Descartes Ray And Characters Of Round Fibers

Descartes ray of the textile fiber is one kind of special reflection phenomenon of the internal surface reflected light when incident light is vertical to the fiber axis of round fiber. Descartes ray often appears in the transparent spheroid, such as water drop which produces rainbow and the transparent micro-bead in micro-bead return reflecting materials, the special light reflecting characteristic of which has close relation with Descartes ray. Although round fiber is not spherical, the path of reflected light is same to that of transparent spheroid with parallel light illumination when incident light is vertical to the fiber axis. Therefore, we can also find Descartes ray in round fiber under the special illumination condition.Descartes ray of the textile fiber is internal reflected light, which has affinity with gloss of textile fiber. It also has relation with exploitation of functionality textile fiber having special visual effect and photoelectricity test and the image analysis technology of textile.This article takes Descartes ray of round fiber as the main object of study, with the aid of the geometry optics and the photometry theory, taking the transparent cylinder as the textile fiber model, and makes the systemic research to the Descartes ray of the fiber, mainly including the producing condition of Descartes ray, the relation between light-receiving range of fiber surface and Descartes ray, the relation between light-receiving range of the fiber internal surface and Descartes ray, Descartes ray relative intensity, absolute intensity, distribution range and so on; We also analyze the main factors influencing the Descartes ray, including refractive index, section roundness diversification, surface diffusion, dispersion for the internal optical asymmetry, internal absorption and change of illumination condition, etc.Moreover, we emphatically analyze the dispersiveness of the fiber Descartes ray and the influence no the fiber Descartes ray for fiber skin-core structure. Under the foundation of theoretical analysis, we have made further studies through experiments. Taking the transparent glass rod as the test specimen, through goniophotometric curve test, we study distribution and the characteristic of Descartes ray of the fiber, influence of the fiber internal surface reflection to Descartes ray, the relation between fiber incident light and Descartes ray, the change of Descartes ray when the incident ray is gradient to the fiber axis, the relation between diameter of the fiber and light intensity of Descartes ray and so on. Taking the transparent glass rod and the transparent fishline as the test specimen, and light dispersiveness principle as the basis, we study the dispersiveness phenomenon and disciplinarian of Descartes ray. We, imitating textile fiber skin-core structure by adding glycerol into the transparent glass tube, test its goniophotometric curve and study its influencing disciplinarian to Descartes ray. Finally, taking T/C plain cloth and spun glass as the test specimen, through testing the light intensity goniophotometric curve, we study the Descartes ray's characteristic of fabric. The main research conclusion is as follows:Descartes ray is a special phenomenon of the first internal surface reflected light when parallel light illuminates transparent spheroid. For round fiber, the path of internal surface reflected light is same to that of transparent spheroid when incident light is vertical to the fiber axis. Therefore, we can also find Descartes ray in round fiber, better transparency and parallel illumination vertical to the fiber axis.The cause of forming Descartes ray is that a wide range parallel incident ray close to Descartes ray incident angle will gather in the internal surface after refraction, and reflect in a small scope in the internal surface. The angles of reflection are close to each other, so the diversity among each refracted ray out of fibers is little, and form Descartes ray with strong intensity and limited distributing scope. We can see the fiber Descartes ray is piled up by three parts; including surface reflected light from the direction of Descartes ray and the superposition of two parts internal surface reflected light. The main reason of Descartes ray is just the first internal surface reflected light near the Descartes ray.Looking from the relative light intensity, we know that the intensity of Descartes ray is far stronger than that of other reflection light, and that is an important characteristic of Descartes ray. Seeing from absolute light intensity, because the transmitted light accounts for approximately 86% in the incident light, and surface reflected light accounts for about 7.5%, the internal surface reflected light only occupies the incident light approximately 6.5%. Comparing to the proportion of transmitted light, internal surface reflected light is lower, and absolute intensity of Descartes ray belonging to internal surface light is limited because of the limit of the internal surface reflected light despite of its strong light gathering. Further considering the projection of Descartes ray from two symmetrical directions and the division of other direction internal surface reflection, the light near the Descartes ray only occupies the incident light 1%. Therefore the light near the Descartes ray is very small.The fiber refractive index has the tremendous influence to the direction of Descartes ray. Increasing along with the fiber refractive index, the angle between Descartes ray and incident light reduces, having retro-reflection. When the index n>1.42, this kind of variation rate from anxiously to slow. Increasing along with the fiber refractive index and reducing the angle, the intensity of Descartes ray boosts up rapidly.The change of fiber diameter does not affect the distribution of fiber reflected light. The relation between light intensity of fiber Descartes ray and the fiber diameter is direct proportion, so, light intensity of the fiber Descartes ray is higher along with bigger diameter. Seeing from the surface conformation, the fiber section out of roundness and the surface smooth finish can affect the fiber Descartes ray; seeing from internal optics uniformity, the crystallization of fiber and internal foreign matter particles also can have the influence to the Descartes ray. Moreover, when the parallel incident light is gradient to the fiber axis, the intensity of Descartes ray will reduce.The fiber Descartes ray meets the requirement of dispersiveness, the direction of dispersiveness light follows the principle of geometric optics. The intensity of dispersiveness light increases along with the fiber diameter increasing, and it reduces along with distance increasing. The width of dispersiveness light is related with fiber diameter, the distance between fiber and observation place, and the size of fiber diameter relative to observation place. While the fiber diameter is small, dispersiveness list laps over to be white.The fiber with skin-core structure also has Descartes ray. Both the internal surface of core and cortex could produce Descartes ray, and the intensity of cortex is far higher than core. The discrepancy increase of refractive index between cortex and core will cause the Descartes ray angle increase of both the internal surface of core and cortex. The increase of fiber cortex thickness can make the Descartes ray angle of fiber core increase, but has less influence to the angle of fiber cortex Descartes ray. Generally speaking, the discrepancy of refractive index between cortex and core is more important to the angle of Descartes ray comparing with the change of fiber cortex thickness.In shuttle fabric the fibers have not obvious Descartes ray characteristic with higher relative light intensity. The primary cause is the diameter of single fiber is too small, causing Descartes ray to be very weak; the position of each fiber is different, making the Descartes ray angle different, and causing the dispersion of Descartes ray. When the shape of single fiber is closer to the transparent cylinder, the internal surface reflected light of fiber is more obvious.