Research On The Deformation Behavior Of Rat Skin Under Creep And Cycles

The mechanical properties of skin are of great significance in such aspects,including clinical treatment of skin diseases, the development of computer aided skindisease treatment technology, evaluating the comprehensive mechanical properties ofartificial skin, and giving an insight into the studies on the mechanical properties ofsoft tissues. However, most of the researchers paid much attention to single-stepexperiments like tension, creep, stress relaxation, or cycles, while few studies werefocused on multi-step experiments.The present study chose back skins of rats as the experimental material. Firstly,uniaxial tension, single-step and multi-step creep tests were carried out. Theinfluences of stress (or strain) rate and creep stress were concerned. Much attentionwas paid to the effects of loading histories of creep and stress relaxation on multi-stepcreep. In addition, microscopic observations to microstructures of the skins aftertension, single-or multi-step creep were carried out based on the paraffin sectiontechnique, HE staining method, and optical microscopy method．It can be found thatskin is a complicated nonlinear and viscoelastic material, and the mechanicalproperties in either the single-step or the multi-step creep were stress dependent.Furthermore, loading histories of creep or stress relaxation had significant influenceon the characteristics of creep. The fiber bundles of the rat skin in creep werestraightened and elongated along the loading direction, gathered and glided. Themulti-step creep with the loading sequence of low stress creep, stress relaxation, andhigh stress creep had the largest creep strain and the lowest void ratio comparing withother multi-step creep loadings.Single-step and multi-step cyclic tests were also carried out taking the effects ofmean stress, stress amplitude and stress rate into account. Microstructures of skinsafter cyclic tests were observed. It can be found that the cyclic loading histories hadsignificant influence on the cyclic properties. The fiber bundles of the rat skin incyclic test deform under alternating loading, take place dislocation glide, generateshort crack (in single-step cycles) or long crack (in multi-step cycles with the variablemean stresses), and end with fatigue failure. The Basquin model combined with the modified SWT model can be considered to predict the low cycle fatigue life of skin insingle-step cycles. Effects of loading histories on the cyclic characteristics aredifferent attributed to the different mean stresses and stress amplitudes.