Study on compressive mechanical tests and constitutive models of cortical bone under different strain rates

Cortical bone, as a critical component of the human skeletal system, effectively disperses and absorbs external impact forces, protecting the internal medullary cavity, surrounding soft tissues, and organs from damage. In order to investigate the mechanical response of cortical bone under impact loading, quasi-static and dynamic compression experiments were conducted on porcine cortical bone at varying strain rates using a universal material testing machine and a split Hopkinson pressure bar apparatus. The compression deformation characteristics of cortical bone were observed by employing ultra-depth three-dimensional microscopy and digital image correlation techniques. A viscoelastic damage constitutive model was applied to fit the experimental data, and the model parameters were determined. The results demonstrate that the compression process of cortical bone is characterized by the initiation and propagation of microcracks, and mechanical properties of the material exhibit significant strain-rate dependence. The elastic modulus, yield stress, and compressive strength increase significantly with increasing strain rates. Under quasi-static loading, the stress-strain curve consists of distinct elastic and plastic deformation stages. In contrast, under high-strain-rate loading, the stress-strain response remains purely elastic at strains below 0.2%, but transitions into a highly nonlinear regime with increasing compression. Notably, no significant plastic deformation occurs under dynamic loading, revealing pronounced viscoelastic behavior. Comparison between the experimental data and theoretical curves from the constitutive model shows good agreement, with minimal deviations between predicted and measured values. The model accurately captures the compressive mechanical behavior of cortical bone across different strain rates. This study provides theoretical references for the treatment of impact-induced human injuries and protective designs.