Skip to main content

Innovative Controllable Meta-Materials

Morphing devices into materials

Home
About Us
Contact Us
Projects
- Active & Perspective
- Completed
Non-Linear Acoustics
NMR Devices
Electromechanics
- Sensing
- Strain Measurements
- FAiMTA
Site Map
Member Login
Tools
Field Aided Manufacturing Technological Approach (FAiMTA)
 

We propose a technology which combines pressure molding short fiber composites and electric field to produce orthotropic composites. Such approach can produce lightweight parts by improving material strength in critical directions, reducing stress concentration near groove corners and moving inclusions in polymer-rich areas at small features of the design. The essence of our approach is in application of electric field to a liquid composite and solidify it in the field presence. Electric field moved fibers inside the polymeric matrix and orients them along the field vector. Similarly, particles and short fibers form chain-like structures directed along the field. Applied uniform electric field produces modified structure which mechanically behaves as orthotropic fiber reinforced composite: which exhibits as a high stiffness in the fiber direction and lower stiffness in perpendicular directions. Electric field applied by electrodes located in strategic areas yields composite part having locally varying anisotropy which reduces stress concentration. The technology has been applied to materials having different compositions and up to 40% density of inclusions. It has been demonstrated that parts manufactured from local reinforced composites may have more 78.5% stress reduction in critical areas.


Alignment of Inclusions

Inclusions in polymeric matrix are electrically neutral and interact with the field through dipole polarization. In the field-aided manufacturing inclusions are manipulated through several effects:

1)    Inclusions are moving if subjected to non-uniform electric field. A motion will be directed in the area where the field is stronger. This effect is called dielectrophoresis and it can be utilized to drag inclusions in polymer-rich areas.

2)    Two or more inclusions in uniform electric field will move toward each other and form aligned with the field chain-like structure, see Figure (a). This effect exists if inclusions and polymeric matrix have different dielectric properties which is always the case in a.c. electric field. The electric field is applied to polymeric suspension all time before solidification and obtained chain-like structure is permanently preserved.

 

Test conditions:

1 vol % MWCN/epoxy resin

E= 400 V/mm,

1-1000Hz sweep

<Click for video> 

3)    Non-spherical inclusion such as fiber or flake will rotate in the field to align its primary axis with the field, see Figure (b). This effect will produce structure formed by aligned fibers.

 

  

Test conditions:

E = 1 kV/mm 

h= 20 poise

t = 24 sec

<Click for video>

 

 

FAiMTA at Work

20vol% Graphite epoxy composites microtailored by a.c. electric field
f = 5Hz and E= 1kV/mm
Electric field can be applied in different manner:
(a) Parallel plate electrodes produce uniaxial structure.
(b) Interdigitated electrodes produce structure aligned along the surface
 
 
 
 
 

 

 

FAiMTA on Microscale

Carbon nano-inclusions in epoxy cured in electric field

 

Micro-post structure (22.7% surface density) that has been plasma-etched in epoxy-carbon composites. The dark areas are 80-nm particles forming larger conglomerates.

 

 


Locally Reinforced Specimen

Quarter-cut of functional graded plate made of CNT-epoxy composite. Inter-digitated electrode configuration is design to reduce stresses around the hole.

 


 
Stress Concentration

In orthotropic material such as uniformly aligned fiber reinforced composite the stress concentration factor reaches 7 which leads to significant overweight of the final part.

In his PhD research project, H.K. Cho, demonstrated that with careful design of the composite and smart selection of fiber orientations, stress concentration can be significantly reduced. Cho’s best results has stress concentration factor as low as  1.52 which corresponds to 78.5% reduction of the stress concentration compared to uniformly orthotropic plate.