Assignment 7
AIM: To perform a side crash test on a neon Dodge model with reduced BIW components against a right pole . To compare the resultant forces acting upon the cross-section of the critical components as well as intrusion and velocities of the critical points in the car.
ABOUT THE SIDE POLE CRASH:
Side crash impact image
This is a very severe test of a car’s ability to protect the driver’s head. As the loading on the car is so localised, deformation can be very high and the pole can penetrate deeply into the passenger compartment. Without effective protection, the pole would strike the head resulting in serious injuries. Head protection airbags – often curtain airbags mounted above the side windows but sometimes seat-mounted thorax/head airbags – have become a common solution but great care is needed to ensure effective performance of such devices.
PROCEDURE:
To complete the analysis of a side-crash of the following steps have to be followed .
1. Import the reduced BIW model into Hypermesh/Hypercrash.
2. Add masses at the appropriate location in order to simulate the testing of a full model in terms of weight
3. Assign contact interface (Type-7).
4. Check for the penetration and connectivity.
5. Add initial velocity to the model
6. Create rigid pole
7. Add appropriate time step to simulation .
8. Create section at the cross member and create output blocks for the normal and tengential forces at these sections.
9. Detect displacement occuring at the critical regions such as hinge pillar , fuel tank and B-pillar by generating nodal output blocks
10. Detect velocity experienced by car door by generating approapriate output block.
Initially , the reduced BIW model was impoted into the hypercrash and is shown below. The unit system is [Kg mm ms]
MASS ADDITION :
In order to improve the accuracy of the reduced BIW model, the mass of the reduced model has to be similar to that of the full model. This will ensure that the kinetic energy experienced by the model while motion is realistic. The mass of the full model is assumed to be 700kg and the centre of gravity align approximately at the centre of the cross member (yellow color) in order to simulate this condition, mass was strategically added to the frame of the reduced BIW mdel by going to the Browser and double clicking on Added mass. The result are shown below:
As we can see, the mass was added until final mass of the 700kg was obtained.The centre of gravity is also in a more realistic location as described in the paragraphs above. This ensures that the masses of the reduced model behaves in a more realistic way.
CONTACT INTERFACE:
Contact interface are so crucial step and dictate the manner in which various components behave when they impact forces upon on another .In the present simulation, comntact Type 7 was implemented .This was done because contact type 7 is the most commonly used and is very general type of contact.It is a node to surface contact types in which surface act as master and nodes act as a slave .The properties were given to the interface in accordance with the recommendedations for the crash analysis and are given below :
The redundant interface were deleted. To add contact interface, go to Loadcase>contact interface. Create a type 7 interface and add the recommended properties to it.
Following the addition of contact interfaces, penetration check was done on the model. No penetration were found .
However, a few components were not connected and this was corrected by going to hypermesh and adding rigid element to connect the components.
INITIAL VELOCITY:
An initial velocity of 35mph was added to the model.Upon conversion, this goes to 15.6464 mm/ms . The velocity was given in y-direction because this is the direction in which the model will impact upon the rigid pole.The velocity can be added by going to load case>initial velocity.
RIGID WALL:
In order to create a rigid wall, go to loadcase >Rigid wall for the purpose of the present simulation , a cylindrical wall was created with the axis of the cylindrical being parallel to z-axis.
Friction of 0.1 was given to the rigid wall.
MODEL CHECKER:
The model has to be checked for any errors or warning which might affect the validity of the results.This can be done in hypermesh by going to quality > Model checker > Run .
The following warning were shown initially :
after fixing some of the warning, the following warnings were displayed, which can be ignored :
TIME STEP:
TIME step can be given by going to hypermesh and selecting Tool>Engine file assistant nodel time step of 0.5 ms was selected and simulation run time was given as 80 ms.
OUTPUT BLOCKS:
Apart from the default output that the hypermesh simulation provides, addtional output blocks are required to check the forces, displacements and velocities that are imparted upon a few critical regions For the present simulation, sections were created on the cross members to check the axial and tengential forces acting ipon their cross-section.Also, displacements occuring on hinge pillar , B-pillar and fuel tank need to be observed and therefore , appropriate nodal output blocks were created for them. The velocity of the car door needs to be calculated and nodal output block war created to detect this as well.
To create a section, go to solver browser in hypermesh, and right click and go to create>sect>sect_circle. Select the elements , nodes, orientation and radius appropriate and create the section. To create the output block, go to TH>Create>sect. Select the sections and add the required outputs i;e normal forces and tangential forces.
To detect intrutions, first create a moving skew on the opposite end of the car. This creates a frame of refrence. The create a nodal output by going to TH>Create>Nodes. Select the node and select the skew frame and give Displacement or velocity as output as required.
RESULTS:
The simulation run time was 13954.87 sec. Maximum energy error was -1.4 % and maximum mass error was 0.000. These values are within the limits for accurate results.
The crash results are shown below for the various orientations.
VON-MISES:
The stress upon impact needs to be distributed along the various frames of the car. Below is the various of stress upon impact.
As we can see, the maximum von-mises stress of the 0.3568Mpa is reached. The flow of stresses seen which indicated a good design.Forces acting upon the various crutial members of the car need to be checked as well.
CROSS-SECTION:
The normal and tangential forces acting upon the cross-section of the two cross-section of the two cross member are plotted below:
The blue curve for frontal cross member and the red curve is for the rear cross-member. The frontal cross member has a maximum normal forces of 0.98KN whereas the rear member has 2.22941KN.As we compare both hyperview and hypergraph at peak value of force the rear cross member has more impact compare to frontal cross-member i;e rear cross member attains maximum force of 2.22941KN.
The frontal member has a maximum tangential force of 5.63304KN and rear member has 4.73231KN.
Therefore, it can be seen that in both the cases, the rear cross member experiences more force and therefore has to be more study in design.Also, both cross member experience more normal force than tangential force and therefore, normal forces have to be priotized.
INTRUSION:
The displacement occuring on the hinge pillar, fuel tank and B-pillar were detected and are plotted below:
The Red curve is for the B-pillar, Blue curve is for fuel tank and green curve is for hinge pillar. As can be seen from the graph, the Hinge pillar experiences the highest intrusion whereas the B-pillar experience lowest intrusion. This is good design as fuel tank can be reinforced further whereas B-pillar which is next to the passenger/Driver needs to displace as less as possible to avoid significance injuries. The fuel tank has maximum displacement of 381.334 mm , hinge pillar has 735.657 mm and B-pillar has 232.307 mm.
PEAK VELOCITY OF INNER DOOR :
Velocity experience by inner door in various axes while impacting
- Velocity along X-axis
The maximum value of velocity of inner door in x-axis attains is 0.696715mm/ms.
- Velocity along Y-axis :
As Y axis is the propogation of car,so upon impact the velocity of car drastically decreases. The peak velocity attains by the inner door is 16.259mm/ms as shown below;
- Velocity along z-axis :
Peak velocity of inner door attains is 16.259 mm/ms .
ENERGIES:
The internal and kinetic energies are plotted below:
As is expected, then kinetic energy(K.E=0.5mv^2) is at its peak initially and upon crash, it losses velocity and hence the kinetic energy increases upon impact as the material absorbs the energy and keep decrease with time,while internal energy keep on increasing with time as due to deformation of body is absorb more energies from the impact. During the runtime of 80ms the net change of kinetic energy is 21100.7 unit and net change of internal energy is 19668.5 unit during the impact.
CONCLUSION:
The effect of different configurations on the performance of a side impact beam from a passenger car was investigated experimentally and numerically with a view to minimise intrusion into the passenger compartment. Side crush was performed successfully with timestep and energy value all being balanced with error.Hinge pillar received the most force on impact and can be fatal for any occupant therefore the stiffness of that should be increased improving the material used. The intrusion by the hinge and fuel tank used to be reduced by adding more components such as beams , absorption pads and cross-rods to absorb more energy before they reached the critical area.