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Stress Relaxation Tester

Stress Relaxation Tester - TT-SR Series

ASTM E328, ISO 15630-3


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

Technical Specifications







ASTM E328, ISO 15630-3






Measuring Range

8 – 200kN

12 – 300kN

16 – 400kN

20 – 500kN

Load Resolution





Load Accuracy


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


Horizontal Span


Ball Screw Stroke


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)



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