Locally Resolved Strain

A laser extensometer type W-80 was used to measure strain at an aluminum sample. The specimen was equipped with 18 markers.

Throughout the experiment, time, force and strain were recorded. The data evaluation software automatically calculates the stress from the force and the initial cross section.

Stress Strain Diagram

The figure on the right hand side shows a stress strain diagram, and two strain time diagrams. The noise in the stress signal represents actual variation in the load of the specimen.
The red curve represents the integral strain measured over the complete length of the specimen. The blue curve shows a strain signal of a small selected range of the specimen.While there is nothing special to be seen with integral strain, the local strain clearly shows step like behaviour.

Distribution of Strain Over The Sample

The next figure depicts the distribution of strain along the specimen over time. Data points connected by the lines 'in parallel' to the zone axis are recorded at the same time. The specimen has an inhomogeneous deformation behaviour. For instance at the end of the experiment, the zones with the larger marker numbers (17-18) reached a certain strain level, while the zones with lower marker numbers (16-17, 15-16, ...) come to this strain level later in time. The strain 'starts' at the right hand side and grows to the left hand side.