抄録
The hydrogel of Wyoming bentonite shows characteristic slip patterns under critical stress σ0, i.e. the shear strength for slip fracture. In the previous paper, the present authors reported that the shear strength of the bentonite gels are related to the shear modulus, G, as follows:
σ0=γ0G, (1)
where γ0 is a proportional constant bearing nearly equal value to the critical strain γc obtained experimentally i.e. 1/10∼1/30, and G varies depending upon the concentration. Those experiments were carried out at the rate of strain ranging from 10-3 to 10-4sec.-1
In this report, the dependence of σ0, γc and G on the strain rate was examined. Fig. 1 gives the stress-time curves obtained at various rate of compression (Rsec-1). The critical shear stress or the shear strength σ0 increases with the increasing strain rate, especially above 10-3sec-1 (Fig. 2). At the lower rates than 5×10-5sec-1, no slip fracture was observed but the specimens showed viscous flow. Fig. 3 shows the dependence of G on the strain rate R, where G takes almost constant value in the range of strain rate, 10-3∼10-1sec-1, but decreases apparently at lower rates of strain than 10-3sec.-1 The critical strain γc obtained experimentally remains almost constant at the strain rate between 10-3∼10-1sec-1 as shown in Fig. 4, when the linear relation (1) holds aproximately between σ0 and G. Dependence of σ0/G on the rate of strain is discussed further.
