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Fracture - Science topic

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Hi all,
I have a question about the simulation of uniaxial tensile test of sheet metal. When I adopted the GTN Porous fracture model (it was embedded into the ABAQUS software) to simulate the uniaxial tensile test of sheet metal, I found that the simulation results vary with degree of the input material plasticity data. When I input material plasticity data upto 4 (extrapolated by swift law), the simulative displacement obviously exceeded the experimental displacement. And When I input material plasticity data upto 0.123, the simulative displacement Roughly equal to the experimental displacement. I can't think through the reasons behind it, and Can someone explain this?
Thanks in advance for any advice!
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Independent of which material model you take, you need to provide information on the hardening behavior in the post-necking regime in order to be able to simulate this region. Getting this information for a real material from experiments is not trivial. Though, there are established methods to extract true-stress vs. true strain data from the post-necking regime, e.g. using Bridgeman's correction or doing an inverse parameter identification (the latter is necessary definiely in case of complex stress states). A pragmatic approach is that you take the true pre-necking data and extrapolate them to the post-necking regime using an analytical law like a power law or a Voce law. Subsequently, the analytical law can be either rasterized to obtain the tabulated data for the built-in plasticity models of Abaqus or you implement it as a user-defined hardening law using the UHARD routine. Our GTN implementation (open source at https://tu-freiberg.de/nonlocalGTN ) supports power-law hardening by default.
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Dear Researchers,
In the study of rock fractures, many values are used to characterize the state of rock fracture, such as fracture density, fracture volume, fractal dimension, etc. These measurements can be used to microscopically express the degree of rock fragmentation and be applied to DFN research.
However, how do establish an effective relationship between microfracture and macro rock mass? For example, can a jointed rock slope express fracture development through slope displacement detected by slope lidar (rock mass volume change is equivalent to further fracture development)? Or is there another way? Looking forward to your good methods.
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I advise You to look at pages 48 and 49 of the attached PDF file, but You will have to translate the text from Russian.
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Yes. I have many researches published and available in RG.
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Both seismic reflection and refraction could give a better resolution.
An example by using seismic reflection is available in one of my papers.
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Dear researchers,
Has anyone used abaqus for fracture crack growth using XFEM.
I wanted to ask if the fracture crack growth criterian as fatigue is available in abaqus 2019 version. Because I could not find in my abaqus expicit/standard.
Please let me know, if you have used any special provision for that.
Thank you,
Asmita
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Asmita Rokaya Yes, thank you, I know one can determine c3 and c4 from the fact that da/dN = C(delta K)^m (Paris Law for FCG)= c3(delta G)^c4 (Abaqus Implementation of Paris Law for FCG), thus manipulate accordingly to determine constants c3 and c4 under the assumption of plain stress or strain.
But, how did you determine constants c1 and c2 for N/(c1*(delta G)^c2)? Thank you in advance,
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I am performing an LCF in Abaqus and I was able to derive the value of C3 and C4 from the Paris law. How to find C1 and C2 values or where to find them..?
what will be the value of power(BK or power-law)........?
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Hello Sharon Pc did you resolve this problem? thanks
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Hi, I want to simulate a crack initiation in a 3D ring model under compression load in Abaqus. The biggest problem is related to the load, I tried to use a load along -Z axys and the second time a pressure along -Z, but I cannot see the fracture. Do anyone know how does it work?
Thank you
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Which Thoracolumbar AO fracture subtype MRI would have the highest chance to change decision-making?
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A3 and a4 fractures in neuro intact patients may be classified as B2 injuries and change initial treatment. I think for A3 and A4 when considering non operative management an Mri is highly recommended.
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Hello All,
I'm looking into measuring crack growth rate using the DCPD method and was wondering if it is possible to use a "bench top power supply" and a multimeter with higher accuracy? Or do I need to have specialized equipment for DCPD measurement?
The materials I'm interested are iron alloys and aluminum alloys.
Compact tensions specimen thickness =< 13mm
Cheers,
Rashiga
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Hi, you don't need any special equipment. We don't use it in our lab either. But it is easier to buy a DCPD. On the other hand, you are a little proud when the system finally runs. :)
We use a nanovoltmeter and a PC with a self-written software in Labview.
You have to measure on your sample the voltage drop at your crack ("active signal") and the voltage at a spot without crack ("reference signal"). In addition, total voltage and total current.
We do the evaluation with Matlab. In the standards, you will find the corresponding formulas for the ratio of electrical voltage to crack length.
I recommend the insertion of striations during the crack propagation test for a better correlation of the crack length. A reference test may be necessary.
Regards,
Michael
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I am looking for an instruction to determine the required time for fracturing polymers to do scanning microscopy.
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Dear all, most literature don't much importance to freezing time, and even cases where it is not mentionned at all. Generally, arbitrary values are taken. For more detail please have a look at the following documents. My Regards
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Fenite and syenite are present in the margins of my study area (ultramafic-alkaline-carbonatite complex). If fenitization takes place along fractures and are relatively thick, then how can I differentiate it from syenitic intrusions? Without geochemistry, can someone suggest the differences from field and petrography. Thank you.
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We can view fenitization is a type of contact metasomatism. The fenite may vary with host rock (syenite or ultramafics) and distribution of carbonatite within them. The fenitizing fluid composition will vary with the type and composition of the intruded carbonatite. Sodic fenite and potassic fenite are commonly associated with syenite. The sodic fenite develops 'albitite' along the contact zone and may be controlled by the fracture system present. Pre-existing potash feldspar is altered to massive albitite. Potassic fenite develops 'ultrapotassic' feldspar. This may be confirmed by variation in petrography from syenite to the suspected fenite zone (and carbonatite). If the fenitization is pervasive, massive and thick, it is possible to distinguish the original and altered minerals at the outcrop. Otherwise we may need geochemical confirmation. Accessory minerals such as pyroxene in the syenite, may be altered to blue riebeckite (asbestiform), following desilication reactions, the silica generated will possess riebeckite needles as inclusions and will be noticed as greyish blue to dark blue (quartz) pebbles (Samalpatti alkaline complex). Pyroxene may be altered to green epidote or dark to greenish black biotite or vermiculite (with or without apatite) , and may be distributed as streaks in the fenite zone. Carbonatite related minerals such as monazite, apatite, corundum may occur in the fenitized zone.
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When describing the fracturing of sulfate-carbonate massif faced the problem of choosing a genetic classification of fractures. Each researcher has its own classification, and I could not find any new, generalized international classification. Tell me which genetic classification of fractures, is the most used among researchers?
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Reservoir Engineering / Groundwater Hydrology
Permeability: Can directly be correlated with Porosity?
Having known that ‘Porosity’ remains just as a ratio and does not depend the pore-size explicitly, while ‘Permeability’ explicitly depends on the solid grain sizes and in turn the diameter of the pore sizes;
Under what circumstances, the traditional (existing) correlations between Permeability and Porosity holds good in Sandstone Reservoirs (leaving aside its correlation in Fractured/Carbonate Reservoirs)?
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Dear Suresh Kumar Govindarajan, more general : diffusability, that covers all parameters, porosity, surface chemistry and interactions (usually refered as inertia or retention, and friction), applied gradient (pressure, concentration, ...), temperature, and so on. My Regards
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I am measuring the angles of fracture surfaces from side view in SEM images. But the images are taken at 70° stage tilt and they are not true side views. In this situation, how can I correct for the values of angles measured at this tilt to convert to true angles?
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I have the same question, did you already find out?
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Please provide formulas to find parameter fracture strain, Displacement at failure, Stress triaxiality, Strain rate..
Thanks in advance
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I am trying to model a 3D End Notched Flexure test using ABAQUS. The end notched flexure specimen consists of two beams with a cohesive element interface and a pre-crack. The test uses a three point bend configuration. The specimen is modeled using solid elements (C3D8) for the ENF arms and the interface is modelled using finite thickness cohesive elements (COH3D8). A pinned and a roller boundary condition is applied to the ends of the specimen and a displacement is applied centrally.
The analysis fails within the first few increments. The error message either reads that the force residuals haven't converged or the cohesive elements show excessive distortion. I have tried using both, Static general step and a Dynamic implicit step with quasi static definition. Refining the mesh and reducing the increment size has not helped. Using cohesive contact instead of cohesive elements did not help either.
Can someone comment on ways to resolve these errors? Attached the .inp file for my analysis.
Thanks in Advance
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Hi Sai Aranke,
When you have damage initiation and progressive damage in your analysis, whether there is "cohesive" in your analysis or not, you should use the Explicit solver to avoid convergence issues. Refer to this link: https://caeassistant.com/blog/abaqus-standard-or-abaqus-explicit/
Moreover, I suggest using cohesive contact instead of the cohesive element.
Also, check the link below. You will find useful tips and tricks about cohesive analysis.
Best wishes.
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I have to work on crack formation to simulate ductile fracture in ABAQUS by using UEL. Can you please suggest to me some explanation videos?
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Dear Yassine Hersi,
I hope this can help you:
step one:
Programming the user element by means of the "uel subroutine" in ABAQUS. You save the file "userfile.f".
step two:
In the input "jobfile.inp" you must identify the user elements, and define their properties, and degrees of freedom. For example:
*USER ELEMENT, TYPE=U1, NODES=3, COORDINATES=2, PROPERTIES=8, VARIABLES=60
1,2
*ELEMENT, TYPE=U1, ELSET=CZ
** PLACE HERE THE COHESIVE ELEMENTS
12360,1376,2923,1325
…….
*UEL PROPERTY, ELSET=CZ
1700,…..
Step three:
If abaqus subroutine is enabled in your computer, you run the uel subroutine in the command window writing this:
Abaqus job= jobfile user=namefile
Best regards
Susana
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I am using AA2024 and other aliuminum alloy as the material for the blank in a tensile shear test,
However I need the Ductile Damage (Fracture strain, stress triaxiality, strain rate) and Shear Damage (Fracture strain, stress triaxiality, strain rate) as well as plasticity.
Thank you.
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To predict the ductile behavior of metals such as steel, aliuminium alloy, etc, the porous metal plasticity (GTN) embbeded in ABAQUS software has been one of the most useful methods.
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How can you estimate fracturing? What coefficients can be used for this?
We have an array of data fractures of different genetic type, laid mainly in sulfate rocks, sulfate-carbonate massif.
All the fractures are already graphically mapped in AutoCad and ArcGis.
How can we qualitatively or quantitatively estimate these fractures? What fracturing assessment methods are available?
How can the assessment of fracturing be translated to the stability of the massif itself?
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Моделирование трещиноватости: практикум по DFN в Petrel 2016-2019: А. А. Козяев, Р. М. Щуковский, К. Е. Закревский: [под редакцией К. Е. Закревского].
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Incomplete femoral neck fractures are often stress-fractures, but sometimes caused by low energy trauma (fall). Would it make sense to have the same management for both types of fractures? I.e. early operation when on tension side, conservative management when on compression side?
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Always err on the side of operative management, because we are not going to lose anything if you fix the neck percutaneously in such cases with CC screws, but if we do not fix, there are always chances though minimal of Displacement, AVN.
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Montezzia fractures
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In Monteggia fractures radial head usually reduced closely after reducing the ulnar fracture and annular ligament is rarely required.
In cases of neglected or chronic Monteggia fractures with chronic radial head dislocation, annular ligament reconstruction may be required to restore the radial head stability.
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Hello,
Can someone kindly explain, the method to calculate the diffusion coefficient within a fracture?
Thank you
Amar
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Do you want to talk about D the effective diffusion coefficient of the dissolved constituent in the fluid of the rock matrix?
The effective diffusion coefficient, D, is dependent on the diffusion coefficient of the dissolved constituent in water and the pore structure of the rock matrix:
D = Phi x Dd
where Dd is the free-water diffusion coefficient of the dissolved constituent and Phi is the formation factor that scales the free-water diffusion coefficient to account for diffusion in the tortuous pore structure of the rock matrix.
The formation factor is a dimensionless term that is less than 1 and can range over several orders of magnitude, depending on the type of rock under consideration (Novakowski and Van der Kamp 1996).
Regards
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Hello,
Can someone help us by explaining the process of calculating the velocity of water within a fracture.
Thanks in advance
Amar
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According to Darcy Law:
V (Velocity) = (K (Permeability)/Miu (Viscosity)) * dP/dL (Pressure Gradient)
Here, K = H^2/12 for parallel plate or fracture, where H is the channel width
Best,
Bijan
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Why do micro-cracks forms in the matrix zones of FRP composites?
(a) Is it a Defect ?
(b) Does it has any effect on the initiation of fracture during the load applied?
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I wouldn't say these micro-cracks are 'defect' if the sizes of the cracks are too small and it's due to environmental loading. Having said that, as Ross mentioned above, it may be accepted or not depending on the purpose and tolerance limit for the application.
If the sizes and number of cracks are too small, it's hard to set a linear relationship between these microcracks and the initiation of fracture during the load applied. However, on a number of occasions, micro-cracks may have an impact on the ultimate load-carrying capacity when micro cracks become the weak zone of the structure. Hope this helps.
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At present, complete geometrical characterzation of a naturally fractured rock mass is always difficult owing to its 3D nature and limited access to all information. Thus, a DFN model is often applied to approximate a real faulted or jointed system. A following numerical simulation can be conducted to estimate the mechanical and hydraulic properties of a fractured rock mass. Undoubtedly, the reliability of the established DFN model is a vital prerequisite for the accuracy of the subsequent analysis of the model. So what are the current methods to verify the consistency between DFN and field measured data? Especially for the 3D information.
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Hi, here is the promised report
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I am carrying out a research on patients with sarcopenia related to fracture rate, using SF-12 version 2 as the QoL tool.
I was wondering if anyone is using the same questionnaire and calculate the scores using SPSS syntax? Thank you very much!
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Could someone send me the syntax of the sf12v2 for SPSS?
I try to get a license of SF12 version 2 scoring is very expensive. I would greatly appreciate it. Thank you very much. My email: sumikao@icn.usyd.edu.au
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What the rail fracture behaviour in LWR or CWR track ? Does it always break from breathing length or any where due to any other reason or decreased temperature .? Is there any specific behaviour please ?
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The crack propagation is due to shear stresses, which are triggered cyclically by the rollover process (rolling contact). In this respect, there is a fatigue fracture. Defects hidden beneath the surface act as crack starter. The higher the stress, the deeper extents the tension field into material. Then the number of defects that can serve as crack starters also increases.
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In recent times, hydrogen (as a fuel) has captured attention of the scientists, researchers, industries, governments and environmentalists. Meanwhile, the researchers in porous/fractured media have proposed temporary and permanent storage of hydrogen. The proponents of temporary or seasonal storage have proposed that since hydrogen consumption would be subject to demand and/or supply fluctuations, so it is proposed to storage them in porous/fractured subsurface geological media. Wettability has been identified as one of the key factor to achieve the hydrogen storage task.
The researchers on the platform are invited to contribute to this discussion as what wettability scenario is desirable for both temporary storage, and permanent storage (in which hydrogen acts like a battery fuel cell - see http://www.hydrogenbatteries.org/What_Is_A_Hydrogen_Battery.htm).
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I could argue with those scientists who argue that the hydrogen wettability of the pores is of great importance. It is better to talk about hydrogen adsorption rather than wettability. After all, hydrogen is not a liquid. Hydrogen adsorption will be in one or two layers, and then, possibly, capillary condensation of hydrogen molecules, but this is also not wettability. If they are stored in storage facilities where there was oil, then hydrogen will dissolve in the pores. It is completely forgotten that hydrogen with various elements forms hydrides. The reaction will be biased towards their formation, since hydrogen will be stored at high pressure (concentration).
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Dear all
please justify where we can use of these non linear properties of concrete in practically.
is there any use of these works, which can be address through decades .
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if medico-legal case comes with fractured tooth segment or avulsed tooth, then how to determine time period or time duration of injury/assault clinically or histologically?
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بحسب مرونة السن
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Pelvic Fracture Urethral Distraction Defect/ PFPUI in adult patient with completely distorted pelvic ring (vertically and rotationally displaced- unstable) following trauma (RTA), 2 yrs back. There was no adequate perineal space to access the urethra The urethral defect was estimated to be 6-8 cm, with a short posterior urethral length. The patient is on SPC.
What options of mgt do we have?
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The primary principle of pelvic fracture urethral destruction defect reconstruction is progressive perineal anastomotic urethroplasty to be done only after an optimal management of the fractured and displaced pelvic bone. However, if the pelvic fracture is not properly fixed or the postoperative imaging shows a faulty fixation, performing urethral reconstruction will be difficult and complicated. This can be due to problems with proper patient positioning, adequate urethral mobilization, achieving tension free anastomosis. In addition, by the time the orthopedic problem is repaired, the risk of anastomosis disruption will not be negligible.
In this patient, i dont think optimal urethral reconstruction can be achieved in the presence of pelvic bone rotational abnormality described above. Hence, a prior orthopedic consultation while keeping the patient on suprapubic catheter drainage is better.
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In a stress-strain curve of an FRP composite, mostly it is represented strain in terms of (%) rather than in (mm). Why it is represented in such a way?
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Strain is any kind of deformation, including elongation. Elongation is the word used if we're talking specifically about tensile strain which the sample deforms by stretching and becoming longer. Usually the percent elongation is calculated, which is just the length of the polymer sample after it is stretched (L), divided by the original length of the sample (L0), and then multiplied by 100.
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After I set up the Pre-meshed Crack, I add the SMART. It shows two options are yellow. One is initial crack, and the other is critical rate. In the initial crack option, i can select the Pre-Mashed Crack, but it's still yellow, which means here has error.
Question:
What the reason would cause this issues?
What initial materials properties i should add?
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Does your mesh contain hex elements? SMART only works with tet meshes.
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I have a skull fracture CT scan dataset, consisting of fracture or normal cases. My question is: Let's say patient-1 has a skull fracture, and his CT scan has 300 Dicom slices. Now should I label every Dicom slice of his CT scan as fractured when I feed these 300 slices into a CNN?
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Paolo Tripicchio I have one more question. If I use every slice as a single input, it has to contain a depth. But all of my DICOM series do not have the same depth. One patient has 300 slices and some other patient has 30 slices. So, how I am supposed to tackle this depth problem when I feed these into a 3d convnet?
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Geophysical model for
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I believe you can investigate Karst and fractured water using TEM and DC methods
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Dear all,
I am looking for a research work that implemented an uncertainty or statistical framework to study the impact of the geometric parameters on the fracture response.
I appreciate any help.
Thank you in advance,
Moj Ab
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Hello. Other than that, I have a question about the johnson-cook damage model. As far as I know, the johnson-cook damage model in Abaqus software is a model that can define damage initiation strain. (attached image: εi=the plastic strain at damage initiation) By the way, why is the "fracture strain" value necessary to obtain the parameters D1, D2, D3.... required for this model? I mean, I thought it might be right to use the strain at the point where the damage initiate, not a fracture strain.
(I accidentally found a very good channel that summarizes the johnson-cook damage model, and in this channel, parameters are obtained through "fracture strain and triaxiality":https://www.youtube.com/watch?v=awpkDOtH6V4&t=1s) Thank you for your reply.
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Dear Junyoung,
Assuming the strain where damage initiates will not be of concern of it is below the fracture strain and hence, definition of damage would be meaningless. Please refer to the following:
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As the title says, I am trying to learn more about fracture analysis and how cracks propagate through brittle materials. Does anyone have any good recommendations on books or other learning material?
Thanks in advance.
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Is there any material /research regarding rail fracture during winter season or due to temperature variations of morning and night which cause contraction .
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Thank you sir akula and Chen ding
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Induced Hydraulic Fracturing by Water-Flooding:
Whether the ‘fracture toughness’
of a consolidated reservoir-formation
@ the beginning of oil production by primary depletion;
and
@ the beginning of water-flooding
would remain the same?
If yes,
how exactly to capture
the spatial and temporal distribution of
break-down pressures?
If not,
Will it be feasible
to capture the various zones
(elastic-zone; transition-zone; plastic-zone)
of an evolving crack
at the fields-scale?
Also, how exactly,
to segregate
the fraction of fluid leak-off
from the walls of the growing fracture
from
that of the flow through the crack?
As the ‘fracture density’
keeps increasing with time
with continuous fluid injection,
whether
the fluid flow regime
will get shifted
from
‘flow through rock-matrix’
to
‘flow through network of fractures’ (still maintain single continuum)?
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It depends on the elastic limit, depletion/injection will reduce and increase the pressure wherein effective stress will increase or reduce in comparison elastic limit, if its below yield limit, expect less change, if its failed, behaviour of the failed material will be different that off intact rock.
On the Leak Off Part: Minifrac-Fall off before main job and falloff after the main job may indicate the different leak off in the system such as Normal (induced frac leak), PDL (pressure dependent secondary frac leak), HR (vertical growth). Fluid properties and rates can be optimized to improve the HF job.
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Has anyone modeled aortic valve calcium plaque crack/failure/fracture? What crack model works the best? Can you also guide me to a good resource where I can find reliable fracture parameters? TIA
Note: I am looking into the 'concrete smeared cracking model', 'concrete damaged plasticity model', and also ductile fracture models. The issue is I have not found any reliable source clearly stating the material property/ a range of property (since calcium deposit material property can vary based on age and some other hemodynamic factors). So I am unable to test out those models.
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Hi everyone,
I'd like to inquire about the best method for monitoring the water level of a borehole with a depth of up to 400 meters. Although the depth of the boundary is unknown, it is assumed to be fractured diorite (upper) and diorite bedrock (lower). I've read about open standpipes and vibrating wire piezometers, but I'm concerned about their long-term reliability. It would be fantastic if you could contribute your practical ideas and opinions. I am open to ideas and eager to learn more from you. Thank you sincerely!
Best regards,
Raymond
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Hi Raymond,
400m is challenging but should work.
a pressure level sensor should work, if they are able to manufacture a 400m gauge wire.
I’ve worked a lot with these devices and they are quite durable. You can set up them for automatic monitoring. If you need a high failure safety, you can setup them in a array of 2 or 3.
if you are looking for manual monitoring devices, a contact gauge is a easy to use tool.
There are some other methods, like pneumatic level monitoring but I have no practical experience in terms of durability.
the diameter of the borehole should be at least 100mm with smooth edges.
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tensile stress-strain behavior reported for fibers in Figure attached, what do you
expect to occur first in a MMC which uses these fibers: fracture of fibers before yield
of the matrix, or vice versa? I'm looking for a answer for my PhD project.
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Dear sir
Boran , Carbon HM, Carbon HS, SiC are more britle among the fibers shown in the graph, they fail first
Generally fibers break after the matrix failure, to decide , which will fail first, it dependes on properties fiber and resin.
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For Fracture Experts, Is there any paper that observes and identifies width details of the mechanical fracture closure and hydraulic fracture closure based on Observation and Measurements?
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You can find good petrophysical articles in this field that have interpreted and analyzed fractures in detail. I suggest you one of my articles.
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Stress-Strain curve for steel specimen need to be investigated
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Anis Hamza Thanks alot sir
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Conceptual modeling of a Fractured Reservoir: Where are we heading towards?
1. Is it possible to secure the actual three-dimensional (and NOT the two-dimensional areal features - in the absence of ‘hydraulic-connectivity with the ensured connected paths of least resistance’) data on fracture attributes such as fracture-density, fracture-length, fracture-width, fracture-spacing and fracture-dip from a real field scenario?
2. If it is feasible, what would be the ‘scale’ at which, these details (fracture attributes) could be expected?
3. If the associated scale of the deduced fracture attributes remains much greater than macroscopic-scale, then, will it be feasible for us to deduce a reasonable REV (associated with the fractured rock reservoir) in order to consider the associated parameters/variables that will probably vary smooth and continuous so that the conventional calculus could be applied with ease? For such conceptual models, whether, stochastics (or the fractals) is ‘the only means’ to characterize the reservoir heterogeneity?
4. In fractured reservoirs, to what extent, the conventional hydro-static pressure and gravity would decide the resultant draining of oil – at the relatively later stage of the production cycle? Also, during the early-phase, whether the expansive force of the gas associated with the oil – will any more remain - the principle source of propulsive energy? Even, if it is so, do we really have a control over the expansion of gas – within the high permeable fracture - which will mitigate the velocity of oil; and in turn, which will try to suppress the frictional resistance? [Assuming that the velocity of oil within the high-permeable fracture cannot be so slow; and subsequently, the relatively higher oil velocity may not allow the gas to flow more rapid – unlike, as observed in conventional sandstone reservoirs.]
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Dear Suresh Kumar Govindarajan, your question is very multifaceted to answer, I will try just only a geophysical ("seismic") point of view to help you, in focus points 1 and 2.
It is usual that fractured reservoirs are heterogeneous at different scales (length, width, density, spacing, dip) in a real scenario. Even with millions of grid blocks, numerical models may not be able to exactly simulating the pressure transient performance of continuously and discretely NFRs (Natural Fracture Reservoirs) containing variable conductivity fractures. Following the first question that you invite to support, “…Is it possible to secure the actual three-dimensional and NOT the two-dimensional…” such as geophysicist, 3D seismic tools are the only ones to illuminate in real THREE-D the fracture systems and estimate these attributes, such as length, width, density, spacing. In three-dimensional 3D reflection seismic surveying, the sound detectors are spread out over an area and the sound source is moved from location to location through the area, to generate a subsequent volume of common depth point stacked reflections.
Also, it is critical to understand the vertical and lateral resolution of 3D seismic, a function of the design, acquisition, processing, and interpretation, on one side, and the depth and natural geological conditions that your study case has. Therefore, the seismic resolution is the real boundary or edge to understand the fracture properties in a real scenario in an oil and gas field.
An acoustic or elastic fracture model derived from seismic is useful but limited. Limited by seismic resolution, both, vertical and lateral, it means, the ability to identify individual peaks on a seismic trace with the top and base of geological unit or bed, or to see fine-scale features in map view. Both kinds of resolution are based on local velocity near the feature of interest and frequency content of the seismic wavelength. Also, remember that seismic data always contains noise as well as signal, the signal-to-noise ratio describes how strong the signal is relative to the random noise.
Fracture density, relative fracture density, for example, has been reported to give a good amplitude signature by dimming over areas of increased fracturing, and in 3D seismic, it may be possible to map this amplitude behavior and identify fracture trends. Also, complex-trace seismic attributes, geometric-interpreters-dependent are useful to illuminate the fracture systems: coherence volume, amplitude extraction, spectral decomposition, curvature, instantaneous-frequency, and a battery of composite combinations. But remember: the seismic interpretation of geological detail simply was unjustified by the resolution of the seismic data; you must understand the limitations of the seismic data to avoid pitfalls. Once a reservoir-characterization problem is identified, fracture characterization, in this case, we geoscientists should be able to select and combine attributes that can better delineate features of interest, choosing only attributes sensitive to the geological problem to be tested.
Let me share this excellent paper: “Fractured reservoir modeling and interpretation”, by Kuchuk, Biryukov, and Fitzpatrick, International Petroleum Technology Conference, Malaysia, 10-12, December 2014.
Best regards, Mario E. Sigismondi
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I have a rather simple geometry consisting of a single lap joint of two sheets, to which I added some pins to increase the strength to fracture.
I initially made the parts in Solidworks and them exported them in a step file.
The problem now is that, every time I try to partition the parts to make them meshable, Abaqus takes hours to do so, or it just closes after some time.
Has anyone encountered similar problems?
I dont know if it is related to my geometry, the type of export file from solidworks, abaqus, etc...
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It depends on the type of geometry.
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Hello everyone,
Hope you are doing great.
I am using coupled temperature-displacement step and coupled temperature-displacement elements as well. I need to use UMAT to model plasticity behavior and fracture. In every run I do, It takes 5-10 days to finish the simulation. I don't know if this is normal for my case study or something is missing?
Usually, I run my job by writing these lines:
---------------------------------------------------------------
abaqus job=xxx.inp user=yyy.for cpus=12 standard_parallel=solver int
OR
abaqus job=xxx.inp user=yyy.for cpus=12
---------------------------------------------------------------
Another thing I'm not sure about is my step setting, which is as follow:
---------------------------------------------------------------
*Step, name=Step-1, nlgeom=NO, extrapolation=NO, inc=1000000, unsymm=NO
*Coupled Temperature-displacement, creep=none, steady state
0.002, 1, 1e-10, 0.002
*Solution Technique, type=SEPARATED
*Controls, reset
*Controls, parameters=time incrementation
5000, 5000, 5000, 5000, 5000, 5000, , , , ,
--------------------------------------------------------------
I appreciate any help you can provide.
Mojtaba Ab
#Abaqus #fem #FE_Analysis #FEM_Simulation #Plasticity #Fracture #Elastic #Simulation
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Abaqus has two different option in order to make you simulation faster.
1- use multiple processors which you currently use
2- use GPGPU acceleration , which uses the GPU (For example CUDA Core in Nvidia Graphic)
I suggest you if its possible and If you have PC with high GPU core , run your model with GPU.
In Abaqus Job Manager this option is available.
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Getting enough information from SEM (scanning electron microscope) is interesting but challenging. I am looking for a document, video, website or something to learn how to interpret the mechanical behavior of metals and metallic composites through SEM results taken from the fractured specimens.
Very appreciated!
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Google "fractographic analysis", "fractography" and "fractographic analysis of metals".
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Yes, it depends on the location of the fracture. Nice article. A good read
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Hello
I want to use ductile damage model in abaqus to simulate the deep drawing of square part. To reach this goal i need to enter values of stress triaxiality and fracture strain during the deep drwing process. I know stress triaxiality = -P/Q wich (P=-1/3(S1+S2+S3)) and Q= von mises equivalent stress. But i don't know how to get the values of the principale stresses and fracture strain experimentally
I get also the values of (S1,S2,S3,von mises) from ODB field output and calculated the stress triaxiality but i don't know if the results are good or not.
Could you help me please?
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Hi,
You can mount a strain gauge on your part. Each set of measurements give you three values. Then the rest of the stress tensor components can be found using the equilibrium equations. When you have all the stress components, you would be able to calculate principal stresses.
Good luck
Farzad
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wants to know the interpretation of fracture surface,
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Hi Sandeep .. I see voids and elongated filaments. It looks like a ductile damage leading to fracture. Damage mirros in the creation of voids, that then grow up till the stress is concentrated in the narrow portion of the undamaged material. This may have caused the strethcing ot the filaments till rupture.
I don't see trace of fibers, but I suspect that this material does not have fibers. It looks to me like a polymer, not reinforced and not a metal. How did this fracture occur?
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plzz guide me regarding my thesis work how to assess stability of microplates and miniplates in midface fractures.
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If you have before and after CBCT scans for surgical purposes, that those can be used to superimpose on the cranial base to identify the movement of any other structures including the fixation plates.
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What are the different replica-making methods available to study the fractured surfaces of worn materials, thread screws, intricate crevices, etc.?
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The classical method is by using silicone-based impression materials made for the casting industry and in dentistry. Together with the production of a positive replica from sort of resin (e.g., epoxy), the combination of materials renders surface detail on the order of 100 nanometers. Addition-cured silicone materials are better at this than condensation-cured materials. We did a study loooonnnngggg ago on this: Bromage TG. Systematic inquiry in tests of negative/positive replica combinations for SEM. Journal of Microscopy 137: 209-216, 1985.
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hello everyone,
i am working on simulating the cracking initiation and propagation using 2D XFEM by ABAQUS using monotonic and repeated loading.
I did two experimental test, fracture test for semi circular asphalt samples under three point load by using constant loading rate of 50/min, i got the load and displacement for test,
the second test, repeated load test by using low load cycle of 15% of fracture load, i got the load, displacement, and horizontal displacement for the SCB sample, the pic of samples and date are attached.
thank you for your time
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Thank you for your answer, already i had used power law and fractional time-dependent viscoelatic element to convert the creep data into relaxation modulus data. After that i have evaluate the data using abaqus.
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Hello all
thanks alot for your support
I got up with a doubt , for simulation normally we use ansys or abacus of tensile testing . But when it come to polymers tensile testing which software need to be used. as the infill pattern will change the effect of fracture , what software we need to use for simulating tensile testing of specimen's. if we go with ansys the dog bone will be treated as simple structure but not infill parameters. can some one clarify my doubt please
need software suggestion to do testing simulation.
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i recommend MSC marc, in nonlinear FEM moddule
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GOR Variation in Fractured Carbonate Reservoir: Different from a sandstone reservoir?
Whether the following statements associated with a sandstone reservoir – will also remain true for a fractured carbonate reservoir?
(A) The gas expels oil from the reservoir formation by means of (a) gas carrying oil with it due to its velocity; and (b) gas driving the oil ahead of an expanding volume of gas.
(B) Since the reservoir pressure gets reduced by the earlier completions, the amount of gas required to expel the same quantity of oil would remain greater; and in turn, the enhanced initial GOR for later completions would result only from the drainage of pressure by the earlier wells.
(C) When the gas acts as the only force that expels the oil from the reservoir-formation, then, the rate of decline of oil production would remain faster than the rate of decline of gas production. Also, an enhanced rate of increase of GOR will always have the greatest decline of oil production.
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I think these papers could help you;
  1. Brine-Dependent Recovery Processes in Carbonate and Sandstone Petroleum Reservoirs: Review of Laboratory-Field Studies, Interfacial Mechanisms and Modeling Attempts, Adedapo Awolayo, Hemanta Sarma, Long Nghiem, November 2018, Energies.
  2. The Geological Characteristics of Reservoirs and Major Controlling Factors of Hydrocarbon Accumulation in the Ordovician of Tazhong Area, Tarim Basin, Haijun Yang, Guangyou Zhu, Yu Wang, Jin Su and Baotao Zhang, June 2014, Energy Exploration & Exploitation.
  3. Major influencing factors of water flooding in abnormally high-pressure carbonate reservoir, Hou Qingying, Chen Kaiyuan, Fan Zifei, Fu Libing, Chen Yefei, January 2017, IOP Conference Series Earth and Environmental Science.
They're available on the ResearchGate Server for download.
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Hydraulic Fracturing Whether mobility and diffusivity will get influenced
if the viscosity of the injected fluid
remains significantly different
from that of the pore-fluid
in the reservoir?
And in turn,
would influence ‘fracture toughness’ and ‘strain modulus’?
If so, fracture toughness can be assumed to be insignificant?
When the crack keeps propagating
within the reservoir formation,
how exactly to define the fluid flow regime
within the crack:
As an Elliptic PDE
because of the closure by the fracture tip
(depending only on the fracture surface boundary values and remaining time-independent)
or
as a parabolic PDE
by assuming a connected fracture network
(with time-dependency as well)?
As the fracture density keeps increasing with time,
whether the fluid storage within the fracture
will still remain negligible
in comparison
with that of
the volume of the fluid injected?
Apart from far-field stress and pore-pressure;
whether viscosity, mobility, diffusivity, elastic modulus and the fluid injection rate - can be considered (approximated)
to be a constant?
Can the fluid flow in a crack
be described
using Reynolds lubrication equation,
when the crack remains closed at its tip
(with zero fracture aperture thickness at a point along its flow direction)?
Can we simply approximate it using a Neumann type boundary condition - by
assuming that the fluid flux gets vanished @ the crack tip)?
Whether application of superposition of elastic dislocations
using singular integral equation
remain valid
for a crack with warped (undulated or zig-zag) fracture surfaces?
In the absence of asymmetry,
can we deduce elastic kernel?
Will it be feasible to deduce
the reduction in pore-pressure loss
resulting from the fluid leak-off (from the crack) -
from that of the additional pore-pressure
induced from the generated cracks –
following the distribution of
initial pore-pressure
at early times?
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You can assume the lubrication theory is valid and the flow is driven by a 2D pressure gradient. Then you solve the equations for volumetric rate and check if this model is valid for your case.
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please,every expert:
I am a new hand, i met a problem like this: my freeze dry powder column will be splited through middle like Seismic fracture whatever i try to adjust the temperature or pressure or time of freeze dry process.
help !
thanks
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Hello. I am new to Researchgate and am enjoying having access to many areas of interest as well as being relevant to my work.
When you test the product (residual moisture content, potency, other critical criteria for example) what results do you get? Are the results satisfactory or not satisfactory?
One of the freeze dried products that I am aware of has a similar situation. It affects a different number of vials each run and the locations are random and occurs regardless of which of the various freeze dryers are used. The cracks go from top to bottom for the product in the vials where this occurs.
The freeze-dried plug/cake has one of two appearances: It either has the crack from top to bottom but the edge of the plug/cake is in contact with the vial edge OR the product has no cracks but the edge of the plug/cake has come away from the sides of the vial.
Vials with cracked plugs/cakes were tested and the product has been found to pass all the tests. After satisfying stability study testing the criteria for the product now takes the cracked plug/cake visual appearance as being acceptable.
Attempts were made at trying to eliminate the cracked plug/cakes but with no success.
There have been presentations I have attended where the presenters have said that maybe too much time is spent looking at issues that are not really issues. In the case of the product I am aware of, the cracked plug/cakes pass all testing criteria and the visual appearance has been listed as acceptable.
One explanation provided was that as the product continues through the freeze drying process the resistance to vapour flow increases and this can result in the pressure being released through the generation of cracks that occur or by the sides of the plug/cake coming away from the vial wall. (like a tug of war between the plug/cake and the vial wall, with the vial wall winning some and the plug/cake winning some)
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I am trying to simulate the Charpy test using Abaqus, could someone specify the boundary conditions that should be taken and which model should be followed.
Should I use the Johnson Cook's model?
How much time can the simulation take on a 4 core laptop?
I tried reducing the meshing to reduce the simulation time, what effect will it have on the results?
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Dear pearl
it is better to used ANSYS LSDYNA or ANSYS AUTODYN instead of ANSYS.
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Purpose is to carry out SEM analysis of PEEK.
For how long the PEEK samples (thickness 3-4 mm) be immersed in liquid nitrogen to carry out cryogenic fracture?
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You just have to keep it in the nitrogen until no more bubbles are formed. When there is no more evaporation the two materials are more or less at thermal equilibrium and you can break your sample.
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I have two materials, aluminum and steel, that I am simulating impact on. Both have the exact same material models:
  • J-C plasticity and damage
  • EOS
  • Specific heat and inelastic heat fraction
  • Damage Evolution via fracture energy, set to zero for both materials
  • Same velocity
  • Same contact parameters (Hard contact, frictionless, general contact)
  • Element deletion is on for both materials
I get a shear plug formation for aluminum (top image), which agrees with my experiments. But somehow for the steel material, the projectile penetrates through the target material (bottom image).
Even if the response isn't via shear plugging, why is the projectile mesh penetrating the target nodes? I would think the material immediately fractures to form a plug anyway if my fracture energy is set to zero.
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Zherui Martinez-Guo I see. I am not sure about the objective. however, If the impactor and the plate have similar Young's modulus, try to change the plug stiffness to a higher value. it may be conducive for the rigid-flexible body contact algorithm.
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Dear.
I have an issue with my simulation on ABAQUS. I simulate a crack in a composite laminate [0/45/0] using cohesive surfaces. The crack is therefore explicitely modeled using a traction-separation law and a Benzeggagh-Kenane progressif damage criterion.
My issue appears when ABAQUS calculates the quadratic stress criterion. Indeed, when I calculate manually the criterion using CPRESS and CSHEAR or S12 and S22, I find the right value. However at the nodes before last in the thickness (cf figure), the criterion is over-evaluated by 7%. It leads to the beginning of damage at these nodes instead of the center of the ply.
My questions are :
Why the value is not right only at theses nodes ?
How the quadratic criterion is calculated (which variables are considered) ?
How to fix this problem ?
Thanks.
PS : The figure shows only the 45° ply and the fracture surface as soon as quad criterion meets 1.
PS2 : Periodic conditions are applied around the cell, Surface-to-surface discretization, thinner meshes show the same issue at the before last nodes.
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i part from fine meshing you need to look at the values of stiffness i.e. knn, kss, ktt. these values are usually high then default values taken by abaqus. you can manually put these values using E/t...where E is modulus and t is adjacent thickness. for typical epoxy the values may range from 10^12 to 10^15 or greater. this may increase your computational time too.
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Looking for some reference to understand or learn numerical modeling for compressible fluids (such as crude oil) - flow through the fracture or space between parallel plates. Thank you.
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non to my knowledge
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Hello everyone.
I am modeling a connection that according to the sections and materials in the numerical model of the article and in the experimental model, bolts fractured. But in the model I made, the bolts increase in length and do not depict fracturing. What adjustments should I make to see the bolts fracturing in Abacus?
I guess bolt property is wrong.
please teach me to correct.
and question else is that diameter of the bolt shank is 21 cm. Do I have to make the hole diameter of the connecting plates 21 cm or 22 cm?
thanks in advance.
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Could you explain which failure model has been used in your simulation? As far as I know, if no mechanical failure or damage is imposed on your material properties, you must expect that the deformation will continue forever without any fracture.
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Hi all,
I'm interested in testing the Hydrogen Embrittlement of several metals. I
Interms of fracture testing and fatigue crack growth rate testing I want to know the difference between the following.
1. Long time H2 exposure in an environmental chamber -> conducting tests in ambient enviroment.
2. Long time H2 exposure in an environmental chamber -> conducting tests in a H2 exposed environment.
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In simple terms, the difference between those two conditions is whether or not the environment during testing is allowing the hydrogen to escape from the metal. After removal from a hydrogen environment, most metals will start to lose their hydrogen content, as the hydrogen atoms diffuse out of the material and recombine to escape as hydrogen gas. The rate of this loss depends on the material (particularly characteristics like diffusivity and solubility of hydrogen); a material like a ferritic steel may lose enough hydrogen content within the order of minutes that mechanical tests will no longer show an effect of hydrogen while an austenitic steel may take days to lose enough to no longer show an effect. Testing in a hydrogen environment removes (or at least reduces, depending on pressure) the driving force for the hydrogen to leave the sample.
So, which test conditions you want to use depends on the material being tested and the length of the test. If the hydrogen content loss in on the order of minutes, by the time the sample is removed from the environment, the test is set-up, and then run, it is unlikely that the results will show any effect of hydrogen. If the hydrogen content loss is on the order of days, then shorter tests (tensile, fracture toughness) can probably be run before losing too much hydrogen, but fatigue crack growth rate tests, which can take months, will show a decreasing effect of hydrogen as the test continues.
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Hey everyone,
Which plasticity model is suitable for modeling 316L selective laser melted steel in miso and micro scale modelling? Is isotropic hardening is good for this type of materials? (I want to model the fracture in melt pools )
Thank you.
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Dear Mojtaba Abdolkhani,
It is preferable to use a modulus of plasticity in the simulation of samples made by selective laser melting of 316L in a vase. This way, the simulation results will be closer to your experimental data. The use of foreign data will lead to deviations, which you will then have to specify with correction parameters. The connections obtained from the laser fusion have a strong influence on the mechanical characteristics and plasticity of the obtained products. Therefore, make standard test specimens by selectively melting the 316L. The obtained data, plasticity model and reinforcement curves are included in the simulation.
Wishing you success in your research.
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Is there any method to find the life estimation of the brittle material with crack?
The question may wrong, as brittle material will fail once its fracture. But is there any method to how long the material will sustain with crack?
Also, these are possible with XFEM crack growth simulation results?
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Dear Mathusuthanan:
In principle, if you are dealing with a structure made of a truly brittle material under a constant applied tensile load in an inert environment as low homologous temperatures, it will fail instantaneously if the stress intensity developed ahead of the crack exceeds the fracture toughness, KIc or Kc, i.e., if the local stress is sufficient to break an atomic bond at the crack tip. If the stress intensity is less than the fracture toughness, the structure in principle will never fail.
However, there are processes - primarily subcritical cracking processes - which permit crack advance at stress intensities less than this critical fracture toughness. It is these processes that determine the (damage-tolerant) life of a structure, which you can estimate in terms of measurements of the crack velocity as a function of the stress intensity (so-called v-K curves). These subcritical cracking processes include environmentally-assisted cracking (e.g., stress-corrosion and hydrogen-assisted cracking), creep crack growth and most importantly fatigue-crack growth (and of course combinations of these processes such as corrosion fatigue and creep-fatigue).
The question that you are actually asking is whether any of these processes can occur in a truly brittle material as again, in principle, the vast majority of these subcritical cracking processes rely on the existence of some degree of plasticity.
The answer to your question is therefore that you first need:
(i) to identify the subcritical cracking process(es) in your material that could extend any pre-existing crack to a length where K = KIc or Kc,
and then
(ii) determine the v-K curve in terms of rate of growth of such cracks as a function of the stress intensity (or stress intensity range if you're under cyclic loads) to enable the determination of how long that it will take before catastrophic failure can occur.
Admittedly, brittle materials are more likely to simply fracture once the stress intensity exceeds the critical value, but some subcritical cracking processes need to be considered. Environmentally-assisted cracking, especially involving hydrogen, is one such mechanism that can dramatically lower the toughness of most materials, including brittle ones. Creep-crack growth is less likely in a prototypical brittle material unless you're at a temperature on the order of at least half the melting temperature. However, although metal fatigue is promoted by local plasticity, such that brittle materials are far less susceptible, toughened ceramics can be prone to fatigue failure by a very different mechanism involving the cyclic degradation of (extrinsic) toughening mechanisms behind the crack tip. I don't believe that this is too pertinent to your problem if you're dealing with a purely brittle material, but if you're interested, the attached paper may provide some guidance.
ROR
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A code describes the capacity of a structural member. The capacity is the threshold of fracture. We found that the capacity is the sole property of the member and therefore is independent of the force? A relation of the following form is proposed.
M/Mo+P/Po+...=<PS(Lambda)
M, P, ... are the applied load
Mo, Po, ... are section capacities
PS(Lambda) = Persian (Shiraz) curve which is an explicit function of the relative slenderness ratio (Lambda).
The proposed interaction equation may be used for design of members of various materials, any section shape, in any temperature , and etc.
Do you agree with the above proposition?
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This seems to be a simple interaction between moment and normal force in a cross-section of a beam. However, for the perfectly plasti