Assignment 5

Assignment 5

Objective : The objective of this challenge is to mesh the bumper model and perform a crash analysis on a crash tube, the analysis is carried out after modifying various interface parameters. The results and the graphs are used to analyze these cases.

CASE 1

• In this case the model is run as it is without any changes. The model is a crash tube with two notches one at the center and the other at the beginning.
• The material starts crushing as the simulation depicts at the dents that is the notches initially, then it collapses entirely.
• This phenomena is clearly observed in the simulation.

• Various plots are being taken to understand the physics.
• At the very start of the entire process in the output block , the TH PART is added and all the components are added into that.
• The look of the various settings is shown below in the pictures.

• When we move on the graphs, various plots such as the Rwall forces the internal energy and the contact energy plot, the part plots of momentum and the velocity are been plotted.

• Contact energy is something generated due to sliding action between the master and the slave.
• Due to the presence of friction we have contact energy, even if there is no friction there will be a min contact energy btw the interfaces.
• From the graph of the internal energy we can see that whenever the tube dents we will have a certain spike in the internal energy.
• As we have two notches in the beginning and the middle the spike of the internal energy is minimal.
• Where as in the for the final dent it is evident that the internal energy spikes the most.
• And after the crush the internal energy flats out.
• Coming to contact energy, the crush tube has a self contact interaction.
• Master is the surface where as slaves are its own nodes, there is no interaction to start with but as we move gradually the contact establishes and the contact energy increases at a slow rate.
• When the tube reaches the final state the contact energy reaches its peak.
• The contact energy peaks to a value of around 2100 units. As the tube crushes the contact btw master and slave increases and as the contact increases the sliding will result in contact energy.
• When the tube crushes completely and as no new contacts have been made the contact energy drops off.

• In this plot the resultant normals as well as the resultant tangential forces are plotted against time.
• As the crush tube crashes into the wall initially most of the energy is consumed as internal energy.
• But when the tube deforms to the maximum level all the energy is used to increase the rigid wall forces.
• This is due to the fact that the deformation is zero so the internal energy raise is also zero.
• The sudden spike in the Rwall force is due to complete deformation of the crush tube.

1P shell X,Ymomentum & velocities 3P shell X,Ymomentum & velocites

5P shell X,Ymomentum & velocities 6P shell X,Ymomentum & velocities

• Before we understand the velocity and the momentum diagrams we have to understand the orientation of the crush tube.
• The origin is at the juncture of the crush tube and the wall.
• The velocity is applied in the z direction, the tube while crushing will generate a velocity in the x and the y direction.
• As the tube crushes and it bulges in x and y direction we have velocities generated in those diections.
• The opposite shells will bulge in opposite direction so the velocity peaks in opposite directions for adjacent parts.
• As we can see the whole geometry is divided into 4 parts, each of the part is subjected to very diff momentum and velocity.
• The variation of momentum and the velocity is due to the fact that the tube is crushing.
• Certain parts of the tube will return to zero velocity and they pick up velocity again.
• The four parts of the tube are 1pshell, 3pshell,5pshell,6pshell.
• From the momentum and the velocity graphs it is clear that all these parts attain max velocity at different stages.

1P&3P shell Zmomentum & velocities 5P&6P shell Zmomentum & velocities

• The zmom_vel starts from negative as we are moving towards origin and the velocity reaches to zero when the tube I completely crushed and the positive velocity is where the material is pushed more into the wall.
• The point where the velocity starts goes positive at the same point we have max contact energy internal energy max and the wall forces peaks.

CASE II

Inact=6

• In this case a certain parameter in the interface settings is changed.
• This can be changed using the hyper crash application, once it is changed it can be saved and RAD file is exported again to solve.
• The option Inacti is chaged to 6, this will take care if there are any intial penetrations.
• We will add TH/PART and the model is solved again inRADIOSS.

Internal Energy Simulation

• The plot almost looks the same as we donot have any intial penetration.
• Even when it comes to the contact energy the plot remains identical.

Contact Energy

Wall forces

• The rwall forces also show similar trend when compared to the previous case.

1P shell X,Ymomentum & velocities 3P shell X,Ymomentum & velocities

5P shell X,Ymomentum & velocities 6P shell X,Ymomentum & velocities

• The moemtum and the velocity plots shows the sequence in which the velocity spikes for different parts. The same explanation in case 1 holds true.
• There is not much difference in the graphs of case 1&2.
• The zmomentum and velocity also shows a good depiction of the motion of the crush tube.
• The shells which are near to the wall starts of with a lesser velocity than the one which are farther away from the wall. This can be seen in different velocities of the two components.

1P & 3P shell Zmomentum & velocities 5P & 6P shell Zmomentum & velocities

CASE 3

Type-11

• In this method a type 11 contact is also established btw master and the slave pairs.
• Type 11 is edge to edge contact, where type 7 is surface to nodes contact.
• Both are added so that some nodes donot fall of into the surface.
• After creating the contact type all the recommended properties are given in the menu bar.
• Then the master and the slave edges are defined and added to the contact type.
• Then the TH PART is created in the output block and the solver is intiated.

Simulation

• Several results are shown in the form of graphs below.

Internal Energy Contact Energy

• The internal energy shows similar trend where as there is significant difference in the contact energy plot.
• This is due to the fact that we have given new criterion for contact i.e Type11.
• So in the previous cases we do have only type 7, so when the material max point of deformation the contact energy will drop off.
• But in this case we have an new high for contact energy, so when the interfacing due to type7 is complete there is still type 11 left over.
• This additional contact interfacing creates some extra contact energy , so the increase in the max contact energy.
• The new max goes beyond 2150 energy units.

1P shell X,Ymomentum & velocities 3P shell X,Ymomentum & velocities

5P shell X,Ymomentum & velocities 6P shell X,Ymomentum & velocities

• The momentum and the velocity pictures yield similar information to that of the previous cases.
• Where the material observes max velocity and the respective momentum are shown .
• All the three velocities and the momentum are noted below.

1P & 3P shell Zmomentum & velocities 5P & 6P shell Zmomentum & velocities

R wall forces

CASE 4

No notch

• The notches in the geometry are removed using the tool transilate.
• The nodes are selected and moved up and down accordingly to remove the notch.
• Once the notches are removed, the crush tube looks as shown in the pictures.

Removing the notch Notch free crush tube

• There are some crucial things to observe in this case, the rwall forces drop a bit and there are fewer spikes in z velocity, the velocity and mom in x and y directions are more noisy than previous.

Simulation

• The max contact energy drops a bit but the internal energy trend is similar.

Internal Energy Contact energy

• X,Y velocities : The velocities are so noisy due to the fact that there is no noise , when we have a notch the the material crushes at aparticular point that gives a particular spike in velocity at a particular point.

1P shell X,Ymomentum & velocities 3P shell X,Ymomentum & velocities

5P shell X,Ymomentum & velocities 6P shell X,Ymomentum & velocities

• Z velocity : The previous cases observed a sudden change in z velocity around 10 second mark , here it is not visible because the notch is removed so there is more a smooth transition.

1P & 3P shell Zmomentum & velocities 5P & 6P shell Zmomentum & velocities

• The max contact energy reduced because the absence of the notch created a regular crush, while in the previous cases when we have notches the irregular crush increase the interaction btw the master and the slave this results in higher contact energy.

R wall Forces

• The rigid wall forces are very less due to the fact that there is no notch.

CASE 5

New Notch

• In this case a new notch is created using the tools translate. The number of nodes are selected and are moved upward or downward to create new notch.
• An complete notch is created all around the crush tube in the similar fashion.
• The pictures below show the notch created in the crush tube.

Pictures showing the notch creation and the notch

Simulation snap

• Due to the presence of the notch the contact energy again increases , as we have only created one notch the contact energy is not that much of the case 1&2.
• The internal energy and other rwall forces are shown below in the pictures.
• The explanation in the above cases also holds good for this case.

Internal Energy Contact Energy

1P shell X,Ymomentum & velocities 3P shell X,Ymomentum & velocities

5P shell X,Ymomentum & velocities 6P shell X,Ymomentum & velocities

1P&3P shell Z momentum & velocities 5P&6P shell Z momentum & velocities

R wall Forces

CASE 6

Notch 2

• In this case a new notch is created in which the the opposite sides of the components are dented to create notch

• As seen it a kind of half notch not a complete notch.
• How this is going to affect different parameters is discussed below.
• Internal energy almost remains constant but the there is a change in the contact energy as we have only half notch. The maximum contact energy reduces.
• The notch increases the contact btw surfaces thus increases the contact energy.

1P shell X,Ymomentum & velocities 3P shell X,Ymomentum & velocities

5P shell X,Ymomentum & velocities 6P shell X,Ymomentum & velocities

• Similarly the velocity and the mom are shown below and the results show the velocity trends with repect to time.

1P&3P shell Z momentum & velocities 5P&6P shell Z momentum & velocities

• The momentum and the z velocity explains the motion of the crushtube in the z direction.

R wall forces

Note : Please find the animation files of all the six cases attached below.

Meshing of the bumper.

• The bumper system is mesh using quad elements of size 6mm.

• The number of elements are adjusted in such a way there is a uniform mesh.
• The bumper system has many sub components each surface is meshed separately with quad elements.

• The crush box has the surface which are not joined, they were joined together using the rigid body connection in 1D elements.
• The rigid body is created using calculate node and the selecting multiple nodes.
• All the nodes on one surface is joined as a single rigid body.

• The similar is done to the surface which is parallel top the previous surface.
• Later the two rigid bodies are connected using the a single rigid body.
• Similarly other side of the crash box is joined using 1D elements.

Note: Please find the attached mesh hm file of the bumper system.