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mvass

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mvass last won the day on October 14 2019

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About mvass

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  1. Hi all, I would like your opinion for a quassi static analysis I am performing that includes 3d contact between a rectangular plate with a bolt hole fitted, a bushing that will be inserted with an interference fit into the plate's bolt hole and an external load. I am thinking to perform the analysis in two steps: First, calculate the stresses from the interference fit of the bushing (no external load). Second (continued from the first step) apply the external load (can be a force, or a pressure load). The question is: what kind of boundary condition will be applied on the bushing during the second step to "lock" it in place to ensure that the bushing will not move in the vertical plane or exhibit a rotation of some kind? Do we need to apply any BC to the bushing? Thank you for advance for your assistance.
  2. Hello, it has been a number of years since my last question on the ability of optistruct/radioss to tackle problems of glue failure/delamination of composite structures. Then I saw this presentation from 2016: http://mtevs.org/images/MTEVS/Projects/CAE/2016-03%20-%20Forum/Altair%20-%20RADIOSS_Moscow_160311_001a.pdf and the picture from page 22: Does anyone know if the model depicted is available? This is exactly what I was looking for. Thank you for your assistance.
  3. Sure: Optistruct 2018 (student version). I've placed the input file in your dropbox. Thank you.
  4. Hello all. I know there is a very good tutorial on the subject (https://www.youtube.com/watch?v=236ofmwz1X4) however I would like to share my latest experience when comparing stress results obtained from two different solvers i.e. MSC NASTRAN and Optistruct. By default NASTRAN calculates stress using the command: STRESS(PLOT,SORT1,REAL,VONMISES,BILIN)=ALL, meaning that (if you neglect the other terms) a bilinear extrapolation is used to get the stresses from the element's centroid to the nodes. Since optistruct/RADIOSS calculates stress at the element's centroid by default, I supposed that the equivalent command in the .fem input file for optistruct would be: STRESS(SORT1,H3D,REAL,ALL,BILIN) = YES (I have replaced "VONMISES" with "ALL" to have all stresses in my output) and performed two examples of simple static analyses: one with shell elements: the well known hole in plate and another with a bracket meshed with solid elements (4 noded tetras). In both cases the results from MSC NASTRAN and Optistruct were identical, as long as in Hyperview I activated the option "use corner data" (participation of element to the node). Without "corner data" activation the difference in VM stress between NASTRAN and Optistruct for the hole in plate problem was 175 MPa (NASTRAN) to 157 MPa (Optistruct). Now: I performed an analysis of a 3d bolted connection (two plates connected with a 3d bolt) with bolt pretension as a first step and a tensile force acting on the top plate of the connection as the second step. Obviously, this problem involved contact between the plates and the bolt. The analysis converged and the results were correct since I knew from published results (and NASTRAN) that max. stress should be approx. 80 MPa. I received the same results with optistruct, but without the "use corner data" activated, although I have used the command described before for stress. If I activate the corner data in Hyperview, then my stresses almost double in magnitude (156 MPa). So, this contradicts with what I have found with my previous tests (hole in plate and 3d bracket). Does it have to do with the "contact"? Thank you in advance for your reply.
  5. Dear PrasannaK, I had a quick look on your approach. It seems that the contact properties defined need some serious adjustments, because if you run the model as per the updated file, the lower plate performs a large rotating motion. I'll have a further look and let you know, although as mentioned before I think I can solve the problem by: a) creating a "freeze" contact between the two plates and simulating the bolt with 1D beam element connected with RBEs to the bushing and plates.
  6. Dear PrasannaK, thank you for kindly replying to my question. I'll have a look on your file later this afternoon, however I must say that I have made some progress myself yesterday: I had to define a "freeze" contact between the two plates, because the axial movement (slide contact, with friction), was causing the "hot spot" on the bushing that I mentioned in my previous post. I am not however sure if that approach is physically correct. As to the contacts, I count the following: bushing-plate 1, bushing-plate 2, plate 1 - plate 2, bolt - bushing. If you also include the bolt's head, then it is bolt head-bushing, bolt head-plate 1, so yes that makes 6 contact surfaces in total. Let me check your file and I'll contact you again. Thank you for taking the time to check my model!
  7. Dear all, Lately I am having some problems solving a problem that might seem "trivial", however I am still having problems getting some meaningful results. As seen from the files attached, the problem consists of two aluminium plates connected with a steel bolt and a bushing. There is a press fit of 0,2mm (if I remember well) between the bushing and the two plates. The upper plate has one of its sides fixed and a compressive force of 90 kN is acted on the lower plate. Although I have simulated the contact* between all components (plates, bolt, bushing) and ran a quassi static NL analysis, I keep getting extremely high stresses at the area seen on the attached picture. It is probably some mistake with the contact there but I cannot find it. Please have a look on the attached .hm file. There are no contacts defined to allow you to use your own approach to the problem. You can use any of the latest HM versions to setup the problem. Thank you in advance for your kind assistance. *: a number of approaches used: friction, no friction, slide, freeze etc. bolt_coupon.hm
  8. Thank you for your reply. As mentioned in my question, I am aware that Simsolid can show the contact forces between two bodies. Word to developers: Add this, and above all the ability to assign composite layups to parts (including post processing tools) and Simsolid will definitely become the software of choice for many-many companies... Respectfully, mvass
  9. Is it possible to see the stress results due to contact? I've seen that forces (resultant and components) between contacting surfaces can be evaluated, but I haven't seen any options for contact stresses. Thank you.
  10. Answer: The use of "R-trias" elements of the right size does the trick...
  11. Hello all, I would like your expert opinion about the surface mesh I am trying to perform on the curved areas of a simple wing (leading edge). Since I would like to export the mesh for a CFD analysis, I am trying to mesh the surfaces with "trias" elements. However I am not happy with the mesh on the leading edges which exhibit a high curvature. I know the result will be better with "quad" elements, however as I mentioned before I would like "tria" elements on my surfaces. The "surface deviation" option meshed the surface (as per attached example) but with too many elements. Can you please have a look on the attached model (note: HM version 10)? Thank you in advance for your assistance. surface_deviation.bmp elevator.hm
  12. Thank you for your reply. In my study, I am not looking for post buckling and my solution scheme does not include a velocity BC like the example shown. Besides the obvious constraints, the load is exerted on the model via an enforced displacement. In addition, I am not looking on a transient NL analysis. But I guess it wouldn't hurt if I'll try to solve the problem with NLPARM and TSTEP card, provided that it is possible. Should I get something worth to write about, I'll post it here.
  13. Hi, any views on my updates about the problem? Thank you in advance
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