Carbon Fiber SMC Technology for Lightweight Structures
Matt Kaczmarczyk | Senior Design Engineer Tim Langschwager | Lead Development Chemist Quantum Composites - AS9100C:2009 / ISO9001:2008 Quantum Composites - AS9100C:2009 / ISO9001:2008 1310 South Valley Center Drive 1310 South Valley Center Drive Bay City, Michigan 48706-9798 USA Bay City, Michigan 48706-9798 USA Phone: 989-922-3863 ext. 116 Phone: 989-922-3863 ext. 120 Fax: 989-922-3915 Fax: 989-922-3915 [email protected] [email protected]
The Composites Group 1 Outline of Presentation
• What is Forged Composite?
• Differences Between CF-SMC and Traditional SMC
• High Flow vs. Low Flow Molding
• Typical Mechanical Properties of CF-SMC
• Important Characteristics of CF-SMC
• CF-SMC Applications
• Processes Comparisons
The Composites Group 2 What is Forged Composite?
• Forged Composites: Term for compression molded CF-SMC
• Manufactured by Quantum Composites
• Headquartered in Bay City, Michigan
The Composites Group 3 CF-SMC First Branded as “Forged Composites”– October 2010 Paris Auto Show
March 2012 Geneva (AventadorJ) April 2012 Beijing (Urus)
Courtesy: Dr. Paolo Feraboli – Automobili Lamborghini Advanced Composites Structures Laboratory The Composites Group 4 Carbon Fiber Sheet Molding Compound
• Glass fiber SMC has been around since the 1960’s
• In 1987 Quantum developed epoxy 3k carbon fiber molding compound
• CF-SMC have been in use since early 1990’s
• What is unique about CF-SMC?
– Quasi-Isotropic properties
– Excellent for fastener-intensive and stiffness dominated parts
– Carbon fiber reinforcement
– High fiber content: Vf 40%+ / Wf 50%+
The Composites Group 5 Carbon Fiber Sheet Molding Compound
Traditional SMC: Sheet Molding Compounds (SMC) have traditionally been a low-performance process: • Glass fiber
• Low fiber content: Vf 18%+ / Wf 25%+ • Low mold coverage/ high flow • Typically polyester resin • Higher specific gravity
CF-SMC: Feedstock material is chopped carbon fiber with resin They are similar to prepreg in principle, but not in practice We define Advanced Compression Molding to differentiate it from the traditional Compression Molding if: • Carbon fiber
• High fiber content : Vf 40%+ / Wf 50%+ • Typically vinyl ester or epoxy resin but also BMI and phenolic • Lower specific gravity
The Composites Group 6 Advanced Compression Molding
• Ability to use the CF-SMC in a repeatable and predictable way to form unique applications • Minimum molded thickness as low as 0.035 in. (1 mm) • Reduced variability in strength • Co-mold with selective UD reinforcement • Understanding the requirements is the key to material selection ‰ Excellent for fastener -intensive and stiffness -dominated parts
The Composites Group 7 Advanced Compression Molding
Example Fabricated (Welded) Steel Tubing Compression Molded CF-SMC
21 lbs 8 lbs
Structural features such as ribs and gussets can easily be molded for acceptable and even matched performance.
The Composites Group 8 Advanced Compression Molding
• Matched-mold process
Figure 1. Mold is closing Figure 2. Mold is opening after cure
The Composites Group 9 High Flow Molding Similar to traditional SMC - fiber “orientation” is not controlled
Cut the material Weigh the charge Prepared Charge
Load the Charge
Courtesy: Premix
The Composites Group 10 Low Flow Molding Similar to traditional lay-up - fiber “orientation” is more controlled
Material is precisely cut and placed into mold
The Composites Group 11 High Flow vs. Low Flow Molding
• Material flow and charge pattern can effect mechanical properties. • Creating a uniform direction of fibers does not necessarily translate into improved strength. • Flow fronts and fiber bunching creating weak areas in the coupons/parts.
Tensile Strength Tensile Modulus 45000 8
40000 7 35000 6 30000 5 25000 4 (psi) 20000 (Msi) 3 15000 2 10000 5000 1 0 0 High Flow Low Flow High Flow Low Flow
The Composites Group 12 High Flow vs. Low Flow Molding
High Flow
Low Flow
The Composites Group 13 High Flow vs. Low Flow Molding
High flow specimen showing fiber bunching at fracture area ( Edge Effect at end of flow)
Low flow specimen showing a more uniform fiber displacement resulting in elevated strength properties.
The Composites Group 14 Comparison of Material Performance Tensile Strength vs. Tensile Modulus
100.00
90.00 (15.2,174.0) Quasi-Iso 80.00 Ti-6-4 Tape 70.00
60.00
50.00 AL6061-T6 40.00
30.00
Tensile Tensile Tensile StrengthStrength(ksi) (ksi) 20.00 Glass SMC 10.00
0.00 0 2 4 6 8 10 12 14 16 18 20 Tensile Modulus (Msi)
Reference Materials Discontinous Carbon Fiber Molding Compound
The Composites Group 15 Fiber Aspect Ratio 3k=100 tows • Higher Fiber Aspect Ratio = – Higher performance – Lower COV strength values – Higher notch sensitivity
3K – 3,000 filaments per tow (roving) 12k=25 tows
12K – 12,000 filaments per tow
50K – 50,000 filaments per tow 50k=6 tows
The Composites Group 16 Comparison of Carbon Fiber Tow (CF-SMC)
Tensile Strength comparison of ASTM Method
70,000
60,000
50,000
40,000
3K SMC 30,000 12K SMC
Tensiel Tensiel Tensiel StrenghtStrenght(psi) (psi) 50K SMC 20,000
10,000
0 ASTM D-638 ASTM D 3039 MD ASTM D 3039 CMD ASTM D 5766 MD ASTM D 6742 MD Test Method
*ASTM D-638 in the graph above uses “as molded” net shape test specimen. ASTM D3039, D5766, and D6742 use specimen machined from molded plaques.
The Composites Group 17 Comparative Properties of CF-SMC
• Moduli as high as prepreg quasi baseline • Unnotched strengths lower than prepreg quasi baseline • Compression higher than tension • Open-hole strengths more appealing • Higher CoV in strength and modulus
‰ Excellent for fastener -intensive and stiffness -dominated parts UNT T mod OHT UNC C mod OHC CoV CoV [ksi] [Msi] [ksi] [ksi] [Msi] [ksi] Aluminum 30 2% 10.0 0% 30 30 10.0 30 Quasi-isotropic fabric 108 4% 6.0 5% 60 70 4.9 45 T700/977-6 3k CF-SMC 47 10% 5.0 10% 37 52 5.4 37 12k CF-SMC 29 18% 5.5 27% 29 42 6.0 33 50k CF-SMC 22 20% 5.5 20%
The Composites Group 18 Comparative Fatigue Curves
S-N curve 50,000
45,000
40,000
35,000
30,000
25,000 3K CF-SMC UTS (psi) UTS 20,000 12K CF -SMC AL6061-T6 15,000
10,000
5,000
0 0 200000 400000 600000 800000 1000000 Life (Cycles)
Tension – Tension 3Hz
The Composites Group 19 Notched Behavior
• Specimens containing open holes fail both in the net and gross section • Typical fastener hole size ¼-inch diameter hole
98.6% failed at hole 3k 1.4% failed away from hole
26.4% failed at hole 12k 73.6% failed away from hole
The Composites Group 20 Effects of Defects
• Difficult for Non Destructive Inspection: signal is noisy • Ultrasonic scans reveal areas of weak reflection or “Hot Spots” – not necessarily defects
DE-LAMINATION FLAW
The Composites Group 21 Modulus Variability
• Modulus measurements either via strain gage or extensometer • High variability encountered (approx 19%) much higher than strength variability (approx 10 %) • Experiments using gage lengths of 0.125, 0.25, 0.5, 1.0 and 2.0 in. • Also 1.0 in. extensometer • Longer gages do not yield better measurements • Measurements vary along length and across width of specimens
The Composites Group 22 Modulus Variability
• Digital image correlation (DIC) • Black speckles are applied to a white background on one side of a specimen • Images are taken during testing by a pair of digital cameras • Post processing allows to measure full field strain • Measurement shows local variations
The Composites Group 23 Fiber Orientation • High degree of influence on mechanical properties, stiffness • Changes with high flow vs. low flow molding process and part geometry • Molded specimens will give high mechanical values due to favorable fiber orientation. • With cut specimens, the fibers are cut in the gage length reducing the strengths by about 25-30% from molded specimens.
Fibers tend to orient in the direction of flow and along the cavities edge .
ASTM D 638 MOLDED SPECIMEN
Fibers are random, but cut at the parts edge
ASTM D 3039 CUT FROM PANEL
The Composites Group 24 Outline of Presentation
• What is Forged Composite?
• Differences Between CF-SMC and Traditional SMC
• High Flow vs. Low Flow Molding
• Typical Mechanical Properties of CF-SMC
• Important Characteristics of CF-SMC
• CF-SMC Applications
• Processes Comparisons
The Composites Group 25 CF-SMC Applications
Carbon-Fiber Sheet-Molded Composite Underbody Diffuser for Nissan GTR
Challenge Lower cost, parts consolidation
Solution • Lower part cost vs. prepreg parts
• Corrosion resistance
• High stiffness
• Good impact strength
• Dimensional stability
• Ability to mold in ribs, bosses, changes in thickness (e.g., for attachment points)
The Composites Group 26 CF-SMC Applications
Carbon-Fiber Sheet-Molded Composite Monocoque Tube and Suspension Arm for Lamborghini Siesto Elemento Challenge Lower cost, cycle time
Solution • Much lower part cost vs. prepreg parts • Lightweight • High stiffness / strength • Faster cycle time than RTM • Higher volume compression molded • Hybrid structures (e.g., Continuous + Discontinuous Fibers)
The Composites Group 27 CF-SMC Applications
The Composites Group 28 Additional CF-SMC Applications
Carbon fiber hood inner structure Carbon fiber fender support http://www.sae.org/mags/sve/12288/
The Composites Group 29 Composite Fabrication Processes (thermoset)
Transfer Compression Molding Injection Molding Molding (CF-SMC)
RTM
Autoclave / Vacuum Bag
Spray-up Hand
Tooling Cost Cost Tooling Lay-up
Production Volume
The Composites Group 30 Thank you!
The Composites Group 31