[en] The critical mixed-mode I/III fracture toughness, J-integrals (J_MC), at room temperature (RT) and 100 degrees C were examined for a V-5Cr-5Ti alloy. Fracture toughness at 100 degrees C was evaluated with a J-integral test and at RT with a K (the stress intensity factor) test. The determination of J_MC was made using modified compact-tension specimens. Different ratios of tension/shear stress were achieved by varying the principal axis of the crack plane between 0 and 45 from the load line. Crack angles used in this study were 0, 15, and 45 degrees. A specimen with 0 degree crack angle is the same as a standard mode I compact tension specimen. In this limit, J_MC becomes J_IC. Specimens were annealed at 1125 degrees C for 1 hour in a vacuum of 10^-7 torr. J_MC and mixed-mode tearing moduli (T_M) were determined at 100 degrees C with the single specimen technique. Crack lengths were calculated with partial unloading compliances. The J_MC values at RT were calculated from critical stress intensity factors (K_C). The results showed that at RT the V-5Cr-5Ti alloy was brittle and experienced unstable crack growth with a mixture of intergranular, cleavage and some microvoid coalescence (MVC) fracture while at 100 degrees C it exhibited high fracture toughness and fractured with a mixture of MVC and intergranular failure. SEM investigation showed that some cleavage facets initiated at grain boundaries. The results suggest a low intergranular fracture strength and tendency towards cleavage fracture at room temperature. Preliminary data from Auger electron microscopy showed significant sulfur segregation on grain boundaries. The possible mechanism which might reduce intergranular fracture strength is discussed

[en] Effects of hydrogen (H) on the mixed-mode I/III critical J integrals (J_MC) and tearing moduli (T_M) were examined for a ferritic/martensitic stainless steel (F-82H) at ambient temperature. A determination of J_MC was made using modified compact-tension specimens. Different ratios of tension/shear stress were achieved by varying the principal axis of the crack plane between 0 and 55 degrees from the load line. A specimen with 0 degree crack angle is the same as a standard mode I compact tension specimen. Specimens were heat-treated at 1000 degrees C/20 h/air cooled (AC)-1100 degrees C/7 min/AC-700 degrees C/2 h/AC. The specimens were charged with H at a hydrogen gas pressure of 138 MPa at 300 degrees C for two weeks, which resulted in a H content of 6 ppm(wt), as measured with the open-quotes inert gas fusionclose quotes technique. J_MC and T_M values were determined with the single specimen technique. Crack lengths were calculated by means of partial unloading compliances. The preliminary results from J integral tests showed that introducing H decreased J_MC and T_M values as compared to those without H. However, the presence of H did not change the dependence of J_MC and T_M values on the crack angles. Both mode I J and T values (J_IC and T_I) exhibited the highest values. Both the minimum J_MC and T_M values occurred at a crack angle between 35 and 55 degrees, corresponding to the load ratio (σ_iii/σ_i) of 0.7 to 1.4

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[en] The existence of a charge at surfaces and interfaces has been explicitly and implicitly demonstrated by experimental investigations. Of more concern, perhaps, is whether or not the existence of these charges alters in a significant way the surface-related properties in ionic ceramics. These experimental issues are considered after a theoretical section in which we present a quantitative treatment of the origin and magnitude of surface charge in ionic crystals. The considerations carry over to some extent to semiconducting crystals, but the covalent bonding and the dominant role of electronic defects greatly complicates the situation. Brief mention is made of some examples of these more intricate applications

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[en] The physical framework employed for most of the current irradiation creep models of cubic polycrystalline materials is a single crystal with a dislocation system consisting of three orthogonal Burgers vectors. The irradiation creep models based on this crystal system can be broken into two categories, one where irradiation creep occurs by dislocation climb alone, and the other where irradiation creep occurs by a combination of dislocation climb and glide. Often, irradiation creep is presumed to proceed by dislocation climb alone at low applied stresses, but by a combination of dislocation climb and glide at higher applied stresses. However, the rules for generalized deformation, as applied to dislocation climb, determine if a polycrystal is capable of deformation by dislocation climb alone. The current work analyzes generalized deformation by dislocation climb of fcc and bcc stainless steel crystals. Some implications for irradiation creep of polycrystalline fcc and bcc stainless steels are discussed

[en] The conditions for significant nucleation of carbon particles to occur in several late-type stellar atmospheres are considered. The theoretical treatment includes the contributions from the translational, rotational, and vibrational degrees of freedom of the nuclei which have been omitted in previous considerations. It is shown that the range of possible surface free energies of the particles, for which nucleation can be achieved in these atmospheres, is small. The effects of electrostatic drag on escaping particles are discussed. Under the conditions considered here, these effects are shown to be of secondary importance to those of viscous drag

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[en] We present an analytical description of the interaction between moving discommensurations and diffusing impurities for a realistic form of the impurity-discommensuration interaction energy. This interaction energy is derived within the framework of the modified sine-Gordon model with either misfit impurities (coupling to the gradient of the order parameter) or elastic-modulus impurities (coupling directly to the order parameter). This interaction potential is then employed in calculating the steady-state impurity concentration profile about the moving discommensuration for arbitrary discommensuration velocity and impurity diffusivity. The impurities provide a drag force on the moving discommensuration, which may lead to hysteresis in the relation between the applied force and the discommensuration velocity. Analytic results for the onset of hysteresis, as well as for the velocities and forces delimiting the hysteretic regime, are presented. Finally, we apply these results to charge-density waves, ferroelectric domain walls, and grain boundaries