Fatigue Life Estimation Research Articles

Fatigue life estimation of additively manufactured AISI 316L stainless steel

Additive manufacturing (AM) is becoming increasingly important in engineering applications due to its technological advantages such as: weight reduction, geometric complexity for functionalised products and near net-shape production. Despite the promising potential, the path towards a complete maturity of AM technology is still challenged by internal defects, which appear to be typical of the process. In particular, metal AM technologies are prone to internal defects, which can have a detrimental effect under fatigue loading. In such a context, the present paper deals with the fatigue life estimation of AISI 316L stainless steel subjected to cyclic loading. More precisely, the fatigue assessment is performed by means of an analytical methodology consisting of the joint application of: (i) a multiaxial stress-based fatigue criterion, named Carpinteri et al. criterion, which exploits the concept of the critical plane, and (ii) a stress averaging method, named Critical Direction Method, in order to determine the orientation of the critical plane. Satisfactory results are here obtained in terms of fatigue life for the examined specimens, regardless of both the specimen geometry (both plain and notched specimens are analysed) and the degree of multiaxiality and non-proportionality.

Comparative analysis of Spectral and Deterministic methods for estimating fatigue life in joint of fixed jacket platform in the Andaman Sea Myanmar

Cyclic wave loads can cause fatigue of the joints in the Jacket Platform structure, which is made of steel material and is prone to vibration resonance. This study compares the fatigue life of the Yetagun North Field (YET-D) jacket platform analyzed using the spectral and deterministic fatigue methods using the API RP-2A WSD standard and adding the Weld Improvement Technique 3D visual model and the analysis is processed using the Structure Analysis Computer System (SACS) Connect Edition v11.3 software. Fatigue analysis of Spectral Method without Weld Improvement Technique has exceeded the service life of 20 years, while some joints are less than the service life using the Deterministic Method, but after the Weld Improvement Technique using the S-N curve WJ3 the joint life increases to exceed its service life. The most critical joint 2043, has a fatigue life of 2.79 years for deterministic fatigue and 64.04 years for spectral fatigue. When WJ3 was applied, the fatigue life increased to 21.3 years and 514.8. Analysis of the fatigue life of Spectral and Deterministic Fatigue Method couplings based on the location of the elevation Joints with the same type of fatigue life will increase when approaching 0 m elevation from the seabed, but the Deterministic Method has a smaller life ratio than the Spectral.

Fatigue Analysis of Printed Composites of Onyx and Kevlar

The transformation of powertrains, powered by internal combustion engines, into electrical systems generates new challenges in developing lightweight materials because electric vehicles are typically heavy. It is therefore important to develop new vehicles and seek more aesthetic and environmentally friendly designs whilst integrating manufacturing processes that contribute to reducing the carbon footprint. At the same time, this research explores the development of new prototypes and custom components using printed composite materials. In this framework, it is essential to formulate new approaches to estimate fatigue life, specifically for components tailored and fabricated with these kinds of advanced materials. This study introduces a novel fatigue life prediction approach based on an artificial neural network. When presented with given inputs, this neural network is trained to predict the accumulation of fatigue damage and the temperature generated during cyclic loading, along with the mechanical properties of the compound. Its validation involves comparing the network’s response with the load ratio result, which can be calculated using the fatigue damage parameter. Comparing both results, the network can successfully predict the fatigue damage accumulation; this implies an ability to directly employ data on the mechanical behavior of the component, eliminating the necessity for experimental testing. Then, the current study introduces a neural network designed to predict the accumulated fatigue damage in printed composite materials with an Onyx matrix and Kevlar reinforcement.

Solution to the problem of low sensitivity of crack closure models to material properties

The paper focuses on differences between crack closure obtained by numerical models and by experimental fatigue crack growth rates, namely for three different steels (bainitic steel, predominantly pearlitic steel and additively manufactured austenitic stainless steel). The experimental data revealed a load ratio effect different from that predicted by the most used plasticity-induced crack closure (PICC) models. The term “irreversibility of plastic deformation” was proposed in this work to be used as a material property to estimate how strong the PICC effect would be in a material. Two basic phenomena, which are usually omitted in other models, were considered in the explanation: (i) cyclic softening/hardening, (ii) brittle microcracking at the maximum load. The strip-yield model has the ability of conducting fast and accurate simulations under the variable-amplitude loading. It was demonstrated that the results of this model are practically independent of the material properties. This is caused by the consideration of only monotonic elastic–plastic material properties. To simulate real load ratio effects, the parameter β in the strip-yield model (constraint factor in compression) is proposed to be used as a variable. It enabled a generation of different ratios of monotonic and cyclic plastic zones, which in turn helped to reproduce the crack closure values observed experimentally. Discussion and explanations were provided regarding the material microstructure. The proposed approach considers unequal tensile and compressive yield stresses caused by the different irreversibility of plastic deformation, which explains the dissimilarities in the load ratio effect observed in the investigated materials. It can also improve the accuracy of residual fatigue life estimations.

The influence of energy density on the low cycle fatigue behaviour of laser powder bed fused stainless steel 316L

Laser powder bed fusion (LPBF) is an additive manufacturing (AM) process capable of single-step fabrication of intricate and complex structures. However, there are multiple engineering challenges associated with the introduction of AM based parts into functional industrial applications due to the lack of understanding of the role that process parameters have on the structural integrity of additively manufactured (AM) components and the subsequent effect this has on the mechanical behaviour of such materials when subjected to cyclic loading conditions. The present work will investigate the low cycle fatigue (LCF) behaviour of LPBF stainless steel 316L components manufactured with different process parameters sets and how this effects the material built in different orientations and the resulting impact this has on the material’s resistance to cyclic deformation. The LCF results are supported by microstructural, fractographic and advanced surface profilometry assessments to investigate the key parameters that control the resulting fatigue performance across three different build orientations. Finally, the generated mechanical data has also been interpreted through empirical fatigue lifing models, and the various data sets have been successfully correlated to enable an estimation of longer fatigue lives.

Comparison of critical plane models for multiaxial fatigue life prediction

Background. The operation of numerous machines and units takes place under conditions of multi-axial cyclic loading, which, as a rule, is non-proportional. Evaluating the fatigue durability of metal alloys under conditions of multi-axial non-proportional loading is a relevant task in modern engineering. Solving this problem requires fatigue calculation methods that would consider operating conditions and properties of structural materials, including factors such as the type of stress state, loading trajectory, material sensitivity to non-proportional loading, and so on.Objective. To conduct a comparative analysis of a range of fatigue life models based on the concept of the critical plane, including the Fatemi-Socie, Wang-Brown, Smith-Watson-Topper, Liu I, and Liu II approaches, and to identify the limits and peculiarities of their application.Methods. The fatigue lives calculated using the selected models were compared with experimental results obtained for various metal alloys subjected to uniaxial tension-compression, alternating torsion, and proportional and non-proportional multiaxial loading.Results. The applicability limits of fatigue life models based on the critical plane concept were analyzed for different metal alloys under conditions of proportional and non-proportional multiaxial loading.Conclusions. The research results demonstrated that models requiring the use of material constants obtained from tests in both tension-compression and alternating torsion provide reliable fatigue life estimates for various types of metal alloys. Calculations based solely on fatigue curves from alternating torsion better correlate with the results of tests on ductile materials, while calculations based on criteria utilizing fatigue curves from tension-compression align more closely with results from tests on brittle materials.

Investigation of failure behavior of glass fiber reinforced epoxy laminate under fatigue loading

Purpose This study aims to evaluate the failure behavior of glass fiber-reinforced epoxy (GFRE) laminate subjected to cyclic loading conditions. It involves experimental investigation and statistical analysis using Weibull distribution to characterize the failure behavior of the GFRE composite laminate. Design/methodology/approach Fatigue tests were conducted using a tension–tension loading scheme at a frequency of 2 Hz and a loading ratio (R) of 0.1. The tests were performed at five different stress levels, corresponding to 50%–90% of the ultimate tensile strength (UTS). Failure behavior was assessed through cyclic stress-strain hysteresis plots, dynamic modulus behavior and scanning electron microscopy (SEM) analysis of fracture surfaces. Findings The study identified common modes of failure, including fiber pullouts, fiber breakage and matrix cracking. At low stress levels, fiber breakage, matrix cracking and fiber pullouts occurred due to high shear stresses at the fiber–matrix interface. Conversely, at high stress levels, fiber breakage and matrix cracking predominated. Higher stress levels led to larger stress-strain hysteresis loops, indicating increased energy dissipation during cyclic loading. High stress levels were associated with a more significant decrease in stiffness over time, implying a shorter fatigue life, while lower stress levels resulted in a gradual decline in stiffness, leading to extended fatigue life. Originality/value This study makes a valuable contribution to understanding fatigue behavior under tension–tension loading conditions, coupled with an in-depth analysis of the failure mechanism in GFRE composite laminate at different stress levels. The fatigue behavior is scrutinized through stress-strain hysteresis plots and dynamic modulus versus normalized cycles plots. Furthermore, the characterization of the failure mechanism is enhanced by using SEM imaging of fractured specimens. The Weibull distribution approach is used to obtain a reliable estimate of fatigue life.

Crack influence and fatigue life assessment in rail profiles: a numerical study

Rail transportation is a pivotal mode of land transport for its efficiency in transporting passengers and freight across short or long distances; hence, the reliability and safety of rail systems are of key importance. Rolling contact fatigue (RCF), characterized by the cyclic loading of wheel-rail contacts, presents a significant challenge in the rail industry. This study presents a comprehensive numerical investigation on the influence of different crack orientations on the contact stress of the rail profile and subsequently the fatigue life. Using finite element analysis (FEA) with Abaqus and FE-safe software, the study examined different crack orientations’ impact on stress distribution and fatigue life of rail profiles. Employing the extended finite element method (XFEM), this study modeled cracks in rail profiles with different orientations: parallel, perpendicular, and oblique to the rail axis. finite element analysis was used to obtain stress distribution results, highlighting the impact of crack presence, and orientation on maximum contact stresses. Subsequently, fatigue analysis was performed using FE-safe software, wherein the FEA results were imported to estimate fatigue life and damage evolution. The study revealed that the presence of a crack significantly influences contact stress, fatigue life, and damage accumulation. The results further demonstrated that crack orientation has an impact on the severity of those effects. Oblique cracks exhibited higher impact compared to lateral and longitudinal cracks. The study provides valuable insights into rolling contact fatigue-related failures, aiding in better understanding and mitigation of such issues, thereby contributing to improved rail maintenance practices and system safety.

A novel approach for corrosion fatigue life estimation under asymmetric cyclic loadings using intrinsic damage dissipation

Numerous scholars have conducted theoretical research on corrosion fatigue lifetime prediction models based on continuum damage mechanics and linear fracture mechanics. However, most of the predicted models require several material parameters, making them difficult to apply in practice. For practical application, the existing models, including the Goodman, Gerber, SWT and Walker models, are empirical or statistical and have not gained wide acceptance. Hence, an urgent need exists for an equally simple, easy-to-apply, and mechanics-based model for engineering applications. Therefore, this study proposes a corrosion fatigue stress equation associated with equivalent life based on the intrinsic damage dissipation energy. The method attached to a material parameter can be used to predict corrosion fatigue lifetime and provides a novel approach for easy application. The comparisons of experimental results and the results predicted by our proposal and the existing models were carried out, indicating that our proposal provides better correlations with experimental results than others. The proposal provides great potential for its simplicity in the evaluation of corrosion fatigue lifetime under asymmetric cyclic loadings.

Non-axisymmetric Modeling of a Moving Heat Source for Thermal Stress and Fatigue Analysis of Railway Vehicle Disc Brakes

Railroad vehicles require the use of disc brakes for safety purposes, however, the brakes are susceptible to thermal stress, which ultimately shortens their lifespan. Hence, to accurately predict the life of railway disc brakes in thermal load simulations, the availability of a model that considers spatial and temporal variations of temperature and thermal stress is essential. A non-axisymmetric moving heat source model was successfully developed to address spatial temperature variations (Deressa and Ambie in Urban Rail Transit 8(3–4):198–216, 2022. 10.1007/s40864-022-00176-9), and this study aims to extend this model to predict thermal stress and fatigue life, and assess its effectiveness. The analysis includes braking time thermal analysis, cooling time thermal analysis, and structural analysis. Spatially varying temperature is incorporated into the structural analysis to calculate thermal stress and strain. A fracture mechanics-based fatigue life estimation method is applied to critical areas of the friction surface. The model is implemented on two braking conditions (service and emergency) and two disc geometries (actual and modified). The model successfully resolves spatial heat considerations by estimating maximum stress variations of up to 46 MPa along the disc circumference. Stress differences of 3 MPa and 6 MPa are observed between the leading and trailing edges of the pad trace during late and mid-braking times, respectively. Fatigue life results identify critical positions and directions for fatigue life initiation. Additionally, these results are in accord with previous observations available in the literature. The proposed model can be easily implemented in various sliding friction applications such as drum brakes, engine pistons/cylinders, and camshafts.

Study on the Effects of Thermal Shaping for 316L Heat Exchange System of Submersible Vehicle on Fatigue Life

In this paper present the effects of 316L steel in the environment of repeated heat load, and the impact of the thermal load on fatigue life. Using thermal fatigue experiments and ABAQUS software, rain flow counting method is used to simplify the strain cycle spectrum of stress load. The Coffin-Manson nonlinear empirical equation was established based on thermal fatigue experiments, and the fatigue life estimation was completed in accordance with the Miner damage accumulation rule and FE-SAFE fatigue software. The test rods were respectively placed at room temperature and heated at 250°C for water cooling for tensile testing. Fatigue tests were performed with 5 strain parameters (0.8%, 0.7%, 0.6%, 0.5% and 0.4%). ABAQUS and FE-SAFE software used to study 316L testing rod fatigue life verification analysis. A composite heat exchange system model made of 316L was designed for the case study. It is found that the fatigue life after heating is reduced by 35% to 12% from the experimental results and numerical simulation calculation. Therefore, when the 316L steel is subjected to thermal fatigue, the fatigue life will be reduced. The research results can provide a reference for the design of heat exchangers using 316 steel in various fields.

Evaluation of fatigue life and osseointegration parameters of carbon-carbon composite material for medical applications

The aim of the present work is to study the strength characteristics Carbon fibre-reinforced Carbon (CFRC) material as an osteoimplant under its stepwise loading and to estimate the parameters of osseointegration at the bone-implant interface from the position of histological analysis and mathematical modeling. Fatigue life estimation of materials for implantation and endoprosthesis is based on the study of its "behavior" and determination of the degree of microstructure transformation under different types of cyclic loading using a system for the analysis of acoustic emission under loading. The key parameter in studying the strength of samples from carbon fiber reinforced composite materials under stepwise loading is the determination of the moment of transition of the controlled object into a pre-destructive state. We propose to use the ratio of degree in the equation defining the relationship between the number of acoustic emission events depending on the loading conditions as a key factor in studying the strength of samples made of CFRC under staged loading. When assessing the properties of implant materials, in addition to the study of strength parameters, an important aspect is the determination of the major biomedical characteristics, in particular, the study of bone tissue regeneration processes at the border of the implant-bone block. The osteoinductive activity of materials for plasty of bone tissue defects and endoprosthetics is one of the parameters of the success of reconstructive measures. In this regard, the use of modern methods of histological analysis and mathematical modeling of osseointegration processes of CFRC specimens will allow to predict the effectiveness of their application in clinical practice when replacing bone tissue defects of different localization and in therapy of patients with degenerative-dystrophic diseases requiring endoprosthesis.

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.

Fatigue life investigation of rubber bearing for heavy trucks: Optimal design by using finite element method with experimental verification

Rubber bearings consisting of multiple layers of rubber and inlaid steel plates play an important role in cushioning and vibration damping on heavy trucks. In this study, the thermo-mechanical coupling approach together with critical plane analysis theory was utilized to predict fatigue nucleation life of rubber bearing. A new criterion for fatigue life estimation of rubber bearings aiming to eliminate the mesh dependence was proposed, that is, the logarithmic average fatigue life of multiple elements in some local areas with low life (accounting for 0.5% of the total rubber elements) was used instead of the shortest life for a single element. The structure of inlaid steel plates was optimized based on the proposed evaluation criterion for longer service life. The simulation results show that the fatigue life of the optimized rubber bearing is increased by 2.2 times compared with that of the original structure, and the experimental results show that the life of the optimized structure is increased by 2.1 times.

Fatigue Estimation Using Inverse Stamping

Reverse engineering methods like 3D scanning are becoming common in engineering practice. These methods enable engineers to reproduce the original shape of a scanned part. If other properties are required, then other reverse engineering methods can follow. Estimation of fatigue is a tricky task even if the material properties of the base material are known. Fatigue is influenced not only by material properties and the part’s shape but also by technological processes. Fast fatigue life estimation of stamped parts using reverse engineering methods is the target of this paper. The forming process, which has a crucial impact on the fatigue of stamped parts, is considered via inverse stamping. Adaptation of inverse stamping method from shell FEM meshes to volumetric meshes is included. The article also discusses the application of two methods, the Material Law for Steel Sheets (MLSS) and the Method of Variable Slopes (MVS). These methods adjust the fatigue curve based on effective plastic strain calculated by inverse stamping. Calculated results were compared with experimental results. In most situations, there is a good agreement between the calculations and the tests of the specimens without surface coatings. Sometimes, the calculated results are more conservative than the experiments. This is acceptable in component design in terms of reliability. When a Zn-Ni surface coating was applied, the fatigue life of the specimen decreased.

On the transition from shear to tensile failure mode in multiaxial fatigue

Depending on several factors, the failure mechanism can change with life for a particular material, from shear in Low Cycle Fatigue (LCF) to tensile in High Cycle Fatigue (HCF). Critical plane-based approaches to multiaxial fatigue have the capability of reflecting the damage mechanisms of the material and can, therefore, not only provide fatigue life estimation under different stress states, but also predict the highest damage (i.e., critical) plane orientation. While Fatemi-Socie critical plane parameter has been used extensively in the literature for many materials with shear failure mechanism, a modified form of the parameter recently proposed by Gates and Fatemi is shown to also be able to capture the failure mechanism transition from shear in LCF to tensile in HCF. The mechanisms by which this parameter accounts for the transition from shear to tensile is discussed in this work. A wide range of materials from the literature with failure mechanism change from shear in LCF to tensile in HCF are evaluated based on this parameter.

Comparing linear damage hypothesis to linear elastic fracture mechanics in the estimation of fatigue life in a high speed light craft

Linear elastic fracture mechanics methods provide a more comprehensive representation of crack propagation compared to traditional methods such as the linear damage hypothesis (or SN curve approach). These techniques have been widely adopted in the aerospace industry, however, their usage in the design of marine structures remains limited. The presented research uses full-scale trial data measured onboard a 111 m wave-piercing catamaran to compare the results obtained from linear elastic fracture mechanics and SN curve-based methods. The results reveal significant differences in estimated fatigue life between SN curve-based methods and fracture mechanics methods. These differences are likely due to limitations in the fracture mechanics model during the crack initiation phase. Changes in fracture mechanics parameters also had a significant effect on fatigue life, suggesting that if accuracy is important then material specific parameters are required. Despite the limitations shown, linear elastic fracture mechanics methods have a higher level of tailor-ability when compared to SN curve based methods and could offer benefits in situations such as the tracking of known flaws or in the assessment of changes to vessel configuration, or usage profiles.

Machine learning-based probabilistic fatigue assessment of turbine bladed disks under multisource uncertainties

PurposeThe multisource uncertainties, including material dispersion, load fluctuation and geometrical tolerance, have crucial effects on fatigue performance of turbine bladed disks. In view of the aim of this paper, it is essential to develop an advanced approach to efficiently quantify their influences and evaluate the fatigue life of turbine bladed disks.Design/methodology/approachIn this study, a novel combined machine learning strategy is performed to fatigue assessment of turbine bladed disks. Proposed model consists of two modeling phases in terms of response surface method (RSM) and support vector regression (SVR), namely RSM-SVR. Two different input sets obtained from basic variables were used as the inputs of RSM, then the predicted results by RSM in first phase is used as inputs of SVR model by using a group data-handling strategy. By this way, the nonlinear flexibility of SVR inputs is improved and RSM-SVR model presents the high-tendency and efficiency characteristics.FindingsThe accuracy and tendency of the RSM-SVR model, applied to the fatigue life estimation of turbine bladed disks, are validated. The results indicate that the proposed model is capable of accurately simulating the nonlinear response of turbine bladed disks under multisource uncertainties, and SVR-RSM model provides an accurate prediction strategy compared to RSM and SVR for fatigue analysis of complex structures.Originality/valueThe results indicate that the proposed model is capable of accurately simulate the nonlinear response of turbine bladed disks under multisource uncertainties, and SVR-RSM model provides an accurate prediction compared to RSM and SVRE for fatigue analysis of turbine bladed disk.

Fatigue life estimate of metallic chain links of mooring systems assuming out of plane bending: From constant amplitude to random loading

In this work, a numerical and analytical study of the fatigue life of chains in the mooring system of FPSO platforms is carried out. Initially, analytical equations are proposed to calculate the stress at the hotspot of the critical chain link, considering axial stresses generated by axial loads and out-of-plane bending (OPB). The analytical equations consider the operating angle of the mooring systems as well as the interlink angle of the links. Thus, the validation of the equations is done by comparing the stress values obtained through numerical simulations of the mooring-fairlead system, where a satisfactory correlation was observed. In addition, loads with constant and variable amplitude are generated as well as random load histories, always between the maximum and minimum operating load of the system, which represent 1/3 and 1/6 of the minimum breaking load (MBL) of the chain link. Based on the Smith-Watson-Topper (SWT) approach, the fatigue life of the chain was estimated, considering the analytical value of the stress at the hotspot based only on the axial contribution and later, due to the axial and OPB contributions. Finally, it was verified that the analytical equations were able to determine the stress values at the hotspot and that the effect of normal stress at the hotspot due to OPB can cause a severe loss in the fatigue life of the mechanical component.

Anti-fatigue optimization of the twisting force arm of landing gear based on Kriging approximate sequential optimization method

ABSTRACT The twisting force arm (TFA) is an important part of the pillar landing gear, anti-fatigue optimization on its structure can improve the reliability of the landing gear. However, the optimization accuracy of the conventional optimization method is limited by the basic topological structure from the views of topological theory. Besides that, the optimization efficiency of the conventional method is also relatively low because of the high computational cost of the fatigue life estimation. In this paper, an anti-fatigue optimization method of the TFA was developed to improve the optimization accuracy and efficiency by using the approximate sequential optimization method after an optimal basic topological structure was obtained. To verify its effectiveness, the proposed method was introduced to the anti-fatigue optimization of a pillar landing gear TFA. The results show that the optimization accuracy of the proposed method is higher than the conventional method, and the computational cost can be reduced 82.35%. This indicates that the proposed method can improve the optimization accuracy and efficiency of the anti-fatigue optimization.