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Found 18 results

  1. Hello All, I'm PG student working for my thesis. I am trying to study the self-loosening behavior of bolted assembly under the effect of transverse excitation. Kindly refer the attached image for reference. looking for guidance for the same as earliest. We have given frictional contact at each contact interface & pretension is applied. BC's applied are "Direct transient (Force Excitation)". The self loosening phenomenon can be understood by monitoring the "Pretension vs time graph" 1. How to generate request for "Pretension vs time graph" ? 2. There are few errors are coming across for transient output request. Is there any sample deck for it ?
  2. Hi ! I have a structure with bolted joints. I have to simulate the strength of the bolt. First I have applied the Pretension Load. Then I have applied the working load to the structure in the next step. My objective is to verify the bolt force is not going above the yield load of the bolt. I tried this with bolt section force, but it is very much equal to the pretension force. No increase in the section force after applying the working load. Is there any other way to investigate the bolts? TIA, Subhu
  3. Hi all, I am exploring the Optistruct pretension manager capabilities instead of preloading the bolts in a "manual" way. Do you know if Optistruct iterates to find the right preload values starting from my input? Example: I need to apply a bolt preload of 20000N. Once applied, I calculate the sum of the gpforces on a section of the bolt and I find the total force to be 18000N. So I have to increase the input preload to 22000N to obtain an actual preload of 20000N. This is because of the elasticity of the components connected. Does Optistruct iterate starting from the input value to find the right preload value? As an additional question, is there a faster way in Hyperview to measure the gpforces on the section of the bolt? It is time-consuming exporting the value to excel to sum them all. Thank and Regards
  4. Hi, While doing a pretension analysis and want to perform loading and unloading analysis with non-linear considerations.Below is how my loadsteps are structured. Loadstep 1 - Pretension SPC NLPARM PRETENSION LOAD Loadstep 2 - LOAD1 SPC LOAD1 NLPARM Subcase Option: CNTNLSUB - (Loadstep1) Loadstep 3 - UNLOAD1 SPC NLPARM Subcase Option: CNTNLSUB - (Loadstep2) With this procedure only Loadstep1 is running and the run gets sopped. I have 2 questions here Q1: Do I have to use STATSUB(PRETENS) along with CNTNLSUB in Loadstep2? Q2: If the above is true then do I also have to use the same STATSUB(PRETENS) in Loadstep3 considering that CNTNLSUB is present? Attached are the snapshots for the Loadsteps. Kindly help.
  5. Hello, 1. I try to simulate a high detailed model of a screw with OptiStruct. Currently the screw will be pretensioned with the pretension function and in the next LoadStep it will be rotated. Now in the following LoadSteps i want to add enforced displacements on the Contact Surface of the screw head. My main problem is the sequence with the enforced displacements. How can every single Loadstep use the results of the previous Loadstep (Stress, Displacement, Contact...)? For the pretension Loadstep i use the function STATSUB(PRETENS), but i dont know if the displacements will be freezed for the next Loadstep and i use CNTNLSUB to consider the contact. 2. The next poblem is, how can i enable/disable contacts between severally LoadSteps without using MODCHG (Older Version of OptiStruct than 14.210)? Thanks!
  6. i am trying to simulate shear failure in bolt in which head of bolt tears off due to shear load. I've used type 13 spring along with a local co-ordinate system and pre-tension curve . What is the best way to capture shear load failure. and what is the best way to apply pretension type 32 or type 13 spring. Should washers be modeled as rigid.?
  7. Hi, Where to apply pretension force in pretension analysis in Optistruct. ? Middle of the bolt or tightening area or thread starting area? Pls find the image rgds, Arul
  8. I have worked before with Pretension analysis and pretension manager on Optistruct. I am obtaining this error at the moment *** ERROR # 3090 *** Normals on the cutting section of PRETENS #20 are not consistent. Do you kow what this means? Thank you!
  9. Hello, I have two square beams in contact. I define master and slave surfaces and impose static friction (mu=0.3) between them with S2S discretization. The loading is pretension through rod elements (modeling a bolt) and I use inertial relief since there are no constraints. I'm using a nonlinear quasi-static solver. I get the following error message. A fatal error has occurred during computations: *** ERROR # 941 *** NON-CONVERGENT NONLINEAR ITERATIONS FOR SUBCASE 1 Suggestions: * Friction or STICK can cause more difficult nonlinear convergence - if feasible try frictionless gap/contact. * This problem has gap elements with friction or stick condition. For more intuitive results and often better convergence, set GAPOFFS on GAPPRM card to AUTO. (This may violate rigid body balance, especially for unsupported ... *** PROGRAM STOPPED: FATAL ERROR(s) ENCOUNTERED. How can I resolve this?I attached the full error message and .out file for your reference. Thanks, Matt Error_Message_Friction_Forum.txt Point_Loading_of_Beams_Reduced_Model_Coarse.out
  10. Dear all, A pretension analysis is usually run before another non-linear analysis, as a first step of the same run. Is there a way to run a pretension analysis (until the end), and then use the results later in a another analysis. So instead of running one after another on the same run, run pretension, then create/run subcases which will reference the pretension results. Basically this becomes usuful if we want to change something in one subcase, then we won't have to run always the pretension step, but just use the results. I hope it makes sense and thank you in advance for your help and valuable time, Elias
  11. Hi, I´m trying to perform a non linear simulation simplifying screws using beams. I need to create a contact between the beam and the plates that are being linked, but I don´t know how to do it. It is necessary tu use a pcontx11? In this case, it is possible to include it in a non linear quasi-static analysis with pretension? And finally is Pcontx11 implemented in optistruct V14? Could you help me, Thanks,
  12. I have a problem if I set bolt pretension force on three bolt and I want to output their force (at Bolt.fem) I have open the control cards > GLOBAL_OUTPUT_REQUEST > PRETBOLT like the photo why it doen't have the pretension reaction force at the .h3dfile? and I have 2 another question 1. If today my model have a lot of face to need contact. Does Optistruct has the instruction to automatic define all the model's contact surfaces? If I just set a slave contact surface it will automatic to search which face will contact with this slave surface (Like LS-DYNA single surface contact) Bolt.fem Is like this? if it's it I want to ask what si Vicinty tolerance and Reverse angle suggest value 2. At the rigid setting, if today I want to set the part to be rigid and set the revolute joint. I set at the model is wrong and I can't know its wrong (I can use RBE2 to do and now I am trying to use rigid part) Rigid.fem *** ERROR # 2975 *** The RBODY with reference grid ID 3836 is constrained by more than six degree of freedom. This is not allowed. *** Run terminated because of error(s) in the input data.
  13. Hello All, I am running a Non Linear Optimization with the following load conditions: STEP-1 Assembly fit using PCONT clearance Pretension STEP-2 Temperature change from 23 degres to -40 degrees Non linear optistruct run was clear but when I run the model for optimization I get the following error: *** ERROR # 415 *** Static Subcase 2 has "STATSUB(PRETENS)" defined. Optimization with compliance cannot be performed. Any suggestions will be highly appreciated. Thanks Praveen
  14. Hello, I have a question regarding the presentation of results. Find attached two pictures of the same result presented in Inspire and Hyperview (from scratch directory. fem & h3d). You can see the result of a screw pretension. The stress distribution look extremely different and i'm a little bit surprising. Is there any reason for that? Best Regards, Mario Pretension.stmod
  15. Dear all, I'd like to ask you a question regarding load sequence definition in case of nonlinear analysis. It's kind of a complex, nonlinear load case which consists of: gravity load, bolt pretension and external load. In the first step I'd like to consider effects related to mass influence (compression of a flange). After the flange is compressed I'd like to apply bolt pretension and at the end consider external load. There is the tutorial about bolt pretension: OS-1390: 1D and 3D Pretensioned Bolt Analysis of an IC Engine Cylinder Head, Gasket and Engine Block System Connected Using Head Bolts What I don't understand is why do I need to specify both CNTNLSUB as well as STATSUB(Pretens) to consider bolt pretension. Isn't it enough to calculate bolt pretension (as nonlinear case) in one load step and then using CNTNLSUB consider it in the next one? In my case I'd like to have following situation: Gravity loading results --> transfared to bolt pretension load step --> transfered (gravity +bolt pretension) to the last load step (external force) Should I use STATSUB(Pretens) as it's show in mentioned tutorial? Best regards Jakub
  16. Hello, while modelling a simple calculation for a pretensioned bolt with 1D elements, i got the following problem: In the visualisation you can see, that the 1D element on which the pretension is applied to gets lengthen. (A 'pretension' is applied, but to the wrong direction.) According to the pretension file (.pret) everything seems to be reasonable, even if i add an additional tension load case after the pretension sub. However the contact forces do not. The '1D bolt' i used is a single ROD element , which is connect to the guiding (independent) node of a RBE2 spider of the washer (shell elements) to both sides. I attached a picture where you can see my definition in the Pretension Manager window. I also attached a picture of the property of the ROD element. I read all the infos in the users guide and online-help, but can't find an answer to my question. How can this problem be solved? Do i have to use a special orientation of the pretension section and how is this defined correctly. Please, i need your help!
  17. Hi there, I'm currently working on a bolt model for blast simulations on bolted plates. The model is quite simple rigid spiders(RB2) at the head and nut end and a spring element in between. The spring is pretensionned using a type 32 property (/PROP/TYPE32 (SPR_PRE)). I'd like to represent the spring failure based on positive rupture displacement but the property doesn't include this unlike /PROP/TYPE4 (SPRING). I'm having trouble finding how to include this criterion in the TYPE32 (SPR_PRE) property. Despite some time spend on tutorials and looking in the theory manual I didn't find what I was looking for. So my question is the following : How can i both include a pretension in the spring and apply a failure criterion ? Best regards,
  18. Hi, I am trying to load a bolted structural model and assign pre-tension to the bolt. I have made a spring element connected between two solid parts of bolt. I can see that pretension can be assigned using spring 13 property and also type 32 spring property. In type 32, what so we mean by Stif0 value? Also how to assign pre-tension using both? Thank you
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