Introduction to Crash Analysis
Transcript of Introduction to Crash Analysis
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Pierre-Christophe MASSON / Technical Specialist / Sept. 2021
INTRODUCTION TO CRASH ANALYSIS
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Agenda
Introduction to Crash Analysis
• Introduction to Crash
• Explicit simulations
• What is Altair Radioss™ & What does it solve?
• FEA Workflow
• Application: Simulation of Crashbox
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INTRODUCTION TO CRASH
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CRASH Analysis
What is Crash analysis?
High velocities (> 1m/s)
High deformations
Passive Safety
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Why doing Crash analysis?
Occupant Safety
Pedestrian Safety
Systems Safety
CRASH Analysis
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Why doing Crash analysis?
Regulations (ECE, FMVSS, ADR, etc.)
New Car Assessment Programs(US NCAP, J NCAP, Euro NCAP, IIHS etc.)
Associations (ADAC)
Internal Requirements
CRASH Analysis
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CRASH Analysis
Why doing Crash simulations?
At early stages of project, only CAD are available
Tests are expensive(especially on prototypes)
Reduce time development
Robustness & Optimization
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ATC’18 – Crash simulation at Groupe PSA / Main Stakes and Challenges
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ATC’18 – Crash simulation at Groupe PSA / Main Stakes and Challenges
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EXPLICIT SOLUTIONS
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FE Modeling of a Physical Problem
Space
• The geometry is discretized by Finite
Elements
Time
• Discretized by Time Step
Physical Laws
• Mass conservation
• Energy conservation
• Momentum conservation
Formulation – Choice of time and space
discretization
• Lagrangian
• Eulerian
• Arbitrary Lagrangian Eulerian (ALE)
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Explicit Methods vs. Implicit Methods
Implicit Methods
The state of a given system is solved for
several time steps at once
Explicit Methods
The state of a given system at a given time
is computed from the state of the system at
an earlier time
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• The time step Dt is the time required for a shock wave (governed by speed of sound) to propagate
across the smallest distance in an element
• An explicit solution is stable if Dt < Dtcritical
• The solution is unstable if information passes across more than one element per time step:
• Stability depends on two factors:
1. Size of smallest element → Numerical
2. Sound propagation speed → Physical
Definition of Time Step
Fext(t)
L
c
lt cD
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Time Integration
Explicit Flow Chart
ttt D+=
externalF
1. Loop over elements
+
=
i
j
j
iij
x
v
x
v
2
1
)( ijij f =
( ) ( ) tttt ijijij D+=D+
2. Assemble
hourglass
FF ,internal
contact
F
= iii mFv
internalF
txxx nnnD+=
−+
21
21
txxxnnn D+=++
211
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WHAT IS RADIOSS™?WHAT DOES IT SOLVE?
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Altair Radioss™: What is it ?
Structural analysis solver for highly non-linear problems under
dynamic loadings
o High Scalability, Quality and Robustness
o Supports Multiphysics simulation and advanced materials
o Used across all industries to improve crash, safety and manufacturability
o For 30+ years an established standard for automotive crash and impact
Automotive
Aeronautics
Consumer goods
Electronics
Defense
Ship building/Navy
Biomechanics
Offshore
….
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Safety dummy models:
Airbag Folding & Deployment:
Failure risk assessment:
Safety barriers models:
WHAT IS RADIOSS?
CRASH & SAFETYIN
AUTOMOTIVE
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WHAT IS RADIOSS?
CRASH & SAFETYIN
AERONAUTICS
Seat & Safety
Bird Strike
Debris impact
Composite Modeling
Failure risk assessment
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WHAT IS RADIOSS?
DROP
Moto helmetBottle
Cellphone
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WHAT IS RADIOSS?
FLUID-STRUCTUREINTERACTION
Aeronautics: Ditching
Defense: Blast
Defense: Ballistics
Tank Sloshing
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WHAT IS RADIOSS?
MANUFACTURING
Additive Manufacturing
Metal Forming
Composite forming
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APPLICATION: CRASHBOX
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Simulation of a Crashbox for Formula Student
• Unit System: kg, mm, ms → GPa, kN, J
• Impactor
o Mass: 300kg
o Initial Velocity: 7 m.s-1 (25kph)
o Kinematic Energy: 7.35kJ
• Input Data:
o geometries (crashbox, anti-intrusion plate, bulkhead and impactor)
o Metal reference for the plate and Honeycomb data for the crashbox
Pictures & Data by Institut für Technische und Numerische Mechanik, Universität Stuttgart
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Standard FE Modelling Workflow
Geometries, Connections (bolts, welding, etc.)
& Materials (BoM)
Main challenge: get geometries as clean a possible
(to reduce the meshing/assembling steps)
Software: Catia, ProEngineer, …
Discretize the geometry
Use FE entities that allows to reproduce mechanical behaviour of the
part (solid, thin shell, beam, …)
Main challenge: stay close to initial geometry, but apply appropriate
meshing rules
Software: HyperMesh, SimLab…
Set properties, materials, contacts, loads, boundary conditions
Check the solver input file with dedicated tools
Main challenges:
Assembling the parts of the model
Preparation of the model in order to run a one-shot simulation
Software: HyperMesh, SimLab, HyperCrash, etc.
Possibly initiated with a solver check of the model
Run the computation
Main challenges: Convergence, Respect of physical Laws,
Computation time
Software: Radioss, OptiStruct, AcuSolve, …
Check the convergence/quality of the simulation
Analysis and interpretation of the results
Main challenge: Extract all significant information from results
Software: HyperView/HyperGraph, …
Geometries +…
Finite Elements
Solver input file(s)
Solver output files
Results
?
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(Crash) FE Model Setup Standard Workflow
Assign Properties (thickness) & Materials
Define Welding, Bolts, Glues & Links, Rigids, etc.
Create interfaces: check & remove intersections, penetrations
BCs, Initial/Imposed Disp./Vel./Acc, Loads, Added Mass, Impactors
Define Measurements
Get the proper geometries, material & connections info
(BoM, Welding database, etc.)
Define Meshing (1D/2D/3D, Elt types) + Meshing Class (size & quality criteria)
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Aluminium
Aluminium Physical & Mechanical proprties
Density 2.8g.cm-3 2.8E-6 kg.mm-3
Module of Elasticity 70 GPa 70 GPa
Poisson’s ratio 0.33 0.33
Yield Strength 300 MPa 0.300 GPa
Tensile Strength 390 MPa 0.390 GPa
Failure Elongation 28% 28%
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Honeycomb
Honeycomb Physical & Mechanical proprties
Density 0.0913 g.cm-3 9.13E-8 kg.mm-3
E11 225.6 MPa 0.2256 GPa
E22 = E33 20 MPa 0.02 GPa
G12 200 MPa 0.20 GPa
G23 = G31 200 MPa 0.20 GPa
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