A biaxial fatigue testing rig which employs cruciform specimens loaded by four double-acting hydraulic cylinders has been improved by the addition of a closed-loop servo-control system. This system enables the loads or strains in the two principal directions to be varied independently of each other. The paper describes the modifications that were made to the system and the various problems then encountered. Further development work was then necessary before the rig operated satisfactorily. The details are published to be of assistance to others who may wish to construct specialist servo-controlled hydraulic testing equipment.
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