RESUMEN
Objective To construct a variable-parameter nonlinear model for the research on stress relaxation properties of human intervertebral disc under the cyclic strain. Methods The variable-parameter nonlinear model combined with experimental data on stress relaxation and creep response of the intervertebral disc were used to study stress relaxation properties under the cyclic strain and compare the differences of linear and nonlinear model in viscoelastic properties of the intervertebral disc. Results The cycle modulus and relaxation coefficient obtained by the variable-parameter nonlinear model under the of frequency 0.01 Hz was very close to the experimental data, and the cyclic modulus under the frequency of 0.1 and 1 Hz were also close to the experimental data, but the relaxation coefficient obtained in 0.1 and 1 Hz had serious distortion. Conclusions The intervertebral disc experiences a nonlinear stress behavior under the compression strain, so the variable-parameter nonlinear model is more suitable for studying the stress relaxation response of the intervertebral disc under the cyclic strain.