Calibration Specimens Research Articles

Acoustoelastic effects in autofrettaged steel cylinders: Scholz, W.; Frankel, J. U.S. Army Armament Research and Development Center, Watervliet, New York (United States), AD-A174-127, 15 pp. (Oct. 1986)

Abstract : Residual stresses in short cylinder sections cut from autofrettaged larger steel tubes have been measured by means of the acoustoelastic effect. Ultrasonic shear waves polarized along the hoop and radial direction and propagating in the axial direction, as well as longitudinal waves, were used. Calibration specimens cut from similar type material were used to determine the velocity changes of longitudinal and shear waves propagating perpendicular to an applied stress. Third order elastic were derived from these measurements. Velocity measurements for zero applied stress along different axes of the cube- shaped calibration specimens indicate the presence of orthorhombic texture. Stress distributions and texture dependent effects within the cylinders have been determined.

A New Mathematical Procedure for NIR Analysis: The Lattice Technique. Application to the Prediction of Sugar Content of Apples

Analytical applications of near-infrared spectroscopy require the determination of calibration equations linking chemical and spectral values. Such equations are difficult to update by including new calibration specimens. A new procedure for prediction which was not based on multiple linear regression has been investigated. This procedure could be included in a data base system. The proposed method consists of three steps: compression of the spectral data by applying principal component analysis, creation of a predictive lattice, and projection of the spectra of unknown specimens on to the predictive lattice. This enables the prediction of chemical data that are not perfectly linked to spectral data by a linear relationship. The procedure has been applied to the prediction of the refractive index of apples. A predictive lattice was designed with the use of 45 specimens of calibration. A prediction with 43 verification specimens gave a standard error of 0.8%, which appeared sufficient for grading apples in quality classes. Further studies are required in order to include the proposed method in spectral libraries specializing in analytical applications.

Feasibility of centralized measurements of glycated hemoglobin in the Diabetes Control and Complications Trial: a multicenter study. The DCCT Research Group.

A method for measuring glycated hemoglobin (Hb A1c) and an accompanying method of specimen transport to a central laboratory were developed for the multicenter Diabetes Control and Complications Trial (DCCT). In the DCCT, results for Hb A1c are used to assess chronic glycemic control for data collection and patient management. During the feasibility phase of the trial, central (CHL) and backup laboratories using automated, "high-performance" ion-exchange liquid-chromatographic methods were established. Whole-blood samples were stored (4 degrees C) at each of the 21 clinical centers for up to 72 h before air-express shipment to the CHL. Quality-control procedures included daily analyses of three calibration specimens. A pooled hemolysate was assayed frequently over time as a long-term quality control (LTQC). After 18 months, within- and between-run CVs were less than 6%. Mean values for split duplicate samples assayed in a masked fashion at the CHL were nearly identical. LTQC results indicated no significant assay drift over time. More than 6000 samples were assayed (mean interval between obtaining the blood sample and completing the assay: less than six days). Hb A1c evidently can be precisely and reliably measured in the context of a long-term, multicenter trial such as the DCCT.

A SIMS calibration exercise using multi‐element (Cr, Fe and Zn) implanted GaAs

AbstractMulti‐element (52Cr, 56Fe and 66Zn) implanted GaAs samples have been prepared specially for SIMS calibration. Absolute chemical measurements gave retained ion doses which agreed to within 12% of the nominal implanted dose (2.0 × 1014 atoms cm−2). Comparative SIMS depth profiles with five instruments gave Cr mode depth data which showed a variability of 5%. After data normalization to a common mode depth (168 nm) the shape of all profiles showed good agreement. SIMS anàlysis of similar samples containing lower dose implants (1.0 × 1013 atoms cm−2) showed that ∼50% of the Cr was contained in the near surface region (0–0.03 μm). This surface peak was not observed in profiles of samples which had been singly implanted with Cr. It is proposed that the Cr surface peak results from radiation enhanced out‐diffusion initiated by the subsequent Fe implant. Whilst the high dose multi‐implant samples showed a similar Cr surface accumulation, its magnitude in relation to the ion implanted dose, was smaller. These samples therefore form reliable calibration specimens for the simultaneous determination of the secondary ion responses of Cr, Fe and Zn in GaAs.

Hot Box Operating Techniques and Procedures: A Survey

Abstract A questionnaire dealing with operating techniques and procedures of guarded and calibrated hot boxes was mailed to 14 hot box operators in the United States and Canada. Questions pertaining to testing capabilities, instrumentation, calibration specimens, steady-state criteria, etc., were asked. Responses from the 13 laboratories returning the survey are summarized in the paper. This information should be of interest to hot box operators, as well as prove helpful in future revisions of the guarded and calibrated hot box test methods.

Towards an acoustoelastic theory for measurement of residual stress

The rudiments of an acoustoelastic theory is developed within the framework of linear elasticity with initial stress. Since no assumption is made about the origin of the initial stress, our acoustoelastic theory will be applicable to evaluation of stress in plastically deformed bodies, provided that the superimposed ultrasonic waves be hyperelastic. New universal relations are deduced. An approach to evaluation of stress which does not use calibration specimens and makes full use of universal relations in our acoustoelastic theory is advocated. Examples are given which illustrate application of our theory to evaluate residual stress in plates. Preliminary corroborations of our theory are provided by the recent experiments of King & Fortunko and Thompson et al.

Removable partial denture design: a photoelastic study.

Quantifiable frozen-stress photoelastic techniques were used to analyze stresses induced in mandibular models by a conventional free-end saddle removable partial denture. Four quasi-anatomical mandibular models were constructed for processing, together with their respective calibration specimens, through identical time/temperature stress-freezing cycles. After processing and slicing, an unloaded control model demonstrated some low-order fringes adjacent to the coronal third of the abutment tooth roots, but was otherwise stress free. A lower bilateral free-end saddle partial denture was constructed and fitted in turn to each of the remaining three models. Each denture/model combination was then loaded and processed through a stress-freezing cycle. After processing, 6-mm slices were cut from selected regions for analysis for the presence of stresses. Using a polariscope with circular polarized, monochromatic light, values for maximum shear stress were calculated at selected points in the slices taken from the three loaded models. Variations up to 28% of the mean were obtained for the three experimental models as compared with the consistent results for the material fringe values obtained from the calibration specimens. The study pointed out the problems involved in using photoelastic stress analysis on complicated anatomical models. The interpretation of the results from such studies should be approached with caution.

Application of the least-squares method to elastic and photoelastic calibration of orthotropic composites

New experimental methods continue to be proposed for determining the in-plane elastic constants of orthotropic composite materials, as no single method has been found completely satisfactory. In particular, the in-plane shear modulus is difficult to measure. In this paper, an orthotropic half-plane subjected to a concentrated edge load is proposed as a calibration specimen. Photoelastic calibration of orthotropic-birefringent composites is also difficult due to the need to conserve the commercially unavailable, difficult-to-make model materials and the absence of many closed-form solutions. In this paper, the orthotropic half-plane specimen is proposed for photoelastic calibration of birefringent-orthotropic model materials also. For elastic and photoelastic calibration of orthotropic materials, the least-squares procedure is used for processing the experimental data.

Sputtered platinum films on colloidal gold particles: a calibration specimen for quartz film thickness monitors

SUMMARYA method for calibrating quartz crystal thickness monitors is described, which makes use of 20 nm platinum sputtered colloidal gold particles. The actual thickness is measured on transmission electron micrographs of gold particles protruding from the edge of fractured, rolled up, carbon films. In the range up to ∼10 nm, the measured thickness for platinum films is ∼17% larger than the figures calculated from mass thickness equations.

Photo-Orthotropic Elasticity: A New Technique For Stress Analysis Of Composites

This paper deals with the application of photoelastic methods to glass fiber reinforced plastics. The basic principles governing the photoelastic response in birefringent orthotropic composites are briefly reviewed. Then, three important aspects of photo-orthotropic elasticity, namely, photoelastic calibration, separation of principal stresses, and application to problems of engineering importance, are considered in detail. A new calibration specimen is proposed for determining the three independent photoelastic constants: an orthotropic half-plane subjected to a concentrated edge load. From the isochromatic response, the three stress-fringe values can be obtained by a least-squares procedure based on the theoretical stress distribution. Next, four methods of separating the principal stresses in birefringent composite models are proposed: the method of drilling small holes at the points of interest, the method of oblique incidence, the method of combining the transmitted photoelastic response with the reflected photoelastic response, and the method of birefringence dispersion.

Stylus instruments and reference specimens

Stylus techniques play an important role in the research and metrology of engineering surfaces. This review will discuss the strengths and limitations of stylus instruments from several points of view, including horizontal and vertical resolution, range, accuracy, and speed. Some important properties of roughness calibration specimens will be described as well as the design, specifications, and potential uses of a new series of sinusoidal precision roughness specimens. Comparisons will be drawn between stylus methods and certain optical techniques, and the results of experiments to relate stylus measurements to optical scattering measurements will be described.

The Measurement of Absorbed Charpy Impact Energy Using a Vertical Drop Tower

Abstract Standard Charpy calibration specimens designed for verification of pendulum impact machines have been tested on a vertical drop tower impact machine. Two different test techniques (optical velocity measurement and integrated digital load-time response) for measuring the fracture energy of these specimens have produced equivalent sets of data which match the range of expected pendulum machine results. The more flexible vertical drop tower machine can therefore be used to measure Charpy impact energies with the same reliability as the conventional pendulum machines.

New Method for the Calibration of the Inertia of Resonant Column Devices

Abstract Resonant column devices are popularly used to evaluate the shear moduli and damping characteristics of soils at small strain amplitude. To use the resonant column technique it is necessary to accurately know the value of the rotational inertia of the top mass of the apparatus JA to evaluate shear modulus values derived from resonant frequency values. The paper describes a new and simple method for evaluating JA for a resonant column device using two calibration rods of known geometry. The advantage of this calibration method is that a value of JA may be determined without having to know the material properties of the calibration specimen. The paper describes the theory of the calibration technique and gives dimensions of typical calibration samples that can be used for resonant column studies. Typical measured calibration values are presented to show the accuracy of the calibration technique.

Progress in the appraisal of surface topography during the first half-century of instrument development

Abstract The principal developments in the stylus measurement of roughness texture are traced. The instrument problems which were encountered, particularly with regard to the requirements of transmission characteristics and reference lines, are outlined. The behaviour of the skid is given further consideration, and a distinction is drawn between the systematic error resulting from its application to instrument calibration specimens and the random error to be expected from all kinds of workpieces. Brief consideration is then given to the development of roundness measurement and the requirements for avoiding excessive eccentricity distortion. Finally attention is drawn to some unfortunate anomalies that have arisen.

Measurements of plastic strain in copper due to sliding wear

Wear experiments have been conducted to determine the plastic strains that are introduced in surface material near sliding wear tracks. Both oillubricated and dry-sliding experiments have been carried out at different sliding distances on surfaces of copper. The strain values were determined from selected-area electron channelling patterns obtained from regions as small as 10 μm in size and 0.05 μm deep around the wear track using a scanning electron microscope. A deformed calibration specimen was used to relate the electron channelling band contrast to the deformation strain. Strain maps were obtained on the wear surface lateral to the wear track and also below the surface using electropolishing metal removal techniques. Particular attention was given to the near-surface strain values. In all cases the maximum strain was found at the wear surface located at the track center and the strains decreased uniformly with depth. Significant large strains were also found outside the wear tracks. The results are compared with those previously reported for iron and with other relevant studies.

Deformation studies at sliding wear tracks in iron

Determinations have been made of strains on the surface and subsurface of specimens of high purity iron after different distances of sliding wear. The method involved the measurement of loss of intensity (contrast) of particular electron channeling lines obtained from small selected areas near the wear track. A calibration specimen, deformed plastically to a range of strain values, was used to relate the channeling line contrast loss to plastic strain. Strain maps lateral to the wear track and below the original surface were obtained after removing controlled thicknesses of iron by electropolishing. In all cases the maximum strain was found at the track center location at the surface and the strains decreased steadily with depth below the track. With a 50 g load the strains vanished at about 40 μm depth. Significant strains were found to exist outside the wear track boundaries. There was no indication of a soft or less-hardened surface layer in any of the specimens studied.

ChemInform Abstract: REDUCTION OF ERRORS IN CERAMIC BEND TESTS

Abstract : Mechanical tests of most ceramics are subject to stringent requirements, more so than tests of materials which possess some ability to undergo plastic deformation. In this paper, sources of stress concentrations and spurious displacements which may be imposed during four-point bend tests of ceramic materials are identified and discussed. Particular areas of concern involve unequal moments at the loading points, twisting due to skewness of the contact lines, wedging stresses at point contacts, and counter moments produced by friction at the loading point-specimen interface. A bend fixture incorporating design features to significantly reduce these effects is described and results of measurements of the surface stresses in calibration specimens under load in the fixture are presented. (Author)

Reduction of Errors in Ceramic Bend Tests

Mechanical tests of most ceramics are subject to more stringent requirements than tests of materials which can undergo plastic deformation. The present paper identifies and discusses sources of stress concentrations and spurious displacements which may be imposed during 4‐point bend tests of ceramic materials. Particular areas of concern involve unequal moments at the inner loading points, twisting resulting from skewed contact lines, wedging stresses at point contacts, and counter moments produced by friction at the loading‐point‐specimen interface. A bend fixture incorporating design features which significantly reduce these effects is described, and results of measurements of the surface stresses in calibration specimens under load in the fixture are presented.

Residual-stress measurement using surface displacements around an indentation

An experimental method is described which can measure the direction and magnitude of residual and applied stress in metals. The method uses optical interference to measure the permanent surface deformation around a shallow spherical indentation in a polished area on the metal specimen. The deviation from circularly symmetrical surface deformations is measured at known values of applied stress in calibration specimens. This deviation from symmetry can then be used to determine the direction and magnitude of tensile residual stress in specimens of the same material. Determination of compressive residual stress is more limited.

A simple technique for removing (111) Cu or Ag single-crystal films from mica and their use in Moiré fringe electron microscope calibration specimens

A technique is described which enables copper or silver (111) films grown epitaxially on mica to be removed from the substrate by means of a two-stage process involving the use of hydrochloric acid and then distilled water.Silver grown epitaxially on the copper films so obtained gives rise to 11·1 Å Moiré fringes which are suitable for the calibration of an electron microscope.