Abstract
Four stainless steel alloys, commonly used for surgical needles were tensile and bend tested. The materials included: ASTM 42000, ASTM 45500, ASTM 30200, and a Feβ12Crβ8.5Niβ3.2Moβ1.9Ti alloy. Small diameter wires in a wide range of strength levels were produced using various heat treatments and/or cold drawing. Samples from each processing condition were tensile and bend tested. Calculated yield moment and ultimate moment were determined using tensile yield strength, the flexural formula (M~(y)~ = Ο~(y)~ I/C), and the shape factor for circular cross sections (M~(u)~/M~(y)~ = 1.7). A deviation was observed between the theoretically calculated yield moment and a 2Β° offset measured yield moment. This was expected because momentβstrain diagrams provide only an approximation of yield moment due to the gradual departure from linearity. The 2Β° offset yield was termed the surgical yield because it represents the strain at which a surgical needle would start to lose functionality. A nonlinear relationship (R) was observed between measured and calculated values. The relationship (R) proved to be a function of cold work by wire drawing as measured by the change in wire length (Ξ__L__), R = a β b * In(Ξ__L__). This suggests that engineers selecting materials for bending applications such as surgical needles cannot use tensile data alone to predict bend strength. Processing history must also be known. Β© 1993 John Wiley & Sons, Inc.