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Published 2008 | Published
Book Section - Chapter Open

Use of cohesive elements in fatigue analysis

Abstract

Cohesive laws describe the resistance to incipient separation of material surfaces. A cohesive finite element is formulated on the basis of a particular cohesive law. Cohesive elements are placed at the boundary between adjacent standard volume finite elements to model fatigue damage that leads to fracture at the separation of the element boundaries per the cohesive law. In this work, a cohesive model for fatigue crack initiation is taken to be the irreversible loadingunloading hysteresis that represents fatigue damage occuring due to cyclic loads leading to the initiation of small cracks. Various cohesive laws are reviewed and one is selected that incorporates a hysteretic cyclic loading that accounts for energetic dissipative mechanisms. A mathematical representation is developed based on an exponential effective load-separation cohesive relationship. A three-dimensional cohesive element is defined using this compliance relationship integrated at four points on the mid-surface of the area element. Implementation into finite element software is discussed and particular attention is applied to numerical convergence issues as the inflection point between loading and 'unloading in the cohesive law is encountered. A simple example of a displacementcontrolled fatigue test is presented in a finite element simulation. Comments are made on applications of the method to prediction of fatigue life for engineering structures such as pressure vessels and piping.

Additional Information

© 2007 ASME. The authors gratefully acknowledge the Naval Nuclear Propulsion (NNP) Fellowship program for supporting this work performed at Bechtel Bettis, Inc. (B8I). Special thanks to Dr. Al DiNicola (BBI) for his ongoing support and insight into the methods and applications presented here, and to Dr. Ron Coffield (B8I) for supporting this work and future applications. Thanks to John Newman (BBI) for his gracious donation of numerical algorithms.

Attached Files

Published - Lucas2008p8487Proceedings_Of_The_Asme_Pressure_Vessels_And_Piping_Conference_2007_Vol_2_-_Computer_ApplicationsTechnology_And_Bolted_Joints.pdf

Files

Lucas2008p8487Proceedings_Of_The_Asme_Pressure_Vessels_And_Piping_Conference_2007_Vol_2_-_Computer_ApplicationsTechnology_And_Bolted_Joints.pdf

Additional details

Created:
August 19, 2023
Modified:
October 20, 2023