Specimen Clamping
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Specimen clamping
Force- and form-fitting specimen clamping
In the quasi-static tensile test, the test specimen is clamped at opposite ends in the corresponding test specimen holders of the material testing machine or suspended in a form-fitting manner (see Figure). The test specimen must be adjusted so that an axial force is applied in the load line of the testing machine (see: load framework) and bending stresses are avoided.
| Figure: | Test specimen clamps for tensile stress with (a) tensile test specimens with shoulder heads as form-fitting clamps and (b) force-fitting clamps |
The test specimen is loaded with a steadily increasing, impact-free force, usually until a fracture occurs.
Requirements for specimen holders
The specimen grips for tensile tests must cover a wide range of applications. The specimen grips form the mechanical connection between the specimen and the material testing machine. Their task is to initiate the movement of the traverse or piston into the specimen and to transfer the test force generated to the force transducer located on the load framework. Modern clamping jaws can also be equipped with pneumatic or hydraulic elements to vary the horizontal holding force.
The specimen grips for tensile tests must ensure the following:
- Axial stressing of the specimen
- Bending stresses must be avoided
- The test specimen must be held in place without slipping until a fracture occurs
- Fracture of the test specimen in the area where the force is applied must be avoided
- The test force must be distributed evenly across the cross-section and transmitted over the entire test length
- Test specimen replacement must be as simple and quick as possible
See also
- Tensile test compliance, Influence of test specimen clamping
- MMB-specimen
- Relaxation plastics
- Viscoelastic material behaviour
- Material testing machine
References
- Dripke, M., Michalzik, G., Bloching, H., Fahrenholz, H.: Mechanische Prüfverfahren und Kenngrößen – kompakt und verständlich, Volume 1: Der Zugversuch bei quasistatischer Beanspruchung. Castell Verlag GmbH, Wuppertal (2002), pp. 58/59 (ISBN 3-934255-50-7; see AMK-Library under C 14)