Fatigue life of a single lap joint with and without special events

Abstract

The development of fatigue-resistant adhesive joints and adjacent parts remains challenging, particularly when simulating crack propagation under fatigue loading. Commercial software packages, such as ABQUS, include cohesive zone elements; however, they usually require user-defined subroutines for fatigue applications. This study combines multiple subroutines to predict the crack path across multiple lamina layers originating from a pre-crack. The interlaminar/adhesive subroutine employs a userdefined material model to assess cohesive stress and damage in the joint [1]. Additionally, a second user-defined subroutine developed at HAW Hamburg was used for intralaminar damage. Both subroutines were incorporated into the FEM software ABAQUS to enable information exchange between material models [2]. This allows the initiation of delamination from the matrix damage, in addition to a crack propagating through the lamina. The evaluation was conducted on a specimen measuring 100 mm × 150 mm, including a single-lap bonded joint. The specimens were subjected to cyclic tension at an R ratio of 0.1. For the impact assessment, a custom mapper developed by Wölfel was used to map the initial damage based on separate impact simulation results, enabling a distinct analysis method for fatigue. Using this method, a validated tool for predicting the fatigue life of a bonded joint was presented.

[1] L. F. Kawashita and S. R. Hallett, "A crack tip tracking algorithm for cohesive interface element analysis of fatigue delamination propagation in composite materials," International Journal of Solids and Structures no. 49, pp. 2898-2913, 2012.

[2] R. Sachse, A. Pickett, M. Käß and P. Middendorf, "Numerical Simulation of Fatigue crack growth in the Adhesive Bondline of hybrid CFRP Joints," in COMPOSITES, Bristol, 2015.