metal
Chinese and foreign scholars can't shine, so they are called translucent mirrors. The mirror faces the sun and reflects light to the wall, but there will be patterns on the back of the mirror. How is it made?
Scholars put forward various assumptions and induction, which are nothing more than two viewpoints:.
Because the structure or composition of each mirror is different, the light reflectivity is different, resulting in different light and shadow; .
Because the curvature of the mirror is uneven and the range of light is inconsistent, the light and shadow points are different.
If you look at the mirror, you can find it in the tissue, and it does have a certain relationship with the thickness of the mirror. Thin mirror (without decoration) has refined grains and no obvious α primary crystals; Coarse grains (with patterns on the mirror back) are coarsened, with obvious α primary crystals. What is the reason why this difference is not opaque in the tissue microscope? There is a bright white film on the surface of the transparent mirror in the Western Han Dynasty, and the whole mirror cover, that is, these mirrors with different original structures are covered with this film, which is almost as good in the sun. So the organization has nothing to do with the translucent mirror of the Western Han Dynasty.
In order to further clarify the difference between self-made translucent reflectors, transparent zinc sulfide is coated first, and then a layer of golden mirror translucent reflector is coated, and the result is a thorough lighting effect. If the vacuum coating method is adopted, the self-made "half lens" mirror is coated with a layer of aluminum or silver, which also presents a translucent effect. In addition, if the texture with poor tissue thickness changes, this phenomenon will be translucent, so even if the thickness varies greatly, the translucent effect is better. But in fact, almost all bronze mirrors have decorative patterns on the back, especially bronze mirrors, and some of them have great differences in thickness, such as the phenomenon that a large number of bronze mirrors are opaque. So this explanation is unrealistic.
Then, is the transparent mirror in the Western Han Dynasty formed due to the curvature difference of convex mirror? Japan can consider the irregular bending of mirrors, because mirrors are different from opaque, translucent and transparent mirrors, and the mirror effect of the former Han Dynasty is not the same as that of Japan. The light reflected by Japanese mirrors is clearer only when it is displayed at a short distance on the screen, and the image reflected beyond a certain distance is blurred; And with the increase of reflection distance and brightness, the shadow part of the image gradually increases, although the transmission mirror of the Western Han Dynasty is weakened. In addition, some hollow specular reflection images, that is, whether the edge pattern is bright or dark. Images reflected by semi-transparent mirrors before the Han Dynasty were bright solids. Judging from the transparent mirrors of Shanghai Museum, their similarities are as follows:
An edge having a width and a thickness surrounding the lens body;
Second, the mirror body is very thin, only 0.5 to 0.9 mm.
3 convex mirror, mirror back and corresponding decoration, except that the mirror curvature thickness of the whole copper mirror is relatively uniform;
Four. A decoration on the back of a mirror, arranged in a protruding ring, but not perpendicular to the circumference of the convex line.
Residual stress is the basic factor of translucent copper mirror.
It is precisely because of these characteristics of the transparent mirror in the Western Han Dynasty, and because the cast copper mirror body is thinner and the cooling speed is faster; The mirror ring is thick and slow, the mirror surface of the mirror body is still thick and the ring shrinks and solidifies, which has certain rigidity. Then the limiting lens on the narrowing mirror ring works. At the same time, the mirror body is solidified, and the lens ring also plays a supporting role. After the cold bronze mirror is assembled, the relationship between the mirror body and the mirror ring is shown in Figure 2. When subjected to radial pressure P and bending moment M(M = RMT), the residual stress generated by the reflector in the main body.
Mirror body. Because the mirror is a convex body, the residual stress tends to be on the mirror and the arch ring. However, the mirror body has a certain stiffness, and only when the mirror body is thinned to a certain extent, the bending stiffness is obviously reduced, and the radial pressure and torque have the effect of mirror deformation and obvious mirror side arching. The thickness of the lens body varies from place to place (thick, thin and unadorned). When the lens body is small, the thickest rigid part is arched, and the thin deformation is greater than the thickest, that is, the thin protrusion is greater than the thickest. This forms an integral convex convex mirror of the light-transmitting mirror to varying degrees. When the bronze mirror is rubbed, the stiffness of the whole mirror body decreases at different rates, and the mirror body is deformed in the whole growth difference. The curvature of the differential mirror is obviously more and more worn and becomes more uneven in the mirror. The difference between the curvature radius of the mirror corresponding to the back decoration and the mirror reflected in the sun is the mirror image of the light and dark image. Fig. 3 shows an enlarged schematic mirror.
The interference method uses the pictures (laser interference images) taken by laser, which can further prove that the transparent mirror of the multi-mirror is a convex mirror with sufficient curvature, and the curvature of the back of the small mirror without decoration is actually caused by the small curvature potential difference, and the fluctuation is only a few microns, which is imperceptible to the naked eye. Only by zooming in can you see the reflected image. As can be seen from Figure 3, there are thick inscriptions, small curvature and thin curvature, and there are no inscriptions. When the light is parallel to the mirror, in which the curvature is relatively large compared with the dispersion of the reflected light projected on the screen, the glare is relatively dark, and in which the focused reflected light is relatively light compared with the reflected light of the surrounding mirror with large curvature, the stereoscopic image displayed by the character pattern in the bright reflected image is opaque.
The mirror image of Japan is hollow, because it uses the method of grinding the edges of handwriting, which is a knot, in which when grinding force is applied, the largest mirror will produce corresponding concave parts and reflected light of a specific focus. This shows that both the transparent mirror and the reflecting mirror in the Western Han Dynasty had a translucent Japanese phenomenon, but the principle was opaque and not exactly the same. In order to make the bronze mirror shine, not only the theoretical mechanism calculated by measuring the overall curvature, but also another experiment proves that the consistency is caused by the curvature difference.
Polishing the residual stress into a translucent mirror will break it, or chisel off the mirror ring and separate the mirror ring from the mirror body, so that the residual stress is released, and you will find that a mirror body is not translucent. Then there is a simple test, which can confirm the above view, that is, milling off a single writing translucent mirror, that is, thinning the thick place and the thin place at the same thickness. According to the above theory, it is the phenomenon of milling thinning, where the curvature of a thin uniform arch changes in the same place, it will be the same, and it should no longer be translucent, and the result is the real situation.
In order to further prove the influence of instantaneous effect on residual stress, a simple experiment was done. When the sunlight is transparent to the mirror, the mirror can hold the ring with four fingers and use the thumb button mirror at the same time, which can find a better translucent effect.
For this reason, in another experiment, an annular copper mirror with the same diameter is at rest (see Figure 4), and a load Q is applied to the central copper buckle. The thick mirror and the thin mirror are on the opposite sides of the mirror, and the radial direction of the numerical value and the circumferential direction of the strain are measured respectively. It can be seen that with the increase of load, the strain increment becomes thinner at its thickest and faster speed ratio. In flexural members, strain is a changing curvature, that is, the magnitude of strain directly reflects the magnitude of curvature, strain can be measured, and stress can also be calculated through strain and stress, so the calculation of curvature relationship can be deduced. Although this loading condition is not exactly the same as the actual mirror, it can at least be said to be simulated additional torque and simulated residual stress of the mirror. After Q is installed, the light transmission effect of the bronze mirror increases. Such test results are directly reflected in the elastic range. From the moment of the lens body, immediately increase the curvature and thinness of different lens body thickness to prove and analyze the above facts.
Some people will ask this question: The transparent mirror of the Western Han Dynasty was more than 2,000 years ago. Can the residual stress last for so long, or will it leave a transparent mirror effect? In the study, according to the physical properties of metals, the residual stress will decrease with the passage of time, and after the residual stress is released for a period of time, it will decrease to a certain value, with the smallest change. More importantly, the original elastic deformation under stress is transformed into fixed plastic deformation, that is, the difference between deformation and certification leads to the maintenance of the whole curvature.
Friction is an important part of translucent mirror and bronze mirror.
Since the Western Han Dynasty, the transparent mirror has been broken, and so has the structure with residual stress. So, if these are not good, as long as the mirror wears thin at a certain time, will it have a translucent effect? In fact, the same mirror has translucent and opaque spots under different polishing methods. For example, the grinding force is uneven, the force around the mirror surface is uneven, and the degree of grinding is different. Some places are very thin and can't be worn for a long time, and some places are not thin enough and translucent. Of course, they can't achieve translucent effect. However, if the correct rubbing method is adopted, the friction between the mirror surface and the optical disc and the rigidity of the lens body will be small to some extent, and the mirror surface will obviously arch, which will cause the mirror surface to bend and have the influence of the difference in light transmittance.
However, it was found that the semi-transparent and semi-reflective mirrors were shattered. As mentioned above, some semi-transparent and semi-reflective mirrors are no longer semi-transparent. However, some translucent mirrors have a faint translucent effect after being broken. So this fact can explain the important role of residual stress and other factors. After our analysis, test and calculation, it is considered that there is extra elastic stress which causes friction and also makes the mirror bow.
Now we can easily analyze the result of the ideal state, as a method of post-grinding mirror image: when copper fetters the mirror blank and starts to grind the disk, the copper mirror is basically a spherical surface with the same curvature as the disk (see Figure 5), which should be completely consistent with the disk, while the disk with spherical radius with very regular curvature radius and mirror curvature radius is R. But after grinding to a certain extent, it actually jumps up a mirror ring or a mirror bulge, which is the average value of the mirror. When the mirror bounces, some decorative patterns are thick and hard, close to the initial curvature radius r; There is no pattern in the bending direction, which is close to the radius of curvature R. When the curvature of the whole mirror is inconsistent, the divergence of reflected light is also different. As a result, decorative patterns corresponding to the mirror back and dark images appeared, showing the so-called light effect. In order to prove this case, during mirror polishing, a special test was made to calculate the potential height f of decoration (see Figure 7), and the result is the same as that of laser.
Fundamentals of deformable mirror interferometry. translucence
The transparent mirror of the Western Han Dynasty depends on: ..
One of its structural features;
2 according to its specific structure, the role of residual stress;
Three kinds. Some friction techniques. These three complementary structures on the Internet are slightly different. The degree of curvature of convex mirror in sunlight is different, and the light reflected by different condensing and dispersive curvatures is also different. This is a mirror image, and its brightness returns to the pattern, resulting in the so-called light transmission phenomenon.
Mao, a native of Yunnan, teaches in the Department of Engineering Mechanics of Shanghai Jiaotong University.