Effects of Defects

One of the uncertainties for the user of composite materials is how to determine whether a defect is benign or not. There are two separate defects that will effect the strength of a composite structure.
(1) Imperfections or flaws from manufacturing of the laminate or assembly of the structure
(2) Damage resulting during handling, installation or in-service use

Understanding the nature of the defect present allows both the effect of this defect to be ascertained and in some instances a forensic examination of a failed part to be carried out for failure analysis. For every composite part, there should be acceptance/rejection criteria to be used during inspection of the part.

MERL staff combine analysis and testing to help identify the effect of a defect on performance of a composite structure. The approach is very dependent on the purpose of the structure, e.g. the presence of microcracking may be less important for a structural application but more so for a fluid containment application.

MERL has a working relationship with NDT Solutions who provide rapid ultrasonic NDT inspection equipment that does not require a liquid coupling agent.

Some examples of possible defects are illustrated below.