Mixed-mode fatigue crack growth under biaxial loading (original) (raw)
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An algorithm for fatigue crack growth applied to mixed and biaxial mode loadings
Procedia Structural Integrity, 2019
Fatigue is still one of the main concerns when dealing with mechanical components failure. While it is fundamental to experimentally determine the fatigue material behavior using standard specimens, testing large and complex component geometries can be complicated. In these cases, the Finite Element Method can be a cost-effective solution but developing fatigue crack growth models is still a complicated task. In order to solve this problem, an algorithm for automatic crack propagation was developed. Using three different modules, the algorithm can generate a complex Finite Element Method model including a fatigue crack; solve this model considering complex loading conditions, by applying the superposition method; and calculate the fatigue crack propagation rate, using it to update the original model. In order to benchmark this solution two different problems were analyzed, a modified compact tension specimen and a cruciform specimen. By modifying the compact tension specimen hole location and simulating an initial crack, it was possible to understand how mixed mode conditions influence the fatigue crack path. Different load ratios and initial crack directions on the cruciform specimen were analyzed. Increasing the load ratio will increase the crack deflecting angle. The obtain solutions were compared with experimental results, showing good agreement. Therefore the developed algorithm can be used to predict the fatigue crack growth behavior on complex geometries and when different types of loads are applied to the component.
Computational Simulation of 3D Fatigue Crack Growth under Mixed-Mode Loading
Applied Sciences, 2021
The purpose of this research was to present a simulation modelling of a crack propagation trajectory in linear elastic material subjected to mixed-mode loadings and investigate the effects of the existence of a hole and geometrical thickness on fatigue crack growth and fatigue life under constant amplitude loading. For various geometry thickness, mixed-mode (I/II) fatigue crack growth studies were carried out to utilize a single edge cracked plate with three holes and compact tension shear specimens with various loading angles. Smart Crack Growth Technology, a new feature in ANSYS, was used in ANSYS Mechanical APDL 19.2 to predict the cracks’ propagation trajectory and their consequent fatigue life associated with evaluating the stress intensity factors. The maximum circumferential stress criterion is implemented as a direction criterion under linear elastic fracture mechanics (LEFM). According to the hole position, the results demonstrate that the fatigue crack grows towards the ho...
Fatigue crack propagation trajectories under mixed-mode cyclic loading
Engineering Structures, 2003
As the direction of the mixed-mode fatigue crack growth may not be known in advance, a new methodology is proposed to simulate the fatigue crack trajectories under general in-plane cyclic loading. The accumulated elastic strain energy is calculated in the vicinity of the crack tip for all possible prospective propagation directions. It is assumed that the fatigue crack extension takes place along the prospective direction which results to the minimum accumulated elastic strain energy in the vicinity of the crack tip. A new factor related to the accumulated elastic strain energy within a circular core around the crack tip seems to be a suitable parameter for predicting the mixed-mode fatigue crack growth path, as well as the fatigue crack growth rate. Using the proposed concept to perform the above predictions, only mode-I fatigue test data are required. Theoretical predictions are correlated well with test results taken by the literature.
Experimental and analytical study of cracks under biaxial fatigue.PDF
Most mechanical components experience multi-axial cyclic loading conditions during service. Experimental analysis of fatigue cracks under such conditions is not easy and most works tend to focus more on the simpler but less realistic case of uni-axial loading. Consequently, there are many uncertainties related to the load sequence effect that are now well known and are not normally incorporated into the growth models. The current work presents a new methodology for evaluating overload effect in biaxial fatigue cracks. The methodology includes evaluation of mixed-mode (KI and KII) stress intensity factor and the Crack Opening Displacement for samples with and without overload cycle under biaxial loading. The methodology is tested under a range of crack lengths. All crack-tip information is obtained with a hybrid methodology that combines experimental full-field digital image correlation data and Williams' elastic model describing the crack-tip field.
Verification of FE model of fatigue crack propagation under mixed mode conditions
Meccanica, 2008
Results of FEM simulations of fatigue crack growth under mixed mode loading are presented in this paper. At Czech Technical University in Prague (CTU) the program code which uses commercial software ABAQUS for fatigue crack simulations has been developed. The program works on basis of gradual crack extending. In simulation are considered small scale yielding conditions. Both classic criteria (J-integral, maximum of hoop stress, Paris law) and two-parameter criteria incorporating T-stress (extended hoop stress criterion and modified Paris law) are used for crack behaviour description. Experiments were carried out on two sets of simple specimens. The results of numerical simulations are compared with carried out experiments. Computed crack growth rate corresponds to experiments for shorter cracks at which T-stress is not significant. Computed crack shapes are in very good agreement with experiments.
PREDICTION OF CRACK INITIATION DIRECTION AND FATIGUE CRACK GROWTH UNDER MIXED MODE LOADING
The present investigation has been under taken keeping in mind some of the problems concerning the crack propagation direction and growth under constant amplitude load in an inclined crack geometry. The present studies mainly focus on to develop and modified the crack growth criterion to account of the effect of biaxial factor, shearing loading and number of stress terms for different criterion. The effect of one, two and three solution on crack initiation angle determined on the basis of DET-criterion & MTS-criterion. It is seen that difference in crack initiation angle (α) obtained from two and three term solution of DET-criterion & MTS-criterion is significant and higher than one term solution. The comparisons of predicted result obtain from using DET-criterion and MTS-criterion has been made. When comparison is made between two terms solution, it is found that growth rate is higher in case of DET-criterion than MTS-criterion when α <45 0 , whereas fatigue growth rate obtain by MTS-criterion is found to be the higher than the DET-criterion for α >45 0. It is observed that only three terms are sufficient to determine the stress and displacement field ahead of the crack tip. Variation of crack initiation angle with crack angle for different biaxial load factor and shear load factor by DET-criterion and MTS-criterion for three term solution is compared. The crack initiation angle also depends upon biaxial factor and shear load factor. NOTATIONS: β = crack inclination angle 0 β = crack initiation angle 2a = Initial crack length r and θ = polar coordinate of crack tip II I K K , = mode I and mode II stress intensity factor xy y x τ σ σ , , = stress components b 1 = Biaxial factor b 2 = Shear or torsional load factor INTRODUCTION: Fracture mechanics has been established as an important principle dealing with the growth of fatigue crack. During recent years, the fracture mechanics has obtained a considerable importance for studding the crack growth behavior under static and fatigue loading. The majority of the research done in the area of fracture mechanics was accomplished in the opening mode only. Hence the practical application of the fracture mechanics is limited. The mixed mode crack growth problem has drawn comparably little attention, but is actually more realistic and possibly more dangerous than mode-I crack. The mixed mode growth occurs when a fatigue crack is nucleated along the inclusions or welded defects located making an angle with the axis of the applied load. The fatigue crack growth under multi axial stress is to be considering as mixed mode. The mixed mode cracks generally propagate in a non-self similar manner. Hence, in case of mixed mode loading condition, the study of the crack initiation angle and crack growth rate is of equal importance. A considerable amount of the work has been done to define governing mixed mode loading and crack growth behavior. Papadopoulos (1987) proposed the DET-criterion is based on determinants of the stress tensor. Using the stress as parameter, MTS-criterion proposed by Erdigan & Sih (1963) is based on the
Experimental and numerical investigations of crack growth under mixed-mode loading
Emerging Materials Research, 2020
Fatigue fracture is the one of the most common failures of mechanical components. This is caused by the initiation and growth of cracks. In this study, mixed-mode I/III fatigue crack growth was studied experimentally and numerically for a cylindrical specimen with a stress ratio R = 0.1 for both loadings. A digital camera was used to monitor the crack growth path in the experimental studies. The crack growth path, crack tip profiles, variations in stress intensity factors (SIFs) and equivalent SIFs were calculated by using the Ansys, FCPAS and Solidworks software, and the results were compared with experimental data. Modeling, meshing and problem-solving were performed using the Ansys software, and the resulting SIFs and equivalent SIFs along the crack front were calculated using the FCPAS software, which was employed with enriched elements. It is seen that the criteria from the literature (Richard, Tanaka, Pook and Ayhan–Demir) can be successfully applied to the problem. The result...
Analytical and experimental studies on fatigue crack path under complex multi-axial loading
Fatigue <html_ent glyph="@amp;" ascii="&"/> Fracture of Engineering Materials and Structures, 2006
In real engineering components and structures, many accidental failures are due to unexpected or additional loadings, such as additional bending or torsion, etc. Fractographical analyses of the failure surface and the crack orientation are helpful for identifying the effects of the non-proportional multi-axial loading. There are many factors that influence fatigue crack paths. This paper studies the effects of multi-axial loading path on the crack path. Two kinds of materials were studied and compared in this paper: AISI 303 stainless steel and 42CrMo4 steel. Experiments were conducted in a biaxial testing machine INSTRON 8800. Six different biaxial loading paths were selected and applied in the tests to observe the effects of multi-axial loading paths on the additional hardening, fatigue life and the crack propagation orientation. Fractographic analyses of the plane orientations of crack initiation and propagation were carried out by optical microscope and SEM approaches. It was shown that the two materials studied had different crack orientations under the same loading path, due to their different cyclic plasticity behaviour and different sensitivity to non-proportional loading. Theoretical predictions of the damage plane were made using the critical plane approaches such as the Brown-Miller, the Findley, the Wang-Brown, the Fatemi-Socie, the Smith-Watson-Topper and the Liu's criteria. Comparisons of the predicted orientation of the damage plane with the experimental observations show that the critical plane models give satisfactory predictions for the orientations of early crack growth of the 42CrMo4 steel, but less accurate predictions were obtained for the AISI 303 stainless steel. This observation appears to show that the applicability of the fatigue models is dependent on the material type and multi-axial microstructure characteristics.
Numerical Simulation of Mixed-Mode Fatigue Crack Growth for Compact Tension Shear Specimen
Advances in Materials Science and Engineering
This work concentrates on the fracture behaviour of the compact tension specimen under mixed-mode loading, and numerical investigation using ANSYS Mechanical APDL 19.2 finite element program with different modes of mix angles is carried out. The prediction of mixed-mode fatigue life under constant amplitude fatigue loading for the compact tension shear specimen (CTS) is employed using Paris’ law model for two different loading angles with agreement to the experimental results. The predicted values of ΔKeq were compared with the experimental and analytical data for various models. Depending on the analysis, the findings of the present study show consistency with the results achieved with similar models of predicting the equivalent stress intensity factor. In addition, the direction of crack growth derived from the analysis was observed to follow the same trend of the literature experimental results.