Stain Rate Research Articles

Superplastic deformation in Ti-4%Al-4% Mo-2%Sn-0.5%Si (IMI550)

The superplastic deformation properties, i.e. flow scenes and stain rate sensitivities, of the commercial alloy Ti-4% Al-4% Mo-2% Sn-0.5% Si (IMI55O) have been assessed in the temperature range 805 to 915° C and for different initial microstructures. Fine grainedα +β microstructures showed superplastic properties at temperatures above 850° C and grain coarsening, which led to increases in flow stresses and e reduction in superplastic properties, was only pronounced at the higher temperatures. In transformedβ microstructures the method of strain rate cycling led to a breakdown of the acicularα platelets end the development of an equiaxed α +β microstructure. At the same time the flow stresses at low strain rates decreased and the strain rate sensitivities increased. Light and electron microscopy showed that theβ-phase became the continuous or matrix phase even at volume fractions below 50% (i.e. at the lower deformation temperatures) and that molybdenum segregation at the longitudinal interphase boundaries (parallel to the tensile axis) occurred. The results suggest that there is a strain distribution between theα-phase and the α-phase, theβ-phase effectively behaving as a deforming mantle around theα grains.

High strain‐rate shear deformation of a polyurethane elastomer subjected to impact loading

AbstractExperimental techniques have been developed to produce and measure large amplitude one dimensional compression and shear waves in a polyurethane elastomer (Solithane 113). Experimental measurements consisted of time‐resolved compression and shear amplitude measurements at different distances from the impact surface. The data were analyzed to provide compression and shear wave velocities, and the corresponding stress‐stain curves on the microsecond time scale. The ability to measure directly the high stain rate shear response is a new development and has provided interesting results. The shear modulus varies between 3 and 9 kbar for compressive stresses ranging between 2 and 14 kbar. In contrast, shear modulus values inferred from quasi‐static measurements of bulk and Young's modulus under static high pressure are negligible. These comparisons suggest a high rate dependence of shear modulus in the glassy state. The shear strain curves suggest an elastic‐plastic response with yield strengths ranging from 0.12 kbar to 0.25 kbar with increasing compression for the compressive stress range investigated. Results of compression experiments are also presented.

Effects of test temperature, alloy composition, and heat treatment on iodine-induced stress corrosion cracking of unirradiated zircaloy tubing

Pressurization tests were run on specimens from three batches of Zircaloy tubing that differed in composition (Zir-caloy-2 versus Zircaloy-4) and heat treatment (stress-relieved versus annealed). The behavior in tests at ~593 K and ~633 K in which specimens were internally pressurized with helium containing a nomical iodine concentration of 60 g/m 2 Zircaloy surface is contrasted with baseline data obtained in the absence of iodine. It is shown that test temperature and heat treatment significantly affect the susceptibility of Zircaloy tubing to iodine-induced stress corrosion cracking (SCC) whereas alloy composition is unimportant. The results suggest that the hoop stain rate is more influential in determining the failure time in iodine SCC tests than either hoop stress or strain, indicating that film rupture may be an important step in the overal SCC process. At ~593 K, iodine SCC of unirradiated Zircaloy-2 tubing appears to be confined to hoop strain rates between about 2 × 10 −8 and 5 × 10 −5 /s, irrespective of the heat treatment of the tubing.

Analysis of Platelet Membrane Glycoproteins in Myeloproliferative Disorders

In myeloproliferative disorders, bleeding tendency and thrombosis were encountered occasionally, in the presence of extremely high platelet counts. Platelet membrane glycoproteins as receptor sites were studied by SDS disc electrophoresis and two dimensional electrophoresis in chronic myelogenous leukemia (CML, 7 cases), polycythemia vera (PV, 2 cases), primary thrombocythemia (PT, 2 cases) and myelofibrosis (MMM, 1 case). In CML group any band of abnormal molecular size was not found but the percent of GP I to all PAS stained peaks was reducedd and GP III was increased statistically. Four peaks labelled with 125I-Na by lactoperoxidase were appeared in accordance with PAS staining in these disorders.In GP I peak, the 125I incorporation rate was not different between normal and myeloproliferative disorders. The percent of PAS staining intensity was decresed in CML but increased in PT, PV and MMM. In GP III peak of CML, the increased percent of PAS staining and the decreased 125I incorporation rate were proved compared to the control. In MMM, PV and PT, it was shown that intensity percent of PAS staining was normal but 125I incorporation rate was decreased against GP III.To analyse the dissociation between PAS stain and 125I incorporation rate, the two dimensional electrophoresis was conduced with non reduced-reduced system. The autoradiographic pattern of this electrophoresis showed seven 125I incorporated spots (GP Ia, Ib, Ic, IIa, IIb, III and IV) in normal. The GP Ib was showed as an unclear spot and GP IV was divided in two spots in 4 of 6 CML cases. The GP IV appeared as a faint spot in two PT cases. In MMM and PV, the autoradiographic patterns were similar to those of CML cases.Association of these findings in surface glycoproteins with abnormalities of epinephrine and collagen induced aggregation in these disorders are under investigation.

Cell structure properties during in situ creep experiments in the H.V.E.M.

The behaviour of the dislocation substructure during the steady stage regime of creep, as well as its contribution to the creep rate, are poorly known. In particular, the stability of the subboundaries has been questioned recently, on the basis of experimental observations |1||2| and theoretical estimates |1||3|. In situ deformation experiments in the high voltage electron microscope are well adapted to the direct observation of this behaviour. We report here recent results on dislocation and subboundary properties during stationary creep of an aluminium polycristal at 200°C.During a macroscopic creep test at 200°C, a cell substructure is developed with an average cell size of a few microns. Microsamples are cut out of these specimens |4| with the same tensile axis, and then further deformed in the microscope at the same temperature and stain rate. At 1 MeV, one or a few cells can be observed in the foil thickness |5|. Low electron fluxes and an image intensifier were used to reduce radiation damage effects.