Thin Tubular Specimens Research Articles

On the Impact Torsional Test by Means of a Dropped Bar

In the present paper we describe the impact torsional stress of a circular bar supported horizontally and subjected to impact torsion, when a cross pin attached to the end of it was struck by a dropped bar. Stresses obtained by experiments were in good agreement with those by one dimensional theory except for the short time after the impact. Therefore it was found that the torsional stress by the present method was approximately estimated by one dimensional theory in relation to dimensions of the dropped bar and the circular bar, material constants of them and the length of the cross pin. In addition, on the basis of the above results an impact torsional testing device of Hopkinson bar type was designed and some experiments were carried out with thin tubular specimens of a low carbon steel (SS41). Torsional stress-strain relations of the material under high strain rates (about 102/s) were compared with compressive ones. As a result, it was shown that Mises' yield condition was valid under high strain rates as well as low strain rates.

焼もどしぜい化材料のき裂発生強度について

The effects of temper embrittlement on the crack initiation properties of 3.5 Ni-Cr-Mo-V steel for large rotor forgings have been studied by using the burst tests with application of internal pressure on thin tubular specimens. The results obtained are as follows.(1) Temper embrittled steels with severe segregation show premature fracture before the point of plastic instability, and the fracture appearance has a very brittled grain boundary fracture mode.(2) The strength against crack initiation, which can be measured by the critical circumferential strain at bursting, decreases remarkably in the materials with fracture appearance transition temperature, FATT, above 100°C.(3) Temper embrittled steels with light segregation, however, fracture at the point of plastic instability and show a more ductile shear fracture mode.(4) The materials having higher yield strength show a noticeable decrease in crack initiation strength.(5) The metal resistance against crack initiation depends upon the nature of defects and properties of surrounding matrix. Temper embrittlement enhances the notch-sensitivity of the matrix.

The strain rate behavior of iron in pure shear

An experimental study of the strain rate behavior of technically pure iron in pure shear is reported in this work. As is well known, most experimental results have been obtained from tension or compression tests; few results on strain rate behavior in pure shear.Furthermore, dynamic tests on thin tubular specimens show several advantages over tension or compression tests.Neglecting strain rate history effects the surface τ = τ(φ, gh) has been experimentally obtained, where τ is the shear stress, φ and η are the shear strain and strain rate respectively. This surface was obtained over the following ranges of strain and strain rate 0 ⩽ φ ⩽ 0.42; 1 × 10−5sec−1 ⩽ η ⩽ 1 × 102sec−1.In addition, a comparison between the effect of strain rate in pure shear, tension and compression tests has been carried out. This comparison enables preliminary data on the strain rate behavior in biaxial states of stress to be obtained.Finally, the basic assumptions of the visco-plasticity theory for complex states of stress have been examined in the light of this experimental evidence.

Plastic Stress-Strain Relationships—Some Experiments to Derive a Subsequent Yield Surface

Experiments have been carried out on thin tubular specimens of alpha brass subjected to various combinations of torque and transverse tension, after initial overstrain in torsion. The loading paths were based upon a yield function expressing one degree of anisotropy which had been found previously to give good correlation of initial radial loading paths. The primary definition of yield used was the “Taylor-Quinney, Lode”; however, “Limit of Proportionality” and “Initial Loading Slope Tangent” definitions have also been investigated. The derived yield surface (Taylor-Quinney) shows strong positive cross effect, rotation, and a Bauschinger effect extending over the whole reversed quadrant to initial loading. No indication of the formation of a corner on the yield surface was found.

A Study of the Effects of Cyclic Thermal Stresses on a Ductile Metal

Abstract The results of a study of cyclic strain and fatigue failure arising from cyclic thermal stresses are reported. By means of a test apparatus described in a companion paper, a cyclic temperature is imposed on a thin tubular test specimen subjected to complete longitudinal constraint. Hence, the cyclic strain is the independent variable. The following studies are reported: (a) Effect of thermal-stress cycling on strain hardening and life-to-failure for a fixed mean temperature, (b) effect of degree and kind of previous cold work on strain hardening and cycles-to-failure, (c) effect of mean temperature on thermal-stress cycling, (d) effect of period of cycle on cycles-to-failure, and (e) effect of prior strain cycling on stress-strain characteristics. The significance of factors such as hysteresis, Bauschinger effect, strain hardening, strain aging, and fatigue-crack formation is discussed, and a mechanism is described to relate these factors. Evidence is presented to show that strain hardening is not an important factor in the problem. The concept of total plastic strain is discussed.

鐵の滲炭並に鋼の脱炭現象の定量的研究(1)

In investigating the cementation of pure iron and the decarburisation of carburised high carbon steels, a dilatometer, which is capable of varying freely the inner atmosphere, was employed. Thin tubular specimens 8mm in outer diameter, 0·75mm in wall thickness and 100mm in length taken as standard, were heated at certain constant temperatures for a long duration in a tubular heat resisting carburising box, in which solid carburising materials were placed or gas current applied. Since austenite increases remarkablely in volume as the cementation proceeds, an l contracts by the decarburisation, the stages of various changes accompanied with these phenomena were precisely traced under various conditions in the carburising box, by measuring the dilatation of the specimens.The contents of the present paper are as follow:-I Intro luction.II Apparatus of experiment.III Samples and experimental methods.IV Preliminary experiments.V Cementation of pure iron by solid carburising materials.A Promoting action of BaCO3 upon cementation.1 Effect of ratio of BaCO3 to charcoal2 Heating time and cementation degree.3 Cementation by repeated heating and cooling.4 Cementation by various carbons.5 Grain size of carburising materials and cementation power.6 Cementation in vacuum and effect of air upon cementation.7 Temperature and cementation effect.B Promoting action of other carbonates upon cementation.a Action of SrCO3.b Action of Na2CO3.c Action of CaCO3 and MgCO3.C Moisture in the carburising materials and cementation power.VI Saturated cementation of iron.1 Implication of saturated cementation.2 Quenching tests.VII Decarburisation of carburised high carbon steels.1 Decarburisation in solid carburising materials.2 Decarburisation in gas current.3 Cementation of the soft steel and decarburisation of the carburised steel.VIII Summary.IX References.

Strength of Materials Subjected to Shear at High Temperatures

Abstract This paper treats of an experimental program which is basically fundamental in the study of creep. Uniformly pure shear is produced in a thin tubular specimen submitted to twist, whereas the usual method employs a solid bar in tension. This torsion form of test permits of greater accuracy in the measurement of creep and provides the simplest stress condition, besides offering other decided advantages. Since this work in twist represents virtually a pioneer attack, it has been necessary to develop practically from the beginning each phase of the investigation. The type of specimen, apparatus for the creep tests, including the measuring instruments, and experimental technique are described. The experiments have been of three kinds: (1) Room-temperature tests were first made to determine the usual physical properties in torsion and in tension; (2) at various temperatures short-duration tests were made to learn the effect of different rates of loading, the modulus of elasticity in shear, and the ultimate strength in shear; (3) at 400 deg. cent. and 500 deg. cent. several creep tests in shear of relatively long duration were conducted. An accelerated method of making creep tests has been devised. In addition several special problems were investigated such as a study of the increase of the yield point by creep and the restoration of the original yield point by annealing, the effect of vibrations which included a continuous record of creep, and the effect of temperature fluctuations.