When installing a standard AN bolt with a self-locking nut in a joint subject to tension loads, what is the proper thread engagement requirement?
ACS code: AM.I.E
Correct answer: At least one thread of the bolt must extend beyond the nut.
Rationale: FAA guidance requires that a bolt of correct length show at least one thread (including the chamfer) extending past the nut after tightening. A bolt threaded flush or short of the nut may not be fully engaged, and stating 'three threads inside the nut' does not address the visible-thread inspection standard used to verify correct grip length.
Why should the threaded portion of a bolt, rather than the grip, never bear the shear load in a joint?
ACS code: AM.I.E
Correct answer: Threads concentrate stress and reduce the effective cross-sectional area in shear.
Rationale: A bolt's grip is the smooth, full-diameter shank designed to carry shear. The threaded section has a smaller root diameter and the thread roots act as stress risers, so loading threads in shear weakens the joint. Threads are not specially case-hardened to brittleness, and the nut does not carry the joint's shear load.
What is the primary purpose of using a cotter pin with a castellated (castle) nut on a bolt?
ACS code: AM.I.E
Correct answer: To prevent the nut from rotating off the bolt.
Rationale: A cotter pin passes through the slots of a castellated nut and a hole in the bolt to positively lock the nut against rotation. It is a mechanical safety device, not a means of adding clamping force or sealing threads; the torque on the nut establishes clamp load.
When using the double-twist method to safety wire two bolts together, in which direction must the wire be installed relative to each bolt?
ACS code: AM.I.E
Correct answer: So that loosening of either bolt tightens the wire.
Rationale: Safety wire must be routed so that any tendency of a bolt to loosen puts tension on the wire, pulling the adjacent bolt tight. Running the wire over the heads or around the grip does not oppose the loosening rotation and would not perform the safetying function.
What is the standard temper designation for aluminum alloy that has been solution heat-treated and then artificially aged?
ACS code: AM.I.E
Correct answer: T6
Rationale: The -T6 temper designates aluminum that is solution heat-treated and then artificially aged. The -T3 temper is solution heat-treated, cold worked, and naturally aged, while -O designates the annealed condition. These designations follow the standard aluminum temper system in the handbook.
In the four-digit aluminum alloy designation 2024, what does the first digit indicate?
ACS code: AM.I.E
Correct answer: The principal alloying element of the alloy.
Rationale: In the four-digit wrought aluminum system, the first digit identifies the principal alloying element group; for 2024 the leading 2 indicates copper as the major alloying element. The first digit is not a percentage, and temper is shown separately by a dash and letter/number suffix.
What is the principal advantage of using a torque wrench when installing a nut and bolt?
ACS code: AM.I.E
Correct answer: It applies a specified, uniform tension to the fastener.
Rationale: A torque wrench is used to develop a specified, repeatable clamping tension by measuring the torque applied, preventing both under- and over-tightening. Proper torque alone does not lock the nut, so safetying is still required, and torquing does not by itself prevent all loosening.
The specified torque for a fastener is 50 inch-pounds, but a 2-inch extension must be added in line with an 8-inch torque wrench to reach the bolt. What reading on the wrench will produce the specified torque at the bolt?
ACS code: AM.I.E
Correct answer: 40 inch-pounds.
Rationale: When an extension is added in line with the wrench handle, the effective lever lengthens and the wrench scale under-reads the true fastener torque. The wrench reading equals desired torque times wrench length divided by (wrench + extension) length: 50 x 8 / (8 + 2) = 40 inch-pounds at the wrench to achieve 50 inch-pounds at the bolt.
Which of the following composite reinforcing fibers is most susceptible to the absorption of moisture?
ACS code: AM.I.E
Correct answer: Aramid (Kevlar)
Rationale: Aramid (Kevlar) fiber readily absorbs moisture, which can degrade the resin bond and reduce strength, so aramid laminates must be carefully dried before repair. Glass and carbon fibers do not absorb water the same way. See FAA-H-8083-30, Aircraft Materials, Hardware, and Processes, on composite materials.
When drilling stainless steel, the technician should use a
ACS code: AM.I.E
Correct answer: drill ground to 120 degrees with a slow cutting speed.
Rationale: Stainless steel work-hardens rapidly and conducts heat poorly, so a slow cutting speed with firm, continuous feed prevents glazing and overheating. A more obtuse 120-degree point reduces cutting load and helps the lip bite before the surface hardens. A fast speed or a sharper 90-degree point would generate heat that hardens the metal ahead of the drill. See FAA-H-8083-30, Aircraft Materials, Hardware, and Processes.
How is a material galvanized?
ACS code: AM.I.E
Correct answer: It is dipped in a bath of molten zinc.
Rationale: Galvanizing applies a sacrificial zinc coating; the classic hot-dip process immerses cleaned steel in a bath of molten zinc that bonds to the surface and protects the steel by acting anodically. Heating in zinc dust is a different process, and spraying nickel is a separate plating method. See FAA-H-8083-30, Aircraft Materials, Hardware, and Processes.
At what temperature range is steel tempered?
ACS code: AM.I.E
Correct answer: Below the annealing temperature.
Rationale: Tempering is a low-temperature reheat applied to already-hardened steel to relieve quenching stresses and trade a little hardness for greatly improved toughness. It is carried out below the lower critical (annealing) temperature so the structure is not re-transformed. Heating to or above the annealing temperature would soften the steel. See FAA-H-8083-30, Aircraft Materials, Hardware, and Processes.
The addition of chromium to steel produces increased
ACS code: AM.I.E
Correct answer: hardness.
Rationale: Chromium is a strong carbide-former, so adding it to steel raises hardness and wear resistance (and corrosion resistance at higher percentages). It does not improve ductility, and toughness is not its primary contribution. This is why chromium steels are favored for hard, wear-resistant components. See FAA-H-8083-30, Aircraft Materials, Hardware, and Processes.
Chromium added to plain carbon steel
ACS code: AM.I.E
Correct answer: increases its resistance to corrosion.
Rationale: Chromium added to plain carbon steel forms a thin, self-healing oxide film that greatly increases resistance to corrosion, which is the basis of stainless steel. It remains a ferrous alloy because iron is still the major element, and it makes the steel harder rather than softer. See FAA-H-8083-30, Aircraft Materials, Hardware, and Processes.
The purpose of case hardening is to
ACS code: AM.I.E
Correct answer: produce a hard case over a tough core.
Rationale: Case hardening is used where a component needs a hard, wear-resistant surface but a tough, shock-absorbing interior. Carbon is diffused into the surface of a low-carbon steel so the case can be hardened while the low-carbon core stays tough. It therefore adds carbon to the surface rather than removing it. See FAA-H-8083-30, Aircraft Materials, Hardware, and Processes.
At normal temperatures, high-carbon steel is harder than low-carbon steel because
ACS code: AM.I.E
Correct answer: of the higher percentage of carbon in the steel.
Rationale: The hardness obtainable in plain carbon steel rises with its carbon content, because carbon allows hard constituents such as cementite and martensite to form. A high-carbon steel is therefore harder than a low-carbon one. Retained austenite actually lowers hardness, so it is not the reason. See FAA-H-8083-30, Aircraft Materials, Hardware, and Processes.
Nitriding is a form of
ACS code: AM.I.E
Correct answer: case hardening.
Rationale: Nitriding is a case-hardening process in which nitrogen is diffused into the surface of a suitable alloy steel to form hard nitrides, giving a very hard, wear-resistant skin without a final quench. It is not tempering (a stress-relieving reheat) nor anodizing (an electro-chemical oxide treatment for aluminum). See FAA-H-8083-30, Aircraft Materials, Hardware, and Processes.
Medium-carbon steel has a carbon content of approximately
ACS code: AM.I.E
Correct answer: 0.3 to 0.5 percent.
Rationale: Plain carbon steels are graded by carbon content: low (mild) up to about 0.3 percent, medium roughly 0.3 to 0.5 percent, and high carbon above about 0.5 percent. Medium-carbon steel therefore falls in the 0.3 to 0.5 percent band, offering a balance of strength and toughness. See FAA-H-8083-30, Aircraft Materials, Hardware, and Processes.
A ferrous metal contains
ACS code: AM.I.E
Correct answer: iron.
Rationale: By definition a ferrous metal is one in which iron is the principal element, the word ferrous deriving from ferrum (iron). Aluminum and magnesium are the basis of non-ferrous light alloys and contain no iron. This is the fundamental division between ferrous and non-ferrous metals. See FAA-H-8083-30, Aircraft Materials, Hardware, and Processes.
With respect to ferrous metals, which of the following is true?
ACS code: AM.I.E
Correct answer: Iron is a main element, and most ferrous metals are magnetic.
Rationale: Ferrous metals have iron as their main constituent, and because iron is ferromagnetic most ferrous metals are magnetic, which is a useful quick identification check. The exception is austenitic stainless steel, which is non-magnetic, so the statement is correctly qualified as most rather than all. See FAA-H-8083-30, Aircraft Materials, Hardware, and Processes.
The annealing of steel is sometimes required because it
ACS code: AM.I.E
Correct answer: relieves internal stress caused by engineering processes.
Rationale: Annealing heats steel and cools it very slowly to soften it, refine the grain, and relieve internal stresses introduced by machining, forming, or welding. It does not increase load-carrying capacity or form a corrosion-resistant layer; if anything it lowers strength while improving ductility and workability. See FAA-H-8083-30, Aircraft Materials, Hardware, and Processes.
On the Brinell hardness scale, a hardened cobalt tool or high-speed steel would have a Brinell hardness number (BHN) in approximately what range?
ACS code: AM.I.E
Correct answer: 600 to 700 BHN
Rationale: Cobalt is used in very hard tool and high-speed steels, which sit high on the Brinell scale, in the region of 600 to 700 BHN. This is far above soft annealed steels (roughly 100 to 175 BHN). The lower ranges correspond to mild or medium carbon steels rather than a hardened cobalt tool steel.
If a metal component is found to be in the tertiary (third) stage of creep, what is the correct action?
ACS code: AM.I.E
Correct answer: Replace the component immediately
Rationale: Creep occurs in three stages, and the tertiary stage is one of rapidly accelerating, irreversible strain that leads quickly to rupture. Crack-arrest or condition-monitoring measures are inadequate once tertiary creep is reached, so the only safe action is to remove and replace the component immediately before it fails.
Phosphate conversion coating of steel is produced by immersing the steel in a solution of
ACS code: AM.I.E
Correct answer: phosphoric acid and metal phosphates
Rationale: Phosphating produces a corrosion-inhibiting, paint-keying conversion coating by immersing the steel in a solution of phosphoric acid and metal phosphates, which react with the surface to form an integral phosphate layer. Nitric and sulfuric acid baths are used for other treatments such as pickling and are not the phosphating solution.
Tempering of a hardened steel involves
ACS code: AM.I.E
Correct answer: reheating below the critical point and cooling slowly
Rationale: Tempering reheats hardened steel to a temperature below the critical point, holds it, then cools it slowly to relieve quench stresses and reduce brittleness. Because the steel stays below the critical point, it is not re-austenitized. Heating above the critical point would be a hardening or normalizing operation, not tempering.
Austenitic stainless steels are best described as
ACS code: AM.I.E
Correct answer: essentially non-magnetic
Rationale: Austenitic stainless steels retain a face-centered-cubic austenite structure at room temperature, which makes them essentially non-magnetic. That same structure means they cannot be hardened by conventional heat treatment and are strengthened only by cold working. Their non-magnetic response distinguishes them from ferritic and martensitic stainless grades.
The desirable properties of normal carbon steel depend largely on the transformation, during slow cooling, of
ACS code: AM.I.E
Correct answer: austenite into pearlite
Rationale: When carbon steel is heated it becomes austenite, and on slow cooling that austenite transforms into pearlite, the layered ferrite-cementite structure that gives normal carbon steel its properties. The reverse change, pearlite to austenite, occurs only on heating, not cooling.
What is the principal difference between annealing and normalizing of steel?
ACS code: AM.I.E
Correct answer: Both are heated above the critical temperature; annealing cools slowly in the furnace while normalizing cools in still air
Rationale: Both annealing and normalizing start by heating above the upper critical temperature to form austenite; the difference is the cooling rate. Annealing cools very slowly in the furnace to give the softest, most ductile result, while normalizing cools in still air, giving a slightly harder, finer-grained, stress-relieved structure.
Normalizing of steel is performed primarily to
ACS code: AM.I.E
Correct answer: relieve the residual stresses left by manufacturing processes
Rationale: Normalizing reheats steel above its upper critical point and air-cools it to refine the grain and relieve the residual stresses left by forging, rolling, or machining, producing a uniform structure. It is not primarily a softening process like full annealing, and heat treatment cannot restore fatigue life already consumed.
During the normalizing process, after heating above the upper critical point the steel is
ACS code: AM.I.E
Correct answer: allowed to cool in still air at room temperature
Rationale: Normalizing is defined by cooling in still air at room temperature after heating above the upper critical point, which is faster than furnace annealing but slower than a quench. Immediate quenching would harden the steel, and very slow furnace cooling would be annealing, so still-air cooling is what makes the process normalizing.
Cast iron is best characterized as a material that is
ACS code: AM.I.E
Correct answer: heavy and brittle
Rationale: Cast iron has a high carbon content, much of it as graphite flakes, which makes it heavy and brittle with little ability to deform before fracture. It is therefore good in compression but poor under tension or shock. Because it is neither tough nor malleable, it is not used for highly stressed aircraft structure.
Exhaust systems are commonly made from stainless steel, which when held at high temperature is susceptible to
ACS code: AM.I.E
Correct answer: intergranular corrosion
Rationale: When austenitic stainless steel is held in a high-temperature range, as around exhaust systems and welds, chromium combines with carbon at the grain boundaries (sensitization), leaving those boundaries depleted of chromium and prone to intergranular corrosion. Filiform and general surface corrosion are more typical of coated or aluminum surfaces rather than this grain-boundary attack.
In the heat treatment of steel, tempering is performed
ACS code: AM.I.E
Correct answer: after the hardening operation
Rationale: Tempering is always performed after hardening, because its purpose is to relieve the stresses and reduce the brittleness left by the quench while retaining most of the gained hardness. Carried out before hardening it would have no effect, and it reduces rather than increases hardness, so it is not used to increase hardness.
If a steel component is operated below its fatigue (endurance) limit, the fatigue life is
ACS code: AM.I.E
Correct answer: theoretically infinite
Rationale: Steels exhibit a true fatigue (endurance) limit: if the cyclic stress stays below this limit, the material can theoretically endure an unlimited number of cycles, giving an effectively infinite fatigue life. Above the limit the life becomes finite and falls sharply as stress rises. The fatigue limit, not the proof stress, governs this behavior.
A low-carbon steel that does not contain enough carbon to harden directly would normally be case hardened using
ACS code: AM.I.E
Correct answer: pack or gas carburizing
Rationale: A low-carbon steel lacks the carbon needed to harden, so its surface is first enriched with carbon by pack or gas carburizing before quenching, giving a hard case over a tough core. Nitriding suits special alloy steels, and flame or induction hardening requires a steel that already has enough carbon to respond to localized heating.
The stress that remains locked within a component after manufacture and all heat treatment, with no external load applied, is called
ACS code: AM.I.E
Correct answer: residual stress
Rationale: Stress that remains within a component after manufacture and all heat treatment, with no external load applied, is termed residual stress. Working or applied stress, by contrast, exists only while the part is actually carrying a load in service. Excessive residual stress is undesirable, which is why stress-relieving treatments are used.
Annealing of steel is performed primarily to
ACS code: AM.I.E
Correct answer: make the metal malleable and easier to work.
Rationale: Annealing softens steel and increases its ductility and malleability, relieving internal stresses so the metal is easier to form and machine. It does not increase strength or toughness, and it does not make the metal brittle; brittleness is associated with hardening.
Tempering of hardened steel is performed to
ACS code: AM.I.E
Correct answer: significantly reduce brittleness without a major loss of strength.
Rationale: Tempering reheats fully hardened steel to a moderate temperature so it loses much of its excessive brittleness while retaining most of its strength and hardness, producing a usable balance of properties throughout the section rather than selectively in the core or surface.
High-speed steel relies chiefly on which alloying element for its ability to cut other metals even when heated to a dull red color?
ACS code: AM.I.E
Correct answer: Tungsten.
Rationale: High-speed steel owes its red-hardness — the ability to hold a cutting edge even when heated to a dull red — mainly to tungsten, which forms stable carbides that resist softening at high temperature. Nickel adds toughness and vanadium is a secondary carbide-former, so tungsten is the key element.
When a low-carbon steel bolt is stretched beyond its elastic limit without breaking, it will
ACS code: AM.I.E
Correct answer: deform permanently.
Rationale: The elastic limit marks the boundary of recoverable deformation. Once a low-carbon steel bolt is stretched beyond it, the strain becomes plastic and the bolt deforms permanently rather than springing back; such a bolt must be replaced. It does not recover its length, nor does stretching make it more ductile.
Fatigue failure of a metal is best defined as
ACS code: AM.I.E
Correct answer: a reduction in strength caused by repeated or alternating loads.
Rationale: Fatigue is the progressive weakening and eventual cracking of a material under repeated or alternating loads, even when each load is well below the ultimate tensile strength. It is therefore best defined as a reduction in strength caused by cyclic loading, distinct from a single overload or a one-time impact fracture.
Cast iron is best described as
ACS code: AM.I.E
Correct answer: heavy and brittle.
Rationale: Cast iron contains a high proportion of carbon, largely as graphite flakes, making it heavy and brittle with very little ductility, so it fractures rather than bends under shock or tension. It is strong in compression but is neither tough nor malleable.
Steel is produced by refining pig iron, blowing air or oxygen through the molten material primarily to remove excess
ACS code: AM.I.E
Correct answer: carbon.
Rationale: Pig iron from the blast furnace has too much carbon to be useful, so steelmaking refines it by blowing air or oxygen through the molten metal to oxidize and remove the excess carbon to the required level. Controlling final carbon content in this way converts brittle pig iron into steel.
In a tensile strength test, the specimen is
ACS code: AM.I.E
Correct answer: pulled in tension until it breaks.
Rationale: A tensile strength test loads a specimen in tension and continues to pull it until it fractures, recording load and extension all the way to failure. This allows properties such as ultimate tensile strength and elongation at fracture to be determined; stopping at the elastic limit or at the UTS would not produce the complete curve to rupture.
An impact test, such as the Izod or Charpy test, is used to measure a material's
ACS code: AM.I.E
Correct answer: toughness.
Rationale: Impact tests such as Izod and Charpy measure the energy a material absorbs in fracturing under a sudden blow, a direct measure of its toughness — the ability to resist shock without breaking. Hardness and ductility are assessed by separate tests (indentation and elongation) and are not what an impact test quantifies.
The Charpy test is used to measure a material's
ACS code: AM.I.E
Correct answer: impact energy.
Rationale: The Charpy test is an impact test: a weighted pendulum strikes a notched specimen and the energy absorbed in fracturing it is read from the swing. That absorbed impact energy measures the material's toughness, or resistance to shock loading. Strain and the modulus of elasticity are obtained from a tensile test, not an impact test.
For most steels, the fatigue (endurance) limit is generally in the region of which percentage of the static ultimate tensile strength?
ACS code: AM.I.E
Correct answer: 40 to 60 percent.
Rationale: For most steels the fatigue (endurance) limit lies roughly at one-half of the static ultimate tensile strength, so the 40 to 60 percent band is the accepted figure. Higher ranges overstate fatigue strength, which is why repeated-load design stresses are kept well below the static ultimate tensile strength.
The ability of mild steel to carry additional load after the yield point is reached is due to
ACS code: AM.I.E
Correct answer: strain hardening.
Rationale: Beyond the yield point mild steel deforms plastically, and the dislocation movement that produces this deformation tangles and multiplies the dislocations, so the metal grows harder and carries more load. This work or strain hardening continues up to the ultimate strength. Necking is the local thinning that occurs afterward, not the strengthening mechanism.
A Rockwell tester is used to perform what type of materials test?
ACS code: AM.I.E
Correct answer: Hardness testing.
Rationale: A Rockwell tester measures hardness by pressing a ball or diamond indenter into the surface under a set load and reading the depth of penetration directly as a hardness number. It does not pull or cyclically load the specimen, so it performs neither tensile nor fatigue testing.
What type of materials test uses a weighted pendulum to strike a specimen until it fractures?
ACS code: AM.I.E
Correct answer: An impact test.
Rationale: A weighted pendulum swung to strike and fracture a specimen describes an impact, or toughness, test such as the Charpy or Izod, which measures the energy absorbed at fracture. A hardness test uses a static indenter and a fatigue test applies many repeated load cycles, so neither involves a single pendulum blow.