Statistical Size Effects and Weibull Analysis in Printed Photopolymers: Defect Populations, Gauge Volume and Design Interpretation

Strength scatter in a printed photopolymer is not a single material constant. It reflects the population sampled: resin and batch, printer and build, orientation and position, wash and post-cure, conditioning, specimen geometry, stressed area or volume, loading and failure mode. A Weibull fit can organize a declared population, but it does not by itself prove a weakest-link mechanism, identify the controlling defect, establish a safe threshold or justify transfer to a larger component.

This review defines a non-compensatory framework for statistical size effects and Weibull analysis in vat-printed thermosets. It separates central strength, distribution shape and lower-tail reliability; requires the estimator, censoring, confidence intervals and model checks to be reported; and distinguishes a change in sampled defect opportunity from geometric, energetic, surface and process-state effects. Effective stressed area or volume is treated as a model quantity tied to the stress field and flaw population, not as nominal specimen volume. Statistical evidence must be paired with fracture-surface or defect observations, while preserving their detection limits. Direct evidence from geometrically scaled DLP specimens, printed dental resins and process-sensitive strength studies supports a state-resolved workflow, but not universal Weibull parameters, specimen counts, allowables or size-scaling laws.