Question

Formula for crosshead displacement and crosshead strain

Answer 1

Explanation:

Crosshead displacement

An approximate measurement of strain and hence stiffness can be obtained by measuring the crosshead displacement of the test frame. The strain is the ratio of crosshead displacement and the initial grip separation. Hence, any slippage within the loading train will produce errors in the strain measurement. The strain values obtained from crosshead measurements will differ from the actual strain in the central region of the specimen. Stiffness measurements directly obtained from the crosshead movement need to be corrected to take into account the stiffness of the loading train. This can be a difficult task as the specimen size and geometry, and the deformation behaviour of the specimen need to be taken into account. Given the small adhesive layer deflections that occur even at large strains owing to thin bond-lines, the accuracy of strains determined using crosshead displacements must be considered suspect and should only be used for qualitative purposes