STIFFNESS OF COMPRESSION TESTING MACHINES

ABSTRACT A ring test with six participating laboratories and rubber stoppers as reference material was performed to monitor the performance of commercial compression testing instruments. Testing conditions were chosen to be in the range of regular compression testing. Small, single screw instruments with a cantilever exhibited a significant deviation in the force/deformation‐response compared with double‐screw instruments with a crosshead. Additional tests made with an external device for displacement recording revealed that these differences have to be attributed to insufficient stiffness and some compliance in the cantilever of the tested single‐screw instruments. Some consequences of the test results for experiments on soft, semi‐soft and rigid food materials are discussed and an equation is developed to correct for the flexing of the cantilever beam in the single screw machine.