Crack Propagation Analysis

Introduction

Adhesive joints are increasingly used in various industries from aerospace to civil. They allow complex shapes to be joined and they also reduce the weight of the structure. Because of this composite materials are often bonded. Composite materials are very anisotropic, in the fibre direction they are strong and stiff however their transverse and shear properties are low. Bonded joints experience peel loading, so the most likely mode of failure is in the transverse direction either in the adhesive or the composite itself.

It is therefore important to study the joints to find reliable methodology to predict the strength of the adhesively bonded composite joints.

Method

A finite element cohesive zone model (CZM) was modelled to predict the peel strength of the joint.

The most widely used method of determining mode I interlaminar fracture toughness (peel strength) of a bonded composite joint is the double cantilever beam (DCB) test [1]. The method is based in linear-elastic fracture mechanics theory [2] and calculates GI using the crack length as well as the applied load, load point displacement crack and initial specimen width. 

Figure 1. Dis-bonding

 

Figure 2. The load/ displacement curves

Conclusions

The predictions of the model have been compared to the experimental data. Fig 1. shows the process of dis-bonding in the model. The load/displacement curves show a good agreement between the numerical prediction and the experimental result as shown in Fig 2.

 

 

References

1 D5528-01 (2008) Standard test method for mode I interlaminar fracture toughness of unidirectional fibre-reinforced polymer matrix composites. Annual Book of ASTM Standards 15.03.

2 Griffith A.A. (1920) The phenomena of rupture and flow in solids. Philosophical Transactions of the Royal Society of London 221(21): 163-198.

 

YouTube Video Link:

http://youtu.be/9wDuB6ZkRBs