Aqueous environment stress

Resistance to stress-corrosion cracking Commercially pure titanium is very resistant to stress-corrosion cracking in those aqueous environments that usually constitute a hazard for this form of failure, and with one or two exceptions, detailed below, the hazard only becomes significant when titanium is alloyed, for example, with aluminium. This latter aspect is discussed in Section 8.5 under titanium alloys. 

Fig. 8.52 Initial stress intensity factor and time to failure for a susceptible titanium alloy tested in a neutral aqueous environment under plane strain conditions...

The influence of water and the phosphoric acid solution becomes clearly demonstrated when one compares the TTF results obtained in air, water and a phosphoric acid solution,. At low stresses (0.6 MPa), hydrolysis, i.e. chemical bulk degradation of the copoly(ester ester) by water and the phosphoric acid solution, is responsible for the failure. However, at higher stress levels, the significant difference in TTF between the aqueous environment and air points to the existence of ESC. The reduced lifetime in the phosphoric acid solution compared to water suggests an increased effect of acid. 

At the high stress levels, 6 to 7 MPa, there is almost no difference between the TTF in water and phosphoric acid solution. There is, however, a significant difference in TTF between the aqueous environment and air. At 6 MPa the TTF in the fluids is less than 5% of the TTF in air. This is a considerable difference but it corresponds with only a small (less than 1 MPa) decrease in tensile strength. 

For reliable high-temperature potentiometric studies, the measured open-circuit potential should be stable and reproducible within a few millivolts or less. Similar to the low-temperature electrochemical measurements, both the indicator and reference electrodes should be used in devising a high-temperature potentiometric cell. Both the electrochemical probes should be resistant to chemical degradation and pressure (mechanical) stress in high-temperature aqueous environment. The development of suitable indicator and reference electrodes that can reliably... 

Virtually all polymeric materials, not just those designed to function in an aqueous environment, will be exposed to environmental water at some stage of their service lives, and water imbibition can have adverse effects on their physical and mechanical properties.Although the polymer itself may be able to tolerate such degradation, if water is absorbed at the interfaces of high moduli materials, substantial swelling pressures and the generation of unwanted stresses can be anticipated. Combined STRAFI and MRM studies of some commercial thermoset adhesives used in the construction industry have... 

Fig. 7.113 Dependence of stress-corrosion-crack-growth rate on stress intensity of a high-strength aluminum alloy in several aqueous environments. Crack orientation TL (stress in transverse direction crack propagation in longitudinal direction). Source Ref 159...

Prior to the 1960s, stress corrosion cracking and corrosion fatigue were principally under the purview of corrosion chemists and metallurgists, and the primary emphasis was on the response of materials in aqueous environments (e.g., sea/salt water), particularly for SCC because of the relative ease of experimentation. Much of the attention was devoted to the understanding of electrochemical reactions that are associated with metal dissolution, crack nucleation, and time-to-failure under a... 

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