Over recent decades, cars have become larger and heavier with every new generation. The main drivers of such a weight increase have been the improved safety and comfort requirements. Decades of R&D investments to tackle this tendency have resulted in a substantially increase in the weight-specific performance of components and assemblies in terms of cost, strength and stiffness. However the need for weight reduction in future electric vehicles (EV), without unduly compromising performance and safety, is even stronger since additional weight translates into either reduced driving range or in larger, heavier and more expensive batteries. Within this context, the European Green Vehicle project ENLIGHT developed highly innovative lightweight material technologies for application in structural vehicle parts of future volume produced EVs. Among others ENLIGHT developed thermoplastic matrix composite and associated manufacturing technologies to a stage that they were applicable at least in medium volume production. The material development was complemented by investigating the required manufacturing and assembly technologies as well. In this paper, a summary of the major results obtained during the 4-year project year will be presented. A special focus will be given to a semi-active composite control arm with significant reduced weight but enhanced NVH properties.

1. © Fraunhofer LBF
ENHANCED LIGHTWEIGHT DESIGN BY COMPOSITES –
RESULTS OF THE PROJECT ENLIGHT
Dirk Mayer, Thilo Bein, Hendrik Buff, Benedict Götz, Oliver Schwarzhaupt , Dominik Spancken
offenSeite 1

2. © Fraunhofer LBF
ENHANCED LIGHTWEIGHT DESIGN BY COMPOSITES –
RESULTS OF THE PROJECT ENLIGHT
Dirk Mayer, Thilo Bein, Hendrik Buff, Benedict Götz, Oliver Schwarzhaupt , Dominik Spancken
offenSeite 2

3. © Fraunhofer LBF
Lightweight Design as an Enabler for Future Mobility
 Decreased vehicle weight…
 Reduces energy consumption
 Less CO2 emission for
combustion engines
 Extended range for electric
vehicles
 Compensates for the added mass
by integration of batteries and
electronics into electric vehicles
 Reduces consumption of ressources
by using less
material
Relaxed
structural
design
requirements
Less motor
power
required
Smaller
battery
required
Reduced
battery mass
Reduced
structural
loads
„Lightweight spiral“, after FOREL - Chancen und Herausforderungen im ressourceneffizienten
Leichtbau für die Elektromobilität 2015// paulbr75, pixabay.com

4. © Fraunhofer LBF
Aims of the ENLIGHT project
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5. © Fraunhofer LBF
Control Arm: The design conflict
Seite 5
Function Requirement
Connect the
wheel to the
chassis
High durability
Handling High stiffness
Low mass
Ride comfort:
Vibration
isolation
High Mass
Low stiffness
Original Golf V part:
4kg mass, steel

6. © Fraunhofer LBF
Lightweight NVH optimization by functional integration
Seite 6
 Tuned Mass Damper
 traditional tool for damping of
structural resonances
 Mechanical oscillator with a
sprung mass tuned to the host
resonance
 Added mass: 5-20% of the
effective host mass
 Shunt Damping
 Integration of piezo elements
(electromechanical transducers)
 Inductive shunting: electromechanical oscillator
 TMD effect without added mechanical inertial masses
 Might be realised by passive components (semi-active
system)

7. © Fraunhofer LBF
Potential performance of semi-active damping
 Main driver for the performance of shunt
damping:
 Generalized electromechanical coupling
coefficient:
 𝑘𝑘𝑖𝑖𝑖𝑖 =
𝜔𝜔𝑛𝑛𝑛𝑛
2 −𝜔𝜔𝑛𝑛𝑆𝑆
2
𝜔𝜔𝑛𝑛𝑛𝑛
2
 GEMCC is influenced by:
 Electromechanic coupling of the material
 Stiffness of the piezo material
 Position of the piezo w/r to the eigenmodes
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Hollkamp, J. J.; Starchville, T. F. (1994): A Self-Tuning Piezoelectric Vibration Absorber. In:
Journal of Intelligent Material Systems and Structures 5 (4), S. 559–566. DOI:
10.1177/1045389X9400500412.

8. © Fraunhofer LBF
Design of vibration control systems – passive and semi-active
Seite 8
 Concurrent design considering mechanical stiffness and dynamic properties
 Integration of piezoelectric elements into the structural design
Baseline structure
 Stiffness k
(design requirements)
 Mass M
 Vibrations at
resonance frequency
M
F
x
1) Initial structure
+ Vibration Absorber
 Stiffness k
 Lower vibrations
 Higher mass
M + M_TVA
MTVA
2) TMD solution
+ Mounted piezo
elements
 Lower vibrations
 Higher mass
M + M_piezo
 Higher stiffness due
to piezo
(overengineered)
Mpiezo
3) Retrofitting of piezos
Integrated piezo elements
 Consider piezo
stiffness in the design
 Stiffnes optimized
 Lower vibrations
 Additional mass
reduced
4) Integrated design

9. © Fraunhofer LBF
CFRP Control Arm
Seite 9
 Woven fiber layers reinforced by uni-directional (DU) tapes
Al / Plastic Insert
Bolt
Laminate
 Bolted aluminum connectors to chassis and wheel

10. © Fraunhofer LBF
Integration of Piezoelectric elements
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 Design procedure:
 Numerical analyses  Structural resonances and respective strain modes  piezo position
 Iterative optimization of GEMCC by changing piezo geometry
 Model order reduction and shunt circuit optimization

11. © Fraunhofer LBF
Optimization results
Initial CFRP part Optimized CFRP part
Smart Structure
(CFRP part + piezo
module)
Lateral stiffness [kn/mm] 219,9 182,0 186,2
Long. Stiffness [kn/mm] 9,906 8,400 9,979
1st resonance [Hz] 62,95 57,92 62,98
Mass [kg] (without fittings) 0,644 0,540 0,600
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Mass of aluminum fittings ~1.5 kg  50% mass reduction with respect to the steel part

12. © Fraunhofer LBF
Comparison with a TMD solution
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 Numerical simulation of a reduced order model
 CFRP part plus 22,5 kg rigid mass (wheel, hub, brakes)
 GEMCC = 0.07
 Shunt circuit enhanced by an active negative capacitance
 TMD at the wheel hub, m = 1,6 kg

13. © Fraunhofer LBF
Manufacturing of a prototype
 Hand lamination
 Stack of 18 PZT transducers DuraAct P-876.A11(50 mm x 30 mm x 100 µm)
 Design changes due to practical reasons: Thinner piezos, application to the inner side of the control arm
 Integration of fibre-optical sensing for monitoring of strains
Seite 13
Piezostack

14. © Fraunhofer LBF
Dynamic analyses in the laboratory
 Free boundary conditions
 Shaker excitation
 Laser Doppler vibrometer for response
measurements
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15. © Fraunhofer LBF
Result
 First resonance at 195Hz
 No frequency shift detectable between open
and short circuited piezos
 Electromechanical coupling very low
 About 6dB reduction
 Less than predicted in the simulation
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16. © Fraunhofer LBF
Durability Testing: Structural stiffness
 Uni-axial cyclic load test
 Load program derived from design loads
 Small loss of stiffness during cyclic testing
 Control arm fails at 200% of the
design load
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17. © Fraunhofer LBF
Durability Testing: Analysis of Piezo Transducers
 Impedance analysis
 0 cycles
 200k cycles
 402k cycles
 No significant changes in the measured
impedance
 Durable coupling to the structure
 Durable stacking and electrical
connection
Seite 17
0 1 2 3 4 5 6 7 8 9 10
x 10
4
10
-1
10
0
10
1
10
2
frequency [Hz]
realImpedance[Ω]
0 1 2 3 4 5 6 7 8 9 10
x 10
4
0
0.5
1
1.5
frequency [Hz]
imagAdmittance[Ω-1]
baseline
after 200,000 cycles
after 402,000 cycles
baseline
after 200,000 cycles
after 402,000 cycles

18. © Fraunhofer LBF
Conclusions
 Integration of semi-active damping with piezos into highly loaded, stiff components is possible
 Concurrent design approach is feasible
 Function integration should be already considered in the early conceptual design stage
 Manufacturing issues should be integrated into the simulation
 Realistic testing of smart structures in the laboratory as an own research topic for future projects
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