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crack initiation simulation with FEM
Tue, 2009-11-17 05:02 - YangTan
hello.all.
i want to simulate the the crack initiation, but i don't know
(1)what criterion should i use for crack initiation.
(2)how to deal with the mesh(unlike other fracture model, there is no crack defined in advance in the mesh).
the material i use is structual steels.
could anyone give me some advice?
thanks.
best regards
Forums:
crack initiation with FEM
Hello Mr Yang Tan,
For a two-dimensional study (2 degrees of freedom/node) the crack can be modeled with non-interlinked elements (i.e different numbers of nodes with the same positions) at the failure for a Finite Element Mesh. Accurate results have to be considered at the head of failure by using special elements for example a triangular element with 6 nodes : espacially 2 nodes with 1/6 of the position near a vertex (node) the 3rd one is at the midle of one edge.
If you need specific formulations for that element I can send you the corresponding information.
You do not need to use criteria of stresses at the analysis step. The Finite Element Method is able to compute strains and stresses at the d.o.f and more. You can use the related criteria only as a method of verification. Elastic Limits of the stresses can also be used to verify the computed values.
Sincerely yours
Mohamed lamine Moussaoui
CC-Dan
CC-Dan
hello.
hello, salutsun
what's the meaning of "cc-dan", a person? but i can't find his paper in the library.
crack initiation simulation with FEM
hello,mohamedlamine
thank you for your reply.
there is something wrong with my internet explorrer these days, so i couldn't reply.
because i don't know where the crack will initiate, so i want to use a
criteria(according to the simulation results) to decide the position
where the new crack initiate, and surrounding the new crack tip with
rossete of triangular element, then calculate for the crack propagation.
so what should i do?
best regards
yang tan
crack initiation simulation with FEM
hello,mohamedlamine
thank you for your reply.
there is something wrong with my internet explorrer these days, so i couldn't reply.
because i don't know where the crack will initiate, so i want to use a
criteria(according to the simulation results) to decide the position
where the new crack initiate, and surrounding the new crack tip with
rossete of triangular element, then calculate for the crack propagation.
so what should i do?
best regards
yang tan
Re Re Crack Initiation Simulation with FEM
Hello Yang,
I don't understand why you are using Rosette method as a criterion of strength. Rosette strain gauges are used to determine the strains of any orientation (angle tetha) with respect for the first direction of the gauge. consequently the strains epsilon1 and epsilon2 can be calculated see the book Resistance des Materiaux, Editions de l'Ecole Polytechnique de Montreal 1987, pp.165-168, ISBN 2-553-00199-1. Do you mean Failure Criteria like Tresca, Von Mises,...
Also, do you want to develop a Finite Element Program by using special Elements or are you using Failure criteria for composite materials in order to determine allowable strength curves in strain space with superposed failure envelopes of plies (in cross-ply laminates) with different orientations ?
Respectuously,
Mohamed lamine MOUSSAOUI
crack initiation and propagation simulation with FEM
Hello, mohamed lamine
Because the structural steels can fracture in a brittle or ductile manner, so i think both the stress and strain criteria maybe wil be used in the corresponding situation. But i am not sure which variable i should use as a criteria, Von Mises , or others.
Yes, i'm developing a FEM program to do the crack initiation and propagation simulatio,the simulated process is that, a load is applied on the plate(two-dimensional), then at some place(according to the simulation results which is defined as criteria), the crack initiate; the load continue to be applied on the plate, new crack will generate,and the old crack will propagate.
My problem is that i don't know how to simulate the crack initiation ,especially how to deal with the mesh to simulate the crack initiation? Usually, pepole will lay a pre-defined crack in their fractrure simulation, but in my simulation, nobody know the position where a new crack will initiate.
regards.
yang tan.
crack initiation and propagation simulation with FEM
Dear Yang Tan,
I don't know if I have understood your doubt completely. Do you want to simulate the propagation of a crack since its nucleation and until the end (a certain number of cycle steps) or solid complete rupture?
In fatigue crack propagation problems (considering a linear elastic problem), we threat this phenomenon divided in three different situations: the nucleation of a crack in the solid, the stable propagation of this crack and the unstable crack propagation until the final rupture. If you want to simulate the second region (stable crack propagation) in a linear problem, the methodology is well developed and stablished. You can use Linear Elastic Fracture Mechanics (LEFM) theory with the Paris law to model the stable crack growth, but it only can be used if the crack is relatively big (you don't model the crack nucleation, so you have a crack in a specific location and with a specific length).
But, if you want to model the crack nucleation, I think the LEFM theory won't work. In this case, you need to consider the high plasticity field involved in the nucleation process. In this case, I am not a specialist, but I can suggest that one needs to recover to Damage Mechanics theory.
If you want, I can send you one work (in English) I sent to a congress, where I simulated the crack propagation of two cracks in the structure using Dual Boundary Element Method (DBEM) instead of FEM (but, you need to consider that both DBEM or FEM are only tools to obtain the elastic field near the crack tip and these results are used to obtain LEFM parameters such as Stress Intensity Factors, for example). Unfortunately, my Master dissertation is not written in English (I wrote it in Portuguese) and I have only this work in English to send to you so far.
Regards,
Marcel Sato
Simulating Dynamic Fracture
Dear Marcel Sato,
Thank you for your help!
I want to simulating the dynamic fracture process, the classical theory of fracture mechanic maybe not useful. So i want to use a criterion combined with the remeshing to reach that. But i don't know how to deal with the mesh, especially when the cracks are near the boundary and two or more cracks interact with each other.
regard,
Yangtan
Dynamic fracture and branched (bifurcated) fatigue cracks
Dear Yangtan,
I am not sure, but I think that there is a brazilian research group that
works with branched fatigue cracks (bifurcated) and they have some good works
published. Although, I don't know if they have worked with dynamic fracture
yet.
http://dx.doi.org/10.1016/j.ijfatigue.2005.07.016
There are some works with dynamic fracture simulation using Boundary
Element Method (BEM) made by some great reaserchers like Aliabadi, Fedelinski
and others. There is a work from a brazilian professor that is very good:
http://dx.doi.org/10.1016/S0045-7949(03)00184-6
I hope it helps you... good luck!
Regards,
MSc. Eng. Marcel Sato
University of Campinas - UNICAMP
Mechanical Engineering Faculty
Department of Materials - DEMA
Re: crack initiation and propagation simulation with FEM
Hello Yang,
One remark: Plate elements are used for flexural bending with at least three d.o.f : one translation and two rotations. And 2D elements are: triangular and quadrilateral ones.
You have to make a decision. the position of the crack has to be
assumed. After that, many simulations can be made after developing a
F.E program. The criterion of Von Mises is used to calculate the
equivalent stress which can be tested with the elastic limit.
Sincerely
Mohamed lamine MOUSSAOUI
mmohamedlamine@yahoo.fr
Dear Mr. YangTang, if
Dear Mr. YangTang,
if you will be using Finite Element Method to study this kind of problem, I can advice you to use this software:
SAMCEF for Fracture Mechanics.
The company that developes this particular CAE application is SAMTECH (from Belgium).
Hope it helps,
Best regards,
Patrizio
Thanks for your
Thanks for your advice
But i can't find the code, Less information can be found. I don't know how it works.
Source code FEM forcrack initiation and propagation
Two links for that code
http://www.ciss.iis.u-tokyo.ac.jp/rss21/en/result/download_fsis/index.php
http://www.esm.vt.edu/~rbatra/
Hi,Nguyen Van
Hi,Nguyen Van Chau
The links you gave me are not about "SAMCEF for Fracture Mechanics", But
from the second link, i find another paper talking about this topic. Thank you
very much!
In that paper, the author used node seperation to simulation the crack
propagation. I am glad to know if there is another way to do that?
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