RADIOSS Interfaces & Study of Effect of Notches Challenge

Objective: To simulate a crush tube with different notch patterns and contact interface and come up with a concise report on how it affects Internal energy, simulation time, plastic train, simulation time.

Modal discussion:

1)The crush tube has two segments upper body and the lower body in between them notches are provided for directing the stress between the component

and by default the interface Type-7 General purpose contact being given.

2)A rigid wall that is infinitely stiffer is set up against the crush tube to perform the simulation.

Modal setup

The setup consists of different components

Rigid wall

Rigid body

Material definition

Contact Interface

Fig-1

Performing a crush tube simulation could be done by setting up all four mentioned parameters to establish how master and slave behavior type-7 (General contact) and Rigid wall 'search region will help to identify slave nodes and Rigid body being master node-set to infinitely stiffener behavior

The interface is crucial and guides the software to give the actual result. It does not allow the body to penetrate or detach based on its function. So, in this case, we have used the "Type 7" interface and "Type 2 (Tied)" interface. Type 7 interface is applied over the whole body as the tube as a whole is going to crush thus self impact
will occur. Type 7 interface can consider the same body as a master surface and slave node when required. Type 7 interface does not catch up with the edge-to-edge contact and penetration is most probable to happen. Thus, to overcome this limitation "Type 11" interface is created to extend our analysis for accurate results. Type 2 interface is
used to create an infinitesimally strong connection between the parts. It does not allow the part to separate and hold two-component together.

Material and physical properties :

So, from the property card, we can see that shell is of type QEPH which is a reduced integrated shell (chance of occurrence of the hourglass). The strain formulation used is a small strain formulation which is comparatively less accurate than a large strain formulation as non-linearity is not taken into effect. The number of integration points along the
thickness is 5 and thickness change is accounted for in the case of deformation

Analysis

case-1

In this case, we will be discussing the Type 7 interface when Inactive is set to 0 (Default). When Inactive is set to default "no action" will be taken towards penetration hence initial penetration will be left as it is without removing penetrations partially or fully.

Internal energy - Deformation

As you compare the energy up to 10 -seconds increases as deformation continues similarly energy remained constant till 19 seconds due to dwelling. Then, there is the hike in increase due to rapid deformation after the upper part is crushed. Finally, a tad amount of energy is dissipated due to the bouncing of the tube.

up to the 10th second, the displacement seems to be linear hence the internal energy after that the dwell (notch)period holding back the displacement, pass 19th second the Internal energy spikes up due to the deformation of the upper part of the tube

Internal energy-plastic strain

If you follow the internal energy curve and plastic strain curve for each time you will find out that when the strain rate increases, internal energy increase too. After the 10 seconds and before the 20 seconds the plastic strain rate is low and so is the internal energy. Hence, if hourglass energy is present in large amounts then the result will vary and will
make no sense while correlating. In this case, hourglass energy is 0 due to QEPH 24 SHELL type

Top part

In part 3 and part 4 (Topmost part), the internal energy is varying unlike the bottommost part of the tube. First, the internal energy is almost zero for up to 8 seconds because the top part of the tube is under no deformation as shown below:
Thus,

Thus, we can say that internal energy will be stored in the body only when the corresponding body will go under deformation. If we see the internal energy between 10 and 27 seconds, then we will observe that there is a quadratic increase in energy. Meanwhile, plastic deformation of the body is also increased.

iii) Contact forces:
a) For part 2 (Bottom part of the tube):
Contact force is useful for analyzing force-induced contact occurring between two parts or self-contact. Contact force data is shown below nodes where maximum contact force is induced due to the contact between the tube part and rigid wall, and self-contact.

The above animation is showing the maximum contact force that occurred in this particular part (part 2) only. The maximum self-contact force occurring is 44.18 N on node 279 at 26 seconds. Then it vanishes suddenly because of the bouncing effect that occurred at last (Check the displacement plot and internal energy plot). From observation, we can
imply that contact energy increases rapidly when the tube is crushed totally which is between 20 to 27 seconds (This time corresponds to the hike in internal energy and displacements).

b) For the Remaining part:

Contact force occurring on part 1 is almost the same as part 2 where both parts are the bottommost part of the tube. And, the contact force occurring on part 3 and part 4 (topmost part) is around 94 N which is the highest value. The pattern of contact force is the same for all the parts of the tube while the magnitude is only different

CASE-2

In this case, the Inactive parameter is set to 6 which means initial penetration will be removed partially whenever detected. So, from here we expect some changes in internal energy. For check purposes, we are going to explore plastic strain, internal energy, contact force, and then rigid wall force. Plastic strain:
The plastic strain is varying in the same way as it was varying in case 1. Moreover, the maximum value for the plastic strain is also the same and occurs at the same location. Therefore, there is no significant change in the result of plastic strain due to Inactive.

Internal Energy:
The variation of internal energy is also the same as case 1. The maximum value obtained for each part for internal energy is also the same which means Inactive does not have a substantial effect on internal energy.
Contact forces:
The variation in the contact forces is almost negligible and resembles case 1 in all manner. So, Inactive does not affect contact forces too.

CASE-3:

As we have activated the Inactive in case 2 for the type 7 interface and noticed no or negligible difference in the result. Now, in this case, we will add one more interface called Type 11 for edge-to-edge contact. This will improve some deformation patterns of the body from the previous case if edge to edge penetration had happened previously.

Let's start our discussion:

In addition to type-7, the type-11 puts more effort into the solver hence simulation time is slightly higher

Before adding interface: 290.4s after adding interface: 304.74

Plastic Strain:
Here, the element id 1027 strain most in part 4 with the maximum value of plastic strain 1.377 mm and the element id 1028 strain most in part 1 with the maximum value of plastic strain 1.251 mm. Now, if we compare this case with the previous case the result will no difference which means type 11 does not have a significant contribution to simulation
output.

Internal Energy:
As we have seen that plastic strain does not affect due to type 11 so we will be expecting no difference in internal energy too.

The pattern of increase of internal energy in both parts is the same as previous case and even the maximum value is the same.
From the figure given below, the energy error that occurred is quite significant which is due to contact energy. This error is substantial in all cases. So, let's know about it a bit.
Initially, the contact energy is constant and increases rapidly around 25 seconds. Below, the total energy of the system is decreased due to an increase in contact energy and shows a significant drop in total energy.
The energy of the whole part

Contact forces:

The contact force occurring, in this case, is also the same as the previous case. The location of occurrence of maximum contact forces is also the same.
In the upcoming three cases, we will discuss the effect of the notch (depression) over the body at various positions. This will have a significant effect on the result in plastic strain, deformation, and energy. The model used for upcoming cases is the model used in case 3.

From case study 1,2,3 we didn't have any significant change in plastic strain and internal energy now, the next three cases with notches will change the output

CASE-4

In the case-4 the crush tube notches were removed to see understand the effect of Plastic strain and internal energies

Plastic strain:

As the depression from the tube is removed. The deformation pattern will be different. We will see that by exploring the plastic strain plot of the element undergoing maximum strain.
From the above plot, we see that bottom part 1 is going under large plastic deformation than top part 4. The maximum plastic strain that occurred at bottom part 1 is 1.669 mm which is greater than case 3. Previously the maximum strain was occurring at top part 4 which is quite opposite in this case.

Between 0-5 seconds the plastic deformation has occurred very rapidly for bottom part 1 which is not true in case 3. The plastic deformation in top part 4 has occurred lately compare to case 3.
Internal Energy:

The internal energy of the top part 4 is still high than the bottom part 1 which is the same as case 3. But the quantity of internal energy for top part 4 is less and bottom part 1 is high compared to case 3. The respite that the pattern of increase in internal energy is the same.

Contact forces:

Contact force, in this case, is quite high compared to case 3 for both parts. The part experiencing high contact force is at the corner of the tube (in all cases). The steep increases in contact force occurred around 25 seconds same as in other cases.

In case 5, the depression is created at the middle of the tube as shown below:

Plastic strain:
From the picture below, the maximum plastic strain is greater for the bottom part and lowest for the top part. The element experiencing the maximum strain started faced plastic strain from the time 5 for the bottom and 10 for the top part.

Internal Energy:
As the depression is created in the tube at the middle part. The internal energy is increased in top part 4 at the cost of a decrease in bottom part 1.

Contact forces:
The contact force is higher for the top part 1, in this case, compare to case 4. The maximum contact forcer is occurring at the edge of the part.

Case 6:
The depression created over the tube is at the opposite side only. The remaining two sides are kept plain straight. Now, let's what differences does it create in the results.

Plastic strain:
The maximum plastic strain, in this case, is less than the plastic strain occurring in this case. The bottom is under a large plastic strain than the top part.

Internal Energy:
The internal energy of the top part of the tube is higher than the bottom part of the tube despite the maximum value of plastic strain is occurring in the bottom part.

Contact force:
The contact force occurring in this is less for both parts compare to other cases as shown below. But one can notice that the higher value of contact is spread over more elements than other cases (Check ISO value for comparison and animation).

Rigid Wall Force for all cases:
From the above plot, we observe that the force acting on the rigid wall is less between 0-5 seconds which is due to the crushing of the lower part of the tube. Thus, crushing absorbs the energy and prevents the force to pass through the rigid wall.

From 8 to 10 seconds, the rigid wall force has increased and that is due to the transition of the deformation. At this time lower part has deformed and the upper part is about to deform.
Then, the upper part starts to deform which again absorbs all the energy thus reducing the rigid wall force (10-15 seconds). Eventually, the upper and lower part will be crushed more but at this time self-contact is maximum thus more amount will pass through the crush tube to the rigid wall. During the last seconds, rigid wall force was reduced to
0 due to the bouncing effect.

Results and Discussion:

• The rigid wall force is higher when the type 11 contact interface is applied in case 3. But the rigid wall force is lowest even when type 11 interface is applied in case 6 and this is due to the opposite notches made on the tube. Energy error is maximum for mid-notches. Energy error increases when the type 11 interface is applied.
  Learning outcomes:
• The relations of the internal energy with contact energy, total energy, kinetic energy, and deformation
• The effect of notches over the rigid wall force, internal energy, and energy error
• Importance of crush and energy absorption in a crash

Conclusion:

The analysis report shows that the crushability of the tube has a direct correlation with the type o interface, Notches patterns, and material used any change in them will affect the intrinsic property of the modal.