Low Carbon Vehicle Technology Project
(LCVTP)
WS 7 Lightweight Structures - Technology Review
November 17th 2011
Geraint Williams
WMG
Practical performance evaluation of
LCVTP WS7 materials technology concepts
Neil Reynolds
WMG
Contents
 Introduction
 Description of the approach to technology performance evaluation
 Coupon level testing
> Materials comparisons
> CAE coupon test study
> TPC aging
 Demonstrator component (beam) testing
> Dynamic crush
> Static flexure
> Fatigue flexure
 Conclusions and next steps
Introduction to WS7 mechanical
characterisation
 Purpose:
> To establish the structural capability of selected lightweight
materials/process technologies against existing benchmarks
 Approach:
> Using a step-wise testing methodology
 Starting at coupon-level standardised testing
 Develop CAE tools
 Culminating in proof-of-concept application related demonstrator
component testing
WS7 Test approach
Selection
Demonstration
Simulation
CR
 Multiple materials - supplier engagement activities
 Standardised testing (tensile, flexure, lap shear)
 Candidate materials versus benchmark materials
 Testing demonstrator parts (flex, crush, impact)
 FE model input and benchmarking
 Develop predictive FE model
 Technology validation
 Benchmark performance against predictive models
Coupon testing
• Static, standardised testing
> Basic engineering data for selected materials
> Detailed CAE input data for reliable predictive design
Coupon testing – aging of PA6-GF
• Material aged using 240 hour salt bath immersion (JLR) then tensile tested
Coupon testing – CAE case study
• 4 tests carried out to develop CAE model input data
> Estimating compressive properties
Values
EA, e11t, xt
Test and Fibre Orientation
UD Tension 0o
EB (=Ec), vBA, e22t, yt UD Tension 90o
GAB, τ1, γ1, gms, sc
sc
, τ1, γ1, gms,
Shear (in lamina plane) +/-45o
GCA, (=GBC)
Shear (interlaminar) 0o
Example Simulation
Coupon testing – CAE case study
Tension testing
0 degrees
90 degrees
0
0.005
0.01
0.015
Axial strain ()
0.02
0.025
Coupon testing – CAE case study
Shear testing
+-45 degree tension
0/90 short beam flex
0
0.05
0.1
0.15
0.2
0.25
Shear strain ()
0.3
0.35
0.4
0.45
0.5
CAE case study outcomes
 Complete, correlated LS-DYNA model for TPC laminate material
> Ability to reliably design with alternative materials
> Approach for generation of CAE input data set transferable and
repeatable for other new materials
 Performance of candidate material evaluated at a material level
> Strength and stiffness
> Failure mode and the effect of fibre angle on failure mode investigated
 Next steps
> Develop techniques for reliable evaluation of compressive properties
> Variable strain rate and fatigue
Demonstrator beam study
 Experimental build-and-test study using a test component representative of
an automotive structural element
> Ensuresrelevanceandtransferabilityofresultstoapplication
> Enables manufacturing and performance to be evaluated in line with
end use expectations
 Split into 3x main sections:
> End-wise dynamic crush
> Static 3-point flexure
> Fatigue 3-point flexure
Beam details
• Cross section: 45 x 75mm, length: 450mm (flex)/375mm (crush)
End-wise crush
 Allows the measurement of the energy absorbing efficiency of candidate
and benchmark materials in front-end crash test scenario
 Dynamic spring-assisted falling weight test at two energy levels:
> 8kJ, 14.6m/s, 133kg
> 4kJ, 7.8m/s, 74kg
 Test set-up is designed to ensure initiation into progressive failure mode,
can evaluate:
> Failure mode(s)
> Average crush force
> Specific energy absorption of each material
End-wise crush - comparisons
 Undamaged length:
> Original length – damaged
Damaged length
region
 Specific energy absorption (SEA, J/g)
> Applied energy / weight of
Original length
damaged region
Undamaged length
End-wise crush - comparisons
 Average crush force:
> E=Fxd
Total energy
Max deflection
> F=E/d
 Incorporates energy
contribution from initiation
peak and other peaks
Average force
Crush – PA6-GF60/Alu 5754
comparison video
Crush – undamaged length
Crush – Average force
Crush – Specific energy absorption
Crush – effect of joint integrity
Non-optimised SPR
Threaded fasteners
Crush – discussion & conclusions
 Generally, the TPC material performs well in crush, with superior specific
properties to the metallic benchmarks
> The SEA of the composite is ≈ 2x that of the metallics The SEA of the
composite is ≈ 2x that of the metallics
 The composite failure mode can be considered ideal as compared to the
metallic failure mode:
> Material is removed from the crush zone once it can no longer absorb
any more energy
 The joint integrity has a large effect on crush efficiency and failure mode
stability:
> Components with low/no SPR flare had significantly reduced crush
efficiency
Flexure testing
 Simply supported 3-point bend
 Beam length: 450mm, span 400mm
> Quasi-static: 50mm/min, tested up and down
> Higher rate: 60mm/s, tested up
 Understand:
> Beam stiffness, strength
> Failure mode
Static flexure response – closure up
Static flexure response – closure down
Flexure stiffness
Flexure stiffness - specific
CAE prediction for optimised TPC
beams
 Linear static FEA
 Formulate optimised
beam lay-up that
matches static stiffness
properties of:
> 5754 aluminium
> DP600
> Original PA6-GF60
beam
Static flexure – discussion &
conclusions
 The specific flexural properties of beams made using TPC material are
comparable to the metallic benchmarks
> CAE results demonstrate the weight saving potential of TPC for
equivalent stiffness
 20% over aluminium, 40% over steel (linear static predictions)
 The flexural failure mode is dominated by local section crush, but is varied
by changing the beam orientation
> Closure plate upwards limits local crushing and promotes joint failure
in composite parts
Flex fatigue - introduction
 To gain a basic understanding of
the fatigue life of the TPC as
compared to the metallic
Peak flex load
materials
80%
 80% and 50% of static load
 R=0.5
6Hz
 Run-out at 1 x 106 cycles
 Failure at 40% stiffness
reduction
Fatigue example – 80%, PA6-GF60
Fatigue
– 50%,
PA6-GF60
Fatigue example
– PA6-GF60
thermography
Test start
Damage onset
Failure
Fatigue example – 50%, PA6-GF60
Fatigue outcomes
example – 50%, PA6-GF60

Fatigue loading at 80% of the static peak load level:
> Both metallic benchmarks continue to 1 x 106 cycles with no stiffness degradation
> All composite solutions fail before 50,000 cycles

At 50% of the static peak load level:
> All composite solutions run-out at 1 x 106 cycles with no stiffness reduction but
measurable static displacement offset (creep)
> The fatigue life load limit for the composite structures lies between 50 and 80%
ultimate flex load

Thermography can be used as a tool to measure damage accumulation within the TPC
structures
> Reduction in stiffness (damage) correlates closely with temperature increases
Overall conclusions
 Engineering polymer TPC glass fibre laminates can offer a structural
alternative to aluminium and steel with significant weight saving:
> Crash: ~50% compared to Aluminium, >50% compared to steel
> Stiffness: 20% reduction on Aluminium, 40%against steel
 Further work:
> Crush: investigate and improve mechanical joining method to further
optimise crush efficiency for TPCs
> Flexure: manufacture and test modified lay-up as recommended by
FEA to confirm performance predictions
> Fatigue: perform in-depth coupon study to determine effect of fibre
lay-up and damage evolution using calibrated thermography