Nonlinear Dynamics of a Harmonically-Excited Inelastic Inverted Pendulum

Issues of dynamic stability for a single-degree-of-freedom system subjected to a time-varying axial load are presented. The linearized differential equation of motion for the model structure is given by the well-known Mathieu equation. Parametric resonance leading to dynamic instability is known to occur for such a system. This paper examines the response of the geometrically exact model for two inelastic constitutive models—an elastic-perfectly plastic model and a cyclic Ramberg-Osgood model. Damage evolution, represented by degradation of the elastic stiffness, is also considered. Analysis results demonstrate behavior that is counterintuitive to what would be expected under static or monotonic loading conditions. Though simple, this structural model helps illustrate the complex features in the response of an inelastic dynamical system.     

The effects of oxygen concentration and temperature on cyclic creep in niobium-oxygen alloys

The effects of dynamic solute-dislocation interactions on cyclic creep in niobium-oxygen alloys have been examined by comparing static and cyclic creep in the dynamic strain-aging temperature range. In all comparisons, the peak stress in cyclic creep tests was identical to the constant stress in static creep tests. Niobium purified of interstitial solutes exhibits classical logarithmic creep at these temperatures under both static and cyclic loading. Alloying with oxygen in solid solution promotes dynamic strain-aging effects under both static and cyclic loading, as indicated by incubation periods and the discontinuous cessation of creep. Reflecting the large contribution of the initial strain, the total accumulated strains observed for static and cyclic creep were virtually identical at all temperatures and oxygen concentrations investigated. Because the initial strain observed under static loading was distributed over several cycles under cyclic loading, it appeared that cyclic creep acceleration occurred early in the tests. However, comparing creep rates at identical strains rather than elapsed times demonstrated that the rate of cyclic creep was slightly less than the static creep rate with the following exception. At 295 K, cyclic creep acceleration that is independent of solute concentration was observed. The observations are considered as manifestations of classical dynamic strain aging behavior. Formerly Graduate Research Assistant, University of Illinois, is now Metallurgist, Southwest Research Institute, San Antonio, TX 78201.     

Ultrastructural PMP22 expression in inherited demyelinating neuropathies

The purpose of this study was to determine the accuracy of a video system which our laboratory has been using to measure soft tissue strain. Both static and dynamic error analyses were performed to assess the accuracy of our video system. Static error was defined as the amount of movement reported by the video system for markers that were stationary. Dynamic error was defined as the difference between the motion of the markers as reported by the video system and their actual motion. Two sets of fluorescent markers were attached to a servo-hydraulic materials test machine. One marker set was attached to the hydraulic actuator (moving markers) and the other set was attached to the base of the machine (stationary markers). Five different marker sizes, five camera distances, and seven different loading rates were studied. Results indicated that the static error was independent of marker size, and that the dynamic error was independent of the loading rate and marker size for loading rates of 50% of the camera field of view (CFV) per second or slower. For loading rates greater than 50 percent of CFV per second, the marker size did have an affect on the dynamic error. The mean static error was found to be 0.026 percent of CFV and the mean dynamic error was found to be 0.062 percent of CFV.     

Free Out-of-Plane Vibrations of Masonry Walls Strengthened with Composite Materials

The natural frequencies and the out-of-plane vibration modes of one-way masonry walls strengthened with composite materials are studied. Due to the inherent nonlinear behavior of the masonry wall, the dynamic characteristics depend on the level of out-of-plane load (mechanical load or forced out-of-plane deflections) and the resulting cracking, nonlinear behavior of the mortar material, and debonding of the composite system. In order to account for the nonlinearity and the accumulation of damage, a general nonlinear dynamic model of the strengthened wall is developed. The model is mathematically decomposed into a nonlinear static analysis phase, in which the static response and the corresponding residual mechanical properties are determined, and a free vibration analysis phase, in which the dynamic characteristics are determined. The governing nonlinear differential equations of the first phase, the linear differential eigenvalue problem corresponding to the second phase, and the solution strategies are derived. Two numerical examples that examine the capabilities of the model and study the dynamic properties of the strengthened wall are presented. The model is supported and verified through comparison with a step-by-step time integration analysis, and comparison with experimental results of a full-scale strengthened wall under impulse loading. The results show that the strengthening system significantly affects the natural frequencies of the wall, modifies its modes of vibration, and restrains the deterioration of the dynamic properties with the increase of load. The quantification of these effects contributes to the understanding of the performance of damaged strengthened walls under dynamic and seismic loads.     

Mechanical and thermal resistance of catalyst carriers based on a highly porous silicon carbide ceramic

The results of testing the crushing and impact strength of granules of SiC catalyst carriers under static and dynamic loading conditions are presented. The thermal stability of these materials was also investigated by tests under the regime: T = 1000°C, t = 10 min, water cool.     

Dynamics of Mechanical Actions on Materials. Part 11. System with Two Irreversibly Deformable Bodies

A rheological model and the dynamics of an open mechanical system are considered including the elastic element of a machine and a composite body consisting of two successively joined irreversibly deformable bodies with a single degree of freedom under the action of an external force. On loading the system below the elastic limit for both bodies the motion of the mechanical system is described by a second order classical dynamic system. Above the elastic limit for one of the bodies system movement is described by a third order dynamic system, and above the elastic limit for both bodies by a dynamic system consisting of two third order differential equations. The solution of this dynamic system has the nature of damping oscillation with an increase in damping factor as there is an increase in the ratio of elastic stiffnesses and strain hardenings to the viscous resistances of the deformable bodies.

     

Dynamics of Mechanical Actions on Materials. Part 11. System with Two Irreversibly Deformable Bodies

A rheological model and the dynamics of an open mechanical system are considered including the elastic element of a machine and a composite body consisting of two successively joined irreversibly deformable bodies with a single degree of freedom under the action of an external force. On loading the system below the elastic limit for both bodies the motion of the mechanical system is described by a second order classical dynamic system. Above the elastic limit for one of the bodies system movement is described by a third order dynamic system, and above the elastic limit for both bodies by a dynamic system consisting of two third order differential equations. The solution of this dynamic system has the nature of damping oscillation with an increase in damping factor as there is an increase in the ratio of elastic stiffnesses and strain hardenings to the viscous resistances of the deformable bodies.     

Visual search for facial expressions of emotions: A comparison of dynamic and static faces.

A number of past studies have used the visual search paradigm to examine whether certain aspects of emotional faces are processed preattentively and can thus be used to guide attention. All these studies presented static depictions of facial prototypes. Emotional expressions conveyed by the movement patterns of the face have never been examined for their preattentive effect. The present study presented for the first time dynamic facial expressions in a visual search paradigm. Experiment 1 revealed efficient search for a dynamic angry face among dynamic friendly faces, but inefficient search in a control condition with static faces. Experiments 2 to 4 suggested that this pattern of results is due to a stronger movement signal in the angry than in the friendly face: No (strong) advantage of dynamic over static faces is revealed when the degree of movement is controlled. These results show that dynamic information can be efficiently utilized in visual search for facial expressions. However, these results do not generally support the hypothesis that emotion-specific movement patterns are always preattentively discriminated. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Notes on effort and achievement-oriented behavior.

Considers a set of assumptions about the antecedents and consequences of effort expenditure when an S is engaged in achievement-oriented activity. Effort expenditure is assumed to have a disutility that increases with the level of effort and a benefit in the form of a proportionate increase in the probability of success on tasks at all difficulty levels. In the static models presented, it is assumed that the level of effort is constant over trials and is chosen so as to maximize the S's expected utility net of the disutility of effort. In the dynamic models presented, it is assumed that the immediately preceding task outcome may influence the current level of effort and choice of task difficulty, and comparisons are made between the asymptotic, dynamic solutions and the optimal, static solutions. The models can be modified so as to be applicable to experiments where the S can freely choose the task on each trial and to experiments where there is no choice of task. It is argued that these models facilitate a systematic treatment of the relationships among effort, task difficulty, and performance efficiency. (35 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Responses of single arterioles in vivo in cat skeletal muscle to change in arterial pressure applied at different rates

The concept of a rate-dependent, dynamic as well as a static component in the myogenic control has been suggested in some previous in vitro and whole organ investigations. The present study is an attempt to reveal a dynamic component in the myogenic response directly on single arterioles by a vital microscopic technique. The study was made on the autonomically blocked vascular bed of cat tenuissimus muscle and performed by analysing the arteriolar diameter changes to an arterial pressure increase and decrease when applied at two different rates. The results demonstrate a transient, dynamic constrictor response upon the phasic increase in pressure and a transient, dynamic dilator response upon the phasic decrease in pressure, the magnitudes of which being related to the rate of the pressure change. The static response developing during the steady-state phase of constant increased pressure was also shown. The dynamic responses were confined to arterioles smaller than about 20 micrometers while the steady-state response was present in larger arterioles as well. Even if the metabolic control system partly could be responsible for the obtained responses, arguments are given that the described reactions are mainly myogenic in nature.     

Nonclassical Stability Problems: Instability of Slender Tubes under Pressure

Several nonclassical stability problems dealing with simple cantilever columns of practical engineering importance are comprehensively presented. The salient feature of these rather peculiar problems is that column instability with a tubular cross section filled with a liquid or subjected to gas pressure may occur while its cross section remains axially unstressed. Interesting subcases are also discussed where the static stability criterion of existence of two adjacent equilibria fails to predict the actual critical load. This leads to the erroneous conclusion that the undeformed configuration is the only equilibrium position, being stable irrespective of the level of external loading. Hence, the dynamic stability criterion which is of general validity must be employed for establishing the critical load. It has also been clarified that the hydrostatic pressure load, although nonconstant-directional, cannot be identified as nonconservative.     

Synthesis and properties of Ti-Al laminated composites with an intermetallic layer

Metal-intermetallic laminated composites are fabricated upon reaction sintering of titanium and aluminum foils of various thicknesses. The mechanical properties of the composites with various metallic and intermetallic component contents are estimated using static and dynamic tests. The mechanical properties of the laminated composites are found to be anisotropic during static and dynamic loading.     

Comparison of Static and Dynamic Lateral Stiffnesses of a Driven Pile

Accurate modeling of support conditions is important in the analysis of bridges for seismic loading. To address the problem of modeling the soil-structure interface of bridges supported by piles driven in loess in West Tennessee, a series of quick-release (“pluck”) tests were performed. In the process of performing the pluck tests, sufficient static lateral load was applied to a large mass supported by a single pile to achieve a prechosen lateral displacement. This load was released; dynamic response was monitored; dynamic stiffness coefficients were calculated. A static stiffness was also calculated as simply the applied load divided by the prechosen deflection. The “secant” stiffness values thus obtained were compared to the dynamic stiffness values, and the two stiffness values were found in all cases to be essentially equal. This fact suggests the use of static lateral load tests to determine appropriate values of stiffness to use in modeling the pier-pile interface for purposes of dynamic analysis of a bridge.     

Experimental and numerical study of diffusion and trapping of hydrogen in plastically deformed A508.Cl.3 steel at room temperature

Hydrogen permeation experiments are performed by the electrochemical method on A508.Cl.3 steel membranes submitted to various stresses. In a first series the stress is kept constant and two successive permeations are conducted; in a second one an increasing stress is applied during the stationary stage of a preliminary permeation. Anomalies of different types (decreasing diffusion coefficient during first permeations in the first series of experiments, abnormal decrease of the exit flux after the dynamic loading in the second series) are encountered and shown to be quantitatively interprétable in terms of irreversible trapping induced by plastic deformations.     

Nonlinear Analysis of Ordinary Bridges Crossing Fault-Rupture Zones

Rooted in structural dynamics theory, three approximate procedures for estimating seismic demands for bridges crossing fault-rupture zones and deforming into their inelastic range are presented: modal pushover analysis (MPA), linear dynamic analysis, and linear static analysis. These procedures estimate the total seismic demand by superposing peak values of quasi-static and dynamic parts. The peak quasi-static demand in all three procedures is computed by nonlinear static analysis of the bridge subjected to peak values of all support displacements applied simultaneously. In the MPA and the linear dynamic analysis procedures, the peak dynamic demand is estimated by nonlinear static (or pushover) analysis and linear static analysis, respectively, for forces corresponding to the most-dominant mode. In the linear static analysis procedure, the peak dynamic demand is estimated by linear static analysis of the bridge due to lateral forces appropriate for bridges crossing fault-rupture zones. The three approximate procedures are shown to provide estimates of seismic demands that are accurate enough to be useful for practical applications. The linear static analysis procedure, which is much simpler than the other two approximate procedures, is recommended for practical analysis of “ordinary” bridges because it eliminates the need for mode shapes and vibration periods of the bridge.     

Combination Resonance Instability of Curved Panels with Cutout Subjected to Nonuniform Loading with Damping

The dynamic instability of doubly curved panels with a centrally located circular cutout, subjected to nonuniform compressive in-plane harmonic edge loading is investigated. The present work deals with the problem of the occurrence of combination resonances in contrast to single (mode) resonances in parametrically excited doubly curved panels with a central circular cutout. The method of multiple scales is used to obtain analytical expressions for the single (mode) and combination resonance instability regions. It is shown that other cases of the combination resonance can be of major importance and yield a significantly enlarged instability region in comparison to the principal instability region. The effects of nonuniform edge loading, centrally located circular cutout, damping, the static, and dynamic load factors on dynamic instability behavior of simply supported doubly curved panels are studied. The results show that under localized edge loading, combination resonance zones are as important as single (mode) resonance zones. The effects of damping show that there is a finite critical value of the dynamic load factor for each instability region below which doubly curved panels cannot become dynamically unstable. A central circular cutout has the destabilizing effect on the dynamic stability behavior of doubly curved panels subjected to nonuniform edge loading. This example of simultaneous excitation of two modes, each oscillating steadily at its own natural frequency, may be of considerable interest in vibration testing of actual structures.     

Increased Lateral Abutment Resistance from Gravel Backfills of Limited Width

Lateral pile cap tests were performed on a pile cap with three backfills to evaluate the static and dynamic behavior. One backfill consisted of loose silty sand while the other two consisted of 0.91- and 1.82-m-wide dense gravel zones between the pile cap and the loose silty sand. The 0.91- and 1.82-m-wide dense gravel zones increased the lateral resistance by 75 to 150% and 150 to 225%, respectively, relative to the loose silty sand backfill. Despite being thin relative to the overall shear length, the 0.92- and 1.82-m-wide gravel zones increase lateral resistance to approximately 54 and 78%, respectively, of the resistance that would be provided by a backfill entirely composed of dense gravel. The dynamic stiffness for the pile cap with the gravel zones decreased about 10% after 15 cycles of loading, while the damping ratio remained relatively constant with cycling. Dynamic stiffness increased by about 10 to 40% at higher deflections, while the damping ratio decreased from an initial value of about 0.30 to around 0.26 at higher deflections.     

济钢副枪系统及其计算机操作

介绍了济钢从荷兰引进的转炉炼钢副枪系统的功能、电气控制系统组成、副枪计算机模式及PLC、HMI的设定.济钢将副枪系统测得的数据与自动化炼钢静、动态模型相结合,实现了快速出钢.     

H-reflex changes in the course of amyotrophic lateral sclerosis

This study was directed at establishing the influence of dynamic loading situations on the sliding characteristics of the Gamma locking nail (Howmedica). It was postulated that the changing regions of load contact area that occur within the sliding mechanism during flexion and extension would favourably modify the jamming behaviour observed under static test conditions. The forces required to initiate sliding of the lag screw in the intramedullary device were investigated under a range of conditions representing clinical situations. The optimum sliding performance of the Gamma nail was shown to occur during test conditions of dynamic loading, when the rate of application of the load was rapid and the cyclic angle of flexion was greatest. The size and weight of the patient also influence the sliding characteristics, as a shorter lag screw length protruding from the barrel and a reduced vertical static load (body weight) yielded a lower axial sliding force. The results under dynamic loading conditions suggest that static testing of sliding hip screws does not accurately represent their clinical performance.     

Field Investigation of a Sandwich Plate System Bridge Deck

This paper presents the results of a live-load test of the Shenley Bridge, the first bridge application of the sandwich plate system technology in North America. The investigation focused on the evaluation of in-service performance including lateral load distribution behavior and dynamic load allowance. Real-time midspan deflections and strain values were measured under both static and dynamic conditions and under various loading configurations to assess the in-service performance. Distribution factors were determined for interior and exterior girders subjected to single and paired truck loadings. In addition, dynamic load allowance was determined from a comparison of the bridge’s response under static conditions to the response under dynamic conditions. From a comparison of measured results to AASHTO LRFD, AASHTO standard, and CHBDC provisions, it was determined that the current provisions tend to produce conservative predictions for lateral load distribution, but can be unconservative for dynamic load allowance. As a result of the testing program containing a single field test, a finite-element model was also used for determination of lateral load distribution and yielded predictions similar to measured results. The results from the finite-element models were often less conservative than the code provisions.