Fatigue-Crack Growth and Subcritical Fracture in Vat-Photopolymerised Thermosets: Crack Preparation, Cyclic Driving Force, Environment and Qualification
Segurola, Juan
2026-08-27 · Informe · Versión 1.1
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Fatigue qualification of vat-photopolymerised thermosets is often reduced to cycles to failure for smooth specimens. That measurement is useful but does not quantify the propagation of a pre-existing crack, the operational threshold below which growth becomes difficult to resolve, or the interaction between cyclic driving force and the printed material state. This review separates unnotched fatigue life, crack initiation, fatigue-crack growth and monotonic instability. It organises the problem around the load ratio R, stress-intensity or energy-release-rate range, maximum-cycle driving force, crack-length measurement, specimen geometry, precrack preparation, build orientation, post-cure, residual stress, temperature, frequency and environment. The literature available for printed photopolymers supports strong process-, orientation- and state-dependence of mechanical response, but direct, standards-complete da/dN datasets for VPP thermosets remain limited. Consequently, metallic-material, bulk-plastic and composite standards are treated as method sources whose scope must be declared, not as automatic validation routes. A minimum reporting matrix and failure-mode table are proposed. The central conclusion is that defect tolerance cannot be inferred from tensile strength, impact resistance, static KIC/GIC, or an S-N curve alone. A defensible claim requires a sharp and documented crack, measured growth under a defined cyclic history, state-resolved conditioning, and an application- specific link between the crack-growth law and the defect population of the printed part.