Eliminating friction between flat specimens and an antibuckling support during cyclic tests using a simple sensor

Abstract

Friction between flat specimens and antibuckling supports during cyclic tests can change the shape of cyclic curves in the compressive direction. Therefore a simple sensor has been designed that can be attached to any pre-existing test rig so that the friction force exerted on a specimen can be measured independently from the stress and the strain. The stress signal obtained during an experimental run is then compared with the friction force signal, and the delay between the signals can be determined. Hence the stress due to the friction is subtracted from the stress signal measured on the test rig to obtain the real stress signal. The method has been validated using two metals: an aluminium alloy AlMgSi0.5 and a complex phase steel CP 800. For the aluminium alloy, a noticeable change in the compressive part of the cyclic curve is observed due to the friction whereas a minor influence of the friction is detected for the steel. However this friction component in the compressive direction can now be eliminated using the friction sensors to establish the true cyclic curves.