# Case Studies

We demonstrate below just some of the simulation capabilities that Hyperon Simulation & CAD Services Ltd can offer.

# Simulation Examples

## Nonlinear Analysis of a Clip Assembly

## Problem Statement

## Simulation Considerations

- Due to the symmetry of the geometry in this study we analyse only one quarter of the model, thus vastly reducing the amount of processing power and time required. This is shown in the first image given below.
- Create a non linear static study defining the material as acrylic (medium-high impact), together with time history parameters.
- Apply symmetry constraints.
- Apply further constraints to the model in order to simulate the moving mechanism.
- Define contact conditions between model components so as to accurately simulate the motion of the components relative to each other.
- Apply mesh control to geometry where high stresses are to be expected.
- Create the mesh.
- Run the analysis and generate stress and time history plots (shown, respectively, in the second and third images given below), together with animations if required.
- Interpet the results.

## Nonlinear Analysis of a Pipe Holder Assembly

## Problem Statement

We perform a nonlinear contact analysis of a rubber-like pipe section and an acrylic pipe holder assembly which is fixed at the back of the holder. The pipe material is hyperelastic and obeys a Mooney-Rivlin material model. The pipe is pushed into the opening of the holder such that it is squeezed into the circular section of the holder. Surface contact is defined between the outer face of the pipe and the inner faces of the holder. We then generate von Mises stress and resultant displacement plots.

## Simulation Considerations

- Create a nonlinear static study defining material properties of the individual components, together with time history parameters.
- Apply constraints and prescribed displacement such that the displacement is linear with time.
- Define contact conditions between model components so as to accurately simulate the motion of the components relative to each other.
- Create the mesh.
- Run the analysis and generate von Mises stress and resultant displacement plots, shown respectively in the first and second plots given above. The images show plot step 12 out of a total of 20. Arrows indicate constraints placed upon the geometry so as to accurately simulate the overall motion of the assembly.

## Drop Test Analysis of a Camera Casing

## Problem Statement

In this study, we will perform a drop test analysis on a camera assembly. Once the analysis has been run, we will discuss how to correctly interpret the results produced. It will be shown that a drop test analysis is capable of using an elasto-plastic material model and we will see how this can affect the results of the simulation. Additionally, we will see that the drop test analysis has some limitations that can be considered in a fully dynamic simulation. Normally, drop testing will include testing from different heights and onto many different surfaces. However, for demonstration purposes, we will drop the camera from one height of 2 m (78.7 in), and consider the floor to be either rigid or flexible. In addition, we will model the camera using an elasto-plastic material and make comparisons.

## Simulation Considerations

- Apply materials; linear-elastic or elasto-plastic material can be defined for the drop test
- Drop test setup; a height or impact velocity can be chosen for the drop test. In addition, gravity is defined.
- Define result options; decide how long the simulation will be run and what options will be saved.
- Mesh the model; create an appropriate mesh that will obtain accurate results for the simulation.
- Run the analysis.
- Postprocess the results; properly analyse the results from the drop test analysis.
- Apply study refinements; examples include using an elasto-plastic material model, considering different surfaces or adding contact between specific geometry to simulate clips, for example, can be applied to make the simulation more realistic.

Considering the first image above we see that the maximum stress with a rigid floor is 1,207.2 Mpa. Although this is an very high value, it may be premature to draw any conclusions on whether the camera is going to get damaged upon impact or not. Very high levels of stresses indicate that the damage is very probable, but the impact simulation models typically need more complex material models and a more realistic description of the target. Case in point, the next image shows the von Mises stress when the camera is dropped onto an elastic floor, showing a dramatically lower value of 88.6 MPa. This should come as no surprise because, of course, no surface is perfectly rigid in reality.

The third image shows the difference that an elasto-plastic model can make, even when dropped onto a perfectly rigid floor. Since the material now exhibits plastic behaviour, the stresses can dissipate, which are borne out in the von Mises plot. The final two plots show von Mises time history plots for the four sensors defined around the base of the zoom lens for both the elastic and elasto-plastic models respectively. As expected, the data points are much lower in the latter compared to the former.

The study suggests that localised yielding will occur at the impact location for a short time during the impact. Whilst this would cause some permanent damage to the cover, it does not inply immediately that the camera would be destroyed. Provided that the optical, electronic and other mechanical components remain functional, the camera could still be used. If we were interested in the effect of the impact on the internal component then we could create a more detailed model and perform a transient shock analysis. This is the subject of a later case study.

## Time History Analysis of a Rectangular Hoop

## Problem Statement

## Simulation Considerations

- Create and run a frequency study using 5 modes. Mode shape 1 of the frequency study is shown in the first image given below; note that since this is a frequency study, the displacements shown are unrealistic.
- From the frequency study set up a new dynamics study.
- Set the properties of the time history study.
- Apply an impulse load to a predefined section of the rim.
- Set the damping properties of the time history study.
- Set the result options for the time history study. Point 1 is chosen as a sensor.
- Create the mesh.
- Run the analysis.
- View time history results (second image given below) and interpret.

The response graph clearly depicts oscillations of the rim. The maximum UY displacement is approximately 5.7 in. The hoop comes to rest at the end at about 0.5 sec. After releasing the load, the rim undergoes free vibrations until it recovers its initial position at about 0.8 sec.

To test the accuracy of the results, run a second dynamic study using 10 modes. The results show minor changes in the response indicating that using 5 modes gives accurate results in this case. In many cases, a larger number of modes may be required.

## Buckling Study of an Aluminium Stool

## Problem Statement

In preparation for the destructive testing of an aluminium stool, we would like to predict its mode of failure and approximate the highest magnitude load that it can sustain without failing. In particular, we would like to determine if the stool can withstand a vertical load of 1600 N (360 lb). Moreover, when it eventually collapses, is it due to stress or due to buckling.?

Note that buckling is always a possibility when slender beams, like stool legs, are under compressive loads.

## Simulation Considerations

- Initially, a static study is performed. We do this in order to determine the static stress distribution within the model. This information will be used later in the analysis, when we

will be interested in whether the stool buckles or yields first. - Material properties of 1060 Alloywith a yield strength of 27.6 MPa (4000 psi) are defined in SolidWorks. These properties automatically transfer to SolidWorks Simulation.
- A directional force of 1600 N is applied to the stool seat. This is the equivalent force of a 360 lb person sitting on the stool and taking his or her feet off the ground.
- The most accurate description of how the stool would sit would be to apply a prescribed displacement of zero in the translational directions. We do this by defining coordinates systems at the base of each leg and then pinning these systems translationally. This will allow for the stool legs to rotate about an axis and buckle.
- Mesh controls are applied where appropriate and then the model is meshed with high quality elements.
- We then run the analysis and generate plots of von Mises stress and stress factor of safety, shown respectively in the first and second images shown below.
- Then create a buckling study, considering only the first two buckling modes. This should be sufficient for a buckling analysis since the first mode and associated magnitude of buckling

force is most important because buckling in this mode most often causes catastrophic failure or renders the structure unusable, even if the structure can withstand the load in its buckled shape. - Run the study using the same external loads and mesh details from the static study.
- Plot both mode shapes and list buckling factors of safety. A plot of the first buckling mode shape is shown in the third image given below. When interpreting the mode shape plots it is
**crucial**to understand that the displacements shown are purely qualitative, just as one would have with the results of a frequency analysis. The numerical values shown are not real displacements. In particular, the plots show the deformed shapes at the onset of buckling based upon the assumptions of linear buckling theory. The numerical values can be used as a comparative tool between different parts of the model, but their actual magnitudes are unknown. In order to determine the correct displacement results, a nonlinear analysis is required to investigate the post-buckling behaviour.**Hyperon Simulation & CAD Services can perform this kind of analysis if required.**

We see from the above that the lowest factor of safety from the static study is 0.98. Additionally, the lowest buckling factor os safety is 25.8. However, while the stress factor of safety is conservative, it describes the load causing the first instance of yielding in the structure, the buckling factors are non-conservative. Most likely, one of the legs will yield before it buckles. Yielding changes the geometry and reduces the buckling load so that finally the stool collapses in a combination of material yielding and buckling. As stated above, in order to analyse this we would require a full non linear study.

## Transient Shock Analysis of an Electronics Enclosure

## Problem Statement

An electronic enclosure is to be subjected to the functional shock test in accordance with the MIL-STD-810G, Method 516.5. In general, this test is conducted to assess the physical integrity, functionality and continuity of the components in shock loading. The referenced test requires that the shock loading is applied independently along all three orthogonal axes. However, the linear dynamics analysis in this case study simulates the classical pulse shock loading applied in the direction of the positive global x-axis.

Note that the MIL-STD-810G, Method 516.5 does not, in general, accept the classical shock pulse loading unless it can be shown thal it approximates the real situation. Furthermore, classical shock loading must then be applied individually in both the negative and positive directions along all three major orthogonal axes.