Testing and mesoscale modelling of hydrogen assisted cracking of magnesium

To rationalise the results of stress corrosion cracking tests on smooth tensile specimens of a magnesium alloy, performed as constant extension rate tensile tests, a mesoscale fibre bundle model is employed in which the material being tested is represented by a bundle of parallel fibres. The effect of hydrogen embrittlement on the stress-strain curves measured at various strain rates is simulated by assuming that the hydrogen is generated in localised corrosion pits and subsequently diffuses into the bulk, thereby reducing the strain-to-failure of individual fibres. The stress-strain curves obtained from these simulations show the same strain rate effect as was experimentally observed.     

Quantitative fractography of 2205 duplex stainless steel after a sulfide stress cracking test

This paper presents the results of SSC (Sulfide Stress Cracking) investigations of duplex stainless steel 2205 resistance to cracking failure under the combined action of tensile stress and aqueous environments containing hydrogen sulfide according to the NACE Standard TM0177-96. The investigations were carried out on 9 test pieces that were loaded with a tensile stress ranging from 1.02 × the yield stress (YS) to 0.72 × YS. The tests were terminated either when the test specimen failed or after 720 h (30 days) – whichever occurred first – in accordance with the standard requirements. Only two of the specimens examined, one loaded with 1.02 × YS and the second one with 0.72 × YS, failed during the test. The resulting fracture surfaces were subjected to qualitative and quantitative fractographic examinations. Quantitative fracture analysis included an estimation of such parameters as linear roughness index R_L, fractal dimension D_F and overlap index O_L.     

Threshold stress intensity factor and crack growth rate for stress corrosion cracking of simulated heat affected zone in caustic solution

The threshold stress intensity factor for stress corrosion cracking (K_Iscc) of the simulated heat affected zone (HAZ) of mild steel in caustic solution has been determined using circumferential notch tensile (CNT) technique. The HAZ microstructure produced upon manual metal arc welding of grade 250 steel was simulated over a length of 35 mm of CNT specimens, using a thermo-mechanical simulator. Inter- and trans-granular stress corrosion cracking has been confirmed using a scanning electron microscope. The results presented here validate the ability of CNT technique for the determination of K_Iscc of HAZ and Base metal. Crack growth rates have also been determined using CNT technique. Further, the effect of microstructures on K_Iscc and crack growth rate is discussed in the present study. The determined K_Iscc of Base metal and simulated heat affected zone in 30% caustic solution is 24 and 45 MPa m^1/2, respectively.