(Problems with) Optimising Brake Disc Design by Simulation (Problems with) Optimising Brake Disc Design by Simulation Bill Young Senior Consultant, Design and Simulation Optimising Brake Disc Design by Simulation

OutlineOutline “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

Weight 3.8kg Investment £150,000 Piece Price £32 1 st Option

2 nd Option Weight 4.2kg Investment £10,000 Piece Price £28

Weight 3.2kg Investment £8,000 Piece Price £16 3 rd Option

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