19-02-2013, 10:10 AM
Engineering materials
Engineering materials.ppt (Size: 966 KB / Downloads: 139)
Metal / Metallic materials
Generally classified as ferrous and nonferrous
Ferrous materials consist of steel and cast iron
Eg. Carbon steel, high alloy steel, stainless steel
Nonferrous materials consist of the rest of the metals and alloys
Eg. Aluminum, magnesium, titanium & their alloys
Materials from each group are further classified and given certain designation according to the ASTM standard
Each has their own unique number/code that represent main alloying elements, cast or wrought and in case of plain carbon – amount of carbon.
Steel can be classified or grouped according to some common characteristic.
The most common classification is by their
Composition
Example : 10xx, 15xx
Strength
Most common material used in construction of structure such as bridge, building and ships
Design and selection for metals
One of the major issues for structural components is deflection under service load.
A function of the applied forces and geometry, and also stiffness of material.
So suitable material and design are needed.
Load carrying capacity of component can be related to the yield strength, fatigue strength or creep strength depending on loading & service condition.
All are structure sensitive.
Changed, chemical composition of the alloy, method and condition of manufacturing, as well as heat treatment
Design for polymer
Polymer – low density, good thermal & electrical insulation, high resistance to most chemicals and ability to take colours and opacities.
But if unreinforced bulk polymer are mechanically weaker, lower elastic moduli & high thermal expansion coefficients.
Improvement – Reinforced variety of fibrous materials
Composites (PMC).
Advantages : ease of manufacturing & versatility.
Can manufacture into complicated shapes in one step with little need for further processing or surface treatment.
Design consideration for polymer
Structural part
When the parts is to carry load
Should remember the strength and stiffness of plastics vary with temperature.
Long term properties
Eg. Creep behavior
Stress raiser
Design for ceramics
Ceramics – inorganic compounds of one or more metals with a nonmetallic element. Eg Al2O3, SiC, Si2N3.
Crystal structure of ceramic are complex
They accommodate more than one element of widely different atomic size.
The interatomic forces generally alternate between ionic & covalent.
usually heat & electrical insulators.
Strong ionic & covalent bonds give high hardness, stiffness & stability (thermal & hostile env.).
(1) Amorphous or glass, (2) crystalline (arrange) & (3) crystalline bonded by glassy matrix.
Designing with composite
A composite materials usually are more expensive on a cost.
Important factors when designing with composite materials is that their high strength are obtained only as a result of large elastics strains in the fiber
Fatigue behavior at low stress level because fibrous composites may have many crack, which can be growing and propagate through the matrix