Purdue University School of Materials Engineering MSE 230 Spring 2005 Exam I February 17 2005 Show All Work and Put Units on Answers Name Recitation Day and Time Recitation Instructor s Name 1 10 2 10 3 20 4 15 5 15 6 15 7 15 Total 100 1 Short Answer 10 pts 1a On the x ray plot below for a sample under no stress indicate which direction the peaks would shift if the sample was pulled in tension while the measurement was made 40 3 58 3 73 2 87 0 100 6 114 9 2 1b Draw in schematically how cold working affects the elastic modulus of a material Assume that the cold work does not crack the material and be very deliberate in your answer GPa CW 10 2 10 pts 2a Schematically illustrate the expected net energy curves for material A and material B such that material A clearly has a lower CTE than material B Bonding Energy r Material A Bonding Energy r Material B 2b Place True or False in the space provided for the following statements The coefficient of thermal expansion is proportional to the melting temperature of the metal Van der Waals bonding arises due to interactions between protons of one atom and electrons of another atom Chlorine 1s22s22p5 is electropositive because it wants to gain an electron A metal that has been subject to only elastic deformation will form a brand new set of strain free grains when annealed 3 10 Slip Directions and Planes 20 pts 3a Draw and label the slip plane on the edge dislocation to the left Indicate which bond s are broken by via the applied shear b On the edge dislocation to the right indicate the stress field s on the drawing Indicate where a solute atom larger than the solvent atoms might accumulate c Draw the 1 11 slip plane for a FCC unit cell z y x d Draw a 2 dimensional representation of this plane using a hard sphere model to indicate how atoms touch or don t touch in this plane Label all the edge lengths of your plane in terms of a e Circle the directions that would make a slip system for the 1 11 plane 111 1 1 0 1 1 1 11 1 1 01 110 20 4 X ray Diffraction 15 pts 4 a Calculate the diffraction angles 2 for the first three peaks in the diffraction pattern of Ni FCC Assume the incident radiation has a wavelength of 0 1542 nm The atomic radius of Ni is 0 125 nm Show all work On the figure below show your answers for each peak calculated labeling the hkl for each Intensity 30 40 50 60 70 80 2 5 15 Fracture Toughness Yield 15 pts 5 Your boss gives you a 20 mm by 5 mm flat plate with a center crack location as shown in the figure assume Y 1 25 It is made from a material with the following properties KIc 13 MPa m y 80 MPa The smallest overall flaw size that is detectable is 5 mm Crack Location Y 1 25 20 mm 5 mm thick a Assuming the plate is loaded to 10 000 N should you be concerned about the load applied Why or Why not b Which of the following would increase m the stress at a crack tip circle all that apply Increasing the crack tip of the radius Decreasing the crack length Increasing the nominal stress applied Making the sample to be tested out of a material with a lower KIc Making the sample to be tested out of a material with a higher KIc 15 6 Strengthening Mechanisms 15 pts 6 A cylindrical rod of 1040 steel originally 10 mm in diameter is to be cold worked Assume that the circular cross section is maintained during the drawing process The final diameter should be 7 6 mm for the application USE A STRAIGHT EDGE TO INTERPRET GRAPHS Using math and text show the processing steps to get a 7 6 mm diameter wire with a yield strength of at least 700 MPa and a ductility of at least 12 elongation A lathe is not available Area of circle d2 4 r2 Note it is possible to get these properties from 1040 steel 15 7 Stress Strain 15 pts 7 Consider a cylindrical nickel wire 2 0 mm in diameter and 3 x 104 mm long with the following properties E 204 GPa y 138 MPa t 262 MPa EL 40 0 3 a Estimate the maximum amount of elastic strain capable by the wire b At the atomic level what gives rise to the elastic strain c What is the value of the elastic strain recovered if the specimen is loaded to 230 MPa then unloaded 15 8
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