AS4 BMI
Matrix
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.
Values for the BMI condition
Other AS4 grades and fills
AS4 is listed in 7 conditions; see the grade overview at AS4.
Compare all 7 grades and fillsHide
| Grade · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness |
|---|---|---|---|---|---|
BMIThis page 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/AS4 | Pick for tough, solvent-resistant, weldable thermoplastic structure and continuous service near 250 °C. | — | 2,130 | — | — |
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 | — | — |
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 | — | — |
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 | — |
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 | — |
What is AS4 BMI?
AS4 BMI is AS4 in the BMI condition — pick when service temperature above the epoxy limit (to ~200–230 °C) is required with the same standard-modulus fiber. AS4 BMI has a tensile strength of 2,050 MPa (297 ksi), stronger than 77% of composite grades. Elongation at break is 1.4% and the elastic modulus is 138 GPa (20 Msi). AS4 BMI has a density of 1.58 g/cm³ (0.0571 lb/in³), lighter than 54% of composite grades. FIBER-12K is the default condition FabDigit quotes; BMI is available on request or by drawing note.
AS4 BMI properties
Typical room-temperature values for AS4 BMI; 14 are specific to this condition. Other listed values are AS4 reference data and may not represent this condition. Bars are the position among composite grades.
Physical1
AS4 BMI has a density of 1.58 g/cm³ (0.0571 lb/in³), lighter than 54% of composite grades.
Mechanical4
AS4 BMI has a tensile strength of 2,050 MPa (297 ksi), stronger than 77% of composite grades. Elongation at break is 1.4% and the elastic modulus is 138 GPa (20 Msi).
Thermal6
AS4 BMI is rated for continuous service to 210°C (410 °F). It conducts heat at 4.5 W/m·K (2.6 BTU/hr·ft·°F), better than 64% of composite grades. Thermal expansion is -0.4 µm/m·K (-0.222 µin/in·°F).
Electrical1
AS4 BMI has an electrical resistivity of 3×10⁻⁵ Ω·m.
Chemical & Environmental2
Corrosion resistance is excellent (85/100), better than 65% of composite grades.
Sustainability3
Producing a kilogram of AS4 BMI takes about 320 MJ of energy and emits 24 kg of CO₂ — more than 72% of composite grades. Typical recycled content is 0%.
Manufacturability1
AS4 BMI's machinability is poor (28/100, worse than 57% of composite grades).
Values are nominal handbook figures for design screening. Confirm any required mill or lot documentation when quoting.
Working with AS4 BMI
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.
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.
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 |
AS4 BMI — frequently asked
What is AS4 BMI used for?
AS4 BMI 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 BMI?
AS4 BMI has a typical tensile strength of 2,050 MPa (297 ksi) — stronger than 77% of composite grades. Strength varies by condition: see the 7 listed tempers.
Is AS4 BMI easy to machine?
Not especially — machinability is rated poor (28/100, worse than 57% of composite grades). 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 BMI be welded?
Not weldable in epoxy/BMI form (bond or bolt); APC-2/PEEK versions can be resistance-, induction- or ultrasonically welded.
What surface finishes work on AS4 BMI?
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.
Can AS4 BMI 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.
What is the maximum service temperature of AS4 BMI?
AS4 BMI is rated for continuous use to about 210°C (410 °F). Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
Sources
- HexTow AS4 / AS4C / AS4D Carbon Fiber Product Data — Hexcel (2020)
- HexPly 8552 Epoxy Matrix Product Data Sheet — Hexcel (2020)
- ASM Handbook Vol. 21: Composites — ASM International (2001)
- MIL-HDBK-17 / CMH-17 Composite Materials Handbook (AS4/3501-6, AS4/8552 data sets) — SAE / CMH-17 (2012)
- APC-2/AS4 Thermoplastic Composite Tape Data — Cytec/Solvay (2015)
Property data is compiled from published supplier and standards handbooks and normalised for comparison. Nothing on this page is a certification — request mill certs, CoC or material test reports with your order.