Design Values for Printed Photopolymers: Why Classical Allowables Methodology Does Not Transfer, and What Does

Statistically based material design values are intended to bound population variability with declared confidence, production representativeness and environmental applicability [1,2]. Classical A-basis and B-basis terminology provides a useful model for distinguishing a population-bound value from a mean, but its labels and tabulated values cannot be copied automatically to vat-photopolymerised materials. An interlaboratory study using aliquots from one photopolymer-resin batch found large scatter in working-curve parameters when procedures, light engines and measurement capability varied [3]. This demonstrates that even a nominally common material can produce incompatible parameter populations when state and method are not controlled. ER-171 defines a bounded path from state-resolved test data to a usable design value: declare the material-process population, preserve independent sampling levels, control method capability, select and justify a distribution or nonparametric approach, calculate a one-sided population bound with declared confidence, apply environmental and process knockdowns separately, and requalify when the population definition changes. It does not prescribe a universal sample size, distribution, allowable, safety factor or regulatory route.