Analysis of creep crack growth in adhesively bonded joints under mode I loading

Meulman, Edwin
Adhesive bonds could replace more traditional mechanical joints, making structures lighter and smoother. Stresses are distributed over a larger area, and dissimilar materials can be bonded, accommodating differences in expansion. These advantages of bonded joints are valuable in industries like automotive and aeronautics, where lightweight and aerodynamic design reduces fuel consumption and service costs. These days structural designs need to be durable. It is crucial to comprehend the long-term performance of bonded joints to create durable ones and establish proper maintenance protocols. A vital aspect that must be considered in designing a durable bonded joint is viscoelastic creep crack growth and how it impacts the structural integrity. Creep crack growth is one of the factors that could impact the longevity of a bonded joint. However, there is a limited availability of test methods and numerical tools to assess the effects of creep crack growth in bonded joints. In this work, a method is developed to obtain the average crack growth rate (da⁄dt) in mode I as a function of the applied energy release rate (G). The method is based on the wedge test, because it has been found as a good candidate to obtain creep crack growth curves of a bonded joint in mode I. Although, the friction between the wedge and the specimen should be considered and reduced to a minimum. A low friction roller wedge is proposed to achieve that, called the Roller Wedge Driven (RWD) test method. Results have shown that the friction of the roller is indeed significantly lower compared to a sliding wedge but cannot be completely neglected in the data reduction to determine the energy release rate. Making use of the designed roller wedge test setup, a RWD creep crack growth (RWDC) method is developed. The roller wedge is loaded with a deadweight which result in a constant energy release rate at the crack tip of the bonded joint. Applying for each specimen a different energy release rate results in different creep crack growth rates. Plotting the results on a log-log scale will produce creep crack growth curves that can be described by a Paris' law-like expression ​
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