True Loading Research Articles

An experimental study of large finite plastic deformation in annealed 1100 aluminum during proportional and nonproportional biaxial compression

A new nonproportional biaxial compression experiment has been developed where a rectangular block first undergoes uniaxial compression and then, after finite deformation, it is subjected to large deformations (up to 45% strain) under biaxial compression. Experimental results on rectangular specimens of annealed 1100 aluminum subjected to uniaxial and biaxial compressive loadings are presented. The experiments include proportional and nonproportional loading paths. Stress and strain measures, directional changes of plastic strain increment, and existence of the von Mises equivalent stress-strain relation at large finite strains are discussed. Small volume changes were computed from the measured strains; however, density measurements after unloading indicate negligible change in density or volume. The classical Prandtl-Reuss equations are shown to predict acceptable results when the true or logarithmic strain loading paths are approximately proportional; however, many constitutive models can predict the experimental results during proportional loading paths. On the other hand, during sharp directional changes in loading paths, the predictions using Prandtl-Reuss equations in terms of deviatoric stress ratios and incremental strain ratios do not agree with experimental data for nonproportional loading paths, especially in the neighborhood of loading path change.

Inverse variational principle in finite elasticity

Although there is a vast literature on the variational principles of the theory of nonlinear elasticity, some basic problems in this field are still open (cf. e.g. [1]). General speaking, almost all the variational principles were studied in the reference configuration ( i.e. undeformed configuration ). Since the loaded boundary is unknown, the well-known dead loading condition should be assumed in this kind of variational principle. Otherwise, the configuration-dependent loading should be considered [2]. In my opinion, the correct description of variational boundary value problem for finite deformation theory is a problem with a movable boundary under the true loading systems [3]. The complete solutions of this problem should include both field functions and deformed configuration. To solve this kind of problem, this paper establishes an Euler-type variational principle in the current configuration by introducing a new variational definition. The critical condition of this principle yields a complete solution of the boundary value problem and the optimal shape condition of the movable boundary. This principle can be applied to problems of optimal shape design.

Vapor Phase Spiking and Thermal Desorption of a Passive Sampler

Vapor phase spiking of passive samplers closely represents the true field sample loading conditions, but requires the preparation of standard vapor mixtures, and accurate knowledge of the dosimeter sampling rate. This represents a limitation during the development of a passive sampler, since the determination of desorption efficiency is required prior to the experimental determination of the sampling rate. A method has been developed and validated that provides a convenient and effective procedure of vapor phase spiking the analyte for desorption efficiency studies during passive sampler development when the dosimeter sampling rate is not yet known. Problems of interferences during the analysis associated with the use of solvents are avoided with this method. In addition, thermal desorption was demonstrated to be an accurate and reproducible method for recovery of benzene from the activated charcoal felt used in this study. A desorption efficiency greater than 95% and constant for a wide loading range of ...

Strength of Indiana Limestone in true biaxial loading conditions : Amadei, B; Janoo, V; Robison, M; Kuberan, R In: Rock Mechanics in Productivity and Protection (Proceedings of the Twenty-Fifth Symposium on Rock Mechanics, Evanston, Illinois, 25–27 June 1984)P338–348. Publ New York: AIME, 1984

Strength of Indiana Limestone in true biaxial loading conditions : Amadei, B; Janoo, V; Robison, M; Kuberan, R In: Rock Mechanics in Productivity and Protection (Proceedings of the Twenty-Fifth Symposium on Rock Mechanics, Evanston, Illinois, 25–27 June 1984)P338–348. Publ New York: AIME, 1984

The inadequacy of existing chlorophyll- a/phosphorus concentration correlations for assessing remedial measures for hypertrophic lakes

Because large reductions in phosphorus loading are required to cause small decreases in mean summer phytoplankton biomass, inaccuracies exist in (1) predicting lake phosphorus concentrations from phosphorus loading models and mean and maximum chlorophyll- a from lake phosphorus concentrations and (2) representative sampling to estimate true phosphorus loading and true mean and maximum chlorophyll- a. Remedial measures to reduce external phosphorus loads—and hence lower in-lake phosphorus concentrations from some 600 mg/m 3 to much lower values of some 100 mg/m 3—will result in the reduction of long-term (several years average) mean—and, more significantly, maximum—open-water summer chlorophyll- a concentrations. However, despite the application of these remedial measures, perturbations in phytoplankton biomass will remain such that, on any particular day during the open-water period, short-term algal blooms or scums will still be sufficiently intense for long-term improvements not to be clearly evident to the casual recreational user of the lake.

Plastic Design of Biaxially Loaded Beam-Columns

In the field of engineering design, it is normal to design steel wide-flange columns as if they were loaded by direct compression or by a thrust with some eccentricity about only one of the principal axes. Only limited design information is available concerning the case where there exists, simultaneously, some eccentricity with respect to each of the major axes. Where careful consideration is given to the true loading on a wide-flange column, it is frequently found that the longitudinal thrust on most columns does have some eccentricity in both principal directions. Figure 1 illustrates this general loading situation. The AISC Specification1 contains plastic design rules for axially loaded wide-flange columns with either no moment or with moment about only one principal axis. The design criteria for the ultimate load-carrying capacity of a biaxially loaded beam-column is obtained by an implied extension of Formulas (2.4-2) and (2.4-3). It has, therefore, been desirable for some time not only to predict the ultimate loadcarrying capacity of a member loaded in this manner, but to provide additional design criteria for the selection of such members. This paper presents a design technique for determination of the maximum plastic strength of biaxially loaded beamcolumns. The loading situation is caused by a compressive force eccentric to each of the two principal axes. The eccentricities are not restricted in any way. The member is an open section, composed of prismatic elements, of the wideflange class, in which no stress reversals occur. The material is assumed to be ideally elastic-perfectly plastic, but may contain residual stresses. The analytical procedure used to determine the ultimate load is based on an equilibrium technique in which the external forces acting on the cross section are equated to the internal resistances of that section as determined by the distribution of longitudinal stresses. The procedure is iterative and non-incremental. The principles of the procedure are presented in this paper as well as the results in the form of an interaction curve, design charts, and the equations of forces as used in the analytical procedure.

Gust Response Factors

The gust response factor is a measure of the effective wind loading on a structure and is intended to translate the dynamic response phenomena due to gust loading into relatively simpler static design criteria. The calculation involves a power spectrum analysis of dynamic structural response of a linear, single-degree-of-freedom system with viscous damping and utilizes reported measurements of wind gust spectra and gust correlation coefficients. Calculated results of this method are presented in the form of charts which permit the direct determination of gust response factors. A rational method of transferring long-term Weather Bureau wind records to rough and obstructed exposures is presented. The effect of gusts on the design and serviceability of buildings is discussed. For large structures, the results of this paper suggest that the use of fastest mile pressures could overestimate the true wind loading on such structures.

The Design of Railway Axles and Locomotive Crank Pins

Abstract Tendencies toward increase in speed have focussed attention on modifications in present axle proportions. High-speed locomotives require corresponding considerations, particularly in the proportioning of locomotive crank pins. Great credit should be given to those responsible for the introduction of the standard A.A.R. axle, which has suitable proportions for normal operating conditions. With increased speeds, modifications of these established proportions are necessary. While the necessity for modification in the proportions has been recognized, the question of proper ratings for high-speed axles is still a matter for considerable discussion. The object of this paper has been to set forth various aspects of loading conditions and stress limitations. A comparison of various methods of axle proportioning has been made with the suggestion of a new interpretation of loadings. While axle design is necessarily empirical, based on statistical data of axle failures, it is desirable to guide the interpretation of such data by closer approximation to the true loading conditions. For this reason, the subject of axle design has been divided into two parts. Part 1 covers the subject of present methods of axle proportioning and an analysis of the division of the loading into various components; some consideration is given to stress concentrations and endurance limits of the material. In Part 2 some characteristics of the nature of dynamic loadings is given, based on simplification of various conditions met in actual operation. Part 3 of the paper discusses a correlated subject, locomotive crank pins.