Question: Write on:Soderberg and Goodman design criteria.
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Subject: Machine Design -I

Topic: Basic properties of Machine design and theories of failure

Difficulty: Medium

md1(66) • 2.6k views
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modified 14 months ago  • written 17 months ago by gravatar for kiran.9870 kiran.987010
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  • Mean stress as well as stress amplitude exist when a component is subjected to fluctuating stresses.
  • It has been observed that the mean stress component has an effect on fatigue failure when it is present in combination with an alternating component.
  • The fatigue diagram for this general case is shown in Fig. below. In this diagram, the mean stress is plotted on the abscissa and stress amplitude on ordinate.
  • The magnitudes of mean stress and stress amplitude depend upon the magnitudes of maximum and minimum force acting on the component.
  • When stress amplitude is zero, the load is purely static and the criterion of failure is Sut or Syt. These limits are plotted on the abscissa.
  • When the mean stress is zero, the stress is completely reversing and the criterion of failure is the endurance limit Se that is plotted on the ordinate.
  • When the component is subjected to both components of stress, the actual failure occurs at different scattered points shown in the figure.
  • There exists a border, which divides safe region from unsafe region for various combinations of mean stress and stress amplitude.
  • Different criterion are proposed to construct the borderline dividing safe zone and failure zone. They include Gerber line, Soderberg line and Goodman line.

Soderberg line and Goodman line

  • Gerber Line: A parabolic curve joining Se on the ordinate to Sut on the abscissa is called the Gerber line.
  • Soderberg Line A straight line joining Se on the ordinate to Syt on the abscissa is called the Soderberg line.
  • Goodman Line A straight line joining Se on the ordinate to Sut on the abscissa is called the Goodman line.
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written 14 months ago by gravatar for kiran.9870 kiran.987010
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