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A process model is presented for the analysis and simulation of impregnation molding of particle-filled, continuousfiber ceramic composites. A multidimensional, transient particle filtration formulation is coupled with isothermal, anisotropic Darcy flow to predict filler-concentration profiles during molding. The particle filtration is insensitive to the injection flow rate; however, in irregularly shaped molds, the geometry of the mold greatly influences the local velocities, which results in local variations in the rate of filtration. Although the preform volume fraction and inlet particle concentration influence the particle accumulation quantitatively, the filtration coefficient and the permeability have a dominant role in setting the filtration trend.

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Selective laser sintering was used for producing uniformly porous and graded porous polyamide structures. The porous structures were infiltrated with epoxy to produce composites. The porous and composite specimens were physically and mechanically characterized. Within the capabilities of the selective laser sintering machine and the materials used, porosities in the range 5–29% could be obtained in a controlled, repeatable manner. The ultimate tensile strength of the produced uniformly porous polyamide structures ranged from 20 MPa (for 29% porosity) to 44 MPa (for 5% porosity). The graded porous structures exhibited continuously changing porosity grades. As the number of grade increments rose, the grade profile fit closely with the design grade profile. The grades need to be constructed at porosities 9% or more for clear grade variation. Five percent porosity remained in all epoxy-polyamide composites after infiltration of the polyamide preforms with epoxy resin. Improvement in strength with epoxy infiltration was observed for preform porosities above 9%. The composite strength varied from 37 MPa to 44 MPa with respect to epoxy resin volume fraction. The maximum strength of the composites was found to be the same as the strength of the sintered polyamide powder (44 MPa).

Selective laser sintering (SLS) is a rapid prototyping technique which is used to manufacture plastic and metal models. The porosity of the final product obtained by SLS can be controlled by changing the energy density level used during the manufacturing process. The energy density level is itself dependent upon manufacturing parameters such as laser power, hatching distance and scanning speed. Through mechanical characterization techniques, it is possible to quantitatively relate the energy density levels to particular strength values. The present study is directed towards manufacturing functionally graded polyamide products by changing the energy density level in a predetermined manner. The mechanical properties of the functionally graded components are characterized by means of tensile testing. Both homogeneous and functionally graded specimens are produced and tested in order to examine the influence of the energy density level on the mechanical response and on the ultimate tensile and rupture strengths. Selective laser sintering is shown to possess the potential to produce functionally graded porous specimens with controlled variations in physical and mechanical properties.