A Device for Biaxial Testing in Uniaxial Machines. Design, Manufacturing and Experimental Results Using Cruciform Specimens of Composite Materials

The present study deals with the design and manufacturing of a mechanical device to perform biaxial testing in universal (uniaxial) testing machines. A review of previous definitions of similar devices is carried out and a new device is conceived and developed. The main improvement with the present device is that it allows different types of biaxial loadings (tension-compression) to be performed with few manipulations. The device allows variable displacement ratio to be used in each loading direction, giving then rise to variable loading ratios. Biaxial tension-tension tests on cruciform specimens made of composite material were carried out using very brittle samples in which the fibre direction was perpendicular to the loading plane. Strain gages were used to monitor the percentage bending parameter so that the correct alignment of the loading could be checked. Values below 5% for the bending parameter were achieved at the moment of failure.