ISSN:0032-3888    

DOI:10.1002/pen.760150302

出版商:Society of Plastics Engineers, Inc.    

年代:1975

数据来源: WILEY

ISSN:0032-3888    

DOI:10.1002/pen.760150303

出版商:Society of Plastics Engineers, Inc.    

年代:1975

数据来源: WILEY

摘要:

AbstractTheoretical projections, based upon the anisotropic character of the polymer chains and supported by recent fiber technology and composite mechanics developments, indicate that an order of magnitude improvement in bulk polymer properties is both technically possible and achievable. The objective of this discussion is to define and discuss some of the major scientific problems associated with the achievement of the maximum mechanical potential of macromolecular (polymeric) solids. Two material paths to achieve maximum response will be considered in detail.1.Composite Materials. This deals with the reinforcement of bulk polymers by one or more phases providing enhanced mechanical properties, such as high‐strength high‐modulus graphite, glass, and polymeric fibers. The latter could include high‐modulus fibrous polyethylene in a polyethylene matrix–a molecular composite.2.Homogeneous Molecular Composites–Ultra Molecular Orientation. Examined here is the way absolute molecular orientation can be developed in both aromatic and olefinic polymers to produce materials with mechanical properties comparable to the defect‐free single crystals of metals. Simultaneously, structure‐property relations are examined in traditional

ISSN:0032-3888    

DOI:10.1002/pen.760150304

出版商:Society of Plastics Engineers, Inc.    

年代:1975

数据来源: WILEY

摘要:

AbstractThe fundamental analysis of the mechanical response of composite media involves investigations on two levels of abstructions: the micro and the macro scale. These areas of study are known as micromechanics and lamination theory. This format is employed to treat a series of problems concerning (1) stiffness, creep, or viscoelastic properties; (2) strength and expansion properties for oriented continuous and short fibers; (3) randomly oriented fibers; (4) injection‐molded materials; and (5) particulate reinforcement

ISSN:0032-3888    

DOI:10.1002/pen.760150305

出版商:Society of Plastics Engineers, Inc.    

年代:1975

数据来源: WILEY

摘要:

AbstractGraphite has a hexagonal close‐packed crystal structure which is strong and stiff in the two directions of the basal plane and, in the third direction—perpendicular to the basal plane—is weak and compliant. High‐performance carbon fibers must make use of the strong directions while suffering from the poor properties of the third. This paper describes, from fundamentals, the processes used to produce high‐performance carbon fibers. The resulting fiber microstructures and the consequences of these structures on properties are

ISSN:0032-3888    

DOI:10.1002/pen.760150306

出版商:Society of Plastics Engineers, Inc.    

年代:1975

数据来源: WILEY

摘要:

AbstractOur preliminary characterization of advanced composite materials has been conducted simultaneously with the development of large‐scale primary and secondary aircraft structures. We have demonstrated significant advantages over metal structure on a one‐to‐one basis. Our efficiency levels gained to date demonstrate that we have extracted about fifty percent of the maximum potential advantage. Recovery of the remaining efficiency will result from understanding material characteristics and development of advanced design concepts. We will develop and demonstrate a summary format for viewing the structural response of monolithic metals and polymers and then document the observed responses of advanced composites within the format. Our data show that the addition of high‐modulus fibers into a polymeric matrix produces a physically distinct material with substantial advantage over unreinforced polymers. The unique properties of composite materials yield a significant advantage in physical properties and in design. Full advantage of material orientation has yet to be developed in a practical design but through examples we can illustrate the potential. We develop two examples: (1) stress concentration control through buffer stripping and (2) fracture control through buffer stripping. The impact of composite material characteristics as aircraft materials and design methods is also r

ISSN:0032-3888    

DOI:10.1002/pen.760150307

出版商:Society of Plastics Engineers, Inc.    

年代:1975

数据来源: WILEY

摘要:

AbstractThis note illustrates how the development rate for the use of composites as engineering materials has recently increased. Reasons for the expected even larger number of applications of composites in industry is explored. The engineering potential of composites is outlined in terms of properties and design aspects and mainly by pointing out how the proper use of a composite requires a clear knowledge of its application as well as the appropriate design technology. Examples of applications in different fields are reported with the aim of showing the high versatility of composites for a variety of engineering applications. The final part is devoted to cost aspects, which are considered in connection with the effects of composite use upon the total structure. The purpose is to show that a large number of interesting applications are already cost effective.

ISSN:0032-3888    

DOI:10.1002/pen.760150308

出版商:Society of Plastics Engineers, Inc.    

年代:1975

数据来源: WILEY

ISSN:0032-3888    

DOI:10.1002/pen.760150309

出版商:Society of Plastics Engineers, Inc.    

年代:1975

数据来源: WILEY

摘要:

AbstractA variety of macromolecular systems including crystalline and oriented thermoplastics, block copolymers, and flexibilized thermosetting resins can realistically be viewed as composite systems. This paper examines the utility of using predictive methods developed for two‐component engineering composites to predict the mechanical properties of macromolecular systems. The concepts presently available for the prediction of stiffness and expansion coefficients of short‐fiber rein‐forced plastics are reviewed with respect to their engineering accuracy in structural systems design. These techniques are then applied to predict the stiffness of a hybrid polymer system lying midway between an engineering composite and a crystalline polymer. The hybrid consists of a polymer matrix (butadiene‐acrylonitrile copolymer) reinforced within‐situcrystallized, low‐molecular‐weight filler (acetanilide). Finally, the composite approach is applied to the prediction of stiffnesses and expansion coefficients of crystalline polyethylene as a function of volume fraction crystallinity and crystalli

ISSN:0032-3888    

DOI:10.1002/pen.760150310

出版商:Society of Plastics Engineers, Inc.    

年代:1975

数据来源: WILEY

摘要:

AbstractUltra‐high‐modulus fibers such as Du Pont PRD‐49 (initial modulus up to ∼1000 g/den) and Monsanto X‐500 (initial modulus up to ∼600 g/den) are spun from solutions. Both polymers are characterized by a high intrinsic rigidity of individual molecular chains and considerable orientation along the fiber axis. The thermodynamics of solution for rigid and semirigid macromolecules is critically reviewed in order to illustrate conditions under which spontaneous formation of highly oriented fibers is expected. In the case of semirigid polymers, the free energy of (random) mixing pure solvent and parallellized polymer may, according to Flory, become positive for some critical value of a “flexibility parameter.” Formation of an ordered phase for semirigid polymers is not, however, observed by lowering temperature or increasing polymer concentration. In the case of rod‐like polymers, still according to Flory, at some critical value of polymer concentration (which decreases with the axial ratio of the macromolecule) the isotropic solution of rods undergoes phase separation with formation of a partly ordered solution. This theoretical prediction is satisfactorily verified by data. While Du Pont fibers are spun from this anisotropic solution, Monsanto's X‐500 only yields an isotropic solution at room temperature up to the limit of polymer concentration at which crystallization occurs. This inability of X‐500 to form anisotropic solutions at the expected critical concentration is attributed to a partial degree of flexibility. Mechanical properties and orientation of fibers spun from the anisotropic solution appear to be superior to those obtained by spinning from isotropic solution, according to Du Pont's results. When a polymer has a partial degree of flexibility, alteration of physico‐chemical variables such as solvent type, solvent composition, temperature, and polymer concentration may still be used in order to increase its rigidity. Theoretical arguments and data supporting this contention are discussed. Moreover, alteration of these variables may also be used to alter the crystallization temperature, allowing formation of the anisotropic solution to occur at a high enough polymer concentration. This expectation was verified in the case of X‐500. Finally, the all important role of mechanical orientation of solutions is emphasized. According to Hermans, under high enough shear stress, the difference between the isotropic and the anisotropic solution vanishes. In line with these consideration, drawing techniques are particularly useful in order to achieve almost‐perfect orienta

ISSN:0032-3888    

DOI:10.1002/pen.760150311

出版商:Society of Plastics Engineers, Inc.    

年代:1975

数据来源: WILEY