(Problems with)
Optimising Brake Disc Design
by Simulation
Bill Young
Senior Consultant, Design and Simulation
Outline
“Design and Simulation”
Simulation Tools
Optimisation Tools
Opportunities for Optimisation
Simulation Tools
“Horses for courses”
Range of analysis types
Durability
Impact and Safety
Range of software
MSC.Nastran
LS-Dyna (explicit and implicit options)
Durability Analysis
Impact Analysis
Fracture Assessment
CFD - Aerodynamics
Brake Disc Analysis
Mechanical, thermal
stress, distortion
Optimisation Tools
“Heuristic approach”
Structural Optimisation – MSC.Nastran SOL 200
Element properties are design variables; nominated objective
function is minimised/maximised
Shape (Topology) Optimisation – Optistruct (HyperWorks)
Elements are potential voids; material is distributed most efficiently
to address loads
Either process needs feeding with appropriate data
Optimisation Inputs
Objective
Lightest (cheapest) design allowing…
Variables
(Real) design parameters to be changed within
design envelope, keeping within…
Constraints
Limits to structural response
Hill-climbing analogy
Case Study:
MG TF Suspension Concept
Re-engineer the system to give improved ride
and handling
Enhance the vehicle’s “sporty” feel
Prolong product life
Lower manufacturing costs
MG TF
Large Impact Load
Weak Points
MG’s Trailing Arm
Concept
Tubular steel fabrication
High strength
Low cost manufacturing
1st Option
Weight
Investment
Piece Price
3.8kg
£150,000
£32
2nd Option
Weight
Investment
Piece Price
4.2kg
£10,000
£28
3rd Option
Weight
Investment
Piece Price
3.2kg
£8,000
£16
Final Design
Spheroidal Graphite Cast Iron
10% lighter than standard cast iron
Over twice as strong
From CAD to parts in 5 days
Optimised for weight and performance
Using analysis at the point of design
Low cost / low investment
Half the price of the fabricated option
Trailing Arm Concept Design
Follow-up exercise
(Optistruct)
Define packaging
space
Bush mounting
Tetrahedral model
Design & nondesign
zones
Trailing Arm Concept Design
Single load case effect (braking)
Reaction at bushes, general stress
determines design
Trailing Arm Concept Design
Multiple load cases
Residual shape: load paths
Most effective use of material
But… manufacturing constraints dictate further
changes (eg stiffness during machining)
Opportunities for Optimisation
“There are no problems, only opportunities”
Tools and computing power exist
Geometry, (material properties) exist
“Opportunity” lies in defining constraints
(combination of loads and limits to
responses)
Dealing With Opportunities
(Not enough directly relevant data)
Conservative assumptions
Averaged/Extrapolated data
Data from “similar” design
Relative, not absolute
Simplify!
Solving Problems - Seizing
Opportunities for Optimisation
Address Definition of Loads and Restraints (Supports)
Thermal – friction-induced
CFD input to heat transfer/temperature prediction problem?
Mechanical – manufacture
Casting/forging simulation for residual stresses?
Mechanical – assembly
Pre-load simulation, tolerance sensitivities?
Mechanical – braking
Local load distribution dependant on other components? Use
more sophisticated (assembly) models? Integrate (ADAMS)
The Problem with Problems…
“For every complex problem, there is a
solution that is simple, neat, and wrong.”
- H. L. Mencken