I am trying to do a fatigue crack growth analysis for a notched steel beam in Mechanical APDL 18.0. I have the S-N curve parameters for the steel material. The element i am using is SOLID185 for steel beam. The notch is in the tension flange and I want to model the crack growth that initiates towards the web. I am using a transient analysis. I am not sure how to simulate the crack growth. Is there any way of simulting the crack grwth in mechanical apdl 18.0
crack propagation using ansys apdl
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The calculation of fatigue crack growth using the corresponding stress intensity factor is the most widely used method for structures under mixed-mode dynamic loading. Using a modified formula of Paris law, a researcher [24] proposed a power law for the fatigue crack growth relationship with , which is specified as
For the CTS specimen, the finite element analysis of the mixed-mode fatigue crack propagation was carried out using ANSYS Mechanical APDL and compared with experimental data for various angles of loading. The predicted values of by the experimental and numerical methods are observed to be in good agreement with the present study results. The mixed-mode fatigue life is predicted and compared with experimental data for two different loading angles of 30 and 60. Interestingly, the theoretically predicted trajectories of the crack growth for all specimens are identical to the experimental determined paths for different loading angles. Furthermore, the predicted values of SIFs (KI and KII) are in good agreement with analytical solutions. It can be stated that the structure of specimen geometry and its configuration play an important role in obtaining higher values of mixed-mode SIFs values. This happens to be significant in terms of applied loads particularly for higher values of KII.
I have a problem with the crack growth simulation using the SMART method in APDL. The model is very simple: a half plate (due to symmetry) with a central crack. One end is fixed and uniform tensile stress is applied to the other surface. The problem is that, even if I have refined the mesh near the crack tip, the SMART remeshing algorithm does not produce new crack surface with a good quality mesh and the propagation is stopped. The mesh is shown in the following picture:
The main objective of this work was to present a numerical modelling of crack growth path in linear elastic materials under mixed-mode loadings, as well as to study the effect of presence of a hole on fatigue crack propagation and fatigue life in a modified compact tension specimen under constant amplitude loading condition. The ANSYS Mechanical APDL 19.2 is implemented for accurate prediction of the crack propagation paths and the associated fatigue life under constant amplitude loading conditions using a new feature in ANSYS which is the smart crack growth technique. The Paris law model has been employed for the evaluation of the mixed-mode fatigue life for the modified compact tension specimen (MCTS) with different configuration of MCTS under the linear elastic fracture mechanics (LEFM) assumption. The approach involves accurate evaluation of stress intensity factors (SIFs), path of crack growth and a fatigue life evaluation through an incremental crack extension analysis. Fatigue crack growth results indicate that the fatigue crack has always been attracted to the hole, so either it can only curve its path and propagate towards the hole, or it can only float from the hole and grow further once the hole has been lost. In terms of trajectories of crack propagation under mixed-mode load conditions, the results of this study are validated with several crack propagation experiments published in literature showing the similar observations. Accurate results of the predicted fatigue life were achieved compared to the two-dimensional data performed by other researchers.
The comparisons of simulated and experimental and numerical crack path performed by [28] and [16] are shown for CT01, CT02, CT03 and CT04 in Figure 4, Figure 5, Figure 6 and Figure 7, respectively. The modified CTS holes were explicitly designed to manipulate the crack direction. As shown in the figures, the crack growth paths are almost identical to the path predicted experimentally and numerically [28] and [16], using boundary element method (BEM) with BemCracker2D software (which is a special purpose educational program for simulating two-dimensional crack growth based on the dual boundary element method, written in C++ with a MATLAB graphic user interface developed by [16,28] and finite element method with Quebra2D (which is a finite element based software developed by [16,28]). Also, it is worth visualizing the maximum principle stress and the equivalent stress distribution of Von Mises of mentioned four different CTS configurations as shown in Figure 8 and Figure 9, respectively. The Von Mises yield criterion is used to compute yielding of materials under multiaxial loading conditions depending on the maximum and minimum principal stress and also the shear stress. As these two figures explicitly demonstrate, there is a significant association between the maximum principal stress and Von Mises stress in the four different models of the CTS.
The obtained SIF data set can be used to construct an easy-to-use formula through the general linear regression technique, expressing the SIF as a function of the interested crack and contact parameters and facilitating the evaluation of the crack propagation behaviour.
High-cycle fatigue can be generally divided into three crack-life stages: crack nucleation, crack growth, and eventually brittle failure. Here, I focus on the second stage - stable crack growth. Under certain conditions, the crack growth can be described by the Paris-Erdogan law (logarithmically linear dependence between the number of cycles and the stress intensity factor $K$). Predictions of the lifetime (number of cycles) of a sample with a pre-existing crack or predictions of the crack path are of crucial importance in assessing the conditions of engineering structures subjected to cyclic loading, such as shafts, switches and others. Furthermore, the ability to predict the crack path using computer simulations allows one to optimize the structure geometry with pre-existing cracks with an effort to prevent the failure.
The aim is to write an APDL script which can be used to model the crack growth in an arbitrary 2D geometry in ANSYS Mecanical APDL using the plane elements. The employed theory is based on the assumptions of the linear elastic fracture mechanics (LEFM).
In this approach, the crack surfaces are modelled explicitly at each time step (crack increment) and the geometry (crack propagation zone) is (re-)meshed at each time step too. Although the remeshing approach may not (in terms of computational time) be very efficient when modelling a crack growth, it does the job.
Notice that the geometry has to contain an area (in this case A3 shown in the figure below) in which the crack is expected to propagate. This area will be (re)-meshed automatically. The keypoint of the crack initiation (KP = 27) and the expected final crack position (KPe = 33) have to be defined on the boundary (NOT within). The size of the crack propagation zone (A3) and the choice of the keypoint of the expected final crack position do not influence the result; however, they influence the efficiency (time to remesh) and stability of the solution.
Abstract:The main objective of this work was to present a numerical modelling of crack growth path in linear elastic materials under mixed-mode loadings, as well as to study the effect of presence of a hole on fatigue crack propagation and fatigue life in a modified compact tension specimen under constant amplitude loading condition. The ANSYS Mechanical APDL 19.2 is implemented for accurate prediction of the crack propagation paths and the associated fatigue life under constant amplitude loading conditions using a new feature in ANSYS which is the smart crack growth technique. The Paris law model has been employed for the evaluation of the mixed-mode fatigue life for the modified compact tension specimen (MCTS) with different configuration of MCTS under the linear elastic fracture mechanics (LEFM) assumption. The approach involves accurate evaluation of stress intensity factors (SIFs), path of crack growth and a fatigue life evaluation through an incremental crack extension analysis. Fatigue crack growth results indicate that the fatigue crack has always been attracted to the hole, so either it can only curve its path and propagate towards the hole, or it can only float from the hole and grow further once the hole has been lost. In terms of trajectories of crack propagation under mixed-mode load conditions, the results of this study are validated with several crack propagation experiments published in literature showing the similar observations. Accurate results of the predicted fatigue life were achieved compared to the two-dimensional data performed by other researchers.Keywords: fatigue crack growth; mixed mode; MCTS; ANSYS; LEFM; fatigue life
Hi, I am doing project on mixed mode crack growth of semi elliptical crack in gas turbine components under cyclic loading. Ansys has capability for finding J,K using CINT command. But, In mixed mode crack growth, i dont know how to deal with nodes and how to create random crack with new node coordinates obtained from previous steps. If you have any ansys code related to creating crack and finding fracture parameters like K, J (mode 1 or mixed mode), Can you please give me the code.
I am a beginner in FEM and just started using ANSYS. I need to study the stresses and SIF at the crack front of an elliptical crack inside a material subjected to a stress perpendicular to the crack plane. Any details on how I should build my model?
I am obtainning the Stress Intensity factors along the front of cracks in a 3D FE models (ANSYS). The loading mode is mixed and Ki, Kii and Kii should be estimated. I have noticed that the SIF strongly depends on the poisson's ratio but i understand Ki does not depends on the elastic properties of material. I know ANSYS calculates the SIF from the displacements at the crack tip using E and mu, but i did not expect so huge differences in SIF values, In fact all analytical predictions for SIF does not depends on poisson's ratio.... 2ff7e9595c
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