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

The cortical bone, an essential component of the human skeletal system, effectively disperses and absorbs external impact forces, protecting the internal bone marrow cavity, surrounding soft tissues, and organs from damage. To investigate the mechanical response of cortical bone under impact loading, quasi-static and dynamic compression experiments were conducted on porcine cortical bone at different strain rates using a universal materials testing machine and a Split Hopkinson Pressure Bar (SHPB) apparatus. Observations of the deformation characteristics of the cortical bone under compression were made using a super-depth-of-field 3D microscopic system and Digital Image Correlation (DIC) technology. The experimental data was fitted using a viscoelastic constitutive model that accounts for damage, to determine the constitutive parameters within the model. The results indicate that the compression process of cortical bone is characterized by the initiation and propagation of bone cracks, with its mechanical properties showing significant strain rate dependency. Both elastic modulus, yield stress, and compressive strength increase markedly with the rise in strain rate. Under quasi-static loading, the stress-strain curve includes stages of elastic and plastic deformation; whereas under high strain rate loading, the stress-strain curve remains elastic until strains less than 0.2%, after which it exhibits pronounced nonlinearity as the compression increases, without evident plastic deformation, revealing certain viscoelastic features. Comparing the experimental curves with theoretical curves derived from the constitutive model, the discrepancy between theoretical values and experimental values is minimal, accurately describing the compressive mechanical behavior of cortical bone at different strain rates. This research provides valuable theoretical reference for the treatment and protective design against human impact injuries. This translation conveys the scientific study's setup, methodology, findings, and implications regarding the mechanical behavior of cortical bone under varying conditions of strain rates, emphasizing the importance of this knowledge for medical applications.