Ultrasonic Determination of Anisotropic Damage in Fibre and Textile Reinforced Composite Materials

The description of the very complex damage and failure behaviour of fibre and textile reinforced composites in damage models is objective of various research efforts. Such models strongly depend on the nature of the reinforcement (fabric, uniaxial or multiaxial layup) and additionally on micro-cracking geometry. With respect to the practical applicability the number of input parameters of damage models should be in a reasonable way as low as possible. However, damage formulations have to be complex enough to cover the physic of the material and the anisotropic characteristic of damage in composites. Within this theoretical and experimental investigation BASTE’S phenomenological model where damage is defined as the change of the elasticity tensor, will be proposed as a suitable description approach. In combination with this model, the determination of the anisotropic stiffnesses by ultrasonic phase velocity measurements will be shown to be the predestined experimental method. A specific ultrasonic device was developed to provide a system for an efficient recovery of the stiffness tensor coefficients from convenient sets of velocity measurements. Linked to a tensile machine, it is possible to measure the anisotropic damage of fibre and textile reinforced composites. The approach has a smeared and general characteristic and is consequently independent and unlimited in terms of the composite reinforcement nature, crack geometry and failure mechanisms.