Bar Loading Research Articles

Adaptive fault bar distribution in a long-distance migratory, aerial forager passerine?

Fault bars are translucent bands produced by stressful events during feather formation. They weaken feathers and increase their probability of breakage, and thus could compromise bird fitness by lowering flight performance. It has been recently suggested (‘fault bar allocation hypothesis’) that birds could have evolved adaptive mechanisms for reducing fault bar load on the feathers with the highest function during flight. We tested this hypothesis by studying first-year individuals of the long-distance migratory, aerial forager barn swallow Hirundo rustica . We predicted that fault bars should be less abundant on the outermost wing and tail feathers, but more frequent on the tail than on the outermost wing feathers. Accordingly, we found that fault bars occurred more often in tertials than in primaries or secondaries. Tail feathers had fewer fault bars than tertials, but more than primaries. Within the tail, the distribution pattern of fault bars was W-shaped, with the highest fault bar load occurring on the streamers and on the two central feathers. Because streamers are the most important tail feathers for flight performance, this finding seems to contradict the ‘fault bar allocation hypothesis’. However, flight performance is much less sensitive to changes in the shape of the tail than of the wings, which could explain why evolutionary forces have not counteracted the increase of fault bars associated with feather elongation during the recent evolution of streamers in the tail of hirundines. © 2005 The Linnean Society of London, Biological Journal of the Linnean Society , 2005, 85 , 455‐461.

Research in the Limiting Efficiency of Plastic Deformation of Multilayer Tension (Compression) Bars

A method is proposed for calculating the limiting loads of multilayer bars in plastic deformation. The regularities of changes in the efficiency factor (EF) of plastic deformation in relation to the elastic moduli of the materials of which the bars are composed, the stress which causes the material plasticity, and variations in the cross-sectional areas of layers are examined. Mathematical expressions are derived which allow one to easily calculate the EF for arbitrary values of variable parameters and to find the limiting values of EF when one of the parameters is changed. The equivalent tension diagram for a multilayer bar is obtained in relation to the strength and stiffness of materials and their number and cross-sectional areas.

A theory for plastic-bonded materials with a bimodal size distribution of filler particles

Plastic-bonded materials are composites consisting of grains of filler material embedded in a polymeric matrix. A micromechanics model is proposed for investigating the mechanical behaviour of plastic-bonded materials having two disparate grain sizes. A hybrid theory is proposed to handle some aspects of the bimodal grain size distribution. Our model uses the first-order method of cells with an eight-cell representative volume element where one of the eight cells contains a large grain and the seven remaining cells contain a mixture of small grains embedded in the polymeric binder material. A Mori–Tanaka-based analysis is used to describe the small grain-binder mechanical response. The small grains in this analysis are assumed to be spherical and uniformly distributed in the binder. In this work, we use the explosive PBX 9501, in its unreacted state, as our test system. The explosive grain particle size distribution of PBX 9501 consists of two broad peaks centred at approximately 1 and 200 µm. The constitutive behaviour of the large explosive grains are assumed to be elastic-plastic and damage by way of micro-crack brittle fracture. Only linear elasticity of the small grains is considered. The rate and temperature dependence of the mechanical response of the polymer binder is accounted for by a generalized Maxwell viscoelasticity model. The theoretical uniaxial stress–strain response for PBX 9501 is reported for quasi-static and split Hopkinson pressure bar loading rates and compared to experimental measurements.

Cyclic Properties of Superelastic Shape Memory Alloy Wires and Bars

This study evaluates the properties of superelastic Ni.Ti shape memory alloys under cyclic loading to assess their potential for applications in seismic resistant design and retrofit. Shape memory alloy wire and bars are tested to evaluate the effect of bar size and loading history on the strength, equivalent damping, and recentering properties of the shape memory alloys in superelastic form. The bars are tested under both quasistatic and dynamic loading. The results show that nearly ideal superelastic properties can be obtained in both wire and bar form of the superelastic Ni.Ti shape memory alloys. However, the wire form of the shape memory alloys show higher strength and damping properties compared with the bars. The recentering capabilities (based on residual strains) are not affected by section size. Overall, the damping potential of shape memory alloys in superelastic form is low for both wire and bars, typically less than 7% equivalent viscous damping. Cyclical strains greater than 6% lead to degradation in the damping and recentering properties of the shape memory alloys. Strain rate effects are evaluated by subjecting the shape memory alloys to loading rates representative of typical seismic loading. The results show that increased loading rates lead to decreases in the equivalent damping, but have negligible effects on the recentering properties of the shape memory alloys.

Deformation behavior of the Zr 41.2Ti 13.8Cu 12.5Ni 10Be 22.5 bulk metallic glass over a wide range of strain-rates and temperatures

The stress-strain relations for the Zr 41.2Ti 13.8Cu 12.5Ni 10Be 22.5 bulk metallic glass (Vitreloy 1) over a broad range of temperatures (room temperature to its supercooled liquid region) and strain rates (10 −5 to 10 3 s −1) were established in uniaxial compression using both quasi-static and dynamic Kolsky (split Hopkinson) pressure bar loading systems. Relaxation and jump in strain rate experiments were conducted to further understand the time dependent behavior of Vitreloy 1. The material exhibited superplastic flow above its glass transition temperature (623 K) and strain rates of up to 1 s −1. The viscosity in the homogeneous deformation regime was found to decrease dramatically with increasing strain rate. A fictive stress model was used to describe the basic deformation features of Vitreloy 1 under constant strain-rate loading as well as multiple strain-rate loading at high temperatures.

Prediction of the maximum load of pre-cracked welded bars using Charpy data according to the default level of the European SINTAP procedure

A number of tests have been carried out on (component-like) welded bend bars in order to establish the probability distribution of critical loads. This information serves as reference solutions for evaluating the Default level of the European flaw assessment procedure, structural integrity assessment procedure, which is based on the yield strength and Charpy data as the only input information often available to the user. Despite the poor input information, the procedure has shown to yield conservative but suitable predictions of the critical load distribution in the ductile-to-brittle transition range.

Damping characteristics of a CuZnAlNi shape memory alloy

In this paper the mechanical behavior of copper-based SMA bars and their potential use for dissipating seismic energy is examined. In particular, results obtained from cyclic tests under tension–compression loading of martensitic CuZnAlNi shape memory alloy bars, with two different processing histories (hot rolled or extrusion), are reported as a function of strain amplitude, grain size and frequency. The stress–strain loops were asymmetric with respect to the central point and rather stable, especially for strains up to 2%. The effective module of elasticity diminishes significantly with strain. From hysteretic cycles, an equivalent damping of 12% was obtained for the larger strains imposed. The maximum tensile strain attained before fracture was 3.5%. Frequency, in the range of interest for seismic applications, had only a small influence on the damping values. For the conditions studied in this research, the bars produced from both processing histories presented similar mechanical properties. Fracture, when it occurred, was due to tensile action and it was rather brittle and intergranular.

Nonperfect Aluminum Beams Subjected to Concentrated Loading

The response of aluminum beams subjected to concentrated loading is investigated experimentally through a series of 52 tests. Three different aluminum alloy AA6082-T6 extrusions are included in the test program: one double T section and two square hollow sections with different wall thicknesses (SHS-3 and SHS-5). These profiles were tested as simply supported beams loaded either at the midspan or at the end supports. The results show that web thickness, flange stiffness, beam span, and overhang are important factors that influence the capacity. In addition, the influence of applying the concentrated load through a circular or rectangular bar was investigated for the SHS-5 extrusion, and for all cases where bending was limited, the circular bar loading significantly increased the capacity. The beams were rotated systematically about the longitudinal axis in order to investigate the influence of loading the specimens on their different sides, and the effect was measured in the range of 3.2–11.4% of the mean values for each cross section and loading case. Furthermore, comprehensive measurements of the material properties and the initial geometry, including geometrical imperfections, were important for investigation of the influence of material and geometry variations on the member response.

Aerogel-based thermal insulation

Commercial development of aerogel granules, produced via ambient pressure processing, for advanced thermal insulation is discussed. By employing modeling and experimental verification, the thermal performance of granule compacts was studied. The application of a novel approach for surface modifying carbon black to the problem of adding opacifiers to silica aerogels is shown and improved thermal and mechanical properties were obtained. When opacified granules are produced with the correct density/strength, the application of a 1 bar load (as is naturally applied in vacuum panels) results in deformation/rearrangement such that a packing fraction approaching one is achieved. The thermal performance of these granule compacts, at ambient pressure and vacuum, is similar to that of aerogel monoliths without the cost and processing problems of monoliths.

Dynamic uniaxial crushing of wood

Experimental results are provided from a series of tests on the uniaxial dynamic crushing of cylindrical specimens of five species of wood selected for the density range they cover and tested up to impact velocities of approximately 300 ms−1. An account of the macro-deformation and micro-deformation modes resulting from quasi-static and dynamic uniaxial compression is given. Measurements of the force pulses generated by the impact of the wood specimens on the end of a Hopkinson bar load cell show that significant enhancements of the initial crushing strengths of the specimens occur under dynamic loading conditions. The deformation mechanisms of wood are localised under quasi-static compression and under dynamic loading conditions they become even more localised and propagate through the material as crushing wave fronts which have some of the characteristics of shock waves. A simple shock model based upon a rate-independent, rigid, perfectly-plastic, locking (r-p-p-l) idealisation of the stress-strain curves for wood is proposed to provide a first order understanding of the dynamic response. This model is particularly successful in predicting the dynamic enhancement of the crushing strength of specimens loaded across the grain as confirmed by comparisons between the experimental data and theoretical results. It is less successful for those compressed along the grain. The source of the discrepancy is discussed and explanations are provided for the fairly constant crushing stress enhancement factor observed at low to moderate impact velocities, for the high impact velocity at which shock-type response is initiated and for the existence of clearly delineated crush fronts which characterise these specimens.

Stability of elastic bars on uncertain foundations using a convex model

A method is presented for evaluating the buckling load of weightless prismatic rigid bars resting on uncertain foundations which are modeled using linear extensional elastic springs. The uncertainty in the spring elements is expressed in terms of a nonprobabilistic convex model. An ellipsoidal bound is used which defines the uncertainty of the foundation in terms of a size parameter and the deviations of the elastic spring constants from their nominal values. The size parameter represents the size of the ellipsoid and is analogous to the standard deviation magnitude in probabilistic analyses. The semiaxes of the ellipsoid are the deviations of the foundation spring constants from their nominal values and they determine the shape of the ellipsoid. A first-order analysis shows that the reduction in the buckling load, when uncertainty in the foundation's spring stiffnesses is present, is a linear function of the size parameter and a nonlinear function of the semiaxes of the uncertainty ellipsoid. For the same uncertainty in the spring elements, different reductions in the buckling load result for beams with multimode buckling.

Component Dowel-Bar Model for Load-Transfer Systems in PCC Pavements

A component dowel-bar model has been developed to simulate the doweled joint in portland-cement-concrete (PCC) pavements. The model consists of two bending beams of finite length, embedded in concrete, connected by a shear-bending beam. The objective is to model the dowel-bar load-transfer mechanism in PCC pavements. The new model can appropriately consider the interaction between concrete and embedded dowels. The model allows a rigorous numerical analysis without an increased number of unknowns. The model can be integrated into a finite-element program to predict the responses of the load transfer system, including distributions of bending moment, shear force and bearing stress of each dowel without using the assumption of effective length. A comparison between experimental and analytical results has verified that the component model can be used to reasonably predict the responses of a dowel bar load transfer system.

Dynamic Behavior of Elastic/Viscoplastic Stepped Bar Due to Torsional Impact.

Two-dimensional elastic/viscoplastic stress waves in a semi-infinite stepped bar are analyzed numerically, when torsional impacts are applied to the end face of the stepped bar. For the numerical analysis, a finite difference method along the bicharacteristic is employed. By examining the distributions of maximum tensile stress arising in the vicinity of the junction of the stepped bar, influences of the stepped bar shape and loading condition on stress concentration are investigated. It is also found that the maximum tensile stress is at the corner of the stepped bar for every numerical condition.

Prediction of the oxygen cost of the deadlift exercise.

The purpose of this study was to examine the relationship between total estimated work, bar load and total oxygen consumption (TVO2) during the deadlift exercise. Forty-two observations of TVO2 during a wide range of deadlifting bouts were made on a heterogeneous sample of 10 males and 14 females. TVO2 was measured by standard open-circuit spirometry. An R of 0.912 for work and TVO2 indicated that total estimated work during deadlifting can be used to predict oxygen cost accurately. The calculated regression equation was TVO2 (litres of O2) = 2.63 + 0.80 work (kJ) with a S.E.E. of 1.50 litres O2. An R of 0.909 for bar load and TVO2 indicated essentially the same predictability using bar load as the independent variable. The calculated regression equation was TVO2 (litres O2) = 2.88 + 0.005 bar load (kg) with a S.E.E. of 1.5 litres O2. Care should be taken when converting oxygen cost to energy expenditure values using non-protein R equivalents, since underestimations are likely, due to the heavy glycolytic involvement.

Increase in calciuria and oxaluria after a single chocolate bar load.

Chocolate, a foodstuff rich in sucrose, fat and oxalate, is considered unsuitable in cases of obesity, diabetes mellitus, urolithiasis and postprandial hypoglycemia. However the pathophysiological effects of chocolate are poorly documented. Therefore we investigated the effects of ingestion of 100 g dark chocolate bar (45 g cocoa and 55 g sucrose) on carbohydrate, calcium and oxalate metabolisms in 10 healthy subjects. Results were compared to those of 55 g sucrose intake (control group) performed on another day. Chocolate caused i) a lesser but longer increase in plasma glucose, insulin, and C-peptide than sucrose (respectively +23% of baseline vs +60%, p < 0.001; +436% of baseline vs +755%, p < 0.01 and +200% of baseline vs +331%, p < 0.01), ii) a striking increase in triglyceridemia, calciuria and oxaluria (respectively +96%, p < 0.01; +147%, p < 0.01 and +213%, p < 0.001). Thus, chocolate (cocoa+sucrose) causes a lesser pancreatic stimulation than sucrose. However, the increases in both calciuria and oxaluria (induced respectively by sucrose and cocoa) following chocolate ingestion might contribute to urinary conditions favoring the development of calcium oxalate calculi.

Long wavelength impact of izod fracture specimens: An experimental/numerical investigation

Elastic wave propagation fields for a stationary crack in an Izod fracture specimen have been investigated. Moire interferometry was used to obtain the asymptotic cracktip displacement fields under Hopkinson bar loading at sampling rates on the order of 100 kHz. Mixed-mode stress-intensity factors as a function of time were extracted from the displacement data using local asymptotic extrapolation. Two-dimensional continuum finite elements were employed and agreement was found between actual experiment and two-dimensional computation.

Load–displacement behaviour of socketed piers—Hamilton General Hospital

Monitoring the settlement behaviour of full-scale drilled pier foundation that are in service is seldom possible. This report describes the instrumentation and monitoring program for three of the drilled pier foundations socketed into weak shale used for the Hamilton General Hospital addition, and presents and summarizes the data collected over a period of almost 2 years.The three socketed piers were constructed so that each had different load support conditions. Pier P5 was conventional, and supported loads through shaft resistance in the soil and rock and end bearing in the rock. Pier K3 was similar except shaft resistance in the soil was eliminated by installing a sonotube casing in the upper portion of the shaft. Pier P3, which also had a sonotube casing, was constructed with a void apparatus at the base to eliminate end bearing resistance so that support was achieved only through shaft resistance in the rock socket.Instrumentation included multiple-point rod extensometers, with remote readout, to measure vertical displacements at the top of the pier, top of the rock, and bottom of the socket. Load cells, reinforcing bar load cells, and concrete embedment strain gauges were also installed in an attempt to determine load distribution in the pier foundations.Under approximately full dead loading, less than 3 mm (1/8 in.) settlement has been observed. The settlement and bottom load cell data suggest that very little of the applied loading (less than 5%) has been transferred to the base of the socket. Key words: rock-socketed piers, settlement, load transfer, weak shale, instrumentation, monitoring, full-scale foundations.

A buckling model for reinforcing bars

An analytical method is developed for determining the buckling load of the longitudinal bars in reinforced concrete elements subjected to high axial loading and large compressive strains. The proposed model is comprised of a beam of infinite length on equidistant intermediate supports having equal stiffness. On account of the presence of the concrete core, the problem becomes one of unilateral instability. The length of the half-wave characterizing the buckled shape is obtained by studying the deflection curves satisfying the unilaterality condition. A general analytical formulation is given which solves the problem in a closed form, whatever the number of supports comprised in the half-wave. A comparison with experimental results by other researchers demonstrates the validity of the model proposed.

Force calculations in the drop forging of porous powder preforms on crank presses

Analytical dependences were obtained for calculating the specific deformation force during drop forging porous powder preforms, with consideration of the dimensions and initial density of billets. These permit construction of a graph of the operational slide bar load of a crank press for a given case of forging. These are principal aspects in planning calculations for equipment and for development of the technical process of drop forging porous billets. A check of the dependences obtained by comparison with experiment indicated adequately good agreement between calculated and experimental data.

Influence of pre-buckling displacements on the elastic critical loads of thin walled bars of open cross section

Nonlinear expressions for the strains occurring in thin walled bars of open cross section, when subjected to axial, flexural and torsional displacements, are incorporated in a general instability analysis based on the vanishing of the second variation of the total potential energy. It is shown that the influence of the pre-buckling displacements is automatically included in the analysis. A closed form solution for the lateral buckling of a simply supported beam subjected to uniform bending agrees exactly with a solution based on the governing differential equations. Solutions obtained using numerical methods are also presented. The significance of the second order axial strains induced by rotation about the shear centre, is investigated by considering the instability of an inverted T- beam subjected to uniform bending.