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Unformatted text preview: Georgia Institute of Technology
ME 3180: Machine Design
Spring 2012: Sections A, RCC, and RPY Homework #4
Assigned on Feb. 3, 2012
Due in class on Feb. 9, 2012 Problem 1 The AISI 1060 HR steel shaft shown in the ﬁgure experiences a fullreversed bending at
the machined groove. Assume the shaft is rotating, operates at 200 °F, and must have a
reliability of at least 90%. Draw the SN diagram and calculate either the safety factor for infinite lifetime or number of cycles to failure for a maximum nominal stress
amplitude of (a) 15 kpsi and (b) 35 kpsi. DJ in. radius T 2.0 I'M. .L Problem 2 The ﬂat bar of AISI 1018 CD steel shown in the figure experiences a timevarying axial
force that ﬂuctuates between 8000 lbs. in tension and 2000 lbs. in compression. Assume
room temperature operation and 90% reliability. Neglecting column action, determine
the appropriate safety factor(s) for the bar. 03?; in. Mali“: T NOTE '. The
T w . .734. ,7 . .
ll: 2 rm 0.533441%)
Wells. Problem 3 A part experiences a combination of bending, axial, and torsional loading such that the
following stresses are created at a critical location: Bending: Completely reversed, with a maximum stress of 60 MPa
Axial: Constant stress of 20 MPa
Torsion: Repeated load, varying from 0 MPa to 50 MPa Assume the timevarying stresses are in phase with each other and the part contains a
notch such that Kﬁbendmg = 1.4, Kﬁaxial = 1.1, and Kﬁtorsion = 2.0. The material properties are
Sy = 300 MPa and Su = 400 MPa. The completely adjusted endurance limit is found to be S6 = 200 MPa. Find the factor of safety for fatigue based on infinite life. Be sure to
check for yielding. ...
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 Machine Design

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