Today's KNOWLEDGE Share:GEOMETRIC LATTICE CORES

 Today's KNOWLEDGE Share:

Geometric lattice cores

When talking about geometric lattice cores, most people think about a core with hexagon shaped cells, which is the basic and most common cellular honeycomb configuration. However, we have other options currently available on the market, such as Flex-Core, Ox-Core and Double-Flex to name a few!

But how to select between them?

The Flex-Core cell configuration provides for exceptional formability in compound curvatures with reduced anticlastic curvature and without buckling the cell walls. Curvatures of very tight radii are easily formed. When formed into tight radii, Flex-Core provides higher shear strengths than comparable hexagonal core of equivalent density.

The “OX” configuration is a hexagonal honeycomb that has been over-expanded in the “W” direction, providing a rectangular cell configuration that facilitates curving or forming in the “L” direction. The OX process increases “W” shear properties and decreases “L” shear properties when compared to hexagonal honeycomb.

Double-Flex is a unique large cell Aluminum Flex-Core with excellent formability and high specific compression properties. Double-Flex formability is similar to standard Flex-Core.

Source: Hexcel/managingcomposites/thenativelab

Today's KNOWLEDGE Share:first composite material manufactured by humans

 Today's KNOWLEDGE Share:

Which was the first composite material manufactured by humans? 

As you may already know, a composite material is, by definition, ''a material that is made of two or more different materials, differentiable at a microscopic level, whose specific properties are better than their separated properties''. 

Just like any topic related to discovering the first application of any new technology, there is still some debate about which was the first composite material developed by humankind. The answer heavily depends on your own interpretation of the definition aforementioned, and also the reliability when dating ancient discoveries. 

Many researchers point out that the first uses of composites date back to 1500 B.C. when early Egyptians and Mesopotamian settlers used a mixture of mud and straw to create strong and durable buildings. The mud acted as a matrix for the random straw reinforcements! Mesopotamians also used straw to provide reinforcement to ancient composite products including pottery and boats. 

Funny to think that, 3500 years ago humans manufactured the first composite material, at a time when this definition was far away from even existing! 

Source:managingcomposites/thenativelab

Today's KNOWLEDGE Share:Composite Essentials

 Today's KNOWLEDGE Share:

 Composite Essentials! 

What are the most common failure modes for carbon fiber composites? Let's check them out in detail! 

This microscopy shows three different failure modes: delamination, tensile fiber fracture, and tensile/shear matrix cracks in a cross-ply laminate!

Fracture analysis when zoomed-in can reveal a lot of info to engineers! 

Bibliographical Reference:

Article ''On the Effective Constitutive Properties of a Thin Adhesive Layer Loaded in Peel'', written by Andersson T and Biel A.

Source:managingcomposites/thenativelab

Today's KNOWLEDGE Share: Composite Essentials

 Today's KNOWLEDGE Share:

Composite Essentials

Let's learn more about the different weave patterns in woven fabrics!

Woven fabrics are woven yarns, rovings, or tows in mat form in a single layer, in which the amount of fiber in different directions is controlled by the weave pattern. The most common are Plain, Twill and Harness Satin! 

In a plain-weave pattern, fibers in 0° and 90° directions are equally distributed. A plain weave carbon fiber sheet looks symmetrical with a small checkerboard style appearance. In this weave the tows are woven in an over/under pattern. 

In a twill weave, the tow strand passes over a set number of tows and then under the same number of tows. The over/under pattern creates a diagonal arrowhead look, known as a “twill line”. 2×2 Twill is likely the most recognizable carbon fiber weave in the industry. It is used in many cosmetic and decorative applications, but also has great functionality, it has both moderate formability and moderate stability. As the 2×2 name implies, each tow will pass over 2 tows then under two tows.

The number in the Harness Satin names indicates the total number of tows passed over then under. For 4HS, it will pass over 3 tows then under 1. For 5HS, it will pass over 4 then under 1, and 8HS will pass over 7 and under 1. Common harness satin weaves are 4 harness satin (4HS), 5­ harness satin (5HS) and 8 harness satin (8HS). As you increase the number of the satin weave, formability will increase and fabric stability will decrease. 

In this picture you can see how the weaving process can yield many different patterns! 

Bibliographical Reference:

Composite Manufacturing - Materials, Product and Process Engineering - Page 54

Elevated Materials Article "Carbon Fiber Weaves: What they are and why to use them"

Source:managingcomposites/thenativelab

Today's KNOWLEDGE Share:FTIR

 Today's KNOWLEDGE Share:

Fourier transform infrared spectroscopy (FTIR) is a fundamental tool for the qualitative compositional analysis of polymeric materials. It allows the user to identify the material being tested. In order to properly interpret the results of FTIR, the key considerations regarding spectral band formation must be understood.

 

 FTIR bombards with infrared energy, and certain frequencies are absorbed by the sample and others transmitted. The frequencies at which the material absorbs infrared energy correspond to molecular vibrations that are produced within the sample. The infrared spectrum representing a material consists of absorption bands associated with discrete functional groups, the building blocks that make up the molecule. The frequency at which a functional group absorbs is based on a number of factors:

 

Atomic weight of the bonded species: Frequency decreases (lower cm-1) with increasing atomic weight.

 

Bond energy: Frequency increases (higher cm-1) with increasing bond energy.

 

Surrounding molecular structure: The adjacent molecular structure changes the vibrations of the subject bond, for example conjugation lowers the frequency (lower cm-1).

  

An important implication of this is the absorption bands associated with halogenated polymers, particularly fluoropolymers. The C-X stretching and bending frequencies occur at lower frequencies (lower cm-1) in C-I < C-Br < C-Cl < C-F < C-H. This is primarily due to the effects of the molecular mass bond energies. Because of this shift, the presence of a halide is often difficult to confirm by means of the infrared spectroscopy.

 

I have illustrated the spectral band shift between analogous C-H bond and C-F bands in polyethylene and polytetrafluroethylene, respectively, in the color-coded graphic below.

Source:Jeffrey A. Jansen

Today's KNOWLEDGE Share:carbon fibers possess such a high modulus in the direction of the fibe

Why does carbon fibers possess such a high modulus in the direction of the fiber?

As many questions related to materials engineering, to answer that we have to understand the unit cell structure of the material, in this case, graphite.

The crystal structure of graphite, consists of sp2 hybridized carbon atoms arranged two-dimensionally in a honeycomb structure in the x-y plane. The layers, termed graphene layers, are stacked parallel to each other in a 3D structure. The most common stacking sequence of the layer planes is the hexagonal form with an ABABAB packing sequence. This way, some atoms (α) have neighbors directly above and below in adjacent planes, while others (β) don’t. The bonding between the layers is van der Waals bonding, so the carbon layers can easily slide with respect to one another.

Due to the difference between the in-plane and out-of-plane bonding, graphite has a high modulus of elasticity parallel to the plane and a low modulus perpendicular to the plane. Thus, graphite is highly anisotropic. The high modulus of a carbon fiber stems from the fact that the carbon layers, though not necessarily flat, tend to be parallel to the fiber axis.

Source:#managingcomposites

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Today's KNOWLEDGE Share-FIRST APPLICATION OF CARBON FIBER

Today's KNOWLEDGE Share:

FIRST APPLICATION OF CARBON FIBERS
Carbon fibers are older than you imagine! The first carbon fibers date back to 1860! In 1879, a certain guy named Thomas Edison chose carbon fibers to manufacture light bulb filaments. At that time, they were not petroleum-based. Instead, they were produced through the pyrolysis of cotton or bamboo filaments. These filaments were ''baked'' at high temperatures to cause carbonization to take place.

But why were they chosen? The answer is pretty straightforward and has nothing to do with high strength! At the time, Edison noticed that their high heat tolerance made them ideal electrical conductors. However, soon later tungsten took over as the light bulb filament of choice in the early 1900s, and carbon fiber became obsolete for the next 50 years or so.

During the 1960s, a Japanese researcher named Akio Shindo, manage to manufacture carbon fibers using PAN as a precursor. This way, his team was able to achieve a filament that had ~55% carbon, using a much more cost-effective production method. This new technology allowed for the resurgence of carbon fibers, but this time, they were here to stay!

Source:composites Industry/managingcomposites