TWI Industrial Member Report Summary 677/1999
E J Kellar, C Vlattas and S M Tavakoli
Despite increasing use in many sectors, wider application of adhesives within industry is restricted by the lack of an effective method to predict long term performance.
A recent survey by TWI has identified that prediction of lifetime of bonded joints, when exposed to service environments, is one of the most significant factors restricting the wider use of adhesive technology in industry. Despite significant research into durability, there remains considerable uncertainty in predicting joint lifetime under typical operating conditions.
The issue of confidence in joint lifetime prediction methods becomes even more acute when the adhesive joint is subjected to a wet environment, accompanied by constant or cyclically applied loads and/or elevated temperatures. The main problem when attempting to formulate any predictive model is that environmental attack typically occurs in the regions at, or very close to, the adhesive/adherend interface. Modelling the rate of such attack and determining the factors which contribute to interfacial failure is very complex. A quantitative assessment of the key mechanisms of fracture of bonded joints is required, if such a model is to be truly generic in nature.
The specific objectives of this project were as follows:
- To acquire fatigue endurance and crack growth data from a galvanneal steel adherend/epoxy adhesive system against which to compare fatigue life predictions based on fracture mechanics concepts.
- To correlate the structural performance of the joints with key constituents and fracture appearance.