Device for biaxial testing in uniaxial machines. Design, manufacturing and experimental results using cruciform specimens of composite materials

Abstract

The present work deals with the design and manufacturing of a mechanical device to perform biaxial testing in universal (uniaxial) testing machines. A review of previous similar proposals is carried out and a new proposal of a device is suggested, allowing tension-tension, compression-compression and tension-compression biaxial testing to be used in single axis machines, with relatively few manipulations. The device allows variable displacement ratio to be used, giving rise to variable loading ratio. A series of experimental biaxial tension-tension tests on cruciform specimens made of composite material have been carried out using samples in which the ftber direction is perpendicular to the loading plane. Strain gages have been used in both loading directions and at both sides of the specimen, to monitor the bending parameters. Values below 5% for the previously mentioned bending parameter have been achieved at the instant of failure. The device allows, in the tension-compression configuration, the use of standard (straight) specimens, by substituting the grips by pushers in the compression loading direction. The device has been designed to be used up to 20 KN.