Who is Xiao Zhang? What happened? It can arouse the attention of the whole network. It turns out that this is a news released by golden eye in 1818: Ningbo boy Xiao Zhang recently took a bath when the toughened glass door of the bathroom of the rental apartment suddenly broke, causing Zhang’s hand injury. Because he could not reach an agreement with the property on the compensation scheme, he contacted the media to expose the matter. < / P > < p > an ordinary civil dispute, unexpectedly, has evolved into the number one hot event in the whole network, and even occupied the top spot of hot search for almost a whole day. Many people are puzzled about the reason why Xiaozhang was the top of the list in airborne search. Only after reading the comments can they understand that the most important reason may be related to Zhang’s appearance. After all, the comments were all uniformly about Zhang Shuai. < / P > < p > the influx of more and more gourd eaters has led to a continuous rise in the popularity of the incident. Even in the afternoon, the topic “how can Zhang be so handsome and injured” rushed to the top five of the hot search. Why does tempered glass have higher strength than ordinary glass? And why did it break suddenly? Is toughened glass and bulletproof glass the same thing? What are the special properties of toughened glass? < / P > < p > with the east wind of Xiaozhang incident, we gourd eaters should learn some common sense of life related to glass besides appreciating Xiaozhang’s beautiful appearance. < / P > < p > in essence, the materials of tempered glass and ordinary glass are similar, and there are no special points. What makes toughened glass produce strengthening effect is its unique manufacturing process. < / P > < p > the normal production process of flat glass is as follows: the raw material is melted at high temperature to form a uniform glass liquid without bubbles; when the glass liquid is cooled to the temperature range for mechanical processing, it is rolled to form a flat plate shape; the internal stress of the cooled glass is very large, and it needs to be annealed again, that is, heating at a lower temperature for a period of time and Slow cooling to reduce internal stress and stabilize internal structure. For tempered glass, a strengthening step should be added at the end of the above-mentioned process. Specifically, after the ordinary glass with definite size is obtained, it is heated to the softening point of about 650 ℃ to 700 ℃, and then the glass is blown with high-pressure air at both sides to rapidly cool it. At this time, the surface of the glass will first cool down and contract, and a structure with high internal compressive stress will be formed in the surface layer of both sides. Then the cooling center will have high internal tensile stress. Finally, a compressive stress layer of about 1 / 6 glass thickness will be formed on both sides of the glass. < / P > < p > then why is the compression on both sides and the tension in the center instead of the reverse? This is mainly because when the two sides of the glass are subject to cold contraction, any position on the surface will be squeezed from all directions, so a compressive stress layer will be formed in the surface layer; and because the cooling in the center is slow, there is no time to shrink, so a tensile stress layer is formed. The stress can be understood as the “internal” force inside the material, and the higher stress means that there is extra energy stored in the material, so the “restless” factor will be formed. For example, during the summer watermelon harvest, some ripe watermelons will burst when they encounter a little external force, which is the expression of internal stress in watermelon. Glass, as a material, has a very remarkable property, that is, it is not afraid of tension and pressure. It has a strong resistance to external pressure load, but the ability to bear tensile load is much lower. If we put a piece of flat glass in a frame around it, it’s like a glass roof or the deck of a glass gallery bridge. We will find that when the glass is affected by the load, the upper part is still in the state of compression, but the lower part is actually in the state of tension. When the load increases gradually, the bending degree of glass is deepened, and the tensile stress under the glass is also increasing. Finally, the lower part of the glass, the unloaded side, will fail first. The compressive stress region on both sides of the toughened glass counteracts the effect of load, and the tensile stress on the weak side of glass (the side without load) will not increase to the same extent as that of ordinary glass, so it is not so easy to fracture. Generally speaking, the strength of glass after strengthening treatment can be increased to more than 3 to 5 times of the original. Although tempered glass has high strength, it is absolutely not impregnable. Moreover, once the toughened glass is damaged, it will disintegrate rapidly and become slag. As we have said above, tempered glass is actually a kind of material with great internal stress. Under normal circumstances, the compressive stress and tensile stress can be balanced, and the glass can naturally maintain a good external state. However, once this balance is broken, the huge internal stress will be released instantaneously, which will be transferred from the weak point of the first failure to the whole glass, making it break quickly. < / P > < p > there are many kinds of weak points that occur first. For example, the collision in the process of glass installation and movement will damage the compressive stress layer on the edge and even the surface and form cracks. If the crack is deep enough to reach or approach the tensile stress layer, the failure of internal balance will make the toughened glass break immediately. Therefore, the movement and construction process of tempered glass should be very careful to avoid any defects. Because even very shallow surface cracks will become the weak link of future fracture. < / P > < p > there are also weak points from the inside, such as impurity particles in the glass manufacturing process. In daily life, tempered glass may disintegrate without any external force, which should be caused by internal impurities. Glass production process, of course, including raw material purification process, but in any case there will be residual impurities. The most common impurity in glass is nickel sulfide, which accumulates in the form of particles inside the glass. Once the external force (or even no external force) is applied, the area around the nickel sulfide particles will break first, and the whole glass will also disintegrate. < / P > < p > in order to avoid the occurrence of this situation, many manufacturers will carry out heat soak test on each piece of glass during the production process of tempered glass. The specific method is to heat the glass to about 300 ℃ and then cool it down. The glass with nickel sulfide can’t withstand this kind of toss and will disintegrate automatically, so as to ensure that the finished products do not contain internal impurities as much as possible. However, it is difficult to avoid the disintegration of tempered glass in principle. In addition to improving the product quality as much as possible, some protective measures can be taken, such as sticking transparent organic film on the glass, so that even if the glass disintegrates, the slag will not be scattered and splashed. < / P > < p > in China, if the toughened glass of building exterior wall is more than 3 meters above the ground, it is required to adopt the film pasting process. However, the disintegration of toughened glass is frightening, but far safer than ordinary glass. The internal structure of tempered glass determines that it will not produce large sharp fragments in the process of disintegration, but form small pieces without sharp edges and corners. Moreover, the so-called disintegration is not like an explosion, and the energy generated by the internal stress of the toughened glass is far from enough to make the fragments fly in all directions, and it is more likely to fall in situ. I’m afraid Xiao Zhang was injured because the tempered glass disintegrated. The distance between him and the glass is too close. I hope he can recover as soon as possible. < / P > < p > many people have seen videos of hammering toughened glass with a sledgehammer on TV, and they are still intact under the hammer. However, the strength level of toughened glass is not enough to resist bullets. The bullet has huge kinetic energy and small action area, so it is not difficult to break the toughened glass. < / P > < p > there are two kinds of real bulletproof glass. One is transparent polymer materials, such as polycarbonate, PVB resin and polyurethane. In the actual manufacturing process, multilayer structure is generally used instead of single thick layer. < / P > < p > the other is the inclusion of a transparent organic layer in the middle of the glass. Generally, the multilayer structure is also adopted. In this way, although the glass will be broken after impact, the organic polymer layer can still make the fragments firmly bond together. < / P > < p > bullet proof glass does not rely on its own firmness to release the bullet, but dissipates the kinetic energy of the bullet through the broken glass and the capture of the resin layer, so as to stay on the resin layer. In order to achieve sufficient bulletproof effect, the thickness of bulletproof glass is also increasing. For example, the transparent mask of bulletproof helmet or the observation window of bulletproof shield is more than 30mm thick. However, in daily life, ultraviolet light will change the properties of the polymer layer, affecting the ballistic effect, so the life of bulletproof glass is about 3 to 6 years. < / P > < p > there is also a kind of glass, which is not as high as bullet proof glass in terms of impact resistance, but also has the characteristics of energy absorption and anti disintegration, which is the so-called anti-theft glass. If the anti-theft glass is hit by a hammer, it will not break down as a whole. Moreover, in a short period of time, the sharps can not break through enough holes for people to enter. It can be said that it is a civil version of bulletproof glass. Although the strength of tempered glass is higher than that of ordinary glass, the heat resistance and thermal shock resistance of tempered glass are not higher than that of ordinary glass, and it is likely to disintegrate under the impact of rapidly changing temperature. When using polarizer to observe tempered glass, if the reflection of light, viewing angle and the color of glass back meet certain conditions, interference fringes will be seen, which is caused by the stress inside. < / P > < p > tempered glass may disintegrate, but this kind of dangerous accident should be avoided. Therefore, the manufacturer should pay more attention to it in the production and subsequent installation process. After all, this can affect everyone’s safety, and it is hoped that there will be no more cases of injury caused by toughened glass. More Samsung devices can now run Android applications on PC through your phone