Composites

Composites Aircraft Non-metallic Structures 737 – Rudder, elevators, radome, wing to body fairings, floorboards, galley walls, lavatory Airbus, 757, 767 – has the almost the same components that are composite SRM – Structural Repair Manual – for structures and composites OHM – Overhaul Manual – maintenance repair and composites Kruger flaps – leading edge Composites materials Honeycomb – Carbon/Graphite – good for primary structural applications; good compressive strength, is highly rigid when in a matrix and has high fatigue resistance; requires lightening protection; corrosive to aluminum

Aramid – Aramid fibers are a class of heat-resistant and strong synthetic fibers. They are used in aerospace and military applications, for ballistic rated body armor fabric, and as an asbestos substitute. The name is a shortened form of "aromatic polyamide". They are fibers in which the chain molecules are highly oriented along the fiber axis, so the strength of the chemical bond can be exploited. Fiberglass – Boron – strictly used in military- F14, like Kevlar- expensive; usually come in unidirectional; has excellent compressive strength and stiffness, and is extremely hard. Ceramic – hi heat resistance, they can be used in areas up to 2,200degrees F; popular for firewall Composites also used 1. Primary Structural 2. Secondary Structural Strength to weight ratio is high Advantages 1. High strength to weight ratio 20% saving 2. Cost effective design – design to be flexible, resistant to vibration, stress fatigue 3. Composites do not corrode

4. Reduce wear Fiberglass – glass fibers that have been spun into yarn and woven into fabric; used for non-structural repairs Three types of fiberglass cloth 1. E-glass – hi electrical resistance; low cost 2. S-glass - hi tensile strength, 40% stronger than E and can stand higher temps; wings; flight controls 3. C-glass – higher chemical resistance; battery compartment, bilge area, anywhere there is hydraulic fluids Composites are highly susceptible to impact damage, with the extent of damage being visually difficult to determine Unidirectional – strength in only one direction Anisotropic – different strengths when measured in different directions Quasi-isotropic – same strength in different directions Tensile strength but weak compressive loads Compressive strength Strengths are determined by fiber orientation patterns. Maximum strength is parallel to the fibers, and loads at right angles to the fibers tend to break only the matrix. Fibers carry the physical loads and provide most of the strength of composites. Kevlar – excellent tensile strength and toughness, but inferior compressive strength when compared to graphite; density and cost are lower than graphite; need special scissors to cut because of stretching; need brad-point drill made for Arimid fabric; fuzzy holes can result from improper cutting and drilling, these fuzzy holes can absorb moisture, the moisture will cause matrix to de-laminate Matrix (Resin) – – –

– Resins

Homogenous resin that, when cured, forms the binder that holds the fibers together and transfers the loads to the fibers Epoxy the most dominant in aviation Epoxy provide high mechanical and fatigue strength, excellent dimensional stability, corrosion resistance and inter-laminar bond, good electrical properties and very low water absorption The changing of the matrix properties by chemical reaction is called the cure

–

Its purpose is not only to give the flexible glass cloth form, but also to carry loads from one fiber to the next.

Polyester Resin – – – –

Isn’t used on structural components; you find at your local hardware store; it is used in aviation for fabricating forms and other tooling The hardening process generates its own heat from a chemical reaction of the resin and hardener Not enough catalyst will slow down the hardening process to the point of unsuitability Too much harder and the mixture will generate so much heat that you will have thermal runaway

Epoxy Resin – – –

It hardens by a chemical process known as cross-linking May not cure if too much resin is used Pot life –the specific time period in which it must be used

Reinforce Plastic Warp – threads that run from one end of a roll of fabric to the other Woof – Also known as fill or weft, the threads that run side-to-side and actually make the collection of long threads into cloth Selvage – when the woof runs to the side of the cloth and turns around the goes back to the other side, it produces a selvage edge. It doesn’t lay down well and is generally trimmed. Bias - Warp and woof threads run parallel to the length, or 90degree, and are difficult to form around a curve. By cutting the material at a 45degree angle to the warp, it can be made to smoothly fit a curve Hot Bonding – –

–

The process that allows the technician to actually control the bonding and curing process The items that are critical to the integrity of the cured repair are: 1. Resin quantity 2. Fiber Contact 3. Vacuum pressure 4. Excess resin removal 5. Applied heat If there is too much resin, the resin will crack under load b4 proper amount is transferred to the next fiber