Shear anisotropy of short glass fibre reinforced thermoplastics injection mouldings

The influence of flow-induced anisotropy on the impact behaviour of injection-moulded short-fibre composites

Creep anisotropy in short fibre reinforced thermoplastics

The uniaxial tensile creep behaviour of several thermoplastics reinforced with short glass fibres has been studied over a wide range of temperatures using specimens machined from a variety of injection moulded bars, discs and plaques. The samples cover a range of fibre volume fractions from 0,10 to 0.22 and mean fibre aspect ratios from 18.5 to 43.0. A detailed quantitative assessment of fibre orientation distribution (FOD) and fibre length distribution has been carried out for each type of moulding used with each material. This structural information, together with fibre volume fraction, fibre modulus and matrix creep data, has been used in the prediction of composite tensile modulus both parallel and transverse to the major flow direction for each type of moulding. For the theoretical predictions, the FOD was treated using the ‘laminate analogy’ approach developed by Halpin et al; the properties of a ply containing uniaxially aligned short fibres being calculated using several different theoretical approaches. At low strains, one of these approaches led to remarkably good agreement between theoretical and experimental composite moduli, over most of the very wide range of materials and temperatures studied. An empirical extension of this approach is also shown to give reasonably accurate predictions of composite creep behaviour at finite strains, where both the matrix and the composite exhibit non-linear viscoelastic behaviour.

Time Dependent Properties of Injection Moulded Composites

The Tensile strength of sheet molding compounds containing circular coutouts is investigated. The results show that sheet molding compounds contain inherent voids making the material unaffected by notches smaller than a certain size, The results show a reasonable fit with a three parameter model.

Notched strength of sheet molding compunds

The anisotropy of flexural stiffness has been examined at low strain using ASTM bar and 3-mm and 6-mm thick edge-gated disc injection mouldings for two glass-fibre-reinforced thermoplastics (GFTP). Experimentally determined values were obtained under three-point bending and compared with theoretical prediction: which took account of the fibre orientation and length distributions in the mouldings. The flexural stiffness of the discs was also studied as a function of direction of test.The prediction of the resulting anisotropies in flexure compares well with experiment, but these anisotropies are markedly different from those measured previously in tension. It is concluded that it is necessary to have a knowledge of the fibre distribution of a GFTP moulding in order to predict successfully its mechanical properties, or to interpret measured data.

Flexural anisotropy of glass-fibre-reinforced thermoplastics injection mouldings

Creep deformation up to 106 s has been measured for beams subjected to pure and three-point bending and for buckling struts made from polymethyl methacrylate, polyvinyl chloride and polypropylene. Of the analytical methods considered for predicting creep, the most accurate was that in which the isochronous stress-strain curves in tension and compression were used in conjunction with equilibrium and strain displacement equations. However, this involved more computation than the other two methods which simply substituted a secant-modulus value from the isochronous curves (1) at the expected maximum stress and (2) at a limit of 1 per cent strain in the established linear elastic formulae for the components. In (1) there was only slight over-estimation of experimental deformations but in (2) there were quite serious differences, particularly at longer times, and small strains.

http://sdj.sagepub.com/content/6/1/53.full.pdf

D McCammond

Papers

Flexural anisotropy of glass-fibre-reinforced thermoplastics injection mouldings

Approximate creep analysis for thermoplastic beams and struts