Experiment No.1 Tensile Test on Mild Steel

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Experiment No. 1 – Tensile Test on Mild Steel | Mechanics of Solids Lab | Universal Testing Machine (UTM) | Stress-Strain Curve Explained

🌟 Intro (Engaging Opening)
Welcome to our Mechanics of Solids Laboratory Series!
In this video, we perform Experiment No. 1 – Tensile Test on Mild Steel, one of the most fundamental and exciting tests in mechanical engineering.
If you’re an engineering student learning about material strength, elasticity, and ductility, this experiment will help you visualize how materials behave under tension and understand key mechanical properties like yield stress, ultimate stress, breaking stress, elongation, and reduction in area.
In this detailed practical demonstration, we’ll use a Universal Testing Machine (UTM) to apply a gradually increasing tensile load on a mild steel specimen until it fractures — and study its stress-strain relationship step by step.
Watch till the end for a full explanation of:
🧩 The working principle of UTM
⚙️ How to prepare and test a mild steel specimen
📈 Plotting and analyzing the stress-strain curve
📚 Viva questions and real-life applications
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🧠 Aim of the Experiment
To conduct a Tensile Test on a Mild Steel specimen using a Universal Testing Machine (UTM) and determine the following mechanical properties:
Yield Stress
Ultimate Stress
Breaking Stress
Percentage Elongation
Percentage Reduction in Area
⚙️ Apparatus / Equipment Required
Universal Testing Machine (UTM)
Mild Steel Specimen (Standard size: typically 200 mm length, 20 mm diameter) Vernier Caliper / Micrometer (for measuring diameter)
Steel Scale (for length measurement) Extensometer (to measure elongation) Graph Sheet or Data Acquisition System (for plotting stress-strain curve)
📘 Theory Behind the Tensile Test
The tensile test is a fundamental experiment in material science that helps determine the mechanical behavior of a material when subjected to uniaxial tension.
When a tensile load is gradually applied to a mild steel specimen, it experiences elastic deformation at first — meaning the material returns to its original shape after unloading. As the load increases, the specimen enters the plastic region, where permanent deformation occurs. Eventually, the specimen reaches its ultimate strength and then fractures.
This behavior is represented on a stress-strain curve, which shows the relationship between the applied stress (force per unit area) and the resulting strain (change in length/original length).
🔹 Key Points of the Stress-Strain Curve for Mild Steel:
Proportional Limit (Point A):
Stress is directly proportional to strain. Follows Hooke’s Law:

𝜎 = 𝐸 ⋅ 𝜀
where E = Young’s Modulus.
Elastic Limit (Point B):
Beyond this, the material no longer returns completely to its original shape.
Yield Point (C to D):
The material begins to yield — deformation occurs at almost constant stress.
Yield stress is found here.

Ultimate Stress Point (E):
The maximum stress the material can withstand before necking.

Breaking Point (F):
The specimen fractures. The stress corresponding to this point is the Breaking Stress.

🧪 Experimental Procedure

Preparation:
Measure the original diameter (D₁) and gauge length (L₁) of the mild steel specimen using a vernier caliper and steel scale.
Record these values carefully for calculation.
Mounting the Specimen:
Place the specimen between the grips of the Universal Testing Machine.
Ensure it is perfectly aligned along the axis of loading.
Setting Up the Extensometer:
Attach the extensometer to measure elongation during loading (or connect electronic sensors if available).
Zero Setting:
Set all dials, scales, or computer systems to zero before applying load.
Applying Load:
Gradually increase the tensile load and observe the readings of load and extension.

Record readings at small intervals up to the elastic limit.
Yield Point Observation:
Note the point at which the specimen begins to yield — elongation increases rapidly without much increase in load.
Ultimate Load and Fracture:
Continue loading until the specimen reaches maximum load (Ultimate Load) and then breaks.
Post-Test Measurements:
Measure the final length (L₂) and final diameter (D₂) at the fractured section.
Applications of Tensile Test
To determine mechanical properties of metals and alloys.
To design safe structural components in buildings, bridges, and machines.
To compare ductility and brittleness of materials.
Used in quality control and research to verify material strength.