TWI Industrial Member Report Summary 728/2001
C I C Manger and R J Scudamore
In many instances throughout industry, uptake of composite materials remains below potential, which is due in part to a lack of design and reliability data regarding joints. It is important to understand how the performance of composite joints is affected by the presence of flaws in either the substrate or joint area. In particular, impact damage resulting in interlaminar delamination is of major concern to structural integrity. Limited qualification of the damage tolerance characteristics of composite materials and joints, plus a perceived lack of design data for the large range of material configurations available, results in high safety factors being applied to designs.
The purpose of this Core Research Programme project is to move towards increased end-user confidence in composite structures and joints by increasing the understanding of flaw tolerance, damage propagation and failure modes in these materials. This will ultimately allow the conservative safety factors used in joint design to be reduced. To help achieve this, design methods, typical flaws or damage experienced in composite materials and joints, joint strength predictive models and damage tolerance analytical tools have been reviewed and critically assessed in a previous TWI Core Research Programme report. The preliminary research into the response of damaged composite joints is limited, concentrating on simple joint geometries and assessment techniques under static loading.
The current study was designed to extend the preliminary work identified in the review report. This work aims to gain a better understanding of the physical and theoretical aspects of the flaw tolerance of composite joints. This will lead towards the development of flaw assessment methodologies for the design and monitoring of composite joints, facilitating increased efficiency and extended joint lifetimes.
- To determine experimentally the effect of adherend flaw size and position and joint geometry parameters on the performance of adhesively bonded composites containing interlaminar flaws under static loading.
- To evaluate experimentally the performance of adhesively bonded composite joints containing interlaminar flaws under fatigue loading.
- To investigate the applicability of current closed form approaches for predicting the structural integrity of adhesively bonded composite joints containing interlaminar flaws.