Www.spacetec.org SpaceTEC ® Certification Readiness Course Materials and Processes I & II.

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SpaceTEC® Certification Readiness Course

Materials and Processes I & II

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Structural Metals-Properties

• Hardness– Ability to resist abrasion, penetration, cutting or permanent distortion

• Brittleness– Property of metal that allows little bending or deformation without

shattering• Malleable

– A metal that can be hammered, rolled or pressed into various shapes without cracking or breaking

• Ductility– Property of metal that allows it to be permanently drawn, bent, or

twisted into various shapes without breaking• Elasticity

– Property enables metal to return to its original shape when the force which causes the change of shape is removed

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Structural Metals-Properties

• Toughness– A material that will withstand tearing or shearing and may be stretched

without being deformed or breaking

• Density– Weight of a unit volume of material

• Fusibility– The ability of a metal to become liquid when heated (can be welded)

• Conductivity– Property which enables a metal to carry heat or electricity

• Contraction & Expansion– Reaction produced in metals as the result of heating or cooling

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Structural Metals-Selection Factors

• Strength– 5 factors effecting strength

are tension, compression, shear, bending & torsion

• Also required selections:– Weight

• Strength/weight ratio is always determined

– Reliability• 2 important factors are

corrosion resistance and workability

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Structural Metals-Selection Factors

• The Prowler was designed with nearly 930 pounds of aluminum - a full 1/3 of the car's weight.

• Casting and extruding aluminum is less costly than steel, and aluminum places less wear and tear on machine tools, potentially reducing costs related to tool maintenance, repair and replacement.

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Metal Types

• Ferrous Metals– Carbon Steel– Nickel Steel– Chromium Steel

• Nonferrous Metals– Aluminum & Aluminum Alloys– Alclad Aluminum– Titanium & Titanium Alloys– Copper & Copper Alloys– Monel– Magnesium & Magnesium Alloys

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Metalworking Processes

• Hot working

• Cold Working

• Extruding

• Welding

• Brazing/Soldering

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Heat Treatment

• Involves the heating and cooling of metals in the solid state

• Changes the mechanical properties so the metal can be more useful

• Metals can be made harder, stronger and more impact resistant or metals can be made softer and more ductile

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Heat Treatment Methods(Ferrous Metals)

• Hardening

• Tempering

• Annealing

• Normalizing

• Case hardening

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Case Hardening

STAGE ONE:

• The steel is heated to red heat. It may only be necessary to harden one part of the steel and so heat can be concentrated in this area. (Select Slide Show)

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Case Hardening

STAGE TWO:

• The steel is removed from the brazing hearth with blacksmiths tongs and plunged into case hardening compound and allowed to cool a little. The case hardening compound is high in carbon.

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Case Hardening

STAGE THREE:

• The steel is heated again to a red color, removed from the brazing hearth and plunged into cold, clean water. (Select Slide Show)

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Case Hardening

• The steel rod should now have a hardened outer surface and a flexible, soft interior. The process can be repeated to increase the depth of the hardened surface.

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Heat Treatment Methods

(Non-Ferrous Metals)• Aluminum alloys

– Solution heat treatment

– Precipitation heat treatment

• Magnesium alloys– Solution heat treatment

– Precipitation heat treatment

• Titanium

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Metalworking Practices

• Additional notes to remember when working with metals:– The material on the outside of a curve stretches,

while the material on the inside of the curve compresses. There is a location near the middle of the metal thickness that neither shrinks nor stretches. This is called the neutral line, or the neutral axis, of the material.

• Reference following slide for example of Pure Bending

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Metal Working PracticesPure Bending

Kinematics of pure bending:

• When a bar is subjected to a pure bending moment as shown in the figure it is observed that axial lines bend to form circumferential lines and transverse lines remain straight and become radial lines.

• In the process of bending there are axial line that do not extend or contract. The surface descried by the set of lines that do not extend or contract is called the neutral surface. Lines on one side of the neutral surface extend and on the other contract since the arc length is smaller on one side and larger on the other side of the neutral surface. The figure shows the neutral surface in both the initial and the bent configuration.

• The axial strain in a line element a distance y above the neutral surface is given by where is the radius to the neutral surface.

M M

Neutral Surface y

lo

l y

Neutral Surface

-y

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• Cold working, strain hardening or work hardening of a metal is done by repeatedly applying a mechanical force to the metal.

• Material Properties & Cold Working

– As the percent of ColdWorking increases:

• Tensile strength - increases• Yield strength - increases• Ductility - decreases• Electrical conductivity -

decreases• Corrosion resistance - decreases

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• A closed angle is and angle that has been bent beyond 90 degrees. • For the greatest strength in a bent piece of material, the layout should always be made

so that the bend will be perpendicular to the grain of the sheet• Note that angle of bend is the angle through which the material has actually been bent. • To illustrate, in Fig. 1, the angle on the drawing is 60 degrees, but the angle of bend A

is 120 degrees (180 − 60 = 120); • in Fig. 2, the angle of bend A is 60 degrees; in• Fig. 3, angle A is 90 − 30 = 60 degrees.

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Corrosion - Classifications

• Direct chemical attack– Battery acid, residual flux deposits, entrapped caustic

cleaning solutions

• Electrochemical attack– Requires a medium (usually water) that conducts tiny

current of electricity– More active metal becomes anodic & less active metal

becomes cathodic– The greater the difference in electrical potential (dissimilar

metals) the greater the corrosion– Most common cause of corrosion

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Corrosion

• 4 Conditions that must exists before corrosion can occur: (Select Slide Show)

– The presence of a metal that will corrode (anode)

– The presence of dissimilar conductive materials (cathode) which has less tendency to corrode

– Presence of a conductive liquid (electrolyte)

– Electrical contact between the anode and cathode

• Rust or corrosion that occurs with most metals is a result of the tendency for metals to return to their natural state.

• Nobel metals like gold and platinum do not corrode since they are chemically uncombined in their natural state.

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Corrosion – Dissimilar Metals

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Forms of Corrosion

Intergranular Corrosion

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Forms of Corrosion

Exfoliation (Intergranular) Corrosion

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Forms of Corrosion

Uniform Corrosion

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Forms of Corrosion

Galvanic Corrosion

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Forms of Corrosion

Concentration Cell Corrosion

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Forms of Corrosion

Pitting Corrosion

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Forms of Corrosion

Crevice Corrosion

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Forms of Corrosion

Filiform Corrosion

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Forms of Corrosion

Stress Corrosion Cracking

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Forms of Corrosion

Corrosion Fatigue

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Forms of Corrosion

Fretting Corrosion

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Forms of Corrosion

Erosion Corrosion

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Forms of Corrosion

Dealloying

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Forms of Corrosion

Corrosion in Concrete

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Forms of Corrosion

Microbial Corrosion

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Corrosion-Preventive Maintenance

• An adequate cleaning

• Detailed inspection for corrosion and failure of protective systems

• Prompt treatment of corrosion and touchup of damaged paint areas

• Keeping drain holes free of obstruction

• Daily wipe down of exposed critical areas

• Making maximum use of protective covers

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Corrosion – Preventive

Maintenance

• Electroplating• Metal Spraying (Metallizing)• Parco Lubrizing• Anodizing

– Anodized surfaces

• Alodizing• Surface Treatment• Protective paint finishes

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Corrosion–Preventive Maintenance

• Use of Chemical Cleaners– When a structure is chemically

cleaned the fayed surfaces should be protected to prevent corrosive materials from seeping between the lap joints. This would cause corrosion to form in an area where it is hard to detect.

– There are two parts to "sealing" faying surfaces:

• surfaces in contact• edges where an electrolyte

(chemical or water) could enter• Lap joints - Many designs have lap joints

in the fuselage skins. If the outside is to remain natural aluminum color, then mask the panel so you can put a chemical conversion coat where the panel is overlapped on the outside.

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Corrosion Removal

• Complete corrosion treatment involves the following:– Cleaning and stripping of the corroded area– Removing as much of the corrosion products as

practicable– Neutralizing any residual materials remaining in

pits and crevices – Restoring protective surface films– Applying temporary or permanent coatings or

paint finishes

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Non-metallic Materials Characteristics (Composites)

• Key terms and practices to remember when working with composite materials:– The basic two part mix for epoxy matrix material is resin and hardener.– One of the best ways of being sure that the matrix resin for a composite repair

has been properly mixed is to mix enough extra resin of each batch to make and identical lay up.

– Pot life is the length of time a catalyzed resin will remain in a workable state.– Molds hold the surface in place while materials cure and harden, they are

called male/female– When replacing honeycomb core material, the ribbon direction of the insert

must be the same as the ribbon direction of the original core.– You can use a ring (coin) tap test on composite structures. A change in the

sound made by the coin being tapped on a piece of composite structure may be caused by damage or by a transition to a different type of internal structure.

– The strength and stiffness of a properly constructed composite buildup depends primarily on the orientation of the plies to the load direction.

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Non-metallic Materials Characteristics

(Composites)• Key terms and practices to remember when working with composite materials

(continued):– Water is the only fluid normally approved for use in machining composite

materials. Any other fluid would contaminate the material and prevent subsequent bonding.

– Hole-filling fasteners such as conventional rivets should not be used in composites structures because of the probability of causing delaminating. When a conventional rivet is driven, it’s shank expands to completely fill the hole. The force applied by the expanded shank will cause the material to delaminate around the edges of the hole.

– When repairing damaged fastener holes in composite panels, chopped fibers or flox cane be added to the wet resin to strengthen the repair. Micro-balloons do not add any strength.

– Superficial scars, scratches, surface abrasions, or rain erosion can generally be repaired by applying one or more coats of a suitable resin, catalyzed to cure at room temperature, to the abraded surface.

– The preferred way of making a permanent repair to composite structure is to remove damaged area and lay in new repair plies, observing the choices of materials, the overlap dimensions, ply orientation, and curing procedures.

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Cellulose Strands

Lignin Polymer

Courtesy : Gary Eisenberg; Antelope Valley Community College; Lancaster , CA

Composites-Wood Structure

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Advantages of Composites

• Stronger and stiffer than metals on a density basis

• Highly corrosion resistant

• Outstanding durability

• Low investment in fabrication equipment

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• Non-metallic materials, also known as composite materials, offer many advantages over other materials. Within aerospace markets, where exceptional performance is required but weight is critical, composites continue to grow in importance. Some of the many advantages of composites are:

• Stronger and stiffer than metals on a density basis

• Highly corrosion resistant • Outstanding durability• Low investment in fabrication equipment• Illustration of the Delta 7425-9.5 rocket

with CONTOUR spacecraft. Photo: Boeing

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• From virtual to real is the track that aircraft follow. Here, the Boeing 787 Dreamliner takes shape. Its fuselage, made of composites, consists of four cylindrical sections.

• Composites, because of their light weight and strength, are gaining favor as a material for aircraft. The Boeing Co.'s 787 Dreamliner, officially unveiled on July 8, 2007 has become the poster child for composites in aircraft design because the design uses the materials extensively. According to Boeing, composite materials constitute about 50 percent of the aircraft by weight.

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Composite Materials within the Aerospace

Industry• Carbon/graphite

• Fiberglass

• Kevlar

• Thermoset Plastic

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Composite Processes

• Wet lay-up• Prepreg lay-up• Filament winding• Press molding• Resin Transfer Molding (RTM)• Resin Infusion• Chopper Gun sprayed materials

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Composite Processes

• Wet Lay Up Process– Epoxy is applied to the

carbon fiber. The finished panel will be cut into test samples.

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Composite ProcessesBACKGROUND (PREPREG MANUFACTURE, LAY-UP AND CONSOLIDATION)

Pre-pegs are thin sheets of fibres impregnated with resin. The most frequently used method ofPre-preg manufacture is the film route, which is illustrated schematically in figure˚1. Tows offibre are pulled along a heated bed, where resin films are brought into contact with them onupper and lower surfaces. The thermal field is controlled so as to reduce the resin viscositysufficiently to allow tow infiltration under the pressure applied via the consolidation rolls andto promote curing . Finally the pre-preg is backed with release film for storage until requiredfor component manufacture.

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Composite Processes

BACKGROUND (PREPREG MANUFACTURE, LAY-UP AND CONSOLIDATION)

Consolidation involves the cutting and stacking of pre-preg layers in a predetermined sequence of fibre orientations within a mould containing release agent and absorption layers. An upper plate is laid on top and this assembly is sealed in a vacuum bag, as shown in figure˚2. The matrix resin is cured by exposure to a defined combination of temperature and pressure. When the lay-up is heated, the constraint offered by the resin decreases as its viscosity falls. Application of pressure forces the fibres together. Therefore the temperature and pressure cycle affects, not only the fibre volume fraction and void content, but also the fibre distribution and alignment. The fibre alignment characterization technique presented here can be applied to fully cured composite components and to prepreg material.

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Composite ProcessesFilament Winding: Process Technology• To begin with, a large number of fibre rovings is pulled from series of

creels into bath containing liquid resin, catalyst and other ingredients such as pigments and UV retardants. Fibre tension is controlled by the guides or scissor bars located between each creel and resin bath. Just before entering the resin bath, the rovings are usually gathered into a band by passing them through a textile thread board or stainless steel comb.

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Composite Processes

Press moldingPress curing uses heated platens to apply both pressure and heat to the part. Presses, in general, operate at 20 - 1000 psi (140 - 7000 kPa) and up to 600°F (320°C). Press curing is very economical for flat parts and high production rates. Tooling requires matched die molds for contoured parts. The following steps are used in press molding:

1. Composite material is placed in the mold cavity.

2. Cure monitoring devices are installed.3. Parts are placed into press and cured.

Pressure, temperature, and time are monitored during the cure cycle to ensure curing parameters are met.

Press curing produces high quality parts with low void content.

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Composite Processes

Resin Transfer Molding (RTM) • Resin Transfer Molding or RTM as it is

commonly referred to is a “Closed Mold Process” in which reinforcement material is placed between two matching mold surfaces – one being male and one being female. The matching mold set is then closed and clamped and a low-viscosity thermoset resin is injected under moderate pressures (50 – 100 psi typical) into the mold cavity through a port or series of ports within the mold. The resin is injected to fill all voids within the mold set and thus penetrates and wets out all surfaces of the reinforcing materials. The reinforcements may include a variety of fiber types, in various forms such as continuous fibers, mat or woven type construction as well as a hybrid of more that one fiber type. Vacuum is sometimes used to enhance the resin flow and reduce void formation. The part is typically cured with heat. In some applications, the exothermic reaction of the resin may be sufficient for proper cure.

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Composite Processes

Vacuum Infusion - The Equipment and Process of Resin Infusion– The Vacuum Infusion Process

(VIP) is a technique that uses vacuum pressure to drive resin into

– a laminate. Materials are laid dry into the mold and the vacuum is applied before resin is

– introduced. Once a complete vacuum is achieved, resin is literally sucked into the laminate via

– carefully placed tubing. This process is aided by an assortment of supplies and materials.

Vacuum infusion provides a number of improvements over traditionally vacuum bagged parts.

These benefits include:• Better fiber-to-resin ratio• Less wasted resin• Very consistent resin usage• Unlimited set-up time• Cleaner

Reference following slide for example of this Vacuum equipment and process

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Composite ProcessesIn the following example, spiral tubing is used for both the resin feed and the vacuum line. Resin will enter on one side and fill the length of the tubing very quickly. At that point, resin will begin to flow across the laminate. While this approach is simpler to set up, the resin will need to travel across a longer distance. Depending on what materials and equipment are used, this distance becomes a significant factor. However, on the up-side, the inside surface texture of the finished part will be consistent.

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Vacuum Bagging Process

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Composites-Boeing 777

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Composites – B2 Stealth Bomber

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Composites – X-47 Pegasus

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All Composite Pegasus Skin


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Pegasus Internal Structure


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Pegasus Engine Fit Check


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All Composite Pegasus Tailpipe

All Composite Tailpipe Weighs Only 35 Pounds


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White Knight & Space Ship One


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Fluid Lines and Fittings

• Repair/Replacement of Metal Tube Lines: Rigid and Flex– Layout of Lines (Flex-Hose)

• Safety reasons• Functional reasons

– Fabrication• Types of materials• Usage

– Proof-Test After Assembly• Hydrostat• Pneumostat • Leak test• Identification

– Installation of Flexible Hose Assemblies and regulator panels• Installation of Rigid Tubing

– When making an installation of rigid tubing, each run of the tubing must have at least one bend in it to allow for the shifting of the line as it is pressurized.

– Dents in the heel of a bend in a piece of hydraulic tubing are not acceptable. Dents in other parts of hydraulic tubing are acceptable in their depth is less than 20 percent of the tube diameter.

• Metal tubing is sized by its outside diameter and flexible hose by inside diameter on all aerospace vehicles. When installing metal tubing, tension is undesirable because pressurization will cause it to expand and shift

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Fluid Lines

Www.spacetec.org SpaceTEC ® Certification Readiness Course Materials and Processes I & II.

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