Analysis And Experiment On Crack Resistance Of Quasi Brittle Engineering Materials

Quasi-brittle materials are widely used in engineering.There are not only stress and deformation under the action of external force,but also are the change of internal defects or micro cracks,and even macroscopic cracks and expansion.On the one hand,the fracture behavior of cast iron with preformed cut is analyzed by its electron microscope photographs in uniaxial tensile.On the other hand,the effect of steel fiber on crack resistance in concrete is discussed through the shrinkage cracking experiment of steel fiber concrete.The main contents are as follows:1.The uniaxial tensile test of cast iron with pre-cut incision was carried out by scanning electron microscope(SEM).As to the damage area image before macroscopic fracture in different load,the electron microscopic image was analyzed through the fracture mechanics theory of solid mechanics.And the affecting factors of microcrack density is analyzed in the paper.2.Based on the mechanism of concrete shrinkage cracking,the experimental study on modified concrete with 1% ~ 3% steel fiber content is carried out,and there is cracking analysis of plain concrete.The effect of steel fiber is analyzed on the cracking resistance of concrete.3.A simple two-dimensional mechanical model was established,according to the cracking experiment of steel fiber concrete.The influence of some factors,such as crack angle relate the steel fiber,the distance relative crack tip and fiber debonding length,was analyzed on the crack tip stress intensity factor of fracture mechanics.For the cracking resistance of concrete,the experimental result is compared with its theoretical analysis to verify the rationality of theoretical calculations.4.Through the finite element analysis program,the properties of materials such as concrete,steel fiber,are involved in the numerical program.For the simulation of concrete shrinkage,the mechanical model is established with a select of corresponding ABAQUS unit type.The stress distribution in the model is obtained by numerical calculation.The tensile strength of the fiber,and the stress intensity factor at the crack tip are also obtained in the calculation.The simulation results are compared with the theoretical results and the experimental phenomena,which verifies the rationality of the finite element model.