Data interpretation and use

Abstract

Material data are an essential input to all fracture and crack growth analysis; without applicable data analysis is not possible. Misinterpretation and misuse of data are major contributors to the acclaimed shortcomings of fracture mechanics, because the data interpretation problem is not a trivial one, especially where it concerns fatigue crack growth. The phrase: ‘data are data, and cannot be argued with’, is commonly misapplied. The statement may be true for the raw data, i.e. a load-COD curve, or a measured crack growth curve, but cannot be applied to the derived data, K _c, K _Ic, J _R, and dα/dN — ΔK. The latter are obtained from the raw data through an interpretation process full of assumptions such as the data reduction procedures stipulated in the relevant ASTM specifications [1–5]. Although these reduction procedures are probably the best available, they are not indisputable.