MultiMechanics Blog

The 5 Most Advanced Composites (and how to virtually test their behavior)

Posted by Andy MacKrell on Mar 3, 2015 4:21:00 PM

One of the greatest strengths of composites is their ability to be combined and used in an infinite number of ways. From race car monocoques, to space shuttle heat sheilds, to bottle openers. 

If not used correctly though, this varietry can also add uncertainty. Whenever one adds variability they are necessarily decreasing predictability. Unless, of course, you have a tool capable of capturing those variables.

Below are The Top 5 most “exotic” and promising composite materials  - and a glimpse into how you can use MultiMech's Material Virtual Testing tools to predict their behavior.

 

1. 3D Woven Composites

Three Dimensional Woven Composites are currently only used in a few niche applications but have enormous potential. One of the biggest challenges of 2d unidirectional and woven composites is the risk of ply delamination. 3D composites solve this problem with the addition of thin "Z-axis" fibers. This small addition virtually eliminates the risk of delamination failure.

One example of these composites in action can be found in GE's LEAP engine fan-blades and fan casing. Using advanced composite materials, the LEAP engine exhibits 75% reduction in noise, 50% reduction in emissions, and a 15% reduction in fuel consumption (a 15% reduction in fuel consumption equates to a 10% decrease in an airline's entire operating expense). 

3d_woven_comp

The reason these materials are sparesly used in the cost and complexity involved in their design. In order to capture this material behavior, you need to model the complex 3d microstructure and account for the non-linear responses due to tow alignment, tow-tow friction effects, and tow-matrix interactions. Luckily, all of this can be done in MultiMech. 

 

2. Ceramic Matrix Composites

A heat shield on a space vehicle will experience temperatures around 1500 °C for a few minutes during reentry. Iron and Steel melt around 1400 °C (not too mention they are very heavy). For extremely high temperature applications, such as this, the only structural materials available are ceramics. 

However, as anyone who has dropped a dinner plate knows, ceramics are bad at withstanding abrupt disturbances like brunt impact, reentry vibrations, and thermal shock. In comes Ceramic Matrix Composites.

By combining the tough, thermally resistant properties of ceramics with a more ductile and tenacious reinforcement (like carbon fiber), you can adequately handle thermal shocks and vibrations and mitigate the growth of microcracks. 

FailureMechCeramic

CMCs are being explored as components for:

  • High-temperature gas turbines such as combustion chambers, stator vanes and turbine blades. 
  • Brake disks and brake system components, which experience extreme thermal shock (greater than throwing a glowing part of any material into water).
  • Components for slide bearings under heavy loads requiring high corrosion and wear resistance.
  • Components for burners, flame holders, and hot gas ducts.

Damage mechanisms for these materials include multiple matrix cracking, followed by fiber fracture and pullout. In these cases it is extremely important to model the  frictional bonding between the matrix and fiber. Using MultiMech's proprietary "crack insertion" and "cohesive zone modeling" technologies, the fiber-matrix interaction can be easily captured.

 

3. Long Fiber Thermoplastics

fiber_gif

As we talked about a few weeks ago, Long Fiber Thermoplastics are being touted as the material that will take composites "mainstream."

Compared to short fiber composites and thermosets, LFTs offer better mechanical properties in terms of elastic stiffness, strength, creep and fatigue endurance, and crashworthiness.  When aligned along the loading axis, long fiber thermoplastics can withstand up to 70% of the load of continuous fiber composites, at a fraction of the manufacturing costs.

curved

The difficulty with LFT's is that their alignment within the part, their degradation during injection molding, and even things like their curvature can have a huge effect on a composite part's mechanical response. In essence one area of your part can behave like steel and another like wood, even though both areas are made of the same "material". 

Luckily companies like Moldflow and Moldex have developed excellent software desgned to predict the behavior of fiber during an injection molding process. And when this injection molding output gets input into MultiMech,our software automatically adjust the fiber orientation and alignment for every element within your structural mesh.  This way you can capture the accurate properties of that element AND predict how the properties will evolve over time. 

Further, MultiMech is the only software available that can model the curvature within long fiber composites, which is shown to play a large role in a part's overall strength. 

 

4. 3D Printed Composites

3D printing is without question, one of the hottest areas of development for engineers and hobbyists alike. It has many potential benefits and applications, beyond the scope of this post. From an analysis perspective, 3D printed objects present unique modeling challenges.  

The simulation challenges stem from the following manufacturing-induced characteristics:3d_printed

  1. Because of the application process, 3d printed parts contain small “voids” where two rows of beads don’t completely touch. Even at low sputtering speeds and high temps, products possess some level of relative bumpiness at the microstructure level.
  2. Because of the heat of the application nozzle, thermal-residual stresses could be introduced within the already-cooled layers below (this same effect is seen in mass concrete applications and high temperature welding). 
  3. In some advanced cases, the printer filaments are infused with short carbon fibers or nano-particles for increased strength. 

As you might guess, a lack of geometric detail here can really "add up"!

MultiMech can capture these nuances using our additive manufacturing simulation technology. We can accurately model the periodic microstructural voids, can capture the structural effects of the carbon reinforcement, and can predict thermal-residual stresses that result from the application of hot material on a cool surface. 

 

5. Ultra High Performance Concrete

Outside the realm of traditional lightweight composites, there are big things happening in the world of construction materials. Largely driven by the need to fix the aging American infrastructure, the industry is developing and testing stronger more resilient forms of concrete. 

The most promising innovation is known as Ultra High Performance Concrete (UHPC). UHPC addresses all the shortcomings of standard concrete by offering:

  • High strength to weight ratios, high tensile strength, high ductility
  • High compressive strength (25k psi)
  • High impermeability (prevents thaw deterioration and corrosion of steel reinforcements)

These characteristics are achieved by including 5 in. long strips of steel fibers (5-8% by weight), finely ground quartz, and a higher percentage of Portland cement into a batch. Applications for UHPC include repair and strengthening of existing structures and the creation of newer, higher performing ones. 

If you look at these structures in terms of the number of “strength affecting” variables, high performance concrete is about as complicated as it gets. Because high performance concrete is both new and complex, the industry has yet to develop any comprehensive design or testing standards. 

On a meso scale, a batch contains heterogeneous particulates, mixed with long steel fibers. The mix is poured and cured in layers, creating the potential for residual stresses within 'cooled' layers. Due to the exothermic nature of concrete curing, the way in which a structure is "heat treated" impacts the overall properties.  

Despite these variables, MultiMech is able to model such a structure by performing a chemo-thermo-mechanico coupling.  We can accurately model both the fibers and particulates. We can also predict the heat generation and dissipation as a result of the concrete curing process. Finally, we can predict the optimal pouring schedule to limit the onslaught of production-induced defects in the concrete. 

additive

 

Here we are modeling the layered manufacturing of a concrete structure. Within that global structure, exists meso-scale elements containing chopped steel fibers. And within the matrix of that meso scale exists a particulate-infused microstructure.

Using multimech, these 3 scales can be simultaneously linked so that you can see how the behavior and evolution of ONE affects the others!

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Topics: Composite Analysis, Virtual Testing