Arte SheetsLearn. Try. Understand.

Aerospace Carbon/Epoxy Prepreg Layup, Autoclave Consolidation & Laminate CPT

Autoclave Prepreg Fiber Volume & Cured Ply Thickness Formula

Calculate Zero-Void Fiber Volume Fraction Vf (%) from Resin Weight Content, Single Cured Ply Thickness CPT (mm), Total N-Ply Laminate Thickness (mm), and Cured Laminate Density (g/cm³).

Prepreg data sheets quote Resin Content by WEIGHT—converting to Fiber VOLUME Fraction shifts laminate thickness and stiffness!

Aerospace prepreg rolls specify dry **Fiber Areal Weight `FAW`** (`g/m²`, e.g. `194` gsm standard `AS4` plain weave or `145` gsm UD tape) and **Resin Weight Fraction `W_r`** (e.g. `0.34` = `34 wt%` epoxy), whereas micromechanics (`E_1 = V_f * E_f + (1 - V_f) * E_m`) and CAD mold offsets depend on **Fiber Volume Fraction `V_f`**! Because carbon fiber (`rho_f ≈ 1.78` g/cm³) is `41%` denser than toughened aerospace epoxy (`rho_r ≈ 1.26` g/cm³), `66 wt%` carbon (`W_f = 1 - W_r = 0.66`) occupies only **`V_f = (W_f / rho_f) / (W_f / rho_f + W_r / rho_r) = 57.88 vol%`** in a consolidated zero-void autoclave cure! Once `V_f` is known, Single **Cured Ply Thickness** follows identically from fiber mass conservation: **`CPT = (FAW / (rho_f * V_f)) / 1,000`** (`mm`)!

Verify on a 16-Ply Quasi-Isotropic `[0/+45/-45/90]_2s` Zero-Bleed Autoclave Panel—Fiber_Areal_Weight `FAW` = 194.0 g/m² (B2), Net_Resin_Weight_Fraction `W_r` = 0.34 (`34 wt%`, B3), Carbon_Fiber_Density `rho_f` = 1.78 g/cm³ (B4), Cured_Epoxy_Density `rho_r` = 1.26 g/cm³ (B5 -> Fiber Volume Fraction `V_f = 57.88%` in E2), and Layup_Ply_Count `N` = 16 plies (B6): Single Cured Ply Thickness `CPT` equals `0.1883` mm (`7.41` mils, E3), 16-Ply Laminate Thickness equals `3.013` mm (E4), and Cured Laminate Density hits `1.561` g/cm³ (E5)!

Aerospace Prepreg Autoclave KPI (FAW=194 gsm, Wr=0.34, rhof=1.78, rhor=1.26, 16 Plies)FormulaVerified Output
Fiber Volume Fraction Vf (%)((1-Wr)/rhof) / ((1-Wr)/rhof + Wr/rhor) * 10057.88% (64.54% after bleed to Wr=0.28)
Cured Ply Thickness CPT (mm)(FAW_gsm / (rho_f * Vf_frac)) / 10000.1883 mm (0.1689 mm @ Wr = 0.28)
Total N-Ply Laminate Gauge (mm)CPT_mm * Ply_Count_N3.013 mm (2.702 mm @ Wr = 0.28)
Cured Laminate Density (g/cm³)Vf * rho_f + (1 - Vf) * rho_r1.561 g/cm³ (1.596 g/cm³ @ Wr = 0.28)

Weight-to-Volume Prepreg Conversion & Exact Cured Ply Thickness Formula

Validate `FAW > 20` g/m², `Resin_Weight_Frac W_r` in `[0.15, 0.65]`, `Fiber_Density > Resin_Density > 0.8` g/cm³, and integer `Ply_Count N >= 1`!

=LET(fa_w, B2, wr_f, B3, rf_g, B4, rr_g, B5, np_c, B6, wf_f, 1 - wr_f, vf_r, (wf_f / rf_g) / ((wf_f / rf_g) + (wr_f / rr_g)), IF(OR(fa_w <= 20, wr_f < 0.15, wr_f > 0.65, rr_g <= 0.8, rf_g <= rr_g, np_c < 1), "Invalid Prepreg Input", ROUND(vf_r * rf_g + (1 - vf_r) * rr_g, 3)))

Bleeder-Cloth Resin-Bleed Consolidation Check (Set Net Cured Resin Weight Wr B3 = 0.28)

Add fiberglass bleeder plies under `6`-bar autoclave pressure so excess resin bleeds down to `W_r` B3 = 0.28 (`28 wt%`): Fiber Volume Fraction E2 compacts up to `64.54%`, `CPT` E3 thins to `0.1689` mm, 16-Ply Panel Gauge E4 drops `-0.311` mm to `2.702` mm (crucial for matched-metal wing-spar clevis shimming!), and Density E5 rises to `1.596` g/cm³!

=IF(ISTEXT(E5), E5, LET(wf_f, 1 - B3, vf_r, (wf_f / B4) / ((wf_f / B4) + (B3 / B5)), ROUND(((B2 / (B4 * vf_r)) / 1000) * B6, 3)))

Try the example

Use the original values or change them to test your understanding.

Further reading