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2. PROPERTIES OF METALS
• TO ESTABLISH A BASIS FOR FURTHER DISCUSSION OF STRUCTURAL METALS., BRITTLENESS,
CONDUCTIVITY, EXPANSION, ELASTICITY, TOUGHNESS, FUSIBILITY, ANDDENSITY

3. STRENGTH
• A METAL'S STRENGTH IS DETERMINED BY THE PERCENTAGE OF PARENT METAL AND OTHER ELEMENTS
USED TO MAKE AN ALLOY.
• STRENGTH IS THE ABILITY OF A MATERIAL TO RESIST DEFORMATION
• STRENGTH IS ALSO THE ABILITY OF A MATERIAL TO RESIST STRESS WITHOUT BREAKING.

5. TENSILE STRENGTH
• WHEN A PIECE OF SHEET METAL IS PULLED FROM EACH END, THE RESULTANT FORCE IS CALLED TENSION.
THE ABILITY TO WITHSTAND TENSION IS CALLED TENSILE STRENGTH, ANDIS MEASURED IN POUNDS PER
SQUARE INCH.
• SINCE THE STRENGTH VALUES FOR SEVERAL METALS ARE RATED TO SEVERAL THOUSAND PSI, THE LETTER
"K" IS OFTEN USED TO REPRESENT THE LAST THREE ZEROS OF THE PSI RATING. THEREFORE, A TENSILE
STRENGTH OF 70,000 PSI IS WRITTEN AS 70 KSL.

7. YIELD STRENGTH
• IT IS THE ABILITY OF A METAL TO RESIST DEFORMATION
• AS THE METAL STRETCHES, THE MOLECULAR STRUCTURE CHANGES ENOUGHTO INCREASE THE METAL'S
STRENGTH AND, THEREFORE, RESIST FURTHER DEFORMATION

8. ULTIMATE STRENGTH
• THE ULTIMATE STRENGTH OF A MATERIAL IN TENSION, COMPRESSION, OR SHEAR, RESPECTIVELY, IS THE
MAXIMUM TENSILE, COMPRESSIVE, OR SHEAR STRESS THAT THE MATERIAL CAN SUSTAIN, CALCULATED
ON THE BASIS OF THE ULTIMATE LOADAND THE ORIGINAL OR UNSTRAINED DIMENSIONS.

9. SHEAR STRENGTH
• SHEAR STRENGTH DESCRIBES A METAL'S ABILITY TO RESIST OPPOSING FORCES
• IN ENGINEERING, SHEAR STRENGTH IS THE STRENGTH OF A MATERIAL OR COMPONENT AGAINST THE TYPE OF YIELD OR
STRUCTURAL FAILURE WHEN THE MATERIAL OR COMPONENT FAILS IN SHEAR. A SHEAR LOAD IS A FORCE THAT TENDS TO
PRODUCE A SLIDING FAILURE ON A MATERIAL ALONG A PLANE THAT IS PARALLEL TO THE DIRECTION OF THE FORCE.

10. BEARING STRENGTH
• IS THE ABILITY OF A JOINT TO WITHSTAND ANY FORM OF CRUSHING OR EXCESSIVE COMPRESSIVE
DISTORTION
• MATERIAL UNDER A COMPRESSION LOAD USUALLY FAILS BY BUCKLING OR BENDING. THE FORCE AT
WHICH SOMETHING BUCKLES WHILE BEING COMPRESSED VARIES WITH AN OBJECT'S LENGTH, CROSS-
SECTIONAL AREA, AND SHAPE.

12. HARDNESS
• REFERS TO THE ABILITY OF A MATERIAL TO RESIST ABRASION, PENETRATION, CUTTING ACTION, OR
PERMANENT DISTORTION
• HARDNESS MAY BE INCREASED BY COLD WORKING THE METAL AND, IN THE CASE OF STEEL AND CERTAIN
ALUMINUM ALLOYS, BY HEAT TREATMENT. STRUCTURAL PARTS ARE OFTEN FORMED FROM METALS IN THEIR
SOFT STATE AND ARE THEN HEAT TREATED TO HARDEN THEM SO THAT THE FINISHED SHAPE IS RETAINED.
HARDNESS AND STRENGTH ARE CLOSELY ASSOCIATED PROPERTIES OF METALS.

13. DUCTILITY
• IS THE PROPERTY OF A METAL THAT PERMITS IT TO BE PERMANENTLY DRAWN, BENT, OR TWISTED INTO
VARIOUS SHAPES WITHOUT BREAKING.
• DUCTILE METALS ARE GREATLY PREFERRED FOR AIRCRAFT USE BECAUSE OFTHEIR EASE OF FORMING AND
RESISTANCE TO FAILURE UNDER SHOCK LOADS. FOR THIS REASON, ALUMINUM ALLOYS ARE USED FOR
COWL RINGS, FUSELAGE AND WING SKIN, AND FORMED OR EXTRUDED PARTS, SUCH AS RIBS, SPARS, AND
BULKHEADS
• DUCTILITY IS SOMEHOW SIMILAR TO MALLEABILITY.

14. BRITTLENESS
• BRITTLENESS DESCRIBES A MATERIAL'S TENDENCY TO BREAK OR SHATTERWHEN EXPOSED TO STRESS,
AND IS THE OPPOSITE OF DUCTILITY AND MALLEABILITY
• A BRITTLE METAL IS MORE APT TO BREAK OR CRACK BEFORE IT CHANGESSHAPE.
• EXAMPLES OF BRITTLE METALS ARECAST IRON, CAST ALUMINUM, AND VERY HARD STEEL

18. ELASTICITY
• IS A PROPERTY THAT ENABLES A METAL TO RETURN TO ITS ORIGINAL SIZE AND SHAPE WHEN THE FORCE
THAT CAUSES THE CHANGE OF SHAPE IS REMOVED.
• AND IS EXTREMELY VALUABLE, BECAUSE IT WOULD BE HIGHLY UNDESIRABLE TO HAVE A PART
PERMANENTLY DISTORTED AFTER AN APPLIED LOAD WAS REMOVED

19. TOUGHNESS
• TOUGHNESS IS A DESIRABLE PROPERTY IN AIRCRAFT METALS.
• TOUGHNESS IS THE RESISTANCE TO FRACTURE OF A MATERIAL WHEN STRESSED. IT IS DEFINED AS THE AMOUNT OF ENERGY
THAT A MATERIAL CAN ABSORB BEFORE RUPTURING, AND CAN BE FOUND BYFINDING THE AREA (E., BY TAKING THE
INTEGRAL) UNDERNEATH THE STRESS-STRAIN CURVE.
• A MATERIAL WITH HIGH STRENGTH AND HIGH DUCTILITY WILL HAVE MORETOUGHNESS THAN A MATERIAL WITH LOW
STRENGTH AND HIGH DUCTILITY.
• ONE WAY TO MEASURE TOUGHNESS IS BY CALCULATING THE AREA UNDER THE STRESS STRAIN CURVE FROM A TENSILE
TEST. THIS VALUE IS SIMPLY CALLED “MATERIAL TOUGHNESS” AND IT HAS UNITS OF ENERGY PER VOLUME

20. TOUGHNESS
• THE TOUGHNESS OF A MATERIAL IS ITS ABILITY TO ABSORB ENERGY IN THE PLASTIC RANGE. THE ABILITY
TO WITHSTAND OCCASIONAL, STRESSES ABOVE THE YIELD STRESS WITHOUTFRACTURING IS
PARTICULARLY DESIRABLE IN PARTS SUCH AS FREIGHT-CAR COUPLINGS, GEARS, CHAINS, AND CRANE
HOOKS.
• TOUGHNESS IS A COMMONLY USED CONCEPT, WHICH IS DIFFICULT TO PINDOWN AND DEFINE. ONE WAY
OF LOOKING AT TOUGHNESS IS TO CONSIDER THAT IT IS THE TOTAL AREAUNDER THE STRESS-STRAIN
CURVE. THIS AREA IS AN INDICATION OF THE AMOUNT OF WORK PER UNITVOLUME, WHICH CAN BE DONE,
ON THE MATERIAL WITHOUT CAUSING IT TO RUPTURE

21. FUSIBILITY
• FUSIBILITY IS THE ABILITY OF A METAL TO BECOME LIQUID BY THE APPLICATION OF HEAT.
• METALS ARE FUSED IN WELDING. STEELS FUSE AROUND 2,600°F AND ALUMINUM ALLOYS AT
APPROXIMATELY 1,100 °F.

22. CONDUCTIVITY
• IS THE PROPERTY WHICH ENABLES A METAL TO CARRY HEAT OR ELECTRICITY
• IF A METAL IS ABLE TO TRANSMIT HEAT IT IS SAID TO BE THERMALLY CONDUCTIVE. HOWEVER, BEFORE A
METAL CAN CARRY HEAT AWAY FROM ITS SOURCE, IT MUST FIRST ABSORBIT THIS ABILITY TO CONDUCT
HEAT AWAY IS CALLED HEAT EXCHANGE.
• METALS THAT CAN CARRY HEAT ALSO CARRY ELECTRONS, MAKING THEM GOOD ELECTRICAL
CONDUCTORS.
• A METAL CONDUCTOR CAN BE A WIRE, AN AIRCRAFT FRAME, OR AN ENGINE

23. THERMAL EXPANSION
• IT IS A PROPERTY OF A METAL TO EXPAND WHEN HEATED AND SHRINK WHEN COOLED
• THE AMOUNT OF EXPANSION OR CONTRACTION IS PREDICTABLE AT SPECIFIC TEMPERATURES AND IS
CALLED ITS COEFFICIENT OF EXPANSION.