Experimental and numerical investigations of crack growth under mixed-mode loading (original) (raw)
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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...
2011
This study considers the numerical and experimental fatigue crack growth under mixed mode I-III in a holed plate with edge crack (Modified Compact Tension Specimens) which made of aluminum alloy 7017 under simple tensile-tension loading. R-ratio (0.01, 0.02) and first angle of crack 30 45 60 (, ,) are variable. Their effects on Stress Intensity Factor (,) K K I III and J-Integral (,) J J I III for both of Fracture mode during the fatigue crack growth has been studied. Also the fatigue crack growth vs. stress intensity factor and J-Integral diagrams has been found and compared to experimental results which show that enhancement in crack angle issues augmentation in mode III and reduction in mode I. In a constant angle, during the crack growth the effect of Mode III will decrease and Mode I will increase. Finally by enhancement in first angle in same crack length, the fatigue crack growth life will increase.
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.
ANALYSIS OF MIXED MODE CRACK INITIATION ANGLE AND FATIGUE CRACK GROWTH
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 largest number of in-service failures results from the scenario involving fluctuating, cyclic or repeated loading, usually combination with static load. Typically, a defect located near a stress raiser enlarges under repeated tensile stresses into a crack that continues to grow stably a small amount during each load cycle until the crack either penetrates the structure or attains critical length, after which unstable crack propagation occurs. 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. 1.0 Introduction 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. The predictions of mixed mode crack growth direction, different criterion have been proposed. Using the stress as parameter, MTS-criterion proposed by Erdigan & Sih (1963) is based on the assumption that the material behaves ideally brittle. This assumption is not supported by all kind of material. SED-criterion of Sih (1974) is based on the minimum strain energy density principle. This criterion corresponds to maximum potential energy, which is regarded as the integral of field variable over some domain rather than a point and is insensitive to sign of the loading. T-criterion proposed by Theocaries et. al. (1982) is also based on the SED-criterion, which is modified by using a variable radius for core region. Papadopoulos (1987) proposed the DET-criterion is based on determinants of the stress tensor. The predicted crack initiation angles by DET-criterion are found to be much higher relative to the one obtained by the MTS or the SED criterion. The theoretical results obtained for different loading cases are shown and discussed by Khan et. al. (2000). They have shown that the result for MTS-criterion and T-criterion match exactly for all loading cases, although both have been derived on different theoretical basis. Prais (1963) co-relate the rate of crack growth to the stress intensity factor for simple opening (mode-I). Robert and Kibla (1971) indicated in their result that the fatigue crack under mixed loading grew in a manner which did not reduce the mode-II component of load to zero and that the growth rate was accelerating by mode-II components of the stress applied simultaneously. A considerable amount of the work has been done to define governing mixed mode loading and crack growth behavior.
The effect of plasticity on incipient mixed-mode fatigue crack growth
Fatigue <html_ent glyph="@amp;" ascii="&"/> Fracture of Engineering Materials and Structures, 2003
Several criteria for the prediction of incipient crack path direction of non-proportional mixed-mode fatigue cracks, immediately after a change of load from steady mode I conditions are investigated. The analysis is based on two-dimensional plane strain FEsimulations in which the actual elasto-plastic stress distribution is used for the MTS, MTSR and MEPSR criteria. The purpose of the analysis is to compare the numerical results with experimental results as well as with previous predictions based on solely elastic stress analyses, taken from the literature. It is shown that the influence from elasto-plastic deformation on crack branching direction is of utmost importance. It is found that the incipient crack growth of metals falls into two categories: high strength metals follow the MTS p criterion whereas more ductile metals follow the MTSR p criterion. The subscript p indicates that the elasto-plastic evaluation of the respective criterion should be used.
Mixed-mode fatigue crack growth under biaxial loading
International Journal of Fatigue, 1984
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.
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
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.
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.