{"$schema":"nativecad-dfm-pack/1","id":"composites","title":"Composites: plies, carbon fibre, sandwich and how they are really made","sector":"composites","version":"2026-11-04","summary":"Ply properties for compositeLaminate with stated knockdowns, process chains and the CAD they demand, tooling and CTE, layup rules with numbers, bonded and bolted joints, sandwich checks, machining, NDT and coupon tests. Numbers tagged SRC or EST in basis.","aliases":["carbon fibre","cfrp","prepreg","laminate","sandwich","ply","plies","ply drop","layup","lay-up","honeycomb","ply book","drape","out of autoclave"],"crossSector":false,"size":"core","sources":[{"id":"ncamp-im7-8552","title":"NCAMP NCP-RP-2009-028 Rev B: Hexcel 8552 IM7 UD 190 gsm 35% RC statistical analysis (B-basis)","accessed":"2026-11-04","url":"https://wichita.edu/industry_and_defense/NIAR/Documents/NCP-RP-2009-028-Rev-B-HEXCEL-8552-IM7-Uni-SAR-4-16-2019.pdf"},{"id":"hexcel-8552-us","title":"Hexcel HexPly 8552 product data sheet (US, FTA-072-2-MY20)","accessed":"2026-11-04","url":"https://hexcel.com/wp-content/uploads/2026/01/HexPly_8552_us_DataSheet.pdf"},{"id":"hexcel-8552-eu","title":"Hexcel HexPly 8552 product data sheet (EU, 2023)","accessed":"2026-11-04","url":"https://hexcel.com/wp-content/uploads/2025/12/HexPly_8552_eu_DataSheet1.pdf"},{"id":"hexcel-m56","title":"Hexcel HexPly M56 out-of-autoclave data sheet","accessed":"2026-11-04","url":"https://hexcel.com/wp-content/uploads/2026/01/HexPly_M56_global_DataSheet.pdf"},{"id":"hexcel-hsd","title":"Hexcel HexWeb Honeycomb Sandwich Design Technology, AGU 075b (2000)","accessed":"2026-11-04","url":"https://www.hexcel.com/wp-content/uploads/2026/01/Honeycomb_Sandwich_Design_Technology.pdf"},{"id":"hexcel-prepreg","title":"Hexcel HexPly Prepreg Technology manual","accessed":"2026-11-04","url":"https://www.hexcel.com/wp-content/uploads/2026/01/Prepreg_Technology-1.pdf"},{"id":"hexcel-hextool","title":"Hexcel HexTool user guide (M61, M81 machinable tooling)","accessed":"2026-11-04","url":"https://www.hexcel.com/wp-content/uploads/2026/01/HexTool_UserGuide.pdf"},{"id":"nasa-pd-ed-1217","title":"NASA Preferred Reliability Practice PD-ED-1217: structural laminate composites for space","accessed":"2026-11-04","url":"https://extapps.ksc.nasa.gov/Reliability/Documents/Preferred_Practices/1217.pdf"},{"id":"cw-tooling","title":"CompositesWorld: Tooling (2015 survey)","accessed":"2026-11-04","url":"https://www.compositesworld.com/articles/tooling-2015","note":"supplier claims in part"},{"id":"dlr-laminate","title":"DLR IB-2025-144 master thesis (Ramesh): laminate design guidelines review","accessed":"2026-11-04","url":"https://elib.dlr.de/216954/1/IB_2025_144_MA_Ramesh_Geschw%C3%A4rzt.pdf"},{"id":"obata-2021","title":"Obata et al., Composite Structures: tapered FRP laminate with ply drop-off","accessed":"2026-11-04","url":"https://eprints.lib.hokudai.ac.jp/dspace/bitstream/2115/86564/1/Compos%20Struct_Obata_final.pdf"},{"id":"osmeda-2012","title":"Osmeda, Institute of Aviation (READ 2012): process-induced distortion in a composite spar","accessed":"2026-11-04","url":"https://read.meil.pw.edu.pl/wp-content/uploads/Program/2012/Papers/Students/Paper_READ2012_Osmeda_Anna.pdf"},{"id":"wiki-invar","title":"Wikipedia: Invar","accessed":"2026-11-04","url":"https://en.wikipedia.org/wiki/Invar"},{"id":"wiki-cte","title":"Wikipedia: Thermal expansion (table of CTE at 20 C)","accessed":"2026-11-04","url":"https://en.wikipedia.org/wiki/Thermal_expansion"},{"id":"nas1-19347","title":"Bailie, Ley, Pasricha: Composite Laminate Design Guidelines, NASA contract NAS1-19347 Task 22, 1997","accessed":"2026-11-04","note":"guideline text seen only in a search excerpt; full report not opened"}],"entries":[{"id":"allowable-knockdowns","kind":"rule","tier":1,"title":"What each strain allowable in this pack assumes","summary":"Rows name their condition. RTD mean: no knockdown, never a design value. ETW B: 250 F wet, B-basis. design-OH: 0.0053 tension, 0.0043 compression, from open-hole QI B-basis (tension CTD, compression ETW), which covers holes and hot/wet but is not a CAI check.","applies":[],"value":{"table":[{"condition":"RTD-mean","covers":"room temperature dry, mean","use":"comparison, sanity only"},{"condition":"ETW-B","covers":"250 F wet, lamina B-basis","use":"matrix-mode hot/wet check"},{"condition":"design-OH","covers":"open hole, hot/wet, QI B-basis","use":"first-pass laminate sizing"},{"condition":"EST-*","covers":"transferred, see row and entry basis","use":"until a test or a supplier value replaces it"}]},"basis":"SRC: NCAMP QI OHT CTD B 44.35 ksi / 8.35 Msi = 0.0053; OHC ETW mod-CV B 30.86 ksi / 7.13 Msi = 0.0043. Tension value is the B-value; compression is modified-CV B. The strains are EST divisions of those two published values.","sources":["ncamp-im7-8552"],"tags":["hot-wet","damage-tolerance"]},{"id":"first-pass-allowable-choice","kind":"rule","tier":1,"title":"Which allowable to use for a first-pass laminate","summary":"Size a first pass on open-hole fibre strain: 0.0053 tension (CTD), 0.0043 compression (ETW), QI IM7/8552, at 1.5 factor of safety and 2.0 around fasteners. Use RTD mean only to compare materials. Then run matrix, buckling and CAI checks separately.","applies":[],"value":{"table":[{"mode":"tension","strain":0.0053},{"mode":"compression","strain":0.0043},{"factor":"general","value":1.5},{"factor":"around fasteners","value":2}]},"basis":"SRC: NCAMP QI open-hole B-basis strength / QI modulus (OHT CTD, OHC ETW); factors 1.5 and 2.0 from NASA PD-ED-1217. EST: other carbon/epoxy systems.","sources":["ncamp-im7-8552","nasa-pd-ed-1217"],"tags":["margin"],"see":["composites/first-vs-last-ply"]},{"id":"mat-im7-8552-ud","kind":"material","tier":1,"title":"IM7/8552 UD tape: intermediate-modulus ply (NCAMP)","summary":"IM7/8552 190 gsm 35% RC: E1 158.5 GPa, E2 9.0, G12 4.7, nu12 0.316, 0.183 mm ply. Strain to failure RTD mean 0.0158 t, 0.0124 c; ETW B 0.0110 t, 0.0071 c. Tg 406 F dry, 321 F wet (DMA).","applies":["primary structure","wing skin","monocoque"],"value":{"table":[{"id":"im7-8552-rtd-mean","kind":"ud","condition":"RTD-mean","E1":158511,"E2":8963,"G12":4688,"nu12":0.316,"tMm":0.183,"rho":1.57,"e1t":0.0158,"e1c":0.0124,"e2t":0.00715,"e2c":0.0294,"g12":0.0194},{"id":"im7-8552-etw-b","kind":"ud","condition":"ETW-B","E1":165474,"E2":5585,"G12":2137,"nu12":0.393,"tMm":0.183,"rho":1.57,"e1t":0.011,"e1c":0.00709,"e2t":0.0037,"e2c":0.0141,"g12":0.0145},{"id":"im7-8552-design-oh","kind":"ud","condition":"design-OH","E1":158511,"E2":8963,"G12":4688,"nu12":0.316,"tMm":0.183,"rho":1.57,"e1t":0.0053,"e1c":0.0043,"e2t":0.0037,"e2c":0.0141,"g12":0.0145}]},"basis":"SRC: NCAMP Table 3-3, normalised to 0.0072 in ply; ksi and Msi converted. Strains are strength / modulus (EST arithmetic). rho from Hexcel 8552/35%/IM7 at 134 gsm: EST same at 190 gsm.","sources":["ncamp-im7-8552","hexcel-8552-eu"],"tags":["b-basis"]},{"id":"mat-twill-2x2-sm","kind":"material","tier":1,"title":"Standard-modulus 2x2 twill prepreg, AS4C 6K / M56 OOA","summary":"2x2 twill AS4C-6K 285 gsm, M56 oven cure, 50.3% Vf as cured: E 67 GPa, G12 3.7, 0.316 mm ply, 1.50 g/cm3. RTD tension 787, compression 807 MPa (normalised to 56% Vf), shear 99 MPa. Strain 0.0117 t, 0.0139 c mean.","applies":["skin","cosmetic ply","bodywork","outer ply"],"value":{"table":[{"id":"twill-2x2-rtd-mean","kind":"fabric","condition":"RTD-mean","E1":67000,"E2":67000,"G12":3700,"nu12":0.05,"tMm":0.316,"rho":1.5,"e1t":0.0117,"e1c":0.0139,"e2t":0.0117,"e2c":0.0139,"g12":0.0268},{"id":"twill-2x2-design-oh","kind":"fabric","condition":"EST-design-OH","E1":67000,"E2":67000,"G12":3700,"nu12":0.05,"tMm":0.316,"rho":1.5,"e1t":0.0053,"e1c":0.0043,"e2t":0.0053,"e2c":0.0043,"g12":0.0145}]},"basis":"SRC: HexPly M56 sheet, EN test methods. EST: E2 = E1 (balanced fabric); nu12 0.05 from the Hexcel woven carbon row; design row transfers NCAMP QI strains from a tape system.","sources":["hexcel-m56","hexcel-hsd","ncamp-im7-8552"],"tags":["fabric"]},{"id":"process-autoclave-prepreg","kind":"process","tier":1,"title":"Hand layup prepreg plus autoclave: the reference chain","summary":"Cut, kit, lay up on the tool, debulk, bag, cure, trim, NDT. Autoclave runs 1-10 bar: one tool face gives a controlled surface and the bag face does not, so hold datums and tolerances on the tool side. Holds thick sections and complex shapes.","applies":["monocoque","wing","primary structure"],"value":{"table":[{"pressureBar":"1-10"}]},"basis":"SRC: Hexcel Prepreg Technology, pressure range and process. EST: the datum consequence is standard practice inferred from a one-sided tool.","sources":["hexcel-prepreg"],"tags":["autoclave"]},{"id":"cure-cycle-8552","kind":"process","tier":1,"title":"Autoclave cure envelope, HexPly 8552 (typical 180 C system)","summary":"8552: full vacuum plus 15 psig; 3-5 F/min to 225 F; hold 30-60 min; raise to 85-100 psig, venting vacuum at 30 psig; 350 F for 120 +/-10 min; cool at 2-5 F/min to 150 F. Thick sections heat slower and need more dwell.","applies":["autoclave","cure"],"value":{"table":[{"step":"ramp","rate":"3-5 F/min","to":"225 F"},{"step":"dwell","time":"30-60 min","at":"225 F"},{"step":"pressure","value":"85-100 psig","ventVacuumAt":"30 psig"},{"step":"cure","time":"120 +/-10 min","at":"350 F"},{"step":"cool","rate":"2-5 F/min","to":"150 F"}]},"basis":"SRC: HexPly 8552 US data sheet cure procedure; the prepreg manual gives the slow-heat advice for large or thick parts. Printed in F and psig, so kept that way.","sources":["hexcel-8552-us","hexcel-prepreg"],"tags":["ramp","dwell","pressure"]},{"id":"tool-material-cte","kind":"material","tier":1,"title":"Tool materials and CTE mismatch","summary":"CTE in 10^-6/C: Invar 1.2, HexTool BMI 4 in plane (47 through thickness), steel 11-13, aluminium 23.1. Part fibre direction near 0 to 2. Over 157 K cure rise, an aluminium metre grows about 3 mm more than carbon. Use Invar or CFRP for long, close parts.","applies":["tool","mould","mandrel"],"value":{"table":[{"tool":"Invar 36","cte":1.2,"gcc":8.05,"use":"long, close-tolerance, high cycles"},{"tool":"CFRP / BMI (HexTool M61)","cte":4,"zCte":47,"use":"low mass, up to 500 cycles reported"},{"tool":"carbon steel","cte":10.8,"use":"short parts, RTM, press"},{"tool":"aluminium","cte":23.1,"use":"small parts, prototypes, fast heat-up"}]},"basis":"SRC: Wikipedia CTE tables; HexTool M61 guide; CompositesWorld for suitability and the 500-cycle HexTool claim (a supplier claim). EST: mismatch arithmetic (23.1 - 2) x 157 K x 1 m, and fibre-direction 0-2 from the sign of Toray fibre CTE plus resin.","sources":["wiki-cte","wiki-invar","hexcel-hextool","cw-tooling"],"tags":["tooling","invar","cfrp-tool","steel","aluminium"]},{"id":"spring-in","kind":"rule","tier":1,"title":"Spring-in on curved sections: compensate the tool angle","summary":"Curved laminates close up on cooling: d_theta = theta x (a_in - a_thru) x dT. FE on 12 ply cross-ply OoA carbon gave 0.2 deg; the measured spar gave 0.5-0.8 deg; a 90 deg corner with 38 x 10^-6 CTE gap and 157 K gives about 0.5 deg. Open the tool angle; iterate.","applies":[],"value":{"min":0.2,"max":0.5,"unit":"deg"},"basis":"SRC: Radford-form equation and 0.18-0.26 deg results, Osmeda 2012. EST: the 0.5 deg arithmetic using resin-dominated through-thickness CTE from that paper. EST: steel or Invar choice has a smaller effect than layup. The paper measured 0.5-0.8 deg against 0.18-0.26 deg predicted.","sources":["osmeda-2012"],"tags":["distortion","compensation"],"see":["composites/tool-material-cte"]},{"id":"layup-symmetric-balanced","kind":"rule","tier":1,"title":"Symmetric and balanced stacking","summary":"Stack symmetric about the mid-plane so B = 0 and the part does not warp on cool-down; pair +theta with -theta so A16 = A26 = 0. The laminate calculator warns B_NOT_ZERO, A16_A26_NOT_ZERO, D16_D26_NOT_ZERO. A +/-theta pair in a symmetric stack takes at least 4 plies.","applies":[],"value":{"options":["B_NOT_ZERO","A16_A26_NOT_ZERO","D16_D26_NOT_ZERO"]},"basis":"SRC: DLR guideline review, symmetric and balance definitions; warning names from the tool help topic in this repo. EST: the 4-ply count is arithmetic (+theta, -theta, mirrored), not stated by DLR.","sources":["dlr-laminate","nas1-19347"],"tags":["warpage"]},{"id":"layup-ten-percent","kind":"rule","tier":1,"title":"The 10% rule","summary":"At least 10% of the fibres in each of 0, +45, -45 and 90, so a secondary load does not meet a matrix-dominated direction. For optimised laminates, a stiffness-based generalised form exists. A pure 0/90 or all-UD skin fails this.","applies":[],"value":{"min":10,"unit":"%"},"basis":"SRC: DLR thesis review of laminate guidelines, citing Abdalla 2009 for the generalised form.","sources":["dlr-laminate","nas1-19347"],"tags":["stacking"],"see":["aerospace/cf-layup-basics"]},{"id":"ply-drop-stagger","kind":"rule","tier":1,"title":"Ply drop spacing and stagger","summary":"Space dropped plies at least 3 ply thicknesses apart (0.55 mm of IM7/8552); that is the floor. Fewest drops per station, cut inner plies first, 0 before 90, keep symmetry, and never drop adjacent 0 and 90.","applies":[],"value":{"min":3,"unit":"ratio"},"basis":"SRC: Obata 2021 list of published guidelines for the 3t, order and symmetry rules.","sources":["obata-2021","nas1-19347"],"tags":["taper"],"see":["composites/ply-drop-taper"]},{"id":"ply-drop-taper","kind":"rule","tier":1,"title":"Thickness taper ratio","summary":"Taper at 20:1 along primary load paths and 10:1 for secondary paths and for stiffener or flange run-outs. Each dropped 0.183 mm ply takes at least 3.66 mm of run at 20:1. 20:1 is the safe first model.","applies":[],"value":{"min":10,"typical":20,"unit":"ratio"},"basis":"EST: 20:1 and 10:1 from NASA contract NAS1-19347 guideline text seen in a search excerpt; the report itself was not opened. Arithmetic with SRC ply thickness.","sources":["nas1-19347","ncamp-im7-8552"],"tags":["ramp"]},{"id":"inside-radius","kind":"rule","tier":1,"title":"Minimum inside radius","summary":"EST: inside radius at least 2 x laminate thickness and never under 3 mm for prepreg on a female tool; tighter corners bridge, resin-pool and open under curved-beam tension. Corner thickness also rises on a female tool and thins on a male.","applies":[],"value":{"min":3,"unit":"mm"},"basis":"EST: shop and guideline practice; no opened source gives a minimum radius. Female-tool thickening and male-tool thinning match search excerpts, not opened. Check with a coupon on your system.","sources":["hexcel-prepreg"],"tags":["corner","bridging"]},{"id":"drape-shear-limit","kind":"rule","tier":1,"title":"Drape: shear angle limit and fabric choice","summary":"EST: woven plies shear before they wrinkle, up to a locking angle near 35-50 deg by weave and temperature. Design to under 30 deg at first pass. Satin drapes best, twill next, plain worst. UD tape has essentially no drape: split it or use a fabric on double curvature.","applies":[],"value":{"max":30,"unit":"deg"},"basis":"EST: all degree figures. Search excerpts confirm a locking angle exists and varies, but no opened paper tabulated it; use cad_flatten_surface or a picture-frame test. SRC: weave ranking, Hexcel Prepreg Technology.","sources":["hexcel-prepreg"],"tags":["wrinkle","locking-angle"]},{"id":"sandwich-wrinkling","kind":"rule","tier":1,"title":"Face wrinkling check","summary":"Wrinkling stress = 0.5 x (Gc Ec Ef)^(1/3). For a 60 GPa face on HRH-10 48 (GW 25, Ec 138 MPa): 296 MPa. Compare with compressive face stress = M / (h tf b). Needs high Ec and flatwise bond strength. Hexcel calls classical forms order-of-magnitude.","applies":[],"value":{"table":[{"formula":"0.5*(Gc*Ec*Ef)^(1/3)","units":"MPa"}]},"basis":"SRC: Hexcel AGU 075b Appendix III formula, for symmetric thin facings on a core much softer than skins. EST: worked number. Study excerpts report classical forms conservative on CFRP.","sources":["hexcel-hsd"],"tags":["skin"]}]}