A PROGRAM OF BASIC RESEARCH ON MECHANICAL PROPERTIES OF REACTOR MATERIALS. Quarterly Progress Report for Period Ending March 31, 1962

Studies were continued on the deformation and fabrication characteristics of reactor materials. Data were gathered on the effect of cold work on the internal friction due to dislocation relaxation oscillation. An interpretation was made of the internal-friction peak in niobium in terms of the relaxation motion of kinks on dislocations in niobium. Efforts were made to extend the technique of quantitative differential thermal analysis to cold-worked iron which was selected as the most readily treated representative of the body- centered-cubic structural metals. Refinements were made in the calorimetric technique itself, leading to an improved procedure of data reduction. Results for the effects of grain size on the stored-energyrelease spectra of high-purity copper were recomputed. (M.C.G.

EFFECT OF NEUTRON IRRADIATION ON MATERIALS SUBJECTED TO MULTI-AXIAL STRESS DISTRIBUTIONS. Quarterly Report for the Period Ending June 30, 1962

Activities in a program to determine the effects of neutron irradiation on A-302B steel are reported. Plans are discussed concerning performance tests on tensile, notched tensile, tube, and Charpy specimens. An irradiation capsule design was finalized. A theoretical analysis of the critical conditions arising in a tube subjected to both internal pressure and axial load is included. (J.R.D.

Effect of Neutron Irradiation on Materials Subjected to Multiaxial Stress Distributions. Quarterly Progress Report, April 1-June 30, 1963

Results are reported for tensile and notched tensile tests on unirradiated and irradiated A-302B steel. The tensile results indicate that neutron irradiation decreases the uniform strain, increases the yield point, and decreases the strain hardening. The notched tensile results showed an increase in the ultimate tensile strength with irradiation. (D.L.C.

A PROGRAM OF BASIC RESEARCH ON MECHANICAL PROPERTIES OF REACTOR MATERIALS. Quarterly Progress Report for the Period Ending June 30, 1962

The effect of modifying the dislocation structure by room-temperature prestraining on the subsequent yielding behavior at 77 deg K is being studied. Results on tantalum single crystals indicated that a considerable decrease in the early yield stress for a given strain is effected by prestraining at room temperature. Twinning was observed in the tantalum at 77 deg K and normal rates of strain. It is shown that the potential barrler to dislocation motion in crystalline solids can be measured in relatively pure bcc transition metals such as Nb, Ta, Mo, and W. Work is being carried out to extend the method of differential calorimetry to measurements of stored-energy-release spectra in deformed bcc metals. Measurements for copper are discussed. (M.C.G.

A PROGRAM OF RESEARCH ON MECHANICAL METALLURGY AS RELATED TO FUEL-ELEMENT FABRICATION. Quarterly Progress Report for the Period Ending June 30, 1961

Results of crawing experiments using 3/8-in. bars to provide rod and tube test specimens are reported. In mechanical metallurgy investigations on the relation of formability to imperfection structure the peierls potentials for dislocation of Nb, Mo, Ta, and W were measured. Design and construction of a microextensometer reported. The investigations of the effects of grain size on the stored energy cold work were extended to a new lot OFHC Cu. In studies of formability relations with imperfection structure, a detailed study is reported on the internal-friction relaxation spectrum of Ta relatively unmodified by impurities. A summary of interstitial impurity effects on the internal-friction of Ta is given. (J.R.D.

A Program of Basic Research on Mechanical Properties of Reactor Materials. Quarterly Progress Report for the Period Ending June 30, 1963

Deformation Mechanisms in BCC Metals. Thin-film microscopic observations are presented for rolled single TA crystals. These observations show numerous areas almost devoid of slip markings. One specimen was annealed in air at 400 deg C to pin all the dislocations; transmission micrography of the annealed specimen indicates a quite low temperature for dialocation rearrangements. A correlation was found between the temperatures of the stages in the amplitude-dependent modulus defect and the deformation-peak temperatures for Nb. It is concluded that much inore extensive dislocation motion is possihle for a given applied stress amplitude at temperatures above the alpha peak than below, and that limited dislocation motion is possible at very low temperatures if the applied stress is great enough. Stored-Energy Release in Deformed Metals. Stored-energy-release measurements were made on Puron and Ferrovac E grades of pure Fe for several grain sizes and strain levels. The results indicate that the stored energies and dislocation densities in Fe are much smaller than in Cu and other metals. (D.L.C.