A study of biaxial viscoelastic behavior

An experimental study is made to investigate the feasibility of determining a viscoelastic stress-strain law for two (or three) dimensional stress conditions by means of one dimensional tests. The conclusions are based upon comparison of theory and experiment for a creep test of a lead plate, subjected to biaxial tension.

The stress-strain law that was selected is given by

S_ij = B σ²/σt² e_ij + c σ/σt e_ij

to cover ehear effects and by

σ_ii = κε_ii

for hydrostatic tension or compression. S_ij and e_ij are respectively the stress deviator and σ_ii and ε_ii are the stress and strain tensors. Uniaxial test data was used to evaluate the constants in the above laws.

The Lapplace transform technique was used to obtain the analytical solution for the strain in the plate as a function of time. Agreement between theory and experiment or the duration of the test, 1200 minutes, was quite good.