Fretting and Repeated-Contact Damage in Printed Photopolymers: Contact Pressure, Slip Amplitude, Debris and Surface Evolution

Fretting is repeated small-amplitude relative motion between loaded contacts. It is not ordinary sliding wear at reduced stroke. Partial slip can nucleate edge cracks while gross slip can generate a broader wear scar, debris and progressive conformity; transitions depend on pressure, tangential force, displacement amplitude, frequency, surface state, environment and counterface. Printed photopolymers add cure gradients, orientation, pixel or layer texture, residual washing products and viscoelastic time dependence. A friction coefficient or wear volume measured in another polymer cannot therefore be transferred safely. This review defines a non-compensatory qualification framework for fretting and repeated-contact damage. It requires measured normal load and local contact geometry, actual rather than commanded slip, loop-resolved tangential force, thermal monitoring, debris accounting and failure-mode attribution. Surface polishing can alter both geometry and near-surface network state; debris can be expelled, retained or transformed into a third body. Qualification must distinguish running-in, stable response and transition, and must reserve a prospective condition for validation. Direct fretting evidence for vat-printed photopolymers remains sparse. Polymer and printed-material studies support the architecture but not universal coefficients. The defensible output is a bounded contact map for a defined printed state, counterface and environment.