AS4: Properties, Grades (AS4C, AS4D) & Uses

AS4 grades and fills

AS4 is supplied in 7 conditions, soft to hard. FIBER-12K is the default FabDigit quotes; the values on this page are for it.

Compare all 7 grades and fillsHide

Grade · open for datasheet	Best for	Tensile MPa	Elong. %
BMI AS4/BMI unidirectional laminate	Pick when service temperature above the epoxy limit (to ~200–230 °C) is required with the same standard-modulus fiber.	2,050	1.4
APC-2 APC-2/AS4	Pick for tough, solvent-resistant, weldable thermoplastic structure and continuous service near 250 °C.	2,130
UD-8552 AS4/8552 unidirectional toughened epoxy laminate	Pick for current-production primary/secondary aerospace structure needing better damage tolerance and hot/wet retention than 3501-6.	2,200
UD-3501-6 AS4/3501-6 unidirectional epoxy laminate	Pick this classic 177 °C-cure epoxy UD system when legacy aerospace allowables and extensive published data are required.	2,280
AS4C Fine-filament (5.1 µm) variant of AS4	Pick when thinner filaments and slightly lower fiber density improve fabric drape and translation in thin laminates.	4,340	1.8
FIBER-12KDefault AS4 12K dry tow	Pick for filament winding, weaving, braiding or in-house prepregging where the bare standard-modulus tow is needed.	4,433	1.8
AS4D Higher-modulus/higher-strength member of the AS4 family	Pick when a drop-in stiffness/strength upgrade over AS4 is wanted without moving to IM7.	4,830	2

Supply forms, finishes and certifications

Ways AS4 is supplied — form, process route, surface or paperwork — without a datasheet of their own. The property values above apply.

Option	What it is	Type
FABRIC-EPOXY	AS4 woven fabric / epoxy laminate	Supply form

What is AS4?

AS4 is Hexcel's standard-modulus, high-strength PAN carbon fiber at 231 GPa tensile modulus, 4433 MPa tensile strength, 1.8 % elongation and 1.79 g/cm3, and has been the reinforcement in long-established prepregs such as 3501-6 and 8552 since the 1980s. It is available as 12K tow, in AS4C and AS4D variants, in epoxy and BMI fabrics and unidirectional tapes, and as AS4/PEEK APC-2 thermoplastic tape. It is the cost-effective choice with the deepest allowables database, but stiffness is well below intermediate-modulus fiber and the machinability score of 30 reflects heavy tool wear; IM7 is the step up when strength or stiffness margin is short. AS4 has a density of 1.79 g/cm³ (0.0647 lb/in³), heavier than 56% of composite grades. AS4 has a tensile strength of 4,433 MPa (643 ksi), stronger than 92% of composite grades. Elongation at break is 1.8% and the elastic modulus is 231 GPa (33.5 Msi).

What is AS4 used for?

aircraft secondary structures
industrial tooling
sporting goods
automotive parts

Advantages

Good corrosion resistance — 90/100, better than 85% of composite grades
Stiff — 231 GPa (33.5 Msi), better than 84% of composite grades
High service temperature — 400°C (752 °F), better than 78% of composite grades

AS4 properties

Typical room-temperature values for AS4-FIBER-12K; bars are the position among composite grades.

Physical1

AS4 has a density of 1.79 g/cm³ (0.0647 lb/in³), heavier than 56% of composite grades.

Density1.79 g/cm³0.06 lb/in³

Mechanical4

AS4 has a tensile strength of 4,433 MPa (643 ksi), stronger than 92% of composite grades. Elongation at break is 1.8% and the elastic modulus is 231 GPa (33.5 Msi).

Elastic (Young's) Modulus231 GPa33.5 Msi

Tensile Strength (Ultimate)4,433 MPa643 ksi

Elongation at Break1.8%

Compressive Strength2,700 MPa392 ksi

Thermal6

AS4 is rated for continuous service to 400°C (752 °F). It conducts heat at 6.8 W/m·K (3.93 BTU/hr·ft·°F), better than 67% of composite grades. Thermal expansion is -0.4 µm/m·K (-0.222 µin/in·°F).

Thermal Conductivity6.8 W/m·K3.9 BTU/hr·ft·°F

Specific Heat Capacity712 J/kg·K0.17 BTU/lb·°F

Thermal Expansion (CTE, 20–100 °C)-0.4 µm/m·K-0.22 µin/in·°F

Max Service Temperature (continuous)400°C752 °F

Min Service Temperature-269°C-452 °F

Limiting Oxygen Index55%

Electrical1

AS4 has an electrical resistivity of 1.7×10⁻⁵ Ω·m.

Electrical Resistivity1.7×10⁻⁵ Ω·m669 µΩ·in

Chemical & Environmental2

Corrosion resistance is excellent (90/100), better than 85% of composite grades.

Corrosion ResistanceExcellent90/100

Chemical Resistance SummaryFiber itself is inert to most acids, alkalis and solvents; performance of a part is governed by the matrix. Strong oxidizers (hot nitric acid, chromic acid) and air above ~400 °C degrade the fiber; direct contact with aluminium causes galvanic corrosion of the metal.

Sustainability3

Producing a kilogram of AS4 takes about 320 MJ of energy and emits 24 kg of CO₂ — more than 72% of composite grades. Typical recycled content is 0%.

Embodied Energy (primary production)320 MJ/kg137,575 BTU/lb

Embodied Carbon (primary production)24 kg CO₂/kg

Typical Recycled Content0%

Manufacturability1

AS4's machinability is poor (30/100, worse than 54% of composite grades).

MachinabilityPoor30/100

Common Calculations4

Specific Strength (UTS / density)calculated2,477 kN·m/kg

Specific Stiffness (E / density)calculated129.1 MN·m/kg

Thermal Diffusivitycalculated5.3 mm²/s

Thermal Shock Resistance Indexcalculated-326

Values are nominal handbook figures for design screening. Certified mill or lot data ships with every FabDigit order on request.

Strength versus weight in the composite family

Yield strength against density for every composite grade FabDigit runs. AS4 is highlighted; hover a dot for its name, or open the interactive family chart.

Working with AS4

Is AS4 easy to machine?

Highly abrasive and delamination-prone — use PCD/diamond-coated tools, high speed with low feed, sharp compression routers, backing plates and dust extraction (conductive dust).

Can AS4 be welded?

Not weldable in epoxy/BMI form (bond or bolt); APC-2/PEEK versions can be resistance-, induction- or ultrasonically welded.

Can AS4 be formed, bent or molded?

Autoclave cure of prepreg (177 °C / 0.6–0.7 MPa for 3501-6 and 8552), or filament winding/RTM with dry tow; thermoplastic AS4/PEEK tape is press- or AFP-consolidated at 380–400 °C.

AS4 chemical composition (wt %)

Limits by weight percent from the governing specification, written the way the spec states them — a single maximum for impurities, a range for alloying elements, and the base element as balance. Nominal is the typical mid-range value.

Element	Spec limit (wt %)	Nominal
carbon (C)PAN-based fiber, non-graphitized standard modulus	93.5 – 95.5	94
nitrogen (N)residual from PAN precursor	3.5 – 6	5
oxygen + hydrogen (surface/residual)surface-treated (oxidized) fiber	0.3 – 1.5	0.8
sizing (epoxy-compatible)GP/unsized/thermoplastic-compatible options available	0.6 – 1.5	1

What surface finishes work on AS4?

Peel-ply or light abrasion plus solvent wipe before bonding; UV-protective primer/topcoat is needed outdoors, and glass or fiberglass isolation plies plus sealant are required at aluminium interfaces to prevent galvanic corrosion.

Other Carbon-fiber composites grades

Closest composite grades by properties

Compare AS4 with…

Benchmark AS4 against the top 3 neighbours

How much does AS4 cost?

AS4 is a high-cost composite ($$$$), pricier than about 78% of the materials FabDigit quotes. Part price depends far more on geometry, tolerance and quantity than on the raw stock — upload a CAD file for a live quote.

AS4 — frequently asked

What is AS4 used for?

AS4 is typically used for aircraft secondary structures, industrial tooling, sporting goods and automotive parts. In short: standard-modulus workhorse fiber; lowest-cost aerospace prepreg fiber; deepest allowables database.

What is the tensile strength of AS4?

AS4 has a typical tensile strength of 4,433 MPa (643 ksi) — stronger than 92% of composite grades. Strength varies by condition: see the 7 listed tempers.