iMechanica - R. Huang Group Research - Comments

CZM in Ansys multiphysics

mystar_bkc10 — Thu, 05 Jan 2012 05:43:36 -0500

Nguyen van Hoan Viettel R&D 380 Lac Long Quan, Ho Tay, Ha Noi, Viet Nam. HandPhone: +84 976 190428 Yahoo: mystar_bkc

Dear Liming Jiang !

I saw that you did CZM in Ansys Multiphysic, i am trying to model it but i havent done even though i tried to follow Help !

pls, guide me in detail how to make CZM in Ansys multiphysic as the problem i posted before :

http://imechanica.org/node/11669#comment-17970

Thank so much

Bondslip for RC frame

aida — Thu, 05 May 2011 10:51:47 -0400

Hi,
I'm newborn in ABAQUS. I want to make a static analysis of RC frame with the
bondslip effect after apply cyclic loading to the frame.

At the moment,I tied the reinforcement bars with the concrete. And manage to
plot hysteress curve of the frame. what I'm aspect was degradation of stiffness
and perhaps I can see pinching behaviour in the hsteresis curve which is not
happen to the current plot.
Detail of my model;
1.2D beam model (beam element for beams and column, truss element for
reinforcement bars)
2.Concrete damage plasticity-concrete model
3. Have inlude damage material properties to concrete and steel.

Hope to get help from you all.

Regards,Ayda

how to define a cohesive zone with temperture dependence behavio

qinfhome2006 — Mon, 14 Feb 2011 12:07:25 -0500

Dr.Huang,

Is there any existing cohesive zone model with temperture dependence property? I have to include a cohesive zone between my two parts, which are not of geometry composed of simple lines but of collection of line segments and curvature. Also I must use dynamic thermal mechanical explicit mode in abaqus. Thanks.

how to set the initial stiffness for contact elements

Liming Jiang — Sun, 24 Oct 2010 03:29:08 -0400

when I'm simulating an interface with cotact 173 in ANSYS ,I got a problem. I used the CZM property when defining the properties of the contact elements, but I found it's not possible to use an absolute stiffness--ansys provides fkn to define the initial stiffness, and we can set fkn with a negative value ,which can be treated as an absolute stiffness in the calculation. But the problem is that the initial stiffness (an absolute one) would not change even if the debonding happened.

so, how to define the absolute stiffness(not a factor) when considering the debonding of the interface

USE OF COHESIVE ELEMENTS IN ANSYS

nadeem — Fri, 15 Oct 2010 04:00:35 -0400

Hi,

i am using ansys to model cohesive zone at fiber matrix interface of a composite. I generated the mesh and solved it but i am facing convergence issues. Can u please guide me in this regard. Thanks.

I shall be extremely grateful

(nadeem_53@yahoo.com)

my answers to Mario

Rui Huang — Fri, 10 Sep 2010 10:13:00 -0400

Dear Mario,

Thanks for your interest in our work. I am sorry that the paper is not clear enough for you. Since the student has graduated and left, let me try to answer your questions as follows.

1) Supposing you mean the computational domain in Fig. 8, it should be clear from the figure that shows the entire domain. Since the problem does not have any length scale other than the initial thickness (h_0), all lengths are normalized by h_0. In ABAQUS, set h_0 = 1 and the length is 10 as you can see more clearly from Fig. 9. So the domain size at the dry state is 10x1.

2) I do not know the exact number of elements in the model. I recall that the mesh was finer near the surface and increasingly coarse away from the surface. For a rough idea, the final crease depth you see in Fig. 8e is about 3-5 element size of the surface. For the convergence study, we tried a few different meshes, but I do not remember exactly how many.

3) The perturbation amplitude can be seen more clearly in Fig. 9a. I believe it is smaller than the element size.

4) Yes. Numerical stabilization has to be used to continue the simulation with creasing. The physical instability causes numerical instability that we have not found a better way to deal with.

5) This is due to the way ABAQUS implements UHYPE subroutine, which assumes an isotropic initial state. We found it the hard way as we tried to use UHYPE at the beginning of this study.

6) Fig. 4a shows that the critical swelling ratio is independent of the wave number as long as the wave number is not too small. The curve bends up at the end of small wave number (long wavelength) because of the substrate confinement effect. In a subsequent paper , by including the effect of surface tension, the curve bends up at the other end as well, resulting in a finite wavelength for the minimum critical swelling ratio.

Swell induced surface instability of confined hydrogel layers

Mario Juha — Thu, 09 Sep 2010 16:04:28 -0400

Dear Professor Rui. I have been studying your paper for several months (and I have to say that I have enjoyed it) I have some questions in regards to the Finite Element Model.

1) What was the size of the domain?

2) How many quad elements did you use? How many different meshes did you use for the convergence analysis?

3) What was the wave amplitude you used for the perturbation? Was it smaller than the element size?

4) Did you use any stablization technique to traverse the crease formation?

5) Why a hyperelastic material subroutine is not able to handle an anisotropic homogeneous initial state? Your explanation in the paper is not clear to me, yet.

On the other hand, Does Figure 4(a) show that the critical swelling ratio is indepent of the perturbation wave number?

Cordially,

Mario Juha

Cohesive Zone Model for Strain Rate & Number of Cycle Dependence

Aliff Farhan — Sat, 17 Jul 2010 01:11:53 -0400

Dear Dr. Huang & Dr. Champaney

I have some question to ask. Is it posible to write Abaqus subroutine for modeling cohesive zone model for strain rate & Number of Cycle depedencecies? As we know already, Abaqus is already implement temperature dependent for CZM in term of stiffness, critical fracture energy and etc.

Thanks

Aliff Farhan

Re: bending modulus of stretched graphene

Rui Huang — Wed, 09 Jun 2010 23:18:00 -0400

Hi Xinghua,

In another paper (Int. J. Appl. Mechanics 1, 443-467, 2009), we described a general approach to define the tangent modulus (stiffness) under combined stretching and bending (Section 2.3). In addition to the in-plane and bending stiffness, there is also a coupling modulus in general. For CNTs under axial stretching, you may follow the procedure in Section 2.5 but add an axial stretch in the X2 direction. As you expected, you may not be able to decouple the three energy terms because of the coupling between bending and stretch.

Hope it helps.

bending modulus of stretched graphene

Xinghua Shi — Wed, 09 Jun 2010 19:39:07 -0400

Thanks Rui! It really helps me a lot!

I have another question that puzzled me recently. In your J. Phys. D: Appl. Phys paper you studied the bending stiffness of graphene in a free state. If the graphene is under uniaxial stretching, how about the bending stiffness? I think it should change, yet how to prove it? According to the procedure you described in the paper, we can calculate the strain energy of a series of CNTs that under axial stretching. Since in this case, the total strain energy consists of bending energy, strain energy in axial direction and in circumferential direction. It seems diffucult to decouple the three strain energies since the CNT is no longer in a free state. Do you have any suggestions?

correction

Rui Huang — Wed, 09 Jun 2010 13:23:00 -0400

A revised version of the manuscript, with a correction to the boundary condition, has been uploaded to replace the earlier version.

Is it possible to perform cutting using cohesive zone model

tirthankar — Wed, 21 Apr 2010 22:57:52 -0400

Dr.Huang

Is it possible to cut along cohesive element using a cutting tool. Is it possible to do withoout Umat?

update

Rui Huang — Tue, 06 Apr 2010 19:03:48 -0400

This paper has been accepted for publication in Physical Review B.

DOI: 10.1103/PhysRevB.81.155410

Re: traction-separation plot

Rui Huang — Sat, 03 Apr 2010 15:14:46 -0400

Pradeep,

The standard implementation of cohesive elements in ABAQUS allows one to define several types of traction-separation relationships. If you want to extract the traction-separation curve to check your result, you will have to output both the traction and the displacement of specific elements (or nodes). I never did this myself, but my student showed me similar plots.

UEL

Rui Huang — Sat, 03 Apr 2010 15:09:16 -0400

Dear Pengfei,

Unfortunately I have no experience using ABAQUS-UEL. Others may come to help. Typically I would think you can use UMAT instead of UEL to define the traction-separation relationship for the cohesive elements, for which the standard post-processing should work.