What will be the estimated cured ply thickness if the density of the graphite fi

Question

What will be the estimated cured ply thickness if the density of the graphite fibers is 1800 kg / m2 given:

Permeability (transverse to the fiber direction) of the fiber bed = P0 = 1.2 x 10-14 m2

It was desired to manufacture a graphite/epoxy laminate consisting of eight prepreg layers with a thickness of 0.150 mm per layer. The fiber areal weight for each prepreg layer was 175 g / m 2. The bottom of the laminate was an aluminum mold (12.7 mm thick) and the top of the laminate had bagging materials (bleeder, breather, etc.). The whole assembly was placed inside an autoclave and subjected to a two stage cure cycle. In this cycle, in the first stage, the autoclave temperature was increased from 20 0C at a rate of 5 0C per minute for 18 minutes and then held constant at 110 0C for 10 minutes. Thereafter the temperature was increased @ 5 0C per minute for 14 minutes to a maximum of 180 0C and held there for 60 minutes. With this temperature schedule, the viscosity reached its minimum value of 1 Pa.s. in about 10 minutes and remained at this value for about 40 minutes before rapidly rising towards its maximum value.
The initial fiber volume fraction V0 was 0.50 and the target final fiber volume fraction is Vf was 0.68. The pressure applied in the autoclave was 80 psi (547 kPa). With this information, the stress or pressure absorbed by the fiber bed was calculated to be about 233.4 kPa.

Explanation / Answer

The blend was prepared by dissolving an equal weight of each component in 1,4-dioxane to yield clear solutions. To isolate the blend, the solution was added to water in a high speed blender. The solid was collected, washed with water and stage-dried to 100°C under vacuum. These powders were used to prepare moldings and films. The blend had an initial Tg of 140°C and the cured resin exhibited a Tg of 245°C, fracture toughness (KIc) of [1.57 MPa m 1/2 (1425 psi in 1/2)] and a coefficient of thermal expansion (23 to 200°C) of 36.8 ppm/°C. Films Thin films [approximately 0.127 mm (5 mils thick)] of the blend were prepared by melt pressing powders of the blend at [6.7 to 10.3 MPa (1 to 1.5 Ksi)] for 0.5 h at 250°C. The film specimens [5.1 cmx 0.63 cm x 0.013 cm (2 in x 0.25 in x 0.005 in)] were bent back upon themselves to place the rounded portion under stress and immersed in hydraulic fluid (Chevron Hyjet IV) for 24 h and in chloroform for 1 h to determine sensitivity towards these solvents. Molded Specimens Powdered blend was compression-molded by heating to 200 ° and then 250°C, each for 0.5 h under [1.4 MPa (200 psi)] in a stainless steel mold. Miniature compact tension specimens [1.6 cm x 1.6 cm x 0.95 cm thick (0.62 in x 0.62 in x 0.375 in thick)] were machined from the moldings and subsequently tested to determine fracture toughness (KIc, critical stress intensity factor) according to ASTM E399 using four specimens per test. Flat moldings [7.6 cm x 7.6 cm x 0.18 cm (3.0 in x 3.0 in x 0.070 in)] were prepared by compression-molding the powdered blend using the conditions described above. Dogbone specimens [6.35 cm x 0.92 cm x 0.18 cm (2.5 in x 0.375 x 0.070 in)] were machined from the moldings and subsequently tested to determine neat resin tensile properties according to ASTM D638 using four specimens per test. Adhesive Specimens Adhesive tape was prepared by multiple coating of 112-E glass (A-1100 finish) with a 1,4-dioxane solution (- 30% solids content) of the blend and subsequently stage dried to 100°C for 1 h after each coat. The final volatile contents of the tapes were less than 1%. Standard adhesive specimens [bond area 2.54 cm (1.00 in) wide x 1.27 cm (0.5 in) overlap)] using titanium (Ti, 6A1-4V) adherends with a Pasa Jell 107 (Products Research and Chemical Corp., Semco Div.) surface treatment were fabricated using conditions similar to those described for the molded specimens. The Ti adherends were initially primed with a dilute 1,4-dioxane solution (- 5% solid content) of the blend and subsequently dried at 100°C for 1 h. Tensile shear specimens were tested according to ASTM D1002 using four specimens per test condition.

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