Assignment 7

Side Crash Analysis of BIW

Objective:

To perform Side crash analysis on BIW and obtain output requests at the following sections:

• Sectional force in the cross member
• Intrusions at B pillar, hinge pillar and fuel tank region and countermeasures
• Peak velocity of inner node of the door 337773

Case setup and execution:

The given reduced element model is imported into HyperCrash and if we check the connection quality,

Menu -> Quality -> check connectivity of tree selection

HyperCrash shows some connectivity issues in the model. Some of the issues are because of the deletion of elements in the reduced element model. Those connections are deleted.

A rigid cylinder with friction 0.1 is created near the B pillar and very close to the left door and Dsearch is provided a value of 500. It tells the solver to use all the nodes within that proximity to use as slave nodes for the rigid cylinder and so it won’t cross the rigid cylinder.

Menu -> Loadcase -> Rigid cylinder

The full 300K element model is opened in another HyperCrash session and both the models are compared for mass distribution and Center of gravity. Mass is added on the reduced model to match the Full scale model in order to capture the exact crash scenario and it is made sure that both model’s center of gravity coincides (The Center of gravity would fall below the driver’s seat in most of the cases).

Menu -> Loadcase -> Added mass

Menu -> Mass -> Balancing (to view total mass and C.O.G)

An initial velocity of 35mph is given to the model in y direction

Menu -> Loadcase -> Initial Velocity (35mph = 15.6464m/s) and select entire model nodes

Sections are created at 2 cross members to analyze the forces passing through them

Data History -> Section -> Section

Now sections are created, we have to record time data in these blocks

Time history -> create new -> TH of section

We also have to include interface to analyze contact forces

Time history -> create new -> TH of interface

The question asked to plot intrusion of 3 nodes, so we need to record time data for nodes

Time history -> create new -> TH of nodes (and enter the node IDs mentioned in the question and Default DEF variable is selected) and movable skew is created on the right rocker which is free from deformations. Since, we need to measure intrusions, we will take the reference point on the driver seat location for which also TH of node is created.

Engine file is edited as shown:

Run: 80ms

DT_ELTYPE_KEYWORD_IFLA : Time step - 0.5 to 0.1 microseconds (the model already has Time step defined for each type of elements)

ANIM DT: Tfreq = 2ms

ANIM_ELTYPE_RESTYPE: ELEM variables = EPSP, ENEM, VONM

ANIM_MASS: On

MON: On

PARITH: On

Print: -100; 55

Tfile: DT_HIS = 0.5

A global contact interface is applied with recommended properties on the whole model. Type 11 contact is applied to specific areas of concern where edge to edge contact is expected. After creating contact interfaces, it is made sure there is no penetrations and intersections in the model. After running simulation, on viewing the animation file, few more parts were showing edge to edge intersection and penetration. So, more Type 11 contacts are added to resolve the issue.

Checks and Debugs:

Now the model checker option in HyperCrash is used to check for errors and warnings in the model.

Menu -> Quality -> Model Checker -> Run

The errors and warnings are corrected, and the model is now ready for running Radioss simulation.

Starter output file (checked Final mass, COG, no incompatible kinematic condition, Normal Termination), Engine Output file are checked, and no issues found.

Mass error is 0.76% and is within 3% allowable limit

Energy error is -1.5% and is within 5% allowable limit

(Hourglass energy + Contact energy)/Total Energy is 1.4% (found by obtaining max value of Hourglass energy, contact energy, and Total energy plots) and is within 15% allowable limit

There is no sudden drop-in Time step (viewed in Engine output file)

VonMisces animation looks smooth

Hence, we can say simulation is good.

Results and conclusion:

• Sectional force in the cross members

The graph shows the forces passing through the cross members. The max force is around 2.829kN for rear cross member and around 6.343kN for front cross member.

• Intrusions in B pillar, hinge pillar and fuel tank region

The graph shows the intrusions of the B-Pillar, Hinge Pillar and Fuel tank nodes. Since analysis didn’t include a dummy and fuel tank, it is not possible to conclude if this is good or bad. In an analysis with these components, if the displacement needs to be limited to save fuel tank/driver, some design modification (can make it thicker, change material) can be made in the B-Pillar, rockers, cross members to absorb more energy.

Math function used for calculating max intrusion

• Peak velocity of inner node of the door

The graph shows the velocity profile of a node in the front door.

Peak velocity = 16.22mm/ms