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MATERIALS M3 > PROPERTIES OF METALS > Flashcards

PROPERTIES OF METALS Flashcards

0
Q

What is the Carbon Equivalent for welding of carbon steel?

A

CE%=C%+Mn%/6+other elements%

If CE%>0.45% then a brittle fracture (crack may develop in the heat affected zone

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1
Q

What do the digits represent in the designation system used by the British Standard for wrought steel (BS970)?

A

First 3 digits represent 100 times the manganese content.
4th digit is A, M or H to indicate whether steel is supplied to the composition of alloying elements, mechanical property or hardenability. The 5th and 6th digits represent 100 times the mean carbon content.
E.g.070M20 (mild steel) describes plain carbon steel containing 0.7% manganese and 0.2% carbon and produced to meet mechanical property requirements.

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2
Q

What are the categories for basic plain carbon steels and example applications of each?

A
  1. Very low carbon content, up to 0.05%, for general engineering applications (steel sheeting)
  2. Low carbon content, up to 0.2%, e.g. 080M15, for car and ship plates
  3. Medium carbon content, up to 0.5%, e.g. 070M20, for pipes, low stressed gears and shafts
  4. Medium-high carbon content, up to 0.8%, e.g. 070M55, for high strength pins, springs and special shafts
  5. High carbon content, greater than 0.8%, for cutting tools
    4
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3
Q

What are the different aluminium alloys and their series numbers?

A 
1000 - Al
2000 - Al+Cu
3000 - Al+Mn
4000 - Al+ Si
5000 - Al+Mg
6000 - Al+SI+Mg (iphone6)
7000 - Al+Zn
8000 - Al+Li (aircraft)
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4
Q

What is fatigue strength and how can it be judged?

A

The resistance to fracture from repeated cyclic stresses. Judged by the UTS.

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5
Q

What is static strength and how can it be judged?

A

The strength of an object under a static load. Judge by yield.

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6
Q

What is proof strength?

A

Proof strength is used when there is no yield point, it is commonly the stress required to produce 0.2% extension and approximates to the yield stress in materials not exhibiting a definite yield point.

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7
Q

What is Young’s modulus?

A

Ratio of stress to strain - stiffness - E=stress/strain

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8
Q

What is shear modulus of elasticity?

A

G=shear stress/shear strain

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9
Q

What is the equation for bedding moment of a beam?

A

M=FL/4 (this is equivalent to force)

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10
Q

What is second moment of inertia for the beam?

A

I=bh^(3)/12 (this is equivalent to area)

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11
Q

Equation for Global (overall) strength? (For beam)

A

Directly proportional to Sy*h^(2)

Sy = yield strength

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12
Q

Equation for local strength ? (For beam)

A

Directly proportional to Sy

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13
Q

Equation for global (overall) stiffness? And for twisting?

A

Directly proportional to E*h^(3)

Twisting: directly proportional to G*h^(3)

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14
Q

Equation for local stiffness? (Of beam)

A

Directly proportional to E

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15
Q

What is the difference between polar moment of inertia and second moment of inertia?

A

Polar moment of inertia relates torsion and second moment of inertia is used when the problem is to do with bending.

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16
Q

Equations for impact strength? (Beam case, local=global)

A

_ _
Directly proportional to U * h (t may also be used instead of h) and U is the impact strength or resistance of the material in question

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17
Q

What is specific gravity?

A

Ratio of the density of the material to the density of water

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18
Q

What is melting temperature?

A

A measure of resistance to high temperature application or ease of manufacture

19
Q

How does melt temp relate to enthalpy?

A

H=mT(melt)Cp

20
Q

What is maximum elongation and what it is another measure for?

A

The max a material can be deformed before fracture, larger elongation means a tougher material and it is another measure for impact resistance.

21
Q

What is hardness a measure of and how can it be measured?

A

A measure of resistance to indentation and how easy it is to machine the surface, represented by hardness numbers: 100 BHN=80 ROCKWELL =115 VICKERS, often hardness=3*yield strength

22
Q

What is specific heat capacity and it’s relevant equations?

A

The energy required to raise the temp of a unit mass of material by 1 degree celcius. Large responsibility for heat generation. For minimum heat generation maximise Cp*m

23
Q

What is fracture toughness & it’s equation?

A

A property which describes the ability of a material containing a crack to resist fracture and relates to stress-intensity factor. K(ic) = stresssqrt(pia) where a is crack length. Kic * t gives toughness/ impact resistance.

24
Q

What is thermal conductivity and it’s related equations?

A

The ease with which heat flows through the material, K. [W/m.degree celcius]. Fouriers law of conduction directly proportional to K/t (K is the coefficient of thermal conductivity and the higher the ratio the better conductivity)

25
Q

What is vibration damping and how can it be measured?

A

The rate at which vibrations decay i.e. the ability of materials to absorb and release strain energy without loss. The longer the wave, the lower the damping ability of the material. This ability may be measured by the ratio of Sy/E (the higher the ratio the better)(if no yield use proof strength)

26
Q

What is coefficient of thermal expansion?

A

Ratio of dimension increase as a result of increasing the material temp by 1 degree C. This could induce thermal stresses or change of dimensions. Extension = alpha * L *deltaT

27
Q

What is electro-magnetic shielding (EMS)?

A

The ability of materials to shield an electronic device from electro-magnetic interference (EMI) generated by another device. Depends on electrical conductivity. Want something thin but very conductive.

28
Q

What is oxidation?

A

When loading on a metallic component is combined with corrosion process, these lead to strength degradation due to the oxidation of the grain boundaries nearer the surface of the metal. This leads to premature failure/fracture which is referred to stress corrosion cracking (SCC) or corrosion fatigue.

29
Q

What are the general oxidation ratings for widely used metals?

A 
Ti, SS - 10/10 - excellent
Cu, Zn - 8/10 - very good
Al - 6/10 - good
Iron & Steel - 4/10 - fair
Mg - 2/10 - poor (except when coated/ anodised)
30
Q

What is galvanic corrosion?

A

An electrochemical phenomena which occurs when two different metals are in contact with a wet salty solution (electrolyte) leading to loss of metal particles.

31
Q

An example of when galvanic corrosion can occur?

A

In bolted connections where three metals are involved. (Have a look at diagrams in notes)

32
Q

What is machinability and how can it be measured?

A

The ability to machine a material in terms of time and effects in cutting tool and material. Measured by Taylor index for machinability (higher the better) could also look at hardness but the Taylor index is more accurate.

33
Q

What is weld ability and how can it be measured?

A

The ratio if welded joint strength to that of parent material. 100% is perfect weldability. Normally weldability is between 50%-90%

34
Q

What is castability and how can it be measured?

A

Measured by one or more of: min wall thickness, melting temperature and shrinkage (all lower the better). Also indirectly relates to machinability and weldability.

35
Q

What is formability and how can it be measured?

A

The ability to deform metal without fracture. May be measured by:

  1. Aspect ratio = H/D (the higher the better)
  2. Radius thickness ratio = r/T (the lower the better)
36
Q

How to measure extrudibility?

A

Min wall thickness or speed of extrusion. If none of these then look at melt temperature.

37
Q

What is heat treatability?

A

The ease with which a metal can be treated to change hardness, strength and ductility.

38
Q

What is tempering?

A

A heat treatment process that improves the ductility and toughness of metals.

39
Q

What is annealing?

A

Annealing is a heat treatment process whereby a metal is heated to a specific temperature and then allowed to cool slowly. This softens the metal which means it can be cut and shaped more easily.

40
Q

What is normalising?

A

The objective of normalisation is to leave the material in a normal state, in other words with the absence of internal tensions and even distribution of carbon. For the process the high temperatures are maintained until the complete transformation of austenite with air cooling.

41
Q

What is hardening?

A

Hardening is a heat treatment process used to increase the hardness of a metal.

42
Q

What is strain hardening?

A

The use of permanent deformation to increase the strength of a metal.

43
Q

What is spring back?

A

The result of a metal tending to return to its original shape after undergoing compression and tension (bending).

44
Q

What is anisotropy?

A

The property of being directionally dependent, as opposed to isotropy, which implies identical properties in all directions. E.g. On one side grains are elongated and on other side they are not, the material will be stronger on the side not elongated.

45
Q

What are the three levels of material property data?

A
  1. Low precision (general tables or CES database)
  2. Class-specific data (handbooks for specific class of materials)
  3. High precision data for the specific material which involves manufacturer data and material consultants.
46
Q

What does the selection of metallic material depend largely on?

A
  1. Physical and processing properties
  2. Manufacturing processes
  3. Product shape
  4. Cost and availability of materials and processes

MATERIALS M3 (5 decks)

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