developing structural natural fiber parts using spray

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