Notes on Tensile Testing

Overview of Tensile Test

• Purpose: To understand material behavior under tensile stress.
• Focus: Yield point phenomenon in materials.

First Tensile Test: Plain Carbon Steel

Test Piece Specifications

• Shape: Cylindrical
• Diameter: 10 mm
• Gauge Length: 100 mm
• Distance marks are drawn to visualize plastic behavior.

Testing Procedure

1. Setup:
   • Upper crosshead positioned correctly.
   • Test piece placed in grips.
2. Extensometer:
   • Swung into position to measure gauge length.
   • Parameters selected on control computer.
3. Conducting the Test:
   • Test piece elongated at a standardized speed.
   • Force recorded and displayed on screen.

Force-Elongation Diagram

• Force (F) plotted on vertical axis.
• Elongation (ΔL) plotted on horizontal axis.
• Initial behavior: Elastic region characterized by a steep straight line.
• End of elastic region indicated by:
  • Sudden drop in force (yield point phenomenon).
  • Permanent elongation occurs if unloaded from this area.

Key Concepts

• Ludas Effect:
  • Almost constant force level with slight fluctuations.
  • After a certain strain (Luda strain), force increases.
• Necking:
  • Occurs after maximum force is reached, causing further plastic deformation.
  • Test piece fractures at the neck.

Strength Properties Calculation

• Upper Yield Strength (Re): F / S0
• Lower Yield Strength (Rel): F / S0
• Tensile Strength (Rm): Fmax / S0
• Percentage Elongation After Fracture:
  • Example: about 30%.
  • Depends on length to diameter ratio.
• Percentage Reduction of Area:
  • Calculated by measuring smallest diameter at fracture.

Second Tensile Test: Precipitation Strengthened Aluminium Alloy

Test Piece Specifications

• Same shape and dimensions as the first test.

Testing Procedure

1. Setup: Similar to the first test with the extensometer positioned.
2. Conducting the Test:
   • Initial linear curve shows elastic behavior.

Force-Elongation Diagram

• Smooth transition from elastic to plastic deformation without a sudden drop.
• Maximum force leads to necking until fracture occurs.

Key Concepts

• 0.2% Proof Strength (Rp0.2):
  • Represents stress causing 0.2% plastic deformation.
  • Calculated by:
    1. Compute elongation for 0.2% strain (0.2 mm for 100 mm gauge length).
    2. Draw line parallel to elastic line through 0.2 mm offset.
    3. Intersection of this line with the force elongation diagram gives FP0.2.
  • Proof Strength Calculation: Rp0.2 = FP0.2 / S0.
• Other calculations (tensile strength, percentage elongation, percentage reduction of area) same as in the first test.

• Understanding these tensile testing concepts is critical for materials science and engineering.