1
Q
mechanical Properites
A
- mechanical Engineers are mostly interested in the strength, hardness and toughness and fatigue and some others
2
Q
Physical Properties
A
- Many properties such as color and texture
- in materials science include things such as magnetic permeability, specific heat, thermal conductivity
*Properties of a material can be measured without the application of force
3
Q
Manufacturing Properties
A
- The ductility and malleability, as well as the heat transfer, fluidity, solidification pattern and melting temperature
- Influence the manufacturing process
4
Q
density
A
- mass of material per unit volume
- SI unit is kilogram per cubic meter ( Kg/M3) Imperial is Lb/Ft3 or Lb/in3
- Density depends on atomic weight, radius and packing effiences in their crystallographic lattice BCC less efficiently packed than FCC
5
Q
Specific heat
A
- Thermal Energy required to raise the temp of a unit mass of material by one degree measured by centigrade or Celsius, Kelvin or F
- to convert C to K simply subtract 273
- to convert C to F Divide by 5, multiply by 9 then add 32
6
Q
Thermal Conductivity
A
- Quantity of heat that will be transmitted per unit area by a material of a given thickness and temperature Gradient
- Influence general Materials that have a high electrical conductivity also have high thermal conductivity and vice versa
7
Q
Coefficient of thermal expansion ( CTE)
A
- Determines the change in length per unit lenght of the material for a one degree change in temp either C or F
- materials that have high melting temp have a low CTE
- Materials that have stronger bonds between atoms need more energy to separate atoms, expand less ( LOW CTE) and need more energy to melt ( HIGH TM). Stronger Materials
8
Q
Autofrettage
A
- Moving parts that require certain clearances for proper functioning
- Shrink fit operations use the thermal expansion property
- Hub is usually expanded by heating, then fitted over a shaft that upon cooling the hub clamps tightly against the shaft
9
Q
Electrical Conductivity
A
- How well materials conduct electrical current
- Measured in units of meter or Foot
- good conductivity called conductors
- Materials that are covalently bonded ( most Ceramics) called resistors
- Materials that can conduct electricity under certain circumstances but not others called semi conductors
10
Q
Dielectric Strenght
A
- Under very high voltages, the resistivity of materials can be broken
- Defined as the voltage per unit lenght necessary for electrical breakdown, material becomes a conductor of direct current
11
Q
Super conductivity
A
- Phenomenon where materials below some critical temperature exhibit zero electrical resistivity
- some ceramics experience superconductivity at very low temps
- Materials with this property at higher temps are constantly sought
12
Q
Diamagnetism
A
- Very weak form of magnetization that is non permanent and persist only while an external field is being applied
- Magnetic susceptibility is negative, the magnetic field is less than that in a vacuum
- attracted towards regions where the field is weak
13
Q
paramagnetism
A
- Magnetic susceptibility is small and positive
- paramagnetic materials acquire the magnetization in the direction of the applied field
- absence of any external magnetic field, the orientation of atomic magnetic field of the material is random
14
Q
ferrimagnetism
A
- poses permeability comparable to most ferromagnetic, but their eddy current losses are far lower because of the materials greater electrical resistivity
- main difference is the change of the volume of magnetic susceptibility over the temp range
- usually oxides of iron combined with one or more transition metals
15
Q
Optical properties
A
- Refer to the response of the material to electromagnetic radiation particularly visible light
- electromagnetic radiation consist of a dual nature a wave and a particle ( Photon)
- Planck has quantified the energy of one photon as E=HC/K
16
Q
Stress Strain curve
A
- Calculated by dividing the applied load ( p) by the original Cross-sectional area (Ao) of the specimen
- true stress: p is divided by the actual area (A) which is constantly changing under the applied load
Linear elastic, Yield Point, UTS, Breaking point
17
Q
Elastic Deformation
A
- In elastic region, stress is linearly proportional to strain
- Known as Young’s modulus, stress/strain
- Stresses required to continue the plastic deformation increase progressively due to strain hardening
- due to dislocations in the crystallographic lattice increase dislocations tangle up and obstruct the movement of each other
18
Q
Tensile test
A
- Testing Under tension provides data for quantifying several mechanical properties such as elastic, modulus, poisons ratio yield and ultimate strength, ductility properties, strain hardening characteristics
- Tensile load is applied but the machine, resulting in the gradual elongation and eventual failure of the specimen
19
Q
Compression test
A
- Applies compressive forces and measures deformation of a cylindrical specimen
- friction between the specimen and the ram causes the cylinder to deform non uniformly: Barreling
20
Q
Modulus of resilience
A
- The max energy that can be absorbed per unit volume without creating a permanent distortion
- area underneath the curve to the yield strength
21
Q
modulus of elasticity
A
- Young’s modulus, quotient of stress divided by strain up to the yield strength or within the elastic region of the material
22
Q
Strain
A
- Elongation change in dimension per unit lenght
- Value essentially dimensionless, since strain is the quotient of a length divided by another length
23
Q
Engineering Strain
A
- Is the change in length divided by the original Length or
Diameter can also be used in place of length
24
Q
True Strain
A
- Calculated by taking the natural log of the quotient where Lf is the final lenght thus
- Once onset of necking occurs, true strain must be calculated by using the quotient of the original cross sectional area (Ao) divided by the instantaneous cross sectional area( Ai)
25
Instability
* Initially the strain hardening more than compensates for the decrease in area, engineering stress continues to rise non-linearly with increasing strain
* Eventually the effect of the decrease becomes greater than the compensation from strain hardening
* Known as instability and reached at the weakest location along the gage lenght
25
Ductility
* total elongation of the specimen due to plastic deformation increase
* upon failure two halves of the broken specimen recover their elastic elongation and separate
* Total elongation measured by the mechanical testing instruments includes the elastic portion
26
hardness
* Ability of a material to resist permanent deformation or penetration when in contact with an indented under load
* Typical hardness test consist of pressing an indenter of known geometry and mechanical properties into the test material
27
hardness test
* Brinell utilizes a spherical indenter
* Vicks and knoop utilizes a pyramidal indenter
* Rockwell test uses a conical indenter tool
* cheap, quick and simple method of mechanically characterizing a material since it requires neither specimen preparation nor expensive testing
28
Toughness
* total area underneath stress strain curve, which measures the energy absorbed by the specimen in the process of breaking
* cannot be calculated algebrically since the plastic region in non linear due to strain hardening
29
fatigue
* it’s progressive, localized, and permanent structural damage that occurs when a material is subjected to a cyclic or fluctuating strain or nominal stresses that have max values less than the static yield strength of the material
30
fatigue Limit/ endurance limit
* Is the amplitude of cyclic stress below which fatigue damage will not occur
* 3 conditions are required for the occurrences of fatigue damage
1. Cyclic stress
2.tensile stress
3. Plastic strain
* all 3 must be present for fatigue cracking to initiate and propagate
31
S-N Plot
Typical plot used to characterize the fatigue of a material is known as S-N plot, stress versus number of cycles
32
Creep
* Applying a constant load and measuring the strain ( elongation) as a function of time
* has 3 stages, 1. primary creep: material starts to elongate
2. Steady strain rate where the rate creating new dislocations is balanced by the rate at which they annilhate each other .
3. Territory creep: necking occurs causing the load to apply higher stresses until failure
*Creep rate increases with temp and load, failure happens sooner
Asnt Studycards Basic Material And Processes
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