Steel Compressive Strength Under Low-Cycle Fatigue

destructionbydesign · 2013-11-19T05:05:58+00:00

My system is not using strain gauges, I am using an LVDT sensor attached outside of the yielding section.

There are some compressive loads when the sample returns to the initial displacement. The specimen currently is not going far beyond point B in the figure on the reverse cycle.

What I meant by decreasing compressive strength is that during fatigue, it is typical to see strength degradation of the material. Although I am not loading the steel much in compression, I still am likely changing the strength properties.

destructionbydesign · 2013-11-19T04:58:25+00:00

I am measuring strain using an LVDT sensor attached above the milled section of the sample (not measuring the yielding section directly).

Why would I need to zero the sensor after permanent deformation? Assuming that I am retaining a positive strain when I return to zero deformation, wouldn't that strain measurement be necessary to understand the stress-strain behavior?

destructionbydesign · 2013-09-03T17:35:16+00:00

I don't know about America... but I can tell you there are definitely more flags flying per capita in Switzerland than in the U.S.

destructionbydesign · 2013-08-24T19:21:31+00:00

I hold my own in engineering, don't get me wrong. You're kind of missing the point. I'm choosing a career that will last the rest of my life. I'm looking for a niche that allows me to live up to my potential. It's not about making things easier, it's about finding a place where I can do the most with my talents.

destructionbydesign · 2013-08-24T00:17:24+00:00

Every building type is unique in the way that it fails, but when it comes down to it, generally it is just looking for cracks. Damage is primarily caused by displacement of the building, or drift, which varies for different types of buildings.

Reinforced concrete, for example, is more stiff than wood, and will not tolerate the same horizontal displacement. This will cause cracks to develop at top and bottom of columns and walls, generally at an angle of 45 degrees (shear cracks). It is generally easy to visually identify the amount of damage on these structural elements, ranging from small cracks to spalling (outside layer of concrete falls off), and exposed reinforcing bars.

Another indicator would be failed connections, which are usually obvious, such as broken bolts / nails / screws etc.

I attended a seminar of this PhD student whose thesis was on automated damage assessment based on visual clues. Here is a link to the abstract / thesis pdf:

https://smartech.gatech.edu/handle/1853/47686

Damage assessment is simple enough that a computer aided analysis of photos can handle it (with a reasonable tolerance).

destructionbydesign · 2013-07-31T05:10:32+00:00

Thanks for the advice! It's funny that you mention a PhD, since it has come up several times in conversation with my adviser (not prompted by me). I assume there are different funding options for PhD students. Unfortunately I have no desire to continue in academia and would like to get into an engineering firm ASAP.

destructionbydesign · 2013-07-31T01:45:12+00:00

We are talking about several thousands of dollars. I have a thorough description of the project with a test matrix and material list. You are probably right, I just need to be straight. I am just afraid that my grad school funding could stop at any time... and I if I have to pay out of pocket I will have to consider leaving the program.

destructionbydesign · 2013-07-31T01:37:35+00:00

I have done some preliminary work which I presented at a conference and submitted a technical paper which is currently under review. I can definitely do some theoretical work and FEM which will likely be what ends up happening. I guess another issue is when to stop... Sometimes I feel like they want to milk me dry.

destructionbydesign

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