(4) The bending strength, the critical crack length andthe critical crack mouth opening of concrete beams are size dependence. Theinfluence of stress-crack opening relationship on the above materialparameters is significant.

Experimental research and theoretical analysis of critical load selection, difference between specimens with and without fatigue crack, and crack length and width effects were carried out.

Crack length estimated by unloading tangent and secant compliances are approximately equal to the traction-free segment of crack and the measured crack length respectively.

the interface stress, beam deformation and energy release rate (ERR) of 4ENF are derived in this study in the new light of the crack tip deformation as well as the numerical finite element analysis.

The result shows that the gas concrete is sensible in crackle,the value of fracture toughness doesn't depend on initial crackle length,and for the large samples,the values of fracture energy and fracture toughness fits the equation K~2_(IC)=EG_F.

Then,two symmetrical minor cracks were placed in the structure,and the effects of variation in the lengths of the minor cracks on the stress intensity factors of the main crack were analyzed.

The influences of the length of cracks and heterogeneity are studied in uniaxial direct tension. Then in uniaxial compression the fracture processes of samples with one or two pre-existing cracks are simulated. And the influences of geometries and distance of two pre-existing cracks on interaction mechanisms of two pre-existing cracks are studied.

The relationship between medial crack length and normal loading was also investigated when specimens were indented by symmetrical wedges with interior angles of 30°-120°.

The magnitude of the finite dynamic stress field depends on the crack length, the parameter describing the functionally graded materials, the circular frequency of the incident waves and the lattice parameter of materials.

It is also found analytically that the energy release rates remain constant once the interface fractures, independent of the initial crack length.

An algorithm for separate determination of the interfacial adhesion and friction from experimental relationships between the crack length and applied load is described.

The effects of crack length and patch geometries including the length and number of plies on the failure behavior of the repair were identified.

The measurement of fracture toughness KIC for 5 rock types, such as marble, granite, limestone, etc., is described in this paper. Rocks and metals manifested different features of behaviors in the research. Experimental research and theoretical analysis of critical load selection, difference between specimens with and without fatigue crack, and crack length and width effects were carried out. It is noted in this paper that the crack propagation mechanism is different between the specimens with and without fatigue...

The measurement of fracture toughness KIC for 5 rock types, such as marble, granite, limestone, etc., is described in this paper. Rocks and metals manifested different features of behaviors in the research. Experimental research and theoretical analysis of critical load selection, difference between specimens with and without fatigue crack, and crack length and width effects were carried out. It is noted in this paper that the crack propagation mechanism is different between the specimens with and without fatigue crack due to the influence of structural discontinuities in rocks, and as a consequence KIC has a noticable difference; the KIC decreases while the crack width is increasing from 0.02 to 0.3 mm5 and the values of KIc for rocks are linear dependent with the tensile strength measured using the Brazil test. Consequently some suggestions for the measurement of rock fracture toughness using three-point-bend method are proposed.

In the case of sub-brittle fracture, at the crack tip there is a small plastic region of which effect should not be neglected. In this paper, the authors consider that both the crack length and the stress at infinity change are due to plasticity, and compared the results calculated by five different methods.

The author used the chevron notched short-rod specimen for fracture toughness test suggested by ISRM in his experiment. The specimen is Kallax gabbro from Sweden with diameter of 71.4mm. Under a certain load level, flourescent penetrant is injected into the crack of specimen. It is then divided into some slices with 4～8mm thick and length of each crack is measured to obtain the crack front in the specimen. It is found that crack fronts can be considered to be straight. Crack length estimated by unloading tangent...

The author used the chevron notched short-rod specimen for fracture toughness test suggested by ISRM in his experiment. The specimen is Kallax gabbro from Sweden with diameter of 71.4mm. Under a certain load level, flourescent penetrant is injected into the crack of specimen. It is then divided into some slices with 4～8mm thick and length of each crack is measured to obtain the crack front in the specimen. It is found that crack fronts can be considered to be straight. Crack length estimated by unloading tangent and secant compliances are approximately equal to the traction-free segment of crack and the measured crack length respectively. The difference between them equals the length of FPZ approximately which is about 10mm.

本实验研究采用国际岩石力学学会建议的V型切口短棒岩石断裂韧度试件,岩石为瑞典的卡莱克思(Kallax)辉长岩,试件直径为71.4mm。把试件加载至不同的载荷水平后,向裂纹注入荧光渗透剂;然后,把试件切成厚度为4～8mm的岩片并测量每一岩片上的裂纹长度,以获得各试件的裂纹前端曲线。结果表明,裂纹前端曲线可以被认为是直线。分析表明,根据卸载切线柔度估计的裂纹长度近似地等于裂纹的无表面力段长度,根据割线柔度估计的裂纹长度等于测量的裂纹长度;两者的差值近似地等于FPZ(Fracture Process Zone)长度,其值约为10mm.