Carbon fiber epoxy laminate

Hexcel’s unidirectional IM7/8552 at 25°C dry has tensile strength and modulus of 2,724 MPa and 164 GPa at 0°, versus 64 MPa and 12 GPa at 90°. Apply the values in their tested directions and qualify the actual layup, ply sequence and manufacturing process. Hexcel 8552 UD mechanical table, p. 2

Specify a material system and laminate

Carbon fiber/epoxy laminate is a family description. Hexcel supplies its 8552 epoxy system with unidirectional and woven reinforcements, while Toray's 2510 is a separately formulated out-of-autoclave prepreg system. A fiber name, visible weave or the phrase “aerospace carbon fiber” does not identify a complete engineering material. Hexcel 8552 product data, Toray 2510 prepreg data

Specify fiber grade and architecture, resin system, prepreg/product code, resin content, ply orientations and sequence, cured thickness, manufacturing route, finish and inspection requirements. Keep a ply schedule tied to a defined part coordinate system. A unidirectional tape, balanced woven fabric and chopped-fiber molding material should not inherit one another's property table.

For a purchased flat panel, identify whether the order controls the laminate construction or only selected measured properties. For a structural part, keep the drawing, material/process specification and acceptance basis together. Replacing a fabric style, resin or cure route is an explicit material/process change, even when the finished surface looks similar.

Directional values: a bounded example

Hexcel's European 8552 sheet carries ©2023. Its IM7 unidirectional data at 25°C, dry list:

These reference values concern the named system and directions. Do not assign the 0° strength to every direction of a multidirectional part, or treat the table as finished-component allowables. The sheet separately identifies other fibers, weaves, conditioning and temperatures. Hexcel 8552 UD mechanical table, p. 2

Retain stacking sequence, thickness, load direction and failure mode with the test evidence. Shear, bearing, delamination and impact-damaged compression each require their own evidence.

Cured thickness is a product and process quantity

For 8552/35%/134 IM7 UD prepreg, Hexcel lists 0.131 mm nominal cured ply thickness and 1.57 g/cm³ nominal laminate density. As an original arithmetic example, 16 plies at that nominal thickness sum to 2.096 mm. This is a preliminary thickness estimate, not an acceptance tolerance or a prediction of another fabric/resin combination. Hexcel physical-property table, p. 2

Use the actual product and qualified consolidation route to establish production thickness. Define where thickness is measured, how local ply drops and overlaps are represented, and whether surface films or coatings are included. Keep measured panel or part results separate from a nominal ply-thickness calculation.

Test method, specimen and value status

ASTM D3039/D3039M-17(2025) addresses in-plane tensile properties of polymer-matrix composites within its stated material/laminate scope. Its public guidance identifies factors including layup, specimen preparation, conditioning, environment, alignment and gripping. A report should retain these conditions, the loading direction and the property definition. ASTM D3039/D3039M scope and use

A short-beam result is a different record. ASTM D2344/D2344M-22 explains that complex stresses and possible failure modes generally prevent relating short-beam strength to one unique material property. Do not silently turn a catalog short-beam or “ILSS” number into a universal in-plane shear allowable. ASTM D2344/D2344M significance and use

Identify whether values are supplier reference data, lot averages, acceptance limits or statistical design allowables. Toray's 2510 sheet explicitly describes its results as lot averages for reference, not specification purposes. Its elevated-temperature wet condition is 82°C testing after conditioning at 160°F/85% relative humidity to equilibrium. Those conditions are part of the result. Toray 2510 notes and disclaimer

Manufacturing route and process control

Toray's sheet is marked 2510 Prepreg System_Rev.6.5.2025 and gives an oven/vacuum route, including a separate cycle for thick laminates. Its instructions address trapped gases, leak checking and exotherm/void concerns. They belong to that material and process envelope, not every carbon/epoxy laminate. Preserve the supplier's full procedure rather than extracting one cure temperature. Toray 2510 processing guidance

For production, define approved storage and handling, material identity, accumulated time outside controlled storage, layup sequence, bagging, cure monitoring and inspection. Record actual part/process temperatures where required; an oven setpoint alone is not the complete thermal history of a thick component. Establish how deviations are reviewed before release.

Agree acceptance for wrinkles, bridging, foreign material, resin-rich regions, voids, disbonds and surface defects according to the part's function and qualified inspection capability. A satisfactory surface does not establish the internal condition of the whole laminate. Process coupons support a defined acceptance plan; they do not automatically represent every local feature.

Environment, damage and assembly

FAA AC 20-107B with Change 1 discusses composite aircraft structure and calls for determining environmental effects on strength, fatigue and stiffness for the material system. Its moisture discussion includes part thickness, diffusion and realistic service exposure. This is an aircraft-specific engineering guidance example, not an approval of any stock panel for aviation use. FAA composite-structure guidance

For an actual component, define temperature/time history, moisture, fluids, ultraviolet exposure, load spectrum and credible damage. A dry room-temperature coupon does not establish hot/wet service, fire behavior or the residual capacity after impact. Set the appropriate inspection and repair basis alongside the design requirements.

Holes, cut edges, bonded interfaces and mechanical joints need their own manufacturing and acceptance requirements. Define drilling/trimming quality, bearing and clamp loads, bond preparation and cure, and environmental protection where applicable. A parent-laminate tensile value cannot establish joint strength or qualify an arbitrary repair. Reassess substitutions and process changes against the complete assembly requirements.

Release record

Retain material batches, product revision, layup/drawing revision, orientation, process history, dimensional and inspection results, and the applicable design/acceptance basis. Keep supplier data separate from demonstrated part performance. Sources were reviewed November 1, 2026; the printed Hexcel copyright and Toray revision string are preserved without assigning revision dates from upload paths.

Related reference

Material selection through production