Question

1. State the difference between I and polycrystalline materials. Deformability of BCC and FCC metals. Strength and UTS of metals. 2. Determine the slip systems in BCC and FCC materials. Show the calculations that support your determinations. 3. Find the indices that represent the planes in the following cubic unit cell and show the X-Ray diffract-ability of the these planes in FCC and BCC structures: 4. A tensile specimen with a 12 mm initial diameter and 50 mm gauge length reaches maximum load at 90 kN and fractures at 70 kN. The maximum diameter at fracture is 10 mm. Determine engineering stress at maximum load (the ultimate tensile strength), true fracture stress, true strain at fracture and engineering strain at fracture. 5. A cylindrical rod 380 mm long, having a diameter of 10 mm, is to be subjected to a tensile load mm when the applied load is 24500 N, which of the four metals or alloys listed below are possible candidates? Based in the data presente hardening? Explain. nted in this table, which material might show the highest strain Modulus of Elasticity Yield Strength Tensile Strength Material Aluminum alloy Brass alloy Copper (MI 255 345 250 450 (M 70 100 110 207 420 420 290 Steel a

Answer 1

1 Difference between single crystal and polycrystalline structure is that in single crystal internal atomic pattern is repeated whereas there is no periodicity across a polycrystalline sample Polycrystalline material - Aggregate of several crystals or grains Single crystal - only one grain or crystal and hence, no grain boundaries. 2.The deformity depends on the fact of slip system. FCC have less slip system when compared to BCC so FCC offers more deformity The deformation of metals involve the motion of large number of defects on certain crystallographic planes. These defects are crystallographic in nature and are commonly called as dislocations. FCC has 12 number of slip systems per unit cell available for detarmatign BCC has 48 number of slip systems. There are 48 systems in BCC lattice but slip plane of each is different The slip plane changes but slip direction doesn't changes and that's why BCC structure mostly deforms by screw dislocation.But in FCC the slip plane and slip direction changes simultaneously and that's why it under goes edge dislocation. That makes the slip plane and slip direction as major parameter to differentiate the deformability of different lattice structure. 3.Ultimate tensile strength (UTS] is the maximum stress that a material can withstand while being stretched or pulled. The ultimate tensile strength of a material is calculated by dividing the cross-section area of the material tested by the stress placed on the material, generally expressed in terms of pounds or tons per square of material. strength is defined as the amount of stress where a predetermined amount of plastic (irreversible) deformation occurs. If the applied stress is lower than the strength the deformation is always elastc strength is always lower than the ultimate tensile strength. 1)1:06 PM