Extensometers for materials testing

Fracture Mechanics Clip-On Gages – Model 3541

For fracture mechanics studies, these COD gages are in compliance with standardized test methods, such as ASTM E1820 for determination of fracture toughness properties of metallic materials.

Epsilon’s experts have many years of experience in the field of fracture toughness and fracture toughness testing. Please feel free to call and discuss your application requirements with them at any time.

In-house frequency testing on small measuring range 3541 units (+2.5 mm/-1.0 mm) was successful to 150 Hz with a ±0.005 inch amplitude. At this level, there was no appreciable change in the noise level compared to lower frequencies.

For longer measuring range units (+10 mm/-1.0 mm), 50 Hz was the maximum frequency that could achieved without excessive noise levels.

Please feel free to contact Epsilon with your own high frequency questions and requirements.

With verifiable CALIBRATION SYSTEM ACCURACY and resolution sufficient to meet the requirements of ASTM fracture toughness gages, you can be assured that your COD gages will perform to your testing requirements.

The Model 3541 is designed for determination of fracture mechanics parameters such as JIC, KIC, R-curve, fatigue crack growth rate (da/dN), and testing to standards such as E1820, E399, E647, etc. These COD gages conform to the requirements of E1820 (the replacement for E813 and E1737) for JIC and R-curve determination. Special configurations are available to meet the requirements of ASTM E399 for fracture toughness (please consult the factory for these configurations). In addition, the modified groove design complies with E1820 tests where greater stability and accuracy results from the sharper groove root. Clip-on gages are used for a variety of fracture mechanics tests, including compact tension, arc shaped, disk shaped, bend specimens or other specimen geometries in compliance with ASTM and other standards organization’s test methods. Clip-on gages can be used directly on test specimens where the knife edges are integral with the test specimen or, alternately, with optional bolt-on knife edges mounted on the test specimen.

Model 3541 crack opening displacement gages are strain gaged devices, making them compatible with any electronics designed for strain gaged transducers. Most often they are connected to a test machine controller. The signal conditioning electronics for the extensometer is typically included with the test machine controller or may often be added. In this case the extensometer is shipped with the proper connector and wiring to plug directly into the electronics. For systems lacking the required electronics, Epsilon can provide a variety of solutions, allowing the extensometer output to be connected to data acquisition boards, chart recorders or other equipment.

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  • May be left on through specimen failure.
  • Full bridge, 350 ohm strain gaged design for compatibility with nearly any test system.
  • Fully enclosed gages are protected from accidental damage.
  • All standard units meet ASTM E1820, ISO 12135, and ISO 9513 Class 0,5 requirements for accuracy. A test certificate for ASTM E1820 is included. Models are available in 2.5 and 4.0 mm (0.10 and 0.15 inch) measuring ranges for ASTM E399 accuracy requirements. A test certificate for ASTM E399 is included with those models.
  • Sharp grooves per ASTM E1820 and E399 for improved stability when mounted.
  • Maximum operating frequency may be from 5 Hz to >200 Hz depending on COD gage and test apparatus configurations.
  • For da/dN testing or pre-cracking, where maximum frequency (>50 Hz) is required, minimum measuring ranges are recommended.
  • For KIC/JIC testing, maximum accuracy is achieved with the smallest measuring range and the largest gauge length that will perform the test.
  • Includes the Epsilon Shunt Calibration System for on-site electrical calibration.
  • Includes high quality foam lined case.

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Excitation: 5 to 10 VDC recommended, 12 VDC or VAC max.

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)

Cable: Integral, ultra-flexible cable, 2.5 m (8 ft) standard

Operating Force: 9 to 14 N (2 to 3 lbs), depending on model



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  • Connectors to interface to nearly any brand of test equipment
  • Available in special versions, including setups for narrow grips or severe environments
  • Bolt on knife edges

Special Models for Other Fracture Mechanics Testing

clip-on_gage_for_chevron_notch_bar_ASTM_E1304-Model_3541CODSpecial units are available for other fracture mechanics tests. For example, the photo to the right shows a gage for ASTM E1304, Standard Test Method for Plane-Strain (Chevron-Notch) Fracture Toughness of Metallic Materials. This example was produced for a 1 inch diameter bar, with 0.4 inches of measuring range. Its performance, design, and accuracy is an enhancement of the design recommended in E1304.


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Ordering Information

Click table options to configure

Gauge Length

mm or inches #
3.0 mm -003M 003M
5.0 mm -005M 005M
8.0 mm -008M 008M
10.0 mm -010M 010M
12.0 mm -012M 012M
20.0 mm -020M 020M
0.100 in -0010 0010
0.200 in -0020 0020
0.300 in -0030 0030
0.400 in -0040 0040
0.475 in -0047 0047
0.500 in -0050 0050

Measuring Range

extension #
+2.5 mm/-1.0 mm -025M¹ 025M
+4.0 mm/-1.0 mm -040M¹ 040M
+7.0 mm/-1.0 mm -070M 070M
+10.0 mm/-1.0 mm -100M 100M
+12.0 mm/-2.0 mm -120M 120M
+0.100”/-0.050” -100T¹ 100T
+0.150”/-0.050” -150T¹ 150T
+0.200”/-0.050” -200T 200T
+0.250”/-0.050” -250T 250T
+0.500”/-0.050” -500T 500T

Temperature Range

degrees #
-270 °C to 100 °C (-454 °F to 210 °F) -LT LT
-40 °C to 100 °C (-40 °F to 210 °F) -ST ST
-40 °C to 150 °C (-40 °F to 300 °F) -HT1 HT1
-40 °C to 200 °C (-40 °F to 400 °F) -HT2 HT2
-270 °C to 200 °C (-454 °F to 400 °F) -LHT LHT

Model Number:  3541_ _ _ __ _ __ _

Model Number:

3541_ _ _ __ _ __ _

Model 3541 Available Versions: The following combinations of gauge length and measuring range listed above are available as standard, except as noted. All are available in any temperature range listed. Other configurations may be available with special order; please contact Epsilon to discuss your requirements.

¹Available with special configuration to meet the requirements of ASTM E399. Please consult the factory.

Example: 3541-0050-200T-LT: 0.50 inch gauge length, +0.20 inch measuring range, low temperature option (-454 °F to 210 °F)


If your unit is in need of service, calibration or repair, initiate the RMA process with us and we will be happy to assist.

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