TAILIEUCHUNG - Handbook of Plastics Technologies phần 6

Các chuyên ngành cơ bản của cơ khí bao gồm: động học, tĩnh học, sức bền vật liệu, truyền nhiệt, động lực dòng chảy, cơ học vật rắn, điều khiển học, khí động học, thủy lực, chuyển động học và các ứng dụng nhiệt động lực học. Các kỹ sư cơ khí cũng đòi hỏi phải có kiến thức và năng lực áp dụng những khái niệm trong môi trường kỹ thuật điện và hóa học. Với một mức độ nhỏ, cơ khí còn trở thành kỹ thuật phân tử - một mục tiêu viễn cảnh của nó là tạo. | PLASTICS AND ELASTOMERS AUTOMOTIVE APPLICATIONS Downloaded from Digital Engineering Library @ McGraw-Hill Copyright 2006 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. PLASTICS AND ELASTOMERS AUTOMOTIVE APPLICATIONS CHAPTER 9 duced a styrene-acrylonitrile SAN continuous phase and a discrete grafted polybutadiene one. The rubber particles are finely dispersed in the rigid phase. Thus a situation is created in which copolymerizing acrylonitrile and styrene in the presence of PBD results in an amorphous molding polymer that is much better suited to automotive applications than the polystyrene homopolymer. Although the addition of the more polar monomer brings about improvements in modulus equally important is a step improvement in resistance to impact damage. Figure shows transmission electron microscopy images of two distinct morphologies present in commercial ABS resins. The darker domains are droplets of grafted polybutadiene that have been stained by osmium tetraoxide. One can see that the rubber particles are very different in terms of average diameter and appearance. Particles with diameters on the order of the wavelength of light can be made with the emulsion process whereas larger particles with occluded matrix resin is very typical of mass. In mass ABS control of the particle size and particle density allows for a broad range of gloss. The key function of the dispersed grafted PBD phase is to dissipate energy in the case of an impact event. There are two types of energy absorption found in ABS crazing and shear banding. In the case of crazing rubber particles can dissipate energy by initiating and terminating this type of microcracking. The initial step in the dissipation process is the deformation of the rubber particles to the point of void formation. This void formation in turn initiates additional crazes that are terminated at neighboring .