Powders of ultra‐high molecular weight polyethylene from three suppliers were characterized for density, crystallinity, particle size, particle size distribution and particle morphology. The powders had molecular weights in the range 2‐5 million. Bulk powder behavior, compressibility, green strength and springback were evaluated and explained in terms of particle characteristics. The green densities of the powders were found to reach a plateau at pressures of about 100 MPa. These plateau density levels were found to depend upon powder, characteristics and to lie between 80 and 90 percent relative density. Green strength is shown to be a unique function of a densification parameter.
Powder Metallurgy (P/M) materials, especially those made of high strength steels, are often reported in the technical literature to have poor machinability when compared to their wrought or cast counterparts. In order to characterize the machinability of single phase P/M materials and to identify the influence of porosity on that behavior, the machinability of P/M 304L austenitic stainless steel was evaluated as a function of porosity, in the range of 64 to 90 percent of theoretical density. Machinability was defined in terms of the average drill point temperature. It was found that the drill temperature increased with porosity to a point. Further increases in porosity produced decreasing levels of average drill point temperature. The nonlinear machinability response was attributed to the offsetting contributions of the thermal conductivity, the work-hardening, and the bulk properties of the P/M material.
The solid‐phase flow behavior of polymers is very important in the mechanical performance and testing of solid polymers and in solid‐phase forming. This paper includes an extensive characterization of the solid‐phase flow curve for a wide range of commercially important polymers. Rigid semicrystalline, ductile semicrystalline, tough ductile amorphous, and two‐phase ductile amorphous resins were studied in both tension and compression. It is clearly shown that semicrystalline polymers normally exhibit a load drop upon yielding due only to geometrical strain softening while the amorphous polymers exhibit yield drops due to material strain softening. New flow equations are given that closely model the observed behavior for all types of materials, over the entire range of strain.
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