Environment-sensitive cracking evaluate

Evaluation of susceptibility to environment-sensitive cracking encounters the usual problems of attempting to simulate in the laboratory conditions that reflect service performance. Two approaches are usually taken, both of which must provide a final consistent prediction of service behavior. One of these approaches is to duplicate as closely as... 

Lisagor, W. B., Influence of Precracked Specimen Configuration ind Starting Stress Intensity on the Stress Corrosion Cracking of 4340 Steel, Environment Sensitive Fracture Evaluation and Comparison of Test Methods, ASTM STP 821, S. W. Dean, E. N. Pugh, and G. M. UgiEmslQf, Eds., ASTM International, West Conshohocken, PA, 1984, pp. 80-97. 

Observations on Stress Corrosion Cracking Initiation Sites in Carbon Steel Conference Corrosion 94, Paper No. 234 NACE, Houston, TX, USA, 1994, 13 S. [4 Van der Sluys, W. A. DeMiglio, D. S. Use of a Constant Delta Test Method in the Investigation of Fatigue Crack Growth in 288 deg C Water Environments. Conference Environment-Sensitive Fracture Evaluation and Comparison Test Methods, Gaithersburg, Maryland, USA, 26-28 Apr. 1982... 

Figure 47 shows taken from Equation 20 versus Vj. It shows that S. is quite sensitive to Vp and is therefore a good means to evaluate v, with the numerical values of Fig. 47. It can be estimated that the tensile modulus E of the bulk PMMA is not affected by the very low pressure toluene gas environment during the short duration of the experiment. The optical craze index in PMMA in air without load is known as n = 1.32, which corresponds to v = 0.6. From the optical interferometry, it is known that the craze just before breakage is twice as thick as unloaded, (v, = 0.3) and hence using Lorentz-Lorenz equation its optical index is n = 1.15. From Figs. 46 and 47 it can be concluded that the bulk modulus around the propagating crack is about 4400 MPa, which is a somewhat high value, in view of the strain rates at a propagating crack tip (10 to s" ). Using the scatter displayed in Fig. 46, it can be concluded from Fig. 47 that the fibril volume fraction is constant, v = 0.3, within a scatter band of 0.08, and is therefore not sensitive to the toluene gas.

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