The power to combine ideas defines the human...
In polymer chemistry there is a theory where time, temperature, and
mechanical properties are tied together by an interconnectivity
that is made evident by the WLF equation.
This interconnectivity is important for tensile tests (and I would
argue that in some way it reaches across the spectrum of all polymer science,
but for now, we'll focus on tensile properties.)
The speed at which you pull the tensile test
sample is important. The temperature
at which you pull the sample is important. If you pull the sample
at a faster speed, you may see a substantially higher adhesive strength. If
you don't see a difference, it may be that your increase in pull
speed wasn't sufficient to make a noticable increase in strength.
If you pull the sample at a higher temperature, the strength will be less.
Intuitively, it is easy to just say "yeah, plastics get 'softer', but for more
a more fundamental argument, you should consider relaxation time of the
polymer chains, and how temperature affects
relaxation time. I'll dig
through the texts to find a reference for this; I think I'll find something
that talks about the temperature dependennce of relaxation time.
If you've played with Silly Putty(tm), a polysiloxane, you may recall
that if you pulled it apart slowly, it stretched, and if you pulled
fast, it ripped. The speed at which you pull dictates the "timescale
of the experiment."
THE WLF IDEAS
Last Update- March 13, 1995- wld