hi, I have a 2D model costituited by elastomer (rectangular block) that sliding on rigid (square) pyramidal substrate; how can i estimate effective contact area of elastomer? Thus, question are: is there a way to solve the contact problem without calculate the pressure field at the coontact interface? Hello, Remi! Good luck I am modeling a transient contact problem using the penalty method instead of the augmented Lagrangian method. Hello Remi, Please someone answer me and correct the error, i'm new of software. The rigid part should be the source in the Contact Pair. The ramping of this parameter will be defined within the study settings. COMSOL document says "A contact pair is a pair that define boundaries where the parts may come into contact but cannot penetrate each other under deformation for modeling of structural contact and multiphysics contact." But there is penetration. if yes, start with very fine indentation and make your steps reseanably small. If you cannot estimate the contact pressure before the solution, you may need to do the analysis in two passes, where you first compute an estimate of the contact pressure using the Penalty formulation. problem with contact pair-penalty factor setting. Note that while COMSOL employees may participate in the discussion forum, COMSOL software users who are on-subscription should submit their questions via the Support Center for a more comprehensive response from the Technical Support team. and similarly in any other directions that need to be restrained. I mean that you can solve any kind of multiphysic problem. The first part (solid.Eequ/solid.hmin_dst) is a geometry/material part of the same form as the E/k expression you mentioned that is automated to get good estimates for E and k. The material stiffness Solid.Eequ is automatically calculated based on the material of the destination surface, and the minimum element size solid.hmin_dst is automatically calculated also from the destination surface. Introduce a new Global Parameter (name it, for example: RampFactor ) and multiply all loads, displacements, and stiffnesses by this factor. thank you previously, Hi, Structural contact modeling is a highly non-linear problem. Thank you for the response. Contact problems with friction should always be solved incrementally using a parametric or time dependent solver since the development of friction forces is history dependent. In some cases, this approach can result in faster computations and provide smoother convergence when compared to the Augmented Lagrangian method. By using Matlab a "perturbed" geometry is generated, by using a morphing mesh approach. In the augmented Lagrangian method, the expression of "pn" is "E_smsld/hmin_cp1_smsld*min(1e-3*5^auglagiter,1)". COMSOL document says The Penalty method is relatively less accurate, but more robust and will require less solver tuning, making it preferable for multiphysics problems and time-dependent models. Hi Pasquale 3. solve the problem with the time-dependent solver. [QUOTE] I have a model that contains an elastic beam that when deflected comes in contact with two different hyperelastic materials one on each side. If you anticipate contact between any sharp corners and surfaces in the model, you should modify the geometry such that the sharp corner is replaced with a rounded boundary, a fillet. Adjust it to linear. When using the augmented Lagrangian formulation there is a Penalty Factor that controls how hard the interface surface is during the iterations, but does not directly affect the converged results. Most contact models will require some changes to the default model settings to solve efficiently. To start a new discussion with a link back to this one, click here. Modeling friction is will often increase the computation time significantly, so if you can reasonably ignore friction, do so. I'd like to solve the contact problem without calculating the pressure at contact pair interface (I have disabled the augmented lagrangian solver). This should not be changed. 1- what do you call solver manager? Hoping this help, regards. The higher the penalty factor the less the overlap between the surfaces (and hence more accurate solution) yet the more ill-conditioned the stiffness matrix will be. I had a problem in fixing the contact parameters of my model that contains a contact between a hyperelastic material and an elastic material. Structural Mechanics To use such a method in COMSOL you just need to replace the Contact normal penalty factor expression in the contact pair by the following expression : k/h Also, the contact pressure penalty factor in penalty method is interpreted as the stiffness of a distributed spring connecting two contact boundaries. Prodotti consigliati Scarica i file del modello It works well. The Structural Mechanics Module User's Guide > Structural Mechanics Modeling > Contact Modeling section. This contact algorithm is based on the penalty factor formulation related to the penetration of the solid parts in contact. Hi Kevin, Thanks : "perturbed" parts are like-real parts which may come from forming processes and are used in automobile applications. 0.3 N) at least. If one part is significantly stiffer than the others, its deflections will be relatively negligible, and it can often be considered as rigid. Happy Birthday, Ellen Swallow Richards. I have set the stiffness value equal to the young's modulus (I have assumed an isotropic elastic material). It is hard to think about your problem without seeing the model. The slate grey sky was turning to a menacing black as the light rain turned into a pelting hail. The ramping of spring constants used for spring foundations on unconstrained domains should begin at the peak value of spring stiffness and then down to zero. Marjan. Good luck, Within the Contact feature, select either the augmented Lagrangian or Penalty as the Contact Pressure Method. [67] have verified the static contact Hertz model in COMSOL Multiphysics for the case of half gold cylinder sitting on a steel block . Sat in the stand at Turf Moor (Burnley FC) watching a Premiership football match on a freezing December afternoon. There adjust discritization to quadratic. The peak value of spring stiffness, k0, should be chosen such that the displacement due to the full applied load is about equal to the element size of the contacting boundaries. You will then see that the higher k the lower the penetration between the two elastic material, but also the lower k the smoother the convergence As surfaces come in and out of contact, load paths and stress states will abruptly change. Dear Comsol users, I noticed that for decohesive settings tag, there is a parameter called shape factor when multi-linear seperation is selected. As surfaces come in and out of contact, load paths and stress states will abruptly change. There are three contact constraint enforcement methods available in Abaqus/Standard : The direct method attempts to strictly enforce a given pressure-overclosure behavior per constraint, without approximation or use of augmentation iterations. When spring foundations and applied loads are in a single model, the applied loads should be ramped up linearly at the same time as the spring constants for the spring foundations are ramped down nonlinearly using the above expression, and shown in the plot below. I will test as soon this procedure on a 3D model and I will update you about results. Veryst Engineering, Dear Nagi, Discussion Closed This discussion was created more than 6 months ago and has been closed. This is described very nicely in the Structural Mechanics User's Guide. May be it is just because visualize problem, but it looks like two domains penetrate each other. Any help would be greatly appreciated! Thank you, This article contains guidance for solving models that include structural contact, and the procedures that should be followed to achieve a converged solution. I found no convergence issue without contact problem. Kindly, find attached two models of my work. The default Penalty Factor contains two preset tuning options: Stability(default) or Speed. If the parts have a similar stiffness, set concave parts as source and convex parts as destination. MEMS & Nanotechnology, Piezoelectric Devices, Geometry, Modeling Tools & Definitions, Structural Mechanics, Understanding the Different Elements of Gear Modeling, Analyzing Reverse Electrodialysis Units with Multiphysics Modeling. For example, the screenshot below shows RampFactor starting at a value of 0.001 and then increasing from 0.1 to 1 in increments of 0.1. Thanks again :). "A contact pair is a pair that define boundaries where the parts may come into contact but cannot penetrate each other under deformation for modeling of structural contact and multiphysics contact." Nagi Elabbasi Remi Magnard. it is a tactile sensor in contact with silicone rubber ( artificial tissue). Finally deselect the augmented lagrangian solver option in the solver parameters (stationary page). Finally deselect the augmented lagrangian solver option in the solver parameters (stationary page). Also, the contact pressure penalty factor in penalty method is interpreted as the stiffness of a distributed spring connecting two contact boundaries. Hi dear Sungho, what is the reason for that? Using a penalty function for contact problem is good alternative of the augmented Lagrangian method available in the structural mechanics module. Thanks again All the best, If the initial overlap is too much convergence may be a problem, but you have them initially forming a line contact which is fine. Are you checking the box of creat creat pair at the end of Geometry? Also, I need to have the solution up to 5N loading, which means according to the model that I upload I have either to extend the para up to 5, or to replace the loading boundary condition in y axis with (- (16.67/568)*para) [N/mm^2]. The information provided may be out of date. [QUOTE] i attach my file, where i wrong? As long as your mesh is not moving, use extension instead of parametric sweep. In the help file, it said:"Note that in the augmented Lagrangian method, the value of the penalty factor does not affect the accuracy of the final solutin, like it does in the penalty method". In your application you can do this just by observing that the model has a symmetric wrt the middle plane (have a look to the attached modified model). When I choose the penalty factor as E/k (I know elastic modulus and I get average mesh size from statics), the result is so strange. Thanks for the interests and help. . Penalty contact adds stiff springs (penalty factor) between the contacting surfaces that are only active when the surfaces overlap. Your internet explorer is in compatibility mode and may not be displaying the website correctly. Reading about contact, I implemented the penalty formulation found in the model "Contact Analysis of a Snap Hook Using a Penalty Formulation". Setting contact pair, meshing and solver setting looks fine, but why convergence strat oscillation up to very high value or down low finally not converge with current setting up??? I also am trying to simulate contact between stent device and blood vessel. She was the first woman to attend, graduate, and teach at MIT. And I tried to apply the penalty method instead of the augmented method but still not working. No matter how I change the contact parameters (i.e. Then remove the contact pressure variable from the solve for list in the solver manager. Many Thanks Ahmad Atieh, hi, The default COMSOL expression in front of Pn has two components. How does COMSOL Multiphysics handle complex-valued numbers and problems in the frequency domain? I would start by examining the error message that COMSOL reports. Nagi Elabbasi We do encourage users modeling contact to be using the latest version of the software, as there have been many algorithmic improvements since these original discussions. It will be great if you can share your experience for this problem. 4. define a parametric solver to fine-tune the load step (use a small parameter-step if the convergence does not appear). Veryst Engineering. Thanks again This contact algorithm is based on the penalty factor formulation related to the penetration of the solid parts in contact. For efficiency, include in each contact pair only those boundaries that have the possibility of coming into contact. Note that while COMSOL employees may participate in the discussion forum, COMSOL software users who are on-subscription should submit their questions via the Support Center for a more comprehensive response from the Technical Support team. and the sensor has a softer silicone rubber in his structure under the beam. The iterative solver will require less memory, but convergence is usually much slower. But there is penetration. listed if standards is not an option). In some cases, this approach can result in faster computations and provide smoother convergence when compared to the Augmented Lagrangian method. I am trying to get what exactly u meant by the order of the discritization and where I can change it. In the contact node under solid mechanics, the expression for penalty factor was not evaluating. If your geometry contains parts that are adjacent to each other, that have mating boundaries, the finalization method should be set to Form Assembly with the Create Pairs of pair type Contact Pair selected. Now my question is And the contact surfaces are defined as contact pairs. If you are solving a time dependent (transient) model, make sure that all prescribed displacements, loads, and stiffnesses of any spring foundations are time-dependent and ramped over a physically reasonable timespans, not just for the solid mechanics physics, but for all other physics that are included if it is a multiphysics model.
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