1 ) Th e re sonator-decay and th e reverberation meth ods for meas urement of the absorption of so und in liq uid s are in wide use, but their theoretical foundation has not hithe rto been investigated.The basic ass umptions are in fa ct invalid, but under most practical condi tions the e rrors a re tole rable, at least for three common geometries.(2) The very large excess losses a lw ays observed at the lower• order modes are id en tifi ed with anelastic effects in the e nve lope, for th e most part, and with viscous boundary-layer effects to a lesser, but very substa ntial extent.For mod es of suffic ie nt Iy high o rde r these become negli gibl e.
Strain hardening plastic deformation of a material possessing a yield locus ( f (σ ij )) which may be written as a homogeneous function of the stress components (σ ij ), and which obeys the classical associated flow rule for metals (e.g. Bishop and Hill, 1951) is considered. The material may be anisotropic and may display plastic dilatation. A method is given for constructing the equivalent plastic strain increment in such a way that the increment of plastic work is always equal to the product of the equivalent plastic strain increment and the equivalent yield stress. Construction of the equivalent plastic strain at a corner in the yield locus is given. The method given here is implied in classical treatments of hardening (e.g. Hill, 1950) but seems not to have been given explicitly heretofore.
A mod el of fr actu re of a duc til e me tal in whi c h s urfaces of un s ta bl e mi c ro cav it y e xpa ns ion occur is pro posed.It is s hown th a t s uc h s urfaces can occur onl y in loc ally pl a ne in cre me ntal s train .The ha rd e ning cond iti ons re quired for th e de ve lopm ent of th ese s urface s a re co ns id er ed.It is s ho wn th at in a mate rial possess in g a n eq ui vale nt yie ld stress (Y) whi c h de pend s upon th e total plas ti c d il a tati on (~) and eq uiva le nt d is torti o na l s t rain (€), th e minimum ratio of dila tati onal softe nin g ( y/ ~ < 0) to di s to rti ona l ha rd enin g ( y/e > 0) und er whi c h a n un st ab le s urface of a dil a ta ti on may fo rm is -2/3.A poss ible e xpl a n ati on, based upon th e model , fo r the lack of c orre lati on be t wee n pl an e s t ra in du c tiljt y a nd d uc tilit y as mea s ure d in a te ns il e tes t is offe red.A lso, th e pe rtin e nce of the mod e l to fra cture of glass y po lyme rs an d e n viro n me nt al s tress crac ki ng of c ryst alli ne po lyme rs is di sc usse d.
The distribution of Arithmetic Average values of s urface roughness across the 120 and 20 microinch patches of NBS Cali-Block " B" have been measured. It is s hown that each distribution can be described in terms of it s mean value and standard deviation. The observed sys tematic di stribution of AA values strongly suggests that the user se lect several widely spaced regions at random on the pat ch when caJibrating a rou ghness measuring instrume nt.
The balance described is a one-pan, two-knife, short arm, 1 kg balance.The ful c rum flat and the suspension support elements are mounted on a bed plate s upported by three pos ts attached to the base.The weight handling mechanism is mounted on a ce nte r co lumn attached to the base.Th e balance ha s two modes of arres tment, th e co nstant load mod e and th e full arrest mode.A doubl e case encloses th e struc ture.Th e re are pos itions for six we ights inside th e balance.Th ese weights ca n be compared with each othe r, accordin g to an appropriate we ighing d es ign, without opening the balance case.Th e operation of the balance and th e wei ght c han ging are through control elements outside the balan ce case.Th e indi cating e le me nts for the in s trum e nts meas urin g th e pressure, te mperature, and re lative humidit y within the balance are located in side the balance.The standard deviation of the balance developed by a se ri es of measure me nt s in th e National Bureau of Standards Experime ntal Mass Laboratory was approximate ly 4 J.Lg.
s uitabl e c hoice of power a nd se pa ra ti ons of comp one nts of the s ys tem.
Fric tion and wear of two diffe rent types of graphit e fiber co mposites we re s tudied in a pin·di sk s lid · ing contac t wear mac hine. Compos ites re inforced (62% by volume) with low mod ulus, high s trength c ir · c ular fib er (Modm or II) exhibited very high res istance to wear [a threshold wear load of 20 N , a max· imum bearing load of 50 N, and a wear coeffi c ien t of 106] when worn by hardened stee l pins. How · ever , the co mpos ite produced extreme abras ion on the s tee l count erface. Composites reinforced (62% by volume) with high modulus, lower strength , non circular fib er (GY70) a lso exhibited high res istance to wear (a thres hold wear load of 25 N, a maximum bearing capacity of 20 N, and a wear coeffi c ient of ]06 ) when worn by harde ned s tee l, but these composites developed a s urface film whic h prevented abrasional damage to the s tee l counterface. Poten ti a l applications of the two different types of composites in bearings are discussed. The ad· vantages of th ese co mposi tes in bearings subject to corrosion, vibrat ion, loss of lubrication, or impact damage are noted.
S lidin g s hort me thods re prese nt a mea sure ment tool of s ubstantial pote nti a l fo r th e me as ure me nt of s ma il loss es s uc h as are assoc iated with wav e gu id e conn ec tors or adaptors.Until rece ntly , how e ve r, th e use of th ese me thod s ha s bee n inhibi ted by the unce rtainty of th e e rror co ntribution du e to non • id ea l s hort be havior.A rece nt analys is by Alm ass y ha s s hown th at by th e use of prope r te chniqu es, th e e rror contribu• ti on from thi s s ource is us ually negli gib le, provid e d th a t th e adaptor (or c onn ec tor) is "we ll matche d."It is th e purpos e of thi s paper to elimin a te thi s latt e r res tri ction , de ve lop addition al me as ure me nt me th od s, and d esc ribe furth e r app lic ations.
In the procedures for microwave power calibration, which are well documented, the subject of mismatch errors (or corrections) plays a major role. In particular, the evaluation of mismatch corrections requires the measurement of complex r eflection coefficients; and the accuracy of this measurement is limited , in part, by connector imperfections. The applica tion of recently developed "power equation" methods to th is problem provides both a simplified determ ination of the mismatch correction (Mgm) and improved accuracy. In particular, the intermed iate step of measuring the reflection coefficients is eliminated, and the precision connector requirement is greatly relaxed. If this new method were adopted at each level of the usual calibrat ion hierarchy, the accuracy of disseminating measuremen ts re ferenced to the primary standards at NBS would be greatly improved. T he accuracy potential was demonstrated in a series of experiments involving the Type N, GPC-7, a nd waveguide flan ge connectors. The outcome of this experi ment al evaluation, in whi ch the "ord inary" Type N performed on a par with GPC-7, rai ses some rather serious questions relative to current trends in connector development.
The steady-state temperature distribution in typical cylindrical high-pressure furnaces has been computed from analytic solutions for various boundary conditions.Either the temperature variation along the cylindrical heater or the power dissipation per unit length is prescribed.The results are tabulated and discussed as an aid in the design of high-pressure furnaces and in the estimation of temperature gradients.Topics considered include: (1) the reduction of temperature gradients around the center of the furnace, (2) the effect of temperature irregularities along the heater, and (3) the effect of the relative thermal conductivity of neighboring components.
A rotating wavelength-ind ependent optical attenuator is d escribed that generates four radiance steps.Ra dian ce ratios between th e steps can be continuously varied.Experiments are performed to assess the operational characteri sti cs of the attenuator.Radiance is determined from measurement s with a hi gh-speed photoelec tric pyrometer.Reco rdin g of signal s is made with a hi gh-speed digital data a cquisition system.The combined measuring and recording systems have a full-scale signal resolution of appro xim ately one part in 8000 and a time r esolution of 0.4 ms.The results of several ex periments on radi ance ratio measurements are found to be in agreement within on e part in 1000.
A simple photoelectric transmi ssion densitometer can be converted in th e laboratory into an in strum ent for measuring spatial variations in spectral density of small areas of thin, n onturbid film s.This is accomplished by adding relatively in expensive co mpon ents that are rea dily available and easily assembled.The basic instrument can be one of a number of commercial densitome ters, consisting of stabilized electroni cs, an adjustable light source, and a photosensitive probe whi ch has a wide ran ge and measures spectral tran smi ss ion density.For continuous s canning of r elatively small sa mpl e areas, th e foll owng additions are needed: (l) narrow• bandpass filt er s; (2) interchangeable fi eld illuminating slits; (3) a short•focal-length illuminating-cond en ser lens whi ch co mpromises between a relatively large num erical aperture and a reasonabl e depth of focus ; (4) a motor-driven stage with adjusta bl e speeds; (5) a li ght diffu ser an d li ght guid e; and (6) a conti nuous, relati vely fa st-res ponse data•recordin g system (such as a fas t• response strip-chart recorder).Tllis instrum ent has b een asse mbl ed and tested es pec ially for measuring patial variations of spectral density produced in irradiated photochrom ic film s; and al so for calibrating a train of irrad iated film sa mpl es, in terms of tran smi ss ion density at a given wavelen gth as a fun ction of irradiance, radiation abso rbed dose, or ph otochemi cal reacti vity.
F actors affecting the (unwanted) se ismic response of infrasonic microphones are indicated.Past measurements of ground motion deduced from the radiated atmospheric sound measured with infrasonic microphones are reviewed, and such measurements are com pared with seismo meter measurements of ground motion.Seismic motions caused by the Japanese earthquake of May 1968 are used in this example.The seismic response of the infrasonic microphone used for this measurement was experimentally determined and the results are presented.A simple method of compensating for interfering seismic effects on microphones is described.
A fin ite•e le ment s truc tural a nalys is is described for a ppli ca ti on to p ro ble ms in whi c h geu me try a nd loa din g a re axi sy mm e tri c a nd mate ri al properti es are iso tro pi c e las ti c .A n a tt e m pt to minimi ze res tric ti ons imposed on th e s ha pe a nd ori e ntatio n of th e tri a ngul a r finit.e•ele me nt s has bee n large ly s uccessful.This fac ilit a tes use of th e a na lys is, with a uto ma ti c finit e•e le me nt mes h ge ne rati on , in pa r a me ter or o ptimi zatio n studi es.A se ri es of la borato ry tes ts to verify t.h e an a lys is a re desc ri bed in w hi c h th e m agnitud e and di s tributi on of bo unda ry load in g was known withi n na rrow limit s.
Chro matographi c paper, sa turated with ammonia, is used to extract the res idual thiosulfate fr om the gelatin layer of processed film.Th e paper is trea ted in a silver nitrate solution and fix ed in an ammonia•sodium chloride solution.Thiosulfat e, if present, forms sil ver sulfid e and the thi osulfate is determin ed by measuring the tran&mission density of the paper darkened by sil ver sulfid e.The paper extraction method is simple, rapid, r equires on ly a densitometer as special equ i pment, and is very sensitive especially when th e tran smi ssion dens ity is measured for two layers of the p' aper.No filters are required.The test read ily reveals th e un eve n distribution of residual thiosulfate on the film.By selective removal of th iosulfa te from the image silver by ammonia a nd potassium bromide soluti ons, it was shown that a small amount of thiosu lfate was absorbed on the im age silver i mmediately af ter processing.
Design and constructional details of a high-speed system for the measurement of selected thermophysical properties of electri cal conductors at te~pe.ratures aoove 2000 K in e~p erime nt~ of subsecond duration are described.Operation al characten stlcs of such a system are given.VarIous phenomena that affect the design and successful operation of the system are discussed and, .wheneverpossible, quantitative results are given.Certain experimental ch ecks to assess the operation of th e system are also described.
d c diffe re nce. a nd a•c voltages relati ve to py le rna l d•c sla nrl a rd s, with 20 ppm (pa rts• pe r• milli on) acc uracy a l audi o frequ e nc ies.T he imprec is ion is less th a n 2 ppm.Co rrec ti ons rela ti ve 10 Ih e ve ry s ta ble middl e ra nges ca n be re de te rm ine d for e very ra nge by a se ve n•ste p inle rcompa ri so n of ce rl ai n adjace nl ranges.
A refractory metal thermocouple research program, directed towards establishing the parameters that are necessary to achieve reliable, long term, high temperature thermocouple performan ce, is outlined.A description of special apparatus for exposing bare-wire thermoelements to high temperatures in vacuum and in high purity gaseous environments is given, and the design and performance of an ultra-high-vacuum, high-temperature furnace system are described.Bare•wire W-3 percent Re and W-25 percent Re thermoelements were exposed at 2400 K in argon, hydrogen or vacuum, and experienced a shift in their emf-temperature relationship upon initial exposure_ After the initial shift, the thermoelements expose d in the gaseous environments experienced no significant further change in their emf-temperature relationship for periods up to 1000 hours_ The thermoelements exposed in vacuum continually drifted in their emf-temperature relationship as a result of the pre ferenti al loss of Re by evaporation.
describes a cascade meth o d whi ch a ll o ws ca libra li on of low po we r me ter-co upl e r co mbin a l io ns fo r me a s ure me nl up 10 th e mega wa lt ra nge.Th e tec hniqu e is based u po n s ys le m lin e a ril Y a nd th e un ce rt a int y limil s are s how n 10 be 1 pe rce nl to 1. 5 pe rce nl us in g NBS low po we r sla nd a rd s .
A modified transient pulse technique for measuring shear and longitudinal sound speeds in solids has been devised.The technique is described and evaluated for both precision and accuracy on a variety of solids.This evaluation has been done by experiments in which the constancy of sound speed with path length is used as the prime test for accuracy.A number of variables such as transducer frequency, transducer size, choice of different coincidence points, etc., have been examined.The transducer bond problem is examined and overcome by the use of a time delay bond.Indicated accuracy of the method is found to be better than one part in 10'.Advantageous sample geometries for accuracy testing are discussed.
