Fatigue Lifetime Research Articles

Investigation of an automotive subsystem submitted to vibration loads considering scatter of influence parameters

Modern vehicles contain numerous subsystems for comfort, safety, electrification and autonomous driving functions that are mounted to the body-in-white structure. These subsystems are submitted to stochastic vibrational loads induced mainly by the road unevenness. The vibration fatigue behaviour of the subsystems and their connection to the body-in-white structure depend on a great number of influence parameters and associated uncertain scatter bands that are usually unknown and difficult to consider in the design process. This study investigates the oscillation behaviour and fatigue life of a current car component excited by vi-brational loads focusing on scatter of relevant influence parameters (mass, stiffness) on a pronounced statistical sample basis. An experimental modal analysis is used to determine eigenmodes and damping characteristics for the three variants: nominal value, increased mass and reduced stiffness. As a further experimental investigation vibration fatigue tests are performed. A probabilistic approach using a simulation tool chain with the aid of commercial computer aided engineering (CAE) programs is proposed to consider scatter effects on the fatigue life of the component submitted to vibration loads and its connection to the body-in-white structure. The simulation fidelity when using uncertain broader scatter bounds is compared to simulation fidelity using both measured data and modal analysis output. Furthermore, correlations between the vibration behaviour and the fatigue of the component are derived. Finally, the hardware fatigue tests results are compared to the simulation results. A very good agreement for eigen-modes, frequency response functions and fatigue lifetime was observed between simulation model and experimental findings. A significant accuracy improvement of the fatigue life simulation using the introduced probabilistic simulation method considering measured scatter bounds for uncertain input parameters is presented.

Fatigue assessment of steel tube-to-flange welded joints with reinforcement ribs subjected to multiaxial loads according to the Peak Stress Method

In fatigue design of welded structures, the Peak Stress Method (PSM) is a FE-oriented tool to estimate the Notch Stress Intensity Factors (NSIFs). In compliance with proper fatigue design curves validated against more than 1300 experimental data, the PSM allows to estimate the fatigue lifetime of welded structures made of either aluminium alloys or structural steels and subjected to uniaxial and multiaxial loadings. Moreover, an interactive analysis tool has also been developed in Ansys® Mechanical to automate PSM application on welded structures and support the FE analyst. In this work, the fatigue strength of complex steel tube-to-flange welded joints with reinforcement ribs has been experimentally investigated under pure bending, pure torsion and in-phase as well as out-of-phase combined bending-torsion loadings. The tested joint consists of a steel SHS tube having 6.3 mm thickness, which is joined at both ends to a 15-mm-thick flange. In addition, tube and flanges are joined by fillet welding to 6-mm-thick steel reinforcement ribs. A test rig has been designed in order to perform the experimental fatigue tests, taking advantage of two hydraulic actuators. The experimental fatigue results have been compared with fatigue lifetime estimations performed using the automated PSM tool.

Fatigue Analysis of Steering Knuckles Using the Local Strain Approach

The study investigates the mechanical properties and fatigue behavior of steering knuckles used on commercial vehicles. The steering knuckle is made of hot forged bainitic steel (18MnCrMoV6-4-8), which is known to demonstrate high levels of fatigue strength, toughness, and hardness. The local strain concept was adopted to assess the durability of the steering knuckle based on the stabilized cyclic material behavior. For this purpose, experimental investigations have been conducted on both the steering knuckle as well as fatigue specimens under constant and variable amplitude loadings. The fatigue specimens were removed from the area next to the crack initiation location, to represent the microstructure in the critical area of the component. Fatigue life estimations were performed under different load ratios using the FKM guideline nonlinear, employing damage parameters PRAM and PRAJ. The assessment enables a fatigue strength assessment for the steering knuckle by considering the local non-linear material behavior. The estimations of the material's fatigue lifetime using the FKM guideline nonlinear approach were unsatisfactory.

EFFECTS OF POROSITY ON THE STRENGTH AND MECHANICAL BEHAVIOUR OF POROUS GEO-MATERIALS UNDER CYCLIC LOADING

Most rocks in nature are porous and usually saturated with different fluids such as water, oil, and gas. The conventional and unconventional hydrocarbon reservoirs are mainly associated with sedimentary formations. The main rocks of these reservoirs are sandstone (porous rock), limestone and oil shale (tight rock), which are associated with varying porosity. Hence, porosity serves as a fundamental parameter for most reservoir rocks. In this research, the effect of porosity on the mechanical behaviour of geo-materials and its fatigue behaviour was investigated. For this purpose, a total of five geo-material sample groups with varying porosities were prepared and designated, i.e. groups A, B, C, D, and E. Group A exhibited the highest porosity 20-21.5%, while group E had the lowest porosity 2-3%, respectively. The conventional quasi-static strength tests and cycle loading tests with constant frequency and amplitude were performed on the samples and different results were obtained. The samples belonging to group E, with the lowest porosity (2-3%), exhibited the highest mechanical strength, elastic modulus and fracture toughness values and the lowest Poisson's ratio compared to those of higher porosity samples. During the cyclic loading period, the fatigue stress-life graph of the E group has the lowest slope compared to the other groups. It means that the slope of the graph increases as the porosity increases in all groups. Therefore, the E group has the lowest porosity and the longest fatigue life time, i.e. porosity and fatigue resistance have an inverse correlation.

Stress-Strain Response and Fatigue Lifetime of EEQ-111 Superalloy in Cyclic Loading at High Temperatures

The material under investigation was polycrystalline Sulzer's nickel-based superalloy EEQ-111 which is equivalent to the original GTD-111 developed in the late 1970s. The EEQ-111 superalloy is typical with coarse polyhedral dendritic grains with an average grain size of (2.48 ± 0.87) mm. The microstructure consists of γ channels, a bimodal distribution of nano-sized coherent γ´ precipitates, γ/γ´ eutectic, and MC and M23C6 carbides. The proportion of casting defects in the material is minimal due to the application of hot isostatic pressing. Low cycle fatigue experiments were executed on solid cylindrical specimens with a gauge length and diameter of 15 mm and 6 mm, respectively. A symmetrical push-pull cycling under strain control mode was utilized at 800°C and 900°C using servo-hydraulic testing machine MTS 810. Hysteresis loops, fatigue hardening/softening curves, and fatigue lifetime curves in Coffin-Manson, Basquin, and total strain amplitude representations were obtained. Analysis of fracture surfaces and secondary cracks from metallographic sections revealed the preferential initiation sites of fatigue cracks that are independent of temperature. In contrast, the fatigue crack propagation is purely transgranular at 800°C, whereas a mix of transgranular and intergranular crack propagation can be found at 900°C indicating grain boundary weakening.

Fatigue lifetime assessment and crack propagation of Ni-based VDM Alloy 699 XA produced by additive manufacturing

The present work focuses on the low-cycle fatigue (LCF) behavior of conventionally and additively manufactured (laser powder bed fusion (LPBF) technique, Ni-based VDM Alloy 699 XA. LCF tests were performed on miniature cylindrical specimens in a symmetrical push-pull cycle under strain control with a constant total strain amplitude at 23°C. Cyclic hardening/softening curves, cyclic stress-strain curves, and fatigue life curves were obtained. Despite the present manufacturing defects associated with the LPBF technology, the fatigue lifetime of the LPBF manufactured material is higher than that of conventionally prepared material. Fatigue crack initiation sites and fatigue crack propagation areas were investigated by means of scanning electron microscopy (SEM). A quantitative fractography of fracture surfaces was introduced to provide a detailed description of fatigue crack growth from the evaluation of striation spacing. The dependency of the stress intensity factor range on macroscopic crack growth rates was displayed in the form of the Paris Law. The differences in fatigue lifetimes and fatigue crack growth rates of additively manufactured and hot rolled solution annealed alloy 699 XA plate material were discussed and correlated with respect to the microstructural specifics of both material batches.

Effect of Training Data Ratio and Normalizing on Fatigue Lifetime Prediction of Aluminum Alloys with Machine Learning

Effect of Training Data Ratio and Normalizing on Fatigue Lifetime Prediction of Aluminum Alloys with Machine Learning

The influence of CFRP fatigue behavior on CFRP-to-steel bonded joints

The application of externally bonded CFRP reinforcements has shown its effectiveness in reducing crack growth in steel elements. However, externally bonded CFRP-to-steel joints may exhibit fatigue degradation when subjected to repeated cyclic loadings, consequently leading to cohesive debonding within the adhesive layer. Therefore, the cyclic degradation of both adhesive and the composite needs to be properly investigated.This work presents the preliminary results of an experimental and numerical investigation on the fatigue damage behavior of CFRP and its possible influence on the load response of CFRP-to-steel bonded joint. The overall fatigue degradation of the joint under single-lap direct shear (DS) conditions is numerically modelled considering separately the damage occurring in the adhesive layer and in the composite patch. The behavior of the adhesively bonded joint is described through a cohesive zone model approach, while the composite damage behavior is described by adopting a fatigue residual stiffness model based on macroscopic stiffness degradation. Experimental results of tensile fatigue tests on rectangular CFRP coupons and of cyclic single-lap direct shear tests are presented and used for the model parameters calibration. Then, the numerical response of DS tests obtained considering the composite material either elastic or accounting for the fatigue damage is compared. The interfacial behavior maintains its role as leading failure mechanism. The introduction of the composite damage behavior shows up in a reduction of the number of cycles at failure, especially for longer fatigue lifetime, while the relative slip between the two adherends is not or slightly affected.

Evaluation of stress-controlled high-cycle fatigue characteristics in PLA-wood fused deposition modeling 3D-printed parts under bending loads.

PLA (Poly-lactic acid)-wood provides more biodegradability through natural fibers, a significant advantage of pure PLA. Nevertheless, these bio-composites may have inferior mechanical properties compared to non-degradable polymer composites, considering the lower strength of natural particles compared to synthetic fibers. This research examines the fatigue behavior of additive-manufactured biopolymer PLA-wood and assesses its comparability with pure PLA. Therefore, solid fatigue test samples were printed using the FDM (fused deposition modeling) method. Afterward, fully reversed rotary bending fatigue experiments were performed at 4 different stress levels (7.5 to 15 MPa) to extract the S-N curve of PLA-wood. Moreover, the fatigue fracture surfaces of the PLA-wood were investigated and compared at the highest and lowest stress levels using an FE-SEM (Field Emission Scanning Electron Microscopy), indicating more ductile fracture marks at higher stress levels. The fatigue lifetime of the PLA-wood decreased by 87.48% at the highest stress level (15 MPa), rather than the result at the lowest stress level (7.5 MPa). Additionally, the results demonstrated that the fatigue characteristics of the printed pure PLA and PLA-wood were comparable, suggesting that the 3D-printed PLA-wood with the used printing parameters can be an alternative choice.

Critical Plane Methodology for Intelligent Prediction of Fretting Fatigue Lifetime Based on Shear Strain Dynamics

Critical Plane Methodology for Intelligent Prediction of Fretting Fatigue Lifetime Based on Shear Strain Dynamics

Solder Joint Geometry Effects on Thermomechanical Fatigue Lifetime of End-Capped Chip Component Assemblies

Solder Joint Geometry Effects on Thermomechanical Fatigue Lifetime of End-Capped Chip Component Assemblies

Multiaxial fatigue on cableway installations components: use of the Dang Van criterion based on detail categories of EN 1993-1-9 standard.

In order to predict fatigue lifetime of cableway installations components, EN 1993-1-9 standard (Eurocode 3) is commonly used. However, EN 1993-1-9 is based on a major hypothesis : stress state has to be uniaxial. But for some components, this uniaxial hypothesis is not verified (for example : fixed grip of chairlift submitted to horizontal tightening stress and vertical load stress, or chairlift structure stressed by gravity and lateral shake when passing a tower). It then appears important to use a fatigue criterion taking into account multiaxial stress state. Our research work proposes to apply for fatigue study the Dang Van criterion, which takes into account multiaxial stress state. Results are then compared to Eurocode SN curves, representing a huge experimental database on unixaxial fatigue, that we propose to use in multiaxial fatigue thanks to an appropriate recalibration. The scientific originality of this work lies in the justification of that Dang Van criterion's recalibration. Therefore, a theorical study ensures that our use of Dang Van's multiaxial criterion is still consistant with the Eurocode SN curve even if these SN curves are experimentally performed under uniaxial stress state. Finally, that hitherto unpublished use of the Dang Van criterion makes it possible to consider the entire database of detail categories defined in NF EN 1993-1-9, by generalising their use for components under multiaxial fatigue.

Modeling of fatigue behavior in pre-corroded AZ31 magnesium alloy

In this paper, the mechanical and fatigue behavior of pre-corroded wrought AZ31 magnesium alloy was studied. For this purpose, the standard 3.5 wt.% NaCl corrosive solution was used. The samples were immersed for 3–24 h to characterize the effect of immersion time on the mechanical properties of AZ31 alloy. Standard specimens were also immersed for 1–3 h for the fatigue testing. Results of tensile tests showed that thorough the immersion of 0–24 h, the deviation of ultimate tensile stress and yield stress were less than 4 % and 6 %, respectively. Moreover, the deviation of elastic modulus was less than 20 %. Although, the elongation was deviated by 81 % through the immersion of 0–24 h. A drastic decrease was observed in the fatigue lifetime of pre-corroded alloy compared to the bare alloy. As the immersion time increased, the fatigue lifetime decreased. Maximum reduction in fatigue strength occurred when the immersion time was 3 h and the stress amplitude was 82.5 MPa. Fatigue results also showed that the Levenberg-Marquardt was a good method to find the materials' constants, as the maximum and average relative errors were 10.28 % and 2.78 %, respectively. The fatigue fracture surfaces of pre-corroded specimens indicated the brittle fracture. The Basquin model was used for fatigue lifetime prediction. A new model was proposed with a new parameter, initial virtual crack size, to relate the immersion time to the fatigue lifetime using the Paris equation. The fatigue lifetime of 1–3-h pre-corroded AZ31 magnesium alloy was estimated by the new model with acceptable relative errors.

Ultrasonic fatigue of unfilled and carbon nanotube (CNT) reinforced polyetheretherketone (PEEK)

Fatigue properties of polyetheretherketone (PEEK) and multiwall carbon nanotube (CNT) reinforced PEEK were investigated with the ultrasonic fatigue testing method. Lifetimes were measured in the high and very high cycle fatigue regime at resonance frequency 19 kHz and load ratio R = -1. Pulse-pause loading served to avoid specimen self-heating and led to effective cycling frequencies in the range from several hundred Hz to about two kHz. Stress amplitude for 50 % fracture probability at 109 cycles is 21.2 ± 4.3 MPa for unreinforced PEEK (22 % of its tensile strength) and 33.5 ± 3.5 MPa for CNT reinforced PEEK (33 % of its tensile strength). Servohydraulic fatigue tests at 22 Hz with CNT reinforced PEEK delivered fatigue lifetimes comparable to ultrasonic tests, i.e. no frequency effect and no influence of load versus displacement control was observed. Keeping specimen temperature far below the glass transition temperature, ultrasonic fatigue testing of a high temperature resistant plastic was successfully implemented.

Durability of CFRP strengthened RC beam after six years exposure to natural hygrothermal environment with sustained loads

Exploring the durability of Carbon Fiber Reinforced Plastic (CFRP) strengthened concrete structures is a significant focus in the field of civil engineering. The majority of the present durability studies, which investigate the combined effects of external and environmental loading on CFRP-strengthened concrete structures, are conducted in accelerated aging environments. Nevertheless, this method fails to accurately reflect the real service conditions experienced by these structures in natural hygrothermal environments. In this study, a 6-year-long natural exposure experiment is conducted on CFRP-strengthened reinforced concrete (RC) beams under sustained loads. Additionally, the static and fatigue behavior of the exposed beam is investigated through both experimental and theoretical methods. The results indicated that the ultimate load of CFRP-strengthened RC beam remained unchanged after 6 years of natural exposure, as compared to that of non-exposed beams. However, noticeable changes were observed in their fatigue performance. The fatigue life decreased by 30 %, 75 %, and 86 % at loading levels of 0.60, 0.65, and 0.72, respectively. The fatigue limit decreased by 10 % and exhibited a dense distribution of cracks. Meanwhile, a fatigue life prediction model for RC structures strengthened with CFRP after long-term exposure to natural hygrothermal environment was established. In this model, the degradation of the CFRP-concrete interface behavior was considered. Through finite element analysis, two failure modes were predicted: fracture of the main reinforcement and the CFRP-concrete interface debonding failure under fatigue load. The corresponding fatigue life times were calculated. This model agrees well with the experimental findings.

Fatigue crack driving force of railway bogie frames using rigid-flexible coupled dynamics: A case for beam model

The stress intensity factor is essential to determine the residual fatigue lifetime of cracked components. However, the traditional method used to determine the stress intensity factor is very difficult to characterize the dynamic behaviors of structure arising from the fatigue crack. This paper proposed a methodology to determine the dynamic stress intensity factor (DSIF) of a crack incorporating with the rigid-flexible coupled dynamics. Firstly, a rigid-flexible coupled dynamic model of cantilever beam representing the typical structure of bogie frame with a straight crack was developed based on SIMPACK platform. In the model, the equivalent spring - contact element was employed to model the contact behaviors of crack interface. Subsequently, the DSIF considering the crack closure effect was calculated by the node displacement extrapolation. The validity of proposed method was demonstrated through comparing the DSIF with those obtained by other analytical methods. The results suggest that the proposed methodology can characterize the closure effect of crack, and yield more accurate estimation for the DSIF. This method establishes a link between the multibody system dynamics and the fracture mechanics, which enable us to calculate the DSIF of crack under the operating condition using a rigid-flexible coupled dynamic model.

In-Situ Fatigue Lifetime Modeling of a Reinforced Membrane by Projecting Critical Accumulated Plastic Dissipation Energy from Pressure Differential-Accelerated Mechanical Stress Tests

Polymer electrolyte fuel cells (PEFCs) have become increasingly appealing over internal combustion engines because of their high efficiency, low operating temperature, and zero CO2 emissions. Nevertheless, the transportation sector necessitates high durability and reliability, which may be difficult to predict for emerging technologies. A crucial aspect is the ability of the thin membranes that conduct ions in PEFCs to endure the chemical and mechanical stresses that arise during dynamic operations. For mechanical fatigue, temperature and relative humidity (RH) fluctuations induce dynamic stresses that lead to the formation and propagation of microcracks in the membrane. As the membrane is confined by other components in the membrane-electrode assembly (MEA), changes in temperature and humidity can generate thermal and swelling strains in the membrane, leading to dynamic and residual stresses [1].The US Department of Energy sets a passing criterion of 20,000 RH cycles for mechanical fatigue assessment. However, many modern reinforced membranes have already passed this threshold without failing [2]. Therefore, Ref [3] introduced a pressure differential between the cathode and anode sides of the membrane at 80°C to speed up the testing. In this research, the pressure differential-accelerated mechanical stress test (ΔP-AMST) method was applied to a reinforced membrane at two different temperatures and with four times faster humidity cycles in a wider range of ΔPs. This objective is to project the mechanical fatigue lifetime from the ΔP-AMST to the membrane under its in-situ conditions by using the critical accumulated plastic dissipation energy (CAPDE) in ΔP-AMSTs and the plastic dissipation energy (PDE) during a single cycle of humidity that the membrane experiences under complete fuel cell settings. The first step involves performing a series of ∆P-AMST, and in the second step, a finite element model (FEM) for ∆P-AMST based on the developed constitutive model for the tensile tests that covers temperature, humidity, and swelling strain impacts is built, and therefore its S-N curve is extracted. Next, a FEM model for a complete fuel cell is created, and the mechanical fatigue life is estimated by dividing the CAPDE in ∆P-AMST by the PDE in one cycle of the in-situ modeled membrane by considering amplitude stress as a link between the full fuel cell model and ∆P-AMST, as illustrated in Figure 1 and verified by previous studies [4,5]. In the final step, we will also discuss opportunities to integrate the present mechanical fatigue model with a chemical degradation module to simulate its impacts on fatigue lifetime. This integration includes the two main effects of chemical degradation, which are reflected in the thickness of the reinforced membrane [6] and its updated CAPDE [7]. Acknowledgments The authors gratefully acknowledge AVL Fuel Cell Canada and Mitacs for supporting this project. The authors also thank Roger Penn and Amy Nelson for technical advice.

High Durability of Pemion® Proton Exchange Membranes in Cross-Pressure Accelerated Mechanical Stress Tests

Polymer electrolyte membrane fuel cells (PEMFC) are the dominant technology for hydrogen-powered fuel cell electric vehicles in clean transportation systems. To be suitable for commercialization and applicability in real-world use-cases, light and heavy-duty fuel cell vehicles require lifetimes of over 8,000 and 30,000 hours, respectively [1]. Hence, enhancing the durability of all fuel cell components, particularly the proton exchange membrane (PEM), is of great importance.Recently, fuel cell membranes based on hydrocarbon (HC) chemistries have become increasingly common in the literature [2]. Materials with polyaromatic backbones, tunable electrochemical properties, and low reactant permeability are increasingly seen as potential alternatives to incumbent perfluorosulfonic acid (PFSA) materials [2]. Additionally, as restrictions on the use of fluorinated materials in various industries continue to grow, the importance of HC chemistries will as well. Sulfo-phenylated polyphenylenes (sPPPs) are a particular class of HC materials that show promise [3]. However, the phase separation between hydrophilic and hydrophobic domains within sPPPs may not be as discrete as in PFSAs [3], requiring higher ion exchange capacity (IEC) values than PFSAs to achieve similar protonic conductivity. High IEC typically results in greater material hydrophilicity, which can render membranes dimensionally unstable in a fuel cell [4].State-of-the-art commercial PEMs are now manufactured as thin films (≤ 18 µm), offering small ohmic loss and therefore high fuel cell performance. To improve dimensional stability and eliminate the risks of electrical shorting, PEMs are commonly mechanically reinforced using a porous, inert, and non-ionic substrate, such as expanded polytetrafluoroethylene (ePTFE). In a work by Miyake et al. [5], sulfonated polyphenylene-based ionomer membranes with flexible polyethylene mechanical reinforcement were prepared and the results indicated promising mechanical properties and improved longevity in RH cycling tests. However, there is still a lack of data about the fatigue durability of HC membranes in the literature, and evaluating and comparing the mechanical durability of numerous PEMs with a mechanical reinforcement layer in a traditional wet-dry cycling accelerated stress test would be a time-consuming and thus costly process [6].In our previous work, [7] we combined constant pressure differential across an ePTFE-reinforced perfluorosulfonic acid (PFSA) ionomer membrane with in-situ RH cycles (ΔP-AMST) to simulate the actual mechanical stresses in the fuel cell environment, while accelerating the durability testing for reinforced PEMs. In this study, ΔP-AMST is used to benchmark the fatigue lifetime curves for Pemion® membranes and compare it with a commercial reinforced PFSA-based PEM. The test temperature was set to 90 °C, and dry and wet (90% RH) phases were 60s and 30s, respectively. The hardware and semi-MEA specifications used for the test are shown in Figure 1a-c. A semitransparent polycarbonate spacer plate with 20 mm thickness and a circular aperture (25.4 mm) in the middle was used to allow free expansion of the membrane (Figure 1d). The cathode side was pressurized to create a cross pressure between the two sides and intensify the stress on the membrane during the RH cycling process. The ultimate failure of the membrane is shown in Figure 1e. The radial stress at the center of the deformed membrane is estimated by Hencky’s solution, as reported in our previous work [7]. Figure 1f demonstrates the estimated nominal stress on the membranes as a function of their lifetimes in terms of RH cycles. According to the fatigue S-N curves, reinforced Pemion® membranes afford longer lifetime than incumbent PFSA materials if the membrane edges are well protected. In addition, the impact of IEC on the fatigue durability of Pemion® membranes is investigated and the results are evaluated against stress of dehydration and dynamic mechanical analysis measurements. Acknowledgements This project was financially supported by Natural Sciences and Engineering Research Council of Canada (NSERC), Ionomr Innovations Inc, Canada Foundation for Innovation (CFI), British Columbia Knowledge Development Fund (BCKDF), Western Economic Diversification Canada (WD), and Canada Research Chairs (CRC).

The role of corrosion pit topography on stress concentration

Smooth semi-ellipsoids are typically used to simulate the effect of corrosion pits on stress, however, this does not account for pit geometry. Three corrosion pits were identified on Nickel Aluminium Bronze samples. These were scanned and converted to finite element models. The linear elastic stress concentration factor (Kt) of the corrosion pit FE models was 1.32–1.65 times larger than for an equivalent smooth semi-ellipsoid. This suggests that detailed consideration of pit geometry is needed to calculate accurate values of Kt and the assumption of a semi-ellipsoidal pit may not be conservative for fatigue lifetime predictions of pitted components.

Simulation of Proton Exchange Membrane Durability Under Fuel Cell Vehicle Operation – a Fundamental Study

Proton exchange membrane fuel cells (PEMFCs) have been proven to be a promising candidate to replace combustion engines due to their zero-carbon emission and high power densities. Despite the recent success in PEMFC commercialization, a number of challenges such as high cost and difficulty in lifetime estimation still hinder their further development. PEMFC durability tests require a long time to complete; therefore, durability predicting models are increasingly important as a supporting tool for further development and implementation.Fuel cell membranes undergo a variety of dynamic conditions during regular operation such as varying temperature, humidity, current density, and cell potential. The cyclic variations of humidity and temperature (hygrothermal variations) during dynamic operation lead to swelling and contraction of the membrane. The fluctuating stress caused by the continuous expansion and contraction of the membrane when confined within the cell leads to mechanical membrane degradation. The recurring swelling and contraction of the membrane which stem from water content changes in the membrane cause fatigue and creep and ultimately the formation of pinholes, cracks, and tears [1-2].Chemical membrane degradation occurs when radicals such as hydroxyl and hydroperoxyl are formed and attack the membrane and is escalated by high operating cell potentials. Chemical degradation results in decay in the ionomer chemical structure, membrane thinning, increased gas crossover, and potential electrode shorting [3]. The outcomes of such degradation are aggravated in the presence of mechanical degradation [4]. Hence, the study of combined chemo-mechanical membrane degradation is crucial for overall fuel cell membrane durability [5].The objective of the present work is to establish a predictive membrane lifetime simulation tool designed to represent chemo-mechanical membrane degradation under various operating conditions for automotive fuel cell applications. To this end, a statistical model is developed based on the membrane fibrillar morphology presented by El Hannach et al. [6-7]. A network of fibre bundles is generated to represent the membrane structure where any bundle is assumed as the primary building block of the membrane [8-10]. Each bundle contains an aggregate of backbone chains with typical mechanical and chemical properties. Mechanical and chemical degradation rates are separately studied and coupled in the model. The thermally activated breaking rate of each fibre is calculated to evaluate the mechanical degradation rate at any given time. In order to calibrate the mechanical degradation rate in the model, the mechanical degradation of a reinforced membrane under cross-pressure accelerated mechanical stress tests ( p-AMST) [11] is investigated to obtain the membrane fatigue lifetime for a variety of cross pressures and temperatures. Then, the genetic algorithm is successfully applied to optimize the experimental parameters considering the least squares method. Furthermore, accelerated membrane durability tests (AMDT) carried out by Macauley et al. [12] are considered to calibrate the chemical degradation rate parameter in the model. Finally, the fully calibrated model is used to estimate the membrane lifetime under realistic fuel cell vehicle operating conditions (e.g. drive cycles).Fuel cell components experience different degradation mechanisms. In this regard, this modelling framework on the membrane lifetime can be used in conjunction with other methodologies on the cathode catalyst lifetime such as [13-14] to scrutinize the key factors and their impacts on fuel cell durability under similar operating conditions. Acknowledgements This research was supported by the Natural Sciences and Engineering Research Council of Canada, Canada Research Chairs, and Simon Fraser University Community Trust Endowment Fund.