Reinforced-plastic microcracking

Molecular orientation results in increased stiffness, strength, and toughness (Table 8-12) as well as resistance to liquid and gas permeation, crazing, microcracks, and others in the direction or plane of the orientation. The orientation of fibers in reinforced plastics causes similar positive influences. Orientation in effect provides a means of tailoring and improving the properties of plastics. 

A fiber reinforced composite material with a polymer matrix will typically absorb moisture in a humid environment and at elevated temperatures. Combined exposure to heat and moisture affects reinforced plastics in a variety of ways. First, the hygrothermal swelling causes a change in the residual stresses within the composite that could lead to microcrack forma-... 

During application, plastics are exposed to ambient conditions where temperature and humidity vary. This combined effect, known as the hygrothermal effect, may influence the mechanical properties of plastics. The properties of glass fiber-reinforced plastics are more affected by this combined influence than by one of the two factors alone. Moisture absorption in reinforced materials is mainly characterized by diffusion. The capillary effect and transport along microcracks is another way to absorb moisture. Moisture absorption by the latter two mechanisms is often a direct consequence of moisture absorption caused by hot and humid ambient conditions. 

Applications of scanning acoustic microscopy include the detection of delaminations, grain structures, voids, microcracks, strain and surface roughness from different plastics and GFR composites. SCAM allows inspection of carbon flbre/epoxy resins and carbon fibre/PEEK composites [396]. Ultrashort probe pulses (50 MHz) provide a resolution of 100 /um and have been used for imaging of bulk microstructure of fibre-reinforced composites [397]. 

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