A methodology for the experimental characterization of energy release rate-controlled creep crack growth under mode I loading

Abstract

Understanding the performance of a bonded joint over time is essential for the design of durable bonded joints and maintenance protocols. Viscoelastic creep crack growth and how it affects the mechanical behaviours of an adhesive is relevant information for a durable design. For this purpose, a method to obtain the average crack growth rate (da/dt) as a function of the energy release rate (G) was developed. The proposed roller wedge driven (RWD) creep crack growth methodology can provide creep crack growth rate curves for a constant applied energy release rate. The RWD test setup was designed by the authors to test mode I DCB-like specimens by using a roller wedge. An advantage of using a moving wedge is that, on average, the crack growth rate equals the displacement rate of the wedge. By changing G for different specimens, a G vs da/dt curve can be obtained for the methacrylate adhesive Araldite 2021–1. The power law regression line of the G vs da/dt curve provides a Pariś law-like equation. Data have shown that applying an energy release rate that is relatively low compared to the fracture toughness of Araldite 2021–1, found by quasi-static testing, will result in creep crack growth. Furthermore, a transition from cohesive to adhesive failure has been observed when the applied energy release rate is lowered. For durability design of bonded joints it must be considered that only using data from quasi-static testing will very likely overestimate the durability of the bonded joint.