Moment-curvature measurement in thin sheet--part II: yielding and kinking in aged steel sheet

摘要

The bending equipment described in Part I is used to study the behaviour of a sample of galvanised steel sheet. The sheet is known to have an internal stress distribution and to exhibit ageing. Tensile and bend behaviour is measured for the sheetin the "as-received" condition, after ageing at 170℃ and 300 ℃ and after ageing and stress relieving at 450 ℃. In the bend test, attention is focussed on the imposed outer fibre bending stress at the limit of linear, elastic bending. In the"as-received" condition, this is substantially less than the tensile yield stress, but increases rapidly with ageing and for ageing at 300 ℃ it is approximately 200 M Pa greater than the lower yield stress in the tensile test. Samples treated at 300 and450 ℃ showed maxima in the moment/curvature characteristic and unstable "kinking" was observed in bending. The bending moment versus curvature diagrams presented indicate material characteristics of importance in technological forming processes which are not easily identified in tensile tests.