Comprised of at least two constituent materials of significantly different physical or chemical properties, composites are of two types: matrix and reinforcement. Modern composites are used in advanced spacecraft engineering and more commonly steel, cement, concrete and asphalt for road surfacing. The earliest composites can be dated back to the use of mud and straw as rudimentary building bricks.
Composites can be split into two main categories, commonly referred to as short fibre reinforced materials and continuous fibre reinforced materials (which are often comprised of a layered or laminate structure). Industrial damage and wear and tear through shocks, impact, loadings or repeated cyclic stresses can cause delamination, a separation of the laminate layers. Fibre pull-out, a separation of individual fibres from the matrix is also a problem.
Non destructive testing is conducted on a timely basis both throughout the production process and the ultimate use of the composite for quality control purposes. Techniques such as ultrasound, acoustic emission, resonant frequency and piezoelectric paint sensors are amongst those that can be used to identify fibre pull-out and delamination.
Alternatively samples can be taken and further studied and analyzed macroscopically, for faults and consistency in production, using a stereomicroscope, or microscopically, using an incident light microscope, in the laboratory.
Key tools and techniques include: stereomicroscopy, inverted microscopes