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Running user subroutine and disp subroutine simultaneously

nitinchandola — Sat, 06 Sep 2008 11:53:18 -0400

I need to run a disp function user subroutine and another user subroutine simultaneously. I tried creating a common library for both but that did not work. I am able to compile both the subroutines and create object files. When I run the analysis it shows an error saying that DISP not found. does anybody have any idea?

Continuum Damage Mechanics and Fracture Mechanics

Michael A. Graham — Fri, 05 Sep 2008 20:46:45 -0400

In Continuum Damage Mechanics (CDM), cracks occur at a level and number such that they are modeled as smeared out continuously. In Fracture Mechanics (FM) some small number of cracks are considered which are of size of the scale of interest. To generalise, CDM is useful to model the degradation of a mechanical body leading up to macrocracks and FM is useful for modeling the mechanical body after cracks on the scale of the structure have formed.

In CDM, the engineer imagines that some of the material has become ineffective at resisting loads. For example, if 20% of the material in the cross-section of a bar has become ineffective at resisting loads and the remaining 80% of the material still behaves as the material normally would, CDM would analyse as though the bar is a normal bar with a full area of material with 80% of the strength and stiffness of the real material. This is extended to multiple dimensions.

In FM, some crack is analysed. Its geometry is important and affects the behaviour of the structure. Traditionally small numbers (think on the order of one) of cracks could be analysed, though modern computational methods allow the engineer to model many cracks. Often the cracks in FM are too large to model as though they were smeared out.

I hope this has helped you with your understanding somewhat.

On differences between CDM and FM

vinh phu nguyen — Fri, 05 Sep 2008 19:28:10 -0400

Hello Praveen,

In below I share with you some understanding on CDM and FM.

I think that the most basic difference between the both is that CDM falls within the standard continuum mechanics framework with continuous displacement field (hence, FEM implementation is rather easy) while in FM, the displacement is discontinuous through the crack face, so you need to use special techniques such as remeshing, meshless or xfem to model this discontinuity in the displacement field.

You can think like this, according to CDM, you smear out the crack over a failure zone where the displacement is still continuous but very high strain.

I am interesting to discuss more on this.

Phu

Many thanks for your kind answere,

Awais Ahmed — Wed, 03 Sep 2008 05:35:19 -0400

Awais Ahmed
Rose School
Pavia,Italy

solved

zhan-sheng guo — Tue, 02 Sep 2008 21:35:18 -0400

thanks prof Suo, i got that.

Having difficulty with posting comments?

Zhigang Suo — Tue, 02 Sep 2008 21:16:42 -0400

Please take a look at this post, "Having difficulty with posting comments?" This post is also placed on the right side of iMechanica, under Quick guide.

why can not load the comment

zhan-sheng guo — Tue, 02 Sep 2008 21:02:50 -0400

gone with the wind

On fatigue in Ansys

pragtic — Tue, 02 Sep 2008 16:48:48 -0400

Hi ingcartun,

Well, I myself have no experience with the fatigue module in Ansys. But what I read about its features some two years ago, it is a very basic module. In fact the automated work concerns reading the stress tensors in individual nodes and relating the local stresses to S-N curves. This necessitates definition of various modifying coefficients, which has to be either input or selected by you. The problem can arise by highly complicated (i.e. more complexly shaped) components, where search for this value is not easy. Anyway, even if you tune the computational results to some experimental tests that you could have, it relates only to the specific notch you examine now. If your goal is to prepare various design proposals, you do not know, if the critical place is not shifted to another locality, which can be quite near.

This is the reason why I keep my fingers crossed to FemFat, with its stress gradient concept, that could at least a bit simplify the work. But still I am not sure how well it works...

I would be quite interested how far the fatigue module in Ansys has got through the time. Have anybody else any experience? Can it assemble the local loading state from non-correlated loads in various load channels?

Back to you, ingcartun - I am not sure, how far away you live, but I would recommend you to visit the PragTic Users' Meeting (see somewhere in the start of this forum). No kidding, this is no promotion. The things you have to do before any such analysis are quite similar and similar should be also the processing of your input. So, it could help you to orient in any program of this kind.

Regards,

Jan

simulation of explosion in ABAQUS

Wladimir — Mon, 01 Sep 2008 10:39:19 -0400

Hi all,

I'm trying to simulate with ABAQUS a explosion of TNT and the effect of that on a metal panel. The metal panel is 200mm away from explosive. It is about 100g TNT. I now about the subroutine VDLOAD. Which options I could use else in ABAQUS? Is it posible to define a explosion lake this with *EOS? If yes, which element type I should use for explosive set? Should I define a element set for air, if I use *EOS?

Thank you

orthogonal machining

iitd.mani — Mon, 01 Sep 2008 06:23:23 -0400

Dear sir,

if i will do the same simulation by using ABAQUS what are all the forces consider and how i will give as input..

it is necessary to write the user subroutine prog.

thanks

Mani

IIT delhi

India

ansys lamb waves

epalmos — Wed, 27 Aug 2008 17:32:46 -0400

Hi, all

I am studying
Mech. Engineering and I have just started using ANSYS. I am trying to simulate
the lamb wave propagation in a plate. My idea is to create a 2D model and use
transient response. But ANSYS gives me the movement of the bar, mode shapes...but
nothing like wave. Can you help me in this? How can I simulate the problem...

Thank you
in advance...Just remember that I don't have a lot of experience in ANSYS...

Hi Awais, Usually, domain

vinh phu nguyen — Wed, 27 Aug 2008 08:33:57 -0400

Hi Awais,

Usually, domain A is a set of elements within a circle centerd at the crack tip and have radius of 3 * area of the element containing the tip. As you know, the interaction integral is independent, so just use quite large factor (3-5) is ok.

Hope it helped.

TO LEARN ABAQUS, come this web:

Nguyen Chau Linh — Wed, 27 Aug 2008 05:30:38 -0400

TO LEARN ABAQUS, come this web:

http://cobweb.ecn.purdue.edu/~ahvarma/

Re: Dilational vs longitudinal wave speed

Biswajit Banerjee — Tue, 26 Aug 2008 23:21:00 -0400

If you think of the crack tip as a point dislocation source, then there are essentially two types of elastic waves that propagate. These are the P-wave (pressure wave or primary wave) that shows up first in an accelerometer trace and the S-wave (shear wave or secondary wave) which shows up later.

The P-wave is also called the "longitudinal wave" because the direction of the particle motion is the same as the direction of propagation. The velocity of this wave is c_p = sqrt{(lambda+2 mu)/rho}. This wave is also called the "dilational" wave. See for example "Waves and Imaging Through Complex Media ".

A good book for the basics is "Wave Propagation in Elastic Solids" by Jan D. Achenbach. Another that is good for applied wave propagation is "Quantitative Seismology - Vol 1" by Keiti Aki and Paul Richards.

-- Biswajit

Effect of reflected stress wave on the local crack-tip fileds

Nguyen Chau Linh — Tue, 26 Aug 2008 22:23:40 -0400

Dear alls,

I have some points which i not yet understood, can you give me some comments:

1. Maybe you know the Book of Anderson (Fracture Mechanics), 3rd edition. In the chapter 4, page 183, example 4.1, i want to know why he use the longitudinal wave speed Cl, because you know, the dilatational wave speed Cd bigger longitudinal wave speed Cl, right?

So dilatational wave in the material body will come to crack tip sooner Cl.

2. Did you know the paper or the other source say about the sinificant effect of reflected stress wave on the local crack-tip fileds?

Please help me!!

Thanks and Regards,,

Chau