Attached herewith a classical paper by Hart on introducing a concept of constant hardness curves refuting that absolute strain should not be considered as a state variable.
The interesting part is he uses a stress relaxation test to prove the same. Stress relaxation test, here refers to a tensile test, where the test is stopped after say certain amount of plastic deformation. The stress drops a little, but the total strain is constant. However, it is argued that there is a small inelastic deformation, which is the cause of this load or stress drop.
My doubt is what is metallurgy behind such inelastic deformation at constant stress at room temperature. Most of the papers i searched on stress relaxation is for high temperature and the conventional creep mechanisms of dislocation climb, grain boundary sliding etc can be easily fit.
Can anyone please throw some light on the governing metallurgical basis for room temp strress relaxation.
| Attachment | Size |
|---|---|
| A phenomenological theory for plastic deformation of polycrystalline metals- Hart.pdf | 1.43 MB |
Hari We have done
Hari
We have done room temp
relaxation experiments on Al and Cu and observe plasticity during relaxation.
The argument follows as...the decrease in load is due to decrease in spring
length (if you can imagine a load cell as a spring) that led to increase in specimen
length (plastic deformation) i.e. both of these events complement each other.
You are right in pointing out
that most of experiment s are conducted at high temp.
AP