The properties of materials will naturally degrade with time by a variety of mechanisms including fatigue, creep, thermal or environmental degradation. Adhesive bonds are particularly prone to environmental or thermal degradation.
In order to assess the long term performance of adhesive joints durability testing is often conducted. This may deploy a variety of test methods. The DTI funded MTS programmes, Project 3, carried out extensive studies of durability. Where durability information is required for new designs then accelerated ageing tests may be used. See method M13.
To assess the long term degradation in properties of an adhesive joint so this can be allowed for in design.
The method may also be deployed in forensic examinations to aid prediction of remnant life.
Test methods such as lap shear tests, wedge tests or tensile butt tests are deployed on joints in the as received condition and after extended or accelerated ageing in the real or simulated service environment to understand the impact of service conditions on joint strength and performance.
In some cases samples of the original joint are not available. In this case a ‘new joint’ may be produced by re-adhesion of the joint following the original bonding procedure.
Durability testing was used to assess the long term performance of bonded joints in the De Haviland Comet aircraft. Durability tests at 40°C, in which the Comet joints were compared with test material prepared at a similar time and stored in laboratory conditions, as well as similar new materials showed no indication of loss of durability in the old Comet joints. Analytical studies of the fracture surfaces of the old adhesives did not reveal any significant deterioration.
E8 Long term adhesve performance De Haviland Comet
DTI MTS Project 3 Report No 9 Forensic Studies of Adhesive Joints. Part 1 - General Introduction and Conclusions, Part 2 - De Haviland Comet February 1996 NPL
