Deformation behavior of a alpha brass in plane stress/plane strain

Abstract

IntroductionGenerally a simple power law ~ = K E" (where K and n are empirical constants called the strength coefficient and the work hardening coefficient respectively) is used to describe plastic stress-strain dependence of deformable metals (1,2). This equation was employed by Low (3) to describe the uniaxial tensile behavior of an annealed 70/30 brass. The slope of the corresponding double logarithmic true stress-true strain plot gives a single value of n. However, this fit is not always adequate. Geil and Carwile (4) reported a deviation in the linearity of the double logarithmic plot for steel. Two sets of K and n values were used to describe the stress-strain relationship in a spheroidized hypo-eutectoid steel by Wilson and Konnan (5). Various reasons, such as grain size effects, cementite particle distribution, cell formation, stacking fault energy, etc. were proposed to rationalize the double-n behavior (6-9). Ollilainen reported a triple-n behavior for a decarburized steel (10).A study by Valkonen (11) of the mechanical behavior of a Clausing specimen was carried out for an AISI 1090 spheroidized steel. A good dimensional description of the Clausing specimen is given elsewhere (12). Fig. 1 shows the geometry and dimensions of the specimen. The deformation field in the gage section of the specimen on applying a uniaxial tensile load is described as plane stress/plane strain. The extent of these states depends on the width to thickness ratio of the specimen (13). The results of Valkonen indicate that the above steel shows a multiple-n type behavior. Three slope discontinuities were presented in the double logarithmic true stress vs. true strain plot. Concurrently, five slope discontinuities were presented in a "unified" plot of the double logarithmic engineering stress vs. true strain plot. Various reasons, relating to both material and constitutive properties, were hypothesized as to the appearance of these discontinuities. Saturation back stress at second phase carbide particles soon after yielding, self-development of a lateral constraint, the nucleation and growth of incipient shear bands etc. were given as plausible reasons.Although the observation of multiple-n behavior has been previously reported in many cases (4-11), it has not found wide acceptance, probably because of a lack of concrete experimental evidence. This work was undertaken in order to investigate further the presence of these slope discontinuities and determine possible reasons for their appearance. 70/30 c~ brass was chosen as the test material, ct brass also shows a propensity for the formation of shear bands. The Clausing specimen was chosen because of its plane stress/plane strain deformation field, its familiarity with the current investigators and its amenability, because of geometry and size, to be tested in smaller capacity mechanical testing machines. Exoerimental ProcedureThe Clausing specimens were machined from a 50.8 mm by 50.8 mm cross-section hot rolled 70/30 cx brass bar. The specimens were machined in such a way tha...

Flow behaviour and microstructural evolution in cold worked 70∶30 α-brass

“…In spite of extensive studies made [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][28][29][30][31][32][33][34][35][36] in a-brass, no report on the effect of heavy cold working on subsequent deformation behaviour exist at low as well as elevated temperatures in the cold worked 70 : 30 a-brass, except in the well annealed a-brass. For instance, the mechanisms for high strength at low temperature and the observed poor ductility at intermediate temperatures are not understood in terms of structure-property correlation in this material.…”