midterm exam past paper, Exams of Materials science

Download midterm exam past paper and more Exams Materials science in PDF only on Docsity! UNIVERSITY OF CALIFORNIA College of Engineering Department of Materials Science and Engineering Professor R. Gronsky Fall Semester 2000 ENGINEERING 45 MIDTERM #1 NAME:______________________________________ (Please Print Clearly) This is a closed book Exam. You must work independently, and no reference materials are permitted. Please use only the pages given here, and write your answers in the spaces provided. Question 1 Choose the best answer. (2 points for each correct answer) a The directional atomic bonds include 1 ionic bonds. 2 covalent bonds. 3 metallic bonds. b Metallic bonding is generally NOT responsible for 1 translucency. 2 malleability. 3 ductility. c The van der Walls bond is a 1 primary bond in polymeric materials. 2 dipole-dipole interaction. 3 charge-transfer fluctuation. d The near-neighbor distances between anions and cations in a ceramic 1 are established by a force balance. 2 are established by a charge balance. 3 are established by the coordination number. e Crystal structure is conventionally described using 1 only one unit cell of the Bravais lattices. 2 lattice and motif. 3 fcc, bcc, or hcp. f During elastic deformation, a metal experiences 1 necking. 2 bond breaking. 3 bond stretching. g Plastic deformation in metallic alloys is the result of 1 necking. 2 dislocation motion. 3 the uniaxial tensile test. h Hardness is a measure of 1 resistance to surface penetration. 2 resistance to deformation in the elastic limit. 3 resistance to formation of circular indentations. NAME:_______________________________ E45•Midterm #1 2000 2 Question 3: (30 points) Identify each of the lattice directions and planes in the following figures relative to the coordinate axes shown. All intersections between the vectors and the unit cells occur at corners or midpoints of cell edges or face centers. Use appropriate Miller indices or Miller-Bravais notation and write answers in boxes provided. Lattice Directions (3 points each) a1 a2 a3 c x y z a b c d e Lattice Planes (3 points each) x y z a1 a2 a3 c f g h i j NAME:_______________________________ E45•Midterm #1 2000 5 Question 4: (20 points) Consider the following schematics showing the deformation sequence of a crystal in response to an applied shear stress. In each case: • label the direction of the shear load that caused the deformation (1 point); • draw the dislocation line and label ξ the dislocation line direction (2 points); • draw and label b the Burgers vector (2 points); • identify the slip plane by shading it in (1 point); • show with arrows the motion of the dislocation during continued slip (2 points); and • specify the type of dislocation (edge or screw) represented by your figure (2 points). (a) (10 points) Type of dislocation = ___________________ (b) (10 points) (Corrupted file) Type of dislocation = ___________________ NAME:_______________________________ E45•Midterm #1 2000 6 UNIVERSITY OF CALIFORNIA College of Engineering Department of Materials Science and Engineering Professor R. Gronsky Fall Semester 2001 ENGINEERING 45 Midterm #1 NAME:______________________________________ (Please Print Clearly) This is a closed book Exam. You must work independently, and no reference materials are permitted. Please use only the pages given here, and write your answers in the spaces provided. Question 3 Identify the lattice directions and lattice planes shown in the sketches below for 3 points each. Note especially the scale markings and use them to precisely identify any fractional intercepts. Be sure that your answer satisfies the special requirement of the four-index Miller-Bravais notation that h + k = -i. x y z a.       b.       c.       d.       e.       a 2a 1 a 3 c f.       g.       h.       i.       j.       E45•Midterm #1, 2001 NAME:_______________________________ 4 Question 4 An alloy of copper and gold forms a special “ordered” crystal structure known as L12 in the Strukturbericht notation. It has a cubic unit cell with Au atoms at the corners and Cu atoms at the face centers. x z y a. Draw and label the contents of the unit cell (5 points) b. Show how to count all of the atoms in the unit cell and use your result to specify the chemical formula of this ordered alloy? (5 points) c. Now specify a Bravais lattice (5 points) AND a motif (5 points) that appropriately describe this ordered L12 crystal structure. E45•Midterm #1, 2001 NAME:_______________________________ 5 Question 5 Consider the following schematic of the atomic arrangements in an fcc crystal (lattice constant = a) that has been subjected to an external load of sufficient magnitude to exceed the critical resolved shear stress for motion of dislocations on the slip plane pictured here. Find the edge dislocation in the fcc crystal illustrated below... a. Locate and label the extra half plane (5 points). b. Locate and label the slip plane (5 points). c. Trace an FSRH Burgers circuit and draw in the Burgers vector (5 points). d. Now specify the Burgers vector’s magnitude and direction with respect to the fcc crystalline coordinate system indicated here (5 points). Remember that b is a lattice vector representing the shortest lattice translation. [111] [101] E45•Midterm #1, 2001 NAME:_______________________________ 6 2. Bonding (20 points) Mark ☒ the ballot box corresponding to the best answer. Two (+2) points for correct answers, -1 if wrong, 0 if blank. (a) “Primary” bonds are formed ☐ by the transfer of primary electrons ☐ primarily between individual atoms or ions ☐ during primary chemical reactions (b) “Secondary” bonds are so-named because ☐ they require secondary electrons to complete the charge transfer necessary for bonding ☐ they occur between groups of atoms after primary bonding has occurred ☐ they result in secondary reactions with reduced effi- ciency relative to primary bonds (c) Consider the following bonding energy curves for two alloys, A and B. a a 0 B o n d in g e n er g y 0 + - A B ☐ A has a higher tensile strength than B ☐ A has a lower elastic modulus than B ☐ A has a smaller lattice constant than B (d) The “octet rule” predicts that Group IV elements ☐ form bonds with four near neighbors ☐ have eight bonding electrons ☐ reside in octahedral sites (e) When compared with materials that form ionic bonds, metallic alloys ☐ melt at higher temperatures ☐ exhibit greater bond directionality ☐ have higher coordination numbers (f) During the formation of covalent bonds, a bonding model called “hybridization” explains why ☐ some bonds show both covalent and metallic character ☐ carbon has more than one isotope ☐ silicon atoms are tetrahedrally coordinated (g) The metallic bonding model explains ductility on the basis of ☐ lack of bonding electrons, yielding weaker bonds ☐ excess of mobile electrons, causing fluid bonds ☐ lack of bond directionality (h) The basis for the van der Waals interaction that causes molecular bonding is ☐ mutual charge symmetry ☐ induced electric dipoles ☐ distortion in electron orbitals (i) One explanation for why graphite powder acts so well as a “solid lubricant” is ☐ carbon atoms in graphite are covalently bonded within planar layers but have weaker secondary bonds between layers ☐ finely-powdered carbon has many unsatisfied bonds at the particle surfaces, which act as a “sea of electrons” to cause lubrication ☐ when crushed into a fine powder, graphite establishes a “polar” distribution of charge, leading to Coulombic repulsion between powder particles (j) The following schematic shows two water molecules in a “bonded” configuration due to ☐ 109.5° covalent bond angles ☐ a functional hydrogen bridge ☐ the ideal radius ratio, 0 < r/R < 0.155 E 45 Midterm 01, 2005 Initials: page 3 of 7 3. Lattice Planes (20 points) The triangles drawn here are sections of planes through cubic and hexagonal lattices. Identify the relevant planes by their Miller indices or Miller-Bravais indices. Four (4) points for correct answers in the boxes provided. x z y (a) x z y (b) x z y (c) c a 3 a 1 a 2 (d) c a 3 a 1 a 2 (e) E 45 Midterm 01, 2005 Initials: page 4 of 7 4. Lattice Directions (20 points) Identify the following directions through both cubic and hexagonal lattices using the appropriate Miller index or Miller-Bravais index notation. Four (4) points for correct answers in the boxes provided. x z y (a) x z y (b) x z y (c) c a 3 a 1 a 2 (d) c a 3 a 1 a 2 (e) E 45 Midterm 01, 2005 Initials: page 5 of 7