Non- destructive evaluation of materials (NDE)
Composite module
Composites are a blend of two or more reinforcing and matrix materials. The reinforcing face material exists as particles or fibers embedded in the matrix phase. An example is a concrete reinforcement with a steal rill bar. Combining these two materials forms a newer material with more advanced properties, and rigidity contributed by the concrete. A natural fiber composite has two components, i.e., the matrix and the reinforcing element. An example of a basic natural fiber composite is bricks made of hay straws with madness used by our ancestors to build houses.
The matrix constitutes polymers which exist in three types: Rubber, Thermoplastics, and Thermosets. The very basic thermosets are Epoxy (EP), which is used a lot in airplane wings. Other thermosets include Vinyl Ester (VE), Phonetics (PF), Polyimide (PL), Urea Formaldehyde (UF), and Melamine Formaldehyde (MF). Thermoplastics, on the other hand, is divided into two components, Commodity, and Engineering, which are then subdivided into other various sub-components. The Commodity has polyethylene (PE), Polypropylene (PP), Polyvinyl (PVC), Polystyrene (PS). Engineering, on the other hand, includes polyamide (nylon, PA, PAG, PA12), Polyphenylene Sulfide (PPS), Polyetherimide (PEI), Polysulfone (PSF), Polymethylmethacrylate (PMMA), Acrylonitrile butadiene styrene (ABS), polyetheretherketone (PEEK), Polyoxymethylene (POM), Polycarbonate (PC). Whereas thermoplastics can be solidified and re-melted, thermosets once solidified cannot be re-melted. A practical illustration is an egg and a block of cheese. Like the thermoset polymer, an egg once solidified cannot be re-melted, but a block of cheese like the thermoplastics can be solidified and re-melted.
Polymer advantages
A polymer has a lightweight with its density ranging between 1 to 2 g/cm3. Additionally, it is resistant to corrosion and electricity. Its thermal conductivity is relatively low with optical properties. Polymers are easily fabricated in a process referred to as formability. It has a finish on the surface and low cost with low energy content.
Thermoplastics have unique properties compared to thermosets, which makes them preferable for more applications than thermosets. One typical characteristic of thermoplastics is improved flexibility, fracture toughness, and greater resistance to impact. Its ability to be recycled and reused makes it economically attractive. It has enhanced joining and assembly methods with rapid cycle times. It has low tooling costs. Thermoplastics have enhanced resistance to corrosion and moisture. The raw materials have an unlimited shelf life. They exhibit tailored product procedures to meet the needs of the application. With thermoplastics, it is possible to eliminate exothermic reactions, toxic or solvent emissions, thereby making them environmentally benign.
Fibers
They are the reinforcement materials in the composite module. Types of fiber include carbon, glass, and Kevlar. Fibers exist as either natural or synthetic. Natural fibers include jute, flax, hemp, and Kenaf. Synthetic fibers, however, are further divided into polymer fibers and mineral fibers. Aramid and Polyethylene (PE) constitute the polymer fibers. Similarly, mineral constitutes basalt, boron, carbon, and glass fibers, which are Quartz, E-glass, and S-glass. The focus here is on the E-glass fiber composites and the Carbon fiber composites.
Fibers also have a large range of fiber forms which exist as either continuous or discontinuous fiber forms. The continuous form constitutes Braided fabric, knitted fabric, woven fabric, unidirectional or multiaxial laminate, continuous fiber mat (CFM. For the discontinuous form, we have Short fiber, long fiber, chopped strand mast (CSM). Sometimes, hybrid fibers exist when, for example, carbon and glass Care weaved together or a combination of kevlar and carbon. One of the reasons why fiber is considered a reinforcement in the polymer matrix is its very high properties.
Polymer matrix composite
A combination of the components, fiber as reinforcement and polymer as the matrix, forms a polymer matrix composite. A combination of thermoset and thermoplastic involves thermoset composition as the base polymer or monomer and a catalyst. Thermoplastic has only one pellet type component, which is heated above the temperature to melt before combining with the fibers.
Rule of mixture
One of the basic but very important theory is the rule of mixture. If the fibers are oriented in the same direction as the loading, we get Young’s modulus in the longitudinal direction. This modulus is the combination of modulus of matrix times the matrix volume fraction expressed as the volume fraction of the matrix, which is added to the volume fractions of fibers times the modular of fiber. Because the modulus of the matrix is relatively low, the contribution is mainly from the fibers. However, there is a derivation to get to this equation, which is not the focus of this composite module. The longitudinal direction is the transverse direction. Initially, we said the direction of the loading is the same as the direction of the fiber orientation, but if the loading is perpendicular to the fiber, the fiber does not align in the same direction of the loading direction. The composite modulus of the whole system is then taken in a transverse direction equation.
Thermoplastic matrix composite
Thermoplastic composites mainly have Continuous, and Discontionouos fiber reinforced thermoplastics. For continuous fiber, there is a unidirectional tape, woven prepreg, and other forms such as braided. Discontinuous fiber, on the other hand, has long fiber reinforced thermoplastics (LFT) and short fiber filled thermoplastics. Our focus will be on LFT. Processes of forming and finishing operations include injection molding, extrusion, compression molding, diaphragm forming, thermoforming, painting, joining, etc. The longer the fabric gets, the more difficult it becomes to process it.
The critical fiber length is one of the tools that will help us derive the definition of short or long fiber reinforcement. If a composite has a discontinuous fiber above the critical fiber length, it is quantified as a long fiber thermoplastic. If it is less than the critical fiber length, it is called a short fiber thermoplastic. Normally, the length of a long fiber ranges between 5 to 50 mm. Any fiber less than that is termed as a short fiber.
Processing – thermoplastic matrix composite
Processing is not as straightforward as the thermoset polymer matrix because of reasons such as high viscosity, even when it is melted. For example, polypropylene above its melting temperature of about 150 to 160 degrees Celcius, does not become fully liquid, which can be combined with fibers. In this process, the polymer matrix materials behave differently between the thermoset and thermoplastic. In this case, there is an intermedium form, which is the Pre-impregnated form. This means that the two components are combined, and this form is used for the final polymer. Rather than one stage, as in the thermoset composite processing, there are two stages in the thermoplastic composite. For the final product, one can opt for any processing techniques such as compression molding, injection molding, extrusion. Our composite module for this class will, however, use the compression molding
A basic concept of pre-impregnation will include fiber rollings going through an impregnation die in the thermoplastic melting process, which is extruded into the die. Consequently, the fiber meets with a molten thermoplastic. Once this is achieved, it is pulled out in a continuous process and becomes the different fabrics. LFT uses the same type of processing but produces granular pre-impregnated pellets. These pellets can then be used to inject molded components or use the compression molding process. Our focus in this class is the compression molding process. In this process, the pre-impregnated pellets are fed into the extruder, which has a barrel and a screw. The pellets are then transported from the feeder towards the front side of the extruder. At the same time, they are being melted. It comes out of the extruder as a charge or extradites. It is a molten thermoplastic fiber. What is melted here is the thermoplastic matrix. The fibers do not get melted because they are needed to be still integrated with no degradation. Once this charge comes out, it is put into a mold or two, and the hydraulic pressure is used to close the top. This process is quite simple, with a similarity of how waffles are made. However, care is needed because the material force presents the possibility of affecting the final material properties of the fiber thermoplastic composites.