Engineering plastic materials

Outlook for advanced engineering materials - plastics, composites and ceramics. Report. R861101. (1986). Arthur D. Little Decision Resources, Cambridge. 

Compared to metals and many other engineering materials, plastics have lower tensile strength, lower elastic modulus, and a higher coefficient of thermal expansion. These differences strongly influence the way joints are designed and adhesives are selected. In the paragraphs that follow the significance of these differences will be briefly analyzed. 

F.. Fitzpatrick, in Engineered Materials Handbook, Vol. 2, Engineering Plastics, ASM International, Metals Park, Ohio, 1988, pp. 128—137. 

Advanced Thermoplastics Materials. Thermoplastics and linear plastics of finite molecular weight that can be fabricated into very complex stmctures by hot melt or injection mol ding are different from the thermoset materials that require cross-linking to build up infinite molecular weight to form network (cross-link) stmctures. Advances in thermoplastic engineering materials include amorphous thermoplastics, crystalline thermoplastics, Hquid crystal thermoplastics, and fluorinated thermoplastics (see Engineering plastics). 

Casey, J. and Naghdi, P.M., Strain Hardening Response of Elastic Plastic Materials, in Mechanics of Engineering Materials (edited by C.S. Desai and R.H. Gallagher), Wiley, New York, 1984, Chap. 4, pp. 61-89. 

Rubbers are exceptional in behaving reversibly, or almost reversibly, to high strains as we said, almost all materials, when strained by more than about 0.001 (0.1%), do something irreversible and most engineering materials deform plastically to change their shape permanently. If we load a piece of ductile metal (like copper), for example in tension, we get the following relationship between the load and the extension (Fig. 8.4). This can be... 

Materials Selection in Mechanical Design Engineering Materials 2 Plastics Materials, 6th Edition... 

From the time that formaldehyde was first isolated by Butlerov in 1859 polymeric forms have been encountered by those handling the material. Nevertheless it is only since the late 1950s that polymers have been available with the requisite stability and toughness to make them useful plastics. In this period these materials (referred to by the manufacturers as acetal resins or polyacetals) have achieved rapid acceptance as engineering materials competitive not only with the nylons but also with metals and ceramics. 

The acetal resins may best be considered as engineering materials. They therefore become competitive with a number of plastics materials, nylon in particular, and with metals. 

Although the first two materials discussed in this chapter, the polyphenylenes and poly-p-xylylenes, have remained in the exotic category, most of the other materials have become important engineering materials. In many cases the basic patents have recently expired, leading to several manufacturers now producing a polymer where a few years ago there was only one supplier. Whilst such competition has led in some cases to overcapacity, it has also led to the introduction of new improved variants and materials more able to compete with older established plastics materials. 

Many thermoplastics are now accepted as engineering materials and some are distinguished by the loose description engineering plastics. The term probably originated as a classiflcation distinguishing those that could be substituted satisfactorily for metals such as aluminium in small devices and structures from those with inadequate mechanical properties. This demarcation is clearly artificial because the properties on which it is based are very sensitive to the ambient temperature, so that a thermoplastic might be a satisfactory substitute for a metal at a particular temperature and an unsatisfactory substitute at a different one. 

Equations 8.24 and 8.25 only apply to elastically brittle solids such as glass. However, many engineering materials only break in a truly brittle manner at very low temperature and above these temperatures failures are pseudo-brittle. These have many of the features of brittle fracture but include limited ductility. This plastic work can be included in the above equations, i.e. 

This plastic deformation is localised around the crack tip and is present in all stressed engineering materials at normal temperatures. The shape and size of this plastic zone can be calculated using Westergaards analysis. The plastic zone has a characteristic butterfly shape (Fig. 8.83). There are two sizes of plastic zone. One is associated with plane stress conditions, e.g. thin sections of materials, and the other with plane strain conditions in thick sections-this zone is smaller than found under plane stress. 

The behavior of materials (plastics, steels, etc.) under dynamic loads is important in certain mechanical analyses of design problems. Unfortunately, sometimes the engineering design is based on the static loading properties of the material rather than dynamic properties. Quite often this means over-design at best and incorrect design resulting... 

Designers with a background in using other materials will recognize both the similarities and the differences in the behavior of the plastics discussed. As an example, impact resistance has been a continuing issue with engineering materials, particularly certain metals with similarities to many of the phenomena observed in plastics. 

El theory In each case displacing material from the neutral plane makes the improvement in flexural stiffness. This increases the El product that is the geometry material index that determines resistance to flexure. The El theory applies to all materials (plastics, metals, wood, etc.). It is the elementary mechanical engineering theory that demonstrates some shapes resist deformation from external loads. 

For plastics, heat capacity is usually reported during constant pressure heating. Plastics differ from traditional engineering materials because their specific heat is temperature sensitive. 

Plastics for engineers materials, properties, applications , Hans Domin-inghaus Hanser Gardner Pubis (1993) ISBN 1569900116. Provides a comprehensive overview in text, tables and graphs, of properties and applications for all plastics of current technical and commercial interest. 

The CRC-Elsevier materials selector , 2nd edition, N.A. Waterman, and M.E Ashby CRC Press (1996) ISBN 0412615509. (Now, also available on CD-ROM). Basic reference work. Three-volume compilation of data for all materials includes selection and design guide. The Materials Selector is the most comprehensive and up-to-date comparative information system on engineering materials and related methods of component manufacture. It contains information on the properties, performance and processability of metals, plastics, ceramics, composites, surface treatments and the characteristics and comparative economics of the manufacturing routes which convert these materials into engineering components and products. 

Engineering Materials Handbook, Vol. 2 Engineering Plastics, ASM International, 1988. 

Hoechst has developed a ehemieal reeyeling plastie for Hostaform, a polyaeetal engineering material. Post-use engineering parts and produetion serap are recovered and converted back into the original monomers by depolymerisation. They are then repolymerised to form plastics with the same molecular structure as before, without loss of quality. The process at Hoechst s laboratory and pilot plant operations is outlined. EUROPEAN COMMUNITY GERMANY WESTERN EUROPE Accession no.497548... 

Details of the chemical composition and properties of the wide range of plastics used as engineering material can be found in the books by Butt and Wright (1980) and Evans (1974). 

Strassberger, F. Polymer-Plant Engineering Materials Handling and Compounding of Plastics, Chemical Engineering, Apr. 3, 1972, p. 81. 

Engineering critical current, 23 823 Engineering gold, 9 812 Engineering materials, fatigue properties database on, 13 494 Engineering plastics, 19 537-538 pigments used in, 19 407 polyamides, 19 772 polymers as, 20 401... 

Based on castor oil derived elastomers and crosslinked polystyrene, a simultaneous mode of polymerization can be successfully employed to synthesize prototype engineering materials such as tough, impact resistant plastics and reinforced elastomers. 

Expressed in the same units, the hardnesses of engineering materials cover a vast range broader than 1 to 100. Plastics are at the bottom end of the range but are of a wide diversity and offer decisive advantages compared to metals, glass, ceramics, wood and others. 

Fibers—about half of all nylon fiber goes into tire, cord, rope, belting, fiber cloth, thread, hose, undergarments, dresses plastics—use as an engineering material, substitute for metal bearings, bearings, cams, gears, rollers, jackets on electrical wire... 

The crosslinking reaction is an extremely important one from the commercial standpoint. Crosslinked plastics are increasingly used as engineering materials because of their excellent stability toward elevated temperatures and physical stress. They are dimensionally stable under a wide variety of conditions due to their rigid network structure. Such polymers will not flow when heated and are termed thermosetting polymers or simply thermosets. More than 10 billion pounds of thermosets are produced annually in the United States. Plastics that soften and flow when heated, that is, uncrosslinked plastics, are called thermoplastics. Most of the polymers produced by chain polymerization are thermoplastics. Elastomers are a category of polymers produced by chain polymerization that are crosslinked (Sec. 1-3), but the crosslinking reactions are different from those described here (Sec. 9-2). 

Figure 5.8 Illustration of (a) ideal elastic deformation followed by ideal plastic deformation and (b) typical elastic and plastic deformation in rigid bodies. From Z. Jastrzebski, The Nature and Properties of Engineering Materials, 2nd ed.. Copyright 1976 by John Wiley Sons, Inc. This material is used by permission of John Wiley Sons, Inc.

Although cellulose nitrate, a semisynthetic plastic and not really an engineering material, was introduced in 1868, the first completely synthetic plastic, phenol-formaldehyde, was introduced in 1909. Phenol-formaldehyde is certainly an engineering material and the first of many such products to excite the imagination of engineers. 

Engineering plastics are most frequently thought of as the acetals, nylons, fluorocarbons, phenolics, polycarbonate, and polyphenylene oxide, to name just a few. These are indeed engineering materials and for such applications are usually used in relatively small... 

In the most general sense, all plastics are engineering materials, in that they offer specific properties which we judge quantitatively in the design of end-use applications. Among die large-volume established thermoplastics, we should certainly pay tribute to the engineering performance of the polyolefins, polystyrene, impact styrene, ABS, vinyls, acrylic, and cellulosic plastics. 

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