What are the functions and application scenarios of a tensile testing machine?

Universal Testing Machine (also known as Tensile Tester) is core laboratory equipment to evaluate materials’ mechanical properties. It is often used together with the ventilation aging test chamber. After materials undergo thermal air aging, the tensile tester measures changes in tensile strength, elongation at break and other indicators, to quantify the degree of material aging.

1. Main Applications

• Tensile Test: Measure tensile strength, yield strength, elongation at break, elastic modulus (most commonly used)
• Compression & Bending Test: For plastics, metals, ceramics and similar materials
• Peel & Tear Test: Peel strength / tear strength of films, adhesive tapes, textiles and rubber
• Shear, Puncture & Burst Test: Composite materials, packaging materials, etc.
• Cyclic / Fatigue Test: Supported on selected models
• Environmental Chamber Integration: Compatible with temperature chambers to run mechanical tests under varying temperatures

2. Working Principle

Specimens are clamped between upper and lower grips. The moving crosshead travels at a constant speed to apply tensile or compressive load to the sample. The load cell records real-time force values, while a displacement encoder or extensometer captures deformation data. The system generates force-deformation / force-displacement curves and automatically calculates all mechanical parameters.

Three closed-loop control modes are available:

1. Stress control: Adjust loading rate
2. Strain control: Adjust deformation rate (widely adopted)
3. Displacement control: Adjust crosshead moving speed

3. Common Test Standards

1. GB/T 1040: Plastics — Determination of tensile properties
2. GB/T 528: Vulcanized rubber or thermoplastic rubber — Tensile stress-strain properties
3. ISO 527 / ASTM D638: Plastics tensile testing
4. ISO 37 / ASTM D412: Rubber tensile testing
5. GB/T 228.1 / ISO 6892 / ASTM E8: Tensile test for metallic materials (usually hydraulic or high-capacity electronic UTM)
6. GB/T 3923 / ISO 13934: Textiles — Tensile properties of fabrics
7. GB/T 8804: Thermoplastic pipes — Determination of tensile properties
8. GB/T 2951.11: Common test methods for insulation and sheathing of electric and optical cables — frequently used for pre & post aging mechanical testing

For aging tests, the aging coefficient (strength after aging / strength before aging ×100%) or retention of elongation at break is used to characterize aging resistance. Therefore, the UTM must accurately calculate these two values.

4. Classification & Machine Structure

Core components: Load frame (single / dual / four-column), servo motor + ball screw drive system, load cell, displacement encoder, grips & accessories.

5. Key Configuration

1. Load Cell: Select measuring range covering 0.4% ~100% of the expected maximum load for guaranteed accuracy. Spoke-type or S-type load cells are common; accuracy class better than 0.5 grade (error ≤ ±0.5%).
2. Grips: Must match specimen type
   • Rubber / elastomer: Pneumatic flat grips or manual wedge grips (prevent slipping or sample crushing)
   • Plastic film / paper: Rubber-faced flat grips or line-contact grips
   • Metal sheet / bar: Wedge grips
   • Woven bag / geotextile: Wave-shaped grips
3. Extensometer: Required for precise gauge-length deformation measurement and elastic modulus calculation
   • Contact type: Knife-edge or pneumatic type; long gauge length (25 mm / 50 mm) for rubber
   • Non-contact type: Video extensometer, suitable for flexible materials and tests inside thermal chambers
4. Software: Real-time curve display, automatic result calculation, bulk report export. Some versions include pre-built templates for aging coefficient calculation.

6. Typical Technical Specifications (Electronic UTM)

1. Max Load: 100 N ~ 300 kN (key parameter for equipment selection)
2. Accuracy Class: Class 0.5 (error ≤ ±0.5%) or Class 1
3. Force Resolution: 1 / 500,000 or higher
4. Crosshead Speed Range: 0.001 ~ 500 /1000 mm/min, stepless adjustable
5. Speed Accuracy: ±0.5%
6. Displacement Resolution: 0.01 μm (rotary encoder)
7. Effective Tensile Stroke: 700 ~1200 mm (dual-space models have separate tensile & compression zones)
8. Data Sampling Rate: ≥100 Hz, up to 1000 Hz for high-end models

7. Selection & Operation Notes (Especially for Post-Aging Specimens)

1. Load range matching: Aged materials may turn brittle with reduced strength, yet the load range should still cover the maximum force before aging. Best accuracy is achieved within 20%~80% of full scale. If force values vary drastically before and after aging, use dual load cells or interchangeable sensors.
2. Grip selection matters: Aged rubber and plastics often become hard and brittle. Standard pneumatic grips may crush samples. Pressure-adjustable pneumatic grips or wave-face grips are recommended. Anti-slip grip faces are required for thin films.
3. Environmental chamber requirement: If high-temperature tensile tests (80℃,100℃) are required instead of only room-temperature testing for aged samples, a high & low temperature chamber is needed, plus compatible extensometers (video extensometer preferred).
4. Same-batch comparison principle: Pre-aging and post-aging specimens must be tested on the same machine with identical parameters, to eliminate system errors between different testers when calculating aging coefficient.
5. Consistent standard method: Tensile speed differs for rubber and plastics (e.g., 200 mm/min or 500 mm/min). Software must support speed switching. For GB/T 528 rubber tests, long-gauge extensometers are mandatory; crosshead displacement cannot be directly used to calculate elongation.
6. Regular calibration: Load, displacement, speed and extensometer shall be calibrated periodically. Load cells require calibration at least once per year.