Crack growth initiation

Fig. 10.5 (a-f) Normalized crack growth velocity A a/K] l versus normalized crack extension A = ball for transient SSC crack growth under constant / loading based on a model for crack growth by grain boundary cavitation (taken from Ref. 45). The parameters K, r A0, and Ass are normalized values of, respectively, the stress intensity factor (which is held constant), the crack growth initiation time, the initial crack velocity, and the steady-state crack velocity. 

The temperature dependence of the fracture toughness for the DGEBA/DDS networks is shown in Fig. 12. Crack growth initiation data are symbolized by the open circles, arrest data by the closed circles, and stable data by the half-filled circles. With the exception of the 1007F/DDS network, the initiation fracture toughnesses increase with the test temperature. In contrast, the arrest values exhibit no noticeable temperature sensitivity, and when observed, the stable fracture toughnesses are of the same magnitude as the arrest values. It is... 

Fracture of polymers, viscoelasticity, crack growth initiation, finite element simulation, crack closure integral, thermomechanical reliability, rate dependence... 

Fig. 6. Images of a loaded crack at 155°C (a) and at 107°C after crack growth initiation (b)...

A typical test load-deflection trace is shown in Fig. 3. In an ideal (elastic) case the load-deflection plot produces a straight line with an abrupt drop of load to zero at the instant of crack growth initiation (crack extension), enabling a straightforward identification of the force required to initiate crack growth. Identification of where the crack growth initiates becomes unclear where the load deflection plots produce curves. The standard recommendation (for consistency) is to define the load Pq that gives a 5% increase in compliance C (i.c.. a 5% decrease in stiffness) as a representative of the load value at the... 

Equation 48 ean be rearranged and integrated between an initial crack length and a final crack length af, where unstable crack growth initiates. 

The following specimens arc used to conduct the experimental measurements of compliance C vs. crack length a. and the load to crack growth initiation P. ... 

Figure 9.46a and b shows the crack growth initiation stress intensity factor, Ki, and SICC growth rate, da/disicc> function of the crack opening displacement (COD)... 

In principle, any body can be characterized by finding C(a) by measurement or computation. Thus, by detecting crack-growth initiation, the G value at fracture, termed Gc, can be found. Subsequent stability can be described in terms of dG/da and dR/da. Some more general aspects to the analysis are also important and, in particular, the fact that G may be described for any elastic body, not necessarily linear, as... 

The time to failure vs. applied stress diagrams are often used for empirical determination of the design life expectancy and stress level where SCC crack growth initiates (Xiscc)-... 

Figure 2.6 Crack growth initial 1 mm crack with BOMPa.m / at -33°C. (Reproduced with permission from Daubert Cromwell.)...

The present paper describes the main elements of a novel concept for lifetime and safety assessment of PE pressure pipes for arbitrary installation conditions based on modem methods of fracture mechanics. At the core of the proposed concept is the accelerated generation of so-called synthetic crack growth curves and corresponding material laws for crack growth initiation and slow crack growth for service-near temperature conditions without the use of stress cracking liquids. 

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