Finite element analysis of human finger injury under blunt impact: Subcutaneous hemorrhage and laceration

• Finite element model of the index finger developed from MRI data. • Model validation confirmed by comparison with volunteer experiment data. • Thresholds for subcutaneous hemorrhage and skin lacerations estimated. • Impact load simulations show hemorrhage at 0.1 J and skin lacerations at 0.6 J. Although previous studies have investigated soft tissue injuries using experiments or computer simulations, few have addressed injury thresholds specific to the human finger, despite the high frequency of finger-related incidents in human-robot interactions. This study aimed to estimate the impact load thresholds that cause minor finger injuries, such as subcutaneous hemorrhage and lacerations, using finite element analysis to enhance the safety of machinery, including cooperative and service robots. A finite element model of the right index finger was developed based on magnetic resonance imaging data from a 28-year-old male participant, incorporating anatomically accurate bone structures with visco-hyperelastic soft tissue properties. The model’s validity was first confirmed by comparing the force-displacement responses from volunteer experiments with simulation results. Subsequent simulations were conducted to estimate the impact load thresholds that induce minor injuries, in which a cylindrical indenter impacted the middle phalanx of the model under varying conditions. Maximum principal strain in soft tissue was used as the injury criterion, with thresholds set at 0.315 in subcutaneous tissue for hemorrhage and 0.260 in skin for laceration. The results indicated that subcutaneous hemorrhage may occur at 0.1 J (3.2 kg, 250 mm/s), while skin lacerations may occur at 0.6 J (19.2 kg, 250 mm/s). Injuries were concentrated near the indenter’s edge, particularly in areas where soft tissue was thinner near the proximal finger base. These findings aid safety designs for collaborative robots, suggesting future research on varied loading conditions and geometries.