Crutch and Cane Tip Failure Physics, and a Wide Wet-and-Mud Tip Design

The rubber tip is where a crutch or cane meets the ground, and it is where the device fails. Under a stated gait model the friction required at the tip is the tangent of the shaft angle: 0.2679 at 15 degrees and 0.3640 at 20 degrees. Against published friction ranges, a standard rubber tip (wet tile mid-range coefficient 0.22, mud 0.20) has slip margins below 1.0 at ordinary gait angles on wet tile (0.821) and mud (0.746). At a peak load of 257.5 N a standard 25 mm tip applies 524.6 kPa and punches through model mud, while abrasive wear removes its 4 mm sole in about 304,994 cycles and shaft buckling (safety factor 11.3) is not limiting. A proposed 90 mm flexible cleated skirt tip raises contact area by a factor of 12.96, cuts mud pressure to 40.5 kPa, limits sink depth to 34.1 mm, restores slip margins above 1.0 at 15 degrees on wet tile, wet concrete and mud, and costs $2.11 per tip in parts. It still fails on ice, oily floors, steep wet slopes, and at 20 degrees on wet tile. SIMULATED, NOT MEASURED: all numbers are reproducible from the deposited compute.py.