Slam Analysis for Closures

Presenter Abi Swaminathan

ContentIntroductionTypes of ClosuresHood Slam Analysis Hood Assembly Boundary ConditionsLoading ConditionTarget for Slam AnalysisTransient Response AnalysisAnalytical Procedure

 

Introduction

Doors are hanged on parts should fulfill diverse requirements over their complete life time.

The main function of hang on parts is to open and close the car.

The damage to the components of the closures induced by the slam , accumulates over the vehicle lifetime and may lead to failure.

Types of ClosuresHoodDecklidHatchbackTailgateSide doorSliding Door

Types of Closures

Hood Slam Analysis

Hood opening/closing is a necessary function in a vehicle.

But the closing often results in an impact known as hood slam.

Impact loads –special case of dynamic loads that occur when there is a sudden change in velocity.

Dynamic loads- Force generated when the vehicle is in motion

Hood Slam AnalysisThe hood slam load- Rotational velocity

applied to the hood in the open position. When the hood reaches the closed (latched)

position, Striker contacts the latching mechanism. periphery of the hood contacts seal(s) and

bumpers. Then sudden impulse results in transient

vibration of the hood sub-system.High transient stresses can result in fatigue

cracks on the hood structure or at the striker to body interface.

Hood Assembly

It includes fully trimmed closures.Body in white front structure – cut

line with SPCInner and Outer PanelsHinge assemblyDoor structural membersLatch/ StrikerAdhesive, Hem, Mastic and weldsSeal

Hood Assembly

a) hood inner b) hood outer c) main reinforcement

d) hood hinge reinforcement e) latch reinforcement

f) assembly without the outer panel.

Hood AssemblyLatch Mechanism which catches, holds, and

releases the striker in hood closing and locking systems

Found on door side in doors, decklids, and tailgates and on body side in hoods

 Striker Small bar on door side of latch

mechanism which strikes the latch on closure and is then held in place until the latch is released

Found on body side in doors, decklids, and tailgates and on door side in hoods

Hood AssemblyWeather-strip seal:• Rubber seal found around doors, glass, and deck lid openings to prevent seepage of water into the vehicle interior

Hood AssemblyHood Bumper:

• This bumper is used on the radiator support and is adjustable in order to help get the correct panel alignment at the front of the hood.

• They also help reduce rattles by minimizing metal-to-metal contact.

Boundary Conditions:

The body side hinges -all six degrees of freedom.

The latch attachment - all six degrees of freedom.

Bumpers -all six degrees of freedom.

Seals -all six degrees of freedom.

Loading ConditionApply initial angular velocity to all rotating

closure parts about hinge pivot.

Angular velocity based on the hood geometry w(omega)= V / r where :w= hood rotational velocity about the hinge pin

centerlineV = the specified linear velocity (normally

specified at the tip of the front of the hood) r = the distance from the hinge pin center line

to the tip of the hood (m) 

Target for Slam Analysis:

Body & Door should provide clearance for Over slam .

The product will meet customer expectations for reliable service under anticipated usage conditions for the useful life of the vehicle.

Typical Hood over travel response curve:

Initial velocity: calculated from height of fall

calculation time: approximately up to 2 ms after reversal point

Time(sec)

Dis

pla

cem

en

t (m

m)

TRANSIENT RESPONSE ANALYSIS (NASTRAN SOL. 129)

Transient response or natural response is the response of a system to a change from equilibrium.

It’s purpose is to identify areas of the hood structure subject to high stress, quantify latch, striker, bumper, and hinge loads, and calculate the structural fatigue damage due to a door impact.

Transient solution Equation Transient solution uses the following equation and

evaluates the structural response with a fixed integration time step (Δt)

 [M]* {u"(t)}+ [C]* {u'(t)}+ [K]* {u(t)}= {P(t)} where [M]: Mass matrix, [C]: Damping matrix,  [K]: Stiffness matrix,  {u"(t)}: Acceleration matrix,  {u'(t)}: Velocity matrix,  {u(t)}: Displacement matrix,  {P(t)}: Applied force matrix, and t: Time  The damping matrix [C] =(G/ ω3)* [K] + (1/ ω4) ∑ GE*[KE]

 where  G: overall structural damping coefficient (PARAM, G)  ω3: frequency of interest in radians per unit time (PARAM, ω3)  ω4: frequency of interest in radians per unit time (PARAM, ω4),  [K]: global stiffness matrix,  GE: element structural damping co-efficient  [KE]: element stiffness matrix.

Analytical Procedure:

Analytical Procedure:

Analytical Procedure:

Analytical Procedure:

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