Localized fluid flow measurements with an He-Ne laser spectrometer

Effect of interstitial solutes on the strength and ductility of titanium

The Stored Energy of Cold Work

Plastic deformation at constant rate and low temperatures starting with 20–30K, as a rule, occurs in the form of oscillations of the deforming stress (serrated deformation). Low-temperature serrated deformation (LTSD) appears under special conditions where deformation occurs as a result of the specific conditions of dislocation dynamics and, possibly, as result of special physical conditions of deformation (low thermal conductivity and specific heat of the sample, heat exchange with the cooling medium). A large number of experimental and theoretical works have been performed since the discovery of LTSD in the 1950s but not even one review has appeared. Further advances in understanding the mechanism of LTSD and the development of a theory of this phenomenon require that the experimental data be systematized. As a rule, individual experimental facts have been used when theories of LTSD have been compared with experiment. The present review attempts to collect as much accessible experimental data as possible, systematize these data, determine the main characteristics of LTSD, examine theoretical hypotheses, compare theory with experiment, and suggest possible mechanisms for low-temperature serrated deformation.

Serrated deformation of metals and alloys at low temperatures (Review)

Computer simulation of the low temperature instability of plastic flow

The temperature transients arising from discontinuous slip in copper‐nickel alloys at helium temperature have been observed with thermometers of defined inertia properties. It is found that this type of slip can propagate through the specimen similar to a Luders band. In the discussed case, the temperature rises from approximately 5°K to approximately 35°K, and the mean value of the volume affected by each slip is 1.4×10−3 cm3. This volume corresponds very closely to the range of thermal diffusion during the time interval of slip. Thus, it is consistent with the assumption that discontinuous slip at low temperatures results from thermal feedback.

Affected Volume and Temperature Rise During Discontinuous Slip at Low Temperatures

A cryostat has been constructed and is described which permits the tensile deformation of metal specimens under loads up to 150 kg and simultaneous measurements of the thermal and electrical conductivity, thermal diffusivity, and heat of deformation, preferably at temperatures of liquid helium. The apparatus is designed to keep liquid helium for approximately 20 h, which permits the investigation of occurrences requiring high resolution in time, as for example the discontinuous slip at low temperatures. The measurement of the temperature and small temperature differences is achieved through the application of gas thermometers in connection with electronic differential pressure sensors of small dead volume. Automatic recording allows for an accurate observation of thermal transients. The thermal conductivity measurements are based on the Kohlrausch method. Some results which are representative for the application of the apparatus are presented.

Apparatus for Low‐Temperature Tensile Deformation and Simultaneous Measurements of Thermal Properties of Metals

A thermometer in contact with a test specimen is inert, if its heat capacity is not small compared with the heat capacity of the specimen. The response of the thermometer to a transient temperature of the specimen can then be described by a transfer function. This transfer function has been determined for the single thermometer and the differential thermometer in contact with a slab whose ends are at zero temperature. Significant simplifications arise, if the inertia of the thermometer is large. Some applications of the theory to calorimetric measurements are discussed.

The Inert Thermometer

The temperature transients arising from instantaneous plane heat sources in a linear heat conductor are analyzed. The thermal conductivity and the specific heat of the conductor are assumed to be temperature independent. Two thermometers are fastened to the conductor. The thermometers possess heat capacity causing inert response. It is found that the position and strength of a heat source can be calculated from the first and second time integral of the observed transient temperature difference between the two thermometers. If the inertia parameter is large, the thermometer heat capacity can be derived from the response to a uniform short heat pulse. The method can be applied to problems of low‐temperature plastic deformation and superconductivity. An experimental example is discussed, in which instantaneous plane heat sources are generated by localized discontinuous tensile deformation at 4.2°K. The positions of the slipped zones and the amount of heat released during each slip are determined.

Determination of Instantaneous Heat Sources with Inert Thermometers

Laser light back‐scattered in nonspecular directions from a rough specimen surface undergoing tensile deformation carries a Doppler shift. The device described employs two slightly separated light probes. The two scattered beams are mixed in a phototube with small aperture, approximately matched to the average speckle size. The strain‐rate is proportional to the differential Doppler frequency. The accumulated strain is found by fringe counting.

Joachim C. Erdmann

Papers

Affected Volume and Temperature Rise During Discontinuous Slip at Low Temperatures

Apparatus for Low‐Temperature Tensile Deformation and Simultaneous Measurements of Thermal Properties of Metals

The Inert Thermometer

Determination of Instantaneous Heat Sources with Inert Thermometers

Remotely Sensing Strain‐Rate Meter Based on the Doppler Shift of Laser Light