tests and two beach-mark tests under eccentric over-rib loading. The structural hot-spot stress at the weld toe on the deck plate is obtained by strain gauges and the linear extrapolation method for each RD specimen before the cyclic loading. Experimental results indicate that five RD specimens suffer from the toe-deck failure modes, while the rests encounter root-deck cracking. The fatigue strength of these new RD joints satisfies the FAT100 hot-spot stress S-N curve based on the IIW design recommendation. Numerical simulation is further conducted to investigate the effect of different cracking modes and welding technologies on the fatigue crack propagation behavior of this new RD joint. Root-deck cracking mode shows weakly higher fatigue resistance than the toe-deck failure case. Using the double-side welds between the U-rib and deck plate, and the thickened-edge U-rib technology can slightly enhance the fatigue life in terms of toe-deck cracking mode in contrast with the traditional single-side groove welds. Experimental and numerical validation quantify the excellent fatigue performance of this new RD joint in comparison with the other types of RD welded joints.

Interior cracking behavior of laser powder bed fused TiC/Ti6Al4V composites under vacuum environment

High and very high cycle fatigue tests were carried out to elucidate the interior crack nucleation behavior in a vacuum environment of a TiC-reinforced Ti6Al4V composite fabricated by laser powder bed fusion. To investigate the failure mechanisms, advanced microscopy techniques such as scanning electron microscopy and electron backscatter diffraction are employed. The first failure mode is the cracking of the inhomogeneous hardening zone (IHZ). The cleavage planes observed inside IHZ suggest that the essence of cracking is lamellar α′-grain fracture. The second failure mode is the lack of fusion (LOF) assisted IHZ cracking. The presence of LOF increases stress concentration and reduces the effective bearing capacity of the material, leading to a significant decrease in fatigue life. The knowledge gained can be utilized to optimize the fabrication process and design of composites, ultimately improving their fatigue resistance and extending their service life in applications.

Utilizing Data-Driven Methods to Predict the Fatigue Life of Cement Concrete Considering Corrosive Environmental Factors

The primary objective of this study is to assess the fatigue resistance of cement concrete when exposed to corrosive environments. To achieve this, experimental results from high-cycle fatigue (HCF) and low-cycle fatigue (LCF) tests conducted on cement concrete samples subjected to various corrosive conditions were used. Various data-driven techniques, including multiple linear regression (MLR), Taguchi sensitivity analysis (TSA), and response surface method (RSM) were utilized. The aim was not only to identify the most influential parameter affecting fatigue life but also to offer a simpler and cost-effective alternative to experimental approaches. Consequently, two key parameters related to the corrosive environment: pH value and immersion time, along with the cyclic force applied to the concrete samples as input variables across different approaches were considered. The number of cycles until sample failure regarded as the output variable in all analyses. Furthermore, the analyses were conducted with the assumption that longer fatigue life is preferable. The findings revealed that the fatigue life of Portland cement concrete consistently decreased with increasing immersion time. Notably, the pH value emerged as the most significant parameter, while the other two factors exhibited equivalent impacts.

Experimental and numerical study on fatigue damage evolution of Q690D welding details

Steel structures are widely used in various types of structures, and welding details, which are fatigue-prone constructions, are typically utilized in steel constructions. In this study, regarding the high cycle fatigue performance and fatigue damage evolution behaviors of high strength steel welding details, experimental and numerical studies have been carried out on two typical types of Q690D high strength steel welding details, including butt-weld connections and cruciform load-carrying fillet weld (CLFW) connections. High cycle fatigue tests have been conducted, SN curves based on effective notch stress have been established and compared with the suggested curves in IIW specification, showing that FAT200 is more suitable for fatigue evaluation of high strength steel welding details. Fatigue damage evolution model and numerical simulation methods for Q690D welding details based on effective notch stress and continuum damage mechanic have been established and validated. Damage evolution analysis of welding details has been conducted based on the proposed numerical simulation method. The simulation method enables accurate characterization of fatigue damage locations.

High-cycle fatigue testing on AM60 magnesium alloy samples for as-received and pre-corroded conditions in simulated body fluid

In this present work, the pure fatigue (PF) behaviors of AM60 magnesium alloys were investigated for the as-received samples, compared to the pre-corroded specimens in simulated body fluid (SBF). The standard fatigue testing specimens were held for 28 days in the SBF, so-called corrosion fatigue (CF) samples, while their weights were recorded. Afterward, bending fatigue experiments were carried out under fully-reversed rotary conditions, within high-cycle fatigue regimes. Moreover, the fracture mechanism was also investigated using field-emission scanning electron microscopy (FE-SEM). The obtained results indicated that the weight of the samples first increased and then decreased with time. The CF lifetime was 71 % of the relative difference, shorter than PF under the lowest stress level (80 MPa) and 38 % of the relative difference, shorter than PF at the highest stress level (140 MPa). The CF lifetime was entirely behind the PF lifetime, and fracture mechanisms were mostly brittle.

Influence of Overheating on High-Cycle Fatigue Characteristics of the Base Metal and Weld Metal of Low-Carbon Steel Welded Joints

The results of a high-cycle fatigue testing of our samples were obtained, and a comparative assessment of the properties of the base metal and weld metal of 09G2S-type steel (13Mn6 according to the DIN17145-80 standard) before and after overheating (1200 °C, 3.7 h) was performed. The welded joints between the sheets of 09G2S steel were obtained through automatic argon arc welding. The fatigue tests were carried out under repeated tensile loading. The “maximum cycle stress—number of cycles to failure” fatigue curves of the samples were plotted. The fracture surfaces of the samples were studied, and the fatigue failure mechanisms were analyzed. It was shown that, during testing, all samples demonstrated cyclic hardening behavior. The samples of the base metal as delivered had the highest endurance limit, and the smallest endurance limit was found in the samples of the base metal and weld metal after overheating, the endurance limits of which were similar. The fracture mechanism of all samples was quasi-brittle with the presence of very thin fatigue micro-grooves. The final rupture of all samples had a ductile dimple type.

A nonlinear cumulative fatigue damage life prediction model under combined cycle fatigue loading considering load interaction

In the present work, combined high and low cycle fatigue (CCF) tests were performed on GH4169 nickel-based alloy under stress-controlled conditions. The interaction between high cycle fatigue (HCF) and low cycle fatigue (LCF) results in a complex process of fatigue damage evolution under CCF loading. Based on the fatigue damage curve and the theory of equivalent damage, considering the interaction between HCF and LCF loading, a nonlinear cumulative damage model is proposed under CCF loading. The proposed model is deduced from the fatigue damage curve under CCF loading, which establishes a connection between the LCF and HCF damage curve. Three materials, including the other two materials, namely TC11 and Al 2024-T3, published in the relevant literature, are used to verify the proposed model. The experimental results demonstrate that the proposed model has better prediction results than those for Miner’s rule and the Trufyakov-Kovalchuk (T-K) model. The validation of the proposed model shows its superior performance.

Effect of ECAP on fracture toughness and fatigue endurance of DED-processed Ti-6Al-4V investigated on miniaturized specimens

Additive manufacturing (AM) has revolutionised the production of complex components with custom mechanical properties. However, as-deposited AM-ed materials often exhibit inferior mechanical behaviour compared to conventionally manufactured counterparts because of defects generated during the deposition. In this study, the effects of equal channel angular pressing (ECAP) on fracture toughness and fatigue endurance of Ti-6Al-4V titanium alloy manufactured by direct energy deposition (DED) are investigated. The aim of this study is to compare the mechanical performance of the material in the as-deposited and ECAP-ed states, exploiting the potential benefits of ECAP in improving the properties of additively manufactured components. ECAP processing is used to induce severe plastic deformation (SPD) and create a unique microstructure in Ti-6Al-4V specimens. As-deposited and ECAP-ed specimens were evaluated using stress intensity factor (SIF) analysis, fatigue crack growth, and high cycle fatigue tests using miniaturized specimens. Fractographic analysis was performed using scanning electron microscopy (SEM) to examine the fracture surfaces and identify the underlying failure mechanisms. The results revealed that while ECAP led to a slight increase in porosity, it significantly reduced fracture toughness and had a negligible effect on the rate of propagation of fatigue cracks. In addition, the ECAP-ed specimens showed reduced fatigue endurance of the material.

Data-driven approach to very high cycle fatigue life prediction

The research on life prediction for mechanical structures in very high cycle fatigue regime is pivotal to improve structure service, but it can be costly and time-consuming to collect fatigue data. In response, the data-driven approach of machine learning emerged as a solution to data insufficiency. In this work, after extracting a small dataset of GCr15 bearing steel subjected to very high cycle fatigue tests from open literature, the Z-parameter model was applied to obtain extended datasets to establish models driven by support vector machine, artificial neural network, and Z-parameter based physics-informed neural network, respectively. With training on extended datasets and the original data as test set, fatigue life prediction for GCr15 steel was carried out and evaluated between these models. Results showed that the physics-informed neural network calibrated by Z-parameter model trained on a larger dataset featured more accurate and reliable prediction than other models did, which demonstrated effectiveness of Z-parameter in data extension and model construction as priori physics knowledge for a data-driven approach. Looking into the future, Z-parameter model deserves more attention to its employment in life prediction for more engineering materials and structures serving in the very high cycle fatigue regime.

Fatigue fracture behavior of a Ti17 joint under various heat treatment specifications prepared by linear friction welding

A comprehensive study to investigate and characterize the fatigue fracture behavior of linear friction welded Ti17 joint and Ti17 joint under various post welding heat treatment (PWHT) specifications is critical to providing a foundation for the life design of a ‘blisk’ manufactured by linear friction welding. This study addressed this issue. High cycle fatigue tests were carried out. EBSD was employed to examine the microstructures in welding center zone (WCZ), thermal mechanical affected zone (TMAZ), heat affected zone (HAZ) and base metal (BM) across the Ti17 friction welded interface. The results show that the as welded Ti17 joint tends to fracture at WCZ &TMAZ during the fatigue service with a life of 45201, where a heterogeneous structure is formed as ‘refined equiaxed β grain - coarse β grain - basket-weave β grain with lamellar α partially dissolved - basket-weave β grain’ corresponding to ‘WCZ - TMAZ - HAZ - BM’. After aging at 550 °C, the Ti17 joint tends to fracture along the boundary between TMAZ and HAZ + BM with a life of 42338, where a heterogeneous structure is formed as ‘α′ colony with coarse ‘α laths’ - basket-weave β grain’ corresponding to ‘WCZ &TMAZ - HAZ & BM’. After aging at 630 °C, Ti17 joint tends to fracture at BM with a life of 75121, where a heterogeneous structure as ‘refined α′ laths with basket-weave characteristics - coarse basket-weave of α′ laths in β grains' corresponding to ‘WCZ &TMAZ -HAZ & BM’ region is formed.

On the microstructure and high cycle fatigue of near-net shape PM-HIPed Inconel 625

This paper investigated the microstructure and fatigue behavior of PM-HIPed Inconel 625. The microstructure was composed of γ phase and (Mo, Nb) carbonitrides located mostly on prior particle boundaries. Despite the presence of these carbonitrides, the samples showed good tensile properties with high elongation. Two different surface conditions, pickled and machined, were used for high cycle fatigue testing under a four-point bending test. The results indicated that pickled samples had 6% lower fatigue strength (at 106 cycles) with three times higher standard deviation compared to the machined ones. Fatigue failure mechanisms were found to be dependent on surface conditions and showed different failure modes due to non-metallic oxide inclusions and surface defects in samples with machined and pickled surfaces, respectively. The effect of type, size, and location of defects, multiplicity of crack initiations, as well as surface roughness were analyzed and discussed.

High-cycle fatigue life assessment of welded cruciform joints of Q460D steel

In this paper, a reliable high-cycle fatigue life assessment method based on unified crack growth approach is presented for welded cruciform joints. Considering the ellipsoidal fracture model of structural steel as the instability propagation (fracture) criterion of fatigue crack, this study investigates the failure mode of the welded cruciform joint of Q460D steel subjected to a high-cycle fatigue test. Following the ellipsoidal fracture model, a set of theoretical calculation and numerical simulation were established to investigate the fatigue cracking of the welded cruciform joints. The theoretical model was further proposed for estimating the fatigue life of the welded cruciform joints of Q460D steel using the unified crack growth approach. Based on the theoretical and simulated results, the unified crack growth approach and the allowable stress fatigue life formula recommended in China's current code “Standard for design of steel structures, GB50017-2017” were then evaluated and compared. The calculation errors of the unified crack growth approach and the fatigue life formula recommended in China's current code are −48.2% ∼ +8.3% and −60.2% ∼ −34.8%, respectively.

A Fatigue Method in the Tension-Compression Axial Stress Control Test of Automotive Sheet Steel

Abstract Focused on the common problem of easy buckling of specimens in the tension-compression axial stress control fatigue test of automobile sheet steel, a stress fatigue test method for thickness less than 2.5 mm was proposed. For two kinds of automobile sheet materials with different strength levels and thicknesses, fatigue specimens with different widths of test section, parallel lengths, and fillet radii are designed. Without the anti-buckling device, high-cycle fatigue tests with a stress ratio Rs = −1 at different stress levels were carried out, and the shape and size of the fatigue specimens of automobile sheet materials were determined by the number of fatigue life cycles of specimens with different sizes under the same stress cycle form. The results show that for automobile sheet steel with a thickness of 1.0–2.5 mm, the recommended sizes of the uniform-gauge fatigue specimens are width of test section w = (1–3) t, parallel length Lp = (1–3) w, and fillet radius r = (3–10) t. For automobile sheet steel with a thickness less than 1 mm, because the time-displacement curve jitters during the test, it is recommended to install an anti-buckling device, specifically the anti-buckling device with mortise and tenon structure by self-design and with a flattop structure recommended by ISO 1099-2017, Metallic Materials—Fatigue Testing—Axial Force-Controlled Method.

High cycle fatigue behaviour of advanced high strength steel sheet (HS1000) in automotive application

The demand for high strength steel ranges from 750 to 1200 MPa in automobile industries to reduce cost, and fuel consumption and increase safety. Stress- controlled high cycle fatigue (HCF) tests for HS1000 steel sheets in transverse direction were conducted to determine the fatigue limit. Cycle softening process occurs in HS1000 steel sheet. Based on controlled material data, HS1000 steel sheet is compared with more common steel grades. The fatigue limit of HS1000 steel sheets is much higher than that of lower strength structural steel and has comparable ductility and high fatigue strength.

Exploring the effect of complex hierarchic microstructure of quenched and partitioned martensitic stainless steels on their high cycle fatigue behaviour

Recent studies have demonstrated the viability of quenching and partitioning (Q&P) treatment for processing martensitic stainless steels showing an improved balance of high strength and sufficient ductility. However, to date, the fatigue behaviour of these materials has not been explored. This study examines the effect of their complex hierarchic microstructure on high cycle fatigue performance. Three steels with different alloying element contents underwent Q&P processing, resulting in multiphase microstructures rich in retained austenite. High cycle fatigue tests and analysis of fatigue fracture surfaces were performed using SEM and EBSD techniques. The results indicate satisfactory high cycle fatigue performance in Q&P treated martensitic stainless steels, surpassing traditional counterparts. Fatigue cracks predominantly form and propagate along martensite packet and block boundaries, while prior austenite grain boundaries and MnS inclusions have minimal influence on fatigue crack formation and growth. Microplastic deformation at the fatigue crack tip enhances local KAM values and triggers localized transformation of retained austenite grains. It is hypothesized that the developed Q&P treated martensitic stainless steels exhibit improved resistance to low cycle fatigue.

Correlation between microstructure and fatigue properties of hot-rolled thick-plate complex-phase steel

Complex-phase (CP) steels, with a multiphase microstructure, offer an excellent combination of high strength, ductility, and formability, making them an attractive alternative to conventional high-strength low-alloy (HSLA) steels in the automotive industry. However, the microstructure and fatigue property relation in CP steels is complex. This limits the full exploitation of CP steels in applications, such as heavy-vehicles, where excellent fatigue performance of thick-plates after punching holes is the critical parameter. In this work, we initiate the study of the relation between microstructure and fatigue properties of a commercial CP steel (800CP) and compare it with a conventional HSLA (500MC) steel. Fatigue property, tensile property, and fatigue crack growth rate (FCGR) testing are conducted and the performance of the two steels is rationalized using detailed microstructure characterization, before and after fatigue testing. FCGR testing shows that, despite a higher yield strength of the 800CP, both steels have a similar propagation rate due to a more tortuous crack propagation path and a higher quantity of secondary crack formation in the 800CP microstructure. The high cycle fatigue (HCF) testing shows that the fatigue limit in the 800CP is 25% higher. This increase in fatigue limit is attributed to the improved resistance to fatigue crack initiation in the 800CP due to its larger fraction of bainite.