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This 3 page Class Notes was uploaded by Courtney Lawrence on Wednesday February 3, 2016. The Class Notes belongs to BUS 201 at University of Rhode Island taught by Professor Sacco in Winter 2016. Since its upload, it has received 62 views. For similar materials see Financial Accounting in Business at University of Rhode Island.
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Date Created: 02/03/16
Exam 1 Chapter Notes: Introduction: Selection of Materials: -ferrous metals: carbon, alloy, stainless, and tool and die steels -nonferrous metals: Aluminum, magnesium, copper, nickel and titanium -plastics(polymers): thermoplastics, thermosets, and elastomers -ceramics, glasses, glass ceramics, graphite, and diamond Selection of Manufacturing Processes: -casting: expendable mold and permanent mold -forming and shaping: rolling, forging, extrusion, drawing, and molding -machining: turning, boring, drilling, milling and shaping -joining: welding, brazing, soldering, and adhesive bonding -finishing: honing, polishing, deburring, coating and plating. Process selection-depends on the geometric features of the parts to be produced, including the dimensional tolerances and surface texture required. Several factors can have a major role in process selection including part size, shape complexity and dimensional accuracy and surface finish required. Examples: -flat parts and thin cross-sections can be difficult to cast -dimensional tolerances and surface finish in hot-working operations are not as fine as those obtained in operations performed at room temperature. Process Substitution- happens for lower cost, the maintenance required, whether the product is for industrial or customer use, the parameters to which the product will be subjected, environmental concerns that have to be addressed, and the products appeal to the customer. The difference between net shape and near net shape is a matter of degree of how close the product is to its final dimensional and surface finish characteristics. The total cost of manufacturing a product generally consists of the following components; materials, tooling, fixed, capital, labor. Chapter 1: The Structure of Metals: The three basic arrangements of metals are: 1. Body-centered cubic-there are 48 possible slip systems, therefore the probability is high that an externally applied shear stress will operate on one of these systems and cause slip. Required shear stress is high. Good strength and high ductility. 2. Face-centered cubic- 12 slip systems. The probability of slip is moderate and the sheer stress required is low. Moderate strength and good ductility. 3. Hexagonal closed packed- 3 slip systems and has a low probability of slip but more slip systems become active at elevated temperatures. Brittle at room temp. All three arrangements can be modified by adding atoms of some other metal or metals, also known as alloying. Allotropism/Polymorphism: the appearance of more than one type of crystal structure in metals Metals can take on different structures at different temperatures when they have multiple phases present and when they have alloying metals. Elastic Deformation: when a single crystal returns to its original shape when the force being exerted on it is removed. Plastic/Permanent Deformation: when the crystal does not return to its original shape when the force is removed. Defects and Imperfections: Point defects: vacancy (missing atom), interstitial atom (extra atom in the lattice) or impurity(foreign atom that has replaced the atom of the pure metal) Dislocations: defects in the orderly arrangement of a metals atomic structure. There are two types, edge and screw- unit cells end up unable to perfectly align. Planar imperfections- Grain boundaries and phase boundaries Volume or Bulk imperfections- Voids, inclusions, phases or cracks Grains: when a crystal grows into a crystalline structure. Each grain consists of either a single crystal (for pure metals) or polycrystalline aggregate (for alloys). Grain boundaries: the interfaces that separate the individual grains Grain size: Large grain size=Low strength=Low hardness=low ductility= rough surface. Usually measured by counting the number of grains in a given area. Grain sizes between 5&8 are considered fine grained. (n-1) ASTM number: N=2 Chapter 2: Tensile Testing: method for determining the mechanical properties of materials -0 = original gage length (usually 50mm) -A0= cross-sectional area usually 12.5 mm -Engineering stress/nominal stress: the ratio of the applied load P to the original cross sectional area A o σ=P/A o -Engineering strain: e=l-l /o o l is the instantaneous length of the specimen. -Permanent deformation occurs when the yield stress of the material is reached -The maximum engineering stress is called the ultimate tensile strength -Neck: the cross sectional area of the specimen is no longer uniform along the gage length and is smaller in the necked region. As the test progresses, the engineering stress drops further and the specimen finally fractures at the necked region -The engineering stress at a fracture is known as the breaking or fracture stress. -The ratio of stress to strain is the modulus of elasticity, E=σ/e -Ductility: the extent of plastic deformation that the material undergoes prior to fracture. -Elongation- (l flo/o )*100 -Reduction of area- (A -Ao/Af)*o00 -True stress(NOT THE SAME AS ENGINEERING STRESS): σ=P/A -True strain: ε=ln(l/l ) o n -The true stress-true strain can be represented by the equation: σ=Kε K:the strength coefficient, n:strain hardening/work hardening exponent The higher the value of n, the higher the strain that a piece if material can experience before it begins to neck. -Increasing the temperature causes: the ductility and toughness to increase, the yield strength and modulus of elasticity decrease -Deformation rate: the speed at which a specimen is being stretched -Strain rate: a function of the specimens length -Strain rate hardening: increasing the strain rate increases the strength of the material -Creep: the permanent deformation of a component under a static load maintained for a period of time. -Ductile fraction usually takes place on the planes on which sheer stress is a maximum. Chapter 3: Physical properties of materials:
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