Crack Propagation in a Toughened Epoxy Adhesive under Repeated Impacts

Ian A Ashcroft,Vadim V Silberschmidt,Benjamin Echard,Juan Pablo Casas Rodriguez

doi:10.1155/2011/301761

Abstract

Adhesives are being increasingly used in structural applications, especially in aerospace, automotive and naval structures, making their structural integrity an important issue. In-service loading histories of such structures usually contain low-energy impacts, repetition of which can significantly affect their performance. This paper deals with the behaviour of the toughened epoxy adhesive FM73 under repeated impacts, known as impact fatigue. Izod impact fatigue tests were performed on FM73 specimens in order to study the evolution of damage and to characterise this via measurable parameters, such as the maximum force and the contact time. A finite element model was developed to simulate the impact tests and this was used to calculate the dynamic strain energy release rate, which was compared with that determined using a simple analytical method. A relationship between the maximum dynamic strain energy release rate and impact fatigue crack growth rate was established that was used as the basis of an impact fatigue crack growth law.

Highlights

Engineering adhesives are widely used in structural applications, especially in the aerospace industry, as an alternative to rivets and other mechanical joints
In order to use adhesive bonding safely and efficiently in structural applications, an ability to predict the response of the adhesive joint to the in-service environment and loading is required
In standard fatigue it is more usual to look for relationships between stress, or force, and Nf, than energy, in this case, the impact energy remains constant throughout the test, the maximum force, and stress, does not

Summary

Introduction

Engineering adhesives are widely used in structural applications, especially in the aerospace industry, as an alternative to rivets and other mechanical joints. In these applications, important advantages of adhesive bonding include weight reduction, sealing ability, increased stiffness, the ability to join thin sections and the removal of the requirement to create a hole in the parent material. Most of the perceived problems are surmountable and, an increase in structural applications for adhesive bonding has been seen in recent years. In order to use adhesive bonding safely and efficiently in structural applications, an ability to predict the response of the adhesive joint to the in-service environment and loading is required. There has been much progress in this regard in recent years, e.g. see Oechsner and da Silva [10], impact fatigue is still a relatively little studied mode of loading for bonded joints

Methods

Results

Conclusion