Notch Sensitivity of Vat-Printed Thermosets: Root Radius, Orientation, Cure State and Fracture-Controlled Design

Notch sensitivity in a vat-printed thermoset is not determined by a CAD radius or elastic stress-concentration factor alone. The realised root geometry, notch depth, edge condition, layer arrangement, wash and cure state, conditioning, material strength, fracture resistance, component scale and loading mode jointly determine whether failure is governed by a finite stress gradient, crack-like fracture or another local mechanism. A printed V-notch, printed U-notch, machined notch, razor precrack, central hole and natural process defect are not interchangeable.

This review defines a non-compensatory qualification framework for fracture-controlled notch design in printed photopolymers. It begins with as-built geometry and a frozen process state, separates nominal strength from local elastic concentration and crack-driving quantities, and requires the selected model to be checked against its mechanical assumptions. Theory-of-critical-distances, finite-fracture, cohesive and mixed-mode approaches may organize evidence, but any fitted material length or fracture envelope remains state- and method-specific until validated at another radius or scale. Direct studies of scaled DLP notches, sharp manufactured cracks, mixed-mode specimens, orientation- and cure-dependent toughness, and printed dental resins support the workflow. They do not establish a universal safe radius, critical distance, knock-down factor, stress-concentration factor or transferable acceptance threshold.