Jamming of fingers: an experimental study to determine force and deflection in participants and human cadaver specimens for development of a new bionic test device for validation of power-operated motor vehicle side door windows

The deformability of human fingers is central to addressing the real-life hazard of finger jamming between the window and seal entry of a power-operated motor vehicle side door window. The index and little fingers of the left hand of 109 participants and of 20 cadaver specimens were placed in a measurement setup. Participants progressively jammed their fingers at five different dorsal-palmar jam positions up to the maximum tolerable pain threshold, whereas the cadaver specimens were jammed up to the maximum possible deflection. Force-deflection curves were calculated corresponding to increasing deflection of the compressed tissue layers of the fingers. The average maximum force applied by the participants was 42 N to the index finger and 35 N to the little finger. In the cadaver fingers, the average of the maximum force applied was 1886 N for the index finger and 1833 N for the little finger. In 200 jam positions, 25 fractures were observed on radiographs; fractures occurred at an average force of 1485 N. These data assisted the development of a prototype of a bionic test device for more realistic validation of power-operated motor vehicle windows.