Study On Fracture Process Of Multiple Cracks In Cement-based Materials

There are many cracks in the engineering materials and engineering structures,and there may be interaction between adjacent cracks,which easily leads to structural damage.Concrete are the main engineering materials in modern times,and most of them contain unequal cracks.The PVA fiber cement-based composites materials have excellent ductility and impede the crack growth.Therefore,it is of great significance to study the fracture process of multiple cracks in cement-based materials.The subject is based on the test and numerical simulation,with the aid of non-contact measuring equipment,the multiple crack interaction,crack initiation and propagation mechanism of cement mortar,concrete and PVA fiber cement-based composites materials were analyzed by prefabricating primary and secondary cracks.The main contents of the paper are as follows:(1)The strength and failure modes of cement mortar specimens with different number of secondary cracks and crack spacing were studied through test and numerical simulations.The results were as follows: The strength of specimens decreases with the increase of the number of secondary cracks;and the strength of specimens increased with the increase of crack spacing;The specimen started to crack from the tip of the primary crack,and the initiation mode was mostly wing crack;There was a good agreement between the test and the numerical simulation;The influence of different crack angles,lengths,spacing and lateral pressure factors on the failure of specimens were studied by the numerical simulation.The results were as follows: The influence of crack angle on specimens was the most obvious,while the influence of length factor was the least;After the crack spacing increases to a certain value,the rise in the strength of the specimen was significantly reduced;The existence of lateral pressure will impede the crack initiation and crack growth..(2)The strength and failure mode of concrete specimens with different number of secondary cracks and crack spacing were studied by means of non-contact measurement via test and numerical simulation.The results were as follows: The change of strength and crack initiation law are the same as those of cement mortar specimens;Strain concentration appeared firstly at the crack tip of the specimen surface,and the strain range and strain between cracks are larger than those at the outer tip of other cracks;Strain cloud maps have obvious stages.(3)The research methods of PVA fiber cement-based composites materials were consistent with those of concrete,and the results were compared with those of concrete.The results were as follows: Both materials had the same regularity of strength change and crack initiation;By comparing the results of concrete,this composite had an advantages of large deformation,high residual strength and good energy absorption capacity;The PVA fiber could effectively prevent the growth of crack;With the increase of the number of secondary cracks,the shear strain of the crack increases,but the shear strain trend of all the cracks in the same specimen was consistent.