Time-dependent crack growth

The figure illustrates type A true CF growth pattern in which the synergistic interaction between cyclic plastic deformation and environment produces cycle- and time-dependent crack growth rates. Tme CF influences cychc fracture, even when the maximum stress intensity factor in fatigue is less than A iscc-... 

The environment in which an article is used may influence bond durability (see also Durability fundamentals). Atmospheric ozone can cause time-dependent crack growth in vulcanized elastomers in addition, ozone can induce failure at a bond with certain bonding agents. Although water is only slightly soluble, it can permeate elastomers by an osmotic mechanism induced by salt-Uke impurities. As a result, the uptake in salt water is generally less than that in pure water. Rubber to metal bond failure has been found to occur in a time-dependent manner under salt water in the presence of electrochemical activity but much more slowly, if at all, in its absence (see also Cathodic disbondment). In the absence of imposed electrochemical activity, effects are likely to depend particularly on the metal used and its corrosion resistance. Provision of a bonded rubber cover layer over all metal surfaces subject to immersion is likely to enhance bond durability. 

Consequences of time-dependent crack growth on the evolution of initial flaw distributions. 

The time dependent crack growth resulting from cyclic loading can be determined by... 

Time-dependent crack growth may also arise when solvents are being absorbed into the adhesive layer [10,46,49]. In this case, the correlation between crack growth rates and stress intensity follows the behavior shown schematically in Fig. 5c. The initial rising portion of the curve is also a power law. Diffusion effects... 

The development of linear elastic fracture mechanics is given with a special emphasis on its application to the testing of polymers. The modelling of crazes and plastic zones is discussed and then developed to describe time-dependent crack md craze growth, including crack stability phenomena. 

Consequently, the parametric response of a material to corrosion fatigue loading may be quite complex, and the description of corrosion fatigue behavior must take into account not only the level of mechanical loading but also the load frequency and the shape of the cycles. Results should be expressed in terms of time related crack growth rate (dfl/dr) rather than the more frequently used cycle dependent crack growth rate (da/dn). 

Eracture mechanics concepts can also be appHed to fatigue crack growth under a constant static load, but in this case the material behavior is nonlinear and time-dependent (29,30). Slow, stable crack growth data can be presented in terms of the crack growth rate per unit of time against the appHed R or J, if the nonlinearity is not too great. Eor extensive nonlinearity a viscoelastic analysis can become very complex (11) and a number of schemes based on the time rate of change of/have been proposed (31,32). 

Sintered sihcon carbide retains its strength at elevated temperatures and shows excellent time-dependent properties such as creep and slow crack growth resistance. Reaction-bonded SiC, because of the presence of free sihcon in its microstmcture, exhibits slightly inferior elevated temperature properties as compared to sintered sihcon carbide. Table 2 (11,43) and Table 3 (44) show selected mechanical properties of sihcon carbide at room and elevated temperatures. 

In the model leading to Eq. 1 and Eq. 2, not only the elastic and plastic flow properties, but also Of must also be assumed to be time-dependent for the results to be consistent with experimental data obtained at different crack growth rates [52]. To illustrate the consequences of this, the time-dependence is grouped together in a single power law term, so that Eq. 1 becomes ... 

DF1C velocities in RBMK TMO-1 samples, depending on temperature are 3-5 times lower than in CANDU pressure tube material. Crack growth in RBMK pressure tube material occurs at larger increments of the crack front. Striation spacing increases with increase in test temperature and appear to be larger in the specimens of the RBMK material than in the CANDU material. 

In this case, crack growth is essentially a time-dependent process and there is no unique method available for characterizing fatigue fracture under extensive... 

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