please see if the following paper can be of some help for you
D'Amore A, Stupak P, Rigale F, Nicolais L (1995). “Uniaxial and Biaxial Flexural Fatigue of Thermoset Based Continuous Glass Mat Reinforced Composites for Automotive Applications”. In: ESIS Publ. (1995) 19 (Impact and Dynamic Fracture of Polymers and Composites). p. 413-421, London:Mech. Eng. Publ
You can find some simple schemes of biaxial tests in D.F. Socie, G.B. Marquis "Multiaxial Fatigue", SAE Inc., 1999. You can also achieve a biaxial state of stress, using the special geometry of specimens.
If you want to perform to proportional biaxial test, you can use specific device to adapt to your uniaxial test machine. Please find here a list of papers on developed devices:
- N. Bhatnagar, R. Bhardwaj, P. Selvakumar, M. Brieu, Development of a biaxial tensile test fixture for reinforced thermoplastic composites, Polymer Testing 26 154–161, 2007.
- P. Boisse, K. Buet, A. Gasser, J. Launay, Meso/macro-mechanical behaviour of textile reinforcements for thin composites, Composites Science and Technology 61, 395-401, 2001
- G. Ferron, A. Makinde, Design and development of a biaxial strength testing device, J. Test. Evaluat. 16, 253–256, 1988.
- M. Geiger, W. Hubnatter, M. Merklein, Specimen for a novel concept of the biaxial tension test, Mater. Process. Technol. 167, 177–183, 2005.