Minimum Section Research Articles

Extensometer probe indentation during low-cycle fatigue of plain and circumferentially notched cylindrical bars at 550 °C

Cyclic stress–strain tests were undertaken at 550 °C on (i) plain and (ii) notched specimens of different acuities in several low- and highly-alloyed ferritic steels (1CrMoV, NF616, TB12M and HCM12A). Axial strains were measured between the minimum sections of the (semi-circular) notches using a longitudinal extensometer, while surface hoop strains were measured by means of a diametral extensometer with probes located at the notch root. Over a period of 100 cycles, softening occurred in both specimen types. Cycle-by-cycle embedding was observed for the (diametral) probe tips and was entirely due to testpiece working in the cyclic state, the sprung-load extensometer force being far lower than that encountered in conventional indentation experiments. An interpretation of the effect is offered (a) in terms of the internal stress state produced during cycling and (b) by an energy argument to explain the ‘ranking order’ of resistance to penetration. The effects of cyclically-induced oxidation, possible mechanisms for the embedding effect and likely reduction in endurance are considered.

The Influence of Viscous Effects and Physical Scale on Cavitation Tunnel Contraction Performance

The general performance of an asymmetric cavitation tunnel contraction is investigated using computational fluid dynamics (CFD) including the effects of fluid viscosity and physical scale. The horizontal and vertical profiles of the contraction geometry were chosen from a family of four-term sixth-order polynomials based on results from a CFD analysis and a consideration of the wall curvature distribution and its anticipated influence on boundary layer behavior. Inviscid and viscous CFD analyses were performed. The viscous predictions were validated against boundary layer measurements on existing full-scale cavitation tunnel test section ceiling and floor and for the chosen contraction geometry against model-scale wind tunnel tests. The viscous analysis showed the displacement effect of boundary layers to have a fairing effect on the contraction profile that reduced the magnitude of local pressure extrema at the entrance and exit. The maximum pressure gradients and minimum achievable test section cavitation numbers predicted by the viscous analysis are correspondingly less than those predicted by the inviscid analysis. The prediction of cavitation onset is discussed in detail. The minimum cavitation number is shown to be a function of the Froude number based on the test section velocity and height that incorporate the effects of physical scale on cavitation tunnel performance.

Reduced Beam Section Spring Constants

A moment connection that includes a wide flange beam with trimmed flanges is commonly known as a Reduced Beam Section (RBS) connection. Accurate analysis of frames incorporating RBS beams requires knowledge of the elastic stiffness matrix of RBS beams. In lieu of using this stiffness matrix, an RBS beam can be modeled as an Euler-Bernoulli frame element with rotational springs at each end, which can be easily implemented in structural analysis software. This paper presents the derivation of the formula for the spring constants of an RBS beam and validates it. From a study of the spring constants for a plethora of RBS beams, it was found that a strong linear relationship exists between the minimum plastic section modulus of RBS beams and their spring constants. This paper has direct applicability to the practical and accurate determination of the elastic drift of a moment frame with RBS connections.

Effect of cyclic loading on tensile properties of PC and PC/ABS

The effects of cyclic loading on tensile fracture properties of polycarbonate (PC) and the alloy of polycarbonate and acrylonitrile–butadiene–styrene (PC/ABS) are experimentally investigated in the paper. Two digital cameras are used to record simultaneously the tensile deformation of specimens and the large deformation and the necking process of these polymers are discussed. Two lateral contractions are not identical at the later tensile stages and the contraction ratios in each lateral direction are related with the tensile strains in axial direction on width and thickness surface. The curvature radiuses at the minimum section during necking process are shown. The volume increases during necking process and then decreases gradually. The yield stress and fracture stress of PC/ABS are lower than that of PC. The degradation of the fracture stress and fracture strain due to the application of cyclic loading is larger for PC than that for PC/ABS, and these can be used to explain qualitatively why PC has higher fatigue crack growth rate than PC/ABS.

Characterization of In-Plane Shear Properties of Laminated Composites at High Strain Rates

The in-plane shear responses of continuous fiber reinforced composite materials under high strain rates were characterized experimentally. The V-notch rail shear configuration was used for characterizing the in-plane shear behavior of Newport NB321/3k70 plain weave carbon fabric/epoxy, NCT/321/G150 Carbon Fiber Unitape/epoxy, NB321/7781 fiberglass/epoxy, Cytec PWC/T300/3KNT plain weave carbon fabric/epoxy and Fibercote 3KPW/E365 plain weave carbon fabric/epoxy systems. The testing was conducted using a servo hydraulic testing machine at nominal stroke rates ranging between 0.00083in/sec to 500in/sec. A maximum average shear strain rate of 654rad/sec was achieved up to shear strain levels of 0.08 radians, during the tests. The stress-strain behavior of all material systems exhibited contrasting behavior with increasing stroke rates. The stress-strain curves for all materials exhibited an asymptotic behavior for stroke rates approaching 10in/sec and were material dependent for stroke rates exceeding 250in/sec. For Newport NB321/3k70 and NB321/7781 systems at the highest test rate, the shear strengths increased by a factor of three relative to that of the quasi-static rate, and were independent of the reinforcement type. The shear strength for Cytec PWC/T300/3KNT, Fibercote 3KPW/E365 and Newport NCT/321/G150 increased until a stroke rate of 100in/sec and later decreased with increasing stroke rate. The failure modes for Cytec PWC/T300/3KNT, Fibercote 3KPW/E365 and Newport NCT/321/G150 were at the minimum section of the shear coupons, while for Newport NB321/3k70 and NB321/7781, failure was observed to change from a shear mode across the minimum section to a complex failure mode away from the minimum section.

Bulk Metallic Glasses: At the Cutting Edge of Metals Research

AbstractGlassy alloys (metallic glasses) are currently the focus of intense research in the international metals community. Setting aside elevated-temperature applications, these amorphous metals have exciting potential for structural applications. When metallic glasses were first widely studied in the 1960s, the alloy compositions then known to be quenchable into the glassy state from the liquid required high cooling rates on the order of 106 K s−1 and were consequently restricted to thin sections. The current interest in metallic glasses has its origin mainly in the increasing range of compositions that can now be cast into glasses at much lower cooling rates, permitting minimum sections of 1 mm to 1 cm or even larger. These bulk metallic glasses (BMGs) are the focus of the articles in this issue of MRS Bulletin. Our goal is to illustrate the major materials issues for BMGs, from processing to structures to properties and from the fundamental science of glasses to viable industrial applications. We hope that the articles, in providing a snapshot of a rapidly moving field, show why BMGs are attracting such intense interest and serve to highlight some challenging issues awaiting resolution.

Morphology of upper airway and surrounding tissues in non-apnea males aged seventy years or over: a magnetic resonance imaging study

To describe the morphology of upper airway in non-apnea males aged seventy years or over. Thirty-one non-apnea males aged 70 years or over [diagnosed by whole-night polysomnography (PSG), apnea and hypopnea index (AHI) < 10 per hour] had been taken magnetic resonance imaging (MRI) scanning. The narrowest point of upper airway was at velopharynx. The mean and the minimum section areas were (190.9 +/- 67.1) mm(2) and (112.1 +/- 47.7) mm(2), respectively. Each sagittal/transverse ratio was between 0.22 and 0.89. It showed an ellipse-like cross-section of upper airway, while velopharynx was the most "slender" segment (sagittal/transverse-caliber was 0.22 - 0.71). The min/max section area of upper airway was between 0.38 and 0.62. It demonstrated that each airway segment was a "cone-like" form, while the velopharynx was the steepest segment. In the non-apnea elderly males aged seventy years or over, the velopharynx was most likely to collapse.

Axial and Diametral Cyclic Stress—Strain Response in Plain and Circumferentially Notched Cylindrical Bars at 550 °C

Cyclic stress-strain tests were undertaken at 550 °C on plain specimens and notched specimens of different notch acuities in several low- and high-alloy ferritic steels (1Cr-Mo-V, NF616, TB12M, and HCM12A). Integrated axial strains were measured between the minimum sections of the notches using a longitudinal extensometer, while surface hoop strains were measured by means of a diametral extensometer with probes located across the notch root. The same extensometry was employed in plain specimens. Over a period of 100 cycles, softening occurred in all plain specimens. These effects were also demonstrated in notched specimens in both axial and diametral directions, although to a lesser degree. From hysteresis loops determined in the notch tests, the cyclic deformation response of the notched regions was expressed in terms of an ‘equivalent gauge length’. Deviations from elastic-plastic behaviour in plain specimens were noted in that the commonly used ‘effective Poisson's ratiO' was greater than calculated. The effect was investigated further by exploring the characteristics of a very shallow notch, induced by straining a plain specimen to the onset of necking and beyond. The implications of observed behaviour in strain-control low-cycle fatigue tests is discussed.

Model of the Commutation Phenomena in a Universal Motor

An equivalent electrical circuit, characterized by the minimum coil sections number necessary to analyze the commutation in a universal motor, is discovered. The model parameters are also determined: in particular, the self and mutual inductance coefficients and the electromotive force induced in the coil sections (taking into account the magnetic saturation), the brush-commutator voltage drop, the electric arc. By means of a numerical solution of the equivalent circuit, the current waveforms are analyzed; the comparison between the computed and measured waveforms of the brush-commutator voltage drops allows to verify the model.

Optimal Design of Parabolic Canal Section

Optimal design equations for a parabolic canal section are presented in this paper. The design equations for a minimum earthwork cost section and a minimum cost lined section are in explicit form and result in optimal dimensions of a canal in single step computations. These have been obtained after applying the Fibbonaci search method on a nonlinear unconstrained optimization problem. The study also addresses the bounds on the canal dimensions and the velocity of flow. A nondimensional parameter approach has been used to simplify the analysis, and a set of graphs for nondimensional parameters are presented as an alternative for design. Design procedures for different cases have been presented to demonstrate the simplicity of the method.

On the effect of a porous insert in the supersonic section of a nozzle upon change in its thrust

A nozzle in which the thermal energy of gases is converted into the kinetic energy of a gas jet is a basic element of the rocket engine. If the pressure in the external medium (or in the engine combustion chamber) varies, the conventional nozzle will not be optimal throughout the entire pressure range: it operates either in the underexpansion or overexpansion mode. The nozzle would be ideal if its expansion degree followed the changes in the external (internal) pressure, preserving an equality between environmental pressure and internal pressure at the nozzle cross section; but it is very difficult to realize this mode. There are various approaches to thrust-loss control in the case of overexpansion. For example, Semenov [1] proposed the use of air blow through an annular slot into the supercritical nozzle section operating in the overexpansion mode. However, this is only a singlestep variation in the degree of the nozzle off-design. The heat-resistant gas-permeable porous materials that are now available equalize, based on their gas permeability, the pressure inside the funnel with that in the environment at the nozzle section operating in the overexpansion mode, i.e., render the nozzle self-adjustable without any additional devices. Therefore, investigation of the effect of a porous insert on the nozzle thrust represents an urgent problem. To experimentally study this effect, we used a differential pendulum setup including reference and working nozzles. The installation was freely suspended on a bearing unit (Fig. 1) and was connected to the fixed base only by an elastic element of the strain-gauge balance; there were no other rigid bonds. The key measuring principle used in this installation is the comparison of the jet thrusts of two nozzles (working and reference), oriented in mutually opposite directions. To determine the effect of the porous insert on changes in the thrust of the nozzle, we performed two experiments with the same prechamber pressure p 0 . In the first experiment, the working nozzle with continuous walls was used, and, in the second, the porous insert was mounted in the supersonic section of the working nozzle (schematically shown by dashed lines in Fig. 2). As a result, the change in the thrust of the nozzle was determined from two experiments carried out with the identical prechamber pressure p 0 . The experimental procedure was described in more detail in [2]. The supersonic section of the nozzle was formed by a cone with a halfopening angle of α = 8i . The porous insert is the duralumin section x 1 < x < x 2 of the conic nozzle in which 1050 round holes approximately 1 mm in diameter with a total relative area of 18% were drilled. The radius of the minimum nozzle section is r * = 19.2 mm; the length of the supersonic section is x sr = 147 mm; and the coordinates of the porous section are x 1 = 82 mm and x 2 = 130 mm (Fig. 2).

Micro Mechanical Model of 3D Woven Composites

A combined beam model representing the periodicity of the microstructure and micro deformation of 3D woven composites is developed for predicting mechanical properties. The model considers the effects of off axial tension/compression and bending/shearing couplings as well as the mutual reactions of fiber yarns. The method determining microstructure by using woven parameters is described for a typical 3D woven composite material. An analytical cell, constructed by a minimum periodic section of yarn and interlayer matrix, is adopted. Micro stresses in the cell under in plane tensile loading are obtained by using the proposed beam model and macro modulus is then obtained by the averaging method. Material tests and a 2D micro FEM analysis are made to evaluate this model. Analyses reveal that micro stress caused by tensile/bending coupling effect is not negligible in the stress analysis.

Design of Minimum Seepage-Loss Nonpolygonal Canal Sections with Drainage Layer at Shallow Depth

Analytical solutions exist for the seepage discharge from polygonal and nonpolygonal canal sections underlain by a drainage layer at a hydraulically infinite depth. These solutions lead to underestimation of the seepage discharge if a drainage layer occurs at a shallow depth. This paper presents solutions for seepage discharge from circular and exponential sections overlying a shallow drainage layer. The discharge has been calculated by a finite-difference-based numerical solution of the differential governing the seepage flow. The phreatic boundaries of the flow domain were described in terms of two parameters that were estimated by a minimization process. Such seepage computations were performed for a large number of independent dimensionless variables of the section geometry. Subjecting the computed seepage to regression analyses, explicit equations for seepage discharge loss have been obtained. Using these seepage loss equations, the design variables for minimum seepage loss have been obtained. The use of the design equations has been illustrated by design examples.

On the onset of necking in the tensile test

A very small inhomogeneity in macroscopic material properties is considered for the investigation of necking of a (polycrystalline) bar in the tensile test. A simple, one-dimensional model is adopted (i.e. spatial variation only along the bar's length), corresponding to which the evolving nonuniformity of cross-sectional area with increasing load, up to the maximum, also is small. The inhomogeneity is represented by a single modulus varying slightly with position, but with the same dimensionless form of the stress–strain curve throughout. A transcendental equation is derived that relates the strains at the weakest and strongest sections to their respective material strengths. It is shown that, at the well known Considère strain (corresponding to the maximum load), the decrease in area at the minimum section is only a little greater than at the strongest, but its rate of change with the latter strain is infinite. The analysis thus gives an idealized representation of the rapid increase in necking that typically ensues from the maximum load in experiments. In an extended Appendix the traditional case of a bar of theoretically homogeneous material is reviewed and reanalyzed, including consideration of rate-dependence.

Application of an extended void growth model with strain hardening and void shape evolution to ductile fracture under axisymmetric tension

Abstract The version of the Gurson model adapted by Tvergaard is extended by fitting, based on numerical results proposed in the literature, the tuning parameters q1 and q2 in order to better capture the effects of the strain hardening and void shape evolution. The model is completed by two types of analytical void coalescence criteria, one for internal necking (Thomason 1968 and 1990) and one for void sheet (McClintock 1968). The validity of the proposed formulation is realized through comparison with more elaborate finite element models found in the literature. Using an approximate description of the variation of the stress triaxiality in the minimum section of an axisymmetric necking zone, the void growth rates and fracture strains are predicted. These are evaluated for several ductile alloys for which the experimental micro-mechanical data are reported in the literature.

Effects of Injection Configuration on Performance of a Staged Supersonic Combustor

Performance of a staged supersonic combustor with two-staged wall injections was examined experimentally in a direct-connected wind-tunnel facility with a combustion heater, which supplied Mach 2.5 airflow with a total temperature of 1500 K. The fuel flow rate through the first-stage wall injectors in the combustor's minimum cross-sectional area section was limited to avoid combustor-inlet interaction, and the second-stage injection in the following divergent section was used to increase the pressure in this section. The performance was compared with that of the combustor with first-stage strut/second-stage wall injection configuration, while the strut was kept installed in both cases. The first-stage wall injection at a fuel flow rate caused a pressure rise almost equivalent to that of the first-stage strut injection, whereas it resulted in the combustor-inlet interaction at a lower fuel flow rate. Staged injection with the first-stage wall injection resulted in lower combustion efficiencies of the second-stage fuel mainly because of poor jet penetration, poor fine-scale mixing, and slower reaction and resulted in poorer combustor performances than those with the first-stage strut injection. Installation of the strut was found to have little effect on the performance of the combustor with the two-staged wall injections.

In-situ Evaluation Of Timber Roof Structures Of Historic Buildings

Condition assessment is an important step before repairs of timber structure. In the past, the experienced master carpenters carried out these works in Taiwan. This paper addresses the inadequacy of the traditional evaluation method, and proposes a new methodology to evaluate a roof structure by taking into account the structural performance. The method can be divided into three steps, first the visual inspection was conducted to record necessary information for further structural studied. Secondly, the structural analysis of the trusses was carried out in order to obtain the stresses in members. Comparing the resultant stress under loading with allowable stress, safety factor in each member was calculated. Finally, the unsafe and suspect members are designated for further nondestructive testing - the drill resistance. After considering the structural performance of the roof structure and condition in each member, the members that cannot meet the requirement will be found and recommended for replacement. Furthermore, the proper minimum section of each member that should be replaced is also proposed in this paper.

Closure to “Design of Minimum Seepage-Loss Nonpolygonal Canal Sections” by Prabhata K. Swamee and Deepak Kashyap

Closure to “Design of Minimum Seepage-Loss Nonpolygonal Canal Sections” by Prabhata K. Swamee and Deepak Kashyap

Discussion of “Design of Minimum Seepage-Loss Nonpolygonal Canal Sections” by Prabhata K. Swamee and Deepak Kashyap

Discussion of “Design of Minimum Seepage-Loss Nonpolygonal Canal Sections” by Prabhata K. Swamee and Deepak Kashyap

Polypyrimidine tract binding protein and poly r(C) binding protein 1 interact with the BAG-1 IRES and stimulate its activity in vitro and in vivo.

The 5'-untranslated region of Bag-1 mRNA contains an internal ribosome entry segment (IRES) and the translation of Bag-1 protein can be initiated by both cap-dependent and cap-independent mechanisms. In general, cellular IRESs require non-canonical trans-acting factors for their activity, however, very few of the proteins that act on cellular IRESs have been identified. Proteins that interact with viral IRESs have also been shown to stimulate the activity of cellular IRESs and therefore the ability of a range of known viral trans-acting factors to stimulate the Bag-1 IRES was tested. Two proteins, poly r(C) binding protein 1 (PCBP1) and polypyrimidine tract binding protein (PTB), were found to increase the activity of the Bag-1 IRES in vitro and in vivo. The regions of the Bag-1 IRES RNA to which they bind have been determined, and it was shown that PCBP1 binds to a short 66 nt section of RNA, whilst PTB interacts with a number of sites over a larger area. The minimum section of the RNA that still retained activity was determined and both PCBP1 and PTB interacted with this region suggesting that these proteins are essential for Bag-1 IRES function.