Stiffness and Thermal Expansion of Short Fiber Composites with Fully Aligned Fibers

Abstract

coating with long-chain molecules following the methods described for making AlN powders hydrophobic is used. [10] Figure 4 shows an RB Al 2 O 3 foam structure. It is produced from a slurry with a pre-oxidized powder, having a rather high viscosity. This results in a foam with a lot of closed windows in the cell structure.For a cell size of 1 mm and densities between 15 and 20 % TD we obtain three-point bending strength values of 3± 7 MPa. Compared with the literature data [1] relatively strong foams are obtained, even without optimization. Figure 5 shows the three-point bending strength for RBAO foams, both for pre-oxidized powders and for powders coated with long-chain molecules, as a function of the density. First results with RB mullite foams give a three-point bending strength of 2 MPa for a density of 15 % TD. Further optimization of these foams will be performed in the near future. It will mainly consist of image analysis and tomography in order to try to find the relationships between the mechanical values, the microstructure, and the processing parameters.RB mullite could be produced starting from a mixture of Al, Si, and Al 2 O 3 . The addition of ZrO 2 accelerates the mullite formation and improves to a great extent the mechanical strength and the density. Longer milling time and thus a finer and more active powder enhances the transformations to the equilibrium phases. CeO 2 and mullite seeds also improve the reaction sintering speed.RB Al 2 O 3 foams in which the reaction of Al with water is prevented can be produced with relatively high three-point bend strength. First results from RB mullite foams indicate that they can be produced with sufficient strength. Driven by these promising results further optimization of RB composites will be performed.Predicting the overall, effective properties of short fiber composites with fully aligned fibers from the properties of the individual phases and the composite's morphology has attracted a great deal of attention during the last decades, and a variety of micromechanics-based and empirical models have COMMUNICATIONS ADVANCED ENGINEERING MATERIALS 2002, 4, No. 12 927 Fig. 4. RB Al 2 O 3 foam produced by the polyurethane sponge technique. 0 1 2 3 4 5 6 7 0 1 0 2 0 3 0 Density (%) 3P-bend strength Fig. 5. The three-point bending strength of the RB Al 2 O 3 foams as a function of the density,~starting from preoxidized powders, r starting from powders coated with long-chain molecules.

Fibre orientation structures and their effect on crack resistance of injection moulded transverse ribbed plate

“…Most authors agree (for an excellent review, see Tucker and Liang 23 ) that the most accurate predictions of the unit elastic properties are from the work of Tandon and Weng, 24 based on the ideas of Eshelby 25 and Mori and Tanaka. 26 The present authors' recent work, using a combination of experimental measurements, characterisation of microstructure and FE techniques, 10,27 has confirmed that this is indeed the best approach for predicting the unit elastic properties. Averaging the unit properties in terms of the FOD is less controversial: again the authors' recent work 28 has helped to confirm the widely held belief that the average properties are determined assuming an aggregate model and constant strain between the units.…”

Finite element predictions for the thermoelastic properties of nanotube reinforced polymers

“…It must be noted that we only validated the Tandon-Weng model for the nanotube reinforced epoxy in the glassy state. In our previous study, we found, however, that the accuracy of the Tandon-Weng model considerably abates for semi-crystalline matrices comprising short glass fibres with aspect ratios between 10 and 30 [34].…”

“…An issue to be addressed is that there are simpler models available than our FE approach and they may also be employed to estimate the properties of fibre reinforced composites. In our previous work we found, however, that both the empirical Halpin-Tsai [32] and the micromechanics-based Tandon-Weng [33] models were not always reliable enough to provide all round accurate effective property predictions for composites reinforced with fully aligned short fibres [34]. For conventional short glass and carbon fibre reinforced composites we also demonstrated that orientation averaging provides a highly accurate route for calculating the linear elastic properties of two phase composites with arbitrary fibre orientation states using reliable property predictions for fully aligned morphologies [34,35].…”

Loss Amplification Effect in Multiphase Materials with Viscoelastic Interfaces

“…Short fiber and continuous fiber reinforced materials commonly offer better reinforcing levels than those achievable with low aspect ratio inclusions at comparable loadings. It has already been shown that one can use the finite element route to extract reliable stiffness predictions for such composite materials. − We surmise that the general purpose time-domain finite element technique introduced in this work should also prove successful in studying and understanding the overall, effective viscoelastic properties of such materials.…”

“…It has already been shown that one can use the finite element route to extract reliable stiffness predictions for such composite materials. [20][21][22][23] We surmise that the general purpose time-domain finite element technique introduced in this work should also prove successful in studying and understanding the overall, effective viscoelastic properties of such materials.…”