Why do materials fail at different rates?

[Astronuc]

Would this not then imply that it does not have to be a rapid change?

Certainly, not in all cases, but the term 'shock' usually infers a 'rapid' change in which a system cannot adapt readily, or dissipate the energy before failure occurs.

I could really use some graphics here. And I can't find an appropriate example online - assuming one exists. There are lots of journal articles one has to buy though.

 

[ShawnD]

I keep the computers running to prevent hardware failures associated with that shock given to all components when you turn the power on and off.

Does anybody remember that episode of mythbusters where they test whether or not leaving the lights on saves power? They showed that the saving power argument was bunk (obviously), but they also showed that when they turned the lights on and off at regular intervals not a single one of their lights lasted more than 2 months. When you're talking about a 60 cent light bulb, yeah I can see how saving power at the expense of the bulb is a good idea. When you start talking about a 2TB array made from 6 hard drives with a total cost of over $1000, does it really make sense to turn it on and off because you might save $5 over the course of a year?


When Russ said he leaves them on in winter, I think he means that power is never really wasted in winter time. Most of the electricity from the computer and monitor turns into heat. Same with light bulbs, the stove, the oven, etc. You're heating your home anyway, so "wasted" electricity in the form of heat isn't exactly wasteful. In summer it's the exact opposite. You're trying to cool your home, so any electric heat from your computer or stove or whatever is adding to the problem, and you end up using even more electricity to power fans and air conditioners.

 

[Cyrus]

Certainly, not in all cases, but the term 'shock' usually infers a 'rapid' change in which a system cannot adapt readily, or dissipate the energy before failure occurs.

I could really use some graphics here. And I can't find an appropriate example online - assuming one exists. There are lots of journal articles one has to buy though.

What I am getting at is this: Let's say, for example, that we have a semi-infinite solid. Then the temperature at any location is a function of:

T=T(x,h,a,k,t)

This means that the temperature at a given point x will vary with t only (considering h,a,k to be relatively constant over the temperature change for a given material).

So the 'speed' at which a material reaches failure is determined primarily by T=T(h,a,k) at a given location. One material will 'fail' faster than another material due to its physical properties (h,a,k), because x is held constant and time is allowed to increase the same for both samples. Time is simply telling you which one fails first. It does not say it failed because it was necessarily rapid.