Simulation Of Fatigue Crack Growth Research Articles

Crack propagation simulation and overload fatigue life prediction via enhanced physics-informed neural networks

The fatigue crack growth simulation and life prediction of structures are implemented in this paper based on the physics-informed neural networks (PINNs). Firstly, the enhanced PINNs are proposed by introducing the crack tip asymptotic displacement fields, so that the crack tip stress intensity factors can be calculated accurately even when the number of collocation points is small and the distribution grid is regular. The enhanced PINNs essentially transform the solution of elastic body containing crack into the optimization of minimizing the constructed loss functions, and can invert the fracture parameters. Then, an automatic crack propagation simulation method is developed based on the enhanced PINNs. The network architecture and the overall node distribution can be unchanged during the crack propagation process, and only new crack surfaces need to be processed and corresponding loss functions need to be modified. Because the nodal refinement around crack-tip is not required, this simulation method is convenient and can accurately predict the mixed-mode crack propagation path. Finally, the fatigue crack growth life algorithm considering overload is developed, where the effect of each overload can be captured by the cycle-by-cycle method. Based on this algorithm, the retardation behavior can be characterized and the fatigue life of structure under the load spectrum with periodic overloads can be accurately predicted. The sufficient examples are given to verify the feasibility and accuracy of the method proposed in this paper.

Fatigue crack growth simulation by extended finite element method: A review of case studies

AbstractNumerical simulation of fatigue crack growth (FCG) is presented, based on the application of the extended finite element method (XFEM). Couple of case studies are presented, as a review of recent experience of the Belgrade school of XFEM simulations, established at the Faculty of Mechanical Engineering. Case studies comprised Charpy specimen with initial crack at the notch tip, oil rig pipe with an axial surface crack, pressure vessels with a crack at the welded joint with connecting pipe, turbine shaft with a crack at the transition radius, optimization of a wing spar in respect to FCG, the effect of mesh size on fatigue life estimation of a stringer panel, fatigue life estimation of wing‐to‐fuselage connecting lug, geometry effect on fatigue life of orthopedic plates and fatigue life of hip implant. Based on these case studies, XFEM is discussed in respect to its accuracy and efficiency. It is concluded that XFEM is a versatile tool for simulation of FCG, providing an excellent option for precise and reliable fatigue life of a cracked component.

A model for modifying the S‐N curve considering the effect of boundary conditions on the fatigue crack growth of welded components

AbstractThe present study proposes a novel model to modify master S‐N curves of components according to their load redistribution capability reflected in different boundary conditions (BCs) based on the fracture mechanics analysis. To that end, a comprehensive numerical study was conducted on a Single Edge Notch Bend (SENB) specimen constrained with different kinematic BCs using discrete fatigue crack growth (FCG) simulation. It was observed that BCs indeed can have a significant effect on the crack growth behavior and consequently on the resulting fatigue life under the same nominal loading conditions. The proposed model was applied to the S‐N curve of a T‐welded joint, and the predicted fatigue life was validated against 3D FCG simulations. Finally, FCG tests were conducted on SENB specimens to experimentally corroborate the effect of BCs on the FCG rate.

Support vector regression-assisted finite element method for mode I-II fatigue crack growth path prediction

Most of failures in mechanical components in engineering are caused by fatigue crack growth (FCG), especially mode I-II cracks. Accurately and fast predict of crack growth paths of mode I-II in structures is important in academic research and engineering applications. Finite element method (FEM) simulation of FCG can be accurately performed for engineering applications. However, the commercial FEM simulation software, e.g., ABAQUS combined with FRANC3D is generally time-consuming. Therefore, an accurately and fast mode I-II crack growth path prediction method is developed by support vector regression (SVR)-assisted FEM analysis. Firstly, the initial location data of FCG path and stress intensity factor (SIFs) are collected by FEM simulations. The SVR model is trained using initial location data and the corresponding FCG path will be predicted for several growth steps. Secondly, the predicted crack results are input into the FEM simulation model to obtain the several other growth steps. Finally, the two procedures are repeat alternately to obtain the full FCG path. The numerical case is given to validate the performance of the present method using the double-hole plates with mode I-II crack growths. Comparisons show that the performance of the present method are superior to those of FEM simulation and SVR alone.

Peridynamic simulation of fatigue crack growth in porous materials

Pores are a key type of concerns in additive manufacturing technology. They can significantly affect materials’ fatigue resistance and fatigue crack growth in the structures. In this paper, an intermediately-homogenized (IH) peridynamic (PD) fatigue crack model is introduced for simulating the fatigue crack growth in porous materials. The effect of micro-scale heterogeneity on fatigue failure is preserved in the IH-PD model, where stochastically-generated pre-damage matches materials’ porosity. The PD J-integral, a key parameter used to connect the fatigue simulation and the experimental measurements, is calculated under different porosities, and the independence of PD J-integral on its integration path is verified. Then, the PD fatigue crack model combined with the IH-PD material model is applied to study the dependence of the crack path and growth rate on porosity in compact tension alloy samples. The normalized fatigue life between experimental measurements and numerical results is compared. The normalized fatigue life-porosity relationship calculated from the IH-PD fatigue model matches the average trend of the experimental measurements.

A numerical framework based on localizing gradient damage methodology for high cycle fatigue crack growth simulations

A numerical framework based on localizing gradient damage methodology for high cycle fatigue crack growth simulations

Quasi-static and fatigue crack growth simulation in co-consolidated thermoplastic joints containing crack arrest features

In the present article, quasi-static and fatigue crack growth in co-consolidated thermoplastic Crack-Lap Shear (CLS) specimens containing two different Crack Arrest Features (CAFs) have been numerically simulated. The substrates have been manufactured from unidirectional T700 carbon fiber reinforced Low-Melt PAEK thermoplastic material. The Friction Stir Spot Welding (RFSSW) and the Induction Low Stir Friction Riveting (ILSFSR) CAFs were studied. Crack growth simulation has been based on the cohesive zone modeling method and has been implemented via the LS-Dyna FE software. Both static and fatigue crack growth models have been successfully validated against results from respective mechanical tests. Both CAFs have been proven capable of delaying crack growth, especially for fatigue loading. An evaluation of various installation parameters of the two features, such as the diameter, the distance to the crack tip, and the installation depth, was performed for the quasi-static loading cases. All parameters have been found to affect the crack stopping efficiency, but the most important effect comes from the diameter of the CAF. Furthermore, a series of quasi-static and fatigue simulations have been run on a mono-stiffener element, representative of an aeronautical structural assembly, in order to evaluate numerically the efficiency of the CAFs at a higher scale. The results showed no crack stopping for the ILSFSR and a low crack stopping for the RFSSW for fatigue loading.

Optimizing structural topology design through consideration of fatigue crack propagation

This paper presents an advanced approach for structural topology optimization by incorporating fatigue crack propagation analysis. The extended finite element method (X-FEM) is employed to model initial crack propagation, while the Paris model serves as the basis for simulating fatigue crack growth. The proposed methodology aims to optimize the structural design by minimizing compliance while considering volume and fatigue constraints. The proposed method employs the developed bi-directional evolutionary structural optimization (BESO) algorithm. The accuracy of the proposed technique is validated through the solution of benchmark problem and is further demonstrated in its effectiveness and robustness by examining several numerical examples. The optimization process considers various crack conditions, including the absence of cracks, horizontal and vertical cracks of different lengths. The optimized topologies obtained through the proposed algorithm clearly demonstrate the impact of crack presence, crack direction, and crack length on the material distribution. Furthermore, the convergence histories of the objective function, represented by mean compliance, highlight the influence of crack length on the stiffness and converged compliance of the structure. The results demonstrate its ability to adapt the material distribution based on fatigue cracks propagation conditions and achieve optimal topologies that balance structural integrity and performance.

Numerical simulation of fatigue crack growth in an engine heat shield

In order to prevent the body from overheating, a corresponding thermal protection device is usually designed on the inner wall of the combustion chamber. The working environment of this thermal protection device is very harsh, and it needs to withstand internal and external pressure loads and thermal radiation loads of the combustion chamber, especially at the connection between the cylinder and the support parts, the force is harsher. In order to avoid engine damage, causing unnecessary losses. In this article, the thermal–mechanical coupling analysis of the heat shield is carried out by finite element method to analyze the thermal stress and mechanical stress. According to the finite element simulation results, the initial cracks are inserted, respectively, at the stress concentration. Using linear elastic fracture mechanics and Forman–Newman–de Koning models, the crack growth lifetimes of cracks at different locations were calculated. The results of the study show that comparing the initial cracks at different locations, the cracks on the side near the edge of the heat shield have the largest reduction in crack growth life of 64.4% and the critical crack length of 52.0%. The linear superposition of thermal and mechanical stresses under different working conditions has different degrees of nonlinear effects on the crack growth life and critical crack length. The research work in this article can provide a basis for the evaluation of fatigue crack growth life of heat shield and can also provide a reference for engine maintenance.

An investigation into the influence of variable amplitude creep-fatigue loading on plasticity-induced crack closure

Finite element simulations of fatigue crack growth (FCG) and creep-fatigue crack growth (CFCG) under constant amplitude (CA) and variable amplitude (VA) loading waveforms are performed to investigate the mechanics of crack opening and closing, which has implications on crack growth rate. The material of study is the ferritic-martensitic steel 9Cr-1Mo (modified 9Cr-1Mo) at 625 °C. Two-dimensional finite element analyses of compact tension (CT) specimens are performed to simulate crack growth under several VA loading scenarios, considering elastic–plastic and creep deformations of the material at the crack tip. In this study, the relevant variable influencing crack growth rate is the crack opening load, caused by the phenomenon of plasticity-induced crack closure. A series of loading conditions were simulated using the finite element method, i.e., fatigue overload (OL) in either CA FCG or CFCG waveforms, creep-fatigue OL in CFCG waveforms, and underload (UL) in CFCG waveforms. The crack opening loads obtained from this study for CA loading in both FCG and CFCG, agree with data from published studies. This study also found that a significant reduction in crack opening loads is experienced by the growing crack when an OL or UL cycle was introduced. Immediately after the OL or UL cycle is applied, the crack opening load increases during both fatigue OL and creep-fatigue OL to values larger than those recorded during CA FCG and CFCG loading, whereas UL waveforms result in consistently lower crack opening loads. The increase in crack opening loads is proportional to both the extent of OL and the duration of hold time in the OL cycle. However, following the application of a UL, the crack opening loads in the subsequent cycles were not influenced by the magnitude of the UL or the duration of hold time in the UL cycle.

Assessment of Crack Growth and Fatigue Life of an Axial Fan Blade Based on a Co-Simulation Approach

Abstract This paper presents static and dynamic stress analyses of an axial fan blade, which were carried out under real-life centrifugal and aerodynamic loading conditions using the Abaqus software. The location of the crack was identified on the pressure side of the blade at the conjunction between the blade and the blade root. It reveals a high agreement between the predicted location of stress distribution and the real origin of the crack location. Furthermore, a fracture mechanics criterion was adopted to simulate fatigue crack growth. This was performed using a fracture analysis FRANC3D code for three-dimensional problems. As a result, the calculated stress intensity factors (SIFs) were presented for the first steps, and the fatigue life of the fan blade was evaluated using the Forman de Koning model at different stress ratios.

ProCrackPlast: a finite element tool to simulate 3D fatigue crack growth under large plastic deformations

Many structural components and devices in combustion and automotive engineering undergo highly intensive cyclic thermal and mechanical loading during their operation, which leads to low cycle (LCF) or thermomechanical (TMF) fatigue crack growth. This behavior is often characterized by large scale plastic deformations and creep around the crack, so that concepts of linear-elastic fracture mechanics fail. The finite element software ProCrackPlast has been developed at TU Bergakademie Freiberg for the automated simulation of fatigue crack growth in arbitrarily loaded three-dimensional components with large scale plastic deformations, in particular under cyclic thermomechanical loading. ProCrackPlast consists of a bundle of Python routines, which manage finite element pre-processing, crack analysis, and post-processing in combination with the commercial software Abaqus . ProCrackPlast is based on a crack growth procedure which adaptively updates the crack size in finite increments. Crack growth is controlled by the cyclic crack tip opening displacement varDelta CTOD, which is considered as the appropriate fracture-mechanical parameter in case of large scale yielding. The three-dimensional varDelta CTOD concept and its effective numerical calculation by means of special crack-tip elements are introduced at first. Next, the program structure, the underlying numerical algorithms and calculation schemes of ProCrackPlast are outlined in detail, which capture the plastic deformation history along with the moving crack. In all simulations, a viscoplastic cyclic material law is used within a large strain setting. The numerical performance of this software is studied for a single edge notch tension (SENT) specimen under isothermal cyclic loading and compared to common finite element techniques for fatigue crack simulation. The capability of this software is featured in two application examples showing crack growth under mixed-mode LCF and TMF in a typical austenite cast steel, Ni-Resist. In combination with a crack growth law identified in terms of varDelta CTOD for a specific material, the tool ProCrackPlast is able to predict the crack evolution in a 3D component for a given thermomechanical loading scenario.

Experimental and computational studies of load ratio effect on fatigue crack growth rates in Alloy 709 at elevated temperatures

AbstractExperimental testing and finite element simulations of fatigue crack growth were performed in austenitic 20Cr‐25Ni (Alloy 709) steel at different load ratios and elevated temperatures. The experimental tests were performed using compact tension specimens, and crack growth rates were measured at stress intensity factors ranging between 5 and 35 MPa√m. Fractographic analysis using scanning electron microscopy indicated crack surface roughness and secondary cracking depending on testing temperature and load ratio. Finite element simulations of fatigue crack growth were performed to compute plasticity‐induced crack opening loads and predict crack growth rates. Predictions of fatigue crack growth rates using finite element simulations were performed using the computed crack‐tip opening loads, and they are shown to match well the experimental measurements.

Experimental Evaluation of Fatigue Properties of Carbon Fiber/Epoxy Matrix Interface and Numerical Simulation of Transverse Cracking under Cyclic Load

This study aims to experimentally evaluate the relationships between the interfacial tensile stress applied to the carbon fiber/epoxy matrix and the number of applied loading cycles when interfacial debonding is initiated. Tension – tension fatigue tests of single carbon fiber embedded specimens were performed, and digital image correlation observations were conducted during the fatigue tests. Changes in the microscopic apparent strain distribution during fatigue tests were utilized to detect the initiation of fiber/matrix interfacial debonding. The results demonstrated that the fiber/matrix interfacial tensile strength degraded depending on cyclic loading. Fatigue crack growth simulation was also performed based on the finite element method considering the strength degradation of the fiber/matrix interface.

Fatigue failure analysis on the 2nd bulkhead beam of the Portuguese Air Force Epsilon TB-30 aircraft

Military aircraft perform demanding maneuvers with a wide range of load factor levels, allowing the growth of fatigue cracks that shall be duly monitored to prevent unexpected failures. In order to monitor the operation of the Portuguese Air Force Epsilon TB-30 fleet that performs basic and elementary piloting training, two systems were installed in these aircraft, allowing the recording of load factor data in the aircraft center of gravity and strain data in two critical locations.This study aims to evaluate and compare the growth of fatigue cracks on the 2nd bulkhead beam, one of the aircraft critical locations, through experimental tests and computational simulations. The methodology used in this work comprised the application of real flight load sequences to a 2024-T351 aluminum specimen that is representative of this critical location.Main results from these fatigue crack growth tests and simulations showed that NASGRO model is the one that comes closest to experimental data with maximum deviations of approximately 8%, presenting a deviation of 18% between the representative and real structures at the final rupture of the specimen. Additionally, experimental results provided knowledge about the component behavior regarding fatigue of materials, namely the evolution of the local strain as a function of the crack length.This study can be used by the Portuguese Air Force engineers to adjust the aircraft maintenance program according to the actual operation regime and consider a possible life extension of this fleet.

Fretting fatigue crack growth simulation and residual life assessment of railway press-fitted axle

To evaluate the inspection interval and safety margin of a railway press-fitted axle with fretting cracks, we conducted a fretting fatigue crack growth simulation and residual life assessment of a railway press-fitted axle by employing an actual load spectrum. The predicted results were compared with the measured crack to examine the effectiveness of various crack orientation criteria for assessing crack growth. Based on the validated crack orientation criteria, a finite element model was built to perform incremental fretting fatigue crack growth analysis. Then, the fretting fatigue crack growth life of the railway axle was predicted using two conventional crack growth rate models and compared with the experimental results. The results indicate that the max(ΔkI*) criterion provides a better approximation of the fretting fatigue crack growth path. The Paris equation can yield excessively conservative prediction life due to the strong load dependence of the effective stress ratio of fretting cracks, which can vary with the crack length and is influenced by press fitting. In contrast, the NASGRO equation yielded prediction results that were closer to the test results and can be utilised to determine the inspection interval. This study can serve as a vital reference for the operation and maintenance strategies for damaged axles with fretting cracks.

Fatigue crack propagation simulation of vertical centrifugal pump runner using the extended finite element method

The performance evaluation of fatigue crack propagation is essential for the safe and stable operation of power plants. In this study, the Walker equation is employed, considering the loading ratio effect. The parameters in the Walker equation for AISI 304 L are fitted by a normal probability distribution based on the experimental information . A numerical simulation of the fatigue crack growth is carried out using the extended finite element method with the Walker equation embended in, and verified on a round compact tension model with the loading ratios of R = 0.1, 0.5, and 0.85. Finally, a fatigue crack growth simulation of a vertical centrifugal pump-turbine runner under turbine conditions is conducted with two crack positions. The crack morphology can be captured together with the corresponding fatigue life by using the developed fatigue crack propagation simulation method based on the extended finite element method. The numerical results can be used as guidance for improving the maintenance plan of pump plants.

Numerical calculation of [formula omitted] to simulate fatigue crack growth under large scale viscoplastic deformations

Crack propagation under low cycle fatigue and thermomechanical fatigue is characterized by high plastic and creep strains that extend over large regions around the crack, so that concepts of linear-elastic fracture mechanics cannot be applied. In these cases, the cyclic crack tip opening displacement ΔCTOD is a promising loading parameter to quantify crack growth. In this work, suitable definitions and Finite Element techniques are investigated and compared for an accurate calculation of ΔCTOD under cyclic mechanical and/or thermal loading. A viscoplastic temperature dependent material model of Chaboche-type is used along with large strain settings, specified for the austenitic cast iron Ni-resist. Extensive two-dimensional analyses of Single Edge Notch Tension specimens revealed that collapsed special crack tip elements are superior compared with commonly used regular quadrilateral 8-node elements. At the same level of accuracy of ΔCTOD, they require an about ten times coarser mesh and show less sensitivity w.r.t. element size for both stationary and propagating cracks. In order to simulate fatigue crack growth, an efficient, fully automated FE-technique is developed for an incremental crack propagation by successive remeshing, whereby the deformations and internal state variables are mapped from the old mesh onto the new one. Recommendations are made regarding important numerical control parameters like optimal size of crack tip elements, length of crack growth increment in relation to plastic zone size and ΔCTOD value.

The onset of unstable fracture and crack deflection of AA7085 in mixed mode I + II loading

The current study focuses on the planar mixed mode fracture of AA7085. A loading device based on the concept given by Richard et al. has been developed for inducing planar mode-mixity in compact tension and shear (CTS) specimens. The CTS specimens extracted from the AA 7085 plate were subjected to mixed mode quasi-static loading after pre-cracking the specimens by fatigue loading under mode-I conditions. The desired pre-cracking length was achieved after performing an extended finite element method (XFEM) based fatigue crack growth simulation. Different mode-mixity has been introduced in the specimens by changing the orientation of the loading device with respect to the loading axis of the machine. Experimentally observed crack deflection was compared with the angles predicted by different planar mixed mode fracture criteria, namely MTS, Richards, and strain energy density. Equivalent stress intensity factors proposed at the onset of unstable fracture have been determined using different criteria and compared with each other. A new equivalent stress intensity factor for mixed mode has been proposed from Shah's equation of fracture locus. It has been found that the equivalent stress intensity factor based on Shah's equation of fracture locus is suitable for the alloy being investigated. The fracture morphology of the fractured specimen was inspected in a field emission scanning electron microscope. Both inter-granular and dimpled ductile fracture was observed in the specimens irrespective of the mode-mixity. Extended finite element simulation was performed to determine tangential stress distribution at a distance around the crack tip.

The influence of microstructure on short fatigue crack growth rates in Zircaloy-4: Crystal plasticity modelling and experiment

Rates of fatigue crack growth in Zircaloy-4 are highly microstructurally sensitive and dependent upon texture. Crystal plasticity finite element modelling with the eXtended Finite Element Method and a stored energy density fracture criterion are used to simulate crack propagation in single crystals and polycrystalline microstructures for comparison with experimental crack growth rate data. Results demonstrate that growth rate fluctuations at microstructural features are driven primarily by elastic anisotropy and yield stress mismatch. Additionally, reduced rate of growth in soft hexagonal close packed grains (relative to the remote loading direction) can be linked with crack path tortuosity, which is shown to be controlled by the cyclic development of an in-plane shear back stress. Most importantly, stored energy density is shown to accurately capture major microstructure-driven differences in crack growth rate. Comparison of simulated fatigue crack growth rates with experimental data enables estimation of the critical stored energy density for crack propagation in Zircaloy-4 to be 250 J/m2.