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Unformatted text preview: UNIVERSITY OF CALIFORNIA College of Engineering Department of Materials Science & Engineering Professor R. Gronsky Fall Semester, 2005 Engineering 45 Midterm 01 INSTRUCTIONS .................. LATTICE seating Please be seated with occupied seats to your front and back, vacant seats to your left and right. ...... CLOSED BOOK format All you need are writing instruments and a straightedge. Please store all books, reference mate- rials, calculators, PDAs, cell phones (OFF), and iPods. ......... NO DISRUPTION rule Questions cause too much of a disturbance to others in the room. Instead of asking questions, write any concerns or alternative interpretations in your answers. ... PROFESSIONAL protocol Engineers do not cheat on the job and they certainly dont cheat on exams. Do not open until START is announced. SOLUTIONS 1 . Mechanical Properties (20 points) Mark ! the ballot box corresponding to the best answer. Two ( +2 ) points for correct answers, -1 if wrong, if blank. ( a ) The compressive stress induced in the volume element shown below is defined by which expression? l w t P ! ! = P ! ( w ! t ) ! ! = P ! ( l " w ) ! ! = P ! ( l " t ) ( b ) The shear stress induced in the volume element shown below is defined by which expression? l w t P ! ! = P ! ( w ! t ) ! ! = P ! ( l " w ) ! ! = P ! ( l " t ) ( c ) In order to convert the data from a load vs elongation plot to a stress vs strain plot, the following information is essential. ! the cross-sectional area of the sample ! the yield strength of the sample ! the geometry of the sample ( d ) Elastic deformation is________? ! linear ! recoverable ! time-dependent ( e ) The gage length of a metallic alloy sample used in the standard uniaxial tensile test ! has the smallest cross-sectional area ! establishes the initial length of the sample ! calibrates the samples elongation to failure ( f ) True stress differs from engineering stress ! in the way tensile test data is collected ! in the way tensile test data is reported ! in the way tensile test data represents the actual sample ( g ) The following data from a uniaxial tensile test of a low carbon steel sample indicates that 200 400 600 0.01 0.02 Strain, ! (mm/mm) Stress, " (MPa) ! it has a lower yield point of 450 MPa ! it has an 0.2% offset yield point of 450 MPA ! it fractured at precisely 0.02% offset ( h ) For the same steel sample as above, an observer in the room would have observed necking in the sample ! just before the sample fractured at 400 MPa ! just when the sample yielded at 500 MPa ! just as the stress exceeded 600 MPa ( i ) An aluminum alloy produced the following stress-strain plot during a uniaxial tensile test. Its yield strength is 200 400 600 0.01 0.02 Strain, ! (mm/mm) Stress, " (MPa) ! 400 MPa ! 450 MPa ! 500 MPa ( j ) Comparing the above plots from a steel sample and an Al alloy sample, it can be concluded that ! the Al alloy has greater elastic recovery after fracture ! the Al alloy has a larger elastic modulus...
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