Assignment 7

Crash Analysis

A crash simulation is a virtual recreation of a destructive crash test of a car or a highway guard rail system using a computer simulation in order to examine the level of safety of the car and its occupants. Crash simulations are used by automakers during CAE analysis for crashworthiness in the CAD process of modeling new cars. During a crash simulation, the kinetic energy, or energy of motion, that a vehicle has before the impact is transformed into deformation energy, mostly by plastic deformation of the car body material (body in white), at the end of the impact.

Data obtained from a crash simulation indicate the capability of the car body or guard rail structure to protect the vehicle occupants during a collision against injury. 

• Side Impact tests: these forms of accidents have a very significant likelihood of fatality, as cars do not have a significant crumple zone to absorb the impact forces before an occupant is injured.
• Pole-impact tests: A difficult test that places a large amount of force on a small proportion on the side of the vehicle.

Objective

The aim of the project is to perform the side crash analysis of a neon BIW model on the rigid pole. The preprocessing is done in the Hypermesh and analysis is done in Radioss solver and the results are interpreted using Hyperview and Hypergraph.

Task

To calculate the below:

• Sectional force in the cross member.
• The intrusion at B pillar, hinge pillar, and fuel tank region & also provide recommendations on what can help to reduce Fuel tank intrusion.
• Peak velocity of the inner node of the door.

Procedure

• The rad file of the reduced car model is imported.

• The unit system is length(mm), time(ms), mass(kg), force(kN), velocity(mm/ms)

Crash Impact Application

Type 7 - A general-purpose interface & can simulate all types of impact between a set of nodes and a master node. 

Type 11 - Simulation of impact between edge to edge contact application.

Type 24 -  Simulation of impact between the surface to surface contact application.

Import Interface parameters

Igap - Determines how the size of the gap is calculated.

Gapmin - It specifies the minimum thickness of the model to avoid numerical issues.

Inacti - Check for the penetration of the elements & removes initial penetration in the model.

Istf - The provide the stiffness of the interface based on the master & slave.

Iform - Sliding forces are computed using the stiffness parameter of the interface.

Stmin - Minimum stiffness to use for the interface.

Idel - It deletes the element if it fails. 

• The type 7 interface is used since it can simulate all types of impact between a set of nodes & master nodes. In hypercrash under contact interface --> new --> Multi usage (type 7) and recommended parameters and friction 0.2 is set.

                                                               Type 7 Parameters

•  The penetration of the model is checked using Quality --> check all solver contact interface and penetration of the model is zero.

• The rigid wall with friction 0.1 is created. The cylinder wall is used for the analysis of the sidewall against the pole.

• The reduced model is used and impact analysis rotates about its center of gravity so the total mass of the reduced & full model must be the same so the few mass are added to the model. The load case --> add mass option is used to add the mass on the model.

• Mass --> balancing option is used to calculate the COG of the model.

• Initial velocity is set using load case --> Initial velocity. Select the type as translation & provide the y velocity as 8.88 mm/ms.

The green arrow indicates the velocity direction along the y-axis. 

• Use model checker to ensure good quality. The errors are selected & the run option is used to the automatic correction of the errors in the model.

• Timestep :0.5 to 0.1 microseconds.

• The simulation is run for 80 ms.

Output Request

A local frame of reference is created in the cross member & the time history TH card is created and sectional force, peak velocity of a node is assigned.

Results

Simulation 

The energy error value is around 2.3% which is in the acceptable range of the element type used & the mass error is 0.9275e-2 which indicates that the added mass to overcome the minimum element failure criteria is very less the increase in kinetic energy will be less.

Section forces in the cross member

The side crash occurs at the driver-side & section 1 represents the drive side cross-member &  section 2 represent passenger side cross member. The driver side has a maximum resultant force of 10kN & the passenger side has a maximum resultant force of 5 kN. 

Peak Velocity

The peak velocity is 9.2 m/s & after the crash, the velocity of the car reduces.

B-pillar

Fuel tank

The intrusion in the fuel tank can be increased by adding a cross member at the fuel tank & the material stiffness must be increased which reduces the intrusion.

Cross-member

Hinge pillar

Energy plot

Contour plot

Displacement

Plastic strain

Specific energy

Von Mises

Conclusion

The side crash analysis of the Neon Chrysler model was performed & the results of the simulation are provided below

Peak Velocity                                                          = 9.2 mm/ms.

Maximum displacement of the Hinge pillar                 = 300 mm.

Maximum displacement of the B-pillar                       = 210 mm.

Maximum Intrusion the fuel tank                              = 190 mm.

Sectional force in cross member (Driver Side)            = 10 kN.

Sectional force in cross member (Passenger Side)      = 5 kN