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Engineering materials. Haseeb Ullah Khan Jatoi Department of Chemical Engineering UET Lahore. Material Properties. Thermal Properties . Plays important role in the success or failure of design. Thermal Expansion It is expansion of material due to increase in temperature.
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Engineering materials HaseebUllah Khan Jatoi Department of Chemical Engineering UET Lahore
Thermal Properties Plays important role in the success or failure of design. Thermal Expansion It is expansion of material due to increase in temperature. a) Linear Expansion This is the expansion in length or in one dimension by rise in temperature. Lf – Lo/Lo = αl (Tf-To)
b) Coefficient of Linear Expansion It is a measure of amount by which a unit length of the material expands when its temperature is raised by 1˚C. c) Surface Expansivity Increase in two dimensions by rise in temperature is called surface expansivity. d) Volume Expansivity Increase in three dimensions by the rise in temp is called volume expansivity. ΔV /Vo =αvΔT
2) Thermal Conductivity It characterizes a material’s ability to transfer heat. or Ability of material to transmit heat energy by conduction. q = -kA(dT/dx) Or k = -q dx/AdT Metals generally have the greatest conductivity. Ceramics are insulators Polymers are poor conductors.
Problem Determine the heat loss through a brick wall 4m by 3m of 0.25 m thickness if the inner surface is maintained at 20˚C and the outer surface temperature is 5˚C. The thermal conductivity of brick is 0.5 W/m-K. Problem Calculate the heat flow per unit area through a wall of a steel furnace with a thickness of 1 inch. When the temperature gradient across the wall is 10˚F. The thermal conductivity of the steel is 26 Btu/hr.ft.˚F.
3) Heat Capacity Amount of energy required to produce a unit rise in temperature. It provides a measure of material ability to absorb heat from the surrounding environment. C = dQ/ dT a) Specific Heat capacity Amount of heat required to raise the temperature of 1 unit mass of a substance through one degree.
Transition Temperature Temperature at which significant changes occurs in the structure of material. c)Melting point Temperature where solid and liquid phases are in equilibrium. d)Boiling Point Temperature where liquid and gas phases are in equilibrium
4) Fusibility Ease with which materials melt. a) High Fusibility Material melts easily at low temperature. b) Low Fusibility Material melts at high temperature. 5) Temperature Stability or Temperature Resistance The ability of material to remain stable with change in temperature.
Mechanical Properties They mainly concerned with the strength of materials. 1. Strength It is measure of material's ability to resist the application of load(force) required during the service of structure or machine without fracture, collapse ore undue distortion (alteration of original shape).
Types of Strength Tensile strength Ability of a material to withstand tensile (stretching) loads without breaking. Compressing Strength Ability of material to withstand compressive (Squeezing) loads without being crushed or broken. Shear Strength Ability of material to withstand offset loads or transverse cutting (shearing actions).
Impact Strength/ Impact Resistance/ Toughness Ability of material to with stand shatters. Or Measure of ability of material to absorb energy up to fracture. If the material shatters, it is brittle, but rubber do not shatter so it is tough. Example is high carbon steel (silver steel). Any material in which spread of surface crack does not occurs or only occurs to small extend is said to be tough. 2.Elasticity Ability of material to deform under load and returns to its original size and shape when load is removed. Iron and rubber
3. Plasticity Ability of material to deform permanently under load and never return to its original size and shape, when the load is removed. Ductility and malleability are the particular cases of the property of plasticity. Ductility This term is used when plastic deformation occurs as the result of applying a tensile load. Example is wire drawing. It can also be expressed qualitatively as either % elongation or % reduction in area.
% Elongation = (Lf- Lo/Lo) * 100 % Reduction = (Ao – Af/ Ao) * 100 Lf & Afare the fracture length and cross-sectional area at the point of fracture respectively. Problem A cylindrical specimen of steel having an original diameter of 12.8 mm (0.505 in.) is tensile tested to fracture. If its cross-sectional diameter at fracture is 10.7 mm (0.422 in.), determine the ductility in terms of percent reduction in area?
Malleability Term applied when plastic deformation occurs as a result of applying a compressive load. Example is forging, rolling etc. Resilience It is capacity of material to absorb energy when it is deformed elastically and then, upon unloading to have this energy recovered.
Brittleness It is the property of a material that shows little or no plastic deformation before fracture, when a force is applied. e.g. steel rod can bend but cast iron snaps when you try to bend it. So cast iron is brittle material. Rigidity (Stiffness) Measures of material’s ability not to deflect under an applied load. Rigid material are not necessarily strong.
Resistivity - • Conductance - Reciprocal of Resistivity • Ohm’s Law - V=IR • Conductor • Semi-conductor (Si, Ge, Al) • Dielectric Behavior • Permittivity - permittivity relates to a material's ability to transmit (or "permit") an electric field Electrical Properties
Stress-strain Relationships Next Lecture
