While hardness and tensile strength aren't directly correlative, there is a well-known link between the two. The reasons behind this are complex, but have to do with the material's ability to withstand molecular shearing along certain lines of force. Metal has a crystalline structure, so when you place a load on it during a hardness test, the load transfers -- not just downward -- but out to the sides. This aspect of material-loading in metal mimics very closely the consequences of bending the material during a tensile strength test. This means that you can fairly accurately estimate the tensile strength of a material like aluminium, copper, steel, brass or iron using only its hardness rating.
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Gather the data regarding your material's hardness on the 3000-kilogram Brinell scale. The material's hardness rating will vary, depending upon whether it's a pure metal or an alloy.
For our example, we'll estimate the tensile strength of 2011-T3 aluminium. 2011-T3 has a Rockwell hardness of B60 and 3000-kg Brinell hardness of 107. If you have the Brinell hardness in a different range, refer to a hardness conversion scale to convert it.
Multiply the 3000-kg Brinell rating by 515, if the Brinell reading is lower than 175. As this is the case with our 2011-T3 alloy, we'll multiply its Brinell hardness of 107 by 515 -- to arrive at an approximate tensile strength of 24995 Kilogram per square inch. Double-checking this against the ultimate tensile strength given at Onlinemetals.com, we find that our estimate is a mere 0.2-per cent off of the material's 55,000 psi rating.
Multiply the 3000-kg Brinell rating by 490 -- if the Brinell rating is greater than 175. Since no forms of aluminium have a Brinell rating that high, we'll use aircraft-grade titanium. This titanium has a 3000-kg Brinell rating of 330. Multiplying that by 490 we get 161,700 psi. Titanium Era states that this alloy's tensile strength is about 150,000 psi, which is about 7.8-per cent off of our estimation.
Tips and warnings
- Bear in mind that these formulas are for estimation purposes only. The fact is, that while there is a correlation between hardness and tensile strength; the correlation will vary depending on that particular material's crystalline structure and hardness.
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