Bolt pretension ansys apdl

Here is my list in order of increasing complexity and modeling fidelity:. This article covers methods A force of lbs is applied at the end of steel plate and the C channel is fixed at the bottom as shown. This is the simplest connection. Bolts and nuts are removed from the assembly.

A bonded connection is created around the bolt hole as shown. The bonded region simulates friction grip of the joint around the bolted connection. This type of connection is ideally used in the global analysis of large assemblies where modeling of bolts will become computationally intensive.

Bolt pretension causes high compressive stress exceeding UTS but deformation is only 0.2mm

A key assumption here is that the bolted joint maintains its friction grip and does not slip. A subsequent sub-modeling analysis of this bolted connection with 3D solid bolts will reveal its true integrity i. The bonded connection enables linear analysis which is much faster than a non-linear contact. The way to create Beam bolts is to import the CAD file into design modeler and use bolt and nut head boundary edge to create imprints on the plate surfaces in contact with the bolt and nut see image below.

If a washer is used, then use the washer boundary edge for imprinting. For reference and mobile surfaces use the hexagonal or circular imprints created in design modeler. Beam Bolts. The red lines represent constraint equations that connect the beam element to bolted faces hexagonal imprints. The beam connection creates constraint equations between beam nodes and reference and mobile surfaces.

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The behavior can be set to rigid or deformable, although none of these options can capture the true stiffness of bolt head and nut. The bolt pretension can be computed using the following formula. In earlier versions APDL commands can be used. The contact between the mating plates is set to frictional.

The third type of bolted connection is a spring bolt.

Non-linear bolted analysis - ANSYS

It is applied in a similar manner to beams. A pretension or pre-load value is defined in the details of spring joint. This is the highest fidelity bolted connection model so far. This model enables us to capture the bolt and nut stiffness as well as post slip effect when the shank comes into contact with bolt hole.

The downside is significant computational cost, in particular, if there are several bolts in a big assembly. Therefore, this analysis is best suited to sub-modeling. The key steps in modeling solid bolts are shown below:.Log In. Thank you for helping keep Eng-Tips Forums free from inappropriate posts. The Eng-Tips staff will check this out and take appropriate action. Click Here to join Eng-Tips and talk with other members! Already a Member? Join your peers on the Internet's largest technical engineering professional community.

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By joining you are opting in to receive e-mail. Promoting, selling, recruiting, coursework and thesis posting is forbidden. Students Click Here. Related Projects. No other loads or BC's are applied, except friction contact between the nuts and members.

The method I use for checking the preload is detailed below: 1. The solution comes back with 0. However, I can believe this because the nuts and washers are also meshed and compressible pieces of the puzzle. I apply this same displacement, 0. I do this by "modeling in" an initial penetration between the nut and the member, and letting the contact work out the rest. To check whether or not the preload has been correctly applied, I look at the sum of the nodal forces FSUM on the surface of the nut.

I put lbs in, so I expect to get lbs out, right? What gives? Is it because the FSUM value is sensitive to mesh density or element type?

Bolt pretension clamps two plates together

Load distribution effects? If this method isn't effective, what other suggestions does anyone have for determining the initial penetration to develop the required clamping force?

Thanks, DBH. I found part of the problem ANSYS workbench is sensitive to where you select on the surface for applying the preload.

The point I had selected was inside one of the nuts. That's what caused my Workbench results to look so funny. Once that was fixed, the preload FSUM fell right into line lbs. Red Flag This Post Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Read this white paper to learn more.While Number 1: First and foremost — info on the new features is more readily accessible with the Mechanical Highlights list.

One you actually do something in Mechanical, though, that list goes away. There is a simple way to get it back: Click on the Project branch in the Mechanical tree, then click on the Worksheet button in the menu near the top of the window.

Bolted Connections in ANSYS Workbench: Part 1

Clicking on the hyperlinks in the list or simply scrolling down gives us more information on each of the listed enhancements. Keep in mind the list is only highlights and by no means has all of the new features listed. Number 2: A major new feature that became available in Number 3: Another really useful enhancement in This means we no longer need to have a geometry representation of a bolt if we want a simpler model.

We can simply insert a beam connection between the two sides of the bolted geometry, and define the pretension on that resulting beam.

Beam connections are inserted in the Connections branch in Mechanical. Once the beam is fully defined, it can have a bolt pretension load applied to it, just like as if the beam geometry was defined as a solid or beam in your geometry tool.

Here you can see a beam connection used for bolt pretension on the left, with a traditional geometric representation of a pretensioned bolt on the right:. Number 4: A very nice capability added in version Contact elements work best when the element sizes on both sizes of the interface are similar, especially for nonlinear contact.

bolt pretension ansys apdl

Contact Sizing allows us to specify an element size or relevance level once, for both sides of one or more contact regions. Just select the desired contact regions with the mouse, then drag that selection into the Mesh branch.

Then specify the desired mesh sizing controls for contact. This is what the dragging and dropping looks like:. Number 5: An awesome new feature in There is a new selection filter just for element face selection, shown here in the red box:. Once the element face select button is clicked, element faces can be individually selected, box selected, or paint selected simply by holding down the left mouse button and dragging.

The green element faces on the near side have been selected this way:. The selected faces can then be converted to a Named Selection, or items such as results plots can be scoped to the face selection:. Number 6: Finally, to finish up, some new hotkeys were added in Two really handy ones are:. We encourage you to try them out on your own, and investigate others that may be of benefit to you. Keep the Mechanical Highlights list from Number 1 in mind as a good source for info on new capabilities.

You must log in to post a comment. Here you can see a beam connection used for bolt pretension on the left, with a traditional geometric representation of a pretensioned bolt on the right: This is what the dragging and dropping looks like: After dropping into the Mesh branch, we can specify the element size for the contact regions: This shows the effect of the contact sizing specification on the mesh: There is a new selection filter just for element face selection, shown here in the red box: Once the element face select button is clicked, element faces can be individually selected, box selected, or paint selected simply by holding down the left mouse button and dragging.

The green element faces on the near side have been selected this way: The selected faces can then be converted to a Named Selection, or items such as results plots can be scoped to the face selection: Number 6: Finally, to finish up, some new hotkeys were added in Like this: Like Loading We use cookies to ensure that we give you the best experience on our website. If you continue to use this site we will assume that you are happy with it.Among the many ways parts can be assembled together, bolts are useful when parts need to be disassembled for maintenance or repair.

They can also be used to connect parts made of dissimilar materials, when welding is more challenging.

From a FEA standpoint, bolts can be modeled in many different ways, from simple links between parts using constraint equations to fully detailed models of the bolts, potentially including full thread details. Whatever the model one will use, simulating bolted assemblies will usually require a multiple steps analysis to mimic the reality. The assemblies are first bolted, and then used in their environment with corresponding loads and boundary conditions.

A structural analysis model will let you apply loads in a similar way. Bolt pretensions are applied first, generating stresses and deformations in the model. Then, once bolts have been locked, additional loads will be applied.

What are the challenges you will face in building such a model? What do you need to look at? Well, one of the biggest challenges when dealing with bolts is that you rarely have a single bolt. In reality, chances are you will have dozens if not hundreds of them. How can you efficiently deal with a high number of bolts? Can you easily setup one bolt and replicate the setup for all other ones? How can you efficiently setup your model to reflect all contacts between bolts and the various connected parts?

The video below demonstrates how to efficiently create pretension bolts in a model and how multiple steps analyses can be used to analyze the design of your bolted assembly. Once the geometry has been imported, contacts will be automatically detected in the assembly. You just have to make sure the contact between your bolts and the connected parts have the appropriate properties, for example frictionless or with a given friction coefficient.

bolt pretension ansys apdl

A nice idea would be to group your contacts accordingly, so you can identify them later when reusing your model. Contacts between bolts and connected parts. Then you need to define the pretension on each bolt. The best solution here is to create the loading conditions on a single bolt and then replicate to all other bolts with the same properties.

In a few mouse clicks, you will generate the conditions on all bolts in your model. Definition of bolt pretension and automated generation of loads on multiple bolts. As mentioned earlier, your simulation will usually have a minimum of two steps: one to apply the pretension, one to apply other loads while bolts are locked in their constrained state. The first one mimics the assembly of your product, the second one the real behavior of your product under real loading conditions.

Whether you define the bolt pretension through a load or an adjustment, you will likely be interested in looking at reaction forces to make sure all loads have been properly applied.

Here again, automation will save you huge amount of times — define the results you want to look at on one bolt and automate the creation of results on all other bolts. Typical results for a bolted assembly. Contact pressure at the bolt head for pretensioned state and under real loading conditions. Stress induced by bolts and pretension results. If you are interested in further detailed analysis of your bolts, you may want to include the details of the thread.

Geometric modeling of the thread would however lead to larger models as capturing the stresses will require a high mesh density. A much better solution would be to model the thread as a contact without the thread geometry available. The contact algorithms would take care of computing accurate stresses as shown below.

Contact us if you need further details on this modeling technique. Simplified model for faster yet accurate analysis of bolt threads.I have a structure with beam bolt connection at its base.

Connection type is body-ground. A pretension of N is applied on each beam bolt. Beam bolt are still physically shown connected to the edges but stretched from ground to the body. I cannot figure out what is wrong with the system. Either beam bolt connection not worked well or huge pretension did this large deformation. I assume you want the beam that gets pretensioned to connect to ground at one end and to connect to the top of a flange of the structure at the other end.

It should have a fixed support at that vertex. Only the other vertex of the beam is scoped to the top of the flange. Therefore that face needs a compression only support. Now how should I generate compression only support at the underside of flange.

Do I generate a body-ground joint connection at the underside of flange? To create a compression only support, click on Static Structuralclick the Face filter, click a face and ctrl-click if there are several faces making up a single plane, the click SupportCompression Only Support.

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An internal solution magnitude limit was exceeded. Please check your Environment for inappropriate load values or insufficient supports. Please see the Troubleshooting section of the Help System for more information. One or more bodies may be underconstrained and experiencing rigid body motion. Weak springs have been added to attain a solution. Refer to Troubleshooting in the Help System for more details.

I have also tried a ground-body joint connection at the lower edge of the each bolt hole.I have done a static structural analysis of an assembled component that uses bolt connections and welds. I had defined two type of loads, 1. Bolt pretension 2. External load as force.

bolt pretension ansys apdl

I have defined bonded contacts for all the bolt, nut interfaces and the surfaces that were mated for assembly. I got a peak von mises stress of MPa, near the bolt hole region, whereas the ultimate strength of my material structural steel in ansys is only MPa.

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So i switched all my contacts to bonded type and got this undesired result. I am sure the component wont fail from the experiments that is it can never develop this high stress value. NOTE I have redesigned my original component with a generic model and have used it for this post.

You will get much better results using Frictional Contact under the heads and nuts than Bonded Contact, but you have to check that the contacts are closed. If any contact is not closed, you have to take corrective action such as setting Adjust to Touch on that contact. You also turn on Auto Time Stepping and set the Initial Substeps to a large number like to give the solver a chance to establish contact before too much bolt pretension has occurred.

Then you have to wait longer for the solution for Frictional Contact because the solver has to iterate to find the contact and it doesn't have to iterate for a Bonded Contact. The load and geometry are almost symmetric. I expect you can ignore that the base plate is wider on one side than the other. Do some geometry simplification. Delete all the small blends on the part with the cylinder except for those on interior corners. Delete all the blends off the screw and nut heads. You are adding a lot of nodes to the model for very little benefit.

It will solve faster is there are fewer nodes. Thank you Peter Although i would find the frictional contact definition quite challenging. Thanks again. And your suggestion about the symmetry of the model, did you mean to suggest me to slice up my whole assembly along the XY plane into half? Updating Bonded Contact to Frictional Contact is as simple as selecting all the bonded contacts in the Outline, and using the pulldown where it says Bonded and picking Frictional and entering a COF.

May i know how u did that? To delete a face in SpaceClaim, click the face and hit the delete key. If it can, SC will trim the adjacent faces to close the gap. One other thing, i shall define frictional contact between surfaces of bolt head and nut head with its components in contact, but do i define all other surfaces in contact to be bonded? For example, the cylindrical pin and the bracket are not supposed to be separated after they are being fastened by bolts, so the surface between pin and bracket should be defined a bonded contact and all other surfaces that have been mated during assembly of components should also be defined bonded contacts.

Am i right here? The only bonded contact would be nut to bolt, except for the bolts that go into the bracket where there is no nut, those could be bonded.

There is an alternate approach that simulates threads, but that might be a topic for another post.

bolt pretension ansys apdl

I have also modeled weld between bracket's side edge and support plate.Posted: Tue Oct 02, am. Dear experts, I have a model with many bolts. I have to apply a pretension. I defined the pretension by hand for every bolt. Is there a method by a APDL command, to change the load for all the bolts in one time, without to change the load by hand one after an other? How to get the reference id for every bolt pretension in the APDL command?

Back to top. Before I answer, why would you want to change the bolt clamp a bunch of times? You do set them all to a value before you hit solve. Would you change them afterwards?

Bolted Connections in ANSYS Workbench: Part 1

You can make the clamp value a variable and read them in. It seems that is not possible to define the Preload as a variable in the Details window of WB.

But thanks for your input.

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Francesco, I may be misinterpreting your question, but in Worbench you can define the bolt pretension using a table. Using the table, you can specify the bolt pretension load value for each time step in an analysis, or you can lock it. If I understand you correctly, you have a lot of bolts with the same bolting process? In that case, I would define 1 pretension how I want it and simply duplicate it as many times as I need.

Then you would just need to attach each to a bolt geometry. Posted: Mon Jan 07, am. Bolt mounting force N! Element type! Start Bolts scan! Center of mass first hole! Center of mass second hole! Evaluaiting bolt corss section an moments of inertia!

Bolt nut or tapped hole! All times are GMT - 7 Hours.


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