Crack Velocity Data Research Articles

Uncertainty in Minimum Lifetime Predictions

The uncertainty in minimum lifetime predictions based on crack velocity, static fatigue, and dynamic fatigue data is estimated by both a Monte Carlo simulation technique and the law of propagation of errors. The statistical analysis of typical data for glass shows that the 2 techniques give similar estimates for the uncertainty in minimum lifetime predictions as long as the coefficient of variation of the experimental parameters does not exceed ∼10%. The estimated uncertainty in the minimum lifetime is used to place confidence limits on failure predictions.

ChemInform Abstract: EFFECT OF TEST ENVIRONMENT ON STRESS‐CORROSION SUSCEPTIBILITY OF GLASS

AbstractDurch Messung dynamischer Ermüdungserscheinungen wird das Spannungskorrosionsverhalten von geschmirgelten, säurepolierten Natron‐Kalk‐ und Borosilicat‐ Gläsern in verschiedenen Lösungen (6n NaOH, destilliertem Wasser, 6n HCl) untersucht.

Effect of Test Environment on Stress‐Corrosion Susceptibility of Glass

The stress‐corrosion susceptibility of abraded and acid‐polished soda‐lime and borosilicate glasses in test environments of 6N NaOH, distilled water, and 6N HCI was measured by dynamic fatigue techniques. Dynamic‐fatigue data for these glasses agree well with crack‐velocity data for the water and 6N NaOH environments. The lack of agreement in the 6N HCI environment suggests that the failure mechanism for glass in HCI is not simply crack propagation by stress corrosion. The agreement in failure predictions based on strength and crack‐velocity data in 6N NaOH and water suggests that either set of data may be used for effective design calculations; however, caution should be used when basing strength calculations on crack velocity data in 6N HCI.

ChemInform Abstract: EFFECT OF SLOW CRACK GROWTH ON THE THERMAL‐STRESS RESISTANCE OF AN NA2O‐CAO‐SIO2 GLASS

AbstractDer Einfluß langsamen Rißwachstums auf die Einwirkung eines thermischen Schocks (Abschrecken in Wasser) wird an einem Na‐Ca‐silicatglas untersucht.

Effect of Slow Crack Growth on the Thermal‐Stress Resistance of an Na2O‐CaO‐SiO2 Glass

The effect of slow crack growth on the thermal‐shock resistance of an Na2O‐CaO‐SiO2 glass was studied. An analytic and numerical technique was developed to calculate the critical quenching temperature difference, ΔTc, of circular rods quenched in water from known crack velocity data. For rods of a specific radius and crack depth, ΔTc, was calculated to be 147°C, in favorable correspondence with experimentally observed values of 155° to 160°C. In the absence of crack growth, ΔTc was estimated to be 238°C, well in excess of the observed value and indicative of the significant effect of slow crack growth on thermal‐stress resistance. It is also shown that crack growth significantly extends the time‐to‐failure to a value much greater than the time of maximum thermal stress. A form of subcritical crack instability is predicted at stress intensity factors well below the critical stress intensity factor, at which catastrophic failure becomes inevitable over the duration of the transient thermal stress. It is suggested that, when all other factors are equal, the effect of slow crack growth on thermal‐stress resistance can be minimized by maximizing thermal diffusivity. It is also argued that surface‐compression strengthening will be more effective than reduction in flaw size in increasing thermal‐stress resistance. Recommendations are made for the design and selection of brittle materials subjected to thermal stress in stress‐corrosive environments.

Effect of Electrolyte pH on Crack Propagation in Glass

Crack velocities in glass in various acids, bases, and neutral solutions were studied using the double‐cantilever‐beam technique. Results are explained in terms of crack‐tip pH, which is controlled by the electrolyte at low crack velocities and by the glass composition at high velocities. The crack‐velocity data are consistent with the known dependence of strength on pH for soda‐lime silicate glass. Results also suggest that the slope of the universal fatigue curve should depend on surface pH.

Dynamic and Static Fatigue of Silicate Glasses

Fatigue of silicate glasses was studied using both static and dynamic tests. Static fatigue data for acid‐etched soda‐lime silicate glass determined at 74°F in 50 and 100% rh can be represented by a single universal fatigue curve (UFC). The UFC for acid‐etched glass does not lie on the UFC of Mould and Southwick, which was determined for abraded soda‐lime silicate glass; the acid‐etched glass was less susceptible to static fatigue. The susceptibility of acid‐etched soda‐lime silicate glass to static fatigue differed little from that of pristine E‐glass and fused SiO2 fibers. Dynamic fatigue data for soda‐lime, E, borosilicate, and fused quartz glasses agreed well qualitatively and quantitatively with fundamental crack velocity data for these glasses; the dynamic fatigue theory of Charles was used in the comparison. The theoretical implications of these results are discussed.

Stress Corrosion and Static Fatigue of Glass

Stress corrosion cracking of six glasses was studied using fracture mechanics techniques. Crack velocities in water were measured as a function of applied stress intensity factor and temperature, and apparent activation energies for crack motion were obtained. Data were consistent with the universal fatigue curve for static fatigue of glass, which depended on glass composition. Of the glasses tested, silica glass was most resistant to static fatigue, followed by the low‐alkali aluminosilicate and borosilicate glasses. Sodium was detrimental to stress corrosion resistance. The crack velocity data could be explained by the Charles and Hillig theory of stress corrosion. It is probable that stress corrosion of glass is normally caused and controlled by a chemical reaction between the glass and water.