Before explaining the cohesive zone model, let’s learn more about the crack in metals.
What is the crack in metals?
Cracks are surface or subsurface fissures that develop in a material. Propagation energy derived from mechanical, thermal, chemical, and metallurgical effects, or a combination of these may influence crack initiation and growth. Various types of cracks exist in metals and can be categorized as cooling, solidification, centreline, crater, grinding, pickling, heat treatment, machining tears, plating, fatigue, creep, stress corrosion and hydrogen cracks. Cracks can grow and lead to complete fracture of the component posing significant threats to component life and may lead to serious injuries or loss of life. Brittle fracture in metals occurs with little or no visible warning. The discovery of any cracks warrants immediate interventions to arrest the cracks before they propagate to the point of fracture.
Evaluating the behaviour of metals during crack propagation requires expensive and time-consuming experiments. This makes the FEA method a great tool for a comprehensive study. Since the model needs to predict the complex behaviour of the material during propagation, various types of simulations are proposed. Each method has a specific benefit which makes it an appropriate technique for different purposes or materials.
The cohesive zone method (CZM)
The Cohesive zone model is the most important evolution in the area of Fracture mechanics. It is widely used to simulate crack initiation and its propagation in solids. It is also an alternative method for model separation. For CZM fracture formation is regarded as a gradual phenomenon in which the separation of the surfaces involved in the crack takes place across an extended crack tip, or cohesive zone, and is resisted by cohesive traction. Thus cohesive zone elements do not represent any physical material but describe the cohesive forces which occur when material elements (such as grains) are pulled apart, therefore cohesive zone elements are placed between continuum (bulk) elements.
 Implementation of Cohesive Zone in ABAQUS to Investigate Fracture Problems by Ajinkya K. Salve, Sudhindra N. Jalwadi
Advantages of cohesive zone method
The CZM has major advantages over conventional methods of fracture mechanics like LEFM(Linear Elastic Fracture Mechanics), CTOD(Crack Tip Opening Displacement) etc. Some of them are as follows:
1.It is useful in predicting the behaviour of uncracked structures as well as the structures including blunt notches
2.In CZM size of the nonlinear zone need not be neglected in comparison with other dimensions of the cracked geometry, in other methods it is so.
3.Even for brittle materials, the presence of an initial crack is needed for LEFM to be applicable, for CZM it is not so.
4.CZM falls in the conceptual framework for interfaces.
In this video, you will learn how to create a simple model to study crack propagation through a part. Cohesive is a method in Abaqus which allows you to analyze the fracture by crack. In addition, this method is very fast and appropriate to create large models. The video is short so you can learn this in less than 11 minutes and you will have the output and Abaqus CAE file.
In this video, we avoid giving too many details so you can easily use the product. Here you can find the following files:
Abaqus files: CAE, ODB, INP, and JNL
Video files: How to create this model.
PowerPoint and Solidworks files
For more information please send me an Email: