Nonlinear acoustic approach to material characterisation of polymers and composites in tensile tests.
The paper reports on experimental study of elastic nonlinearity of polymers and glass fibre-reinforced (GFR-) composites in a wide range of tensile stress applied (up to a fracture limit). Focused slanted transmission mode (FSTM) of air-coupled ultrasound is adapted for remote generation and detection of flexural waves in the samples of plastics. Local noncontact measurements of flexural wave velocity as a function of static strain are used to calculate the second-order nonlinearity parameters beta2 and study their behaviour through a loading cycle. Molecular untangling and crazing phenomena are identified, respectively, with maxima of positive and negative beta2 in thermoplastics. In composites, mechanics of fibre-matrix interaction is considered for brittle and plastic fractures. Hysteresis in velocity variation during loading-unloading cycle is used as an indicator of residual defect accumulation.
Solodov
I
I
Institute for Polymer Testing and Polymer Science (IKP)-Nondestructive Testing, Stuttgart University, Pfaffenwaldring 32, Stuttgart D-70569, Germany. solodov@ikp.uni-stuttgart.de
Pfleiderer
K
K
Gerhard
H
H
Busse
G
G