Simulation Of Crack Propagation Of Non-crystalline Materials Under Impact Loading

The non-crystalline material is also called amorphous or glassy materials,they represent a large class of rigid solids,compared with the crystalline material,they have high toughness,excellent magnetic properties,simple manufacturing process and many other advantages as a result of their internal structure of "characteristics of short-range order and long-range disorder",so they have been more and more widely used in military and other aspects of life.Poly methyl methacrylate(PMMA)as a member of the non-crystalline material,is widely used in automobile,aircraft windshield,instrumentation,lighting because of its highly transparent,non-toxic and tasteless and excellent optical properties.However,PMMA has a certain fragility,which is very sensitive to the impact.So,in order to make it better applied to all walks of life,it is necessary to study its fracture behavior under impact loading.This paper summarizes the development of PMMA at present and establishes a mesh that can represent the characteristics of the structure of non-crystalline materials.Verified the characteristics of the model's "short-range order and long-range disorder" by the radial distribution function,which is the current mainstream verification method.The spring stiffness coefficient is calculated through the quantitative parameter mapping method proposed by Gusev,using the energy criterion based on the Griffith energy balance model as the principle of fracture.Then,the model is regarded as an ideal homogeneous PMMA material,and given its parameters,the crack propagation simulation under impact load is carried out on the two-dimensional model of prefabricated crack.In this paper,the numerical simulation of the model is performed using four different loads under the same conditions.The results show that there are several different stages during the crack propagation.The crack will begin to propagate along the pre-crack when the initial load is large enough,and with the further increase of the initial load,the rate of increase of the tensile stress at the crack tip accelerates.The velocity of the crack tip began to increase after the tensile stress reaches a critical value,the acceleration also increases as the initial load increases.After analyzing the fracture under each load in detail,we find that there are three stages in the crack propagation process.Firstly,the crack propagates along the prefabricated crack,and the fracture surface is relatively smooth.Secondly,some micobranches occur along with the main crack.In the end these microbranches increase and their own extension length also increases.Throughout the process,there are also three different stages about the speed and the tensile stress of the crack tip.They are described in detail in this paper and compared with some experimental results in the literature.