OWMMCB2
Tutorial 6
Shaft Design
QUESTION 1
Estimate the endurance limit of a 32mm diameter rod of AISI 1035 steel having a machined
finish and heat-treated to a tensile strength of 710 MPa.
QUESTION 2
Two steels are being considered for manufacture of as-forged connecting rods. One is AISI
4340 Cr-Mo-Ni steel capable of being heat treated to a tensile strength of 1820 MPa. The
other is a plain carbon steel AISI 1040 with an attainable Sut of 791 MPa. If the rod is to have
a size giving an equivalent diameter of De = 20 mm, determine if there is any advantage for
using the alloy steel for this fatigue application.
From the above the AISI 1040 actually offers a higher endurance limit meaning it is more
suitable for the fatigue application.
QUESTION 3
A shaft is loaded in torsion such that Ma =60 Nm, Ta = 40 Nm, Mm = 50 Nm and Tm = 30 Nm.
For the shaft Sut = 700 MPa and Syt = 560 MPa and a fully corrected endurance limit of SE =
210 MPa is assumed. Let Kf = 2.2 and Kfs = 1.8. Using a design factor of 2.0, calculate the
minimum acceptable diameter of the shaft using Soderberg’s equation.
QUESTION 4
QUESTION 5
A 25mm steel shaft is supported at the ends in two pillow block bearings. It has three balanced
masses connected to it as indicated. Determine the first critical speed of the shaft using:
a. Rayleigh's method
b. Dunkerley's method
c. Superposition