Pressure dependence of the yield stress of potassium at low homologous temperature

Abstract

Tensile stress-strain curves for polycrystalline potassium were obtained at liquid-nitrogen temperature (T=0.23Tm) and up to a pressure of 5.15 kbar. Pressure shifts the stress-strain curve upward. The yield stress versus pressure was measured. Theoretical dislocation models for the effect of pressure on the yield stress are reviewed herein. It is shown that the effect of pressure on the yield stress owes its origin to the effect of pressure on the effective elastic constant only. The present experimental results for the yield stress σ0 as a function of pressure P are in excellent agreement with the equation σ0=σ00[1+(Ce′0/C0) P], where σ00 is the yield stress at zero pressure, Ce0 is the value of the elastic constant Ce=G/(1−ν) at zero pressure, and Ce′0 is the value of the pressure derivative of the elastic constant Ce at zero pressure. Here G is the bulk shear modulus and ν is Poisson’s ratio. If Ce′0/C0 is replaced by E′0/E0 (where E is Young’s modulus) or G′0/G0 the agreement is also within experimental error. In this study, the yield stress was found to increase by 42% at 5.15 kbar.