Measured Strain Values Research Articles

Type II Dislocation Loops and their Effect on Strain in Ion Implanted Silicon as Studied by High Resolution X-ray Diffraction

AbstractP-type (100) silicon wafers were implanted with 28Si+ ions at an energy of 50 keV and to doses of 1 × 1015, 5 × 1015 and 1 × 1016 cm−2, respectively, and annealed in a N2 ambient at temperatures ranging from 700°C to 1000°C for times ranging from 15 minutes to 16 hours. The resulting microstructure consisted of varying distributions of Type II end of range dislocation loops. The size distribution of these loops was quantified using plan-view transmission electron microscopy and the strain arising from these loops was investigated using high resolution x-ray diffraction. The measured strain values were found to be constant in the loop coarsening regime wherein the number of atoms bound by the loops remained a constant. Therefore, an empirical constant of 7.7 × 10−12 interstitial/ppm of strain was evaluated to relate the number of interstitials bound by these dislocation loops and the strain. This value was used successfully in estimating the number of interstitials bound by loops at the various doses studied provided the annealing conditions were such that the loop microstructure was in the coarsening or dissolution regime.

95/00714 Method for charging of raw materials into blast furnace

In the reverse osmosis plants based on Dupont technology for water desalination, permeators form the basic units of the process. Each permeator consists of membranes in the form of hollow fibres housed in a cylindrical GRP shell. This work was aimed at studying the performance of shells which have been in operation for a period of 5 years, in order to assess their suitability to be reused after they have consumed their suggested lifetime. Each shell contains sharp steps at each end as a result of a circumferential groove cut on the inside tube wall. A series of strain gages were installed mainly within the region of steps at one end of the shell. It was found that as the pressure was applied, the measured strain values were particularly high in the axial direction inside the groove.

Magnetic anisotropy in epitaxial Ni/Cu(001) thin films: Effects of misfit strain on perpendicular magnetic anisotropy (abstract)

Several epitaxial magnetic systems, notably Fe/Ag(001) and Fe/Cu(001), exhibit perpendicular magnetic anisotropy (PMA) over a relatively narrow thickness range, approximately 2–6 ML. Recently, it has been shown1,2 that a similar region of perpendicular anisotropy exists for Ni/Cu(001), but over a much broader range of film thicknesses extending up to approximately 40 ML. The effective anisotropy energy density can be written as Keff = −2πM2s + 2B1ε(t)+ (2KN/t), which includes magnetostatic (MS), magnetoelastic (ME), and Néel (averaged over two surfaces) terms. The effective anisotropy vanishes at the perpendicular to in-plane transition thickness of about 60 Å. If we assume bulk values for MS and B1, the ME coupling coefficient, and use our measured strain values ε(t), we find that the Néel term is an order of magnitude smaller than the ME and MS terms. These large competing terms therefore control the PMA in this system. We have extended our studies of PMA in Ni/Cu(001) to include Cu1−xNix (0%<x<50%) alloy substrates for which the misfit strain with the Ni film is reduced. We find that the perpendicular-to-in-plane transition, at t≊40 ML for Ni/Cu(001), shifts to thinner nickel layers as the misfit strain is decreased by deposition on Cu1−xNix substrates. This further confirms the important role of ME energy in PMA for this system.

Behavior of stepped GRP shells used in the reverse osmosis permeators for the water desalination process

In the reverse osmosis plants based on Dupont technology for water desalination, permeators form the basic units of the process. Each permeator consists of membranes in the form of hollow fibres housed in a cylindrical GRP shell. This work was aimed at studying the performance of shells which have been in operation for a period of 5 years, in order to assess their suitability to be reused after they have consumed their suggested lifetime. Each shell contains sharp steps at each end as a result of a circumferential groove cut on the inside tube wall. A series of strain gages were installed mainly within the region of steps at one end of the shell. It was found that as the pressure was applied, the measured strain values were particularly high in the axial direction inside the groove.

Damage detection in smart structures using neural networks and finite-element analyses

An important aspect of the smart structures concept is the automated structural health monitoring of aircraft structures. This requires detecting damage and assessing its effect on structural performance. The authors present a new approach to detecting and defining large area damage on a structure. The approach is based on using a neural network to deduce the damage size and location from measured strain values at discrete locations. The neural network is trained using results from finite-element analyses. Several examples illustrating this approach are presented.

Strain in evaporated Nb thin films

Strain behavior of polycrystalline Nb thin films deposited onto oxidized silicon substrates using an electron gun in a high vacuum system was studied by an x-ray diffraction technique. The sign and magnitude of strain in Nb thin films were found to have a strong dependence on the film thickness. For films thinner than approximately 10 nm, the compressive strain was observed, which was considered to be due to diffusion of impurity atoms, most likely oxygen, into grain boundaries of Nb films within an extremely short distance from the film surface. For thicker films, the tensile strain was observed and a strong dependence of the strain (normal to the film surface) on crystal orientations of grains was observed. This dependence agreed very well with the one calculated using a biaxial stress model. The biaxial stress applied in the planar direction was calculated to be 1.0×1010 dyne/cm2 from the measured strain values. The present result indicates that the strain in the Nb films is not induced by temperature increase during the film preparation, but it is more likely due to grain growth during and/or immediately after the film deposition. Based on the biaxial stress model and strain distributions parallel and normal to the substrate planes and strain energies stored in grains with different crystal orientations were calculated.

On the evaluation of elasto-plastic strains measured with strain gages

The analysis of plane-stress conditions using strain gages is feasible even when the deformations of the materials are in the elasto-plastic range. The calculation of stresses from the measured strain values is based on an analysis which requires knowledge of the stress-strain curve of the material as obtained from a uniaxial tensile test. In this paper, the practical procedure of such an analysis is described together with the application of a nomograph to allow a simplified evaluation to be made of the results of measurements. A numerical example is also given.

Tensile performance of packaged optical fibers

Abstract The tensile testing of packaged optical fibers involves the measurement of elastic strains in the range 2–10%. Under these conditions slippage at the tensile grips can produce erroneous results when a nonextensometric method of measurement (e.g., in positive production testing) is used. Slippage of packaged silica fibers (polypropylene/silicone resin-coated silica fibers) observed when using standard pneumatic parallel-faced jaws has been eliminated by using 50-mm-diameter pulley grips with suitable clamps to hold the fiber ends. With this arrangement clean fiber failures are obtained within the gauge length. A correction factor has been estimated for the measured strain values by a theoretical analysis of the measured tension/extension curves for the composite polypropylene/silicone resin-coated fibers. Statistical data have also been obtained for polypropylene-(PP) coated lead silicate fibers and PP-coated “plastic clad” silica fibers. In the latter case, true failure had been obscured by the onset of fiber slippage within the PP jacket.

Fracture of Defects Approaching a Free Surface

A testing program has been run using off-centered-cracked (OCC) plate specimens to demonstrate the fracture characteristics of tunnel defects in specimens with various ligament lengths between the near surface crack tip and a free surface. Measured strain values and the fracture results compared favorably with theory up to the limits of the analyses. An empirical equation which calculates the near surface stress intensity provides extended calculational capabilities. In addition, fatigue crack growth and fracture velocities plus fracture toughness were measured for a Cr-Mo-V steel.