This is the MOST Comprehensive video about Ductile Damage.
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- Опубликовано: 14 июл 2024
- This video shows a detailed illustration of the theory and simulation around ductile damage using a cylindrical dogbone specimen and steel material. Here, the parameters in the ductile damage are described extensively and illustrated in how these can be input into an ABAQUS model. The video ends with illustration of how to extract stress-strain plot from the simulation.
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TIME STAMPS
00:00 - Intro
00:44 - Theory: Describing specimen design and dimensions
01:27 - ABAQUS: Setup of the test specimen
02:30 - ABAQUS: Meshing of specimen
03:03 - ABAQUS: Steps to instruct mesh for element deletion
05:08 - Theory: Specifying the Elastic Properties
06:40 - Theory: Specifying plastic properties
13:49 - ABAQUS: Specifying damage parameters
14:33 - Theory: Describing the principle of damage evolution
17:03 - Theory: Describing Element stiffness degradation graphically
18:25 - Theory: Linear Damage Evolution Law:
18:38 - Theory: Tabular Damage Evolution Law
19:41 - Theory: Exponential Method Damage Evolution Law
21:20 - ABAQUS: Specifying displacement at failure parameter
25:07 - ABAQUS: Specifying loading step
25:29 - ABAQUS: Specifying STATUS output request needed for Element Deletion
27:34 - ABAQUS: Requesting History Variables from Reference Point
27:55 - ABAQUS Simulation Results
29:01 - ABAQUS: Extracting Stress-strain Plot from Simulation
31:05 - Outro
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Finally best explanation of this topic, thanks
Glad it was helpful! That is what my intention was and I am glad that vision is achieved. Cheers!
Excellent video!! Keep them coming Dr. Okereke
Thanks very much. I will keep going. Any suggestions for future videos?
I have a particular interest in modeling superplasticity of metals, maybe use some of your syntactic RVEs to investigate the effect of the voids on the overall behavior of the material!!
Yes, that is fine. I think you can also look at the video about Triaxiality - some of the ideas in that video might help you with the superplasticity argument. Well done!
one of good explanations for the ductile damage so far
Glad you enjoyed it and felt that way about it. I wanted to make a comprehensive video about ductile damage that tries to show the whole theory and simulation setup for viewers. Glad it struck a cord with you!
@@MichaelOkereke Thank you for your great effort. I was wondering if the method you described can be applied to truss elements like T3D2 or beam elements like B31.
I will not think so, as the element type used here are 3d continuum elements so am not sure you can use it for the beam or truss elements.
@@MichaelOkereke I am wondering if there is a different approach. This would be significantly important when modelling actual-size reinforced concrete subjected to severe loading such as cyclic load. In this case, the rupture of the reiforcing bar could be identified at critical locations (plastic hinge locations). Anyway, thank you, Dr. Michael Okereke, for your reply
thank you so much sir
Most welcome
Great video! One thing you might have missed is converting thr density to tonne/mm^3 as opposed go kg/mm^3.
Not really...I was working in an SI unit with mass in a unit of kg. Also, the Pa is N/mm^2 and N = kg.mms^(-2). Therefore, it's better specified in kg. However, if your masses are in tonnes, then indeed you are right.
Please Sir tell how to break porous metal material in abaqus
hello sir, thank you for your clean explanation. but there is something i want to share with you.
based on ABAQUS documentation, "Fracture Strain" means "Equivalent fracture strain at damage initiation". so there is a contraction between what you defined in the video and ABAQUS documentation. in another way, the strain you defined in the video, is more like "rupture strain" based on ABAQUS documentation. have I missed something ?
Thank you for the video. So if we change the mesh size do we also need to change the displacement at failure parameter?
Thank you for this video, can you give us an example on the damage of an RVE as an example: Concrete with aggregats or Porous material.
Good question. I keep planning to make such video. Please watch the space.
Sir, in your video you refer the "Fracture Strain" set in ABAQUS as the value when it totally damaged. I think "Fracture Strain" in ABAQUS might be the fracture strain at damage initiation, which you called epsilon zero.
Was going to ask this as well. Because I believe equivalent plastic displacement is then used to get from this value to the point of failure in the damage evolution module.
Hi, good question. If you look at the graph, the initiation aof damage is at the UTS and there D = 0, which suggests that damage has started and this will evolve with changing D until D = 1 (complete damage). Complete damage occurs at the fracture/separation of the specimen. The strain at which this happens is the fracture strain.
It could not be at the epsilon_0 (which is equivalent to start of the plastic strain), as this corresponds to the UTS. The specimen cannot fracture at this point rather it will be the final point of yielding. Eventual fracture/separation of the specimen happens at what I have called fracture strain.
Within a single element, when damage initiates, we need to know when a failed element will be deleted from the model. This corresponds to the fracture strain through the displacement at failure. Once this is obeyed, the element is then deleted from the model since element deletion is swithced on. Other elements around the failed element might have D values not up to 1 and so not approached the fracture strain. Once they meet this condition, the elements would then fracture and be deleted from the the model.
If you do not believe me, I asked ChatGPT to define fracture strain and here is the answer:
"In the context of continuum damage mechanics, fracture strain is defined as the strain at which a material undergoes fracture, leading to the complete loss of load-carrying capacity in the material. It is The strain value at which a material experiences fracture due to the accumulation of damage, resulting in a complete loss of its structural integrity."
I believe this is consistent with what I have tried to explain above.
@@MichaelOkereke Thank you sir, that's very clear. But in Abaqus manual Ductile Damage Section, the "Fracture Strain" is defined as Equivalent fracture strain at damage initiation, not the end. I tested it in abaqus and plotted the stress-strain curve, and the "Fracture Strain" input value is really just the initial failure strain.
In which case you go with ABAQUS... the documentation will not lie.
How to find the characteristic length for tetragonal element?
The simplest way is similar to what I did here but replace the volume of the cubic element by the volume of a tetragonal element, but still take the cube root of that volume.
Take volume of a tetragon = a^2c where a = edge length of a regular square base of the tetragon and c is height.
I think you could assume that the elements you are dealing with are regular tetragons even though in more cases it would be irregular but deviations from edge length, 'a' and 'c' can become an error measure which you can factor too in determining the characteristic length.
Sir, what will be the characteristic length for a tetrahedral element?
I had a thought about it and the simplest way is similar to what I did here but replace the volume of the cubic element by the volume of a tetrahedron shape, but still take the cube root of the volume of the tetrahedron. Take volume of a tetrahedron = a^3/(6*square-root(2)) where a = edge length of a regular tetrahedron. I think you could assume that the elements you are dealing with are regular tetrahedrons where in more cases it would be irregular but deviations from edge length, 'a' can become an error measure which you can factor in in determining the characteristic length.
excuse me, Can I ask some question that is not relative with this video ?
My model is hybrid composite between KFRP and CFRP under low velocity impact condition but I cannot get force value or plot force and time graph. Can you explain how to I solve this problem.
Thank you immensely for your thorough explanation! 🌟
However, I have a question: Why use an explicit solver? What advantages does it bring? If the problem is tackled using Abaqus Standard, what changes? To my knowledge, Abaqus Explicit is typically essential when a problem encounters significant forces due to mass or intricate frictional forces-neither of which seem pivotal in this case. What, then, justifies its use here?
You are right... it could be easily done with ABAQUS Implicit and it would work.
However whenever there is significant possibility of nonlinearity, damage, impact or the examples you cited, it is usually recommended to include an ABAQUS Explicit step as its better suited to deal with the convergence of such unstable simulations. I hope it makes sense.
please do a video on hybrid metal matrix composite RVE with fracture analysis
This is a good question. I have not done this before but should be interesting. What is the matrix and metallic reinforcement you are taling about. What is the hybrid material?
@@MichaelOkereke it may be aluminum matrix and TIB2 + SiC particle reinforcement. Analysis should be on damage initiation, crack propagation and interfacial debonding.
basically for understanding the deformation and fracture mechanism of MMCs.
What about Lode Parameter ?
Good question!
Lode parameter is definitely essential for describing plasticity of materials. I have not specified it here as the ductile damage model that comes with ABAQUS, and which was reviewed in this video does not have need of this lode parameter. Just like the stress triaxiality, the lode parameter gives and indication of the dominant stress state in the model.
Lode parameter, typically represented by mu, can be: mu = 1 (pure shear stress), mu = 0 (uniaxial stress) and mu = -1 (corresponds to a stress state where principal stress, σ2 =σ3 (triaxial compression). It is similar to the stress triaxiality term which gives us an indication of the stress state (dominating) the simulation.
If you want to learn a bit more about the lode parameter and the like for a triaxially loaded system, then watch this video of mine: ruclips.net/video/HJ3JzPUhz1U/видео.html).