Introduction to Design

A machine part is to be designed for the load coming on it. The load can be static, which does not vary with time or dynamic, and which varies with time. To design a component, the designer should know the following:

• • Intensity and type of load (see Section 5.2 for various types of loads)

• • Any variation in load: Constant or varying with time, shock or impact, etc.

• • Material with which it is to be made (refer Chapter 2 for the selection of material)

• • Strength of selected material: Strength is the stress, which a material can take without Failure

• • Shape of the component: Stress concentration caused by any sudden change in cross section (see Chapter 9 for stress concentration) and

• • Environment (clean and corrosive) in which the part is to be used.

Designing for strength involves the calculation of the size of a component to withstand the load coming on it. After designing the size of a component, its design may have to be modified for many other parameters, like ease of production, number of parts to be manufactured, facilities in workshop, cost of manufacturing for a selected process, ease of maintenance, overall cost, kinematics of the machine part, lubrication of the part, use of standard parts, weight, safety in operation, aesthetic appeal to eye etc.

Types of Loads

Any machine element is subjected to one or more than one type of load. Loads are of many types:

• • Tensile load The component is pulled from the ends [Figure 5.1(a)].

• • Compressive load The component is compressed at the ends [Figure 5.1(b)].