Laser Speckle Extensometer
The laser speckle extensometer is a laser extensometer for contactless two-dimensional strain and deformation measurements on materials in real time .
The measuring principle is based on the evaluation of speckle patterns , which are reflected back from the surface of the measuring objects when illuminated with coherent laser light. One or more cameras record the pattern and evaluate it using FFT correlation analysis.
The Laser Speckle Extensometer is able to record the surface movements of the measuring object 2-dimensionally (XY-direction) without contact and to determine the "true" or logarithmic expansion based on the local measuring object displacement . The technical elongation can be determined if the originally selected partial patterns are followed in the camera image and the measuring length thus increases with the measured elongation of the material. The "true" or logarithmic expansion is measured if the selected patterns and their position are not tracked and thus only the movement of the surface past the selected measurement positions is recorded as the pattern flow.
The Laser Speckle Extensometer works without marks. This means that there is no external influence on the sample before or during the measurement. By using area cameras, the longitudinal and transverse expansion of materials can be recorded and evaluated at the same time. High and low temperature measurements in climatic chambers down to −40 ° C or ovens up to 1600 ° C are also possible, as measurements can also be made through multiple thermal glazing.