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LCF Testing in High Pressure Hydrogen Environments

Low cycle fatigue (LCF) testing in high pressure hydrogen environments has been developed at TWI as part of a Single Client Project.

Results allow the Strain-Life fatigue relationship to be determined for materials whilst subjected to hydrogen embrittling environments. Particularly useful for the aerospace, automotive and power generation industries, as the demand for hydrogen as an energy resource increases.

Test Summary

Tests follow the guidelines of ASTM E606 and allow for the elastic-plastic cyclic response of materials to be characterised at pressures up to 450bar and temperatures between ambient and 80°C.

Bespoke grips have been designed and manufactured to verify specimen alignment to ASTM E1012. Thus minimising the risk of buckling and ensuring accurate and repeatable strains are applied to each specimen.

Tests are run in strain control using a Class 1 contact extensometer. A variety of waveforms, frequencies (ie strain rates) and stress-ratios can be applied at total strain ranges typically up to 2%. 

Results

Test results obtained from each test include the:

  1. Stress-strain hysteresis loops;
  2. Fatigue crack initiation life;
  3. Fatigue crack propagation life;
  4. Peak stresses and strains, modulus and plastic and elastic strains for each cycle.

 

The hysteresis loops, Figure 1, provide information on the work hardening or softening behaviour of the material.

While the stabilised peak stresses and strains and the total number of cycles to failure data enable the Basquin-Manson-Coffin Strain-Life Equation constants to be determined (Figure 2).

Figure 1. Hysteresis loops for cycles 1 to 4 showing work hardening behaviour
Figure 1. Hysteresis loops for cycles 1 to 4 showing work hardening behaviour
Figure 2. Basquin-Manson-Coffin Strain-Life Equation
Figure 2. Basquin-Manson-Coffin Strain-Life Equation

For more information please email:


contactus@twi.co.uk