What is the apparatus used for a tensile test?
- Nafisa Nazneen Choudhury
- May 30
- 2 min read
A tensile test measures how a material behaves when pulled apart, giving critical data like yield strength, ultimate tensile strength, elongation, and modulus of elasticity.
To perform a tensile test properly, several key pieces of equipment are required:
1. Universal Testing Machine (UTM)
The core machine used in tensile testing is the Universal Testing Machine. It applies a controlled tensile force to the specimen while continuously recording the load and the corresponding elongation. UTMs can be either electromechanical or servo-hydraulic, depending on load requirements and precision needs.
Electromechanical UTMs are ideal for lower loads and high precision testing.
Servo-hydraulic UTMs are preferred for very high-capacity test,s such as for metals and structural materials.
2. Grips and Fixtures
Grips hold the specimen securely during testing to avoid slippage and ensure accurate force transmission.
Wedge grips are the most common for metals.
Pneumatic grips are used for soft or thin materials like plastics and textiles.
Hydraulic grips are used when a very high clamping force is needed for thick or hard specimens.
Each grip type must match the sample material and geometry to prevent premature failure outside the gauge length.
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3. Extensometers
An extensometer measures the change in length of the specimen directly and precisely. It ensures accurate determination of strain, especially during the elastic deformation range.
Clip-on extensometers are attached directly to the specimen.
Non-contact extensometers such as laser or video extensometers are used when traditional clip-ons might interfere with delicate or very soft samples.
4. Load Cells
A load cell converts the tensile force applied by the UTM into an electrical signal that can be measured and recorded.
Load cells must be calibrated according to ISO 7500-1 or ASTM E4 standards to ensure test validity.
They must have a capacity slightly higher than the maximum expected test load to avoid overloading and damage.
5. Specimen Preparation Tools
Accurate specimen preparation is critical for valid results. Common tools include:
Precision cutting machines or shears to create standard specimen shapes.
Surface grinders or polishers for removing surface defects that could initiate premature fracture.
Micrometers and Vernier calipers for measuring specimen dimensions with high accuracy.
Basic standards for specimen preparation are covered here: ASTM E8 / E8M - Standard Test Methods for Tension Testing of Metallic Materials
6. Data Acquisition System (DAQ)
The data acquisition system records load, displacement, and optionally strain in real-time. It must have high sampling rates and minimal signal noise.
Most modern UTMs integrate software-controlled DAQs capable of plotting stress-strain curves instantly.
Advanced systems allow custom scripting for cyclic, creep, or fatigue testing extensions.
Final Note:
While a basic tensile test setup can be relatively simple, achieving accurate, repeatable, and standards-compliant results demands careful attention to apparatus quality, calibration, and proper specimen handling.
If you are preparing a detailed lab report or research project, it is highly recommended to cite the standards like ASTM E8, ISO 6892, or relevant national codes, depending on the material and industry requirements.
