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Institute for Design and Precision Engineering
Machine Elements Group
Research Group „Wire and Springs“
Univ.-Prof. Dr.-Ing. Ulf Kletzin
9th INTERNATIONAL CONGRESS
of Spring IndustryTaormina, Italy - 29.09.2017
NEW CONCEPT FOR COMPOSITE
COMPRESSION SPRINGSby
Martin Petrich, Jorge Llimpe, Stefan Titze, Ulf Kletzin
Institute for Design and Precision Engineering, Machine Elements Group
Department of Mechanical Engineering, Technische Universität Ilmenau, Germany
03677/69-1865
WB 428029.09.2017
Martin Petrich
+49 (0) 3677/69-1865
TU Ilmenau - Germany
Campus of TU Ilmenau© Stephan Pöhler – www.helibild.de
Institute for Design and Precision Engineering
Machine Elements Group
Research Group „Wire and Springs“
Univ.-Prof. Dr.-Ing. Ulf Kletzin
Page 1
1. Introduction to composite springs
2. Theoretical description
3. Development of a manufacturing method
4. Comparison of theoretical and practical results
5. Conclusion and Outlook
NEW CONCEPT FOR COMPOSITE COMPRESSION SPRINGS
AGENDA
Martin Petrich
+49 (0) 3677/69-1865
TU Ilmenau - Germany 29.09.2017
Institute for Design and Precision Engineering
Machine Elements Group
Research Group „Wire and Springs“
Univ.-Prof. Dr.-Ing. Ulf Kletzin
Page 2
1. Introduction to composite springs
2. Theoretical description
3. Development of a manufacturing method
4. Comparison of theoretical and practical results
5. Conclusion and Outlook
NEW CONCEPT FOR COMPOSITE COMPRESSION SPRINGS
AGENDA
Martin Petrich
+49 (0) 3677/69-1865
TU Ilmenau - Germany 29.09.2017
Institute for Design and Precision Engineering
Machine Elements Group
Research Group „Wire and Springs“
Univ.-Prof. Dr.-Ing. Ulf Kletzin
Page 3
Composite production
(in general) [1]
Leaf spring [2] Meander spring
Bellow spring [4] Disc spring [4]
Power spring [5] Spiral spring [6]
1. Introduction to composite springs
[2]
Martin Petrich
+49 (0) 3677/69-1865
TU Ilmenau - Germany 29.09.2017
Layering / Shaping /
Fibers Matrix Laminate (ply) Pressing / Curing → Composite
[3]
Institute for Design and Precision Engineering
Machine Elements Group
Research Group „Wire and Springs“
Univ.-Prof. Dr.-Ing. Ulf Kletzin
Page 4
C-spring [7] [8]
Helical compression spring
[9] [10]
1. Introduction to composite springs
Martin Petrich
+49 (0) 3677/69-1865
TU Ilmenau - Germany 29.09.2017
Summary – composite springs
+ investigated and used for over 50 years
+ excellent spring characteristics
+ corrosion resistance, internal damping,
fatigue behaviour
+ lightweight design
+ functional integration
- expensive moulds
- slow manufacturing (handwork, curing time)
- often high safety factors
Institute for Design and Precision Engineering
Machine Elements Group
Research Group „Wire and Springs“
Univ.-Prof. Dr.-Ing. Ulf Kletzin
Page 5
➢ Fiber composites represent excellent spring materials:
• very good mechanical and chemical properties at low density
• various types of fibers (textiles) and matrix materials available
• redundant fatigue behaviour (detectable)
• local layup adaptions for precise adjustment of characteristics
• …
➢ Why should a new composite compression spring be developed?
• compression springs are frequently used
• simple shape for easier and cost efficient production
• usage of common (flat) textile fabrics
• various possibilities (parameters) for adjusting the spring curve
➢ The composite volute spring with rectangular cross section
is a suitable solution for the demands!
1. Introduction to composite springs
Motivation
Martin Petrich
+49 (0) 3677/69-1865
TU Ilmenau - Germany 29.09.2017
Calculation?
Manufacturing?
Institute for Design and Precision Engineering
Machine Elements Group
Research Group „Wire and Springs“
Univ.-Prof. Dr.-Ing. Ulf Kletzin
Page 6
1. Introduction to composite springs
2. Theoretical description
3. Development of a manufacturing method
4. Comparison of theoretical and practical results
5. Conclusion and Outlook
NEW CONCEPT FOR COMPOSITE COMPRESSION SPRINGS
AGENDA
Martin Petrich
+49 (0) 3677/69-1865
TU Ilmenau - Germany 29.09.2017
Institute for Design and Precision Engineering
Machine Elements Group
Research Group „Wire and Springs“
Univ.-Prof. Dr.-Ing. Ulf Kletzin
Page 7
According to [11], the force-displacement-curve is
linear for s ≤ 0,6 sc:
𝐹 = 𝑞3 ⋅2⋅𝐺⋅𝑏⋅𝑡3
𝜋⋅𝑛𝑓⋅ 𝑟𝐾1+𝑟𝐾𝑛 ⋅ 𝑟𝐾12 +𝑟𝐾𝑛
2 ⋅ 𝑠
with 𝑞3 =𝛽𝑡−0,63
3⋅𝛽𝑡and 𝛽𝑡 = 𝑏/𝑡
G – shear modulus
b – strip width
t – strip thickness
nf – number of active coils
2. Theoretical description of the volute spring
Spring curve – linear part
29.09.2017
Martin Petrich
+49 (0) 3677/69-1865
TU Ilmenau - Germany
[11]
Institute for Design and Precision Engineering
Machine Elements Group
Research Group „Wire and Springs“
Univ.-Prof. Dr.-Ing. Ulf Kletzin
Page 8
For s > 0,6 sc the number of active coils nf
reduces, the characteristic becomes
non-linear (progressive):
𝐹 = 𝑞3 ⋅𝐺⋅𝑏⋅𝑡3
𝜋⋅𝑟𝐾𝑥2 ⋅𝑛𝑓 𝑟𝐾1+𝑟𝐾𝑛
⋅ 𝑠
with 𝑟𝐾𝑥 = 𝑟𝐾𝑛 +𝑚 ⋅ (𝑟𝐾1 − 𝑟𝐾𝑛)
and 1 ≥ 𝑚 ≥ 0 for segmentation into intervals.
This approach can be used to analyze a spring
that is known in its dimensions.
A dimensioning (design) on this basis is not
possible due to the numerous parameters
to be determined.
Evaluation of test designs
2. Theoretical description of the volute spring
Spring curve – non-linear part
29.09.2017
Martin Petrich
+49 (0) 3677/69-1865
TU Ilmenau - Germany
[11]
Institute for Design and Precision Engineering
Machine Elements Group
Research Group „Wire and Springs“
Univ.-Prof. Dr.-Ing. Ulf Kletzin
Page 9
Composite strips consist of several layers with
possible variations in fiber orientation,
thickness, fiber material, etc.
For complex layups, a common procedure is the
calculation of the engineering constants, based
on the Classical Laminate Theory (CLT).
Otherwise, test specimen can be produced for
more accurate input values.
2. Theoretical description of the volute spring
Martin Petrich
+49 (0) 3677/69-1865
TU Ilmenau - Germany 29.09.2017
Mechanical properties of the composite
Mt
F
Mt
The strip material of the spring is basically
loaded by a torsion moment Mt, which results
from the force. Therefore, the shear modulus
G has to be considered.
Simplification
Institute for Design and Precision Engineering
Machine Elements Group
Research Group „Wire and Springs“
Univ.-Prof. Dr.-Ing. Ulf Kletzin
Page 10
2. Theoretical description of the volute spring
Martin Petrich
+49 (0) 3677/69-1865
TU Ilmenau - Germany 29.09.2017
Spring examples - Mechanical properties of the composite
In this example, the engineering constants are calculated with
the Excel-sheet AlfaLAM [12]
Input values:
• 8 layers of E-glass fibers with epoxy matrix
• Fiber orientation 45°and - 45°(symmetrical)
• Fiber volume content 𝜑 = 0,4 (medium value)
Output values:
• Stiffness matrix and flexibility matrix of composite
• Strain and stress (layer wise)
• Coefficients for engineering
Institute for Design and Precision Engineering
Machine Elements Group
Research Group „Wire and Springs“
Univ.-Prof. Dr.-Ing. Ulf Kletzin
Page 11
2. Theoretical description
Martin Petrich
+49 (0) 3677/69-1865
TU Ilmenau - Germany 29.09.2017
Spring examples – glass fibers
Spring 1
b = 40 mm
t = 1,52 mm
nf = 3
rK1 = 28,5 mm
rK3 = 21 mm
L0 = 100 mm
G = 8674 N/mm²
Spring 2
b = 32 mm
t = 0,75 mm
nf = 3,5
rK1 = 17,8 mm
rK3,5= 13,5 mm
L0 = 105 mm
G = 8674 N/mm²
[11]
0
20
40
60
80
100
120
140
160
0 10 20 30 40 50 60
Fo
rce
[N
]
Displacement [mm]
Calculation of glass fiber volute springs
Spring1_Calc_linear
Spring1_Calc_nonlinear
Spring2_Calc_linear
Spring2_Calc_nonlinear
Institute for Design and Precision Engineering
Machine Elements Group
Research Group „Wire and Springs“
Univ.-Prof. Dr.-Ing. Ulf Kletzin
Page 12
1. Introduction to composite springs
2. Theoretical description
3. Development of a manufacturing method
4. Comparison of theoretical and practical results
5. Conclusion and Outlook
NEW CONCEPT FOR COMPOSITE COMPRESSION SPRINGS
AGENDA
Martin Petrich
+49 (0) 3677/69-1865
TU Ilmenau - Germany 29.09.2017
Institute for Design and Precision Engineering
Machine Elements Group
Research Group „Wire and Springs“
Univ.-Prof. Dr.-Ing. Ulf Kletzin
Page 13
3. Development of a manufacturing method
Winding technology
Martin Petrich
+49 (0) 3677/69-1865
TU Ilmenau - Germany 29.09.2017
Preparation
• Manufacturing a winding core
• Preparation of a carrier film
• Pre-cutting fibers/textiles
Lamination• Fiber layering
• Wetting with resin
Winding• Winding from inner
to outer diameter
• Curing (tempering)
Post-processing
• Releasing from core
• Removing carrier film
• Grinding / cleaning
Institute for Design and Precision Engineering
Machine Elements Group
Research Group „Wire and Springs“
Univ.-Prof. Dr.-Ing. Ulf Kletzin
Page 14
3. Development of a manufacturing method
Martin Petrich
+49 (0) 3677/69-1865
TU Ilmenau - Germany 29.09.2017
Testing the manufacturing method
Carrier filmGlass fibers
Winding
Demoulding
Finishing
Institute for Design and Precision Engineering
Machine Elements Group
Research Group „Wire and Springs“
Univ.-Prof. Dr.-Ing. Ulf Kletzin
Page 15
1. Introduction to composite springs
2. Theoretical description
3. Development of a manufacturing method
4. Comparison of theoretical and practical results
5. Conclusion and Outlook
NEW CONCEPT FOR COMPOSITE COMPRESSION SPRINGS
AGENDA
Martin Petrich
+49 (0) 3677/69-1865
TU Ilmenau - Germany 29.09.2017
Institute for Design and Precision Engineering
Machine Elements Group
Research Group „Wire and Springs“
Univ.-Prof. Dr.-Ing. Ulf Kletzin
Page 16
Spring 1
b = 40 mm
t = 1,52 mm
nf = 3
rK1 = 28,5 mm
rK3 = 21 mm
L0 = 100 mm
G = 8674 N/mm²
Spring 2
b = 32 mm
t = 0,75 mm
nf = 3,5
rK1 = 17,8 mm
rK3,5= 13,5 mm
L0 = 105 mm
G = 8674 N/mm² 0
20
40
60
80
100
120
140
160
0 10 20 30 40 50 60
Fo
rce
[N
]
Displacement [mm]
Measurements - Glass fiber springs
Spring1_#1
Spring1_#2
Spring1_#3
Spring2
0
20
40
60
80
100
120
140
160
0 10 20 30 40 50 60
Fo
rce
[N
]
Displacement [mm]
Comparison of calculated and measured forces- Glass fiber springs -
Spring1_Calc_linear
Spring1_Calc_nonlinear
Spring1_#1
Spring1_#2
Spring1_#3
Spring2_Calc_linear
Spring2_Calc_nonlinear
Spring2
4. Comparison of theoretical and practical results
Martin Petrich
+49 (0) 3677/69-1865
TU Ilmenau - Germany 29.09.2017
Measurements of spring characteristics – glass fibers
Institute for Design and Precision Engineering
Machine Elements Group
Research Group „Wire and Springs“
Univ.-Prof. Dr.-Ing. Ulf Kletzin
Page 17
0
20
40
60
80
100
120
140
160
0 10 20 30 40 50 60
Fo
rce
[N
]
Displacement [mm]
Measurements - Carbon fiber springs
Spring1_#1
Spring1_#2
Spring1_#3
Spring3
Spring 1
b = 40 mm
t = 1,32 mm
nf = 3
rK1 = 28,5 mm
rK3 = 21 mm
L0 = 100 mm
G = 24316 N/mm²
Spring 3
b = 11 mm
t = 1,32 mm
nf = 3,25
rK1 = 19 mm
rK3,5= 15,5 mm
L0 = 100 mm
G = 11906 N/mm²
(+20°/-20°layup)
4. Comparison of theoretical and practical results
Martin Petrich
+49 (0) 3677/69-1865
TU Ilmenau - Germany 29.09.2017
Measurements of spring characteristics – carbon fibers
0
20
40
60
80
100
120
140
160
0 10 20 30 40 50 60
Fo
rce
[N
]
Displacement [mm]
Comparison of calculated and measured forces- Carbon fiber springs
Spring1_Calc_linear
Spring1_Calc_nonlinear
Spring1_#1
Spring1_#2
Spring1_#3
Spring3
Spring3_Calc_linear
Spring3_Calc_nonlinear
Institute for Design and Precision Engineering
Machine Elements Group
Research Group „Wire and Springs“
Univ.-Prof. Dr.-Ing. Ulf Kletzin
Page 18
4. Comparison of theoretical and practical results
Martin Petrich
+49 (0) 3677/69-1865
TU Ilmenau - Germany 29.09.2017
Comparison of calculated spring rates
0
0,5
1
1,5
2
2,5
3
3,5
4
4,5
5
0 10 20 30 40 50 60
Sp
rin
g r
ate
[N
/m
m]
Displacement [mm]
Comparison of spring characteristics GF_Spring1_linearGF_Spring1_nonlinearGF_Spring2_linearGF_Spring2_nonlinearCF_Spring1_linearCF_Spring1_nonlinearCF_Spring3_linearCF_Spring3_nonlinear
Institute for Design and Precision Engineering
Machine Elements Group
Research Group „Wire and Springs“
Univ.-Prof. Dr.-Ing. Ulf Kletzin
Page 19
4. Comparison of theoretical and practical results
Martin Petrich
+49 (0) 3677/69-1865
TU Ilmenau - Germany 29.09.2017
Simplified comparison to helical compression springs (steel wire)
• Composite springs
are not competitive in
case of these properties
• The composite springs
are not optimized
• Other advantages have
to be considered for the
choice of composite
materials
→ functional integration of
damping characteristics
(replacement of spring-
damper-units for example)
“Productivity”:
- composite: about 1 per mould in 4-12 hours, with tempering, depending on matrix
- steel springs: several per second* According to DIN 2098
Spring 1 Helical spring* Spring 1 Helical spring*
Glass fiber Spring Steel Wire Carbon fiber Spring Steel Wire
d mm - 1,25 - 2,00
b mm 40 - 40 -
t mm 1,52 - 1,32 -
nf 3 18,5 3 8,5
rmin mm 21 - 21 -
rmax mm 28,5 - 28,5 -
Dm mm - 10 - 20
L0 mm 100 93,5 100 94
Ln mm 40 30 40 27,6
R linear N/mm 1,35 1,37 2,50 2,44
Fn N 80 87,1 120 162
G N/mm² 8674 81500 24316 81500
Weight g 70,5 6,2 49,3 16,4
Material costs € < 5 € << 1 € < 10 € << 1 €
Institute for Design and Precision Engineering
Machine Elements Group
Research Group „Wire and Springs“
Univ.-Prof. Dr.-Ing. Ulf Kletzin
Page 20
Spring1 dimensions
b = 40 mm t = variable
nf = 3 nt = 5
rK3 = 21 mm rK1 = variable
a = 0,1 mm
Comparison by spring rate R
→ significant advantages for fiber materials
→ good accordance to the weight of the test springs
Steel CFRP GFRP
ρ [g/cm³] 7,90 1,42 1,74
G [GPa] 70,0 24,3 8,7
R [N/mm] 2,33 2,23 2,24
t [mm] 0,85 1,25 1,90
m [g] 197 54 108
Rtest [N/mm] - 2,5 1,35
ttest [mm] - 1,32 1,52
mtest [g] - 49,3 70,5
4. Comparison of theoretical and practical results
Martin Petrich
+49 (0) 3677/69-1865
TU Ilmenau - Germany 29.09.2017
Simplified comparison to volute springs (steel strip) linear calculation
0
5
10
15
20
25
30
35
40
45
50
0,0 0,5 1,0 1,5 2,0 2,5 3,0
Spri
ng
rate
R [
N/m
m]
Strip thickness t [mm]
Material comparison
R steel R CFRP R GFRP
0
5
10
15
20
25
30
35
40
45
50
0,0 0,5 1,0 1,5 2,0 2,5 3,0
Spri
ng
rate
R [
N/m
m]
Strip thickness t [mm]
Material comparison
R steel R CFRP R GFRP
0
50
100
150
200
250
300
0
5
10
15
20
25
30
35
40
45
50
0,0 0,5 1,0 1,5 2,0 2,5 3,0
Wei
ght
m [
g]
Spri
ng
rate
R [
N/m
m]
Strip thickness t [mm]
Material comparison
R steel R CFRP R GFRP
m steel m CFRP m GFRP
0
50
100
150
200
250
300
0
5
10
15
20
25
30
35
40
45
50
0,0 0,5 1,0 1,5 2,0 2,5 3,0
Wei
ght
m [
g]
Spri
ng
rate
R [
N/m
m]
Strip thickness t [mm]
Material comparison
R steel R CFRP R GFRP
m steel m CFRP m GFRP
0
50
100
150
200
250
300
0,0 0,5 1,0 1,5 2,0 2,5 3,0
Wei
ght
m [
g]
Strip thickness t [mm]
Material comparison
m steel m CFRP m GFRP
Institute for Design and Precision Engineering
Machine Elements Group
Research Group „Wire and Springs“
Univ.-Prof. Dr.-Ing. Ulf Kletzin
Page 21
1. Introduction to composite springs
2. Theoretical description
3. Development of a manufacturing method
4. Comparison of theoretical and practical results
5. Conclusion and Outlook
NEW CONCEPT FOR COMPOSITE COMPRESSION SPRINGS
AGENDA
Martin Petrich
+49 (0) 3677/69-1865
TU Ilmenau - Germany 29.09.2017
Institute for Design and Precision Engineering
Machine Elements Group
Research Group „Wire and Springs“
Univ.-Prof. Dr.-Ing. Ulf Kletzin
Page 22
- Composite springs have various advantages
- Composite volute spring was not tested and used so far
- Existing theoretical description can be used in first proximity
- Mechanical properties can be calculated by common theories
- Manufacturing method was developed and successfully approved
- Measurements of force-displacement-curves have shown a good comparability to
calculated curves for both glass and carbon fiber composites
- Almost linear spring characteristics, no fatigue up to the block length, no setting
- Simplified comparison to helical steel wire springs shows disadvantages in weight
but significant advantages by comparing volute springs
5. Conclusion and Outlook
Conclusion
29.09.2017
Martin Petrich
+49 (0) 3677/69-1865
TU Ilmenau - Germany
Institute for Design and Precision Engineering
Machine Elements Group
Research Group „Wire and Springs“
Univ.-Prof. Dr.-Ing. Ulf Kletzin
Page 23
- Adjustment of spring characteristics by several
parameters (layup, fiber orientation, coil distance)
- Testing different load cycles and fatigue properties
- Investigations on frictional behaviour and damping
- Improved production / automation
- FEM-simulations for layer wise stress/strain/fatigue analysis
- …
5. Conclusion and Outlook
Outlook
29.09.2017
Martin Petrich
+49 (0) 3677/69-1865
TU Ilmenau - Germany
Institute for Design and Precision Engineering
Machine Elements Group
Research Group „Wire and Springs“
Univ.-Prof. Dr.-Ing. Ulf Kletzin
Page 24
Thank you for your kind attention!
M. Sc. Martin Petrich
E-Mail: [email protected]
Phone: +49 (0) 3677 69 1865
Research Group Wire and Springs
Machine Elements Group
Max-Planck-Ring 12
Werner-Bischoff-Bau WBB 4260
98693 Ilmenau
Germany
Martin Petrich
+49 (0) 3677/69-1865
TU Ilmenau - Germany 29.09.2017
Institute for Design and Precision Engineering
Machine Elements Group
Research Group „Wire and Springs“
Univ.-Prof. Dr.-Ing. Ulf Kletzin
Page 25
Ressources[1] R&G Faserverbundwerkstoffe GmbH: „Composite materials handbook“;
URL: http://www.r-g.de/w/images/6/69/R%26G_Handbuch.pdf; Waldenbuch, 2009
[2] Stimpfl, J.: “Leichtbau in faserverstärktem Kunststoff für Fahrwerksfedern im Automobil“;
VDFI Lecture event „Federn aus faserverstärkten Kunststoffen“, Siegen, 20.04.2016
[3] DANTO-Invention GmbH & Co. KG: „DANTO Feder“; URL: http://www.hannovermesse.de/
produkt/feder-aus-faser-kunststoff-verbunden/2310289/L161872; last visit: 26.07.2017
[4] Hufenbach, W.; Werner, J.; Körner, I.; Köhler, C.: „Neuartige Leichtbaufedern in Faserverbundbauweise –
Bauweisen / Auslegung / Fertigung“; Ilmenauer Federntag; 2010
[5] Scharr, G.: „Faserverstärkte Kunststoffe – Federwerkstoffe für den Leichtbau“; VDI-Berichte Nr. 1972; 2006
[6] Zemann, R.: „Federleicht“; URL: https://www.tuwien.ac.at/aktuelles/news_detail/article/8511/;
last visit: 26.07.2017
[7] Otto Bock Healthcare Deutschland GmbH: „C-Walk Prothesenfuß 1C40“;
URL: http://www.ottobock.de/prothetik/produkte-a-bis-z/prothesenfuesse/c-walk/; last visit: 26.07.2017
[8] Michel, S.: „Schneckenblattfeder“; URL: http://schneckenblattfeder.de/brochure/sbf-produktinfo.pdf;
last visit: 26.07.2017
[9] Sardou SA: „Helical coil springs“; URL: http://www.sardou.net/images/ressort/DSC01555_petit.JPG;
last visit: 26.07.2017
[10] Leichtbauzentrum Sachsen GmbH: „Schraubendruckfeder aus Faserverbundkunststoff“;
URL: http://industrieanzeiger.industrie.de/wp-content/uploads/2/9/2997285.jpg; last visit: 26.07.2017
[11] Meissner, M.; Schorcht, H.-J.; Kletzin, U.: „Metallfedern“; 3. Auflage, Springer Vieweg, 2015
[12] Weber, T.: „AlfaLam“; Excel-sheet Version 1.3.1; URL: http://www.klub.tu-
darmstadt.de/forschung_klub/downloads_3/downloads_klub.de.jsp; last visit: 30.07.2017
Martin Petrich
+49 (0) 3677/69-1865
TU Ilmenau - Germany 29.09.2017