FRONTAL CRASH ANALYSIS

OBJECTIVE: To perform a frontal crash simulation using Radioss as a solver.

STEPS:

  1. View components: In the NEON FRONT model there are 75 components.
  2. ASSIGNING MATERIAL ID, PROPERTY ID, AND CARD IMAGE: For rigid bodies, card image is none and prop id, mat id is unspecified.
  3. CONTACTS: Under groups, contact cards are defined. For type 7 Gmod_id(S) is set as nodes and surf_id(M) is set as surfaces. In our case, all components are master as well as slaves.
  4. BOUNDARY CONDITIONS: Using BC manager, boundary conditions are created. In the given model, only one BC was created, which is velocity in x directions. Using this option other BC like gravity loads, SPC, imposed displacements, etc can be easily created.                                                                   
  5. CREATING IMPORTANT ENGINE FILES: To run the model engine files, termination time, animation frequency, time history output frequency, and the nodal time step is always defined.
  6. OUTPUT CARDS: To get von mises stress, hourglass energy and other energy plots these cards are created.
  7. SOLVE: Under analysis, Radioss with -nt 4 is used to solve the model.

Neon 300K elements is the reference file. This model is a full-scale model. The simplified model used for the frontal crash has 95475 elements.

UNIT SYSTEM: The unit system followed is Kg Kn mm ms.

ADDED MASS: The initial weight of the model was 188kg. To reach the target weight of 700kg, extra weight was added on the base of the car so that the center of gravity of the vehicle was in the line with the driver.

INITIAL VELOCITY: Initial velocity of 15.56m/s were given to all nodes of the model. This was given under the boundary condition manager.

CONTACT INTERFERENCES: Already defined contacts were deleted and a new global contact was defined.

Type 7 contact was defined with the recommended properties  given below:

IGAP=2: Set a variable gap to take into account the true distance between parts.

GAPmin=1: Specify the minimum thickness of the model to avoid numerical issues. Typically half of the thinnest part.

Inacti =6: Remove initial penetrations where possible. Elsewhere, reduce to less than 30% of the defined gap.

Istf =4: Set stiffness of interface based on the softer of master and slave. It helps when stiffness is calculated between material like foam and steel.

Stmin=1000N/mm: Specify a minimum stiffness in contact to avoid too soft contact.

Idel=2: Remove slave nodes from contact because of element deletion.

Iform=2: Friction formulation based on stiffness. For the edge to edge(type11) contact, we should never define friction.

Fric: 0.2

Also, Type 7 contact between bumper and rail was defined.

 PENETRATIONS AND INTERSECTIONS CHECKS: Before running the model all penetrations and intersections were removed by selecting the nodes and moving manually.

REVIEWING PARTS FOR CONNECTIONS: Connections between parts were checked and any floating spring or objects were removed.

RIGID WALL CREATION: An infinite plane rigid wall was created in front of the car with Dsearch= 1000 and friction 0.1

CONTROL CARDS: 

OUTPUT REQUESTS AND TH FILES:

  • Sectional force in the rails at the location of indicated node 174247.
  • The axial force received on the rails from the bumper.
  • Shotgun cross-sectional forces.
  • A pillar cross-section.
  • Acceleration curve received on the accelerometer at base of B pillar (on B pillar rocker).
  • Intrusions on the dash wall 66695,66244

RESULTS:

 

SECTIONAL FORCE IN RAIL AT NODE 174247:

From the plot, we can see the max force on the rail components is 21KN around 15 milliseconds. After this, there is a large deformation around node 174247. During the deformation phase from 15 to 30 milliseconds, the sectional force dropped gradually. After the collision, the least force across the section was observed at 30 milliseconds.

SHOTGUN CROSS-SECTIONAL FORCES: LEFT AND RIGHT

The above graph shows the sectional force received by a shotgun. The maximum force for the left section, during the collision, is 14KN at 40 milliseconds. From animation files, we can observe left shotgun deformed less, hence higher reaction force was seen. The right shotgun was deforming continuously so lesser sectional force was seen as cross-section was constantly changing.

A-PILLAR CROSS-SECTIONAL FORCES: LEFT AND RIGHT

A pillar left received more reaction force during the collision. From the animation files also we can see more deformation on left A-pillar.

CROSS-SECTIONAL FORCES AT BASE OF B PILLAR:

RAIL CROSS-SECTIONAL FORCES:

ACCELEROMETER VALUES AT BASE OF B PILLAR:

Two accelerometers were placed at the bottom of B-pillar to measure the sudden change in velocity.TH for these two accelerometers was created to view their plots.

The max acceleration received is just after the collision around 2milliseconds. This sudden change in acceleration is due to the instant drop in velocity from very high value to almost zero.

INTRUSION ON DASH WALL: At node 66695 and at node 66244

DASH WALL INTRUSION:66695

The intrusion is measured with respect to node 121751.

Before collision distance between points was 734.771.

After collision distance between nodes was 597.115

so the intrusion of the dashboard is  137.657

The intrusion at node 66244 with respect to node 122048

The initial distance between the two nodes was 781.808mm.

After the collision, the distance was 621.271

The intrusion at node 66244 was 160.537

A plot of relative displacement of the node was plotted and is shown below:

ENERGY PLOT:

From the above plot, we can see kinetic energy is getting converted into internal energy. Ideally, all KE has to be converted into internal energy and total energy must be constant.

Hourglass Energy and contact energy must be maintained under recommended values. In our case due to QEPH shell formulation, HG energy was below 5%.

Max's energy error was  -1.4% which is under the recommended value.

Mass error was between 0.019 to 0.02kg(2%-5%). Mass was added to the node whose time step was below a defined time step of 5 microseconds. 

ELAPSED TIME = 10123.10 s

LINK TO FILES

https://drive.google.com/drive/folders/1M-HL4RQS3_EDj47OZ4WeVgAcFQLKGa4b

 


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