structure test 3, sem 2

37問 • 2年前

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What is aircraft corrosion? (2 Types)

is the deterioration of metal by chemical or electrochemical attack. It can take place internally and/or on the surface. Deterioration may change the surface, weaken the interior and damage, or loosen adjacent parts. •chemical deterioration •electro chemical deterioration

What type is most common cause of aircraft corrosion?

ELECTROCHEMICAL ATTACK

Is corrosion a natural phenomenon?

YES •water or water vapor containing salt combines with oxygen in the atmosphere to produce the main source of corrosion in the aircraft.

What causes direct chemical attack?

is an attack resulting from a direct exposure of a bare surface to caustic liquid or gaseous agents. (battery acid, residual flux deposits, entrapped caustic cleaning solutions)

What are conditions that must exist for electrochemical corrosion to occur?

4 CONDITIONS MUST EXIST BEFORE THIS CORROSION CAN OCCUR: 1. The presence of a metal that will corrode (ANODE) 2. The presence of dissimilar conductive material (CATHODE) which has less tendency to corrode 3. Presence of a conductive liquid (ELECTROLYTE) 4. ELECTRICAL CONTACT between the anode and cathode

What are common electrolytes?

• ANY MOISTURE - water (salt) • ACID (sulphuric, uric) • ALKALINE (cleaners)

Does the cathode or anode get eaten away?

anode

What does a greater distance between metals on the galvanic series chart indicate?

The greater the distance apart on chart, the FASTER the anode will corrode.

List and describe factors affecting corrosion.

1. SIZE OF ANODE AND CATHODE • small cathode, large anode (slow corrosion) •large cathode, small anode (fast corrosion) 2. TEMPERATURE •More corrosion in tropical areas 3. TIME •Exposed to corrosive environment 4. TYPE OF ELECTROLYTE • any moisture-water (salt) • acid (sulphuric, uric) • alkaline (cleaners)

uniform corrosion

MOST COMMON FORM of corrosion. Characterized by corrosive attack (direct chemical attack) proceeding evenly over the entire surface area. •caused by the reaction of metallic surface with atmospheric contaminants and exposure to oxygen.

PITTING CORROSION

localized form of corrosion by which cavities or “holes” are produced in the material. This is most common on aluminum and magnesium. It penetrates deep into the surface and is likely the result of uniform surface corrosion. It usually appears as clumps of white powder or gray dots on surface.

GALVANIC CORROSION

also known as DISSIMILAR METAL CORROSION. This refers to corrosion damage induced when two dissimilar materials are coupled in a corrosive electrolyte.

FILIFORM CORROSION

A form of oxygen concentration cell corrosion. Often caused by wash primer not curing properly. Wash primer requires air to cure appears as a thread or wormlike lines. Sometimes looks like a puffiness under the skin. - Is first noticeable around rivet heads and along lap joints. There is no cure for this type of corrosion, short of a completely stripping and redoing the aircraft

INTERGRANULAR CORROSION

A form of oxygen concentration cell corrosion. Often caused by wash primer not curing properly. Wash primer requires air to cure appears as a thread or wormlike lines. Sometimes looks like a puffiness under the skin. • Is first noticeable around rivet heads and along lap joints. There is no cure for this type of corrosion, short of a completely stripping and redoing the aircraft

EXFOLIATION CORROSION

extreme form of intergranular corrosion which occurs mainly in extruded parts (angles, channels) and along grain boundaries. Metals tend to separate or delaminate.

STRESS CORROSION

Occurs from the combined influence of tensile stress and a corrosive Environment (Intergranular cracking) •Commonly found between rivets and stressed skins, pressed in bushings, tapered fittings.

FRETTING CORROSION

•causes smoking rivets • Combination of corrosion and wear. • Oxidation is the most common element. • Relative movement between 2 surfaces. • Metal oxides become trapped between 2 surfaces.

MICROBIAL CORROSION

Found at the bottom of fuel tanks (dark sludge\slime). Caused by microbial growth and reproduction in aviation fuel

What is another term used for uniform corrosion? What is uniform corrosion called that occurs on steel surfaces?

SURFACE CORROSION – RUST

What type of corrosion can result from uniform corrosion and is most commonly found on magnesium and aluminum alloys?

PITTING CORROSION

What is another term used for galvanic corrosion? What is an example of this type of corrosion discussed in class?

DISSIMILAR METAL CORROSION

What type of corrosion has a worm like pattern and can lead to intergranular corrosion?

filoform corrosion

Which type of corrosion occurs along grain boundaries and below the surface?

INTERGRANULAR CORROSION

What is an advanced type of corrosion that exists along grain boundaries? What appearance would indicate this type of corrosion?

EXFOLIATION CORROSION – METALS SEPARATE OR DELAMINATE

What type of corrosion can occur as a result of two surfaces rubbing against one another? What appearance would be present?

FRETTING CORROSION – “SMOKING RIVETS”

What is a common cause of FATIGUE CORROSION?

(aka STRESS CORROSION) - caused by pressurization and depressurization of the structure or cyclic stress. This occurs between lap seams and fasteners.

How can corrosion be prevented? What tools are required to inspect for corrosion?

PREVENTIVE MAINTENANCE • Frequent cleaning • Detailed inspection for corrosion • Quick treatment of corrosion and touchup of damaged paint areas • Keeping drain holes free of obstruction • Daily wipe down of exposed critical areas • Make maximum use of protective covers • Store in well-ventilated areas

Where are common areas on an aircraft where corrosion may occur?

• BATTERY COMPARTMENTS - Fumes • LAVATORIES, BUFFETS, AND GALLEY Spills • EXHAUST TRAILS - Exhaust deposits are corrosive • BILGE AREA - Lowest part fuselage • WHEEL WELLS - Exposed to environment • HINGE AREAS - Moving parts/Fretting corrosion • LEADING EDGES - Exposed to environment • EXTERNAL SKINS – Exposed to environment • FLEXIBLE HOSE ASSEMBLIES – Moving parts

What holds a high shear rivet in place?

COLLAR

List types of blind fasteners, when are blind fasteners used?

•BLIND RIVETS “are used when there is access to only one end of the rivet” • POP RIVETS • CHERRY MAX • RIVNUT

What is an interference fit?

called a PRESSED FIT or FRICTION FIT • fastener has a larger diameter than the hole so force is needed for installation

List fasteners that require interference fit.

o HI LOKS o HI SHEAR RIVETS o TAPER

What is the min/max number of threads required when installing a hilok?

1 and 3

What tool can be used to stop a hilok from spinning during installation?

ALLEN KEY

In what increments are hilok diameter and length measured?

•DIAMETER = 32nds •LENGTH = 16ths

Where are camloks commonly used? How many components does a camlok assembly consist of? What tool is required for install?

COWLING and FAIRINGS Camloks consist of three parts: • studassembly • grommet • receptacle

Describe application and installation of rivnuts and nutplates

RIVNUT - It is a one-piece internally threaded and counterbored tubular rivet that can be anchored entirely from one side NUTPLATE – use a nutplate jig todrill nutplate rivet holes for installation

Composites test 2

Zachary Halycz · 54問 · 2年前

Composites test 2