摘要:

A study was made of (110) fracture in LiF using birefringence and etch‐pit techniques. Fracture always occurred parallel to birefringence bands, and it is suggested that the stress of these bands aids (110) crack propagation. Surfaces formed by (110) fracture appear to be flat. If (100) steps are present, as suggested by Kuznetsov, they are less than 100 Å in height. By comparing etch‐pit density data with birefringence data, it is estimated that only about one in twenty etch pits was due to single, unpaired dislocations. All the rest were probably caused by dipoles.

ISSN:0021-8979    

DOI:10.1063/1.1702702

出版商:AIP    

年代:1963

数据来源: AIP

摘要:

A theoretical analysis has been made of the friction stress opposing the movement of both superlattice slip dislocations and twinning dislocations which arises from their interaction with antiphase domains in B2‐, DO3‐, and L21‐type superlattices, all of which are based on the body‐centered cubic structure. In the case of superlattice slip dislocations, this interaction results in the well‐known maximum in yield stress at some critical antiphase domain size. Twinning dislocations, on the other hand, require stress levels about twenty times greater than the maximum value calculated for superlattice dislocations; however, this friction stress decreases for domains smaller than the critical size. In both DO2‐ and L21‐type superlattices, second nearest neighbor as well as first nearest‐neighbor ordering energies are found to play an important role in the resistance to dislocation motion. These results agree well with the limited number of experimental observations obtained by other investigators with the Fe3Al superlattices.

ISSN:0021-8979    

DOI:10.1063/1.1702703

出版商:AIP    

年代:1963

数据来源: AIP

摘要:

The electron‐voltaic effect in commercial siliconp‐njunctions is used to determine the distribution of radiation defects with penetration distance for a 500‐keV electron beam inn‐type silicon. It is shown that the concentration of radiation defects falls off far more rapidly than previously reported by Vavilovet al., who used changes in resistivity to determine the distribution. Their experimental data are reinterpreted and found to be in reasonable agreement with the electron‐voltaic data. Attempts are made to explain the experimental data by constructing radiation defect vs depth curves using various relations for the probability of defect formation as a function of electron energy, and for electron energy as a function of penetration distance. Reasonable agreement exists between such theoretical curves and the experimental data.

ISSN:0021-8979    

DOI:10.1063/1.1702704

出版商:AIP    

年代:1963

数据来源: AIP

摘要:

The forced vibration problem of a finite sphere with an exciting source embedded inside it has been treated. The source is assumed to oscillate sinusoidally and the complex dilatational modulus is used to describe the motion inside the sphere. It is found that if the outer surface of the sphere is restrained from radial displacement, the ratio of the amplitude of a midpoint (between the outer surface of the sphere and the inner exciting source) to the amplitude of a point on the exciting source could be used as an indication of the dilatational properties of the sphere. Therefore, from the criterion of maximum amplitude ratio in conjunction with the frequency, the dilatational properties of a testing material can be determined. This method can be applied to viscoelastic fluids as well as solids.

ISSN:0021-8979    

DOI:10.1063/1.1702705

出版商:AIP    

年代:1963

数据来源: AIP

摘要:

Electrical charges developed during plastic deformation of sodium chloride were investigated. Experiments are chosen (orientation and shape of the crystals; direction of applied stress) to enable the edge and screw components of dislocation loops to emerge separately on two different pairs of the external surfaces of the specimen. The experimental results indicate that an electrical charge is associated only with the edge components of dislocation loops. It is also found that in tensile experiments of a bent specimen (accidentally or intentionally) negative charge appears on the concave side and positive charge appears on the convex side, and the negative charge is larger, in absolute value, than the positive charge, in the early stages of deformation. A model is proposed to explain these results.

ISSN:0021-8979    

DOI:10.1063/1.1702706

出版商:AIP    

年代:1963

数据来源: AIP

摘要:

The effect of preferred orientation on the Hall effect in titanium was examined in an attempt to resolve the inconsistent results of previous investigators. Three specimens of iodide titanium were prepared with different textures and the Hall coefficient of each was measured between 4.2° and 295°K. The Hall coefficient was found to depend on both temperature and preferred orientation. At room temperature, it was determined to be −1.8×10−11m3/C in two specimens and +1.2×10−11m3/C in a third one. From the x‐ray analysis of the texture and the Hall coefficient data, it was concluded that the positive component of the Hall coefficient was associated with the hexagonal axis of titanium, being parallel to the magnetic field. An approximate calculation estimated the principal components of the Hall tensor to beR∥= +4.2×10−11andR⊥= −7.7×10m3/C, whereR∥is the Hall coefficient when the magnetic field is parallel to thecaxis andR⊥the Hall coefficient when the magnetic field is perpendicular to thecaxis. The values ofR∥andR⊥given above can account for the spectrum of previously published Hall values for titanium.

ISSN:0021-8979    

DOI:10.1063/1.1702707

出版商:AIP    

年代:1963

数据来源: AIP

摘要:

Etch pits on (001) surfaces of calcium tungstate crystals, formed on treatment with hot dilute solutions of hydrochloric acid, were identified to be dislocation etch pits. The technique is able to follow the motion of dislocations during annealing by the formation of new sharp‐bottomed pits adjacent to flat‐bottomed pits at the initial dislocation positions. Inclusions, both solid and gaseous, are an important source of dislocations in crystals of calcium tungstate grown from the melt.

ISSN:0021-8979    

DOI:10.1063/1.1702708

出版商:AIP    

年代:1963

数据来源: AIP

摘要:

Evidence for the existence of ultrasonic internal conical refraction in rocksalt and calcite single crystals was obtained by observing the behavior of shear waves along one of the axes of threefold symmetry in each crystal. A method of selective absorption was used in conjunction with pulse‐echo ultrasonic attenuation measurements. Absorbing material was pasted at various spots on the bottom of the specimen opposite the transducer to map the energy density in the wave. Positions of maximum flux coincided with predictions when the shear wave was not perturbed by misorientation‐induced ultrasonic double refraction.

ISSN:0021-8979    

DOI:10.1063/1.1702709

出版商:AIP    

年代:1963

数据来源: AIP

摘要:

Internal friction in a series of V‐H alloys has been measured over the temperature range −190° to +210°C. The hydrogen compositions varied from 1.2 to 14.5 at.% and two frequencies, 75 and 270 cps, were used. For each frequency a single peak was observed having an amplitude which increased essentially linearly with hydrogen concentration. This is suggestive of stress‐induced ordering of the hydrogen atoms in the vanadium‐hydride lattice. Comparison of the activation energy and temperature of this peak with that reported by the authors for the tantalum‐hydrogen system indicates that the hydrogen atoms are located in the tetrahedral interstices.

ISSN:0021-8979    

DOI:10.1063/1.1702710

出版商:AIP    

年代:1963

数据来源: AIP

摘要:

The formation of point defects during plastic deformation and their subsequent interactions with dislocations in high‐purity copper was studied using a low‐temperature strain‐aging technique. The point‐defect‐dislocation interaction gave rise to a small yield point whose magnitude depended on the temperature and time of aging after deformation. The annealing kinetics indicated that two types of point defects were formed by deformation in concentrations which depended on the prestrain and prior history of the specimen. A mechanism for the point‐defect annealing was proposed to account for the experimental results and was used to calculate the diffusion‐activation energy of the defects in the lattice and along the dislocations. Based on this mechanism, the defects were tentatively identified as the interstitial and the divacancy. The temperature dependence of the yield point was examined and was shown to be consistent with an elastic interaction due to the dilatation around the point defects. The results indicated that the point defects retained their identity on arrival at the dislocation rather than becoming incorporated into the dislocation structure.

ISSN:0021-8979    

DOI:10.1063/1.1702711

出版商:AIP    

年代:1963

数据来源: AIP