Influence of High Hydrostatic Pressure on the Flow Stress of Copper Polycrystals

Abstract

The influence of high hydrostatic pressure on the flow stress of polycrystals of high-purity copper (OFHC) and of tough pitch copper (TPC) has been studied at room temperature and compared with that obtained with pure aluminium polycrystals which has already been reported by the authors. Pressurizing under pressures up to 15000kg/cm2, tensile tests at atmospheric pressure and under 12000kg/cm2 using the differential pressure method, and tensile tests under a constant hydrostatic pressure of 12000kg/cm2 have been carried out. Results obtained are as follows: (1) Pressurizing up to 15000kg/cm2 gives no effect on the flow stress of OFHC copper at atmospheric pressure. As for TPC, a remarkable increase of flow stress at atmospheric pressure is observed at the beginning of deformation after pressurizing under 12000kg/cm2. The increase of the flow stress falls rapidly with increasing strain and becomes almost zero at about 40% strain. The repeated pressurizing during tensile testing has the same effect as that due to the pressurizing applied only once before deformation. (2) The change of flow stress observed by the differential pressure method with the pressure difference between atmospheric pressure and 12000kg/cm2 is about 2.2% for OFHC copper and about 2.6% for TPC. The change in OFHC copper agrees with that in the shear modulus of copper measured by Lazarus. (3) Tensile tests under a constant pressure of 12000kg/cm2 show that the flow stress of OFHC copper increases by about 2% at the beginning of the deformation and by about 5.5% under about 15% strain or more as compared with that at atmospheric pressure. As for TPC, the change in the flow stress is approximately expressed as a sum of the amount measured for OFHC copper and that due to the effect of pressurizing for TPC.

Electron Microscope Observation of Dislocation Structure in Pressurized Tough Pitch Copper

“…No pressurizing effect is thought to appear in pure metals of the cubic system, but it is observed in the case of tough pitch copper containing many Cu2O inclusions, since the compressibility of these inclusions is much different from that of copper. The pressurizing effect in tough pitch copper has been briefly described in a previous paper (7). In the present paper, the results of transmission electron microscopy observation on the dislocation structure induced inclusions in tough pitch copper by pressurizing up to 15 kb are reported and the mechanism of the pressurizing effect in this material is discussed.…”

Influence of pressure dependence of the yield criterion on the strain-rate-intensity factor

“…All these solutions have been found for pressure-independent yield criteria. It is, however, known that many metals reveal some pressure dependence of the yield criterion while the incompressibility equation is satisfied with a high accuracy [8][9][10][11]. The double-shearing model proposed in [12,13] satisfies these requirements and can be adopted for describing the deformation processes of such metals [9].…”

“…It is convenient to introduce a Cartesian coordinate system xy whose axes coincide with the planes of symmetry of the layer. Thus x ≡ α and y ≡ β, and ξ αβ should be replaced with ξ xy in (8). Due to symmetry, it is sufficient to obtain the solution in the domain x ≥ 0, y ≥ 0.…”

Axisymmetric Thermo-Elastic-Plastic Problem Under Plane Stress Conditions

“…In the case of isotropic materials, Plastic yielding of some metallic materials is affected by the hydrostatic stress [36][37][38][39][40][41]. In many cases the yield criterion proposed in [42] is adequate for such materials.…”

“…The yield criterion of some metallic materials depends on the hydrostatic pressure [36][37][38][39][40][41]. According to [37,40,41] a suitable pressure-dependent yield criterion for a wide class of metallic materials is the one proposed in [42].…”