Developing Structural Natural Fiber Parts Using Spray Transfer
Molding ( STM) process
Joint development
Elias Shakour, Ph.D. Jeffery Dodge Ph.D., Xhulja Biraku– BASF Corporation
Alper Kiziltas , Ph.D.- Ford Motor Company
Mihaela (Miki) Banu, Ph.D.- University of Michigan
Outline
• Concept of Lightweight Sandwich Materials
• Honeycomb Technology
• Spray Transfer Molding (STM) Process
• Sustainable Polyurethane (PU) Application
• Natural Fiber- Bamboo fibers
• Test results
• Future work
Concept of Sandwich Materials
3
Sandwich concept for light-weight designs (core material mainly carries shear load)
Flexural rigidity:D = E*I
EI = Flexural rigidity of sandwich
Ef = Modulus of faces
Ec = Modulus of core
b = Width
t = Thickness of faces
c = Thickness of core
d = Distance of face middle axes
E*I = Ef
bt3
6
btd2
2+ Ef
bc3
12+ Ec
Faces with thickness t
Foam core
L/2 L/2
d
b
h c
Single skin – tWeight: 1Strength: 1Stiffness: 1
Sandwich – 2tWeight: 1.06Strength: 3.5Stiffness: 7
Sandwich – 4tWeight: 1.09Strength: 9.25Stiffness: 37
Flexural rigidity:D = E*I
4t
t 2t
Honeycomb Concept
PU bridging honeycombHigh stiffness and strengthI- Beam concept
Traditional STM –Polyurethane Honeycomb Process
SpraySandwich Mounting
MoldingReady-Made Part
Process
1. Sandwich assembly
2. Spraying of PU system on both sides
3. Compression molding & PU reaction
4. Extraction
7
PU Honeycomb Applications
Hatchback
Loadfloor
Sunshade
Interior
Arm RestPackage
shelf
Interior
door
Transition to Sustainable solution
Sustainable Polyurethane
• Elastoflex 28690
• High percentage of sustainable bio-based content
• Low demold time
• Non-sag formulation
• Good open time to make large parts
• Compatible with multiple reinforcement fibers
30.03.2012 9
Comparison of Standard PU Vs New PU
Mechanical performance of sustainable PU is similar to the commercial PU
15 mm paper core height on 450 (grams/ m2) chopped random glass
Why Bamboo as a Structural approach
❑Renewable Resource: Depending on thespecies, bamboo can be harvested in one to fiveyears.• Hardwoods like oak take at least forty years to
mature.
❑Growth Rate: Some species of bamboo growmore than three feet each day!• No plant on the planet features a faster growth rate.
❑Superior Mechanical Behavior (Particularly Flexural): Bamboo has relatively high strength and stiffness compared to other natural fibers
❑Low Density: Bamboo has ~1.1 gr/cm3• E-Glass fiber 2.6 gr/cm^3
❑Can be extracted as long or continuous fiber
❑ Bamboo Fibers: Elastic modulus Ef = 22.8 ± 2.8 GPa by nanoindentationEf = 30.1 ± 3.0 GPa by micro tensile testingTensile strength σf = 1000 ± 300 MPa.
Bamboo Structural and Mechanical behvior
Structural part – Bamboo Honeycomb loadfloor
Honeycomb Bamboo
Testing results of Honeycomb materials
• Bamboo ( 35% 4” random)
• Hemp (70% hemp, 30 polyester)
• GF ( 40% chopped glass fiber)
0
2
4
6
8
10
12
14
16
18
0 1 2 3 4 5 6 7
Fle
xure
str
ess
( M
PA
)
Strain
Flexural 3 point bending
Hemp
GF
Bamboo
• Bamboo showed a decent strength behavior.• To increase strength:
• Increase the height of the honeycomb
• Increase volume fraction of bamboo
• Showed good energy absorption • Has a long tail (post failure) shows
higher elongation
• Had similar stiffness like glass fiber matts
Failure mode
• Glass fiber • Fractured on the top surface• When fractured created sharp
edges
• Hemp• Fracture on the top surface• First to fail
• Bamboo • Did not fracture , bended and
paper core buckled• No sharp edges
Hemp
Glass fiber
Bamboo
Next steps as future work
Loadfloor Door panel
• With Ford’s support
• Run life cycle impact of bamboo fibers composites for the automotive parts
Conclusions
• Identified Elastoflex 28690 works well with Bamboo fibers
• Bamboo fibers are in the range of high strength and high stiffness
• Were able to manufacture honeycomb bamboo plaques.
• Natural composites reinforced bamboo fiber has high energy absorption
• Bamboo fiber fits well for structural and semi structural parts in the automotive industry
Thank You
Lightweight CompositesProperties as a Function of Fiber-Length
