Mechanical Response And Fracture Mechanism Of Tempered Laminated Glass Under Impact Load

The central and western regions of Inner Mongolia are located on the high-pressure front edge of Mongolia and the center of sandstorm high activity area in China.The unique climate and geographical environment of this complex region can easily cause strong winds carrying sand particles,falling objects from high altitudes and other impact loads to the impact damage to the tempered laminated glass material.The damage caused the durability and safety of building glass envelope structure to decline.This study based on the actual service environment of tempered laminated glass damage by impact in the central and western regions of Inner Mongolia.The spherical pressure impact test was carried out.According to the spherical pressure impact load,a complex stress wave was generated inside the tempered laminated glass,and the external appearance was small deformation,combined with the fracture process after impact,apply stress wave basic theory to analyze the internal shock stress wave response law;apply elastic mechanics and composite material mechanics to analyze the impact dynamic response law of external deformation and stress;apply fracture mechanics to analyze the crack propagation law of tempered laminated glass under impact load and the mechanism of impact fracture with surface damage,and then the influence of surface damage on the impact resistance of tempered laminated glass is studied.This project was funded by the National Natural Science Foundation of China(Grant No.11662012)and the Inner Mongolia University Youth Science and Technology Talent Support Program(Grant No.NJYT-17-A09).The specific research content is:1.According to the ball pressure impact test,the initiation,propagation,and fracture processes of radial cracks and annular cracks after the impact damage of tempered laminated glass are discussed,and the causes of the two types of cracks are analyzed.The internal complex stress waves and the external manifestations are small deformation determines the potential damage area(interface(1),free surface);simulates the contact impact process of strong wind carrying sand particles and falling objects from high altitude,analyzes the relationship between the steel ball impact load and the impact height,indicating the maximum Impact force,impact action time,impact contact area,and maximum contact stress change with the impact height of free fall;three fracture modes and three fractures criteria of brittle materials are analyzed,which provide theoretical basis for subsequent analysis.2.The impact of steel ball will excite complex transmission and reflection waves inside the material.The basic theory of stress wave is used to establish transmission and reflection attenuation models in the thickness direction of the laminated glass,and the characteristic line solution method is used to solve the attenuation law of the stress wave on the front,combined with the potential damage area,the failure mechanism of tempered laminated glass under stress wave is proposed,and the influence of the wave impedance difference and thickness of each layer of material on the stress wave is analyzed,and the structure design of laminated glass with unequal thickness is carried out.The results show that: the impact stress wave presents an exponential decay law,and attenuates to the failure locations produce transmitted and reflected waves.First,select a sandwich material with close wave impedance to control the reflected wave amplitude at interface 1,and then increases the thickness of the laminated glass to reduce the reflected wave amplitude at the free surface,and increasing the thickness of the glass is more significant than increasing the thickness of the sandwich.when both sides are impacted,the laminated glass should be designed with equal thickness;when one side is impacted,the impacted surface is designed to be thicker than the non-impacted surface,which has obvious advantages.3.The impact of the steel ball will cause small external deformation of the material.Applying elastic mechanics and composite material mechanics,a dynamic response model is established,and the stress field,strain field and displacement of the tempered laminated glass under impact are analyzed.According to the law,the influence of glass type,load type,thickness,and equivalent method on the dynamic response of tempered laminated glass is studied,and the structure design of laminated glass with unequal thickness is carried out.The results show that the force and displacement response are divided into contact loading period,contact unloading period,and late release period.They increase first and then decrease.The greater the impact force,the shorter the impact time and the time required to reach the peak displacement,the greater the peak displacement reached.The stress wave propagates symmetrically and continuously attenuates so that the displacement field,strain field,and stress field are symmetrically distributed,and the impact of load has the greatest impact on the impact point,and the lower surface of the impact point area is pulled and tensile failure occurs,the boundary area is compressed under pressure,while the damage on the upper surface is just the opposite.The mechanical response of homogeneous glass of the same thickness is smaller than that of laminated glass,and the mechanical response caused by dynamic load is less than static load;the degree of reduction of mechanical response of increasing the glass thickness by the same multiple is about increase 3 times the thickness of the interlayer.4.According to the internal and external mechanical response of material caused by the impact load,which causes the brittle fracture of tempered laminated glass with surface micro-cracks.Apply fracture mechanics to analyze the law of crack propagation.The ring-shaped micro-crack is formed when the maximum tensile stress at the boundary of the circular contact zone is greater than the surface tensile strength.Radial cracks are caused by micro-cracks or defects that continuously produce a small amount of separation after being impacted,and finally expand and penetrate.Annular cracks are formed by fan-shaped glass beams formed after radial cracks are broken and connected after being impacted.Both are open fracture modes of cracked bodies.According to the criterion stress intensity factor criterion,the critical condition of crack propagation is established,and the impact fracture mechanism of tempered laminated glass with surface damage is studied,and then the influence of surface damage on the impact resistance is studied.The results show that the crack fracture process under impact load is divided into two stages: crack initiation and crack propagation.The crack initiates in the compressive stress layer,and the external field stress needs to overcome the expansion resistance and pre-applied internal stress;When the crack expands to the tensile stress layer,only the expansion resistance needs to be overcome.Although the greater the tempering stress,the greater the fracture strength,but it will decrease with the increase of the deepest surface crack depth,that is,the surface damage will reduce the impact resistance of glass.