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The application of advanced materials in components and structures has evolved due to the need to reduce structural weight and improve performance. Other attributes of composite materials, such as corrosion resistance, excellent surface profiles, enhanced fatigue resilience, and tailored performance, have also been significant contributors to the rapid rise in composite materials application. As a result, these new materials are required to perform at higher stress levels than previous applications while also providing adequate levels of damage tolerance.
Type of damages
Manufacturing and defects/damages
Manufacturing damage includes anomalies, such as porosity, microcracking, and delaminations resulting from processing discrepancies. It also includes such items as inadvertent edge cuts, surface gouges, scratches, damaged fastener holes, and impact damage. Manufacturing defects include:
Delamination
Resin starved areas
Resin rich areas
Blisters, air bubbles
Wrinkles
Voids
Thermal decomposition
Examples of flaws occurring in manufacturing include a contaminated bond-line surface or inclusions, such as prepreg backing paper or separation film, that is inadvertently left between plies during layup. Inadvertent (non-process) damage can occur in detailed parts or components during assembly or transport or during operation.
A part is resin rich if too much resin is used, for nonstructural applications this is not necessarily bad, but it adds weight. A part is called resin starved if too much resin is bled off during the curing process or if not enough resin is applied during the wet layup process. Resin-starved areas are indicated by fibers that show to the surface. The ratio of 60:40 fiber to resin ratio is considered optimum. Sources of manufacturing
defects include:
Improper cure or processing
Improper machining
Mishandling
Improper drilling
Tool drops
Contamination
Improper sanding
Substandard material
Inadequate tooling
Mislocation of holes or details
Damage can occur at several scales within the composite material and structural configuration. This ranges from damage in the matrix and fiber to broken elements and failure of bonded or bolted attachments. The extent of damage controls repeated load life and residual strength and is critical to damage tolerance.