User login

You are here

Comments

Subscribe to Comments feed
Comments
Updated: 4 hours 27 min ago

invited speaker talk is announced --- JF Molinari from EPFL

Thu, 2017-09-21 06:10

In reply to 10th European Solid Mechanics Conference – ESMC 2018

The invited talk of the Mini Symposium "Fatigue and Tribology" will be

J . F. Molinari from EPFL 

"Numerical prediction of evolution of surface roughness during dry sliding".

Re: Comments on the Unusual Thermo Course

Tue, 2017-09-19 16:56

In reply to Thermodynamics in twenty-some slides for advanced elasticity

I just came back from the lecture.  In 90 minutes, I only went through the first 15 slides.  Slide 15 is a highlight:  the Gibbs-Maxwell surface.  

This class is a graduate class on  Advanced Elasticity, as I noted before.  A few places in the class later use thermodynamics in nontrivial ways.  Yet thermodynamics is not listed as prerequisite.  These slides are a compromise.  A reminder for some students, but a quick introduction for others.  I have no illusion that students will master the subject using these slides.  

But a student in class pointed out an error on slide 3.  I'll post the updated one on next Thursday, after I go through the rest of the slides in class.

These twenty-some slides were extracted from slides I prepared for an undergraduate course on engineering thermodynamics  

John W. Hutchinson isn't an appropriate speaker

Mon, 2017-09-18 20:05

In reply to NEW.Mech 2017 at MIT on October 14

John W. Hutchinson is known for his plagiarism practice. He owe MIT an apology. I guess his legs won't stop shaking from the first step he set foot on MIT campus.

Comments on the Unusual Thermo Course

Mon, 2017-09-18 12:51

In reply to Thermodynamics in twenty-some slides for advanced elasticity

Dear Zhigang,

What a nice opportunity to get back talking to you!

...

I deliciously, devotedly, and deliberately went through [actually devoured] the first three slides of your rather unusual slides on thermo.

Wonderful!

I want to go deeper into their implications, but, for the paucity of time, I can't.

But here is a timely friendly comment: In constructing your very first slide, you have begun getting into some certain abstractions, which, to my naive mind, are (and are wont to prove to be) valid.

Congrats, and not only keep up the good work at enlightening the small, subtle, simple, so very young and at times frail humanity---perhaps, may be, so very promising (at least to their own parents)---but also keep on reminding us of the ever-widening possibilities, of the things possible (without a special separate effort on your part, I mean).

In short: Good work, and keep it up, though, the pace might not be too mild. In case it proves to be too strong/rapid for your class (and which class does not complain?) adjust it dynamically... Though I won't hold you responsible for that. As a tenured professor (esp. in USA, esp. in Harvard), you can always gauge and calibrate your students dynamically. Their grades are in your hands. I am more than certain, they will be given the relative justice. That's not the point...

The point is: Sometimes us the S&T folks can get lost in the syntax of the pedagody, of the received opinion concerning what is supposed to be "oh so effective" pedagogy so much, get lost under the weight of the tradition of having to teach a course a certain way so much, that despite intentions to the contrary, we might get lost in the other direction.

My congrats were generally in the direction of encouraging you what I perceived to be the right direction.

But then, again, the judgment was based precisely on only the first 3 slides. ... I must now wonder: How would you treat a student who kept himself awake for the first 3/27X60 minutes of an hour-long lecture?

Anyway, very best wishes to you and your students, of course.

Sincerely,

--Ajit

 

Dear Rui

Fri, 2017-09-15 09:04

In reply to Journal Club for September 2017: Some recent developments in constitutive modeling of glassy polymers

Dear Rui,

Many thanks for your contribution to this journal club issue and I look forward to your future contributions as delineated in your post. The use of modified internal variables have been a very powerful appropach to developing constitutive models for polymers. Thanks for bringing to attention your work and classical work of Tool and others. The furhter challenge perhaps lies in modeling physical phenomena for which a transition of length scales (call it effective field theory applied to thermo-mechanics of nano-heterogeneous metastable media) masks the observed macro-scale phenomena which can be naturally explained by a stochastic description. My hope is that this very limited journal club post attracts the attention to such situations.

Regards,

  Alireza.

We will not officially record the talks

Thu, 2017-09-14 11:11

In reply to NEW.Mech 2017 at MIT on October 14

Hi Bafty,

Thanks for your interests! We will not officially record the videos, so please join the event if you are interested. 

Best,

Xuanhe

Dear Xuanhe Zhao,

Thu, 2017-09-14 10:15

In reply to NEW.Mech 2017 at MIT on October 14

Dear Xuanhe Zhao,

thank you for the announcement, the talks seems great. It would be great to have a recordnig of them. Don't you plan it?

 

Thanks,

Bafty

Open to whole mechanics community in US and worldwide.

Wed, 2017-09-13 10:39

In reply to NEW.Mech 2017 at MIT on October 14

A few updates on NEW.Mech 2017

1. The workshop is organized at New England Area, but open to the whole mechanics community in US and worldwide. Welcome all!

2. Registration for the workshop is free, but please do register to secure your seat.  Seats are limitted and we will announce registration deadline shortly. Register!

3. The titles of keynote talks have been announced on NEW.Mech 2017 website. Truly impressive and diverse talks and more in one day, Oct 14 2017!

Huajian Gao – Professor of Engineering, Brown University
Talk Title: Mechanics of cell interaction with low-dimensional nanomaterials

John W. Hutchinson – Professor of Engineering, Harvard University
Talk Title: Shell buckling—the old and the new

Subra Suresh – President-Designate, Nanyang Technological University, Singapore & Vannevar Bush Professor of Engineering Emeritus, MIT
Talk Title: Cell mechanics and human diseases

Franz-Josef Ulm – Professor of Civil & Environmental Engineering, MIT
Talk Title: Urban physics: Is Boston a liquid or a solid? A quantitative mechanics approach to cities' sustainability and resilience

element or contact activation/deactivation

Tue, 2017-09-12 10:46

In reply to ABAQUS ELEMENT DELETION

Hello,

I am not sure about your question but, yf you want to activate/deactivate elements/contacts you should have a look at the "*model change" in the abaqus documentation.

Best regards,

Cristian

Great thanks!

Fri, 2017-09-08 15:52

In reply to UMAT for viscoelasticity

Great thanks!

Any documents/papers on CZM

Fri, 2017-09-08 05:47

In reply to cohesive zone modeling of interface fracture

Any documents/papers on CZM formulation for one dimensional problems? 

I did search a lot on this

Thu, 2017-09-07 13:46

In reply to odb

I did search a lot on this topic. But didn't find anything related. That's when I asked if anyone used any different approach to this problem or not.

 

Thank for the suggestion anyways.

Experimental testing video

Thu, 2017-09-07 12:17

In reply to Understanding the strength of bioinspired soft composites

Experimental testing video can be found here https://www.youtube.com/watch?v=5lMaexXsOdk

odb

Thu, 2017-09-07 09:37

In reply to Abaqus Python : reading odb file for field frame data

Subscribe to and seek assistance from the
ABAQUS mailing list
https://groups.yahoo.com/group/ABAQUS
or
http://www.eng-tips.com/threadminder.cfm?pid=799
or from the ResearchGate discussion forum.

Search the archive of the list before posting in it.

Good luck

Frank

UMAT for viscoelasticity

Wed, 2017-09-06 10:03

In reply to VISCOELASTIC UMAT

My thesis is now on
https://depositonce.tu-berlin.de/handle/11303/1574

implementation of a UMAT for a Kelvin-Voigt model:
http://imechanica.org/node/19884

Read also
https://polymerfem.com/forum/finite-element-modeling/constitutive-models...

Good luck

Frank

Dear Alireza,

Wed, 2017-09-06 07:39

In reply to Journal Club for September 2017: Some recent developments in constitutive modeling of glassy polymers

Dear Alireza,

Thanks for this nice review on the modeling glassy polymers. Indeed, the behaviors of glassy polymers show complex dependence on temperature, rate, thermal history as well as mechanical deformation, which raises a great challenge for developing constitutive models to describe them.

In addition to the above-mentioned approaches, another approach based on effective temperature has also been developed to describe the nonequilibrium behaviors of amorphous solids. The concept effective temperature originates from Tool’s fictive temperature [1]. By introducing the configurational entropy as a thermodynamic conjugate variable to the effective temperature, a fully consistent nonequilibrium thermodynamic framework has been built [2,3]. Based on the works of the physical community, we have developed a finite deformation continuum mechanics version of the effective temperature theory [4-6]. More importantly, we show that the effective temperature theory can quantitatively capture the dependence of stress response on temperature, strain rate, physical aging, and mechanical pre-deformation [4]. The effective temperature theory can also describe the experimentally measured DSC results, including an increase of enthalpy overshoot with aging, a decrease of enthalpy overshoot with mechanical deformation and the appearance of an undershoot of deformed glassy polymers [6].

Currently, we are also using the effective temperature to describe the mechanical instability of polymers, such as necking and shear banding. Hope we can obtain some preliminary results in the very near future.

Rui

Reference:

[1] A.Q. Tool, 1946. “Viscosity and extraordinary heat effects in glass”. J. Am. Ceram. Soc. 29, 240.

[2] T.M. Nieuwenhuizen, 1998. “Thermodynamics of the glassy state: effective temperatures an additional system parameter”. Phys. Rev. Lett.80, 5580.

[3] E. Bouchbinder, J.S. Langer, 2009. “Nonequilibrium  thermodynamics of driven amorphous materials .II. effective-temperature theory”. Phys. Rev. E. 80, 031132.

[4] R. Xiao, T. D. Nguyen, 2015. “An effective temperature theory for the nonequilibrium behavior of amorphous polymers”, J. Mech. Phys. Solids, 82, 62.

[5] R. Xiao, T. D. Nguyen, 2016. “A thermodynamic modeling approach for dynamic softening in glassy amorphous polymers”, Extreme Mech. Lett., 8, 70.

[6] R. Xiao, G. Ghazaryan, T. A. Tervoort, T. D. Nguyen, 2017.  “Modeling the energy storage and structural evolution during finite viscoplastic deformation of glassy polymers ”, Phys. Rev. E., 95, 063001.

Veamy v1.1.1 (software for VEM) is out with PDF Manual

Tue, 2017-09-05 22:59

In reply to Veamy: an extensible object-oriented C++ library for the virtual element method

Veamy v1.1.1 is out. 

Download the source code + Veamy Primer v1.1 (PDF Manual):

http://camlab.cl/research/software/veamy/

From Veamy v1.0 to Veamy v1.1.1:

  • Add documentation.
  • Add method to include custom precision for printing output data.
  • Add plane stress material formulation.
  • Update installation instructions.
  • Include more tests and mesh examples.
  • Fix several bugs.

Features:

Free and open source C++ library that implements the virtual element method. The current release of this library allows the solution of 2D linear elastostatic problems.

  • Includes its own mesher based on the computation of the constrained Voronoi diagram. The meshes can be created in arbitrary domains, with or without holes, with procedurally generated points.
  • Meshes can also be read from OFF-style text files (an example can be found in the test folder).
  • Allows easy input of boundary conditions by constraining domain segments and nodes.
  • The results of the computation can be either written into a file or used directly.
  • PolyMesher meshes and boundary conditions can be read straightforwardly in Veamy to solve 2D linear elastostatic problems.

Hi Frank! Thank you for

Tue, 2017-09-05 21:55

In reply to Viscoelastic UMAT: Maxwell and Kelvin

Hi Frank! Thank you for sharing your UMAT code here. I just started working on the viscoelastic material and will need to implement a nonlinear anisotropic viscoelastic material in UMAT. Your code seems to be a great start. You mentioned above the pdf write up for derivation. I was wondering if you may share it and your PhD thesis, the ilnk above doesn't work? My email is sergkuznet@hotmail.com

Thank you!

Pages

More comments

Syndicate

Subscribe to Syndicate