The techniques available for making predictions of structural component lifetimes are currently limited to 2D. For example, in linear elastic fracture mechanics, the crack tip stress state, used to relate crack growth rates to lifetime, has only been calculated for simple geometries (e.g. compact tension specimen in plane-strain (2D) conditions). Extending the 2D fracture theory to 3D via finite element analysis is still limited because key input parameters (e.g. fracture toughness, Young’s modulus) are measured under 2D conditions. The uncertainty from these approximations leads to lifetime predictions which can vary by an order of magnitude. The necessary measurement to inform lifetime predictions is the 3D stress state at a crack tip.