方解石多晶集合体的高速率简单剪切变形实验研究

本文介绍了方解石多晶集合体在高应变率(373S^-1到1507S^-1)下简单剪切变形实验,结果表明,破裂形式和应变率有关,随着应变率的增加,从晶间微破裂为主变为晶内微破裂和粉碎为主。

A STUDY OF SIMPLE SHEAR DEFORMATION OF POLYCRY- STALLINE CALCITE AGGREGATES AT HIGH-RATE

The dynamic deformation behavior of polycrystalline calcite has been studied at several very high strain-rates (373s^-1 to 1507s^-1), confining pressure of 0.1 MPa, and temperature of 20℃, by means of the torsional Kolsky bar modified for simple shear. An alloy (AZ8GU) was used as the material of torsional bars (G=26800 MPa,=2800 Kg/m³). The incident, reflected and transmitted torsional pulsed were recorded using an oscilloscope. The shear stress, strain and strain-rate were evaluated from the recorded torsional pulse signals by means of a miniprocessor.The elastic modulus of dynamic shearing determined is about 810 MPa. The relation between strain-rate and shear strength estimated is:r=2.95 × 10² exp (3.54 × 10^-2τ)The effect of increasing strain-rate is, as expected, to rise the shear strength appreciably, which seems reasonable and is consistent with other work. Due to the preferred orientation of grains in the specimen, the fracture stress may exhibit a more complex evolution with increasing strain-rate. The fracture mode in deformed specimen depends on strain-rate. Notably, three macro-mechanical fractures: shear-tensile fracture, shear-tensile and shear-compressive conjugate fracture, and shear smashing fracture are observed under varying strain-rate conditions. Detailed petrographic and scanning electron microscope (SEM) observations of deformed specimens show that slip of grain boundaries, mechanical twinning, intercrystal micro-fracturing and intracrystal micro-cracking, as well as smashing are the principal mechanisms of dynamic deformation. With increasing strain-rate of deformation, there is a transition from dominantly intercrystalline micro-fracturing to dominantly intracrystalline microfracturing or smashing.