Effect of molecular weight distribution on the structure and mechanical properties of ultradrawn, ultra-high molecular-weight polyethylene cast from solution. II. Drawability and mechanical properties

Effect of molecular weight distribution on the structure and mechanical properties of ultradrawn, ultra-high molecular-weight polyethylene cast from solution. II. Drawability and mechanical properties

micromechanical model. This model is employed to calculate the overall instantaneous material matrix at material points of a macromechanical finite el...

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micromechanical model. This model is employed to calculate the overall instantaneous material matrix at material points of a macromechanical finite element model of the structure being analysed. It is shown that the response of laminated composite structures to thermal and/or mechanical loads can be predicted by use of a specific micromechanical model associated with general purpose finite element programs.

ORGANIC FIBRES Effect of molecular weight distribution on the structure and mechanical properties of uitradrawn, ultra-high molecular-weight polyethylene cast from solution. II. Drawability and mechanical properties Liu, L.B., Murakami, N., Sumita, M. and Miyasaka, K. Journal of Polymer Science Part B Vo127No 12 (1989) pp 2441-2450 Two commercially available samples of ultrahigh molecular-weight polyethylene (UHMWPE) having polydispersities of 3 and 5 (narrow and broad respectively) are solution cast and ultradrawn. Tensile measurements are performed along with dynamic mechanical measurements. It is found that molecular-weight distribution has a marked effect on ultradrawability and thus on the ultimate mechanical properties of the UHMW-PE. Narrow polydispersity UHMW-PE shows a higher modulus than broad polydispersity UHMW-PEat the draw ratios considered. Proposals to account for this in morphological terms are included. Effects of molecular weight distribution on the structural and mechanical properties of ultradrawn, ultra-high molecular-weight polyethylene cast from solution. I. Thermoluminescence and NMR Liu, L.B., Murakami, N., Sumita, M. and Migasaka, K. Journal of Polymer Science Part B Vo127 No 12 (1989) pp 2427-2440 Two experimental samples of ultra-high molecular weight polyethylene (UHMW-PE) having polydispersities of 3 and 5 respectively are crystalfized/gelled from solution and ultradrawn. Thermoluminescence (TL), DSC and NMR are employed to investigate structural and thermal properties. The TL peak intensity is related to the morphology of the ultradrawn UHMW-PE films. Chain-folded films are found to have a weak TL peak integrated intensity, whereas extended chain films have a strong integrated TL glow intensity. Conclusions on the drawability of UHMW,E of differing polydispersities are made. Effects of fibre orientation on the stress distribution on model composites Fan, C.F. and Hsu, S.L. Journal of Polymer Science Part B Vol 27 No 13 (1989) pp 2605-2619 The effect of fibre orientation in poly (2,4bexadiyne-1,6-diol bisphenyl urethane) (eoa)/epoxy model composite is analysed by means of a Raman mechanical technique. Fibre axial strain is found to decrease as the orientation angle increases. The observed compressive failure of the fibre at high orientational angle occurs due to lateral shrinkage associated with the matrix. Experimental data is found to fit well an analysis performed using the Eshelby equivalent inclusion method.

RESIN MA TRICES Amplitude and counts per event analysis of the acoustic emission generated by the transverse cracking of cross-ply CFRe Favre, J-P. and Laizet, J.C. Composites Science and Technology Vol 36 No 1 (1989) pp 27-43 Acoustic emission signals are monitored in order to study the multiple fracture processes of carbon fibre/epoxy cross-ply laminates. The objective of the study is to establish a satisfactory statistical model of the failure of the transverse layer. Several commercially available fibre-resin systems are tested to keep the study general. Specimens are monitored by X-radiography during testing to obtain visual confirmation of the onset of cracking. Results obtained show that, except when the transverse plies are thin, acoustic emission signals associated with cracking can be adequately selected from overall noise emissions of loaded cross-ply CFRPlaminates. Characterization of the fracture toughness property (Glc) of composite laminates using the double cantilever beam specimen Lee, S., Gaudert, P.C., Dainty, R.C. and Scott, R.F. Polymer Composites Vo110 No 5 (1989) pp 305-312 The double cantilever beam specimen was used to determine the interlaminar fracture toughness (GI¢) of four unidirectional carbon fibre epoxy composites. Three toughened epoxies (Narmco 5245C, Hexcel F584 and American Cyanamid 1806) were compared with a baseline untoughened epoxy matrix, Narmco 5208. Gic values were compared with short beam shear strength and scanning electron microscope fractography. The toughened resins exhibited Grc values between 2.4 and 4.0 times greater than the baseline material. However fibre bridging was observed in two of the toughened resins, which limits the validity of matrix toughness comparisons. Intelligent tailoring of composite laminates Sun, C.T. Carbon Vo127 No 5 pp 669-687 In this paper the failure of graphite/epoxy composites by impact damage, interlaminar shear and opening mode delamination is reviewed. The suppression of these modes of failure are discussed in terms of composite design, stitching, use of adhesive layers and the modification of edge geometry. Mechanics of composites materials: past, present, and future Chamis, C.C. Journal of Composites Technology and Research Vol 11 No 1 (1989) pp 3-14 This article reviews fibre resin composites mechanics. Alternative methods are compared through their correlation with experimental data. This assessment is presented by grouping composite mechanics into seven disciplines: (1) micromechanics, (2) macromechanics, (3) combined stress failure, (4) laminate theory, (5) singularity mechanics, (6) life/durability, and (7) structural analysis. The scale of sophistication of each mathematical model for each discipline is described. The article proposes that progress will occur as a result of less conventional and more innovative methods which are dedicated, adaptive and expert-system-driven.

The possible mechanisms of polymer-filler interaction in polypropylene-CaCO 3 composites Pukanszky, B. , Tudos, F., Jancar, J. and Kolarik, J. Journal of Materials Science Letters Vol 8 (1989) pp 1040-1042 The objective of this letter is to study the different effects of low and high molecular mass surface modifiers on the tensile yield stress of polypropylene-calcium carbonate composites and to show that the difference is the result of different interaction mechanisms. The surface treatments used were stearic acid and maleated polypropylene. Tensile tests of the specimens showed that the addition of stearic acid results in the decrease in yield stress, while the addition of maleated polypropylene substantially increases the yield stress. The authors relate the difference in hehaviour to the chain length of the modifiers due to their similar chemistry, an acid function on a hydrocarbon chain. The authors also report that in the case of the maleated polypropylene a larger interphase region exists suggesting the interdiffusion of the maleated polypropylene modifier and the matrix chains. This interdiffusion could explain the higher tensile stress observed for the maleated polypropylene modified composite. Thermal ageing Haskins, J.F. S A M P E Journal Vol 25 No 2 (1989) pp 29-33 The effects of thermal ageing on the strength and continuity of various boron/epoxy, graphite/epoxy and graphite/polyimide composites was studied. Six-ply unidirectional and cross-ply laminates were fabricated for each system. Samples were exposed to both ambient and reduced pressures at a variety of temperatures. Properties studied were weight loss, change in ~ , retention of tensile strength, fatigue properties, compressive and shear strength. Thc effects of ageing on properties were discussed. Thermal bonding of carbon fibre PEEK composites Cantwell, W.J.. Davies, P., Jar, Y., Richard, H., Dausch, H. Journal oJ Material Science Letters" Vol 8 (1989) pp 1035-1039 This letter discusses the problems associated with the bonding and repair of carbon fibre reinforced poly-ether-ether-ketone (PEEK) which has a lack of inherent adhesion to conventional epoxy based adhesives. In particular this letter outlines work carried out by the Authors to join these materials in a conventional heated press at 380°C. The effect of weld time and test temperature on the bond were made in a lap-shear joint test. The results show that carbon fibre PEEK composites thermally bonded joints are stable to 160° and superior to epoxy bonded joints, even at low temperatures. Thermoplastics for space Barnes, J.A. and Cogswell, F.N. S A M P E Quarter(v Vo123 No 3 pp 22-27 The available data relevant to one particular thermoplastic composite, carbon fibre reinforced PEEKis reviewed, thus showing it to be a good candidate for use in the space environment. The extreme conditions encountered by space structures are detailed, and the performance of carbon fibre/PEEK composite in these conditions is evaluated.

COMPOSITES. MAY 1990

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