Fatigue Crack Growth Analysis of Modified Compact-Tension Specimen - ANSYS Workbench


This tutorial includes step-by-step fatigue crack analysis of Modified Compact-Tension Specimen.
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Step 1: Overview
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 (Workbench) 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.
This tutorial is mostly based on "Numerical Analysis of Fatigue Crack Growth Path and Life Predictions for Linear Elastic Material" paper by Abdulnaser M. Alshoaibi and Yahya Ali Fageehi.
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Step 2: Setup
- Drag and Drop a Static Structural Analysis on ANSYS Workbench Main Menu:
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Step 3: Engineering Data (Material Model)
- The selected material for this tutorial is "SAE 1020 Carbon Steel".
- The material model consists of Isotropic Elasticity, Tensile Yield Strength, Tensile Ultimate Strength and Paris' Law Parameters(C and m).
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Step 4: Geometry (SpaceClaim Model)
- The dimensions of Modified Compact-Tension Specimen (MCTS) which has been created on SpaceClaim could be seen below:
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Step 5: Defining the Crack (Named Selections)
- In order to define the crack edges and surfaces, the "Named Selection" menu must be used:
- While defining the crack front and crack surfaces, the edge and the surfaces which could be seen on below figure have been used as Named Selections:
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Step 6: Defining the Crack (Pre-Meshed Crack & SMART Crack Growth)
- With the Named Selections which have been created on previos step, "Pre-Meshed Crack" has been defined as below:
- "SMART Crack Growth" with 0.1 of Stress Ratio has been defined with Pre-Meshed Crack:
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Step 7: Mesh Operations
- The default mesh operations with the "Body Sizing" have been implemented:
- "Sphere of Influence" has been used as Refinement Type:
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Step 8: Boundary Conditions
- The Boundary Conditions have been implemented as below figure:
- Simulating the Movement of the Pins (2 Yellowish Edges):
- Simulating the Symmetric Movement (1 Yellowish Edge):
- Simulating the Plane-Strain Conditions (2 Yellowish Faces):
- The plane strain conditions have been simulated as zero displacements on front and back surfaces (please see the Z-direction on above figure):
- Load on Upper Pin:
- Load on Lower Pin:
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Step 9: Solver Options
- Solver Options with 12 Substeps could be seen below:
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Step 10: Results
- Total Deformation:
- Equivalent Stress:
- SIFS (K1):
- Crack Extension Probe:
- Total Number of Cycles Probe: