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59 Cards in this Set
- Front
- Back
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What are physical properties? |
Properties that define the behaviour of materials in response to physical forces other than mechanical. |
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What are four examples of physical properties? |
- Volumetric - Thermal - Electrical - Electrochemical |
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What must components in products do? |
1) Conduct electricity or prevent its conduction 2) Allow heat to transfer (or not) 3) Transmit light (or not) 4) etc. |
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What are volumetric and melting properties? |
Properties related to the volume of solids and how these properties are affected by temperature. |
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What are the three volumetric and melting properties? |
- Density - Thermal expansion - Melting point |
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What is density determined by? |
Density is determined by atomic number, and other factors such as atomic radius, and atomic packing. |
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What is specific gravity? |
The density of a material relative to the density of water. |
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Why is density important? |
It is important to know the weight a component will have when made of a specific material. |
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What is the strength-to-weight ratio? |
Tensile strength divided by density. It is useful in comparing materials for structural applications in aircraft, cars, and other products where weight and energy are concerns. |
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What is thermal expansion? |
A decrease in density with increasing temperature. |
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How is the thermal expansion measured? |
It is measured as the coefficient of thermal expansion. |
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What is the formula for the change in length given a particular temperature change? |
L2-L1=αL1(T2-T1) α is the coefficient of thermal expansion. |
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What is thermal expansion used for in manufacturing? |
It is used in shrink fit and expansion fit assemblies. |
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What are shrink and expansion fit assemblies? |
Assemblies in which the part is heated to increase it's size, or cooled to decrease it, in order to permit insertion into another part. When the part returns to ambient temperature, a tightly-fitted assembly is obtained. |
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When can thermal expansion be a problem and why? |
It can be a problem in heat treatment and welding due to the thermal stresses that develop in the material during the processes. |
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What is the heat of fusion? |
The heat energy required at the melting temperature to accomplish transformation from solid to liquid. |
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What is the solidus? |
The temperature at which the melting begins in an alloy. |
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What is the liquidus? |
The temperature at which the alloy has completely melted. |
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What happens to an alloy between the solidus and the liquidus? |
It becomes a mixture of liquid and solid metals. |
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What occurs when melting noncrystalline materials, such as glasses? |
A gradual transition from solid to liquid state occurs. The solid material gradually softens as the temperature increases, finally becoming liquid at the melting point. |
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What happens to noncrystalline materials as they soften? |
They gain a consistency of increasing plasticity as it gets closer to the melting point. |
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How is melting important in manufacturing? |
It is ussed in metal casting, plastic molding, and sintering of powdered metals. |
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What is metal casting? |
When metal is melted and then poured into a mold cavity. Metals with lower melting points are easier to cast. |
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What is sintering or powdered materials/ |
Heating of powdered metals approaching the melting point in order to achieve bonding of the powders. |
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What are five thermal properties? |
Thermal expansion Melting Heat of fusion Specific heat Thermal conductivity
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What is a thermal property? |
One in which heat determines the thermal energy level of the atoms, leading to changes in the materials. |
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What is the volumetric specific heat? |
The quantity of heat energy required to raise the temperature of a unit volume of material by one degree.
Volumetric specific heat = ρC |
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What is thermal conductivity? |
A materials capability to transfer heat through itself by the physical mechanism of thermal conduction. |
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What does thermal conduction involve. |
The transfer of thermal energy within a material from molecule to molecule by purely thermal motions. No mass transfer. |
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What are the units for the coefficient of thermal conductivity k? |
J/s mm °C |
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What is thermal diffusivity? |
The ratio of thermal conductivity to volumetric specific heat. |
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What is the formula of thermal diffusivity? |
K = k/(ρC) |
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Why are thermal properties important in manufacturing? |
Because heat generation is common in many processes. |
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What is mass diffusion? |
The movement of atoms or molecules within a material or across a boundary between two materials in contact. |
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What are two surface hardening treatments based on diffusion? |
Surface hardening treatments based on diffusion include carburizing and nitriding. |
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What is diffusion welding? |
When two components are pressed together and diffusion is allowed to occur across their boundaries, creating a permanent bond. |
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How is diffusion used in electronics manufacturing? |
It is used to alter the surface chemistry of a semiconductor chip in very localized regions to create circuit details. |
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What is the movement of charge carriers driven by? |
The presence of electric voltage. |
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What is the movement of charge carriers resisted by? |
The inherent characteristics of the material, such as atomic structure and bonding between atoms and molecules. |
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What is Ohm's law? |
I=E/R
I - current E - voltage R - resistance |
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How is resistance dependent on a material's length? |
Resistance in a uniform section of a material (like a wire) depends on its length, cross-sectional area A, and it's resistivity. |
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What is the formula for the resistance of a material? |
R= r * (L/A) |
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What are the units or resistivity? |
Ωm |
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What are properties of resistivity? |
It is not a constant, and it varies with temperatures. In metals, it increases with temperature. |
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What is conductivity? |
The reciprocal of resistivity. Its units are (Ωm)^-1 |
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Why are ceramics and polymers usually poor conductors? |
Because their electrons are tightly bound by covalent and/or ionic bonding. |
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What is a semiconductor? |
A material whose resistivity lies between insulators and conductors. |
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What is the most common semiconductor material? Why? |
Silicon, largely because of its abundance in nature, relative low cost, and ease of processing. |
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What makes semiconductors unique? |
Their capacity to significantly alter conductivities in their surface chemistries in very localized areas to fabricate integrated circuits. |
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What is electric discharge machining? |
Machining that uses electrical energy in the form of sparks to remove material from metals. |
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Which welding processes use electrical energy? |
Arc welding and resistance spot welding. |
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What is electrochemistry? |
The field of science concerned with the relationship between electricity and chemical changes, and the conversion of electrical and chemical energy. |
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What is an electrolyte? |
An ionized solution. |
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What are electrodes? |
Where the current enters and leaves solution in an electrolytic solution. |
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What is the anode? |
The positive electrode. |
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What is the cathode? |
The negative electrode. |
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What is electroplating? |
An operation that adds a thin coating of one metal to the surface of a second metal for decorative or other purposes. |
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What is electrochemical machining? |
A process in which material is removed from the surface of a metal part. |
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What else is electrolysis used for in manufacturing processes? |
The production of hydrogen and oxygen. |
