Isothermal Stress Relaxation Tester for Reinforcing and Prestressing Steel
Isothermal Stress Relaxation Tester – Precision Testing to ASTM E328 & ISO 15630-3 Standards
An Isothermal Stress Relaxation Tester is a specialized instrument used to evaluate the stress relaxation behavior of metallic materials under constant strain at a fixed temperature over a defined period of time. This type of testing is essential for assessing material performance in long-term load-bearing applications, such as in prestressed steel reinforcement, wire, strand, and bars.
Torontech’s Isothermal Stress Relaxation Testers are designed to perform accurate and repeatable measurements in accordance with international standards ASTM E328 and ISO 15630-3, making them ideal for both quality control laboratories and R&D environments.
Torontech's Stress Relaxation Tester - TT-SR Series is used to determine stress-relaxation of metals, such as pre-stressed concrete strand, pre-stressed concrete bar, steel rope...etc. To determine stress-relaxation of a material the specimen is deformed a given amount and decrease in stress is recorded over prolonged period of exposure at constant elevated temperature.
ASTM E328 Standard Test Methods for Stress Relaxation Tests for Materials and Structures. This method covers the standard test methods for stress relaxation tests for materials and structures. Stress relaxation in a material is an important characteristic to consider when designing with mechanical fasteners that must hold with a permanent tightness. Long term failure of fastener might occur if stress relaxation is not considered.
According to ASTM, applications that are often tested with this standard include, bolted of riveted assemblies, press of shrink-fit components, rolled-in tubes, gaskets tightness, constraining force of springs, and stability of wire in pre-stressed concrete. This test is also valid for measuring stress relaxation of a material an area of high stress concentration. The test environment must be highly controlled to prevent changes to the material due to environmental conditions.
- Real-time display load versus time, temperature versus time and relaxation rate versus time curves
- Automatic calculate 1000 hours tensile stress relaxation rate.
- High-precision temperature recorder attached to record the influence of room temperature variations
- Servo-controlled drive system ensures the high precision load/displacement/strain close-loop control as well as low noise
- User configurable test methods and customizable report template
- Self-alignment design on specimen anchorage to ensure the high accuracy
- Patent calibration system is mounted on machine to calibrate not only the load cell but also the whole system without disassembly the load cell from machine
What Is Stress Relaxation?
Stress relaxation occurs when a material subjected to constant strain experiences a gradual decrease in stress over time. This phenomenon is particularly critical in applications where mechanical tension must be maintained over extended durations, such as in bridge cables, pre-stressed concrete, or steel reinforcement used in construction.
Key Applications:
- Prestressed concrete reinforcement (steel strand and bar)
- Wire and cable stress performance analysis
- Evaluation of long-term mechanical stability of metals
- R&D material development and certification testing
Compliance Standards:
- ASTM E328 – Standard Test Methods for Stress Relaxation Tests for Materials and Structures
- ISO 15630-3 – Steel for the reinforcement and prestressing of concrete – Test methods – Part 3: Prestressing steel
Features of Our Isothermal Stress Relaxation Tester:
- High-precision load and displacement measurement
- Stable isothermal environment with precise temperature control
- Long-duration test capability (up to 1000+ hours)
- Fully automated data logging and result analysis
- Optional extensometers for precise strain control
Our system ensures that test specimens are subjected to constant strain while maintaining a stable temperature, enabling accurate monitoring of the stress decay curve over time.
| Model | TT-SR-200 | TT-SR-300 | TT-SR-400 | TT-SR-500 |
| Standards | ASTM E328, ISO 15630-3 | |||
| Capacity | 200kN | 300kN | 400kN | 500kN |
Measuring Range | 8 – 200kN | 12 – 300kN | 16 – 400kN | 20 – 500kN |
| Load Resolution | 7N | 10N | 12N | 15N |
| Load Accuracy | ±1% | |||
| Load Measuring Accuracy | ±0.1% of reading to 1/100 of load weighing system capacity meets or exceeds the requirements of the following standards: ISO 7500-1, EN 10002-2, ASTM E4, JIS B7721 | |||
| Creep of Load Cell | 30 minutes ≤ 0.02% | |||
| Position Accuracy | ±0.5% | |||
| Horizontal Span | 1850mm | |||
| Ball Screw Stroke | 100mms | |||
| Loading Speed | 100 - 5000N/S | |||
Speed Accuracy | Set speed＜0.05% - Max. Speed: ±1%, set speed ≥0.05% - Max. speed:±0.5% | |||
Temperature Accuracy | Temperature sensor resolution: 0.1℃, temperature sensor accuracy: ±0.3℃ | |||
Position Measurement Accuracy | ±0.01 of reading or 0.0001 mm, whichever is greater | |||
| Specimen Dimensions | ||||
PC Strand (mm) | Φ12.7 - Φ15.24 | Φ12.7 - Φ15.24 | Φ12.7 - Φ15.24 | Φ15.2 - Φ21.8 |
PC Wire (mm) | Φ3 - Φ9 | Φ3 - Φ9 | Φ3 - Φ9 | Φ3 - Φ9 |
PC Bar (mm) | Φ7 - Φ18 | Φ7 - Φ18 | Φ7 - Φ18 | Φ7 - Φ18 |
| Power Supply | Please specify voltage and frequency before placing the order. Standard optional voltages 3ph, 220/380VAC, 50-60 Hz, Power must be free of spikes and surges exceeding 10% of the nominal voltage. | |||
| Operating Temperature | 0 to +38°C (+32 to +100°F) | |||
| Humidity Range | 10% to 90% non-condensing | |||
| Storage Temperature | -40 to +66°C (-40 to +150°F) | |||
| Machine Dimension | 1950 × 540 × 1015mm (L × W × H) | |||
| Weight | 1400kg | |||
| Standard Configurations | Main unit | Control unit | ||
| Servo systems: driver and motor | Speed reducer | |||
| Synchronous toothed belt | Temperature recorder | |||
| Anchorage | Computer | |||
| ToronSoft | Printer | |||
| Linear gauge extensometer | ||||
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| Calibrate load cell on machine. There is no need to remove load cell from testing machine and calibrate it on other machines, the master load cell is available to be installed next to the machine load cell for calibration. | Anchorage | |||
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