Frontal Crash analysis according to FMVSS 208 standards

Objective:

Simulate a frontal crash of the Neon car model with appropriate interfaces, boundary conditions. Required outputs are obtained from the frontal crash simulation and analyse the results.

Case setup:

• The frontal crash model with only components which in the focus for frontal crash analysis is imported into the hypermesh with radioss as the solver.
• Model is checked for its unit system by comparing the values of density and young’s modulus values in the material cards and [Kg mm ms] is used.
• Unsupported cards are deleted from the model.
• The interfaces which are present in the given model are deleted as they don't include all the components of the model.

• Type 7 interface is created with self impact. The type 7 interface is defined as shown below.

• Model is checked for intersections and penetrations. As no such intersections are found, no action is taken.
• A rigid wall is created with the friction of 0.1 and dsearch is taken as 1000mm.

• The model is compared with full-scale 300K model and the masses are added to adjust the position of Centre of Gravity accordingly. The added masses are listed below.

Name (Location)	Mass added (Kg)	Components/Elements
Radiator	15	Radiator component
Engine	50	Rail components
B-pillar	68.142	B-pillar components
Front seat support rail 1	80	Seat reinforcement component
Front seat support rail 2	150	Mid rail component
Floorboard	150	Floor elements

• The boundary condition of the initial velocity of 35mph i.e. 15.56 m/s is applied to the model.

• Using model checker, required corrections in the model are done. Errors from the model are dealt with accordingly and corrections are done in the model.
• The joints which don’t have any significance in this model are deleted i.e. spherical and translational joints. Significance of joints is lost if all the required components of the joint are not present in the current model.

• Floating elements and the free nodes are deleted from the model.

• Empty and unused categories are deleted from the model.

• Time step is monitored and appropriate time steps are used accordingly.

• Accelerometers are placed on the nodes of B-Pillar components at nodes: 20687 on the left side and 21687 on the right side.

• Sections are created at rail & bumper, in between the rails at node 174247, at the shotgun and at A-pillar cross-section with their individual frames and suitable elements are selected for each section (Through Gshell sets).
• Two springs having very low stiffness is defined to record the intrusions of nodes: 66695 and 66244.

• The model is executed under radioss with help of 4 threads.

Results and conclusions:

• Centre of gravity is adjusted to the required range of its position by adding the masses to the model at different locations and the whole mass of the model is brought from 188kg to 700kg.

• The simulation ran for 80 seconds run time, with normal termination. The total number of cycles is 80001 and elapsed time is 5106.80 sec. Energy error starts with 0% and ends with -2.5% while following a decreasing trend. Mass error is below 2% having a maximum value of 0.02977. Very constant No elements are deleted from the model.

From the time step plot, it can be observed there is a rise in time step between (0,5) secs. This shows the car model hits the rigid wall at 3.5 sec. Later the time step is controlled to be almost constant till the end of the simulation.

• Animation

From the simulation output, it can be observed that most of the crash energy is absorbed by the bumper and other connected components. Crash energy is almost absorbed and very fewer stresses passed into the later components, thus securing the passengers by maintaining the structure with fewer deformations in the cabin.

• Intrusions: To record the intrusions on the dash wall for nodes 66695 and 66244 nodes, two straight springs with low stiffness are defined and the elongations in the spring can be considered as intrusions. Spring 532714 includes node 66695 and spring 532715 includes node 66244.

The intrusion of node 66695 is 188.83mm and node 66244 is 167.29mm. Plots of the intrusions show no deformations in the dash wall till 10th second.

• Accelerations on the nodes which are on the base of B-pillars.

• Sectional force plots

Axial forces from bumper to rail.

Cross-sectional forces in the rail components @node:174247.

Shotgun cross-section forces.

A-pillar cross-sectional forces.

The plots of sectional forces at rails, shotgun and A-pillar have a decreasing trend of scale on the Y-axis (I.e. Values of Forces) for the same scale of X-axis (I.e.Time). From this, we can say that the forces are distributed along the path in the components of the car model as the force travels towards the rear (I.e. rails>shotgun>A-pillar & goes on).