METHOD OF MEASUREMENT OF STRESS AND STRAIN WHOLE PROCESS MATERIAL PARAMETER BY USING OF HYDROSTATIC PRESSURE UNLOADING

摘要

A method of measurement of stress and strain whole process material parameter by using method for hydrostatic pressure unloading is disclosed, which is directed to the cyclic test of loading and unloading. With the assumption that only the deviator stress generates damage to the sample, a test method of the hydrostatic pressure unloading is invented in order to calculate mechanical parameters in different stages of stress and strain. Nine mechanical parameters can be calculated in connection with hexahedral pores connecting samples in the true triaxial test. Six mechanical parameters can be calculated for non-pores connecting samples. Nine mechanical parameters can be calculated in connection with hexahedral pores connecting samples in the traditional triaxial test. Six mechanical parameters can be calculated for non-pores connecting samples. The specific expressions and test methods are provided.

主权项

1. A method of measurement of stress and strain whole process material parameter by using of hydrostatic pressure unloading, being inappropriate for the residual traction stress not to be considered for the simulation of cyclic mechanical behavior, wherein: when a loading stress is greater than a proportional limit stress, unloading is carried out in different stress states until the hydrostatic pressure tends to zero and corresponding material parameters are calculated according to a linear segment of unloading curve; for pores connecting material, when the external loading stress is greater than the proportional limit stress and under a condition without drainage, unloading is carried out by water pressure in arbitrary stress states until the water pressure tends to zero and the corresponding material parameters are calculated according to a linear segment of unloading curve of the water pressure;specific steps are as follows:
(1.1) applying a hydrostatic pressure first in a true triaxial test, assuming σ11=σ11H, σ22=σ22H, σ33=σ33H, a relation between the hydrostatic pressure and an initial strain εiiH is:
σiiH=Ciijj0εjjH, i,j∈(1,3)   (1)where Ciijj0 is an initial stiffness matrix;
(1.2) applying a deviator stress q, q=σ11+σ11H−σ11H; when the applied deviator stress is greater than the proportional limit stress qYield, linear stress-strain relations are expressed as:
σ11+σ11H=C11jjbεjj   (2)σiiH=Ciijjbεjj,i∈(2,3), j∈(1,3)   (3)where Ciijjb is a stiffness matrix after exceeding yield limit stress space;
for the material parameters in stress state exceeding yield limit stress space, magnitudes thereof are calculated according to the linear segment of unloading curve and unloading is carried out until the hydrostatic pressure tends to zero, C1111b,C1122b, C1133b is calculated using the equation (2), C2222b, C2233b, C3333b is calculated using the equation (3), as known from the symmetry of the stiffness matrix, C2211b=C1122b, C2233b=C3322b, C3311b=C1133b, C2211b, C3311b, C3322b are checked at the same time, that is, calculating the six material parameters and checking the three material parameters; when the material is completely isotropic,∑j=13C11jjb=∑j=13C22jjb=∑j=13C33jjb,the volume modulus CV,CV=∑i=13∑j=13Ciijjbcan be calculated; or when equal amounts are unloaded in three directions at the same time, 1/CV can be calculated;
(1.3) closing a valve and carrying out non-drainage test for pores connecting material after the application of the hydrostatic pressure is completed under a condition of saturation, assuming that Bishop effective stress exists, then the equation (2) and the equation (3) are expressed as
σ11+σ11H−α11P=C11jjbεjj   (4)σiiH−αiiP=Ciijjbεjj, i∈(2,3),j∈(1,3)   (5)under the condition of saturation in which material stiffness parameters Ciijjb are obtained and the external applied stress σii, i ∈(1,3) is kept constant, the water pressure of non-draining test is unloaded from Pa to Pb, the strain εii then sprung back from εiia to εiib, the corresponding amount of deformation spring back is εiia−εiib=−Δεii, the equation of increments for the equation (4) and the equation (5) are:
αiiΔP=CiijjbΔεjj(αii,i∈(1,3))   (6) Pa−Pb=ΔP three Biot coefficients α11, α22, α33 can be calculated from the equation (6).