The in-plane und out-of-plane deformation of materials or composites due to external loads or internal stresses can be investigated by means of digital image correlation.
In digital imagecorrelation (e.g. microDAC, VedDAC),sequences ofimages are compared on the basis of grey values. Image sequences can be recorded for materials under stress or in a stress-free state (e.g. via trench method). The observed deformation allows conclusions to be made about longitudinal and lateral stress-strain behaviour. Various forms of analysis are possible such as:
- Residual stresses: Using a focused ion-beam (FibDAC method), a crack is introduced on the sample surface and the residual stresses can be derived from the deformation behaviour (e.g. with cure shrinkage)
- Poisson’s ratio: Under strain, the out-of-plane deformation can be observed and from this the Poisson’s ratio can be determined.
- Crack tip identification, crack development: An image sequence taken during stress testing (e.g. mixed mode bending) can be used to identify the crack tip and the length of a crack. Together with stress measurements, it is then possible to use FEM simulation to determine critical fracture parameters.