Fundamentals of SolidWorks Simulation

SOLIDWORKS SIMULATION

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Contact Sets in SOLIDWORKS SIMULATION

Simulation Contact Set

SolidWorksSimulation of assemblies or multi bodies requires the application of contact sets to define the interface between two objects.  If the contact sets are not defined properly we will obtain incorrect results.

Consider a simple weldment framed structure with a steel plate sitting on top.  

This weldment is fixed at the end of each leg and has a load applied to the plate on top.

By default, SolidWorks Simulation treats weldments as beam elements and the plate on top as a solid element.  As such we have two different element types in this analysis; therefore we need to define a contact set.  As an option we can use the “automatically find contact set” function by selecting a beam element and the plate.  The software will find the connecting surface where you may apply a condition, in this case bonded.  This is repeated for all four faces.

Upon closer inspection, we find those contact sets to be a face to face contact

Following the creation of the contact sets we can mesh our model and run the analysis

However in doing so will result in an error message. 

This is because the contact set defined was incorrect.  When the contact sets were created they were treated as faces, however since this is a solid to a beam element, we need to select the beam element contact set under “Type”.  By redefining all four contact sets, remeshing and running the study, we now have the correct results.

Application of Loads in SolidWorks Simulation

Simulation:  Application of Loads

 SolidWorks Simulation allows users to set up and run tests using finite element analysis (FEA).  The manner in which a user sets up a test will determine whether the results are an accurate result of real-world conditions.  (Also Read:Symmetry in SolidWorks Simulation -Guide to applying loads and restraints appropriately)

Consider the electrical component shown below.  The main grey surface consists of ceramic porcelain whereas the small red parts indicate components that generate heat on the board.  We are interested in the heat distribution for this part under working conditions.

In order to set up the problem we define the material properties for each component.  This includes the red electrical components as well as the grey ceramic porcelain.  Following material definition, we define heat generation power of 0.2W for the red components and convection of 0.2 W/m^2 K for the outside surfaces.  The convection is a mechanism of heat transfer used to dissipate the heat.  

It is important to pay attention to detail when defining a simulation study.  Consider the definition of 0.2W heat generation for the red components.  The user must differentiate whether the heat generation is generated for each component or whether it is generated across the sum total of components.  This is an important distinguishing factor.  In this case it is set to “Per item” which is correct.

Furthermore, as a tip, if the user were to use symmetry to divide a heat generating part in half and the heat generation is defined in terms of Watts, it follows that the Watt value must also be divided by half since Watt is a total heat generating value.  The relationship is similar to that of force and pressure.

Once the analysis is successfully set up we need to mesh the component.

Once the component is meshed, we may run the analysis.  According to the conditions set for this thermal analysis we are seeing a maximum value of 460C occurring on the inner components.  The heat generated from the components travels outward to a temperature of 427C towards the outer edges of the ceramic porcelain.  

The manner in which the simulation analysis was set up can greatly affect the results.  

Bolt Fracture

Case Study: Bolt Fracture 

Hardware such as bolts, nuts and washers are generally used for connections and fixtures.  They form an integral part of the component structural integrity.  Bolts are governed by standards such as ASTM and are typically stamped with an identifying marking on the head during the manufacturing process.  The bolts selected for any application typically take into account the manner in which it is applied while taking into account the most prevalent mode of failure.  It follows that it would be in the designer’s best interest to understand how bolts fail and to avoid those situations.

Consider a simple bolt modeled in SolidWorks:

Roundhead Bolt 12mm DIA x 152MM LONG ASTM A307

It is worth noting that the tensile strength for that grade of bolt is approximately 60,000 PSI.  Therefore, using plain carbon steel as a template, the tensile strength was adjusted accordingly.

Next, we can set up a test scenario using SolidWorks Simulation where the bolt is fixed at the top with a base tensile load of 10,000 PSI applied at the bottom

We can now mesh the bolt

After running the Static analysis we can do a section plot to understand how the stress a distributed in the cross section of the bolt.  We find that the highest point of stress concentration occurs at the neck as expected with a value of 28,067 PSI.  

Note that this value is fairly close to yield strength of the material 31,994 PSI.  If a stress value approaches the yield strength, the general assumption of linear behavior of the material begins to breakdown.  Therefore it is in our best interest to run a non-linear analysis as well.

Creating a new non-linear study and running a similar analysis we find that the actual stress is approximately 27,197 PSI. This value is less than the linear analysis but it is still close to yield. 

Given these results it would be in the designer’s best interest to either reduce the load, increase the bolt diameter or chose a higher grade bolt.

Sometimes bolt failure can occur due to other circumstances as well.  Specifications such as how much a bolt must be tensioned at installation can make a difference.  In other cases large batches can yield bolts with manufacturing defects which may fail below the yield stress.  

Difference between Direct Transfer and Rigid Connection

In SolidWorks Simulation you may define external loads known as remote loads.  Upon creation of a remote load you have the option of setting it to be either Direct Transfer or Rigid Connection.  What is the difference?

Consider a simply supported cantilever composed of two parts: front and back: 

We may create a simulation study that reflects the cantilever beam loading conditions.  It is fixed on one end and has a load applied on the other end.

We can simulate the results of this study by excluding half of the beam and applying a remote load in place.  

When creating a remote load, the user must specify whether it is a direct transfer or rigid connection

Direct Transfer: Assumes that the component between the remote force and the connection point is adequately flexible, allowing the structure to deflect.  The program decomposes the remote force into a shear force and coupling moment acting on the connection face.  This allows the connection face to distort.  Displacements must be within the small displacement assumption.

Rigid Connection:   Applies rigid links/ connections from the remote load to the connecting face.  As a result when the face deflects, the face shape is maintained.  High stresses can develop near faces with rigid connections.

The results of the remote load direct transfer is shown below:

The results of the remote load rigid connection are shown below:

At first glance the results are not easily distinguishable; however upon closer inspection along the vertical axis of the connection face reveals that the stress distribution from the direct transfer and rigid connection options are different.

Choosing whether the remote load will be applied as a direct transfer or rigid connection will affect the simulation results.