Learn
Reference pages on the part of materials work that goes wrong quietly: the difference between a specified minimum and a typical value, what a mill certificate does and does not certify, how PREN is calculated and what it ignores, and how to write a material decision down so it survives review. Each page is updated in place and carries the date it was last checked.
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How far to trust a computed property
Computed band gaps run about 40% low and formation energies carry errors near 100 meV per atom. What that means for an engineer reading an open database.
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How to document a material selection decision
What a reviewer asks six months later, the seven things a defensible record contains, and a minimum version you can write in fifteen minutes.
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Material indices, and where the exponents come from
E/rho, E^(1/2)/rho, sigma^(2/3)/rho — where the exponents come from, why they let you rank materials early, and what an index quietly assumes.
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PREN: a ranking number, not a qualification
PREN = Cr + 3.3Mo + 16N ranks stainless grades by composition. It is not a qualification for service, and the difference matters when chlorides are involved.
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Reading a mill certificate
What each EN 10204 inspection document actually proves, why a 2.2 is not a 3.1, and how to tell whether the numbers on the page belong to the steel you received.
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Specified minimum or typical value — which number are you holding?
A datasheet typical value and a standard's specified minimum are different numbers doing different jobs. Using one for the other is a costly and common error.
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The Ashby method, and the assumption underneath it
The four steps of Ashby's material selection method, what material indices and property charts do, and the one assumption in it that no longer holds.
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The material selection process, end to end
From a design requirement to a decision somebody else can audit: translate, retrieve, assess, compare, export — and where each step usually goes wrong.
What this page does not cover
- Grade-specific data. Property values live on the material pages, one grade at a time, with an evidence level per row.
- The grading scale itself. Defined once, on the E-ladder page.