Central Point Load Research Articles

In situ elasticity and adhesion measurement of biomembrane by a video enhanced depth-sensing indentation technique

Elasticity and adhesion of a prestressed circular biomembrane to planar graphite surface was investigated by a video enhanced depth-sensing indentation technique. This biomembrane was a combination of human skin cells and biodegradable polymer. Using this kind of membrane as a skeleton facilitated the easy formation of the hybrid sponges into desired shapes that had a high mechanical strength, while the collagen micro sponges nested in the pores, which allowed the cells to interact with the collagen surfaces. A homemade indenter apparatus was constructed to meet force and displacement resolutions of 0.1 μN and 10.0 nm. The indenter possessed the capability of measuring the applied force and resultant displacement simultaneously. By armed with a high magnification side-view system, it could record lateral profile variation of biomembrane, which was essential for observing and analyzing its gradually rupture. A linear theoretical elastic solution was applied to quantitatively interpret the measured central displacement of the membrane under a central point load. Elastic modulus of the biomembrane could be easily determined once the applied force and the central displacement, together with the essential dimensions were known. The biomembrane “jump-into” an adhesion contact when the punch approached the range of the intersurfaces force across the punch-membrane gap. A “pull-off” event was observed at a nonzero contact circle when the tensile load reaching a critical threshold. This technique provided the capability of measuring mechanical behaviors of prestressed ultra thin tissue and thin-walled biocapsules with a residual stress.

Distortional buckling in monosymmetric I-beams

This paper deals with distortional buckling of simply supported monosymmetric I-beams under three types of load: a central point load, a uniformly distributed load and a uniform sagging moment. ABAQUS is used for the investigation. Top-flange and bottom-flange load positions are considered for the first two load cases. It is found that for comparatively short beams, buckling may be governed by distortion of the web. Moment modification factors are calculated based on the present analysis, which accounts for the distortion of web and these are compared with those based on SSRC Guidelines, which are based on lateral-torsional buckling analysis only. It is seen that for short beams, provisions in SSRC Guide-1998 seriously overestimate the critical load.

Analytical solutions for flexure of clamped rectangular cross-ply plates using an accurate zig–zag type higher-order theory

Clamped cross-ply plates are analyzed here using a higher-order theory based on a realistic thickness-wise displacement field that accounts for a zig–zag variation of the in-plane displacements. Rigorous analytical solutions are obtained for this difficult problem using a methodology developed recently wherein simple Fourier series solutions of a corresponding simply-supported plate are superposed, each such component solution being summed without truncation using MATHEMATICA. Numerical results, for square homogeneous and three-layer plates under uniform and central point loads, are compared with those based on the classical and first-order theories.

Characterization of the mechanical properties of microscale elastomeric membranes

This paper reports on a novel method to characterize the mechanical properties, such as the elastic modulus, of circular microfabricated elastomeric membranes by measuring their load–displacement curve (compliance). An ultra-precision instrument was developed to simultaneously measure both the applied forces and the resultant displacements of the membrane under a central load. During all the deformation experiments, a high-resolution optical microscope system was used for viewing the side-view of the deformed membrane and thereby the complete membrane deflection profile was obtained. In the current experiment, measurements were performed on a set of thin, circular silicon rubber membranes with a thickness of 180 µm. A theoretical linear elastic solution was applied to quantitatively correlate the elasticity to the measured membrane compliance under such a central point load. Viscoelastic response of the membranes used was not manifested; therefore, it had no effect on the determination of Young's modulus of the membranes in the current work. The good agreement between the experimental results and the theoretical analyses facilitates the determination of Young's modulus of the membrane.

집중하중을 받는 Grillage의 소성 붕괴하중 산정 및 일반식 도출

For the grillage which is common types of structures in marine and land-based structural system, the elastic response and design methods are usually applied. However, plastic analysis and design methods are considered Tn those structures to maintain the structural stability at the limit states. In grillage design, the central intersection point load may be used as a worst loading condition. However, a point load may often move around on the grid system. in such case, the worst load point would not necessarily be at the central point. To investigate the variation of plastic collapse load according to the location of moving load between intersections, the plastic collapse loads are obtained for the three types of grillages with simply-supported ends. From the result of each case, it is confirmed that the worst load point is located between intersections. General formulae related with plastic collapse loads for the three groups of grillages with simply-supported boundaries are derived. Those plastic collapse formulae for the grillages are applied to the design of pontoon deck, and optimum design procedure is illustrated. Consequently, general formulae for the plastic collapse of grillages derived from this study can be easily applied to the plastic analysis and optimum design of similar grillages.

Instantaneous velocity displacement and contour measurement by use of shadow moiré and temporal wavelet analysis.

A temporal wavelet analysis method is proposed for velocity, displacement, and three-dimensional surface-profile measurement of a continuously deforming object by use of the shadow moiré technique. A grating is placed close to a deforming object, and its shadow is observed through the grating. The moiré fringe patterns, generated by the interference of the grating lines and their shadows, are captured by a high-speed CCD camera with a telecentric gauging lens. Instantaneous frequency of gray-value variation is evaluated point by point with the continuous wavelet transform. From the instantaneous frequency of each point on the object, the velocity, displacement, and high-quality surface profile at different instants can be retrieved. In this application, two specimens are tested to demonstrate the validity of the proposed method: One is a small coin with a rigid body motion, and the other is a simply supported beam subjected to a central point load. The results are compared with those obtained from temporal Fourier-transform and mechanical stylus methods.

The exact weight of discretized Michell trusses for a central point load

A discretized optimal structure is derived in a closed analytical form based on Michell truss. The result shows that the discretized optimal structure is most similar to Michell truss in topology and shape. The difference in volume, displacement and strain energy between the discretized optimal structure and Michell truss decreased sharply as the number of members increased in discretized structure. A discretized optimal structure may be obtained from Michell truss by using finite members. This work is meaningful for studying discretized optimal topology based on Michell truss. This result is useful for engineering structural design.

The relationship between torsional rigidity and bending strength characteristics of SA pine

Synopsis The modulus of rigidity, G, and bending moment ofelasticity, MOE, of SA pine are evaluated from a direct torsion test and bending tests. Specimens were subjected to a series of tests with the view to determining direct torsional rigidity, apparent bending modulus of elasticity and pure bending modulus of elasticity. Torsional rigidity and bending modulus of elasticity results from central point and third point loading are compared. Often timber is used as structural bending elements that are subjected to torsional and horizontal shear, the influence of which is in many cases neglected. The modulus of rigidity is especially important when calculating the lateral-torsional buckling resistance of bending members and when members are subjected to torsional loads. This study was based on a series of laboratory experiments on actual sized timber with the focus and emphasis on mechanical properties and statistical significance.

A novel technique for characterizing elastic properties of thin biological membrane

We present a new technique to characterize the elastic properties of a thin biological membrane. An effective instrument that embodies video enhanced microscope was developed primarily to provide the capability of simultaneously measuring both the applied force and the resultant displacement of the biological membrane under a central point force. A theoretical linear elastic solution was applied to quantitatively interpret the measured central deflection of the membrane under a central point load. The Young’s modulus of raw and boiled Leghorn egg inner tissue can be easily determined once the applied point load and the central deflection, together with the essential dimensions are known. The viscoelasticity property of natural tissue was manifest in the experiment. The experimental results have verified that the novel technique is applicable to determine the Young’s modulus and other viscoelatic properties of thin biological tissue.

Analysis of Variables Influencing the Average-Residual Strength of Fiber-Reinforced Concrete

Abstract The ASTM C 1399, Test Method for Obtaining Average Residual-Strength of Fiber-Reinforced Concrete, became a standard of ASTM International in December 1999. The test method was developed to provide a practical method, both functionally and economically, for evaluating the performance of fiberreinforced concrete (FRC) of any mixture design. The method is a flexure test and the result, the average residual strength (ARS), is a useful parameter in design and quality control testing. The current standard requires a third-point flexural loading-configuration that complies with ASTM C 78, Standard Test Method for Flexural Strength of Concrete (Using Simple Beam With Third-Point Loading), and net-deflection data analysis. Five factors, consisting of loading configuration, deflection measurement, support apparatus, testing machinery and fiber material type are used as test variables in this research in a testing program suited to the application of a statistical analysis of variance procedure, ANOVA, for their affect on ARS. The results of the test program show that no significant effect is found on the value of ARS computed according to ASTM C 1399 for the modified ASTM C 78, MC78, test apparatus when using either gross or net deflection, or when using third-point or centerpoint loading. There is a significant effect on the value of ARS computed according to ASTM C 1399 for the ASTM C 78 test apparatus when comparing the same test variables.

Lateral buckling of I-section composite beams

Lateral buckling of a laminated composite beam with I-section is studied. A general analytical model applicable to the lateral buckling of an I-section composite beam subjected to various types of loadings is developed. This model is based on the classical lamination theory, and accounts for the material coupling for arbitrary laminate stacking sequence configuration and various boundary conditions. The effects of the location of applied loading on the buckling capacity are also included in the analysis. A displacement-based one-dimensional finite element model is developed to predict critical loads and corresponding buckling modes for a thin-walled composite beam with arbitrary boundary conditions. Numerical results are obtained for thin-walled composites under central point load, uniformly-distributed load, and pure bending with angle-ply laminates. The effects of fiber orientation, location of applied load, and types of loads on the critical buckling loads are parametrically studied.

Lateral buckling analysis of thin-walled laminated channel-section beams

The lateral buckling of a laminated composite beam with channel section is studied. A general analytical model applicable to the lateral buckling of a channel-section composite beam subjected to various types of loadings is derived. This model is based on the classical lamination theory, and accounts for the material coupling for arbitrary laminate stacking sequence configuration and various boundary conditions. The effects of the location of applied loading on the buckling capacity are also included in the analysis. A displacement-based one-dimensional finite element model is developed to predict critical loads and corresponding buckling modes for a thin-walled composite beam with arbitrary boundary conditions. Numerical results are obtained for thin-walled composites under central point load, uniformly distributed load, and pure bending with angle-ply and laminates. The effects of fiber orientation, location of applied load, and types of loads on the critical buckling loads are parametrically studied.

Shear Strength in Structural Composite Lumber

A study has been conducted to evaluate the shear strength of 44 × 184 mm and 44 × 305 mm laminated veneer lumber and parallel strand lumber using ASTM shear block tests, center-point bending tests, and five-point bending tests. In the center-point bending tests of specimens with joist orientation, the specimens have been remanufactured into “I” shapes to promote longitudinal shear failures rather than bending failures. The ratio between the average apparent shear strength from the five-point and center-point loading tests ranges from 1.34 to 1.53. Similarly, the ratio between the average apparent shear strength from the five-point loading tests and the ASTM block shear tests ranges from 1.03 to 1.39.

Moment Value at the Center of Circular Plates Under Central Point Load

It is a well-known fact that the bending moment at the center of a circular plate under a central point load becomes infinite. So, “what is a sensible finite moment value, that one may adopt, at the center of a circular plate under a central point load?” This study addresses this interesting and fundamental question. In order to obtain a finite value to the bending moment, we draw upon the exact deflection expressions from the classical and higher-order plate theories of Mindlin and of Reddy, and make some reasonable assumptions such as the maximum deflection of Mindlin plate being equal to the maximum deflection of the corresponding Reddy plate and the constancy of the Mindlin shear correction factor.

Mechanical behaviour of ferrocement composites: an experimental investigation

In-plane tension, compression and bending tests were conducted on plain mortar and ferrocement specimens with woven and welded meshes. Tension tests were also carried out on meshes. Bending tests were conducted using specimens with centre point loading. The objective of the study was to investigate the behaviour of material reinforced with varying number of mesh layers and orientations and to evolve a set of elastic and inelastic material properties. It is observed that the conventional empirical relations based on mortar crushing strength overestimate the mortar modulus. The elastic moduli obtained using the rule of mixtures compares well with the values evaluated from the tests on ferrocement specimens. The 45° orientation emerges as the weakest configuration both in terms of the Young's modulus and ultimate stress because of the lowest volume fraction of wire mesh in the direction of loading at this orientation.

Fracture Mechanics of a Shaft-loaded Blister Test – Transition from a Bending Plate to a Stretching Membrane

A linear elastic solution is proposed for a circular disc in transition from a plate-like (pure bending) to a membrane-like behavior (pure stretching) under a central point load. The strain energy release rate for film delamination is found to be G = χ(Pw 0/πa 2) with χ a numerical constant varying from 1/2 for a plate-like disc to 1/4 for a thin flexible membrane.

Experiments and theory on deck and girder crushing

This paper is concerned with theoretical and experimental analysis of deep plastic collapse of a deck or deep girder subjected to an in-plane, concentrated load. A theory is derived which is valid until initiation of fracture in the structure. The presented experimental results show load–deflection curves and modes of deformation for decks, stringer decks and deep thin-walled beams subjected to central or excentric point loads between transverse frames. Based on theory and experiments, various modelling aspects of the local/global failure of the beams are discussed. The agreement between the theoretical closed form solutions and the experimental results is good.

Thermal cycling, critical current vs. strain, and finite element modelling of 1, 7, 19 and 37 filament Ag/Bi-Sr-Ca-Cu-O (BSCCO) tapes

Transport critical current, I/sub c/, distribution measurements, thermal cycling experiments and critical current vs. strain (I/sub c/ vs. /spl epsiv/) experiments were carried out on silver clad 1, 7, 19 and 37 filament Bi-Sr-Ca-Cu-O (BSCCO) tapes. The transport critical current distribution of silver clad Bi-Sr-Ca-Cu-O tapes are measured using a measurement system capable of making 10 /spl mu/m steps along 120 mm long tapes. The tapes are subjected to thermal cycling and repeat measurements of the I/sub c/ are made. The critical current vs. strain experiments are carried out by centre point loading of the tapes. Elastic-Plastic Finite Element Modelling (FEM) of a monocore tape is carried out. Our analyses show the variation of the transverse stress, /spl sigma//sub yy/, across the width of the tape.

Development of high-order manifold method

The Manifold Method of Material Analysis (MM) with high-order displacement functions has been derived based on triangular meshes for the requirement of high accurate calculations from practical applications. The matrices of equilibrium equations for the second-order MM have been given in detail for program coding. The derivation of the method is made by means of approximation theory and very few new mathematical concepts are used in this paper. So, it may be understood by most engineering researchers. By close comparison with widely used Finite Element Method, the advantages of MM can be seen very clearly in the following aspects: (1) the capability of processing large deformation and handing discontinuities like block oriented Discontinuous Deformation Analysis method; (2) making element meshes easily and (3) using high-order displacement functions easily. The C program codes for the second-order MM has been developed, and it has been applied to the example of a beam bending under a central point loading. The calculated results are quite good in agreement with theoretical solutions. By contrast, the results calculated for the same model by use of the original first-order MM are far from the theoretical solutions. Therefore, it is important and necessary to develop high-order Manifold Method for the complicated deformation problems. © 1998 John Wiley & Sons, Ltd.

Geometrically non-linear dynamic analysis of laminated shells using Bézier functions

In this paper a geometrically non-linear theory for the analysis of open deep laminated shell panels is presented. Parabolic variation of the transverse shear stresses through the thickness of the shell and the effects of rotary inertia are included in the formulation. Linear and non-linear stiffness matrices are derived using orthogonal curvilinear coordinate system for a general doubly curved deep laminated shell. The solution of the equation of motion is based on the Ritz method. Therefore, the Bézier surface patches are used as the admissible displacement fields to represent the shell's middle surface displacement and rotation components and the resulting equation of motion is solved to obtain the transient response, using Beta- m time integration and Newton-Raphson iterations. A very good convergence of the responses is observed by using only the fifth order Bézier surface patches. The dynamic responses of cross-ply laminated circular and non-circular cylindrical panels pinned at the straight edges under a central point load are studied. Effect of the eccentricity on the dynamic response of non-circular cylindrical panels having the same plan form as the circular cylindrical panel is also examined.