Application of hybrid force/position control on parallel machine for mechanical test

The quality of mechanical test is strongly linked to the control of boundary conditions and loaded tool path in applied forces or displacement of a tested specimen. In this article, a hybrid force/position control algorithm is adapted to parallel kinematic mechanical test machine with regards to the tested specimen behavior and realized mechanical test. This control algorithm is illustrated on a Nooru-Mohammed test performed on Gough Stewart platform and validated experimentally on a 5 bar parallel mechanism. The principle of the Nooru-Mohamed test consists in submitting a double notched concrete test part to a position slope, inducing a combination of shear and tension loading. The extra degrees of freedom of the parallel machine are used to control boundary conditions.