Instructional Objectives
At the end of this topic, the readers should be able to understand
Types of loading on machine elements and allowable stresses.
The concept of yielding and fracture.
Different theories of failure.
Construction of yield surfaces for failure theories.
Optimize a design comparing different failure theories
The load may be classified as:
Static load- Load does not change in magnitude and direction and normally increases gradually to a steady value.
Dynamic load- Load may change in magnitude, for example, traffic of varying weight passing a bridge. The load may change in direction, for example, the load on the piston rod of a double acting cylinder.
Theories of failure
When a machine element is subjected to a system of the complex stress system, it is important to predict the mode of failure so that the design methodology may be based on a particular failure criterion. Theories of failure are essentially a set of failure criteria developed for the ease of design.
Summary of this topic
Different types of loading and criterion for design of machine parts subjected to static loading based on different failure theories have been demonstrated. Development of yield surface and optimization of design criterion for ductile and brittle materials were illustrated
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