Lesson Notes By Weeks and Term v4 - SHS 3
Properties of Materials
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Properties of Materials
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Subject: Manufacturing Engineering
Class: SHS 3
Term: 1st Term
Week: 17
Grade code: 2.1.2.LI.2
Strand code: 1
Sub-strand code: 2
Content standard code: 2.1.2.CS.1
Indicator code: 2.1.2.LI.2
Theme: Manufacturing Materials and Technologies
Subtheme: Properties of Materials
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This lesson introduces the fundamental concepts of how materials behave when forces are applied to them. In Ghana, from the steel rods used in building our homes and schools to the springs in a tro-tro's suspension, understanding how materials respond to loading is crucial for safety, efficiency, and innovation in manufacturing and construction. Why does the Adomi Bridge hold its own weight and the weight of countless vehicles every day without collapsing? Why does a blacksmith heat and hammer a metal to shape it? The answers lie in the concepts of load, stress, and strain.
This section breaks down the core ideas you need to understand. We will go through them one by one. A. Loading
Definition: A load is simply an external force or set of forces applied to a material or structure.
When we talk about the effect of loading, we are interested in how the material internally responds to these external forces. There are three primary types of loading: Tensile Load (Tension): This is a pulling force. It tends to stretch or elongate the material. Example: The steel cables holding up a bridge, or a rope used in a tug-of-war. Compressive Load (Compression): This is a pushing or squeezing force. It tends to shorten or compress the material. Example: The concrete pillars holding up a building, or the legs of a chair when you sit on it. Shear Load (Shear): This force acts parallel to the surface of the material, tending to cause one part of the material to slide over another. Example: The force on a bolt holding two plates together, or the action of scissors cutting paper. B. Stress (σ)
Definition: Stress is the measure of the internal force that particles within a material exert on each other in response to an external load. It is defined as the force per unit of cross-sectional area.