Anisotropic biological bone micro-grinding mechanical behaviors

Micro-grinding is widely used in orthopedic surgery. However, as an anisotropic and viscoelastic fiber-reinforced composite material with hard and brittle, biological bone tissue is prone to excessive mechanical stresses during micro-grinding. This can lead to force-induced damage, micro-crack formation, and even bone fractures. Current models inadequately account for bone tissue anisotropy, resulting in reduced accuracy that limits the application of micro-grinding technology. To address this, we propose a novel method for characterizing hard-brittle bone tissue mechanical properties and micro-grinding forces. First, based on hyperelastic strain energy theory and generalized viscoelastic model, we established an anisotropic hard-brittle bone tissue nonlinear viscoelastic constitutive model and experimentally validated it. Second, we divided the bone micro-grinding removal process into ductile regime removal stage and brittle fracture removal stage, then developed an anisotropic hard-brittle bone tissue micro-grinding force model by incorporating the established constitutive model. Subsequently, bone anisotropy was classified into three principal orientations—vertical, crossed, and parallel—with experimental validation of the micro-grinding force models in each orientation. The results demonstrated force prediction errors within 8.57% (x-axis) and 9.86% (y-axis) for vertical orientation, 14.64% (x-axis) and 15.74% (y-axis) for crossed orientation, and 14.05% (x-axis) and 9.05% (y-axis) for parallel orientation. Further, to investigate the effect of micro-grinding parameters on anisotropic hard-brittle bone tissue grinding forces, single-factor grinding experiments were conducted. The results show that lower grinding depth and feed rate combined with higher wheel speed can reduce grinding forces. Under identical conditions, grinding forces follow: vertical direction > cross direction > parallel direction. This study provides theoretical foundations and technical support for optimizing bone grinding processes and precise force control.