Viscoelastic Materials and MWCNT Enhance Composites

Multi-wall carbon nano tubes are being dispersed into viscoelastic materials to create specific geometries for engineered composite applications. This research and development is named Composite Tempering. The technology is based on using viscoelastic materials with MWCNT and engineered application methods to enhance engineered composites. For example: carbon fiber, fiberglass, and other structural material with resin applications.

The research for some materials like photopolymer, powders, and some resin is in its advanced stages. The initial commercialization with this technology has reached the rapid prototyping and SFF industry in the form of RP Tempering technologies.

The next evolution of this nano-materials technology is in the early- to mid-stages with carbon fiber lay-ups. This materials process will work with both autoclave and compression-molding processes. No geometry to date has been too simple or complex when applying the Composite Tempering shapes. The expected range of results from initial testing were:

Standard isotropic carbon fiber lay-up verses applied CF Composite Tempering

• Increase impact strength and impact resistance
• Enhance inner laminar shear resistance
• Reduce chances for catastrophic break from impact
  • Compression mode
  • Tensile mode
• Material reduction(CF) reducing cost
• Weight reduction and avoidance by reducing CF
• Increase torsion durability during physical application use
• Increase three- and four-point flex strength
• Do not change tensile strength, elongation or flexural modulus
• Reduce vibration signatures
• Damping enhancements
• Does not change the useable physical design of part geometry
• No delimitation will occur form this process

Basic theory

These pre-manufactured shapes from Par3 Technology are placed in-between the layers of the carbon fiber lay-up. The nanocomposite materials will not delaminate the prepreg carbon fiber lay-up. The shape shown is for round strands of composite tempering materials with MWCNT. Other shapes are being researched and tested.

In this particular application the strands are round about 0.0005" in diameter. They are placed in between each layer of carbon fiber prepreg in alternating patterns. Other designs and patterns could be used to achieve specific results, from flat to spherical. [See Composite Tempering Strands (Alternating) below.]

Tempered vs. Non-Tempered

When the tempering technique and materials are applied initial results show promising results in compression mode. The stress, shown below in the before and after pictures, redistributes considerably in comparison on a tempered part. This will reduce the chances of a catastrophic break in compression mode. On the tensile side the stress all goes to the outside top corner of each side. FEA compared to the actual test results, in a photopolymer, showed results where within 5%. (See Before Tempering and After Tempering Screen Shots.)

Before tempering

After tempering

When the tempering technique and materials are applied initial results show promising results in three-point flex and torsion strength. The screen shots on the following page, of a tensile bar being flexed, demonstrate that the tempered parts has higher strength verses a non-tempered part. In the three-point flex picture the stress seem to move away form the mass in the center where a fracture normally happens and redistributes outward. We see in the Torsion pictures the stresses stay at the end of the tempered part where the force is being applied. On the non-tempered part the mass consolidates toward center of the part faster fracturing long before the non-tempered part. When this was tested in actual photopolymer parts the results where within 10%.

Reducing vibration

In order to reduce structure-borne vibration, several methods are available. Sometimes just changing the system's stiffness and/ or mass will alter the resonant frequencies. This, in turn, will reduce the unwanted vibration as long as the excitation frequencies do not change. But in most cases, the amplitude of the vibration needs to be isolated or dissipated by using an isolator or by applying damping materials.

Damping comes in two forms: material damping and system damping. Material damping is inherent in the material of choice while system damping can be controlled at the boundaries and interfaces.

The introduction of dampening materials into or onto a structure is commonly used today in automotive, aerospace, appliance, HVAC, and other applications. They can either be applied as an unconstrained (free) layer or a constrained layer. Both are highly dependant on placement on or in the structure and the range of operating temperatures that the structure will see. The unconstrained layer is the simplest way to apply damping into a structure (i.e. paints, tape, laminate, epoxy). The material is bonded to the outside layer of the structure. The unconstrained layer of material dissipates energy as the structure goes through cyclic deformation.

Fractured and Non-Fractured

Tempered and Non-Tempered

The constrained Composite Tempering geometry is one of the most efficient ways of introducing damping into a structure. The material can be a single thin sheet or a number of strands that are placed within the material walls during the manufacturing process. The shear bond of the materials dissipates energy as the structure go through shear cyclic deformation.

This structure of tempering compound in this case is 5mm diameter placed in evenly spaced straight lines between each layer of carbon fiber prepreg. These strands will alternate between each layer in a isotropic pattern. We can do this seamlessly and should perform better during a high impact situation holding the geometry together.

By forming a composite multi-layer with tunneled shapes alternating directions between each layer will form a substantially 3D tunneled structure. The infrastructure of engineered tempering strands will have a predetermined cross-sectional shape.

Much more testing will have to be done in the carbon fiber and other engineered materials. This photopolymer and many other materials have completed materials testing and the results are proven. Par 3 Technology is currently testing their tempering technology in multiple materials and designs.

Par 3 Technology
Cookeville, TN
par3technology.com