Cycle Fatigue Life Research Articles

Fatigue Crack Growth Analysis in Modified Compact Tension Specimen with Varying Stress Ratios: A Finite Element Study

In this study, the primary objective is to analyze fatigue crack propagation in linear elastic fracture mechanics using the SMART crack growth module in the ANSYS Workbench, employing the finite element method. The investigation encompasses several crucial steps, including the computation of stress intensity factors (SIFs), determination of crack paths, and estimation of remaining fatigue life. To thoroughly understand crack behavior under various loading conditions, a wide range of stress ratios, ranging from R = 0.1 to R = 0.9, is considered. The research findings highlight the significant impact of the stress ratio on the equivalent range of SIFs, fatigue life cycles, and distribution of deformation. As the stress ratio increases, there is a consistent reduction in the magnitude of the equivalent range of stress intensity factor. Additionally, a reciprocal relationship is observed between the level of X-directional deformation and the number of cycles to failure. This indicates that components experiencing lower levels of deformation tend to exhibit longer fatigue life cycles, as evidenced by the specimens studied. To verify the findings, the computational results are matched with the crack paths and fatigue life data obtained from both experimental and numerical sources available in the open literature. The extensive comparison carried out reveals a remarkable level of agreement between the computed outcomes and both the experimental and numerical results.

A new approach for correlating Paris parameters with fatigue life of aircraft fuselage panels

This work presents a numerical technique that establishes a relationship between the C and m parameters of the Paris Law and the number of fatigue life cycles. This relationship is particularly important for determining the material's ability to withstand a specified number of cycles in an aircraft fuselage design. The methodology is based on a multiscale problem and comprises two stages: the macro model, which focuses on internal stresses and critical point location, and the micro model, which considers the critical fatigue life cycle number (n) across a "grid" of C and m parameters, resulting in the optimal curve N(C,m). To validate the adopted methodology, the academic program BemCracker2D has been used to calculate the internal stress fields, simulate cracks, and estimate fatigue life. Three case studies were conducted, and the results indicated that the range of C and m values obtained depends on the configuration of the macro model, the physical parameters of the material, and the defined number of cycles in the design. Ultimately, this computational technique allows for generalization to any fuselage damage analysis model, providing C and m Paris parameter data to mitigate fatigue damage.

Assessing Fatigue Life Cycles of Material X10CrMoVNb9-1 through a Combination of Experimental and Finite Element Analysis

This paper uses a two-scale material modeling approach to investigate fatigue crack initiation and propagation of the material X10CrMoVNb9-1 (P91) under cyclic loading at room temperature. The Voronoi tessellation method was implemented to generate an artificial microstructure model at the microstructure level, and then, the finite element (FE) method was applied to identify different stress distributions. The stress distributions for multiple artificial microstructures was analyzed by using the physically based Tanaka–Mura model to estimate the number of cycles for crack initiation. Considering the prediction of macro-scale and long-term crack formation, the Paris law was utilized in this research. Experimental work on fatigue life with this material was performed, and good agreement was found with the results obtained in FE modeling. The number of cycles for fatigue crack propagation attains up to a maximum of 40% of the final fatigue lifetime with a typical value of 15% in many cases. This physically based two-scale technique significantly advances fatigue research, particularly in power plants, and paves the way for rapid and low-cost virtual material analysis and fatigue resistance analysis in the context of environmental fatigue applications.

Investigating and modelling of highly stressed firearms parts

Recently, there have been too many Pulemyot Kalashnikova Modernizirovannyi (PKM) machine gun bolts that have failed during the firing process. Due to the increased temperature, higher propellant gas pressure, and thermal accumulation, the bolt body is exposed to sever circumstances for ablating, corroding, and erosion. In this paper, the reasons of failure of PKM bolts during firing were evaluated first based on metallurgical experiments. Then, analysing the failure is done by create an accurate finite element model of the bolt body, calculating the cyclic fatigue life and safety factor, determining the causes of failure and be verified showing that failure locations are exactly as shown in the photographic record. the original bolt dimensions were measured using laser scanning, and a CAD model of the bolt was created. Photographic records, visual inspection, chemical analysis, SEM, and hardness measurements, all these metallurgical experiments have been done. The stress distributions and fatigue behavior of the failed bolt are both determined using the Finite Element Method (FEM). This study suggests that fatigue played a role in bolt failure. Furthermore, SEM examinations reveal that the materials contain dimple fractures. The bolt’s fatigue life was decreased by these dimpled fractures.

Investigation of the Combined Influence of Temperature and Humidity on Fatigue Crack Growth Rate in Al6082 Alloy in a Coastal Environment

The fatigue crack growth rate (FCGR) of aluminium alloys under the combined influence of temperature and humidity remains a relatively unexplored area, receiving limited attention due to its intricate nature and challenges in predicting the combined impact of these factors. The challenge was to investigate and address the specific mechanisms and interactions between temperature and humidity, as in coastal environment conditions, on the FCGR of aluminium alloy. The present study conducts a comprehensive investigation into the combined influence of temperature and humidity on the FCGR of the Al6082 alloy. The fatigue pre-cracked compact tension specimens were corroded for 7 days and then subjected to various temperature and humidity conditions in a thermal chamber for 3 days to simulate coastal environments. The obtained data were analysed to determine the influence of temperature and humidity on the FCGR of the Al6082 alloy. An empirical model was also established to precisely predict fatigue life cycle values under these environmental conditions. The correlation between FCGR and fracture toughness models was also examined. The Al6082 alloy exhibits a 34% increase in the Paris constant C, indicating reduced FCGR resistance due to elevated temperature and humidity levels. At the same time, fatigue, corrosion, moisture-assisted crack propagation, and hydrogen embrittlement lead to a 27% decrease in threshold fracture toughness. The developed model exhibited accurate predictions for fatigue life cycles, and the correlation between fracture toughness and FCGR showed an error of less than 10%, indicating a strong relationship between these parameters.

High-Cycle Fatigue Life Behaviour of Fabricated Glass Fibre-Reinforced Polymer

This study focuses on the fatigue behaviour analysis of glass fibre-reinforced polymer (GFRP) composite specimens under high-cycle fatigue loading conditions. Therefore, property validation is recommended in the material development process upon further investigation of the fabricated GRFP. This study aims to evaluate the behaviour of the fabricated GFRP fatigue specimen when subjected to high-cycle fatigue loads and compare it to existing studies. A GFRP fatigue test sample was fabricated using the hand layup process into a flat rectangular panel, which was then cut into a small dimension of 28×2×0.2 cm fatigue specimen. Fatigue tests were performed on five flat specimens at different constant amplitude loads or stress levels between 40% and 80% of ultimate tensile strength to obtain the stress–life curve for the fabricated GFRP. Results showed that the high-stress levels of 80% contributed to the most reduced fatigue life cycle of GFRP. This result is consistent with previous studies and lies within the published life cycle range, validating the fabricated GRFP. A new parameter called the failure modulus, or Mf, may be used to quantify a particular set of fatigue tests.

Development of cashew nut shell lignin-acrylonitrile butadiene styrene 3D printed core and industrial hemp/aluminized glass fiber epoxy biocomposite for morphing wing and unmanned aerial vehicle applications

The aim of this study was to develop a lightweight epoxy based biocomposite for morphing wing and unmanned aerial vehicle (UAV) applications. The proposed composite was developed using a 3D printed high stiffness lignin-Acrylonitrile Butadiene Styrene (ABS) core and industrial hemp with aluminized glass fiber epoxy skin. The ABS was reinforced using lignin macromolecule derived from cashew nut shells via twin screw extruder and the core was printed using an industrial grade 3D printer. Furthermore, the composites were prepared by compression moulding with an ABS-lignin core and hemp/aluminized GF surface and characterized according to respective American society of testing and materials (ASTM) standards. The findings indicate that the addition of 30 vol% Al-glass and hemp fiber with lignin strengthened ABS core improved the mechanical properties. The composite material designated as “E2” exhibits the maximum mechanical properties, providing tensile strength, flexural strength, Izod impact, interlaminar shear strength (ILSS), and compression values of, 136 MPa, 168 MPa, 4.82 kJ/m2, 21 MPa, and 155 MPa respectively. The maximal energy absorbed by composite designation “E2,” during drop load impact test is 20.6 J. Similarly, the composite designation “E2”gives fatigue life cycles of 33,709, 25,781 and 19,633 for 50 %, 70 % and 90 % of ultimate tensile strength (UTS) and 32.5 (K1c) MPa⋅m and 0.76 (G1c) MJ/m2 in fracture toughness and energy release rate respectively.

Effect of Stress Ratio and Loading Inclination on the Fatigue Life of Carbon-Fiber-Reinforced Polymer Composites: Multiscale Analysis Approach

The integration of mesoscale modeling and macroscale experimentation has emerged as a promising approach for understanding and predicting the mechanical behavior and fatigue performance of fiber-reinforced polymer composites. In this work, the mean field homogenization technique is implemented to predict the fatigue performance of the carbon-fiber-reinforced polymer composites under cyclic loading conditions. To predict the number of fatigue cycles, Modified Gerber criteria are used with the stress-based Tsai–Hill failure indicator. Fatigue strength factor (α) and creep rupture strength factor (β) are experimentally evaluated and further implemented in a computational approach to predict fatigue life cycles of the composite. The effect of composite constituents, stress ratio, and loading direction are investigated in detail against the fatigue performance of the composite. Fatigue cycles are predicted at individual matrix and fiber levels at various stress ratios of 0.2, 0.4, 0.6, and 0.8 at different loading inclinations. The experimental results are compared with the mesoscale S–N curves.

Isothermal and thermomechanical fatigue behavior of Ti-2Al-2.5Zr titanium alloy

In-phase and out-of-phase thermomechanical fatigue (TMF) tests in the temperature range of 200–400 °C and isothermal fatigue (IF) tests at 400 °C were conducted to investigate cyclic deformation behavior and fatigue life of Ti-2Al-2.5Zr alloy. The back stress and the friction stress were extracted, and the internal stress competition mechanism underlying the cyclic hardening/softening behavior was clarified. The fatigue life of TMF and IF exhibited slight differences at strain amplitudes greater than 0.6%, whereas it depended on loading modes at the strain amplitude of 0.4% owing to the increase in the relative deviation in the plastic strain energy density and in the peak stress.

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.

Effects of rolled fibrous microstructure on fatigue properties of extruded Cu-5Al planar micro springs

Planar micro spring is an important elastic component in microelectromechanical system devices, and one of its main failures is fatigue. In this work, a new method to improve the cycles of a planar micro spring by introducing pre-rolled fibrous microstructure was proposed. Cu-5Al alloy billets with a fibrous microstructure rolled at room temperature with a reduction ratio of 70% were obtained. Three types of planar micro springs with fibrous microstructure were prepared through extrusion by varying the angle between the fibrous microstructure direction and the extrusion direction. Fatigue tests were conducted using a customized micro-fatigue test system. The best fatigue performance was obtained by preparing the micro springs with the fibrous microstructure direction perpendicular to the extrusion direction, while the worst fatigue performance was obtained by preparing the planar micro springs with the fibrous microstructure direction parallel to the extrusion direction. The fibrous microstructure direction affected the local strain in the micro springs. The fibrous microstructure slightly affected the location of the crack initiation region but significantly affected the area of crack initiation and steady-state expansion region of the micro spring. The fatigue life cycle of extruded Cu-5Al alloy planar micro spring with the pre-rolled fibrous microstructure improved by 58% more than that of extruded Cu-7Al alloy planar micro spring without the pre-rolled fibrous microstructure. Micro spring fatigue life cycle decreased with increasing strain amplitude. This work provides a new approach for preparing planar micro springs with high fatigue performance.

Fatigue Crack Growth Studies under Mixed-Mode Loading in AISI 316 Stainless Steel

The objective of this study is to examine the behavior of fatigue crack growth (FCG) in the mixed mode (I/II) of the AISI 316 austenitic stainless steel alloy, considering mode mixity angles of 30°, 45°, and 60°. This particular alloy is widely used in the marine industry and various structural components because of its exceptional properties, such as high corrosion resistance, good formability, weldability, and high-temperature strength. By investigating the crack growth behavior, the study seeks to provide insights into the material’s durability and potential for long-term use in demanding applications. To analyze fatigue crack growth behavior using linear elastic fracture mechanics (LEFM), this study utilizes compact tension shear (CTS) specimens with varying loading angles. The CTS specimens provide an accurate simulation of real-world loading conditions by allowing for the application of various loading configurations, resulting in mixed-mode loading. The ANSYS Mechanical APDL 19.2 software, which includes advanced features such as separating, morphing, and adaptive remeshing technologies (SMART), was utilized in this study to precisely model the path of crack propagation, evaluate the associated fatigue life, and determine stress intensity factors. Through comparison with experimental data, it was confirmed that the loading angle had a significant impact on both the fatigue crack growth paths and the fatigue life cycles. The stress-intensity factor predictions from numerical models were compared to analytical data. Interestingly, it was observed that the maximum shear stress and von Mises stresses occurred when the loading angle was 45 degrees, which is considered a pure shear loading condition. The comparison shows consistent results, indicating that the simulation accurately captures the behavior of the AISI 316 austenitic stainless steel alloy under mixed-mode loading conditions.

Effect of Mg on elevated-temperature low cycle fatigue and thermo-mechanical fatigue behaviors of Al-Cu cast alloys

The effects of Mg addition on the cyclic deformation and fatigue life behaviors of Al-Cu 224 cast alloys were investigated under isothermal low cycle fatigue (LCF) at 300 °C and out-of-phase thermo-mechanical fatigue (OP-TMF) in the temperature range 60–300 °C. The results show that all tested alloys experienced cyclic softening during both LCF and OP-TMF, whereas the softening ratio of Mg-containing alloys was lower than that of the base alloy free of Mg because of the lower coarsening rate of θ'-Al2Cu precipitates. Under both LCF and TMF, near-surface porosity and brittle intermetallic particles were considered sources of crack initiation. TMF lives were inferior to LCF lives under the same strain amplitude because of the combined damage effect of the cyclic mechanical and thermal loadings. Under LCF, the addition of Mg enhanced the fatigue performance because of the co-existing θʹ and θʺ precipitates and the higher thermal resistance of θʹ; under TMF, it led to a slight reduction in fatigue performance. The hysteresis energy model was successfully applied to predict the LCF and TMF lifetimes. The predicted results agree well with the experimentally measured LCF and TMF lifetimes.

Deformation microstructure dependence of low cycle tensile fatigue life of NiTi wires

This study prepared near-equiatomic NiTi wires with excellent cyclic tensile fatigue life and proposed the mechanism by which deformation microstructure impacts fatigue life. The fatigue life of Ni50.2Ti49.8 was discovered to be 1.8–2.1 times greater than Ni50.9Ti49.1 by the low cycle fatigue test with various test conditions (loading stress is 700 MPa/900 MPa, frequency is 5 Hz/2.5 Hz, and stress ratio is 0.1/0.2) at room temperature. Ni50.2Ti49.8′s matrix phase is R + B19′ with fewer slip systems. It tends to coordinate deformation with twinning, stacking faults, and wave dislocations during cyclic tensile. Cross-grain boundary twinning strengthens grain boundaries. Also, twinning can expand available space for dislocation movement, thereby reducing stress concentration and extending the fatigue life of Ni50.2Ti49.8. Ni50.9Ti49.1′s matrix phase is B2 + R and easy to form planar dislocation. This reduces the space for dislocation movement and causes premature fatigue fracture. Moreover, the second phase Ni4Ti3 in Ni50.2Ti49.8 is distributed uniformly throughout the matrix and exerts a strong pinning influence on the dislocation movement. This also facilitates the formation of multiple deformation microstructures in Ni50.2Ti49.8.

Experimental and Numerical Investigations of High-Cycle Fatigue Properties of HTRB630 High-Strength Steel Bars

To explore the application of heat-treated ribbed bar (HTRB) type HTRB630 high-strength steel bars in reinforced concrete bridges, the tensile test and high-cycle fatigue test are carried out. Then, the high-cycle fatigue properties of the specimens are analyzed and discussed from median stress-number of loading cycles (S-N) curve, P-S-N curve, comparison with 500-MPa grade steel bars, and fatigue fracture mechanism. Finally, their high-cycle fatigue properties are investigated numerically, and the influence of stress ratio on their fatigue properties is discussed. The results indicated that the probability-stress-number of loading cycles (P-S-N) curve with a confidence level γ=75% and a reliability guarantee rate P=97.7% is more accurate than the median S-N curves for the fatigue design of reinforced concrete bridges. In the P-S-N curve, the stress ranges at 2 million and 10 million cycles are 237.03 and 203.38 MPa, respectively. In the median S-N curve, the stress ranges at 2 million and 10 million cycles of fatigue life of steel bars are 262.77 and 236.08 MPa. The fatigue properties of the specimens are higher than those for the 500-MPa grade steel bars. The fatigue fracture of the specimens consists of a fatigue source zone, crack propagation zone, and transient fracture zone. Microscopically, it is a cleavage fracture in the crack propagation zone; it is micropore aggregation fractures in the instantaneous fracture zone. At a given fatigue life, the fatigue stress range decreases as the stress ratio increases. The fatigue properties of the specimens are better at a higher stress ratio with the same maximum stress.

Fatigue crack growth behavior of SS316L deposition from wire arc additive manufacturing

Wire arc additive manufacturing has shown the potential to build large metal parts with high deposition rates and low cost of production compared to other additive manufacturing techniques. Austenitic stainless steel 316L is known for corrosion resistance and weldability, which makes it a strong candidate for building and repairing marine and offshore parts, with wire arc additive manufacturing. These parts experience fluctuating loads during service, which necessitates the fatigue performance study of wire arc additively build stainless steel. This work investigates the fatigue crack propagation behavior of stainless steel 316L depositions from wire arc additive manufacturing. Single beads of stainless steel 316L were deposited layer by layer to fabricate the wall structures. From the wall structures, the specimens were prepared for the tensile and fatigue crack growth rate tests along the traverse and build directions. In conjunction with mechanical testing, electron back-scattered diffraction and scanning electron microscopy techniques were employed to characterize the microstructure. Microstructural observations showed the presence of columnar dendrites along the build direction. The electron dispersive spectroscopy revealed the elemental diffusion at the layer interfaces due to the remelting of the layers. Differences in mechanical properties were observed across the two directions. Along build directions, the ultimate tensile strength was 8 % higher and yield strength was 7 % lower than the respective strengths along the traverse direction. The build direction also exhibited 46 % higher fatigue life cycle than the traverse direction. The difference in properties across different orientations was closely associated with the microstructural variations. Overall, the mechanical performance of the wire arc additively deposited SS316L is better than the previously reported selective laser melted SS316L.

Investigation on Fracture Performance of Hot-Mix Asphalt with Reclaimed Asphalt Pavement under Fatigue Loading

Reclaimed asphalt pavement (RAP) has been widely used in asphalt pavement. However, the fatigue performance of hot-mix asphalt (HMA) with RAP is a critical factor to ensure durability. In this study, fatigue tests using an Overlay Tester (OT) were conducted using a novel load-controlled mode. RAP contents were 0, 25% and 50%, respectively. In the cyclic loading, fatigue life and energy parameters were measured. Results indicated that RAP decreased both the fracture energy and tensile strength. Fatigue life was determined using two methods. RAP was proved to be beneficial in prolonging the fatigue life using the two methods at 25 °C. However, opposite conclusions were made about the effect of RAP on fatigue life at −10 °C. At −10 °C, compared to HMA without RAP, the cumulative dissipated energies decreased by 49.1% and 77.3% when RAP contents were 25% and 50%, respectively. At 25 °C, compared to HMA without RAP, the inclusion of 25% RAP increased the cumulative energy by 31.1%, while 50% RAP decreased the cumulative energy by 41.2%. The developments of the dissipated energy and the cumulative energy were consistent with the fatigue life results determined by the first method.

Simulation-based Fatigue Life Analysis of Polyimide Film in Afterburner Fuel Distributor

Aiming at the problem of premature failure of organic material polyimide film in the afterburner fuel distributor of a turbofan engine, the material parameters of polyimide film and the temperature and the fluctuation amplitude of the film during use were obtained based on previous investigation. The finite element simulation model of polyimide film was established in ANSYS software to study the Mises stress distribution and weak area distribution of the film when the film fails in the form of fracture. Based on the fatigue life calculation theory of probabilistic fracture mechanics, the fatigue life cycle times and their variation rules of the film under different reliability were obtained. The results show that there is stress concentration in the film, and the stress con-centration and weak area of the film occur at the outer edge of the film clamping. The fatigue life cycle times of the film under different reliability are calculated, and the fatigue life cycle times decrease with the increase of reliability.

Fatigue analysis of wind turbine blade for various materials

A 300 kW horizontal axis wind turbine with S809 airfoil is considered for predicting the fatigue life. The wind turbine blade is designed using Blade Element Momentum (BEM) method. The blade geometries such as chord and pitch angle distributions are determined accordingly the blade is modelled using CREO software. The method of analysis is done by considering both static and transient conditions with varying boundary conditions and different loading pressures. The objective of this work is to identify the fatigue life cycles of the wind turbine blade for various composite materials (Shokrieh and Rafiee, 2016) under various operating conditions. Modelled blade is analysed at both static and transient conditions by considering various composite materials as wind turbine blade material. Simple cyclic loading conditions at stress ratio, R = −1 and R ≠ −1 are considered for the transient analysis. Static analysis is done by taking a single cut-out velocity of 12 m/s. Steady loading and response conditions are assumed; that is, the loads and the structure's response are assumed to vary slowly with respect to time. The fatigue life of the wind turbine is calculated for Glass fibre reinforced plastics-glass fibre, Carbon fibre, Technora fibre, Kevlar fibre and E-glass materials and thereby suggesting the best material having high fatigue life, less damage factor and good safety factor.

In-situ experimental investigation of the small fatigue crack behavior in CP-Ti: The influence of micronotch size

The influence of the micronotch size on the small fatigue-crack behavior of CP-Ti was investigated in this study. With an increase in the equivalent micronotch size, the fatigue life and average crack-arrest cycle decreased. Microstructural analysis revealed that crack arrest results from high-angle grain boundaries, and the post-arrest behavior is mainly characterized by the connection of main and secondary cracks, or the alternation of the slip system. A high crack propagation rate is correlated with prismatic <a> slip. The activation of other slip modes may decrease the crack propagation rate. The micronotch size affected the distribution of the crack growth regions but had little influence on the long crack propagation rate.