Short fibre reinforcement

Characterising glass fibres in an injected moulded polypropylene plate (a) Fibre length distribution (Mine, R J. et aL, Compos. Sci. Tech., 62, 1445, 2002) (b) theoretical angular distribution (Mine, R J. et al., Compos. Sci. Tech., 64, 1081, 2004) Elsevier. 

Two concepts from fibre-reinforcement theory are of general use in polymer mechanics. The first is the effect of inclusion shape on the anisotropic elastic moduli of a composite. Two rules control the effects of fibre reinforcement  

Finite element modelling of the effects of a 14% volume fraction of glass fibre with an aspect ratio of 30 (Fig. 4.29b), used fibre orientations that fitted a maximum entropy distribution. It predicted that the longitudinal Young s modulus increased non-linearly with cos B, and that constant strain conditions applied for averaging the properties of the unidirectional composite. 

Assumptions must be made about the matrix and interface behaviour before Eq. (4.27) is integrated. If the matrix remains elastic and the interface does not fail, the shear stress rises to a maximum at the fibre ends, where the tensile strains in the fibre Cf and the matrix differ the most. Flowever, a ductile polypropylene matrix is assumed to yield in shear at a stress Ty = 20 MPa. This will occur near the fibre ends, so the interface shear stress is 

Variation of longitudinal Young s modulus of glass-fibre-reinforced PP with (a) Fibre aspect ratio and volume fraction (Chao, L.-P. and Wang, Y.-S., Polym. Compos., 21,20 2000) John Wiley and Sons Inc. reprinted with permission (b) orientation average cos 6 (Mine, R H. et ai, Compos. Sci. Tech., 64, 1081,2004) Elsevier. Dashed line, constant strain solid line, constant stress averaging. 

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Tsai, S.W. and Hahn, H.T. Introduction to Composite Materials, Technomic Westport, CT (1980). Folkes, M.J. Short Fibre Reinforced Thermoplastics, Research Studies E ress, Somerset (1982). Mathews, F.L. and Rawlings, R.D. Composite Materials Engineering and Science, Chapman and Hall, London (1993). 

Foldi, A.P., Design and applications of short fibre reinforced rubbers, in Short Fiber-Polymer Composites, De, S.K. and White, J.R. (Eds.), Woodhead Publishing, Cambridge, 1996, Chapter 9. 

The effects of processing will be illustrated by considering injection moulding of a semicrystalline polymer. The molten plastic is injected into the mould under high pressure and temperature. The edges of the mould retard flow and cool more rapidly, leading to a boundary layer of high shear, which in semicrystalline polymers leads to orientation of the polymer chains and of short fibre reinforcements parallel to the direction of flow. At the centre the structure is less oriented. Where two separate flow streams meet, there is a... 

In summary, therefore, processing, and in particular injection moulding, can introduce limited chemical degradation, local polymer orientation, orientation of short fibre reinforcements, internal stresses, warpage, shrinkage and defects such as weld lines and voids. 

Most tests will be made on standard test pieces which may be pieces cut from a component or a sheet, or they may have been moulded separately from the same material. Where test pieces or sheet are produced for the trials it is important that they are produced in as near as possible the same way as the product and that the processing conditions are recorded. Different results can be expected from compression and injection moulding or from extrusion (where a choice is possible). Directional properties can result from the conditions of flowing and cooling in a mould. For example, in a study at ERA, the creep strain of unfilled HDPE, either individually moulded or cut from square plaques, varies by up to a factor of two depending on the orientation of flow [40]. This difference becomes even more marked with short fibre reinforcement. 

Short fibre reinforced polyamide E-glass Aramid Carbon... 

Table 6.30 shows the properties of the same thermoplastic (short fibre reinforced polyamide) reinforced with the same level of the three main reinforcement fibres, illustrating the effect of the fibre nature. 

Future prospects for thermoplastics and thermoplastic composites 7.5.5 Short fibre reinforced thermopiastics to compete with LFRT... 

HTPC (Hybrid ThermoPlastic Composite) bumper beams made by Plastic Omnium are used by General Motors on the Pontiac Montana, Chevrolet Venture and Oldsmobile Silhouette. Continuous woven fibres are overmoulded with a long or short fibre reinforced polypropylene to save weight (6 kg), enhance impact resistance (20-40%) and integrate numerous functions such as reinforcement ribs. The process is fully automated. 

Sato N., Kurauchi T., Sato S. and Kamigaito O. (1983). SEM observation of the initiation and propagation of cracks in a short fibre reinforced thermoplastic composite under stress. J. Mater. Sci. Lett. 2, 188-190. 

Folkes, M.J. (1982) Short fibre reinforced thermoplastics. Research Studies Press, Chichester, UK... 

Over the last decade, considerable efforts have been committed to the toughening of sialons and substantial progress has been achieved using various reinforcements. According to the form of reinforcement, sialon composites can be classified as either particle reinforced, discontinuous fibre (whiskers/ short fibres) reinforced, or continuous fibre reinforced. 

Large aspect ratio Because the reinforcements are nanosized, the large aspect ratio (length/diameter) could make the composite behave like a continuous fibre composite. This scenario is unlikely as the aspect ratios of the NWs used are "- 100-200, which are lower than the value of "-T000 or so for a transition between short-fibre reinforced composite behaviour and the long-fibre reinforced one [18]. The specimen dimensions are also much larger than the NW dimensions. The anomalous increase from the relatively smaller sized specimens is ruled out. 

In-plane alignment of the fibres Due to the very nature of the technique used for processing the NW composites, inplane alignment of the NWs is a realistic possibility. From the Krenchel theory of short-fibre reinforcements [20], the orientation and length effects can be incorporated using an efficiency factor to evaluate E,... 

Kenny et al. (1995) examined the chemorheology and processing of short-fibre-reinforced BMC polyesters. They found that the presence of fillers (CaC03 and glass fibres) increases the reaction time. Also they found that the chemorheology could be described by considering both a shear-thinning model (typical of suspension theory) and the Macosko model (Equation (5.8)). 

Key words magnesium matrix composites, magnesium alloys, creep, short-fibre reinforcement, particle reinforcement... 

Monolithic and short-fibre reinforced squeeze cast... 

Klein CP AT, Wolke JGC, de Blieck-Hogervorst JMA, de Groot K (1994) Features of calcium phosphate plasma-sprayed coatings An in vitro study. J Biomed Mater Res 28 961-967 Knepper M, Milthorpe BK, Moricca S (1998) Interdiffusion in short-fibre reinforced hydroxylapatite ceramics. J Mater Sci Mater in Med 9 589-596... 

Ruys AJ, Milthorpe BK, Sorell CC (1993) Short-fibre reinforced hydroxylapatite effects of processing on thermal stability. J Aust Ceram Soc 29 39-51... 

Damage tolerance of fibre reinforced thermoplastic composites Processing of polymer matrices using resin transfer moulding Fractal analysis of wear in short-fibre reinforced thermoplastic composites Rheology flow behavior of associative polymers in coating applications Kevlar-thermoplastic composites... 

Friedrich K, Walter R, Voss H, Karger-Kocsis J. Effect of short fibre reinforcement on the fatigue crack propagation and liacture of PEEK-matrix composites. Composites 1986 17 205-16. http //dx.doi.org/10.1016/0010-4361(86)91004-9. 

Walker L, Hu XZ. Mode I delamination behavior of short fibre reinforced carbon fibre/ epoxy composites following environmental conditioning. Compos Sci Technol 2003 63 531-7. http //dx.doi.org/10.1016/S0266-3538(02)00224-5. 

Science and engineering of short fibre reinforced polymer composites... 

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