Strain-life Relationship Research Articles

Predicting fatigue life with the IMWCW under complex loading

The Integration Modified Wöhler Curve Method (IMWCW), a novel approach for predicting fatigue life under complex strain-based non-proportional loading paths is introduced in this research. This method integrates concepts from the Modified Wöhler Curve Method (MWCW) with the principle of damage incremental integration to provide a more nuanced prediction of material fatigue. Besides two established E-N curves (strain-number of cycles) for uniaxial tension and torsion, a new fundamental E-N curve that characterizes the strain-life relationship under complete non-proportional loading paths is introduced. A novel strain path decomposition technique is presented, which dissects an infinite number of instantaneous micro-elements along any loading path into components parallel and perpendicular to the proportional loading direction. It is assumed that each instant will cause fatigue damage to the material. A concurrent model for the incremental integration of damage is formulated, allowing for the calculation of cumulative damage. The model is further expanded to provide analytical expressions for proportional loading and non-proportional loading, linking them to three fundamental E-N curve, so as to calibrate the parameters required for the integration model. The empirical validity of the model is confirmed through experimental testing on 7 different metallic materials under 20 loading conditions, with 391 data points analyzed. The results demonstrate that 91% of the model's predictions fall within a scatter band of 2, confirming its robustness and reliability in forecasting fatigue life in complex, real-world scenarios.

Low-Cycle Fatigue Behavior and the Combined Cyclic Hardening Material Model of Plate-Shaped Zn-22Al Alloy for Seismic Dampers.

This study investigates the potential of the plate-shaped Zn-22 wt.% Al (Zn-22Al) alloy as an innovative energy dissipation material for seismic damping devices, since plate-shaped material is more suitable to fabricate large-scale devices for building structures. The research begins with the synthesis of Zn-22Al alloy, given its unavailability in the commercial market. Monotonic tensile tests and low-cycle fatigue tests are performed to analyze material properties and fatigue performance of plate-shaped specimens. Monotonic tensile curves and cyclic stress-strain curves, along with SEM micrographs for microstructure and fracture surface analysis, are acquired. The combined cyclic hardening material model is calibrated to facilitate finite element analysis. Experimental results reveal exceptional ductility in Zn-22Al alloy, achieving a fracture strain of 200.37% (1.11 fracture strain). Fatigue life ranges from 1126 to 189 cycles with increasing strain amplitude (±0.8% to ±2.5%), surpassing mild steel by at least 6 times. The cyclic strain-life relationships align well with the Basquin-Coffin-Manson relationship. The combined kinematic/isotropic hardening model in ABAQUS accurately predicts the hysteretic behavior of the material, showcasing the promising potential of Zn-22Al alloy for seismic damping applications.

Low-cycle fatigue mechanical behavior of 30CrMo steel under hydrogen environment and numerical verification of chaboche model

In order to investigate the fatigue behavior of the hydrogen storage material, 30CrMo steel, in a hydrogen environment, an electrochemical hydrogen charging method was employed. Low-cycle fatigue experiments were conducted on the material to obtain half-life stress–strain hysteresis curves, cyclic response characteristics, and strain-life relationships under different hydrogen charging durations. The results indicate that the material exhibited an overall cyclic softening behavior, transitioning from ductile fracture to brittle fracture after hydrogen charging, resulting in a significant reduction in fatigue life. The Manson-Coffin formula was fitted based on material cyclic response characteristics and strain-life relationship curves. Additionally, fatigue toughness and Chaboche kinematic hardening models were fitted based on low-cycle fatigue test data. Finite element analysis was used to validate the accuracy and reliability of the Chaboche kinematic hardening model. The Chaboche kinematic hardening model showed minimal error compared to experimental data and accurately described the influence of hydrogen on the low-cycle fatigue mechanical behavior of 30CrMo steel.

Low-Cycle Fatigue Behavior of Wire and Arc Additively Manufactured Ti-6Al-4V Material.

Additive manufacturing (AM) techniques, such as wire arc additive manufacturing (WAAM), offer unique advantages in producing large, complex structures with reduced lead time and material waste. However, their application in fatigue-critical applications requires a thorough understanding of the material properties and behavior. Due to the layered nature of the manufacturing process, WAAM structures have different microstructures and mechanical properties compared to their substrate counterparts. This study investigated the mechanical behavior and fatigue performance of Ti-6Al-4V fabricated using WAAM compared to the substrate material. Tensile and low-cycle fatigue (LCF) tests were conducted on both materials, and the microstructure was analyzed using optical microscopy and scanning electron microscopy (SEM). The results showed that the WAAM material has a coarser and more heterogeneous grain structure, an increased amount of defects, and lower ultimate tensile strength and smaller elongation at fracture. Furthermore, strain-controlled LCF tests revealed a lower fatigue strength of the WAAM material compared to the substrate, with crack initiation occurring at pores in the specimen rather than microstructural features. Experimental data were used to fit the Ramberg-Osgood model for cyclic deformation behavior and the Manson-Coffin-Basquin model for strain-life curves. The fitted models were subsequently used to compare the two material conditions with other AM processes. In general, the quasi-static properties of WAAM material were found to be lower than those of powder-based processes like selective laser melting or electron beam melting due to smaller cooling rates within the WAAM process. Finally, two simplified estimation models for the strain-life relationship were compared to the experimentally fitted Manson-Coffin-Basquin parameters. The results showed that the simple "universal material law" is applicable and can be used for a quick and simple estimation of the material behavior in cyclic loading conditions. Overall, this study highlights the importance of understanding the mechanical behavior and fatigue performance of WAAM structures compared to their substrate counterparts, as well as the need for further research to improve the understanding of the effects of WAAM process parameters on the mechanical properties and fatigue performance of the fabricated structures.

Low cycle fatigue behaviour of wire arc additively manufactured ER70S-6 steel

Wire arc additive manufacturing (WAAM) is a method of 3D printing that is well suited to the cost-sensitive construction industry. Fundamental test data on the mechanical properties of WAAM materials, especially under cyclic loading, are however lacking. To bridge this gap, an experimental study into the low cycle fatigue (LCF) behaviour of WAAM ER70S-6 steel has been conducted and is presented herein. Following quasi-static mechanical and geometric characterisation, a series of as-built and machined coupons was tested in different directions relative to the print layer orientation (θ = 0°, 45° and 90°) under constant amplitude LCF loading, covering a range of strain amplitudes from ±0.2% to ±2.0%. Fractographic analysis of the tested coupons was also performed to assess their failure mechanisms. On the basis of the experimental results, strain-life relationships and cyclic stress-strain curves were derived. The geometric undulations of the as-built coupons resulted in a weakening in the LCF properties, and the weakening effect increased with the loading angle θ and strain amplitude. The cyclic hardening/softening response of the WAAM material varied with the imposed strain amplitudes, while significant non-Masing behaviour was observed.

Fatigue database of complex metallic alloys

The past few decades have witnessed rapid progresses in the research and development of complex metallic alloys such as metallic glasses and multi-principal element alloys, which offer new solutions to tackle engineering problems of materials such as the strength-toughness conflict and deployment in harsh environments and/or for long-term service. A fatigue database (FatigueData-CMA2022) is compiled from the literature by the end of 2022. Data for both metallic glasses and multi-principal element alloys are included and analyzed for their statistics and patterns. Automatic extraction and manual examination are combined in the workflow to improve the efficiency of processing, the quality of published data, and the reusability. The database contains 272 fatigue datasets of S-N (the stress-life relation), ε-N (the strain-life relation), and da/dN-ΔK (the relation between the fatigue crack growth rate and the stress intensity factor range) data, together with the information of materials, processing and testing conditions, and mechanical properties. The database and scripts are released in open repositories, which are designed in formats that can be continuously expanded and updated.

Fatigue database of additively manufactured alloys

Fatigue is a process of mechanical degradation that is usually assessed based on empirical rules and experimental data obtained from standardized tests. Fatigue data of engineering materials are commonly reported in S-N (the stress-life relation), ε-N (the strain-life relation), and da/dN-ΔK (the relation between the fatigue crack growth rate and the stress intensity factor range) data. Fatigue and static mechanical properties of additively manufactured (AM) alloys, as well as the types of materials, parameters of AM, processing, and testing are collected from thousands of scientific articles till the end of 2022 using natural language processing, machine learning, and computer vision techniques. The results show that the performance of AM alloys could reach that of conventional alloys although data dispersion and system deviation are present. The database (FatigueData-AM2022) is formatted in compact structures, hosted in an open repository, and analyzed to show their patterns and statistics. The quality of data collected from the literature is measured by defining rating scores for datasets reported in individual studies and through the fill rates of data entries across all the datasets. The database also serves as a high-quality training set for data processing using machine learning models. The procedures of data extraction and analysis are outlined and the tools are publicly released. A unified language of fatigue data is suggested to regulate data reporting for the fatigue performance of materials to facilitate data sharing and the development of open science.

Low-cycle fatigue behaviour and fracture feature of stainless-clad bimetallic steel

The stainless-clad (SC) bimetallic steel that is manufactured by metallurgically bonding stainless steels as cladding metal and conventional mild (CM) steel as substrate metal, is a kind of advanced steel with low cost, high strength and outstanding corrosion-resistant performance. Such advanced steels are especially competitive in the application of engineering structures with demands of high corrosion resistance. Unfortunately, the cyclic behaviour of the SC bimetallic steel is different from that of CM steel or stainless steel, and the research work on the SC bimetallic steels from material level to structural design level for the applications in structural engineering field is very limited. Therefore, this paper aims to investigate the low-cycle fatigue behaviour of the SC bimetallic steel made by hot roll bonding of austenitic stainless steel (S31603) and CM steel (Q355B). The test adopted a constant strain amplitude cyclic loading system with strain ratios of −1 and 0, a strain rate of 0.5%·s−1 and strain amplitudes varying from 1.00% to 2.50%. The fracture feature, cyclic characteristic, stress-strain response and the influence of surface defect and strain rate are analysed herein, and the strain-fatigue life curves are fitted and predicted by adapting the Basquin-Coffin-Manson model and Kuroda model. Research outcomes show that the introduction of cladding steel could significantly improve its ductility and low-cycle fatigue life; the fatigue life of the SC bimetallic steel is generally 30% ~ 60% higher compared with the corresponding CM steel, indicating its excellent low-cycle fatigue behaviour. The low-cycle fatigue life of the two steels could be well predicted by the strain-life relationship with adapted Basquin-Coffin-Manson model and Kuroda model, and the former is indicated superior to the latter in terms of the essential meaning and applicability.

Fatigue behaviour and damage mechanisms under strain controlled cycling: Comparison of Flax–epoxy and Glass–epoxy composites

Recent research showed that strain-controlled (constant strain-amplitude) cycling may be ideal for natural-fibre-composite (NFC) fatigue testing, since enforcing constant strain-rates eliminate the apparent modulus ‘improvement’ reported by several stress-controlled studies. This article re-examines Flax-reinforcement as an alternative to Glass by fatigue testing under constant strain-amplitude. Two Glass–epoxy crossply configurations ([0/90]3S, [±45]3S) are tested alongside four commonly-studied Flax–epoxy layups ([0]16, [0/90]4S, [±45]4S, quasi-isotropic [0/45/90/-45]2S). Fatigue endurance plots for all layups are modelled by linearised logarithmic strain-life relationships, for which unique parameters are identified. Evolution of several mechanical phenomena (stiffness damage, inelasticity, peak-stress) are evaluated as potential indicators of progressive damage, correlated with SEM-observed microstructure cracking. Flax–epoxy specimens have superior resistance to stiffness loss, lower inelastic strains , and withstand higher stresses per-unit-density, when compared to similar Glass-specimens. Flax remains a promising alternative to Glass for mechanical reinforcement against fatigue degradation in engineering structures.

Fatigue Life Prediction of Machined Specimens with the Consideration of Surface Roughness.

The fatigue strength and fatigue life of high-strength steels are greatly affected by their surface roughness. This study investigates the underlying mechanisms responsible for fatigue failure of the high-strength steel 42CrMo. Bending fatigue tests of stepped shafts with different levels of surface roughness were conducted to observe the fatigue live reduction affected by surface topography. Besides, the mechanical properties of 42CrMo and its strain–life relationship were established. Moreover, the analytical formulas to describe the stress concentration factor (SCF) and fatigue notch factor (FNF) induced by surface topography were introduced. To estimate the fatigue life of machined specimens with the consideration of surface roughness, the elastic portion of the total strain–life curve of the material was revised with the proposed analytical FNF imposed by surface topography. Comparisons between the estimated fatigue lives and experimentally obtained fatigue lives show that the effect of surface roughness on fatigue lives could be estimated effectively and conveniently by the proposed procedure.

Superior low-cycle fatigue performance of iron-based SMA for seismic damping application

This study reveals the superior low-cycle fatigue performance of iron-based shape memory alloy (Fe-SMA) for seismic damping application, catering to the need for more durable, resilient, and perhaps fatigue-free structural systems in seismic active regions. The study commences with material tests examining both the macroscopic and microscopic properties of Fe-SMA under monotonic and cyclic loading, followed by calibration of combined hardening parameters to facilitate numerical modelling. A Fe-SMA shear damper specimen is tested, and its behavior is compared with its mild steel counterpart. Among other findings, the study revealed good ductility of Fe-SMA with a fracture strain of up to 55% under monotonic loading. The fatigue life of Fe-SMA is from 4007 to 83 when the strain amplitude increases from ±1% to ±9%, and the values could be 10 times that of common structural steel. The cyclic strain-life relationships of Fe-SMA can be readily presented by the conventional Basquin-Coffin-Manson relationship. Both kinematic and isotropic hardening characteristics of Fe-SMA are observed, and a combined kinematic/isotropic hardening model with calibrated parameters is shown to adequately capture the hysteretic behavior of the material. The subsequent damper tests provide further evidence of its superior fatigue performance, where a fatigue life of 173 cycles is observed for the Fe-SMA damper under a constant rotational angle of 4%, in contrast to 16 cycles for its normal steel counterpart. The unique phase transformation characteristic of Fe-SMA could also affect the fatigue failure mode, where different crack patterns are observed for the dampers with the different materials.

A Nonstationary Uncertainty Model and Bayesian Calibration of Strain-Life Models

Abstract The Coffin–Manson–Basquin–Haford (CMBH) model is a well-accepted strain-life relationship to model fatigue life as a function of applied strain. In this paper, we propose a nonstationary uncertainty model for the CMBH model, alongside a Bayesian framework for model calibration and estimation of confidence and prediction intervals. Using Inconel 617 coupon test data, we compared our approach to traditional stationary variance models. The proposed uncertainty model successfully captures the fact that the variance of strain amplitude decreases with increasing fatigue life. Additionally, a discussion on how to use the proposed Bayesian framework to compensate for the lack of data by using prior information coming from similar alloys is also presented considering Hastealloy-X and Inconel 617 coupon data.

On the Microstructure of Laser Beam Powder Bed Fusion Alloy 718 and Its Influence on the Low Cycle Fatigue Behaviour.

Additive manufacturing of Alloy 718 has become a popular subject of research in recent years. Understanding the process-microstructure-property relationship of additively manufactured Alloy 718 is crucial for maturing the technology to manufacture critical components. Fatigue behaviour is a key mechanical property that is required in applications such as gas turbines. Therefore, in the present work, low cycle fatigue behaviour of Alloy 718 manufactured by laser beam powder bed fusion process has been investigated. The material was tested in as-built condition as well as after two different thermal post-treatments. Three orientations with respect to the building direction were tested to evaluate the anisotropy. Testing was performed at room temperature under controlled amplitudes of strain. It was found that defects, inclusions, strengthening precipitates, and Young’s modulus influence the fatigue behaviour under strain-controlled conditions. The strengthening precipitates affected the deformation mechanism as well as the cycle-dependent hardening/softening behaviour. The defects and the inclusions had a detrimental effect on fatigue life. The presence of Laves phase in LB-PBF Alloy 718 did not have a detrimental effect on fatigue life. Young’s modulus was anisotropic and it contributed to the anisotropy in strain-life relationship. Pseudo-elastic stress vs. fatigue life approach could be used to handle the modulus-induced anisotropy in the strain-life relationship.

Strain life analysis of the first wall mock up under ITER-relevant heat flux conditions

Abstract The ITER first wall (FW) panels consist of plasma facing Be tiles, the CuCrZr alloy heat sink, and the stainless steel structural material. A copper layer of 1−2 mm is used between the Be tile and the CuCrZr for stress compensation. The results of cyclic high heat flux (HHF) tests employing an electron beam facility indicate that the failure/weak spot usually occurs at the joint corners between the Be tile and the copper layer. 3-D FEM (finite element method) thermo-mechanical analysis utilizing ANSYS software has been conducted to simulate the performance of a FW mock up (MU) under cyclic HHF test. The elastoplastic analysis results indicate that the copper layer is most sensitive to plastic deformation, and eventually the most risky location for failures. With the ANSYS strain-life fatigue module, based on the strain-life relation of copper from the ITER handbook, the fatigue life of the MU was predicted via FEM simulation. The results show that, when loaded with 2 MW/m², the small scale MU and the semi-prototype MU have a predicted life time of 12,220 cycles and 10,834 cycles, respectively. Although the shortest life time is located at the upper surface of copper which is joined to the Be tile, the major part of the copper has a life time of the same scale, which lies in the range of 10000–30000 cycles. When loaded with 2.5 MW/m², the life times of the MUs are 7432 cycles and 7343 cycles, respectively.

High-Strain Low-Cycle Fatigue Behavior of Thermomechanically Treated Rebar

Low-cycle fatigue (LCF) behavior of a thermomechanically treated Fe 500 grade rebar has been evaluated under high-strain ranges to understand its seismic performance. The total strain-controlled LCF tests have been performed at five different strain (1.0, 2.0, 3.0, 4.0 and 5.0%) ranges at ambient temperature until failure maintaining a constant true strain rate of 1 × 10−3 s−1 and a fixed strain ratio of − 1. Fatigue data have been analyzed following strain-life relationship; while, macro- and micro-features of the failed specimens have been critically examined under SEM. Evaluation of fatigue behavior has been supplemented by microstructural characterization apart from measurements of hardness and tensile property. Continued cyclic softening has been observed till failure, and the cyclic yield strength is found to be significantly lower than the monotonic one. Cross-sectional microhardness measurements of rebar before and after fatigue reveals significant reduction in hardness specifically in the rim region with tempered martensite microstructure. The strain-life relationship accurately predicts the cyclic plastic behavior of the selected rebar which also exhibits non-Masing behavior. The fatigue crack is always found to initiate from the transverse rib root and propagates along the rim region following the rib.

A fatigue damage evaluation using local damage parameters for an offshore structure

The fatigue design of offshore structures normally uses wave and wind fatigue loading. Currently, fatigue analyses for fatigue damage accumulation assessments of this type of structure are based on signal–noise (S–N) curves for welded structural components, the hot-spot stress approach and the Palmgren–Miner law – according to design codes. Fatigue analyses in design codes and/or recommended practices are supported by global structural analysis. In this paper, a global–local fatigue methodology applied to an offshore jacket-type platform using a local approach through the notch strain damage parameter is proposed. The local approach is based on Neuber's rule combined with the Ramberg–Osgood description. Then, the Coffin–Manson strain–life relation together with the Palmgren–Miner linear damage rule are used to evaluate the fatigue damage accumulation for the critical tubular welded joint. For application of Neuber's rule, the stress concentration factor values are calculated, according to Efthymiou's analytical equations, for the connection under consideration. The proposed methodology is compared with the simplified fatigue analysis presented in the Det Norske Veritas (Norway) and Germanischer Lloyd (Germany) DNVGL-RP-C203 recommendations. These analyses were performed using wave loads from the scatter diagram collected in the North Sea, which were computed through the fifth-order Stokes wave theory and the Morrison formula.

Low and ultra-low-cycle fatigue behavior of X52 piping steel based on theory of critical distances

The cyclic failure observed in structural components such as pipelines subjected to extreme loading conditions highlights some limitations concerning the application of existing fatigue damage models. The evaluation and prediction of this type of failure in these steel components under large-scale plastic yielding associated with high levels of stress triaxiality are not sufficiently known nor explored. This fatigue domain is conventionally called ultra-low-cycle fatigue (ULCF) and damage features are representative of both low-cycle fatigue (LCF) and monotonic ductile fracture. Thus, in order to understand the ULCF damage mechanisms both monotonic and LCF tests are required to get representative bounding damage information to model the material damage behaviour under such extreme loading conditions. This paper aims at exploring the Theory of Critical Distances (TCD) in the LCF and ULCF fatigue regimes, including the application of the point, line and area methods. The application of the TCD theories has not been explored so far in the ULCF fatigue regimes, despite its promising results in the LCF and high-cycle fatigue. An experimental program was carried out on several specimens’ geometries made of X52 piping steel. In detail, smooth plane specimens and notched plane specimens were cyclic loaded under tension/compression loading in order to obtain fatigue lives within the range of 101–104 cycles. In addition, cyclic bending tests on notched plane specimens were also incorporated in this study. Finite element simulations of all small-scale tests were conducted allowing to derive elastoplastic stress/strain fields along the potential crack paths. The numerical data were subjected to a post-processing in order to find characteristic lengths that can be treated as a fatigue property according to the TCD. A unified strain-life relation is proposed for the X52 piping steel together with a characteristic material length, consisting of a practical relation for pipeline strain-based design under extreme cyclic loading conditions.

Low cycle fatigue, deformation and fracture behaviour of Inconel 617 alloy

Inconel 617 alloy is one of the potential materials for high temperature applications such as steam generator super heater, re-heater parts and intermediate heat exchangers in gas cooled reactors. In the present study, low cycle fatigue tests were performed on solution annealed Inconel 617 alloy at room temperature and 750 °C in air, under fully reversed axial strain controlled mode at constant strain rate of 5x10−3s−1 to determine the influence of temperature on low cycle fatigue (LCF), deformation and fracture behaviour. Symmetrical triangular wave form and total strain amplitude ranging from ±0.20% to ±0.50% were used at the two temperatures to study fatigue behaviour. The cyclic stress responses and strain life relations were analysed at these temperatures. While there was continuous cyclic hardening at room temperature at lower strain amplitudes (±0.20% and ±0.25%), cyclic softening was observed after initial cyclic hardening for 100 cycles at higher strain amplitudes (±0.42% and ±0.50%) with a transition at ±0.375% strain amplitude. Continuous cyclic hardening was observed up to peak hardening at 750 °C irrespective of the strain amplitude. The number of cycles to fracture (fatigue life) decreased with increase in temperature. Number of cycles to peak hardening increased with decrease in strain amplitude at both the temperatures. The degree of cyclic hardening increased with increase in strain amplitude. Non-Masing behaviour is observed at both the temperatures. TEM studies revealed change in dislocation substructure and precipitation of carbides with increase in temperature and strain amplitude. SEM examination of the failed samples revealed increase in inter-striation spacing and also extensive branching of cracks at higher strain amplitudes with increase in temperature.

Stress-Based Model for Lifetime Estimation of Bond Wire Contacts Using Power Cycling Tests and Finite-Element Modeling

In this paper, a lifetime model for bond wire contacts of insulated gate bipolar transistors (IGBT) power modules is reported. This model is based on power cycling tests obtained under accelerated conditions, and a finite-element model taking into account the electrical, thermal, and mechanical coupling. It allows us to estimate the bond wire lifetime for a large scale of junction temperature swing amplitudes (ΔT <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">j</sub> ) and stress durations (t <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ON</sub> ). To build it, a numerical design of experiment was performed in both high and low stress values (ΔT <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">j</sub> ). Then, a strain-life curve has been constructed where the average strain values on a defined volume around the contact areas between top-metallization and the most exposed bond wires to fatigue and liftoff have been used. As a result, it has been shown that the total strain is linearly dependent with ΔT <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">j</sub> and power law dependent with t <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ON</sub> . The combination of the strain-life relation and the strain dependency with stress parameters leads to the lifetime relationship. The obtained lifetime model has been satisfactorily validated with some additional experimental points obtained from literature and with a large range of values for t <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ON</sub> . This methodology can be easily replicated to other structures and is quite generic.

Low and high cycle fatigue of automotive brake discs using coupled thermo-mechanical finite element analysis under thermal loading

To predict the thermal fatigue life and thermal stress phenomena of a brake disc, it is necessary to study the thermo-mechanical coupling effect in terms of braking conditions. Thermal fatigue stress of automotive brake discs was analyzed by using the coupled thermomechanical finite element (FE) simulation. The FE model was developed by considering the effect of conduction and convection heat transfer by frictional heat generation and film condition. Experimental boundary conditions of the brake dynamometer were applied to the simulation model. The structural stress due to the stress concentration effect on the bolt holes was also confirmed. The thermal fatigue life of the friction surface and the bolt holes was differently estimated depending on the influence of the stress amplitude. The strain-life relationship was used to predict thermal fatigue life in view of elastic and plastic deformation. The fatigue cycle ratio was also presented to calculate the fatigue life for different braking pressures.