Residual-Stress Measurement in Photopolymerised Parts

Residual stress in photopolymerised parts is not observed directly. It is inferred from deformation, strain release, diffraction, optical response or a coupled constitutive model. Each route samples a different spatial scale and stress component, and each embeds assumptions about elastic behaviour, geometry, material symmetry, time dependence and the stress-free reference state. A value obtained from a thin coating on a beam is therefore not interchangeable with a near-surface hole-drilling result or a lattice-strain measurement.

This review defines a measurement architecture for residual stress in cured photopolymers and photopolymer-based parts. Curvature and cantilever methods, incremental hole-drilling, sectioning and relaxation, diffraction and coupled in-situ instruments are compared by measurand, invasiveness and model dependence. Particular attention is given to viscoelastic recovery, cure-state evolution, fixture compliance, thickness ratios, anisotropy and the frequent absence of a usable crystalline diffraction signal in neat amorphous networks. Validation requires synthetic or reference cases, repeat measurements, independent deformation fields and sensitivity to constitutive inputs. The central conclusion is that a residual-stress result is defensible only when the released or retained strain signal and the inverse model that converts it to stress are both reported. This review does not prescribe cure-shrinkage control, warpage mechanisms or universal stress limits.