In the past decade, natural-fiber composites with thermoplastic and thermoset matrices have been embraced by European car manufacturers and suppliers for door panels, seat backs, headliners, package trays, dashboards, and interior parts. Natural fi bers such as kenaf, hemp, fl ax, jute, and sisal offer such benefi ts as reductions in weight, cost, and CO 2 , less reliance on foreign oil sources, and recyclability. However, several major technical considerations must be addressed before the engineering, scientifi c, and commercial communities gain the confi dence to enable wide-scale acceptance, particularly in exterior parts where a Class A surface fi nish is required. Challenges include the homogenization of the fi ber's properties and a full understanding of the degree of polymerization and crystallization, adhesion between the fi ber and matrix, moisture repellence, and fl ame-retardant properties, to name but a few.
The high strain-rate constitutive behavior of polymer composites with various natural fibers is studied. Hemp, hemp/glass hybrid, cellulose, and wheat straw-reinforced polymeric composites have been manufactured, and a split-Hopkinson pressure bar apparatus has been designed to measure the dynamic stress-strain response of the materials. Using the apparatus, compressive stress-strain curves have been obtained that reveal the materials' constitutive characteristics at strain rates between 600 and 2400 strain/s. Primary findings indicate that natural fibers in thermoset composites dissipate energy at lower levels of stress and higher strain than glass-reinforced composites. In the case of thermoplastic matrices, the effect on energy dissipation of natural fibers vs. conventional talc reinforcements is highly dependent on resin properties. Natural fibers in polypropylene homopolymer show improved reinforcement but have degraded energy dissipation compared to talc. Whereas in polypropylene copolymer, natural fibers result in improved energy dissipation compared to talc. These data are useful for proper design, analysis, and simulation of lightweight biocomposites.
If NDAM = 0, P a r t s 1 and 2 of S w i l l be calculated if W1 # 0. and the Mode 1 contribution (free g a s) is only used to damp the Q and R functions. Note 2. If NDAM = 1 only S1 w i l l be calculated, Note 3. A tape containing S(CY, 8) for ~1 = CY(^),. .. ,CY (NREST-1) must have been saved. i+19 it19 Note 4. Time integrals a r e cut off at t i if max(Q., Rj)/Q1 S CRIT3. J = l J j=i 9 Note 5. If JS3 < 0 and X3()JS3)) < 0, a Debye spectrum, f(w3) = u; , w i l l be'calculated. Note 6. If S (a , 8) x eo/' < EPS-Max (S(cq 8) x e 8 / 2-6), this (CY, 6) point is not punched. EPS = 10 is a n adequate choice. Note 7. If Card 22 is blank, punching and e r r o r map printout a r e skipped and code returns to Card 23 for next input. I I Note 8. If NREST < 0, a previously calculated S(a, p) deck is read and all Q! points from INREST1 on a r e r ecalculated.
One of the primary projected advantages of the new cyclic thermoplastic- based composites, in addition to their ability to be processed by liquid composite molding, is their potential "recyclability." This paper describes a first attempt to prove the technical feasibility of recycling a cyclic polycarbonate-matrix continuous-glass-fiber composite by two common processes: compression molding and injection molding. The results are somewhat mixed but still encouraging. Parts were reprocessed from ground-up continuous-fiber composites by both injection molding and compression molding. The effects of environmental exposure (water and ethylene glycol) on the composite prior to recycling were also investigated. The injection molded parts exhibited excellent mechanical properties, in some cases exceeding those of the analogous commercially available injection molding grade. The compression molded recycled material, however, showed very poor tensile properties, but its impact properties compared well to comparable commercial materials. The mixed performance of the compression molded material was characterized by microstructural inhomogeneity and matrix microcracks thought to be due to processing deficiencies. Work continues toward improving the quality of these cyclic thermoplastic materials and the recycling processes.
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