Since my IPCC Track Width Calculator, I have been thinking about how to make an online alternative to Under Pressure. The material choices in Under Pressure are a good starting point for my version.
The strength properties of a material are used to predict the pressure (depth) at which material failure will occur. Bearing stresses (average seat stresses) and membrane stresses (axial, hoop and meridional stresses in shells and tangential and radial stresses in plates) are compared to uniaxial strengths of the material to predict failure. Shear stresses are compared to shear strengths of the material to predict failure. Uniaxial strengths (Yield Strength for Metals, Ultimate Tensile and Compressive Strengths for Ceramics and Glass, and Ultimate and Working Strengths for Plastics) are provided by the material choices database to predict material failure due to bearing and membrane stresses. Predicted material failure due to shear stresses is based on the criteria that the shear strength of the material is equal to 1/2 of its uniaxial strength. This failure criterion for shear is known as the “Maximum Shear Stress Theory.” The type of uniaxial material strength used by Under Pressure to perform a pressure vessel analysis depends on the behaviour of the material.
The Under Pressure application comes with a database of commonly used pressure vessel material choices. Materials are grouped into the following main categories:
- Ceramics
- Glass
- Metals
- Plastics
Each of the categories has a set of required properties; some of the properties are common, like Density and Poisson’s ratio, but some, like Yield Strength, are specific to one material class. These tables below are from the “Details on Materials” section of the Under Pressure Manual. I have converted the numbers from the original imperial to SI values (imperial in brackets)
Definitions of Material Properties
Ultimate Strength (tensile)
The maximum uniaxial tensile stress the material can withstand without failure.
In the tables below, this is UST, and is expressed in both Mpa and Ksi.
Ultimate Strength (compressive)
The maximum uniaxial compressive stress the material can withstand without failure.
In the tables below, this is USC.
Yield Strength
Uniaxial stress at which the yield (permanent deformation) of the material is initiated.
In the tables below, this is YS.
Ultimate Strength
The maximum uniaxial stress the material can withstand without failure.
In the tables below, this is US.
Working Strength
Maximum stress allowed in the material during service, as defined by the pressure vessel designer.
In the tables below, this is WS.
Young’s Modulus
The average ratio of stress to strain for stress below the proportional limit is the measurement of material stiffness.
The Young’s Modulus (also known as Elastic Modulus) and Poisson’s Ratio of a material are known as the material’s elastic constants. The elastic constants are used in the evaluation of stresses and deflections of a pressure vessel geometry. The elastic constants are used to predict the pressure at which thin-wall buckling will occur for pressure vessel shell geometries such as tubes, spheres, and hemispheres. Thin-wall buckling of tubes, spheres, and hemispheres is dependent on the material’s elastic constants and geometry (i.e. the material and geometric “stiffness”) and is independent of the material’s strength.
In the tables below, Young’s Modulus is YM.
Density
Mass or weight per unit volume of material. The density of a material is used to calculate an indicative in-air and water weight (weight when submerged) of a pressure vessel geometry.
In the tables below, this is Den.
Poisson’s Ratio
Absolute value of the ratio of lateral strain to axial strain.
In the tables below, this is PR.
Ceramics
Ceramics are characterised by large differences in the magnitudes of the material’s tensile strength and compressive strength. Consequently, when evaluating stresses in ceramic, glass, and similar brittle materials, it is essential to compare tensile stresses to tensile strengths and compressive stresses to compressive strengths.
| Sub Category | Name | UST Mpa (Ksi) | USC Mpa (Ksi) | YM Gpa (Mpsi) | Den g/cm³ (lb/in³) | PR |
|---|---|---|---|---|---|---|
| Alumina | 94%1 | 193 (28) | 2103 (305) | 303 (44) | 3.6 (0.13) | 0.21 |
| Alumina | 96%2 | 221 (32) | 2063 (300) | 324 (47) | 3.71 (0.134) | 0.23 |
| Alumina | 99.5%3 | 379 (38) | 3482 (380) | 379 (54) | 3.88 (0.14) | 0.22 |
| Alumina | Sapphire4 | 276 (40) | 2068 (300) | 345 (50) | 3.96 (0.143) | 0.29 |
| RC-HP-DBM w/Mgo5 | 345 (50) | 3447 (500) | 386 (56) | 3.96 (0.143) | 0.22 | |
| Silicon Carbide | Silicon Carbide6 | 307 (44.5) | 2496 (362) | 393 (57) | 3.04 (0.11) | 0.19 |
Glass
Glass is characterised by large differences in the magnitudes of the material’s tensile strength and compressive strength. Consequently, when evaluating stresses in ceramic, glass, and similar brittle materials, it is essential to compare tensile stresses to tensile strengths and compressive stresses to compressive strengths.
| Sub Category | Name | UST Mpa (Ksi) | USC Mpa (Ksi) | YM Gpa (Mpsi) | Den g/cm³ (lb/in³) | PR |
|---|---|---|---|---|---|---|
| Glass | BK-77 | 34 (5) | 1448 (210) | 82 (11.9) | 2.51 (0.0906) | 0.206 |
| Glass | Pyrex | 34 (5) | 1448 (210) | 61 (8.9) | 2.24 (0.081) | 0.2 |
| Glass | Quartz | 34 (5) | 1448 (210) | 73 (10.75) | 2.19 (0.079) | 0.19 |
| Glass | Vycor | 34 (5) | 1448 (210) | 73 (10.75) | 2.19 (0.079) | 0.19 |
Metals
Metals are typically characterised as ductile materials. Ductile materials are defined by a value of stress (yield strength) at which permanent deformation of the material is initiated. The commencement of permanent deformation (yielding) of a ductile material is generally considered to be the point at which material failure occurs for the purposes of performing structural analysis. The magnitude of uniaxial stress that initiates the yield of ductile materials is essentially the same for either a compressive or tensile load.
| Sub Category | Name | YS Mpa (Ksi) | YM Gpa (Mpsi) | Den g/cm³ (lb/in³) | PR |
|---|---|---|---|---|---|
| Aluminium | 2024-T38 | 248 (36) | (10.5) | (0.101) | 0.33 |
| Aluminium | 5052-H34 | 172 (25) | (10.1) | (0.097) | 0.33 |
| Aluminium | 5082-H329 | 152 (22) | (10.1) | (0.097) | 0.33 |
| Aluminium | 5456-H11110 | 179 (26) | (10.2) | (0.096) | 0.33 |
| Aluminium | 6061-T61112 | 241 (35) | (9.9) | (0.098) | 0.33 |
| Aluminium | 6262-T9 | 379 (55) | (9.0) | (0.098) | 0.045 |
| Aluminium | 7075-T61314 | 427 (62) | (10.3) | (0.101) | 0.33 |
| Nickel | K Monel15 | 621 (90) | (26) | (0.306) | 0.32 |
| Nickel | Monel16 | 172 (25) | (26) | (0.319) | 0.32 |
| Stainless Steel | 17-4 PH H90017 | 1172 (170) | 197 (28.5) | 7.81 (0.282) | 0.27 |
| Stainless Steel | 17-4 PH H107518 | 862 (125) | 197 (28.5) | 7.83 (0.283) | 0.27 |
| Stainless Steel | 17-4PH H115019 | 689 (100) | 197 (28.5) | 7.86 (0.284) | 0.32 |
| Stainless Steel | 304, 303, 304L, 316L20 | 179 (26) | 200 (29) | 7.92 (0.286) | 0.27 |
| Stainless Steel | 31621 | 179 (26) | 200 (29) | 7.92 (0.286) | 0.27 |
| Steel | Carbon Steel2223 | 248 (36) | 200 (29) | 7.86 (0.284) | 0.32 |
| Steel | Low Alloy24 | 483 (70) | 200 (29) | 7.89 (0.283) | 0.32 |
| Titanium | Common Pure2526 | 379 (55) | 107 (15.5) | 4.51 (0.163) | 0.34 |
| Titanium | Ti-5Al- 2.5Sn27 | 758 (110) | 107 (15.5) | 4.48 (0.162) | 0.31 |
| Titanium | Ti-6Al-4V28 | 820 (119) | 110 (16) | 4.43 (0.16) | 0.31 |
References
- “MIL-HDBK-5, Metallic Materials and Elements for Aerospace Vehicle Structures,” Department of Defence, United States of America, Washington, D.C.
- “Engineering Data For Aluminium Structures,” the Aluminium Association Incorporated, 900 19th St., N.W., Washington, D.C. 20006.
- “Metals Handbook,” American Society for Metals, Metals Park, Ohio.
Plastics
Plastics are typically characterised by material strengths that are heavily dependent on service temperatures and the duration of the applied load (creep behaviour). For this reason, it is often convenient to define these materials in terms of an Ultimate Strength and a Working Strength when performing structural analysis of plastic materials. The Ultimate Strength of a plastic
is the stress required to fail a material for a short-term load applied at room temperature. The Working Strength of a plastic is the maximum allowable stress selected by the designer to account for the effects of creep behaviour or any other factors that could affect the structural performance of the plastic. In general, the material specifications in the Under Pressure manual used a working strength equal to 1/10 of the ultimate strength. This may be conservative for some applications.
Analysis of plastic composite materials (e.g., fibreglass tubes) should be approached with caution. The properties of many composite materials are directional, such that large variations in strength and modulus exist depending on the orientation with respect to fibres, cloth, etc. Analysis of this material directionality, along with unique composite failure modes such as delamination are beyond the scope of this calculator.
| Sub Category | Name | US Mpa (Ksi) | WS Mpa (Ksi) | YM Gpa (Mpsi) | Den g/cm³ (lb/in³) | PR |
|---|---|---|---|---|---|---|
| Composite | Glass/Epoxy29 | 69 (10) | 6.9 (1) | 13.79 (2) | 1.85 (0.0667) | 0.4 |
| Thermoplastic | Acetyl30 | 62 (9) | 6.2 (0.9) | 2.83 (0.41) | 1.46 (0.0526) | 0.4 |
| Thermoplastic | Acrylic31 | 55 (8) | 5.5 (0.8) | 2.41 (0.35) | 1.15 (0.0417) | 0.35 |
| Thermoplastic | Nylon 632 | 41 (9) | 6.2 (0.9) | 1.38 (0.2) | 1.11 (0.04) | 0.4 |
| Thermoplastic | Polycarbonate33 | 55 (8) | 5.5 (0.8) | 2.07 (0.3) | 1.20 (0.0435) | 0.4 |
| Thermoplastic | Polypropylene34 | 30 (4.3) | 3.0 (0.43) | 1.10 (0.16) | 0.89 (0.0323) | 0.4 |
| Thermoplastic | PVC3536 | 41 (6) | 4.1 (0.6) | 2.41 (0.35) | 1.32 (0.0476) | 0.36 |
References
- “Plastics, Edition 8, Thermoplastics and Thermosets,” D.A.T.A. Inc., A Cordura Company, 9889 Willow Creek Road, P.O. Box 26875, San Diego, CA 92126.
Making a Material Choice
These are the same materials that I used in some of the Pressure Vessel and ROV Viewport Dome posts,
- Coors Ceramic Compay Technical Data Sheet Composition AD-94
- Coors Ceramic Compay Technical Data Sheet Composition AL-600
- Coors Ceramic Compay Technical Data Sheet Composition AD-99.5
- Compressive Young’s Modulus = 55 Mpsi Crystal Systems Technical Data Sheet
- estimated values
- Reaction Bonded Coors Ceramic Company Technical Data Sheet
- Schott Glass Technologies Inc. Technical Data Sheet
- Compressive Young’s Modulus = 10.7 Mpsi
Compressive Yield Strength = 34 Ksi - Compressive Young’s Modulus = 10.2 Mpsi
- Compressive Young’s Modulus = 10.4 Mpsi
Minumum Welded Yield Strenght = 22 Ksi - Aluminium 6061 is one of the most commonly used alloys, known for its excellent corrosion resistance, machinability, and moderate tensile strength. It’s widely used in automotive and aerospace applications, as well as in bicycle frames and electronic devices.
- Compressive Young’s Modulus = 10.1 Mpsi
Compressive Yeild Strength = 34 Ksi
Minimum Welded Yield Strength = 15 kpsi - Aluminum 7075 is stronger than 6061 and is typically used in aircraft structures and other high-stress environments where lightweight materials are needed without sacrificing strength.
- Compressive Young’s Modulus = 10.5 Mpsi
- 66 Ni – 29 Cu – 3 Al Annealed, Age Hardened
- 67 Ni – 30 Cu Annelade Condition
- Compressive Young’s Modulus = 30 Mpsi
- Compressive Young’s Modulus = 30 Mpsi
- Compressive Young’s Modulus = 30 Mpsi
- Anneald Conditions,
Compressive Young’s Modulus = 28 Mpsi
Above properties hold for other 300 Series Austenitic Stainless Steels such as 303, 304, 304L and 316L - Anneald Conditions,
Compressive Young’s Modulus = 28 Mpsi
Above properties hold for other 300 Series Austenitic Stainless Steels such as 303, 304, 304L and 316L - Carbon steel is known for its high tensile and yield strength, making it ideal for heavy-duty applications like bridges, buildings, and automotive frames. Its cost-effectiveness and durability are why it’s widely used in construction and manufacturing.
- AISI 1025 Carbon Steel
- AISI 4340 Nickle-Chromium-Molybdenum Steel annealed Condition, Higher Strengths can be achieved through heat treatment
- Commercially pure Titanium
- Grade 2 (compositon CP-2)
Compressive Young’s Modulus = 16.0 Mpsi - Annealed Condition
- Annealed Condition
Compressive Young’s Modulus = 16.4 Mpsi - Moulded, Glass fibre-filled Epoxy Matrix
Compressive Ultimate Strength = 18 Ksi - Injection moulded or extruded, unfilled
Compressive Ultimate Strength = 5.2 Ksi
Commercially known as Celcon, Delrin, etc. - Cast rods or sheets,
Compressive Ultimate Strength = 11 Kpsi
Commercially known as plexiglass, etc. - Moulded or Extruded, unfilled
Compressive Ultimate Strength = 10 Ksi - Moulded or Extruded, unfilled
Compressive Ultimate Strength = 12 Ksi
Commercially known as Lexan, Melon, etc - Moled or Extruded, unfilled
Ultimate Compressive Strength = 6 ksi - Polyvinyl Chloride
- Moled or Extruded, Rigid
Compessive Ultimate Strength = 8 Ksi