Open modes

A crack in a body may grow as a result of loads appHed in any of the three coordinate directions, lea ding to different possible modes of failure. The most common is an in-plane opening mode (Mode I). The other two are shear loading in the crack plane (Mode II) and antiplane shear (Mode III), as defined in Figure I. Only Mode I loading is considered herein. 

Attention will be restricted to the strain-energy-release rate for the opening mode. This mode occurs for the plate with a centrally located crack of length 2a under load P in Figure 6-11. 

The symmetric stress-intensity factor k, is associated ith the opening mode of crack extension in Figure 6-10. The skew/-symmetric stress-intensity factor l<2 is associated ith the fonward-shear mode. These plane-stress-intensity factors must be supplemented by another stress-intensity factor to describe the parallel-shear mode. The stress-intensity factors depend on the applied loads, body geometry, and crack geometry. For plane loads, the stress distribution around the crack tip can always be separated into symmetric and skew-symmetric distributions. 

The above discussion has assumed that the crack is loaded in mode 1 (the crack opening mode, with a tensile stress normal to the plane of the crack). Hydrogen has relatively little effect in modes II or III, as these generate shear stresses at the crack tip, rather than tensile stresses, and the shear behaviour of steels is relatively little affected by hydrogen, presumably because dilation of the lattice at the crack tip (which does not occur in modes II and III) is required for hydrogen accumulation. 

Otofuji (1996) proposed a double door opening mode with a fast spreading rate of 21 cm/year for the evolution of the Japan Sea, caused by the injection of asthenosphere with a low viscosity beneath the Japan Sea area. 

Fig. 19 Ring opening modes dicarbene (a), 7t-adsorbed olefin (b), metallocyclobutane (c). Adapted from ref. 49.

The second dimer-opening mode observed resulted when a surface atom diffused to the site of a surface dimer and bumped a nearby atom into the center of the dimer. This mechanism resulted in atoms which occupied lattice sites, and produced a surface dimer which remained open for the course of the simulation. Because the final atomic positions corresponded to lattice sites, and because a high rate of surface diffusion was required to produce the bump , this mechanism was associated with the high-temperature epitaxial growth mode identified by Gossmann and Feldman. 

Fig. 3.29. Modes of interlaminar crack propagation (a) Mode I opening mode (b) Mode II sliding shear...

The EDT specimen shown in Fig 3.34(a) has been used to characterize the interlaminar failure of the composite in opening mode I (Whitney and Knight, 1985). The straight-sided tensile specimen has starter cracks placed along the free edges at the laminate mid-plane (Fig 3.34(a)). Due to the low interlaminar shear... 

One of the most important properties which control the damage tolerance under impact loading and the CAI is the failure strain of the matrix resin (see Fig. 8.8). The matrix failure strain influences the critical transverse strain level at which transverse cracks initiate in shear mode under impact loading, and the resistance to further delamination in predominantly opening mode under subsequent compressive loading (Hirschbuehler, 1987 Evans and Masters, 1987 Masters, 1987a, b Recker et al., 1990). The CAI of near quasi-isotropic composite laminates which are reinforced with AS-4 carbon fibers of volume fractions in the range of 65-69% has... 

Using these patterns, it was possible to speculate on the preferred epoxidation sites and possible ring opening modes, which could induce similar charge delocalization paths. In relation to metabolic epoxidation and subsequent DNA adduct formation, these patterns pointed to the possible importance of K-region and M-region epoxides for some of the methano-PAHs. 

Figure 5.39 The three modes of crack surface displacement (a) opening mode (b) sliding mode and (c) tearing mode.

Fracture Properties of Candidate Metals. Recall that the opening mode stress intensity factor for the case of a component containing a single edge crack in tension, Ki, is given by Eq. (5.47), where Y = 1.12 for the geometry under consideration here ... 

Similar data can also be obtained for vapour pressure systems from the DIERS bench-scale apparatus operated in the open mode (see Figure A2.5). A high back pressure is superimposed on the containment vessel to suppress, boiling of the sample. An adiabatic Dewar calorimeter can also be operated in this mode if it has the facility to vent to an external containment vessel. 

Secondly, Irwin 6) found that the stress field around a sharp crack in a linear elastic material could be uniquely defined by a parameter named the stress-intensity factor, K and stated that fracture occurs when the value of K, exceeds some critical value, K C. Thus, K, is a stress field parameter independent of the material whereas Klc, often referred to as the fracture toughness, is a measure of a material property. Again the subscript I is used to denote the tensile-opening mode. 

According to LEFM the stress singularity at the tip of a (sharp) crack of length a can be conveniently described using a stress intensity factor K(a) in the crack opening mode K(a) is given by ... 

On the left side, the window labelled available in open mode only, displays features available with a standard GC/MS. This includes a file manager to handle files, a word processor to edit files, display of online data during analysis (total... 

The system is dispatched with a commercial spectral database and a copy of the OCAD, which are both available if analysis is conducted in open mode. If the instrument is operated in blinded mode and AMDIS security level filters are applied, the limitations as outlined in Section 5 above apply. 

The open version of AMDIS is only available when the instrument is operated in open mode. In addition to the functions of the on-site version of AMDIS as described above, the open version allows for displaying the entire chromatogram and the spectra of all peaks present in it. Chromatographic peaks and their spectra are shown independently from any match of the spectrum to the mass spectra present in the library used. The open version of AMDIS is not restricted to the use of the on-site target library onsite.msl but can utilize any other AMDIS library installed. 

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