Characterization of the mechanical properties for cranial bones of 8-week-old piglets: the effect of strain rate and region

Due to ethical reasons, piglets have often been employed as surrogates for children in biomechanics studies. To our knowledge, no public data detailing the mechanical properties of cranial bones for 8-week-old piglets are available. In this study, tensile tests were conducted on frontal, parietal, and occipital bone specimens derived from 8-week-old piglets at different strain rates. The cranial bone specimens exhibit obvious linear elastic behavior and an insignificant plastic stage prior to failure. The mechanical property of the parietal bone is very close to that of the frontal bone, and the property differs significantly from that of the occipital bone. The average elastic modulus and ultimate stress of the parietal/frontal bone are 4.19 times and 2.75 times as high as occipital bone, respectively, whereas the average ultimate strain is about 25% times lower than that of the occipital bone. In addition, the cranial bone exhibits significant strain-rate characteristics. As the strain rate increases from 0.001 to 10 s(-1), the average elastic modulus and ultimate stress of the parietal/frontal and occipital bone increase by about 88% and 59%, and 94% and 96%, respectively. In contrast, the average ultimate strain of the parietal/frontal and occipital bone decreases by about 32% and about 17%, respectively. The quantitative relationship between the mechanical parameters of the cranial bone and the strain rate based on the experimental data is established. A strain-rate-dependent elastic constitutive model was developed through user material subroutine and implemented into LS-DYNA. Simulation results using the self-developed material subroutine code showed that this constitutive model can be used to predict the responses of cranial bone specimens under different tensile speeds.