Strain Driven Versus Stress Driven

[Transient1]

Can someone expand on the idea of a structures response being strain driven versus stress driven?

When one says the response of the structure is strain driven, is this simply saying it is a non-linear response (creep or plasticity)?

 

[JAE]

Maybe help us out by telling us the context in which you've seen these phases?

 

[Transient1]

This is in regards to solder creep where a paper wrote, that over temperature the change from stress- to strain-drive solder response takes place.

 

[apsix]

I'll have a stab at it:
To me strain driven implies that deflection or deformation is critical, while for stress driven strength would be critical.

 

[MikeHalloran]

Now I'm curious: Is the paper available to us?



Mike Halloran
Pembroke Pines, FL, USA

 

[rob768]

just a guess: in a strain driven construction, the deflection in determined by external force and overall shape of the construction. I am thinking of a ship, where the degree of bending is determined by the total section modulus. For instance doubling the thickness of deck plating has near-zero effect on stress under same loading conditions. In stress driven constructions, there is a direct relation between area of cross section and external force (for instance a load hanging on a rod).

 

[Transient1]

It's from Appendix A of IPC-D-279. Unfortunately, its not available for free. I'm leaning towards a stress driven effect is one where stress is linearly proportional to strain. Then once it becomes plastic, a certain level of the strain becomes irreversible and that becomes the driving mechanism for the response of the system. Stress and strain are no longer directly proportional.

 

[HgTX]

My understanding, which may be wrong, is this:

A strain-driven system means that something else is inducing a deflection (or, I suppose, a thermal expansion or contraction). Any stress seen in the member is an effect of the induced strain.

An example of a stress-driven system would be, say, something acting under gravity loads. Any strain seen in the member is a result of the induced stress.

In practice, I've only dealt with these terms in the context of testing machines. In a system that is not linear elastic, you will get different stress-strain curves and hysteresis loops depending on whether you control the stress or the strain. Apparently this also comes up in the context of metal crystal growth, but I don't know anything about that.

Hg

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[Transient1]

Hg,

Yeah I think your on the right line.

In the contex of solder, I understand it to be:

In a limited temeprature range your in the "elastic" region of the solder. The strains are due to the imposed stresses of the material from CTE mismatch. If you increase the temeprature you enter the non-linear region of the material (Creep). Creep induces a strain which alters the stress response of the material. So then it is a strain effect inducing a stress. Similarly, with plastic strain which induces residual stresses despite the change in loading after the yield point was reached.

 

[HgTX]

Is creep of solder different from creep of a base metal? I think of creep as being a stress-driven phenomenon, a deformation that occurs under constant load, without any kind of deformation induced by an outside source pulling or pushing through a particular distance.

Hg

Eng-Tips policies: faq731-376

 

[Transient1]

Yeah you are right, creep is a stress and temperature driven phenomenom. Hmm, I feel I'm no closer to defining this. The idea that temperature causes two materials to expand and the differences in their strains causes a stress...definately fits the bill in my mind as a strain driven response. Then, are there any other strain driven phenomenom?

Applying a force to a material which induces a stress or creep strain, makes sense in my mind that the response is only due to the applied force. Any other thoughts?