Fracture characteristics

Microstructurc. Crystal size, porosity, and impurity phases play a major role in fixing the fracture characteristics and toughness of an abrasive grain. As an example, rapidly cooled fused aluminum oxide has a microcrystalline stmcture promoting toughness for heavy-duty grinding appHcations, whereas the same composition cooled slowly has a macrocrystalline stmcture more suitable for medium-duty grinding. 

A proposed mechanism for toughening of mbber-modifted epoxies based on the microstmcture and fracture characteristics (310—312) involves mbber cavitation and matrix shear-yielding. A quantitative expression describes the fracture toughness values over a wide range of temperatures and rates. 

One way of looking at the fracture characteristics of a ductile material is by measuring the amount of plasticity at a crack tip prior to crack propagation (Fig. 8.84). One test which measures this is the crack-tip opening displacement (CTOD), 5. Wells has found that 6 can be related to the strain energy release rate, G, by the formula ... 

A more universal fracture characteristic for use with ductile materials is the J integral . This is similar to CTOD but relates a volume integral to a surface integral and is independent of the path of the integral it can be classed as a material property. The J integral can also be used to predict critical stress levels for known crack lengths or vice versa. 

To ensure quality control material suppliers and developers routinely measure such complex properties as molecular weight and its distribution, crystallinity and crystalline lattice geometry, and detailed fracture characteristics (Chapter 6). They use complex, specialized tests such as gel permeation chromatography (2, 3), wide- and narrow-angle X-ray diffraction, scanning electron microscopy, and high-temperature pressurized solvent reaction tests to develop new polymers and plastics applications. 

Fig. 8-55 Overview of RPs directional properties (a) polar directional, (b) different fiber orientations and tensile fracture characteristics, and (c) stress vs. strain diagrams of RPs.

External mechanical damage, and all dents affecting acetylene girth welds or seam welds that are known to exhibit brittle fracture characteristics, may be repaired with a full encirclement steel sleeve with ends welded to the pipe. 

Liu Y-N, Li M, Gu Y, ZhangX, Zhao J, Li Q, et al. The interfacial strength and fracture characteristics of ethanol and polymer modified carbon nanotube fibers in their epoxy composites. Carbon. 2013 Feb 52(0) 550-8. 

Microstruvture. Cry stal size, porosity, and impurity phases play a major role in fixing the fracture characteristics and toughness of an abrasive grain. 

TRANSITION TEMPERATURE. 1. An arbitrarily defined temperature within die temperature range in which metal fracture characteristics determined usually by notched tests are changing rapidly such as from primarily fibrous (shear) to primarily crystalline (cleavage) fracture. 

Furthermore, the fracture characteristics will be defined in the frame of linear elastic fracture mechanics (LEFM), assuming a purely elastic response of the material (stress proportional to infinitesimal strains). However, LEFM can be extended to materials that exhibit inelastic deformation around the crack tip, provided that such deformations are confined to the immediate vicinity of the tip [25]. 

It is worth noting that most of the fracture characteristics reported in this paper correspond to stable crack propagation. 

Several kinds of specimen geometries have been used to determine fracture characteristics. Only two are considered here and are schematically shown in Fig. 9 information on others can be found in [4]. 

In this section, the temperature and MW dependencies of the fracture characteristics, K c and Gic, obtained by three-point bending measurements, are examined [53]. 

The fracture characteristics, K c and Gic, as a function of temperature are shown in Fig. 81. Furthermore, on this figure are shown the results, obtained for BPA-PC with two different MWs, BPA-PC(18) and BPA-PC(31), whose the characteristics are given in Table 7. 

MW independence of the fracture characteristics over a broad low temperature range. Over this range, JCic and Gic exhibit a slight decrease with increasing temperature. 

Fig. 13.20 Schematic representation of the impingement and the subsequent flows in the weldline region gray areas indicate cold regions of the melt dashed lines denote regions undergoing extensional flow. [Reprinted by permission from S. Y. Hobbs, Some Observations on the Morphology and Fracture Characteristics of Knit Lines, Polym. Eng. Sci., 14, 621 (1974).]...

Fracture characteristics observed from line pipe through the transition temperature.. 119... 

---