University Partnerships

Over the last few years, the demand for testing solutions that accommodate smaller and smaller specimens has grown. Sometimes specimens are small because they are taken from components with small geometries and sizes, or sometimes it is useful to examine the scaling effects of the material characteristics. Even in the fields of standardization, standard mini-specimens have already been defined for various materials.

In this context, ZwickRoell has begun a joint project with the Lucerne University of Applied Sciences and Arts aimed at optimizing how such mini-specimen are handled.

For this project, a new specimen grip for micro tensile specimens has been designed as part of a bachelor's thesis. The paper examines both the handling and alignment of small specimens.

Direct strain measurement is particularly important. A high resolution and a high degree of accuracy is vital since the absolute deformation often equals only a few µms due to the dimensions of the specimen. That is why laserXtens compact HP is the ideal extensometer. Only one non-contact measuring system can deliver reliable test results for specimens with these dimensions.

The image below shows a titanium alloy specimen from the IISc Bangalore with a complete stress-strain curve. The black curve was measured by laserXtens compact and the red curve was measured with the moving crosshead.

ZwickRoell decided to design a fixture for a biaxial tensile test based on a publication submitted by Nihon University for the 2011 ZwickRoell Science Award. In contrast to a standard biaxial testing machine, the multi-axial stress state is achieved in a universal testing machine by means of a deflector.

The deflector is mounted in a standard testing machine and a compressive force is applied across four arms to a cruciform specimen in the X and Y directions. The force values are recorded by four load cells, and the deformation of the specimen is recorded from below by a videoXtens or laserXtens system.