Fracture behavior

Since the Broeklehurst review, most investigations of the fraeture behavior of graphites have foeused on nuelear graphites and many have employed LEFM to characterize fracture behavior [38-47]. The following general conelusions can be drawn from is work ... 

Fracture Behavior of Small Flaws in Nuclear Graphites... 

Thus, if the ratio AT//3 is constant, then the behavior shown in Fig. 12 could be described by the net solution. For many polymers, the characteristic ratio is around 7-10, the ratio Mo/j is the molecular weight per backbone bond (ca. 30-50) and will not vary extensively, b = 1.54 A and the density is about 1 g/cm such that the parameter is nearly constant. Since K is not very sensitive to the polymer properties, Eq. 6.5 is considered to describe the observed fracture behavior shown in Fig. 12. However, the data are not expected to fall on the straight line due to differences in K and j6 for each polymer. As a specific test case, consider... 

Herbert T. Corten, Micromechanics and Fracture Behavior of Composites, in Modem Composite Materials, Lawrence J. Broutman and Richard H. Krock (Editors), Addison-Wesley, New York, 1967, pp. 27-105. 

Table 7-17 Example of a simplified readout for TPs toughness or fracture behavior Izod impact test results...

The fracture behavior can be attributed to strain softening [91] in the deformation zone [92, 93] or to stress-activated devitrification [89, 96]. The strands are comparatively free to move in the strain softened regions of the deformation zone. The van der Waals interaction between adjacent strands is greatly reduced and the clearence between molecular segments is enlarged. 

Hannah, R.R., Harrington, L.J. and Potter, J.S. Jr. "Post Fracturing Behavior of Fracturing Gels and Its Influence on Fracture Closure and Proppant Distribution," SPE paper 9331, 1980 Annual Fall Technical Conference and Exhibition of SPE of AIME, Dallas, September 21-24. 

Uarpinski, N.R. "In Situ Measurements of Hydraulic Fracture Behavior," Sandia Report SAND83-1826, July 1985. 

The mass fraction crystallinity of molded PHB samples is typically around 60%. As shown in Table 3, PHB resembles isotactic polypropylene (iPP) with respect to melting temperature (175-180°C), Young s modulus (3.5-4 GPa) and the tensile strength (40 MPa). In addition, the crystallinity of iPP is approximately 65% [18]. Accordingly, the fracture behavior of PHB may be anticipated to be tough at room temperature. Molded PHB samples do indeed show ductile behavior, but over a period of several days at ambient conditions, they slowly become more brittle [82, 85, 86]. Consequently, the elongation to break of the ultimate PHB (3-8%) is markedly lower than that of iPP (400%). 

Fig. 12A,B The relation between the aluminum content and the fracture behavior of the SA fiber...

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