M40J vs M55J
Composite · grade comparison
M40J and M55J are both composite grades. M40J is the stronger of the two: tensile strength 4,410 MPa (640 ksi) against 4,020 MPa (583 ksi) for M55J, about 10% more. M40J is the more ductile: elongation 1.2% versus 0.8% for M55J. M40J is lighter (1.77 g/cm³ vs 1.91 g/cm³ for M55J) and M55J is stiffer (540 GPa vs 377 GPa).
M40JChoose it when strength drives the design, or when the part is bent, formed or impact-loaded.
M40J vs M55J: propertiesHow to read these bars
- One bar per material. A full bar is the highest value among all composite grades in the FabDigit library; each bar is drawn as a share of that.
- The better value (by the usual engineering direction) is in bold. Rows with no direction — density, thermal conductivity — have no bold.
- Values are typical room-temperature figures for the condition named on each card.
- Confirm against the certified mill or resin datasheet before design release.
How to read these bars
- One bar per material. A full bar is the highest value among all composite grades in the FabDigit library; each bar is drawn as a share of that.
- The better value (by the usual engineering direction) is in bold. Rows with no direction — density, thermal conductivity — have no bold.
- Values are typical room-temperature figures for the condition named on each card.
- Confirm against the certified mill or resin datasheet before design release.
Mechanical
Strength, stiffness, ductility and hardness at room temperature.
Elastic (Young's) Modulus
Poisson's Ratio
Tensile Strength (Ultimate)
Elongation at Break
Compressive Strength
Physical
Density and transition temperatures.
Density
Water Absorption (24 h)
Thermal
How each material carries heat and how hot it can run.
Thermal Conductivity
Specific Heat Capacity
Thermal Expansion (CTE, 20–100 °C)
Max Service Temperature (short-term)
Same in both: Max Service Temperature (continuous) 400°C752 °F · Min Service Temperature -269°C-452 °F
Electrical
Conductivity and insulation.
Electrical Resistivity
Volume Resistivity
Chemical & Environmental
Corrosion and environmental resistance (0–100 scores).
Corrosion Resistance
UV / Weathering Resistance
Manufacturability
FabDigit workshop ratings (0–100 scores) — how each material behaves on the machine.
Machinability
Polishability
Sustainability
Primary-production footprint per kilogram.
Embodied Energy (primary production)
Embodied Carbon (primary production)
Embodied Water
Same in both: Typical Recycled Content 0%
Common Calculations
Ratios derived from the values above.
Specific Strength (UTS / density)
Specific Stiffness (E / density)
Thermal Diffusivity
Thermal Shock Resistance Index
Strength versus weight
Yield strength against density for every composite grade in the FabDigit library; the compared grades are highlighted. Up and left is stronger for its weight.
Manufacturing and finishing
| Capability | M40J | M55J |
|---|---|---|
| Default condition | — | — |
| Relative cost | $$$$ High | $$$$ High |
| Min. machined wall | — | — |
| Best machined surface | — | — |
M40J vs M55J — frequently asked
Is M40J stronger than M55J?
Yes. M40J has a typical tensile strength of 4,410 MPa (640 ksi) against 4,020 MPa (583 ksi) for M55J — about 10% more.
Which is cheaper, M40J or M55J?
Both sit in the same relative cost tier ($$$$, high); the part price will be decided by machining time, tolerance and quantity rather than by the material.
Which is easier to machine, M40J or M55J?
M40J, by a small margin. Both rate poor for machinability — 25/100 against 18/100 for M55J.
Ready to make it?
Upload a CAD file and FabDigit prices the part in M40J and M55J side by side — material, machining time, tolerance and finish in one quote. Certified material data ships with the order on request.
Typical handbook values for the conditions named above, normalised for comparison. Hardness on non-Brinell scales is converted approximately for charting only. Request certified data with your order for design-critical properties.