COMPLETE EIGEN-SOLUTIONS FOR ANTI-PLANE NOTCHES WITH MULTI-MATERIALS BY SUPER-INVERSE ITERATION

Ln this paper, the super-inverse iterative method is proposed to compute the accurate and complete eigen-solutions for anti-plane cracks/notches with multi-materials, arbitrary opening angles and various surface conditions. Taking the advantage of the knowledge of the variation forms of the eigen-functions, a series of numerical techniques are proposed to simplify the computation and speed up the convergence rare of the inverse iteration. A number of numerical examples are given to demonstrate the excellent accuracy, efficiency and reliability of the proposed approach.

New Methods of Determining the Mixed Mode Stress Intensity Factors for V-Shaped Notch

In this paper, on the basis of the stress field given by D.H.Chen, three new photoelastic methods are developed for determining the stress intensity factors K1 and K2 of V-shaped notch. Some photoelastic experiments are performed on a skew -symmetric 45° notch. Measurements of the coordinates components of r,θand fringe order N are made for progressively smaller fringes and used in the proposed methods to solve K1 and K2.Plots of apparent K vs. r/l are made and extrapolated to the notch tip to yield the true values of K1 and K2.The results obtained by the three methods are very close to each other. When the notch problem is simplified as a crack problem, the corresponding equation is identical to the one proposed by D.G. Smith, which shows that the proposed methods are applicable for both notch and crack problems.

Rockburst process and strength-weakening effect of the high-stress circular tunnel under internal unloading

To investigate the influence of unloading effect of a circular tunnel face on rockburst process,by innovatively combining rock drilling unloading devices and triaxial systems,the strain rockburst simulation under the entire stress path of“high initial stressþinternal unloadingþstress adjustment”(HUS test)was realized for the intact cubic red sandstone samples(100 mm×100 mm×100 mm).Comparative tests were conducted on cubic red sandstone samples with prefabricated circular holes(425 mm)under the stress path of“prefabricated circular hole+þhigh initial stress+stress adjustment”(PHS test),thereby highlighting the influence of internal unloading on rockburst failure.The test results revealed that with an increase in vertical stress,the sidewalls in both the HUS and PHS tests suffered strain rockburst failure.Compared with the PHS test,the initial failure stress in the HUS test is lower,and it is easier to induce sidewall rockbursts.This indicates that the internal unloading influences the sidewall failure,causing an obvious strength-weakening effect,which becomes more significant with an increase in buried depth.The strain rockburst failure was more severe in the HUS test owing to the influence of internal unloading.V-shaped rockburst pits were formed in the HUS tests,whereas in the PHS test,arcshaped rockburst pits were produced.It was also found that strain rockburst failure may occur only when the rock has a certain degree of rockburst proneness.

Influence of maximum principal stress direction on the failure process and characteristics of D-shaped tunnels

To investigate the failure process and characteristics of D-shaped tunnels under different maximum principal stress directions θ, true-triaxial tests were conducted on cubic sandstone samples with a through D-shaped hole. The test results show that the failure process can be divided into 4 periods:calm, buckling deformation, gradual buckling and exfoliation of rock fragment, and formation of a Vshaped notch. With an increase in θ from 0° to 90°, the size of the rock fragments first decreases and then increases, whereas the fractal dimension of the rock fragments first increases and then decreases. Meanwhile, the failure position at the left side shifts from the sidewall to the corner and finally to the floor, whereas the failure position at the right side moves from the sidewall to the spandrel and finally to the roof, which is consistent with the failure position in underground engineering. In addition, the initial vertical failure stress first decreases and then increases. By comparing the results,the failure severities at different maximum principal stress directions can be ranked from high to low in the following order: 90°>60°>30°>45°>0°.