Assignment 6

Assignment 6

Aim - In this simulation we are studying the front impact of a car frame using non linear analysis. A front impact against rigid wall, during a crash and its passengers withstand very high level of acceleration (negative in the sense of deceleration). This simulation output suggest how the structure will deform in plastic manner, manual injury and also give knowledge for providing adequate space for the occupants within it. Examples Of the system that are used in motor vehicle safety include ABS, airbags, seatbelts , head resistant’s, anti intrusion bars, inner padding, laminated wing shields, crumple zone etc.

Objective -To perform a front impact analysis on neon_side_reduced_0000 model, which shows the energy distribution along the structure of the model, rate of deceleration along x, y, z axis, intrusion.

Methodology –

1. Unit system

Open neon_front_0000.rad file in note pad and check the unit system of the model [kg mm ms or mg mm s] and same recheck the units in hyper crash by opening the model on pop up window or on property card in which the rho, E, or other parameters value says the units of the model. Which is easy to read the model and it will quite easier to give loading inputs, property inputs etc.

2. Contact Interface

The contact interfaces are applied for eliminating any overlaps or penetration between interacting surfaces. The presence of initial penetration show adverse effect on the simulation means it will not show the deformation of the body in adequate manner.

There are several types of interface are available in radios. But each of these interfaces was developed for specific application field. However this application of field is not the only selection criteria. Some interfaces have their limitation so each interface used by their application, advantages.

Type 7- use for solid contact impact at all speeds.

Recommended parameters:

• Istf =4

Interface stiffness is the minimum of the master and slave stiffness.

If istf=2, 3, 4, 5.

K=max [Stmin, min (Stmax, Kn)]

Where, Kn is computed from master segment stiffness Km and slave node stiffness Ks:

Istf=4, Kn= min (Km,Ks)

Km is master segment stiffness and computed as:

When the master segment lies on shell or is shared by shell and solid:

Km=Stfac⋅0.5⋅E⋅t

• Igap=2

Variable gap +gap scale correction of computed gap

Max {Gapmin, min[Fscalegap⋅ (gs+gm), Gapmax]}

Where,

Gm: master element gap

= t/2: with t being the thickness of the master element for shell elements

Gs: slave nodes gap

= t/2: with t being the largest thickness of the shell elements connected to the slave node

• Idel=2

When a 4node shell, 3node shell or solid element is deleted, the corresponding segment is removed from the master side of the interface. It is also removed in the case of explicit deletion using radioss engine keyword/del in the engine file.

Additionally, non-connected nodes are removed from the slave side of the interfaces.

• Stmin= 1000 N/mm

Minimum stiffness (used only when istf=2, 3, 4, 5)

• Gapmin= 0.5 mm
• Minimum gap for impact activation

If master segments are shell and solid elements,

Gapmin =min (tm,lmin/2)

Where, tm – the min thickness of the master shell element, for Igap=1, 2, 3.

Lmin – the smallest side length of all master segments (shell or brick)

• Inacti=6

Inacti is deactivation flag of stiffness in case of initial penetration.

=6 – gap is variable with time, but initial gap is adjusted as (node is slightly depenetrated)

• Iform=2

Friction penalty formulation type

=2 – stiffness (incremental) formulation

• Fric =0.2

Process:

• Open neon_front_0000 model in hyper mesh - model browser – groups- create new – give card image = type 7- grnod_id =select all nodes- surf_id =select all elements –give above parameters.
• Delete all other groups because as create interface for whole car body so other groups will create difficulty to the simulation.

3. No penetration and intersection

• This check is necessary because of penetration and intersection the simulation result will not get in proper manner or simulation will not run or shows error.
• Penetration and intersection will occur because of the gapmin value, it should be lmin/2 foe shell and solid elements.

Process:

• In hyper mesh –tool menu- penetration check- in selection =select group –check-close.
• If the penetrations are occur then select all and click on automatic penetration /intersection fix-close.

4. Rigid body correction

• Rigid body is set of slave nodes and master node. Which didn’t have any displacement, or any loading condition etc

Process:

• In hyper crash –tool menu-model checker –radioss block.
• Run the error – It will show where the error is in rigid body for correcting.

5. Rigid wall

• Rwall is nodal constraint applied on a set of slave nodes in order to avoid the node penetration to the wall. If contact is detected, then the slave node acceleration and velocity are modified.
• In the simulation there is no gap to determine whether or not a slave node is in contact. Contact occurs only when the slave node impacts the rwall surface.
• The slave nodes tangential velocity can be modified using flag slide: if default value =0 enables model the pure sliding during contact. If set to 1, no sliding is allowed, the slave nodes are tied in the tangential direction. If set to 2, friction based on coulomb model is enable
• There are 4 type in rwall so the infinite rigid wall is used which is planer wall and will preferable for frontal impact.

Process:

• Hyper crash –right click- create – rwall-select node- give normal-slide=2-fric =0.1.

6. Admass to the car to reach the target weight 700kg while getting cg about req. range.

• Assign additional non structural mass to nodes or group of nodes. Optionally the total additional non structural mass of a part or a group of parts can be defined (applied to shell and solid only) or a surface mass can be assigned to surface and radioss would then compute the added node based mass value using area (volume)-weighted distribution.

Process:

• By comparing the full scale 300k node model; adding the additional weight to reach the target weight 700kg while getting CG about required range.
• Hypercrash –right click- create –admas- assign name-mass type=1- grnod_id-mass= 511.5745562707959kg.

7. Initial velocity

• Defines initial velocity on group of nodes.

Process:

• Give the initial velocity of 15.64mm/ms to the whole body nodes.
• Hyper crash –right click- create – boundary conditions- initial velocity-name= ini_vel-give direction vx=15.64-grnod_id-enter

8. Use model checker to ensure good quality

• This is the tool for checks before running a model are related to :
• Meshquality
• Spring definition
• Intersection and penetration in interface definition
• Checking incompatible kinematic conditions:
• No common slaves node between rigid bodied
• Only free master node
• Spherical inertia for the small ones
• Mass and center gravity
• Thickness of parts
• Initial velocity value and direction
• Rigid wall normal material law : unit system consistency
• Free nodes
• Monitored volume
• Connectivity and parts
• Mesh size between connected parts

Process:

• Hyper mesh-tool-model checker-error-run
• If any error occur then click on automatic correction

9. Time step: 0.5 to 0.1 microseconds

• Engine keywords-DT-DT NODA-tmin=0.001

10. Run 80ms

• Engine keywords-RUN-tstop=80

11. Output request:

• Create fix frame on indicated nodes
• Create sections in the rails at the location of indicated node 174247, rails, shotgun, A pillar.
• Sectional force in the rails at the location of indicated node 174247

The resultant sectional force in the right and left rails at the location f indicated nodes 174247,179120 are plotted using hyper graph.

The RH rail sectional force is 26.92KN and The LH rail sectional force is 22.29KN

• Axial force received on the rails from bumper

The resultant sectional force in the right and left rails from the bumper at the location of indicated nodes 148462,147343 are plotted using hyper graph.

The RH rail sectional force is 10.54KN and The LH rail sectional force is 10.31KN

• Shotgun cross sectional forces

The resultant sectional force in the right and left shotgun at the location f indicated nodes 144433,139604 are plotted using hyper graph.'

The RH rail sectional force is 10.71KN and The LH rail sectional force is 8.25KN

• Hinge pillar sectional forces

The resultant sectional force in the right and left rails at the location f indicated nodes 7929, 4929 are plotted using hyper graph.

The RH rail sectional force is 5.89KN and The LH rail sectional force is 5.29KN

• A pillar cross sectional forces

The resultant sectional force in the right and left rails at the location f indicated nodes 113394,103242 are plotted using hyper graph.

The RH rail sectional force is 7.37KN and The LH rail sectional force is 3.81KN

• Acceleration curve received on the accelerometer at the base of B pillar

At the LH rocker acceleration is 5.42mm/mm2 and At the RH rocker acceleration is 1.27mm/mm2

• Intrusion on the dash wall 66695, 66244

The node 66244 has elongation about 3.41mm, and the node 66695 has an elongation 2mm.

• Energy plot

Energy error = -1.1%

• Displacement

Maximum displacement of car body is 1.25e+3mm

• Von mises result

The maximum stress is occur at the door side of car which is 3.661e-01N/mm2

Result

Energy error = -1.1%

Mass error = 0.3001E-01

Time taken = 6362.73 s

No of cycle = 80001

Von mises stress= 3.661e-01N/mm2

Displacement = 1.25e+3mm

At shotgun The RH rail sectional force is 10.71KN and The LH rail sectional force is 8.25KN

Intrusion on the dash wall 66695, 66244=3.41mm and 2mm

LH rocker acceleration is 5.42mm/mm2 and At the RH rocker acceleration is 1.27mm/mm2

At a pillar The RH rail sectional force is 7.37KN and The LH rail sectional force is 3.81KN

At hinge pillar The RH rail sectional force is 5.89KN and The LH rail sectional force is 5.29KN

On rails from bumper The RH rail sectional force is 10.54KN and The LH rail sectional force is 10.31KN

At 174247and 179120 The RH rail sectional force is 26.92KN and The LH rail sectional force is 22.29KN