Cylindrical specimens

In this paper, discontinuities in cylindrical specimens were studied by ultrasonic reflection tomography. The aim was threefold. First, to localize discontinuities from circular C-scan images. Second, to reconstruct quantitative cross-sectional images from circular B-scan profiles (i.e., reflection tomograms). Finally, to obtain three-dimensional information (i.e., discontinuity location, dimension and type) by stacking these reflection tomograms in multiple planes, in the third dimension. 

In order to ensure perpendicular beam incidence on the cylindrical specimen, the circular B-scan profiles were acquired by high frequency (narrow beam) transducers in a synthetic circular aperture array. From these profiles two-dimensional reflection tomograms were reconstructed using a filtered backprojection technique. Straight line propagation was assumed. Several artificial discontinuity types in a cylindrical Plexiglas (Perspex) specimen were compared with similar artificial discontinuities in a cylindrical A/Si-alloy [2]. Furthermore, examples of real discontinuities (an inclusion and a feed head) in the cylindrical AlSi-alloy are presented. 

Some of the problems often encountered during ultrasonic inspection of plane specimens are also found on cylindrical specimens. For example, problems associated with the directional characteristic of the ultrasonic transducer. Furthermore, the discontinuity influences the shape and propagation direction of a reflected pulse, causing wave mode transformation. In addition, the specimen influences the shape and amplitude of the reflected pulse by sound absorption. 

Some discontinuities may be identified by a conventional two-dimensional ultrasonic technique, from which the well-known C-scan image is the most popular. The C-scan technique is relatively easy to implement and the results from several NDE studies have been very encouraging [1]. In the case of cylindrical specimens, a circular C-scan image is convenient to show discontinuity information. The circular C-scan image shows the peak amplitude of a back-scattered pulse received in the circular array. The axial scan direction is shown as a function of transducer position in the circular array. The circular C-scan image serves also as an initial step for choosing circular B-scan profiles. The latter provides a mapping between distance to the discontinuity and transducer position in the circular array. 

More recently, the circular array was proposed to assess the reflectivity of cylindrical specimens [3]. First, a circular C-scan image was obtained. The total scan time was about 25 min., which does not include a relatively time consuming alignment of the specimen. From the circular C-scan image, circular B-scan profiles were chosen in specific planes. The transducer was a focused high frequency transducer with a center frequency of 25 MHz of the transducer bandwidth. This frequency corresponds to a wavelength of 0.11 mm and 0.25 mm in the Plexiglas specimen and the AlSi-alloy, respectively. Additional experimental parameters are presented in Table 1. 

Several discontinuity types in Plexiglas and A/SZ-alloy cylindrical specimens were studied by... 

X-ray powder diffraction studies are perfonned both with films and with counter diffractometers. The powder photograph was developed by P Debye and P Scherrer and, independently, by A W Hull. The Debye-Scherrer camera has a cylindrical specimen surrounded by a cylindrical film. In another commonly used powder... 

Over 25 years ago the coking factor of the radiant coil was empirically correlated to operating conditions (48). It has been assumed that the mass transfer of coke precursors from the bulk of the gas to the walls was controlling the rate of deposition (39). Kinetic models (24,49,50) were developed based on the chemical reaction at the wall as a controlling step. Bench-scale data (51—53) appear to indicate that a chemical reaction controls. However, flow regimes of bench-scale reactors are so different from the commercial furnaces that scale-up of bench-scale results caimot be confidently appHed to commercial furnaces. For example. Figure 3 shows the coke deposited on a controlled cylindrical specimen in a continuous stirred tank reactor (CSTR) and the rate of coke deposition. The deposition rate decreases with time and attains a pseudo steady value. Though this is achieved in a matter of rninutes in bench-scale reactors, it takes a few days in a commercial furnace. 

In order to test the strength of a ceramic, cylindrical specimens of length 25 mm and diameter 5 mm are put into axial tension. The tensile stress a which causes 50% of the specimens to break is 120 MPa. Cylindrical ceramic components of length 50 mm and diameter 11 mm are required to withstand an axial tensile stress with a survival probability of 99%. Given that m = 5, use eqn. (18.9) to determine oh... 

For a thicker laminate than in Figure 6-26, the critical length is longer and the curvatures are smaller. For example, for a [04/904]-,-laminate, the critical L is 71 mm. Moreover, what was a circular cylindrical specimen at 50 mm for a [02/902lx laminate becomes a saddle-shaped specimen [6-38]. 

Triaxial compression tests are another means of determining shearing strength of a soil. A complex device is used to apply pressure along the sides of a cylindrical specimen and axially down the axis of the cylindrical specimen. In general, triaxial tests are superior to direct shear tests since there is better control over intake and discharge of water from the specimen. 

NOTE 1 Tensile properties shall be determined bp tests on cylindrical specimens conforming to the requirements of ASTM A-STO, 0J% offset method. 

In the case of the ASME codes for nuclear pressurised components, the questions of fatigue design and of flaw evaluation are dealt with separately in ASME Section III and Section XI Appendix A, respectively. The design S-A curve for machined butt welds typical of thick section pressurised components is set at a factor of two on stress range or twenty on cyclic life, whichever is more conservative, below the mean of S-N data developed on smooth cylindrical specimens in air. (A somewhat similar design curve obtained by a different method from experimental S-A data for machined butt welds is given in British Standard 5500.) These safety factors are intended to encompass any adverse influence of minor weld defects, size effects, data scatter and environment. As far as environmental effects are... 

Fig. 19.9 Methods of mounting specimens, (a) Wire soldered to metal specimen, wire being enclosed in glass tube (b) specimen completely encapsulated in cold-setting resin and resin ground down to expose one face (c) specimen clipped into machined p.t.f.e. holder (d) Stern-Makrides pressure gasket for cylindrical specimen (e) pressure gasket for sheet or foil ...

Quartz fine aggregate and normal Portland cement were used to prepare mortar with a w/c of 0.5. A cylindrical specimen, 43 mm in diameter and 50 mm long, was cast and cured under sealed conditions for 3 days at 23 °C. The specimen was then oven dried at 105 °C for 1 day prior to exposure to lithium nitrate solution. The specimen was then placed such that the bottom of the cylinder was submerged approximately 1-2 mm into a lithium nitrate solution with Teflon tape applied to the curved surface. 

Time of setting of concrete mixtures by penetration resistance Change in height at early ages of cylindrical specimens from cementitious mixtures... 

Several additional, non-microstructural, inputs are required for the fracture model (i) Particle critical stress intensity factor, KIc. Here, the value determined in a previous study (Klc = 0.285 MPa in )[3] was adopted for all four graphites studied. This value is significantly less than the bulk Klc of graphites (typically -0.8-1.2 MPa rn). However, as discussed in the previous section, when considering fracture occurring in volumes commensurate in size with the process zone a reduced value of Klc is appropriate (ii) the specimen volume, taken to be the stressed volume of the ASTM tensile test specimens specimen used to determine the tensile strength distributions and (iii) the specimen breadth, b, of a square section specimen. For cylindrical specimens, such as those used here, an equivalent breadth is calculated such that the specimen cross sectional area is identical, i.e.,... 

The cylindrical specimens (exposed area 3-10 cm ) were placed vertically in the cell. The specimen holder was provided with a collar that was filled with argon during testing. The crevice between the specimen holder and specimen was filled with a stream of argon to hold back solution from the crevice. However, distribution of the gas is critical and difficult to control satisfactorily. 

Figure 16. Electrode for pitting measurements with cylindrical specimens using the Avesta cell principle. The modification of the specimen holder is described in ASTM GS. Designed by Mathiesen and Maahn. (Reprinted from Ref. 73 by permission of the authors.)...

Compressive strength, or ability of a specimen to resist a crushing force, is measured by crushing a cylindrical specimen (ASTM-D-695) as shown in Figure 14.14. Here a sample of specified dimensions is placed between two heads, one movable and one set. Force is applied to the movable head moving it at a constant rate. The ultimate compression strength is equal to the load that causes failure divided by the minimal cross-sectional area. Since many materials do not fail in compression, strength reflective of specific deformation is often reported. 

Let the reaction be first order, and assume that the specific rate constant and effective diffusion coefficient are constant throughout the rod. It can easily be shown that, for a cylindrical specimen, the differential equation to be solved is... 

Figure 7. Plot of effective gage length (EGL) vs. strain comparing the Saylak cylindrical specimen with the JANAF specimen. Three propellant formulations were tested (83)...

Forced sinusoidal oscillatory torsion imposed by mechanical drive to hollow cylindrical specimen through bell-crank arrangement... 

Absorption. The effect of absorption of X-rays in a powder specimen is to diminish the intensities of reflections at small angles much more than those of the back reflections (see Fig. 68). Corrections cart be calculated for cylindrical specimens of known diameter (Bradley, 1935), these corrections being valid also for cylindrically shaped single crystals. For crystals of natural shape completely bathed in the X-ray beam, it... 

The simplest way to construct these electrodes is to solder or glue with silver epoxy resin a cylindrical specimen of the electrode material to a stainless steel shaft. A mantle of epoxy resin or plastic is then made around the disc to the shape required. 

The elongation measured over a fixed gage length, and the reduction of area of the section at the fracture are measures of ductility. In cylindrical specimens, the area is readily determined from the final diameter at the fracture. The percent reduction of area is then determined as original area minus final area, divided by original area. 

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