Submodeling is a technique you can use to reduce solution time without sacrificing accuracy of results. A common strategy you can use to look at the overall behavior of an assembly or complex part of a large model is to simplify the model during preparation by removing small details, like fillets and holes. Simplifying models in this way can have a significant impact on run times. This simplification, while not excessively affecting overall model stiffness, may result in lower resolution of localized stresses. Submodeling is such a technique — it enables you to solve a locally refined model with all of the geometric details required to solve accurate stresses.
Thank you for bringing this up — a really valuable comment for sure! Not only does it rapidly create the submodel but the cut planes named selections are automatically created as part of this process! Hi Lukasz, Always interesting to read your blogs. Since your model has nodes and space between them, outcomes are a bit tricky. When you apply the load to a point no areathe stress is infinite force is divided by zero area. OK Learn More.
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Net Engineering my life. Resources  Pilkey, W. In both cases this corner leads to a singularity. Further away from the disturbance the results will not be perturbed. The example below shows stress concentration results for a full model gearbox. Suddenly, the top and bottom free surfaces are Ansys model stress concentration example the action of a singular point force respectively! It is clear that the stresses at the corners do not converge even with more than From left column select Solid and from right column select Quad 4node 42 and click OK. Create geometry of the non-superelement Silicone :. Click 'Pick All' button. Apply loads to the super-element.
Arjen asked me recently about stress singularity.
- Cracks, sharp edges, and holes: no, this article does not pertain to the stressful road conditions in the Midwest after a long winter season.
- It relies on discretizing a continuum domain into finite elements.
- Submodeling is a technique you can use to reduce solution time without sacrificing accuracy of results.
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Skip to main content. Advertisement Hide. Conference paper First Online: 03 November This is a preview of subscription content, log in to check access. Muminovic AJ et al Analysis of stress concentration factor using different computer software solutions. Kisija J et al Determination of stress concentration factor via numerical methods: bar of circular cross section with U-shaped groove subjected to tension and bending. Kacmarcik J, Beslagic E, Spahic D New mathematical model of stress concentration factor in tension of rectangular bar with opposite edge U-notches.
Yeh ST et al Using trapezoidal rule for the area under a curve calculation. Santos A Determination of stress concentration factor on flat plate of structural steel, Universidad Pontifica Bolivariana Seccional Bucaramanga. Floridablanca, Colombia Google Scholar. Enab TA Stress concentration analysis in functionally graded plates with elliptic holes under biaxial loadings.
Sburlati R Stress concentration factor due to a functionally graded ring around a hole in an isotropic plate. Wiley, New York Google Scholar. McGraw-Hill, New York. Personalised recommendations. Cite paper How to cite? ENW EndNote. Buy options.
Generate the super-element by condensing several elements together. Acin has kindly explained that this is due to the fact that stress values are computed at Gaussian points, which are located inside the elements. To learn more, check out SpaceClaim. When do they pose for concern? Mesh the block:. On the other hand, they must restrain the vertical movement of the clamped section.
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This has led to an inevitable increase in the geometric complexity of mechanical components. While this has allowed components to perform multiple functions, it has led to complex load transfers and possible concentrations of stresses. A stress concentration is defined as a high localized stress, compared to the average stress of the body, and is typically found in a region that has an abrupt geometric change. This article will walk through the basics of a stress concentration, offer real-world examples to illustrate the concept, and outline methods for reducing stress concentrations in your designs.
Stress concentrations are relatively straightforward when it comes to identifying where they will be located and whether they have contributed to failure. They will be located in the small radii and sharp corners that are in a load path. The image below shows a component that will have rollers on the smaller diameter shafts on both ends, with a load applied to the top flat surface. The image below is a rendering of the subassembly that this component goes into, including the rollers with bearings.
Now we can see that the smaller diameter shafts meet the center portion of our roller support with a relatively abrupt radius. If we zoom in on this radius, we can see that it comes in at only 0. If you recall from above, a sharp corner or radius will be the location of a stress concentration. The load case has already been discussed, but we can refer to the illustration below for a refresher.
We have a downward force of lbs, and we have fixed the surface of the shaft where the rollers will sit. The only remaining step is to run the simulation and process our pretty pictures! In the image below, we can see the beautiful red spots that indicate a stress concentration. We can see that this is the highest stressed feature, and this would be the first location to fail under cyclic loading though it would most likely occur on the bottom side loaded in tension, instead of the top compressive side.
It would initiate as a small surface crack that eventually propagated through the component to complete failure. There are also a few basic formulas to define the max stresses in this type of geometry when we have a bending moment applied. The formula in this case is as follows:.
In many simple geometries, the stress concentration factor is defined for a range of geometries. The chart below shows the curves of these factors and the dependency on the ratios of the critical dimensions.
This chart is used by dividing the large diameter by the smaller diameter first. Next, we look at the ratio of the radius to the smaller diameter. Now that we understand the basics, we can step into some examples of correcting stress concentrations. If you recall, we had a very small 0. The first image is the original stresses, and the second is the reduced stresses with the larger radius. We can see that the stresses have gone from 14, psi all the way down to 3, psi.
While this differential is pretty extreme because of the extremely small original radius, it drives the point home of just how much a stress concentration can influence the stresses in the part.
The first part is a support bracket that holds a brass pin. The brass pin typically has an upward load applied, and the base is bolted to a fixed plate, as shown in the setup image below. As you probably expected, we ran the FEA again to get a baseline stress value before making any changes.
The results of this study are shown below. The stresses at the base with the small radii 0. By now, we can guess that a larger radius should help lower the stresses here, even with a much different load case and geometry. In the next simulation, I have increased the radii from 0. If I wanted to get even lower stresses, I could do so by thickening the flange to which this assembly is attached.
You can see the light blue coloring that gives an indication of how this part is deflecting under a load. In our next example, we have a flat plate with a diamond shaped hole cut out of the center. There is a load applied on one end, while the other end is fixed, as shown in the setup below.
If that is the case, you were absolutely correct. The next image shows the results of this simulation. We can see the stress concentration is exactly where we expected. We know we can make the radii bigger, but what if we wanted the option of drilling that hole out, instead of requiring a mill or punch?
Can we use a larger diameter circle, effectively reducing the total material in the part, and still lower the stresses? As the image below details, the same simulation was run with a round hole that is greater in diameter than the distance from the top to the bottom of the diamond-shaped hole above.
In a similar approach but different application, it is common for repair centers to drill a hole at the end of a crack to relieve the high stress concentration associated with the very small radius at the tip of a crack. I hope by now the idea of locating and reducing stress concentrations is clear, and you are well on your way to improving a design.
While I used an FEA program here to determine the magnitude of stresses, there are some general guidelines that can be used to improve a design. When it comes to common methods of reducing stresses, the following list includes some simple items to get you started quickly:. Add stress-reducing holes at the end of slits, sharp angles, or cracks to relieve high stress concentrations. Refer to stress concentration charts to understand when you are in a region of diminishing returns with respect to radius size.
Do not make a large size transition between loaded features. The stiffness mismatch will drive the stress concentration much higher. Remember that the stress concentration is based on a ratio, not a magnitude. This list is not fully comprehensive, but it should cover the basic concepts that every designer should know in order to improve their design skills.
Through the examples and analysis above, it should be clear exactly why we need to be concerned with stress concentrations. By incorporating these concepts through your design, you should be able to achieve higher load ratings, reliability, and fatigue life.
I encourage design teams to talk through product requirements and design choices to ensure the proper blend of aesthetics and function. There will always be tradeoffs, but proper analysis can help achieve an optimized solution. Main navigation What is Fictiv? Written by Sean Thomas. Breadcrumb HWG Design. Stress Concentration Overview Stress concentrations are relatively straightforward when it comes to identifying where they will be located and whether they have contributed to failure.
The image below shows all of this in a graphical format. General Guidelines and Issues to Avoid When it comes to common methods of reducing stresses, the following list includes some simple items to get you started quickly: Make radii in a load path as large as you are comfortable making them. Limit the ratio of the large feature to the small feature, where possible. Some common issues to avoid are: Do not use sharp corners along a load path. Was this article helpful? Help us by sharing.
Last page. Threaded connections, such as bolts and nuts, are used in a wide variety of applications, ranging from plastic toys to massive bridges.
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