SSRT: Slow Strain Rate Test
Definition:SSRT is also called constant extension rate tensile test, which is a standard testing method of extending materials at constant strain rate.
Explanation:SSRT is usually conducted in a climate chamber, in which the materials are exposed to given environment (temperature, fluid media, gas, etc.). It is mainly used to evaluate the environmental effects on the material fracture or stress corrosion cracking susceptibility. The important characteristic of SSRT is the low strain rate, e.g. in the range of 10-8 to 10-3 s-1. Materials show different crack susceptibilities depending on the applied strain rate. The susceptibility to cracking is evaluated by the stress-strain curves, the reduction of ultimate strength, elongation, and fracture head area due in the exposed media which is compared with the results in the inert condition.

In SFB, SSRT is employed to rank the susceptibility of twinning induced plasticity (→TWIP) steels to hydrogen induced cracking (→HIC). The applied strain rate has been 10-6 s-1, at which the investigated materials have high crack susceptibility. The figure reveals large reduction in ultimate stress and elongation values in X60Mn22 due to precharged hydrogen. In contrast, the Al added TWIP grade X60Mn17Al1.1 exhibits high resistance to HIC. Besides, the fracture surfaces from the failed specimens give abundant information concerning the damage mechanisms.
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Evaluating susceptibility to hydrogen induced cracking in high manganese steels by slow strain rate test.
SFB-Link:The investigated high manganese steels show different susceptibility to HIC. Slow strain rate tests with hydrogen pre-charged materials are performed to rank the crack susceptibility. The fracture surfaces are analyzed to study the underlying fracture mechanisms.
References:Standard ASTM G129-00 (2006), "Standard Practice for Slow Strain Rate Testing to Evaluate the Susceptibility of Metallic Materials to Environmentally Assisted Cracking", ASTM International.
X. Guo, W. Bleck, Delayed fracture in CrNi- and Mn-based austenitic steels: effect of austenite stability, hydrogen and tensile strain rate. Proceeding of Steel Hydrogen Conference, Gent, Belgium (2011) 197-208.