A recipe on paper is a hypothesis. A physical profile is evidence. Reverse engineering uses both: properties guide the recipe, and the recipe is only accepted when the properties match.
The core set
| Test | What it measures | What it hints at |
|---|---|---|
| Hardness (Shore A or IRHD) | resistance to indentation | filler level, crosslink density, plasticiser |
| Density | mass per volume | filler type and level, polymer type (fluoroelastomers are about 1.8 to 2.0 g/cm³, hydrocarbon rubbers 1.0 to 1.3) |
| Tensile strength and elongation | stress and strain at break | reinforcement, polymer strength, crosslink density |
| Modulus at 100 % and 300 % | stiffness at strain | filler loading, structure, crosslinking |
| Tear strength | resistance to crack growth | polymer type, filler reinforcement |
| Compression set | recovery after sustained squeeze | cure state, polymer stability at temperature |
| Fluid swell | volume and property change in fluid | polymer polarity, plasticiser, crosslink density |
| Low-temperature tests (TR10, brittleness) | stiffening and recovery in the cold | glass transition, plasticiser, polymer |
What each pair of numbers tells you
- High hardness with low modulus suggests a high filler level with weak reinforcement or heavy plasticiser.
- High tensile with high elongation points to a reinforcing filler in a strong polymer.
- Density that does not fit the recipe suggests a missing or extra mineral filler.
- Large fluid swell in a polar fluid suggests low polymer polarity or low crosslink density.
Test conditions are part of the result
Compression set at 22 h and 100 °C is not the same as 70 h at 200 °C. The sample geometry, button or O-ring, changes the number. Write the standard, temperature, time and geometry next to every result. When comparing two compounds, run them side by side in the same batch.
Order of work
Start with the non-destructive tests, hardness and density, on the whole part. Then cut test pieces for tensile and tear. Reserve enough sample for compression set and fluid immersion, which need the most material.
Sources and further reading
- ASTM D2240 and ISO 48-4 (hardness), ASTM D412 and ISO 37 (tensile), ASTM D395 and ISO 815-1 (compression set), ASTM D792 and ISO 1183 (density), ASTM D471 and ISO 1817 (fluid immersion), ASTM D624 and ISO 34-1 (tear).
About this article. It is original writing prepared from public sources, standards and general industry practice. It is not a copy of any book or standard and it is not engineering advice. Confirm values against the current edition of the standard and test in your own application. Only analyse material you own or are entitled to analyse.
