CAE_Tech_Seminar_PD

Vehicle Integration – Safety & Structures
16th June 2011
© Copyright Tata Motors Ltd.
1 steve.fletcher@tatamotors.com
CAE Technical Seminar
Overview of Safety & Structural CAE
Steve Fletcher
Lead Engineer – VIG Safety & Structures
steve.fletcher@tatamotors.com

16th June 2011
Contents:
1. What is CAE
2. FEA basics
3. The virtual test laboratory
4. Capabilities
5. Limitations: Variation in the real world
6. Overcoming Limitations: Modelling for the real world.
7. Benefits of CAE
8. Future technologies

16th June 2011
CAE Tools Overview
CAE is a complimentary tool set to CAD & CAM
Computer Aided Design
Computer Aided Engineering
Computer Aided Manufacturing
They all use a common database system referred to as PLM/PIM – Product
Lifecycle/Information Management to ensure continuous development of a common set of a
data (i.e. the product)
CAE
CAD CAMPLM

16th June 2011
CAE Tools Overview
Computer Aided Engineering
CAE is generic term used to describe many
computer tools to support engineering
development.
Three of the best known tools are:
FEA: Finite Element Analysis
Stress analysis, crashworthiness, NVH,
Durability
CFD: Computational Fluid Dynamics
Aerodynamics, fluid flow
MBDS: Multi Body Dynamics Simulation
Kinematics and dynamics tool
FEA
CFD
MBDS

16th June 2011
This is no different in principle to the hand calculations that engineers have been used for
hundreds of years.
The formulas and calculations are the same as those used in classical text books which have
been used through the years from Watt & Stephenson to Issigonis & Dewis.
q
dx
wd
EI
dx
d






2
2
2
2
L
l
A
F
E



12
3
BD
I yI
M 


16th June 2011
Finite element analysis is simply a higher fidelity method for calculating the load carrying
capability of structures – we are the 21st century ‘Stress Calc’ Guys’.
10mm
10mm
The design is split up into small pieces (elements). It is relatively straight forward to characterise an
element, to know the effect of applying a load to it. Simple mechanical tests can be completed on physical
materials. The computer joins millions of these ‘elements’ together and the loads are transferred between
them.

16th June 2011
The Virtual Test Laboratory
There are several ‘flavours’ of finite element analysis which lend themselves to different types
of structural analysis:
Crashworthiness = Non-Linear Dynamic Explicit Analysis
Considers material behaviour beyond it’s yield point
Solves the equation F=ma (Newton's 2nd Law)
NVH (Noise/Vibration/Harshness) = Linear Implicit Eigen value Analysis
Considers material only in it’s elastic region
Solves F=kx and derive Eigen values (know solutions)
Durability = Non-Linear Implicit Static Analysis
Considers material behaviour beyond it’s yield point
Solves the equation F = kx
These tools enable engineers to support the design team to ensure that designs meet
performance requirements whilst minimizing weight, cost and complexity.

16th June 2011
Capability: Crash Analysis – Full Vehicle
We can assess the crashworthiness of structures in the virtual world, supporting all
engineering aspects from structural layout development to detail design of components:
Full crash model, comparison to physical test
Overall the CAE model shows very good agreement to the physical test, there are some minor differences in collapse of the
hood mechanism. The pitch of the model is less than in test, but this is only evident from c.80ms.

16th June 2011
Capability: Crash Analysis – Component & Sub-System
Curtain Airbag Deployment
This airbag uses an advanced technique called Corpuscular Particle Method (CPM).
This models the gas inside the airbag as individual particles, more accurately characterising the fluid flow in the bag.

16th June 2011
Capability: NVH Analysis
213Hz 219Hz
233Hz 240Hz
EV Power train Stiffness
The solutions are then
realised by the design team to
achieve cost,
manufacturability and
assembly requirements and
then reassessed by the CAE
team.
In this case the solutions
achieved the required
stiffness's, lowest mode
increased from 89Hz to 213Hz

16th June 2011
Capability: Durability Analysis
We can assess the durability of structures in the virtual world, supporting all engineering
aspects from structural layout development to detail design of components:
Speaker Grill Durability Analysis
525g steel ball of diameter 50mm dropped from a height of 406mm.
Contact velocity = 2.8m/s.
Material used for fret: 1.0mm thick, Stainless Steel, 200MPa yield.
Target: No permanent damage to parts.

16th June 2011
Benefits of using CAE in the design process
Minimise the amount of physical testing required. = Cost Save
Compress design and development timelines = Cost Save
Minimum faults/flaws in the final design (FMEA/FMA) = Better Designs / Cost Save
Increased opportunity to interrogate the design = Better Designs
Enable development of ‘disruptive’ designs in virtual space = Better Designs
Assess new test requirements earlier = Better Designs / Cost Save
Assess new materials/technologies earlier = Better Designs / Cost Save
Therefore:
More, quicker, better and increasingly cost effective products.

16th June 2011
Limitations: Capturing the real world
It is important to remember that we are building ‘models’ of the real world. The real world has
huge noise and variance which is difficult to capture and characterise.
Real World Issues
- Variance in base material properties, sheet steels can be
supplied with strength +/-20%
- Mild Steel = 140-200MPa strength
- E34 / HSLA340 Steel = 340 – 420 MPa
- Changes in material properties from forming processes
- Stamping can induce work hardening and thinning, very
significant on HSS.
- Casting process can change porosity leading to brittle
material properties.

16th June 2011
Changes in material properties from forming processes
The original material properties
and part thicknesses are from
laboratory tests on stock
material.
When the panel is formed the
material will become thinner as
it stretches (strain) around the
tool.
This straining will effectively
increase the material strength
in local regions, making the
load carrying capability of the
structure change.
Base sheet metal is 2.1mm thick with 0% strain

16th June 2011
Real World Issues
- Changes in position of dummies
- CAE achieves design position
- Physical Test achieves with a 25mm window.
- Tolerance of build of components
- CAE achieves design position
- Real world has significant tolerance allowed
- Other:
- Dummy calibration
- Spot welding location accuracy
- Fatigue modelling (real world repeatability has
shown factor of 3 in variance)

16th June 2011
Limitations: Computer says ‘No’.
There are also issues and problems to be resolved in the
virtual world:
- Computational rounding
- Computer codes round numbers. Sometime in
different ways (to more/less decimal places)
- This can make significant differences when
you complete millions of calculations.
- Appropriate characterisation techniques
- Are the assumptions made in the model
appropriate to capture the physics?
-Rubbish in = Rubbish Out
We are trying to capture the real physics with the simplest computational methodology, this is
always a compromise between accuracy and model build/run speed.
This means balancing engineering judgment with mathematical rigour.

16th June 2011
Overcoming limitations
Methods we can use to counter these issues include:
-Robustness assessments.
- Running multiple models with varying parameters to understand statistical
likelihood of performance.
-Rather than aim to achieve performance in a single condition, we aim to achieve
confidence that our fleet of vehicles will achieve the required performance.
4.64.34.0
Performance
Nominal Design
Model

16th June 2011
-Robustness assessments.
- Running multiple models with varying parameters to understand statistical
likelihood of performance.
-Rather than aim to achieve performance in a single condition, we aim to achieve
confidence that our fleet of vehicles will achieve the required performance.
4.64.34.0
Performance
Model
Family of results

16th June 2011
Robustness Example: Longitudinal Collapse Sub Model
B001Baseline
B002Wall+5deg
B003Wall-5deg
B004WallFric0.1
B005WallFric1.0
B006BumperFree
B007Gauge2.85mm
B008Gauge2.95mm
B009Yield323MPa
B010Yield363MPa
Run Description Mode Absorbed Energy (kJ) @ 30ms
B001 Baseline 1 22.0kJ
B002 Wall +5 deg 2 15.7kJ
B003 Wall -5 deg 3 16.4kJ
B004 Wall Fric 0.1 1 23.0kJ
B005 Wall fric 0.8 1 23.0kJ
B006 Bumper B/C’s off 2 17.6kJ
B007 Gauge 2.85mm 3 16.3kJ
b008 Gauge 2.95mm 2 17.8kJ
B009 Yield 323MPa 3 14.8kJ
B010 Yield 363MPa 2 18.3kJ
Three modes of collapse for the rail occur.
Modes 1 and 3 (Green & Pink) are quite similar
in directions, but the hinges occur a slightly
different places.
Mode 2 (Blue) is very different in hinge location
and direction.

16th June 2011
- Correlation activities
- Component tests
- Drop tests
- Crush tests
-Material Testing
- Tensile coupon tests
- Compression & shear testing
-More complex/sophisticated modelling methods
- Orthotropic material characterisation
- Advanced joint modelling (Bolts, Welds, Rivets, Adhesive)
- Inclusion of forming and assembly effects
- Inclusion of gravity effects (pre event, i.e. sag of dummies, belts,
suspension)

16th June 2011
The Future: Advanced Optimisation & Concept Modelling
Optimisation and concept modelling.
Advanced concept
generation tools are
available where basic
structural layouts can be
rapidly generated and
assessed.
These can be coupled with
optimisation tools to derive
the optimal structural
layouts for varying vehicle
configurations.

16th June 2011
The Future: Human Modelling
Several organisations are developing FEA models of humans, including Ford with THOR and
Toyota with THUMS (pictured).

16th June 2011
The Future: What’s Next?
There is a continued push to place CAE further up stream in the design process:
-Advanced optimisation and concept modelling.
-Human modelling
-Meshless methods (meshing process can be time consuming)
-Faster computers, Moore’s law still holds true (computing processing speed doubles every 2
years)
-CAE for all, the integration and simplification of CAE tools to move from a specialist tool to a
generalist tool (designers will complete their own engineering assessments).
-Specific developments:
- Advanced material characterisation (orthotropic, plasticity, creep, mesh
independent)
- Dummy modelling improvements

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