3541 Fracture Mechanics Clip-On Gages to Determine Fracture Toughness of Metallic Materials

The Model 3541 has been developed to determine fracture mechanics parameters like KIC, JIC fatigue crack growth rate (da/dN), R-curve, and testing to standards such as E399, E647, E1820, etc. These COD gages comply with the requirements of E1820 (the replacement for E1737 and E813) for R-curve and JIC determination.

Special configurations are available to meet the ASTM E399 requirements for fracture toughness (customers can check with the factory for these configurations). Additionally, the modified groove design is in compliance with E1820 tests where higher accuracy and stability results from the sharper groove root.

Clip-on gages are used for a range of fracture mechanics tests, including disk shaped, arc shaped, compact tension, bend specimens, or other specimen geometries that comply with ASTM and other standards organization’s test methods. Customers can use clip-on gages directly on test specimens where the knife edges are integral with test specimen or with optional bolt-on knife edges mounted on the test specimen.

As the Model 3541 extensometers are strain gaged devices, they are compatible with any electronics developed for strain gaged transducers. These extensometers are often connected to a test machine controller. The extensometer’s signal conditioning electronics is normally integrated with the test machine controller or may often be added.

In this case, the extensometer is supplied with appropriate wiring and connector to plug directly into the electronics. Epsilon can provide a range of solutions for systems that lack the required electronics, enabling the extensometer output to be connected to chart recorders, data acquisition boards, and other equipment.

  • Experts from Epsilon have many years of experience in the field of fracture toughness and fracture toughness testing. Customers can call and discuss their application needs with Epsilon at any time.
  • In-house testing on small measuring range 3541 units (+2.5/-1.0 mm) were successful to 150 Hz with a ±0.005” amplitude. At this level, there was no significant change in the noise level compared to lower frequencies.
  • The maximum frequency for longer measuring range units (+10 mm/-1.0 mm) was 50 Hz and this could be attained without excessive noise levels.
  • Customers can contact Epsilon with their own high frequency questions and requirements.
  • COD gages will perform to a customers’ testing requirements to meet the needs of ASTM fracture toughness gages with verifiable calibration system accuracy and resolution.


The key features of the 3541 fracture mechanics clip-on gages are as follows:

  • Full bridge, 350 ohm strain gaged design for compatibility with almost any test system.
  • Minimum measuring ranges are recommended for da/dN testing or pre-cracking, where maximum frequency (>50 Hz) is required.
  • Maximum accuracy can be attained with the smallest measuring range and the largest gauge length for KIC/JIC testing.
  • Fully enclosed gages protect from accidental damage.
  • Includes high–quality, foam lined case.
  • Depending on COD gage and test apparatus configurations, maximum operating frequency may be from 5 Hz to >200 Hz.
  • May be left on through specimen failure.
  • All standard units meet the requirements of ASTM E1820, ISO 12135, and ISO 9513 Class 1 for accuracy. A test certificate for ASTM E1820 is also included. For ASTM E399 accuracy requirements, special models are available in 2.5 and 4.0 mm (0.10 and 0.15”) measuring ranges, and with these models, a test certificate for ASTM E399 is included.
  • Sharp grooves complying with ASTM E1820, E813, and E399 enable improved stability when mounted.


The main specifications of the 3541 fracture mechanics clip-on gages are as follows:

  • Cable: Integral, ultra-flexible cable, 2.5 m (8 ft) standard
  • Excitation: 5 to 10 VDC recommended, 12 VDC or VAC max
  • Operating Force: 9 to 14 N (2 to 3 lbs), depending on model
  • Output: 2 to 4 mV/V, nominal, depending on model
  • Linearity: ≤0.15% of full scale measuring range
  • Temperature Range: Standard (-ST) is -40 °C to +100 °C (-40 °F to +210 °F)


The following options are available with the 3541 fracture mechanics clip-on gages:

  • Shunt Calibration
  • Connectors to interface to nearly any brand test equipment
  • Bolt on knife edges
  • Available in special versions
  • Severe environment versions available

3541 Fracture Mechanics Clip-On Gages to Determine Fracture Toughness of Metallic Materials


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