Fracture Mechanics Analysis For ?-? Mixed Mode Fracture In Concrete

The study of fracture characteristics of concrete structures under external loads is of great significance to the anti cracking design of concrete structures and the residual strength of damaged structures.The fracture properties of quasi brittle materials such as concrete and other brittle materials are different from those of metal materials.The fracture characteristics are greatly influenced by the fracture process zone(Fracture Process Zone).For concrete structures,they are usually under the action of combined stress field.Most of the cracks in the structural concrete exist in the form of composite.The most important part is the composite cracks of type I and II.Research on the composite load,fracture characteristics of concrete materials,concrete specimen fabricated straight partial cracks,studied with the mixed mode crack propagation by three point bending load,joint distance ratio and offset center cracks on fracture properties of concrete etc..The cracking load,the peak load,the fracture criterion and so on are studied.The main conclusions are as follows:(1)Based on the digital image correlation method,respectively measurements are320mm×100mm×80mm 400mm×100mm×100mm 480mm×100mm×120mm and 560mm×100mm×140mm.The three point bending test specimens during the test loading process are used to prefabricate the opening displacement,tangential displacement and size of the fracture process area.The results show that the fracture height ratio has a great influence on the length of the fracture process zone relative to the offset position of the crack,and the length of the fracture process zone is smaller and smaller with the increase of the slit height ratio.(2)Three point bending tests were carried out on the concrete with a size of400mm×100mm×100mm and the ratio of slit height to 0.2,0.3,0.4 and 0.5 respectively.The influence of crack height ratio on initiation load,peak load and final fracture angle was studied.With the increase of the slots ratio,both the crack load and the peak load tend to decrease,but the final fracture angle increases with the increase of the height ratio.(3)Comparative Analysis Based on the theoretical data of fracture criterion analysis and maximum circumferential stress criterion of finite fracture mechanics shows that the final fracture angle of specimens increases with the increase of crack height ratio and the increase of crack offset distance.