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I'm doing experiments with an elastomer and I'd like to know how I should determine tensile strength in practice. Is this the point where I begin to observe tears in the elastomer or where the material breaks into at least two pieces?

Note:

The setup I'm using involves a rectangular sample of the elastomer which is loaded vertically using increments of known mass. The elastomer has clamps applied at both extremities where it's fixed at one end and the load on the elastomer at any instant is known. It's assumed that breaking is nearly instantaneous (this is what has been observed from prior experiments) so the relevant dimensions for the cross-sectional area are assumed to be those prior to breaking.

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  • $\begingroup$ What do you mean by tensile strength? Do you mean stiffness coefficient (like a spring) of the material? $\endgroup$
    – lucas
    Jun 30, 2016 at 10:22
  • $\begingroup$ I mean ultimate tensile strength(corrosionpedia.com/definition/1126/…) $\endgroup$
    – user29305
    Jun 30, 2016 at 10:32
  • $\begingroup$ Do you have a tension test machine? $\endgroup$
    – lucas
    Jun 30, 2016 at 10:50
  • $\begingroup$ I'm doing simple elongation tests. There's no machine. I think I can get reasonable estimates using this approach. What do you think? $\endgroup$
    – user29305
    Jun 30, 2016 at 10:59
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    $\begingroup$ What do the tears you are observing look like? I know that in our group the people who did similar tests kept the load constant for a certain time after increasing it by a step because the break into two pieces sometimes took a bit of time to form. I sadly do not know the official definition. If I was in your shoes, I would measure both points (even though the "appearance of tears" is a bit subjective) $\endgroup$
    – Sanya
    Jun 30, 2016 at 12:15

1 Answer 1

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You do not necessarily see a break. The ultimate tensile strength is the highest stress you can apply. The highest point on the stress/strain curve.

If you reach this value of stress, your material will continue to elongate but at a smaller force. So it will elongate freely and quickly to a large strain. When it has strained an amount where the equipment doesn't pull anymore, it simply stays elongated.

Ceramics and many metals will break before thus point because they cannot elongate enough for them to be relaxed in the equipment setup, but elastomer can and so will not necessarily break. For most of them of course; it depends on the exact material. The ultimate tensile strength is therefore not necessarily indicated by the point of breakage / failure in the case of elastomers.

But if you do see breakage like tearing, it indicates that ultimate tensile strength has been reached.

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