Study on the Effect and the Eliminate Method of Preloading Force on the Compression Tests of Liver Tissue

The mechanical response of liver tissue is commonly characterized by compression tests of specimens. The preloading force between the compression platform and the specimen is often ignored in compression tests. In the present study, unconfined and no-slip compression tests of liver tissue with preloading forces were performed. Based on collected mechanical responses of unconfined compression tests with five preloading forces, the influences of the preloading force on the constitutive model parameters and elastic moduli were analyzed. An indirect optimization method was proposed to eliminate the influence of the preloading force. Pre-strain caused by the preloading force is considered in the constitutive model in this method. The collected mechanical responses are applied to obtain the constitutive model and preloading model PUCT parameters with proposed indirect optimization method. Based on the optimization constitutive model parameters, FE models with different sample sizes were established. Preloading model PNSCT was established by numerical tests with different sample sizes. Based on the preloading model PNSCT, the collected mechanical response of no-slip compression test with a preloading force (0.05 N) was corrected. The results show that the indirect optimization method can eliminate the effect of the preloading force on liver tissue properties, and the corrected mechanical response is closer to the actual mechanical response.