Today, more than ever, engineering applications are often interdisciplinary; involving the interrelationship of several of the basic engineering science like mechanical, electrical, chemical, etc. therefore the modern engineer must have a fundamental knowledge in each of these areas. An understanding of how bodies respond to applied loads, the main emphasis in Strength of Materials, is a part of this knowledge. (Andrew Pytel, 1987)
Strength of materials deals with the relations between externally applied loads and their internal effects on bodies. Moreover, in this field, the bodies are no longer assumed to be rigid; deformation however are small but of major interest.
In mechanical design, the engineer must consider both dimensions and materials properties to satisfy requirements of strength and rigidity. When loaded, a machine part or structure should neither break, nor deform excessively.
It is of importance to study the effects of external forces on a given body. There are many kinds of forces and these forces are classified according to nature or orientation and effects of the applied load on the member.
The two most common forces are compression and tension. Collectively these forces are called axial force. Axial force occurs when the applied load or force is parallel to the axis of the member or the cross section is perpendicular to the load. (Andrew Pytel, 1987)
Tensile force can be represented when the applied load results to the elongation of the member. It is a pulling action on the member that tends to elongate, while compression is the opposite effect of tensile force. Compressive force tends to push the member resulting to shortening.
In engineering design like structural or machine design, it is of importance to study compressive force as well as tensile force. But the discussion will focus on compressive force. When compression force is applied in a member, the member experiences a pressure which is known as stress. Stress can be determined by dividing the value of the force applied over the cross section area of the member where the force is applied. Thus this stress is known as compressive stress. From the equation of determining the compressive stress of a member, higher compressive force will increase the compressive stress. It is very important to know that the area must be perpendicular to the force. Stress has the unit of force per unit area and usually expressed in metric system as Newton per square meter or Pascal or in English system as pounds per inch.
Compressive force is usually applied on bars, columns, cylinders and pistons. It is of great importance to know the physical properties of a member so that to perform the function efficiently. Properly selecting the right kind of material for a given load is a prerequisite in machine design for example. When selecting the right material in a machine structures like cylinder and piston, the designer must consider the maximum applied compressive force that can with stand by the piston as it compress the mixture of fuel and air in the combustion chamber. The piston will experience compressive stress as it goes up to compress the mixture. Moreover, the connecting rod, which connects the piston to the crankshaft, to deliver the pressure from the combustion of the fuel and air mixture to produce power that will be utilized in moving a vehicle. It is important to consider the properties of a material so that failure of a member will be minimized. Another concept of compression in the field of mechanical engineering is the application of an internal combustion engine. In this system, the mixture of fuel and air is compressed. As the mixture is compressed, the internal energy of the mixture increases. The temperature and pressure as well increases. Because of this, a little amount of energy like ignition will result to combustion of the compressed air producing power.
In general, compression is important to understand in the field of engineering so that the engineer can select the proper material and proportion it to enable a structure or machine to perform its function efficiently.
Andrew Pytel, F. L. S. (1987). Strength of Materials (4th ed.): HarperCollinns Publisher.
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