[8cyVn4RJ]

From Top Science Blogs ‏@topscienceblogs

A pre-crack might propagate or stick under mechanical and electrical loading: (Science in China Press) Electric ... http://tinyurl.com/927xstu

http://www.eurekalert.org/pub_releas...medium=twitter


" A pre-crack might propagate or stick under mechanical and electrical loading



IMAGE: This is a schematic illustration of the hysteresis loops of a crack width versus (a) the applied displacement under a constant applied electric voltage, and (b) the applied electric voltage...
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Fracture under combined mechanical and electric loading is currently a hot research area in the global fracture community, while electric sticking is a major concern in the design and fabrication of micro/nanoelectromechanical systems. Professor ZHANG Tong-Yi and his student, Mr. Tao Xie, from the Department of Mechanical Engineering, Hong Kong University of Science and Technology, found that the two problems are switchable, depending on the loading conditions, sample geometries and material properties. Based on his 20-year research experience on the fracture of dielectric and piezoelectric ceramics, Prof. ZHANG developed a novel pre-cracked parallel-plate capacitor model to analytically investigate the role of electrostatic tractions in fracture and electric sticking behaviors."Prof. ZHANG and Mr. Tao Xie provided a new fracture criterion based on the energy release rate and crack opening. Their work, entitled "Effect of electrostatic tractions on the fracture behavior of a dielectric material under mechanical and/or electric loading", was published in SCIENCE CHINA Technological Sciences, 2012.

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[suilusargaino]

A bit small-scale for me jj

[8cyVn4RJ]

A bit small-scale for me jj

oh go on!

[8cyVn4RJ]

What about this engineering development then?

"
Rise of the markerbots

Engineering students are often asked to sketch structures to show they understand certain concepts.
Grading such sketches can be overwhelming for tutors, who may preside over 1000 students on a course.
So Stephanie Valentine of Texas A&M University and her team have developed Mechanix, artificially intelligent software that grades sketches.
First, the tutor draws the correct answer into the system, which recognises the image and the maths behind it.
This is then compared to students' responses.
An intelligent tutor also gives students guidance as they draw.
In tests on 122 students at Texas A&M, those who used Mechanix performed 15 per cent better on an assignment."

http://srlweb.cse.tamu.edu/srlng/research/project/18

[suilusargaino]

Hmmm, based on the performance of the "intelligent" camera on my laptop, which is supposed to recognise me every time I switch on, but instead thinks I'm a different person every time the light changes, or I move rooms, or I sit slightly further away, or I wash my hair, I'm still pretty skeptical about "intelligent" software.

[8cyVn4RJ]

And I couldn't help wondering about there being only one correct response.

[suilusargaino]

Yes, good point.

I do wonder with many of these things whether they work pretty well with "typical" students, and terribly with the rest.

[Ndptbudd]

That sounds very much like the tutorial system that we had running in my engineering course in the 1970s, except that it wasn't based on sketches, but a set of questions and answers. If you didn't get it correct, the system would provide you with appropriate hints. It all ran on dumb terminals hooked up to a mainframe. I don't know if we were 15% better for having a computer as a tutor.

[Thomas12400]

The OP is interesting. Scaling to geologic systems could explain why some faults produce electromagnetic signals before rupturing. This could lead to development of short-term predictive devices for earthquakes.

[8cyVn4RJ]

The OP is interesting. Scaling to geologic systems could explain why some faults produce electromagnetic signals before rupturing. This could lead to development of short-term predictive devices for earthquakes.

oh; I had heard of that.
Thanks ... every bit helps

[ceagstuntee]

> any engineers care to try explaining this please?

The bonding of atoms in a solid is to a large extent electrostatic. Linus Pauling showed that even covalent bonds have an electrostatic energy component.

The opposite edges of a crack carry electrical charges. These will tend to hinder crack development if of opposite charge (by drawing the opposite faces of a crack together) but enhance it if of like charge, locally on the atom-by-atom scale. What this means is that combining mechanical and electrical loading can have a different effect to that of mechanical loading alone. I take it that this is what is meant by "Effect of electrostatic tractions on the fracture behavior of a dielectric material under mechanical and/or electric loading".