摘要:

The design and performance of equipment to measure film toughness under impact loading is described. The measured quantity is the amount of energy absorbed by a film when a ball is projected through it. The velocity of the ball can be varied from about 20 ft/sec to 800 ft/sec. A conditioning chamber permits testing over a temperature range of −40°C to +80°C. Individual tests require a specimen of film of about 1¼×1¼ in. and can be made at the rate of about 2/min. Results are given for films of several commercial materials.

ISSN:0021-8979    

DOI:10.1063/1.1722741

出版商:AIP    

年代:1957

数据来源: AIP

摘要:

A theory is presented which describes the development of surface grooves at the grain boundaries of a heated polycrystal. The mechanisms of evaporation‐condensation and surface diffusion are discussed with the use of the Gibbs‐Thompson formula and the assumption that the properties of an interface do not depend on its orientation. For the idealized case in which only one of the mechanisms is operative, the groove profile is shown to have a time‐independent shape whose linear dimensions are proportional tot½for evaporation‐condensation, and tot½for surface diffusion. The proportionality constants are evaluated, and criteria are developed which permit one to estimate which process predominates in practice. Order of magnitude agreement is obtained with estimates of actual grooving speeds and profiles.

ISSN:0021-8979    

DOI:10.1063/1.1722742

出版商:AIP    

年代:1957

数据来源: AIP

摘要:

According to simple theory, torque measurements on cubic single‐crystal disks should give values for the crystal anisotropy constants,K1andK2, that are independent of field above some minimum saturating field. Our experiments on {100} and {110} disks of 3¼% silicon‐iron, and previous experiments of others, show that this theory is inadequate. In a more refined theory it is assumed that the edges of the disk are not saturated even in high fields. The observed increase in the peak values of the torque with increasing field can be attributed to a very small variation of the net magnetizationIas the disk is rotated in the field. This variation must be such thatIis largest in the hard directions of magnetization and smallest in the easy directions. Direct observation of the domain patterns on a {100} disk appears to confirm these assumptions. For both {100} and {110} disks,K1′ (the effective value ofK1) varies as 1−c/√Hover the range 1000 to 20 000 oersteds. The correspondingK2′ values for the {110} disk show a more complicated dependence onH. Values ofK1′ found from torque peaks differ somewhat from those obtained from torque slopes; the difference between the smallerK2′ values is much more serious. The discrepancy is attributed to the particular way in whichIvaries with disk rotation.

ISSN:0021-8979    

DOI:10.1063/1.1722743

出版商:AIP    

年代:1957

数据来源: AIP

摘要:

Single‐domain particles of 40:60 cobalt‐iron alloy have been prepared with a median diameter of 200 angstrom units, a median elongation of 5.4:1, and an intrinsic coercive force of 1950 oersteds. By compacting these particles to various packing densities and degrees of alignment, shape anisotropy fine‐particle magnets have been made with magnetic properties duplicating those of each of the Alnico permanent magnet alloys, including maximum energy product values above five million gauss‐oersteds. It is concluded that the Alnico alloys and the fine‐particle magnets derive their properties from very similar, but not identical, shape anisotropy effects.

ISSN:0021-8979    

DOI:10.1063/1.1722744

出版商:AIP    

年代:1957

数据来源: AIP

摘要:

A method is presented for estimating the nonlinear noise contribution in an oscillator at low levels of oscillation. This involves obtaining an approximate solution of a nonhomogeneous van der Pol type of nonlinear differential equation driven by noise. The method of solution is based upon the reduction of the equation to a linear form. The nonlinear contribution can then be obtained by computing the power spectrum output of a cube law rectifier. The calculations indicate a variation of nonlinear noise with rf level. Such variation is observed in nuclear and electronic magnetic resonance devices used for the detection of magnetic absorption in paramagnetic materials.

ISSN:0021-8979    

DOI:10.1063/1.1722745

出版商:AIP    

年代:1957

数据来源: AIP

摘要:

When a glass capillary tube filled with alternating drops of mercury and electrolyte is made to vibrate mechanically, an alternating voltage is available across terminals inserted in its ends. This effect has been attributed to changes in the surface area of the interfaces [E. Yeager and F. Hovorka, J. Acoust. Soc. Am.25, 447 (1953)]. New experimental evidence indicates that at low frequencies the output voltage depends on motion of the liquid drops with respect to the capillary tube. A first‐order approximation theory which takes into account the tube compliance and the relative motion of the liquid drops with respect to the capillary tube has been obtained and is found to agree qualitatively with the experimental data relating: (1) tube output voltage to frequency at fixed amplitude of vibration; (2) tube output voltage to relative motion of the drops at fixed frequency; and (3) short‐circuit current output to relative motion for fixed capillary radius, independent of mercury‐electrolyte proportions for a given electrolyte. Theory indicates that the voltage is a function of the length of mercury in a tube rather than of the number of interfaces; this result seems to be in agreement with the data.

ISSN:0021-8979    

DOI:10.1063/1.1722746

出版商:AIP    

年代:1957

数据来源: AIP

摘要:

A dislocation climb creep model is considered which does not require the production of immobile dislocations. The creep equation that results from the analysis iscreep rate=A&sgr;3sinh(B&sgr;1.5/kT)exp(−Q/kT),whereAandBare constants, &sgr; is the stress,Qis the activation energy of creep andkThas its usual meaning. This equation is quite similar to one previously proposed.

ISSN:0021-8979    

DOI:10.1063/1.1722747

出版商:AIP    

年代:1957

数据来源: AIP

摘要:

The problem of thermoelastic damping at the boundary between dissimilar solids is investigated for the case of small, sinusoidal, longitudinal disturbances of long‐wavelength propagating normally through the interface. The relevant equations are derived from thermodynamic considerations, and it is found that the mechanical energy absorption per unit time is proportional to the square root of the disturbance frequency.

ISSN:0021-8979    

DOI:10.1063/1.1722748

出版商:AIP    

年代:1957

数据来源: AIP

摘要:

The activation field of BaTiO3c‐domain crystals may be calculated from an experimental determination of the frequency dependence of the coercivity. The ratio of activation fields above and below the orthorhombic transition is equal to the respective ratio of coercivities. The decrease in coercivity in passing through this transition is related to the change in thickness of the space charge layer within the ferroelectric.

ISSN:0021-8979    

DOI:10.1063/1.1722749

出版商:AIP    

年代:1957

数据来源: AIP

摘要:

The experiment reported in this paper was designed to obtain data on the dynamics of a nonrotating, conical‐nosed projectile penetrating randomly‐packed sand. Positionversustime measurements for the projectile in sand were obtained by means of a photographic‐electronic chronograph developed for the purpose. The striking velocityv0of all rounds was about 700 m/sec. The negative acceleration of a 5‐in. long, 0.50‐caliber, 80‐gram projectile was found to be roughly expressible by the equation−dv/dt=&agr;v2+&bgr;v+&ggr;where the coefficients &agr;, &bgr;, and &ggr; are positive constants. This general relation includes as special cases the conventional penetration formulas of Robins‐Euler, Poncelet, and Re´sal. A new theory of penetration is proposed based on the equations:−dv/dt=&agr;v2,v0>v>vc;−dv/dt=&bgr;v2+&ggr;,vc>v>0where the coefficients &agr;, &bgr;, &ggr; are positive constants and &agr;<&bgr;. An abrupt transition in the drag force that occurs at the critical velocityvcof about 100 m/sec is believed due to transition from inelastic to quasi‐elastic impact.

ISSN:0021-8979    

DOI:10.1063/1.1722750

出版商:AIP    

年代:1957

数据来源: AIP