Glass is a typical brittle material. Crack initiation around inclusions is one of the important factors that lead to sudden fracture of glass. Fatigue crack initiation around inclusions usually takes three forms: inclusion crack, delamination of inclusions from that glass matrix material, and crack on slip lines in the matrix material. The main reason for different forms of fatigue crack initiation caused by inclusions is the difference between inclusions and matrix in elastoplasticity and thermoplasticity. For the inclusion whose thermal expansion coefficient is greater than that of the matrix, it shrinks faster than the surrounding materials after heat treatment, which causes tensile stress at the interface between the inclusion and the matrix, weakens the bonding strength between the inclusion and the matrix, and easily leads to the separation of the inclusion and the matrix, resulting in stress concentration and crack initiation. The crack initiation is affected by the shape and orientation of inclusions. When the thermal expansion coefficient of the inclusion is less than that of the matrix, the shrinkage of the inclusion is slower than that of the surrounding matrix during the cooling process, resulting in the compression stress of the inclusion, so that the interface between the inclusion and the matrix can transfer stress. At this time, the elastoplasticity of the inclusion itself will affect the initiation of fatigue cracks.

Glass inclusion crack initiation mainly has the following two aspects: (1) The elastic modulus of the inclusion is larger than that of the surrounding matrix. During the loading process, the inclusion will bear a large load, and it is easy to cause its own fracture initiation fatigue crack. At this time, according to the previous analysis, since the stress concentration area is at the two pole points of the inclusion, the crack propagation is affected by the local stress, and the maximum stress is close to the pole of the inclusion, and the fatigue crack is easy to initiate at this position. (2) The modulus of the inclusion is smaller than that of the matrix. During the loading process, it will bear a small load and increase the stress of the matrix around it, which will easily lead to the generation of slip bands and cause the matrix to crack and initiate fatigue cracks. At this time, if the external load is tensile stress, all the principal stresses near the inclusion poles are tensile stress, and the maximum principal stress is greater than the far-field stress. Because the shape of the inclusion is generally asymmetric, the initiation and propagation of cracks are also asymmetric, focusing on the side of the inclusion with large stress near the two poles.

Another key factor leading to sudden glass fracture is the thermal residual stress near the inclusions, especially the inclusions existing in the tensile stress zone of tempered glass. Because the residual tangential tensile stress around the inclusion particles is superimposed with the tensile stress of the tempered glass, the plane tensile stress perpendicular to the glass surface around the particles reaches the maximum. When the local tensile stress reaches a certain extent, the glass will be broken. Obviously, the maximum tensile stress area around the inclusion is the source of glass fracture. In addition, when the maximum tensile stress is close to the fracture strength of the glass, a dangerous unstable system is formed. Once there is a temperature change or an external force, the local stress peak may exceed the strength value and damage occurs. The local residual stress in glass is mainly caused by the difference of expansion coefficient between glass and inclusion particles. According to the theory of elasticity, the extrusion stress is mainly determined by the temperature difference, the difference between the expansion coefficients of the two materials and the elastic coefficient. The stress state in the glass around the particle is spherically symmetric and attenuates rapidly with distance. The absolute value of radial and tangential stress is twice as different, that is, the absolute value of the maximum radial stress is twice as much as the tangential stress at the same point.