High Cycle Fatigue Behavior Research Articles

Influence of uniaxial and equi-biaxial tensile pre-straining on the high cycle and notch fatigue behaviour of AA2024-T4 aluminium alloy

The present study investigates the impact of different tensile pre-straining (equi-biaxial and uniaxial) on the tensile, high cycle and notch fatigue behaviour of AA2024-T4. EBSD examination of the pre-strained specimen shows more substantial lattice distortion than the material with 0% pre-strain. Pre-strained specimens exhibit increased ultimate tensile strength, yield stress, and reduced ductility, irrespective of pre-straining paths. Moreover, a significant enhancement in fatigue performance is observed, with a 13% and 21% improvement in fatigue strength for uniaxial and equi-biaxial pre-strain, respectively, at an optimal fatigue lifetime of approximately 1 × 106 cycles. The theory of critical distance is utilized to predict fatigue life with double-edge semi-circular notches for each pre-strained condition, and predicted life falls within a scatter band ± 2.

Effect of pre-corrosion on crack initiation behavior of friction stir welded aluminum alloy 2024-T3 in high and low cycle fatigue regimes

The effect of microstructural inhomogeneity and pre-corrosion in 3.5% NaCl solution is investigated on the fatigue crack nucleation behavior of welded AA2024-T3. The localized corrosion affects the heat-affected zone more than the weld nugget zone. The formation of corrosion pits often occurs in the region between the adjacent Al-matrix and intermetallic particles due to the reverse polarity behavior of S-phase precipitates (Al2CuMg) in the saltwater environment. Further, the long-term stability of the welded joint is examined by immersing the specimens in 3.5% NaCl solution for different time intervals ranging from 10 hrs to 200 hrs. After 100 hrs of immersion in the salt water, high and low cycle fatigue behavior of the corroded samples has been examined. Long-term exposure to the saltwater environment results in intergranular corrosion due to localized pitting. The micro-mechanism of the pitting process under salt water and its effect on fatigue lives is studied.

An Experimental Investigation on the High Cycle Fatigue Behavior of Resistance Spot Welded Ultrahigh Strength Steel

An Experimental Investigation on the High Cycle Fatigue Behavior of Resistance Spot Welded Ultrahigh Strength Steel

Effect of natural and artificial defects on multiaxial fatigue of 4140 steel

Despite the prevalence of small defects and multiaxial stress conditions in load-bearing engineering components, their combined effect on fatigue strength is not usually considered in the literature. In this study, the high-cycle fatigue behavior of 4140 steel with its inherent non-metallic inclusions, and with an artificial surface microhole, is investigated under axial/torsional loading. The multiaxial fatigue tests were performed under in-phase and out-ot-phase loading, employing different ratios between the shear and axial stress amplitudes. Microscopy of failed specimens indicated a tensile-dominated crack formation mechanism in most of the tests. Analysis of the test data using a area-based critical plane criterion showed that predictions of fatigue strength and crack direction can be made with accuracy sufficient for engineering calculations.

Effects of foreign object damage on high-cycle fatigue behavior of Inconel Alloy 690TT steam generator tubes

The process of foreign object impact on Alloy 690TT steam generator (SG) tubes under high-speed water flow was simulated using quasi-static indentation method. Morphologies of foreign object damage (FOD) were detailed characterized, and the fatigue curves and fatigue strengths were acquired for smoothed and three types of FOD-affected specimens. Results indicated that the fatigue strength of the impacted specimens reduced with the increase of defect depth, and there was an exponential relationship between fatigue strength and defect depth. Fatigue cracks all initiated at the root of the defect groove, and as the depth of defect increased, the number of fatigue crack sources gradually increased. Finally, the fatigue strength was predicted by the fatigue notch factor and damage tolerance method, and the fatigue performance evaluation diagram of the SG tube damaged by foreign object based on El Haddad model was established.

Effect of Corrosive Environment on the High-Cycle Fatigue Behavior of Reinforced Concrete by Epoxy Resin: Experimental Study.

Large engineering structures made of various materials, including concrete (e.g., bridges, dams, buildings, and multilevel car parks), steel (e.g., power towers, ships, and wind turbines), or others, are often subjected to severe vibration, dynamic, and cyclic loads, which lead to crack initiation, crack growth, and finally structural failure. One of the effective techniques to increase the fatigue life of such structures is the use of reinforced materials. In the meantime, environmental factors, such as corrosion caused by corrosive environments, also affect the fatigue behavior of materials. Therefore, the main purpose of this paper is to study the influence of corrosive environment on the high-cycle fatigue (HCF) behavior of concrete reinforced by epoxy resin. For this purpose, five corrosive environments with different intensities, including fresh air, water: W, sea water: SW, acidic: AC, and alkaline: AL, were considered and the laboratory samples of conventional concrete (CC) and polymer concrete (PC) were immersed in them for one month. Next, axial fatigue tests were performed under compressive-compressive loading with a frequency of 3 Hz on cylindrical specimens. Moreover, to achieve reliable results, for each stress amplitude, the fatigue test was repeated three times, and the average number of cycles to failure was reported as the fatigue lifetime. Finally, the stress-life cycle (S-N) curves of different states were compared. The results showed that polymer concrete can resist well in corrosive environments and under cyclic loads compared to the conventional concrete, and in other words, the epoxy resin has performed its task well as a reinforcer. The results of fatigue tests show that the load bearing range of 10 tons by CC has reached about 18 tons for PC, which indicates an 80% increase in fatigue strength. Meanwhile, the static strength of samples in the vicinity of fresh air has only improved by 12%.

A systematic review on high cycle and very high cycle fatigue behavior of laser powder bed fused (L-PBF) Al-Si alloys

The recent attention towards additive manufacturing (AM) of metallic alloys, particularly Al-Si alloys, has been significant due to its important role in the design and development of complex structural components in aerospace, defense, and automotive industries. The use of AM technology, specifically Laser powder bed fusion (L-PBF), enables the creation of lightweight structures with flexible geometries that were previously not achievable through conventional manufacturing methods. Al-Si components fabricated through L-PBF are often subjected to long periods of loading in high cycle fatigue (HCF) and very high cycle fatigue (VHCF) conditions. Therefore, it would be extremely important to investigate fatigue characteristics of these components under both HCF and VHCF regimes. However, it is important to recognize that the fatigue performance of L-PBF Al-Si alloys in HCF and VHCF regimes is not fully understood due to the complex nature of fatigue responses in these regimes. Various factors such as microstructures, defects, porosity, and processing parameters, can potentially influence the fatigue behavior in these regimes, further complicating the analysis. Therefore, optimizing process parameters and post-treatments is essential to achieve the optimal fatigue performance for load-bearing components in both HCF and VHCF conditions. In the past few years, several studies have been conducted to investigate the effect of critical parameters on the fatigue performance of L-PBF Al-Si parts in HCF and VHCF regimes. This article aims to provide a comprehensive and in-depth analysis of recent research findings regarding important factors such as residual stress, surface roughness, build parameters (e.g. build orientation), microstructural characteristics, post-processing methods, manufacturing flaws, specimen shapes, load ratios. These factors can have a significant impact on fatigue properties of L-PBF Al-Si alloys, particularly in the HCF and VHCF ranges. In order to realize the full potential of the L-PBF Al-Si alloys in the development of advanced structural components, this study primarily focuses on identifying key areas that require attention.

Notch effect in very high-cycle fatigue behaviour of a structural steel

The presence of a notch or a detail which leads to stress concentration due to complex geometries has a considerable impact on the fatigue life of engineering structures. Therefore, on the one hand, the notch effect must be investigated and considered in the fatigue assessment of these structures. On the other hand, in the last decades, an interest in studying the very high-cycle fatigue regime (VHCF) has been perceived, due to the extension of the service life of engineering components beyond the 10 million cycles. Thus, the notch effect in the VHCF regime was analysed for the S690 structural steel. Therefore, an analytical approach to design notch specimens was developed and a numerical simulation was performed to assess it. Then, an experimental campaign with smooth and notched specimens with two different stress concentration factors was performed in an ultrasonic fatigue machine to assess the VHCF behaviour. The mechanisms of failure and fracture surfaces were also investigated. It was observed a fully notch sensitivity as well as the dominance of surface crack initiation for the S690 steel in the VHCF regime.

Roles of microstructures in high-cycle fatigue behaviors of 42CrMo high-strength steel under near-yield mean stress

In this study, high-cycle S-N characteristics and fatigue cracking behaviors under near-yield mean stress of 42CrMo steel with two different fine/coarse-grain tempered sorbite/bainite microstructures (FGM/CGM) were investigated. The results show that fatigue strength is greater for FGM than for CGM as expected, but fatigue crack growth (FCG) threshold is higher for the latter. Compared to FGM with a single crack source, CGM has multiple fatigue sources together with higher-degree ratchetting-fatigue damage, i.e., plastic-strain, dislocation cells and sub-grains, thus accelerating fatigue crack initiation. In the near-threshold regime, roughness-induced crack closure in coarse-microstructures of CGM leads to FCG retardation behavior, which increases FCG threshold. In the Paris regime, CGM presents a similar FCG rate to FGM. Microstructure barriers (i.e., crystal interfaces, carbides and interfaces with different orientations), secondary cracks, crack-path fluctuations, ratchetting and plastic strain jointly result in severer crack-tip stress shielding effects in CGM than in FGM. However, fatigue crack tends to propagate through the high Schmid factor region with {110}<111> slip system with lower slip resistance in FGM but not in CGM, which facilitates fatigue cracking of the former. Under the combined effects of the above factors, similar FCG rates are thus exhibited in both steels with different tensile strengths.

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.

Effect of Pore Defects on Very High Cycle Fatigue Behavior of TC21 Titanium Alloy Additively Manufactured by Electron Beam Melting

Titanium alloys additively manufactured by electron beam melting (EBM) inevitably obtained some pore defects, which significantly reduced the very high cycle fatigue performance. An ultrasonic fatigue test was carried out on an EBM TC21 titanium alloy with hot isostatic pressing (HIP) and non-HIP treatment, and the effect of pore defects on the very high cycle fatigue (VHCF) behavior were investigated for the EBM TC21 titanium alloy. The results showed that the S-N curve of non-HIP specimens clearly had a tendency to decrease in very high cycle regimes, and HIP treatment significantly improved fatigue properties. Fatigue limits increased from 250 MPa for non-HIP specimens to 430 MPa for HIP ones. Very high cycle fatigue crack mainly initiated from the internal pore for EBM specimens, and a fine granular area (FGA) was observed at the crack initiation site in a very high cycle regime for both non-HIP and HIP specimens. ΔKFGA had a constant trend in the range from 2.7 MPam to 3.5 MPam, corresponding to the threshold stress intensity factor range for stable crack propagation. The effect of pore defects on the very high cycle fatigue limit was investigated based on the Murakami model. Furthermore, a fatigue indicator parameter (FIP) model based on pore defects was established to predict fatigue life for non-HIP and HIP specimens, which agreed with the experimental data.

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.

High cycle fatigue behavior of spot welds in DP 780, TRIP 780 and DC04 steel

In this study, a methodology was successfully developed and validated to evaluate the behavior of spot welded joints of DP780, TRIP780 and DC04 steels in high cycle fatigue. Test specimens were made with three spot welds and Wohler curves were developed using the uniaxial tensile/traction load adopting the Owen R90C90 method. The spot welds showed an increase in fatigue life and a reduction in the maximum load, similar to steels. The influence of mechanical strength and material thickness tested and the types of fractures that occurred were compared. In low cycle regions, spot welds showed greater dispersion at maximum loading, between the different materials, and in higher cycle regions, this dispersion was reduced. The results obtained by adopting this method using three spot welds showed greater repeatability and less variation between the specimens of the same material. This developed method can be used with increased reliability to develop automotive bodies and spot welded components.

Fatigue Resistance of an Anodized and Hardanodized 6082 Aluminum Alloy Depending on the Coating Thickness in the High Cycle Regime

In this study, the high cycle fatigue behavior of an anodized 6082 aluminum alloy is investigated. Main focus is on the most relevant influencing factors for crack initiation and propagation under cyclic loading and damage mechanisms considering coating type, thickness, and residual stresses. The bare substrate is compared to anodized and hardanodized specimens with three coating thicknesses, for each coating type, in the range from 20 to 70 μm. Coating hardness and microstructure as well as residual stresses are analyzed. Fatigue and fracture behavior under alternating tension–compression loading is determined. Dependent on the coating thickness, the fatigue strength is reduced by 8%–50% after anodizing and by 50%–62% after hardanodizing. As the coating thickness is equal to the initial crack length from a fracture mechanical point of view, stress intensities at the crack tips are higher for thicker coatings respectively longer initial crack lengths. Therefore, propagation of fatigue‐induced cracks from the coating into the substrate is promoted for a higher coating thickness resulting in premature failure. A significant correlation between the coating thickness and tensile residual stresses induced by both coatings in the subjacent substrate is not found and residual stress influence on the overall fatigue strength is only minor.

In vitro fatigue behavior and in vivo osseointegration of the auxetic porous bone screw

The incidence of screw loosening, migration, and pullout caused by the insufficient screw-bone fixation stability is relatively high in clinical practice. To solve this issue, the auxetic unit-based porous bone screw (AS) has been put forward in our previous work. Its favorable auxetic effect can improve the primary screw-bone fixation stability after implantation. However, porous structure affected the fatigue behavior and in vivo longevity of bone screw. In this study, in vitro fatigue behaviors and in vivo osseointegration performance of the re-entrant unit-based titanium auxetic bone screw were studied. The tensile-tensile fatigue behaviors of AS and nonauxetic bone screw (NS) with the same porosity (51%) were compared via fatigue experiments, fracture analysis, and numerical simulation. The in vivo osseointegration of AS and NS were compared via animal experiment and biomechanical analysis. Additionally, the effects of in vivo dynamic tensile loading on the osseointegration of AS and NS were investigated and analyzed. The fatigue strength of AS was approximately 43% lower while its osseointegration performance was better than NS. Under in vivo dynamic tensile loading, the osseointegration of AS and NS both improved significantly, with the maximum increase of approximately 15%. Preferrable osseointegration of AS might compensate for the shortage of fatigue resistance, ensuring its long-term stability in vivo. Adequate auxetic effect and long-term stability of the AS was supposed to provide enough screw-bone fixation stability to overcome the shortages of the solid bone screw, developing the success of surgery and showing significant clinical application prospects in orthopedic surgery. Statement of significanceThis research investigated the high-cycle fatigue behavior of re-entrant unit-based auxetic bone screw under tensile-tensile cyclic loading and its osseointegration performance, which has not been focused on in existing studies. The fatigue strength of auxetic bone screw was lower while the osseointegration was better than non-auxetic bone screw, especially under in vivo tensile loading. Favorable osseointegration of auxetic bone screw might compensate for the shortage of fatigue resistance, ensuring its long-term stability and longevity in vivo. This suggested that with adequate auxetic effect and long-term stability, the auxetic bone screw had significant application prospects in orthopedic surgery. Findings of this study will provide a theoretical guidance for design optimization and clinical application of the auxetic bone screw.

Numerical Analysis and Experimental Investigation of High Cycle Fatigue Behavior in Additively Manufactured Ti–6Al–4V Alloy

Additive Manufacturing (AM) of the Ti–6Al–4V alloy has gained significant importance across various industries, including biomedical, aerospace, cellular, and land vehicle applications, due to its numerous benefits. The certification of performance and reliability of AM materials, particularly for critical applications, heavily relies on evaluating fatigue strength. In this study, a numerical analysis based on the finite element method is presented to predict the High Cycle Fatigue (HCF) behavior of AM Ti–6Al–4V alloy. The investigation focuses on exploring the sensitivity of material fatigue life to surface roughness and Ultimate Tensile Strength (UTS). Uniaxial tensile and High Cycle Fatigue (HCF) tests were conducted on Ti–6Al–4V alloy samples extracted from rectangular walls manufactured using the Laser Metal Deposition (LMD) process. The walls were surface machined prior to sample extraction. Porosity and surface roughness measurements were performed on the samples. Numerical simulations of the HCF tests were carried out, considering various surface roughness ranges and UTS values. The numerical results were then compared to experimental data. The findings consistently demonstrated that higher surface roughness led to a shorter fatigue life, while higher UTS values resulted in a longer fatigue life. The numerical solutions aligned with the experimental results, indicating the efficacy of the finite element method in predicting the fatigue behavior of AM Ti–6Al–4V alloy. These insights contribute to a better understanding of the relationship between surface roughness, UTS, and fatigue life of Ti–6Al–4V alloys manufactured by AM.

Stress and strain calculation method for orthotropic polymer composites under axial and bending ultrasonic fatigue loads

Accelerated fatigue testing is one potential solution to evaluate the very high cycle fatigue behavior of composite materials within a reasonable amount of time. The ultrasonic fatigue testing methodology can be adopted to realize fatigue experiments up to 109 cycles at 20 kHz, compared to conventional fatigue experiments usually carried out between 5–50 Hz. The determination of cyclic stresses during ultrasonic loading remains to be one of the major challenges. The cyclic stresses during ultrasonic fatigue loading were investigated for a carbon fiber 5H satin fabric reinforced in Polyetherketoneketone (CF-PEKK) composite material. Two experimental setups were developed to perform ultrasonic testing under uni-axial and three-point bending loading conditions. A 3D-Scanning Laser Doppler Vibrometer (3D-SLDV) and a single-point Laser Doppler Vibrometer (LDV) were integrated into the test systems to measure the oscillation displacement of the CF-PEKK specimens during ultrasonic cyclic loading. These displacement measurements were used to calculate the resulting strains and stresses under elastic loading conditions. The experimental results were found to be in good agreement with those obtained from finite element models, providing evidence for applying the proposed method.

High-cycle fatigue behavior and chemical composition empirical relationship of low carbon three-sheet spot-welded joint: An application in automotive industry

In this paper, the authors have attempted to provide an empirical relationship between the fatigue behavior of three-sheet spot-welded joint and the chemical composition of low carbon steel. To this end, the application of this joint in the automotive industry was considered and laboratory samples were prepared based on the actual specifications in the industry, including the raw material (i.e., material and thickness of the primary sheets), the resistance spot welding (RSW) process parameters, and other factors. The results of tensile and quantometric tests along with microscopic observations were utilized to evaluate the raw material and to study the compliance of the steel grade with the required standards. Next, axial cyclic test was performed in order to extract the high-cycle fatigue (HCF) properties of three-sheet spot-welded joint. Finally, a relationship between the number of cycles to failure of the spot-welded joint, repetitive load level, and the percentage of constituent elements was presented by multiple linear regression (MLR) technique. The results showed that the greatest effect of the constituent elements is when we are in the regime of low-cycle fatigue (LCF) and by moving towards the HCF regime, its importance decreases until it becomes almost ineffective in the very-high-cycle fatigue (VHCF) area. In addition, the presented relationship is able to predict the fatigue behavior of three-sheet spot-welded joint via the chemical composition of the primary sheet and the cyclic force with a maximum error of 13.8% compared to the experimental results.

Influence of trace rare earth elements on very high cycle fatigue behavior of hot rolled bearing steel

In this study, the effect of trace rare earth (RE) elements on the fatigue property of bearing steel in very high cycle fatigue regime was investigated. For this purpose, ultrasonic tension–compression fatigue tests were conducted on specimens extracted from hot rolled bearing steels with and without RE addition. Crack propagation behavior within the characteristic “fish-eye” (FiE) area and the non-inclusion induced fatigue failure were analyzed after the fatigue test. Results showed that the addition of trace RE can modify inclusions to varying degrees. Further, it significantly reduces the volume fraction of inclusions as well as the number of large inclusions. Consequently, the fatigue life of bearing steel is more than doubled based on the 10% and 50% failure probabilities. During the propagation of cracks within the FiE area, the microstructure and intrinsic defects in bearing steel exhibit high sensitivity to the instantaneous driving force for crack propagation. The discontinuity in their size may result in abnormally slow crack propagation. For the non-inclusion induced fatigue failure of bearing steel, microcracks preferentially form at the junction of lath interfaces or at the enclosed area of martensite laths/plates which tend to grow along the interfaces perpendicular to the loading direction.

Effects of as-built surface with varying number of contour passes on high-cycle fatigue behavior of additively manufactured nickel alloy 718

High cycle fatigue life of laser-powder bed fusion (L-PBF) parts depends on several factors; as-built surfaces, when present, are a particular concern. This work measures as-built L-PBF surfaces with X-ray computed tomography, and uses rotating beam fatigue testing to measure high cycle fatigue life. Surfaces with different, but consistent, characteristics are achieved by building vertical specimens and changing only the number of contour passes. In this way, specimens with three different levels of surface roughness are compared to standard polished specimens. The results from this show that surface roughness increases with decreasing number of contour passes, but the impact on fatigue lifetime is not trivially related. Electron microscopy and x-ray computed tomography images show multiple initiation points and complex surface topology, but that surface feature depth is not necessarily correlated to failure location. Two primary conclusions are that (1) for the case of as-built surfaces loaded in bending, one contour pass is sufficient to achieve peak as-built performance; (2) surface feature depth, even when measured using metal-penetrating imaging, is not strongly associated with failure location in our data. When assessing AM surfaces, more factors (e.g., grain orientation) may be required to mechanistically understand the performance implications.