Geometry Independent R‐curves in a Titanium Alloy Using a Normalised Axis for Crack Growth

Abstract

Data from a study of the effect of geometric variation on J-R curves for a titanium alloy in three-point bending are presented up to large amounts of growth. Four series are reported, various widths, various a / W ratios, various thicknesses and various absolute sizes, all failing in the limit load regime by stable tearing. Analysis is made in terms of J,-R curves, adjusted to a common initiation toughness, J , , to clarify the effects of geometry. Strong trends are then found with absolute size over a four fold range and with width over a two fold range; a weaker trend with a / W over a four fold range but practically none with thickness over a nine fold range. Many of these trends are different from those reported for other more ductile materials but consistent in some cases with those reported for another high strength material, HY130. All the deep notch cases (14 tests) reduce to a single group when plotted as J,,, against a normalised abscissa, Aa/b,, with a very slight trend to a higher curve for the thinner pieces. NOMENCLATURE a = crack length b = specimen ligament ( W-a) B = specimen thickness E = Young's modulus C = elastic energy release rate J = J-integral S = specimen span U =work done w = internal energy W = specimen width q = eta factor (relating work done to the J-integral) u = stress Subscripts c = critical fl = flow i = initiation m = modified J-integral o = original PI= plastic component of the J-integral tot = total (elastic plus plastic) value of the J integral y = yield

Some Mechanical Characteristics of Nitrogen Structural Steels

“…The influence of test specimen geometries and test methods on the deformation and fracture characteristics has been studied frequently (e.g. [5,6]). In most cases the final microstructure and mechanical properties are developed only after heat treatment.…”