Experiment Analysis Of Fracture Strength For Engineering Brittle Materials

Fracture mechanics is a part of solid mechanics, which is used to study the break failing and crack growth law of solid material structure. The bearing capacity research of the defect material structure is an important part of fracture mechanics. The fracture mechanics can be applied to estimate the theoretical bearing capacity of member. It is related with structure's security reliability and optimized design. The stress intensity factor, the energy release ratio and the fracture exhaust energy are material structure's important parameters in fracture mechanics. The parameters were used to analyze the breaking strengths of cast iron, concrete and carbon steel in this paper. The material structure's break proceeding was investigated, and the theory method of estimating the structure's bearing capacity is presented with the compare of the experiment results. The main research work is following as1. The material structure strength and performance can be shown by its breaking process. The three-point bending specimens of cast iron and compact tension specimen of concrete were measured with electrical strain gauges equipment. A series of experimental curves were obtained and analyzed, such as the crack opening displacement in damaged area vs the loading, beam neutral layer position vs loading, and position of cohesive crack tip vs loading. For another cast iron three-point bending specimen, electronic speckle pattern interferometry was used to observe the crack tip field's changing with loading. With finite element analysis software ANSYS, one torsion sample was analyzed in shear stress distribution.2. In bearing capacity's research aspect:(l) A series of test samples were loaded by torsion equipment on different incision size bars of cast iron and steel materials. (2) The three-point bending experiments of 8 sized prefabricated incision cast iron specimens were finished, and the same experiments were also done on the smaller dimension specimen with prefabricated incision of same material; (3) Four kinds of size concrete compact tension fracture specimens were tested in the paper; (4) The stress intensity factor were calculated and its size effect was analyzed for two series of concrete compact tension specimens and a series of concrete three point bending beam's experimental result of formerly researchers.Through the stress intensity factor's computation formula and the double K fracture criterion, the theoretical computation method of structure bearing capacity was separately presented for different specimens. The theoretical values of bearing capacity of different samples were obtained, then the calculated peak values were compared with its corresponding experimental peak values. Just one's relative error is bigger than 10% among the 57 group specimens, so the method of estimating structures' maximum bearing capacity is feasible.