Hello Stressers!!!

I have read an article in one of the reputable FEA software regarding creep as shown below.

"The creep strain is increasing faster than the total strain. Thus not all of the creep strain is being added to the total strain. In other words, the creep strain accumulated at this point cannot all be translated into increased deformation, and thus the elastic strain is reduced over time as well, causing some stress relaxation."

Basically I'm confused why the "creep strain is increasing faster than the total strain?". My thought is that total strain = elastic strain + creep strain, therefore since creep strain is the only variable dependent with time not the elastic strain then why does creep strain is increasing faster, I'm thinking the total strain and creep strain has same rate.

Kindly correct my thought process fellow stressers.

Many Thanks,
Cheers

Imagine a case where your material magically switches from 100% elastic strain to 100% plastic strain. Your total strain didn't increase, but your plastic strain increase is infinitely faster than your total strain.

Hi Michael,

Thanks for the explanation. I'm a bit confused because I'm thinking in linear fashion (superposition of strains). But creep and plasticity is non-linear. Anyway, the FEA software I'm using have a creep analysis which considers relaxation already (which I think is a standard in all FEA software packages). I have tested it with a load that exceeds the expansion stress allowable in ASME B31.3 and the software will not converge to a solution due to excessive deformation which make sense (due to elastic follow up phenomena). But when I lower the load to an acceptable level as per ASME B31.3 the software predicts stress relaxation in the course of time which coincides with the concept of elastic shakedown. I'm just confused of how creep strains have faster rate than total strains. Anyway, stress re-distribution concept comes into my mind just like the 2Sy allowable concept of ratcheting.

Any other opinion is greatly appreciated.

Cheers!!

I have even tried a sensitivity test of varying the initial load and see at what load the system will experience pure creep and I observed that at a certain load an unlimited displacement is happening infinitely which can be considered the rupture point of material. I noticed that there's a certain load which the material will experience pure creep and almost no relaxation (almost constant elastic load).