TWI Frequently asked questions
by Richard Court
It is possible to obtain information about the longer-term performance of an adhesive joint by exposing the joint to a controlled environment, where factors such as temperature and humidity can be defined or varied according to the end-needs of the assembly/joint under test. Such an environment would be more extreme than that normally seen by the assembly in its standard operating condition. The higher temperature and humidity increases the rate at which the joint degrades and ages, and hence the testing is 'accelerated'.
The user must be aware of two potential problems with accelerated ageing. The first is that it can be difficult to relate the length of time that the joint survives in its accelerated ageing environment to the length of time that the joint would survive in-service. For example, an accelerated ageing test at 85°C and 85% humidity might cause failure in 3 months, but it is then difficult to predict how long the joint will survive at 25°C and 50% humidity - probably longer than 3 months is the only real certainty. The second problem is that if the temperature and humidity of the accelerated process are very different from that experienced in-service, the type of failure may be changed, i.e. the failure mechanism will not be the same. This means that the information obtained from accelerated ageing is not relevant to how the joint may fail in-service.
In spite of these problems, accelerated ageing is a useful tool which allows different adhesives, surface treatments and joint systems to be tested more quickly than would be possible if only the actual in-service operating conditions were used.
Further information
FAQ: What are the factors that will affect the durability and lifetime of an adhesive joint?
For assistance with this technology please contact Adhesives, Composites and Sealants
