Showing papers in "Journal of Basic Engineering in 1959"

The Failure of Structural Metals Subjected to Strain-Cycling Conditions

Abstract: Data showing the isothermal strain-cycling capacity of three metals, inconel, Hastelloy "B," and beryllium, are presented. It is noted that at frequencies of 0.5 cycles per minute the data satisfied am equation of the form N/ sup alpha / epsilon /sub p/ = K, where N is the number of cycles to failure, epsilon /sub p/ is the plastic strain per cycle, and alpha and K are constants whose values depend on the structure and test conditions. Data on Ihconel are given to establish the effect of grain size, specimen geometry, temperature, and frequency. It is found that at temperatures above 1300 F, grain sine amd frequency exert a pronounced effect on the rupture life. Fine-gralned metal survives more cycles before failure than coarsegrained material. Lomg time cycles shorten the number of cycles to failure when the strain per cycle is low. Thermal strain cycling dain for ihconel are compared to strain cycling data at the same mean temperature. Good correlation is found to exist between the two types of data. (auth)

Multiaxial Creep Studies on Inconel at 1500 F

Abstract: The effect of multiaxial stresses on the creep rate and rupture life of inconel at 1500 deg F was investigated. A large range of principal-stress ratios in tension-tension and tension-compression states was studied using axially loaded pressurized tubes. The creep-rate results were compared with both the von Mises (distortion energy) and the Tresca (maximum-shear-stress) criteria. Correlation of the creep-rate results was slightly better using the von Mises criterion; however, the simpler and more conservative Tresca criterion appears to be quite adequate for design considerations The results of the rupture tests appear to support the maximum principal-stress criterion for time-dependent fracture under multiaxial stress conditions. It was shown, however, that in applying this criterion it is important to compensate for the reduction in rupture life caused by changes in the stress state associated with deformation. Rupture strains were found to be directly related to the deviatoric stresses for constant maximum principal stress. The shear strain at rupture was found to be constant for the same maximum principal stress in tension-tension stress states, thus showing that under these conditions the total ductility of the metal was not impaired by increasing the hydrostatic stress. In tension-compression states, the material sustains greater shear strainmore » before rupture. (auth)« less

Correlation of high temperature creep and rupture data

Abstract: The problem of correlating high temperature (T>0.45 T/sub m/) creep and rupture data has been considered in light of the most recent theoretical and experimental information. It is concluded that the deformation of metals and alloys at high temperatures is diffusion controlled and the activation energy is given by the activation energy for self-diffusion of the base metal or diffusion of the alloying constituents. This activation energy should be independent of stress. For low stresses, the dislocation theory predicts a power stress law with an exponent of approximately 4. Experimentally a hyperbolic sine stress law of the form sinh STA sigma / sigma /sub 0/(T)!/sup n/ is very frequently observed over the entire stress range. The change in structure during creep is difficult to predict. It is frequently assumed that it is constant at the minimum creep rate or at the time of rupture. In many cases this appears to be a reasonable assumption, if the stress constant sigma /sub 0/ is taken as a function of temperature. The equations most frequently employed for correlating creep and rupture data are at variance with one or more of these conclusions, and hence can lead to serious error when used for extrapolatingmore » short time data to long times. An equation is presented which correlated high temperature creep and rupture data. (auth)« less