Materials / Compare
Plastic PMMA vs. Steel AISI 4340
Compare Plastic PMMA vs. Steel AISI 4340 strength, stiffness, weight and thermal properties.
| Try it on a partA bracket to run stress or thermal on, free in your browser | Open in LessCAD | Open in LessCAD |
|---|---|---|
| Mechanical | ||
| Yield strength | not given (tensile used) | 1,035MPasourcetypical, transverse |
| Ultimate tensile strength | 80MPasourcetypical, 23 °C | 1,140MPasourcetypical, transverse |
| Compressive strength | 110MPasourcecompressive yield stress, typical | not sourced |
| Flexural strength | 115MPasourcetypical | not sourced |
| Elongation at break | 5.5%sourcetypical | 18%sourcetypical, transverse |
| Young's modulus (stiffness) | 3.3GPasourcetypical, short-term | 200GPasourceMIL-HDBK-5J design value (AISI 4340, quenched and tempered) |
| Density | 1,190kg/m³sourcetypical6.59x lighter | 7,840kg/m³sourcetypical |
| Strength to weight | 67.2kN·m/kg | 132kN·m/kg1.96x higher |
| Stiffness to weight | 2.77MN·m/kg | 25.5MN·m/kg9.19x higher |
| Poisson's ratio | 0.37sourcetypical | 0.32sourceMIL-HDBK-5J design value (AISI 4340, quenched and tempered) |
| Shear modulus | 1.2GPa | 75.7GPa62.9x stiffer in shear |
| Bulk modulus | 4.23GPa | 185GPa |
| Speed of sound | 1,665m/s | 5,049m/s |
| Thermal | ||
| Thermal conductivity | 0.19W/m·Ksourcetypical | 37.5W/m·Ksourcetypical197x more heat through a fin |
| Thermal expansion | 70µm/m·Ksource0-50 °C | 11.3µm/m·Ksourcemean, -18 to 93 °C |
| 100 mm part over a 50 °C swing | 350µm growth | 56.5µm growth6.19x less |
| Specific heat | 1,470J/kg·Ksourcetypical | 448J/kg·Ksourcetypical |
| Heats up and cools (diffusivity) | 0.109mm²/s | 10.7mm²/s98.2x faster |
| Thermal shock resistance | 41.5W/m | 11,678W/m282x more resistant |
| Max service temperature | 80°Csourcemax. permanent service temperature | not sourced |
| Values for | Röhm PLEXIGLAS GS 0F00 cast acrylic sheet, typical values at 23 °C / 50 % RH (Röhm Technical Information Ref. No. 211-1) | Carpenter (Latrobe) Lescalloy 4340 VAC-ARC datasheet; mechanical row for 1100 °F temper; physical properties grade-level |
Every value links to the document that states it. "Not sourced" means no citable source states it (or only a specification minimum); figures computed from it are left out too.
Questions
Is Plastic PMMA stronger than Steel AISI 4340?
Steel AISI 4340 is stronger: its yield strength is 1,035 MPa against tensile strength 80 MPa for Plastic PMMA (12.9x).
Which is lighter, Plastic PMMA or Steel AISI 4340?
Plastic PMMA is lighter: 1,190 kg/m³ against 7,840 kg/m³ for Steel AISI 4340.
Which is stiffer, Plastic PMMA or Steel AISI 4340?
Steel AISI 4340 is stiffer: Young's modulus 200 GPa against 3.3 GPa for Plastic PMMA, so the same part in Steel AISI 4340 deflects less under the same load.
Which is lighter for the same job, Plastic PMMA or Steel AISI 4340?
For the same stiffness or strength: Plastic PMMA is lighter for a stiff panel or plate, strong beam, strong panel or plate; Steel AISI 4340 is lighter for a stiff rod or tie (tension), stiff beam (bending), strong rod or tie.
| Part that must be | Plastic PMMA | Steel AISI 4340 |
|---|---|---|
| Stiff rod or tie (tension) | 9.19x heavier | lighter |
| Stiff beam (bending) | 18% heavier | lighter |
| Stiff panel or plate | lighter | 1.68x heavier |
| Strong rod or tie | 1.96x heavier | lighter |
| Strong beam | lighter | 20% heavier |
| Strong panel or plate | lighter | 1.83x heavier |
For the same stiffness or strength, mass scales with density over stiffness (or strength) raised to a power set by how the part is loaded: 1 for a rod in tension, 1/2 for a beam in bending, 1/3 for a panel (the standard material-selection indices).
Which conducts heat better, Plastic PMMA or Steel AISI 4340?
Steel AISI 4340 conducts heat better: 37.5 W/m·K against 0.19 W/m·K for Plastic PMMA.
Which expands less with temperature?
Steel AISI 4340 expands less: 11.3 µm/m·K against 70 µm/m·K for Plastic PMMA.