Environmental Stress Cracking in Printed Photopolymers: Applied Stress, Sorption, Crazing, Crack Growth and Recovery

Environmental stress cracking is a coupled failure process. An environmental agent that produces modest swelling or property drift in an unloaded specimen can accelerate craze initiation or subcritical cracking when tensile stress, residual stress or constraint is present. Conversely, a stressed specimen may survive in air but fail during exposure. Printed photopolymers add orientation, layered defects, wash history, conversion gradients, support scars, surface inhibition and residual stress to this coupling. Unconstrained immersion, ordinary creep and post-exposure strength loss are therefore informative controls but are not, alone, environmental stress cracking tests.

This review defines a non-compensatory qualification framework for printed photopolymers under combined stress and environmental exposure. It separates uptake, plasticisation or antiplasticisation, swelling, crazing, crack initiation, crack growth and final rupture; distinguishes constant-load, constant-strain and bent-strip methods; and requires stress relaxation, changing geometry and chemical activity to be reported. Mass recovery after desorption does not prove mechanical recovery, while absence of visible cracks does not prove unchanged residual strength. Direct evidence confirms environment-dependent mechanical drift in printed photosensitive polymers, but much mechanistic environmental stress cracking literature concerns thermoplastics. That evidence can guide test logic and diagnostics, not establish quantitative limits for crosslinked vat photopolymers. No universal safe-solvent list, critical stress, exposure time or recovery factor is supported.

Keywords: printed photopolymer; environmental stress cracking; solvent sorption; applied stress; crazing; crack growth; residual strength; recovery