Lesson Notes By Weeks and Term v4 - SHS 3

Lesson Video

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Performance objectives

• Explain key tensile properties: stress, strain, and modulus of elasticity.
• Understand how to perform a tensile test on mild steel.
• Interpret a stress-strain graph from test results.
• Recognize the real-world applications of tensile properties.

Lesson summary

Welcome, future engineers! Today, we are exploring one of the most important topics in manufacturing: understanding how materials behave when you pull them. Imagine the iron rods that hold up the buildings in our cities like Accra and Kumasi, or the steel cables used in cranes at Tema Harbour. What stops them from snapping under heavy loads? The answer lies in their tensile properties. This lesson will take you through the process of a tensile test, a fundamental experiment used by engineers to measure a material's strength, stiffness, and ductility.

Lesson notes

What is a Tensile Test?

A tensile test is a destructive test process that provides information about the tensile strength, yield strength, and ductility of a material. In simple terms, we take a standard-sized sample of a material (called a specimen) and pull it from both ends with a machine called a Tensometer or Universal Testing Machine (UTM) until it breaks.

While pulling, the machine measures two things: The Force (Load) being applied to stretch the material. The Elongation (Extension), which is how much the material stretches.

From this data, we can calculate important properties and plot a graph that tells us the complete story of how the material behaves under tension. Key Definitions and Formulas Tensile Stress (σ) Stress is the measure of the internal force that the particles of a material exert on each other per unit of area. It is the force applied divided by the original cross-sectional area of the specimen. Formula: σ = F / A₀ Where: σ (sigma) is the stress. F is the applied force (in Newtons, N). A₀ is the original cross-sectional area (in square metres, m²). Units: Pascals (Pa) or Newtons per square metre (N/m²). In engineering, we often use Megapascals (MPa), where 1 MPa = 1,000,000 Pa.

Evaluation guide

• Measure the tensile properties of steel using the tensile test.
• Experi
• ential Learning: Let learners in mixed -ability groups perform a tensile test on mild steel to
• determine its tensile properties such as stress, strain, modulus of elasticity and elastic deformation.