Fast fracture mechanisms

The testing consisted of a series of fast-fracture mechanical testing tensile and interlaminar, as well as durability testing 30 Hz fatigue and creep tests. All testing was done per ASTM standards. The mechanical testing was done either at room temperature or at 982 C. All the durability testing was done at 982°C. 

Based on our observation, a membrane degradation and failure mechanism under the RH cycling, a pure mechanical effect is theorized as the following sequence electrode-microcracking- - crazing initiation at the electrode/electrolyte interface - crack growth under stress cycling- -fast fracture/instability. 

A molecular transition model involving the -relaxation in PMMA has been first put forward by Johnson and Radon They explained the transition in crack speed behavior based on a correlation between the temperature dependence of a time to failure inferred from fracture experiments and the temperature variation of the reciprocal frequency of the P-relaxation peak. They thus assumed that the crack transition is caused when the P-process is fully active. Also the fracture mechanics parameter K, governing the transition from slow to fast crack growth, shows a time and temperature dependence equal to that of the p-transition... 

SEM is a fast method for obtaining detailed morphological information for different polyolefins. This method is valuable tool for the analyses of polyolefins, and it is extensively used for the analyses of failure and fracture mechanics, shape and particle size, filler dispersion, and orientation in polymer matrices [90]. A few nanometer spatial resolution and a large depth of field can be obtained by SEM, and it can work up to 100 times that of an optical microscope in some cases. From these feamres, information about topography of the sample surface can be obtained necessary for a deeper understanding of the interaction between the substrate and the surface treatment [91]. 

The mechanisms responsible for fracture in structural ceramics at elevated temperatures have been reviewed [154]. Sensitivity to flaws or microstructural inhomogeneities which nucleate microcracks are among the failure mechanisms. The flaws which control failure under creep conditions are different from those responsible for fast fracture at room temperature. A common feature is the development of cracks through gradual damage accumulation, depend on the microstructure. The role of cracks in the deformation and fracture behavior of polycrystalline structural ceramics have been reviewed [155]. 

TABLE 5. Mechanical Ptoperties-Room Temperature 0/90 Fast Fracture Data... 

VI.6] ASSOCIATION FRANgAISE POUR LES REGLES DE CONCEPTION ET DE CONSTRUCTION DES MATERIELS DES CHAUDIERES ELECTRO-NUCLEAIRES (AFCEN), French Nuclear Construction Code RCCM Design and Construction Rules For Mechanical Components of PWR Nuclear Facilities, Subsection Z, Appendix ZG, Fast Fracture Resistance, Framatome, Paris (1985). 

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