iMechanica - ES 242r - Comments

Records of a course

Zhigang Suo — Mon, 31 Aug 2009 22:03:37 -0400

Li Han: I don't recall that the full course was recorded, but some lectures might be. I don't know who has these CDs.

Li Han

Li Han — Mon, 31 Aug 2009 15:25:57 -0400

Dear Zhigang,

I remember the course has been recorded. I am just wondering who to contact to revisit these valuable materials. Thank you.

Li Han

Distance Education

Daniel Andersson — Tue, 26 May 2009 04:05:23 -0400

Distance education open up many possibilities, more and more courses are being available, which I believe benefits both the university and the people, knowledge that before was limited to a few can now be accessed to many.

http://www.aptgroup.com/

Going soft

Zhigang Suo — Sun, 22 Feb 2009 11:38:00 -0500

Dear Michelle: Thank you for pointing out this lack of soft materials in the mix of topics. I'm teaching a course on advanced elasticity now, drawing on rubbers, gels, and polyelectrolytes.

Small structures topics

MichelleLOyen — Sun, 22 Feb 2009 10:29:18 -0500

Hi Zhigang,

I read the list of topics covered here with interest in that they seem to be (as is often in mechanics) specific to certain engineering materials classes; given your nice recent work on hydrogels, if you ran this module again would you include new material on polymers and hydrogels? I would think basic rubber elasticity concepts and certainly poroelasticity or diffusion-related phenomena would round out this list of topics nicely for a more broad set of base materials!

There seemed fewer options

Kejie Zhao — Sat, 21 Feb 2009 23:52:20 -0500

There seemed fewer options for mechanics student this term, and Hopefully this excellent course will be lectured in next spring.

"I have taken a class that

s.mccallion — Fri, 05 Dec 2008 11:51:52 -0500

"I have taken a class that the professor made slides with some missing
information that you add in as the lecture progresses. This definitely
keeps you following the lectures."

I like this format of lecturing, for the same reasons as stated. Also, some lecturer's suffer from a terrible case of can't-write-very-neatly-itis. This is not a personal attack on any lecturers (I know there are many here!), it's just a fact of life that not everyone has legible hand writing. Leaving spaces to be filled in definitely helps keep the students' attention, and reduces the hand work required by the lecturer.

I am definitely not in favour of lectures that are conducted solely on power point. First of all, something ALWAYS go wrong. Also, with chalk/pen in hand the lecture tends to become more dynamic, particularly when the lecturer has developed a class to ask many questions, afterall a picture is worth a thousand words.

A larger history can be displayed over several boards, allowing several 'slides' to be in the viewing range of the students. The lecturer also retains the ability to quickly jump back to prior board work when a student asks a question, which is particularly important with many students puzzling over a question for a minute or so before making themselves heard.

I could criticise powerpoints for quite some time, but they do of course have some fantastic advantages when used effectively. I'm about to complete a masters level course in material mechanics with a strong focus on the computational aspects of the subject. My lecturer has created some excellent presentation modules in mathematica which were invaluable for showing the effects of hardening in a much clearer manner than he could have done by hand (perhaps he just downloaded those modules, I know wolfram makes a lot of stuff freely available).

My friends keep talking of

johannabartley — Mon, 10 Nov 2008 12:22:50 -0500

My friends keep talking of COD's and CTOD's and though they learn at the Ohio Dominican University they couldn't tell me the difference between the two notions. Thanks for asking and thanks to all of you who answered.

my test

Manfred H Ulz — Mon, 10 Nov 2008 05:27:17 -0500

Thank you for the hint.

Blogging with LaTeX!!

HsiaoYing Shadow Huang — Thu, 21 Aug 2008 17:20:09 -0400

Hi Alex,

Thanks for this info. Finally I am able to type math entries in the blogs. I've tried it out and it worked perfectly.

Thanks again!!

Comprehensive Distance Education

Noel M. Dioyan — Fri, 11 Apr 2008 09:56:43 -0400

That is very interesting idea sir,if imechanica can provide a distance education from all field of engineering mechanics.The whole world is watching all the comments and suggestion in this site. Maybe, We here from asia can be benefited in your great proposal " Education without boundary" reagardless of distance,races,ethnics and culture..

Hi aswani kumar i am

ravitejk4u — Sat, 03 Nov 2007 00:24:44 -0400

Hi aswani kumar

i am ravitej, doing my mtech in IIT kanpur. from ur posting i can guess that u had great knowlwdge in theoritical concepts of strength of materials.i want to ask a doubt regading strength of materials.

i want the mid point deflection in case of "four point bend test" on a
specimen of length 140mm, width of 40mm and thickness of 10mm.

Problem is that, beam theory is valid if the cross-sectional
dimensions are less than axial dimensions. Here this condition is
violated. i had modeled the specimen in Abaqus and the diffection at
mid point is almost double that of the actual diffection calculated
from beam theory.

how can i find the theoritical difflection at mid point in this case?

i had one option, using timoshenko beam theory and applying larger
deflection theory. will it be a reasonable approximation in this case?

please help me in this aspect.

Ravitej Kommana
IIT Kanpur
INDIA.

hi Jamilla

prashant sharma — Wed, 03 Oct 2007 14:27:33 -0400

i am MSc. Engineering by research student with mechancis.

my research works include. study of aero engine turbine disk for protential instabilty using ABAQUS, i have to perform analysis to simulate and predict the bursting phenomenon of disk for which i have to do elastic-plastic analysis and finally bursting of disk in which crack initiation and finally frature have to taken in to account.

so i was wondering if i have some tips regarding the Fracture mechanics particualy crack intiation phenomenon using Cohesive zone model techique from you.

thanks

prashant sharma

prashantsharma8@gmail.com

COD and CTOD:

Gopinath Venkatesan — Mon, 23 Jul 2007 17:18:48 -0400

To my knowledge, COD is first introduced by Boyle [1962] for measuring cracklength directly (I mean without measuring from microscope readings). This is essentially a strain gage reading for compliance (inverse of stiffness, COD/Load). I thought CTOD is the displacement of the crack tip and is different from COD. All these days, I convinced myself that CTOD is developed for elastoplastic while COD can take care of LEFM area but now confused. I will go through the references cited by Wu. Thanks.

Gopinath

COD & CTOD (Reply to Ling Zhu)--Fracture Mechanics class

Xiangfa Wu — Mon, 23 Jul 2007 15:34:02 -0400

Dear Ling, COD as a criterion is used for crack growth in elastoplastic materials, for which the K-criterion does not hold due to the finite plastic zone near crack tip. However, within the framework of SSY, COD-criterion is equivalent to K-criterion (Kanninen and Popelar, 1985). COD-criterion is considered as a supplementary fracture criterion for elastoplastic materials before the evaluation of J-integral (A.A. Wells, 1979) to be discussed in this class. The typical definition of CTOD for cracking in ductile materials can be found in the following link: http://www.efunda.com/formulae/solid_mechanics/fracture_mechanics/fm_epfm_CTOD.cfm

Based on my understanding, COD and CTOD indicate the same term though they may have a little difference in literature here and there. For example, the COD-criterion was discussed in detail in the classic textbook: Advanced Fracture Mechanics (Kanninen and Popelar, 1985), in which the term COD is actually also the CTOD. While in the textbook Cracks and Fracture (Broberg, 1999, pp. 575), it says that COD and COA (crack opening angle) are often written as CTOD (crack tip opening displacement) and CTOA (crack tip opening angle). Also, in some literature, it says that COD is the total displacement at crack tip (usually mixed-mode crack), while CTOD indicates the crack tip opening displacement due to pure mode I loading [e.g. Sha et al., Int. J. Fracture 104 (2000) 409-423]. There may be many others. Therefore, when we use COD or CTOD, we need to take care of the definition used in context. Hope this would make it clear.