Longitudinal Compressive Load Research Articles

Determination of strain components in low-cycle multiaxial fatigue tests on tubes

Many thermal cycling tests are characterized by an equibaxial stress distribution. To simulate this kind of loading under isothermal conditions at room temperature, a test facility for multiaxial isothermal tests on tubes has been developed. The tubes are subjected to a longitudinal tension compression load within a superimposed circumferential load using internal and external pressures. Owing to the gradient of stresses and strains over the wall thickness, the stress-strain distribution at the inner tube wall differs markedly from the values outside. Therefore they have to be calculated depending on the measured forces, pressures and the dimensions of the specimen. In the present paper, measurement and evaluation of the stress-strain distribution over the tube wall are described.

Vibrations and stability of smooth and ribbed spherical bands

Vibrations of preloaded smooth and ribbed spherical bands are studied. A solution of linearized movement equations in displacements is presented in the form of single trigonometric series for a circumferential coordinate. Critical loads and natural vibration frequencies are determined with a linear and geometrically linear stress-strained state of static equilibrium. The effect of a longitudinal compressive load on the magnitude of minimum natural frequencies for oscillations of smooth and ribbed spherical bands is considered as a specific example.

Compression Loading of Laminates: In Situ Failure of 0° Unidirectional Plies

Consideration is given to failure of filament-dominated laminates subjected to compression loading. Of particular interest is the interaction between longitudinal compression loading and transverse loading (tension and compression). Data obtained in conjunction with a mini-sandwich specimen are used to generate failure stresses. Classical lamination theory, including thermal residual stresses due to cure is utilized for determining ply stresses. Residual stresses are based on initial elastic properties, while mechanical stresses are based on secant modulus at failure (compression stress-strain curve for both unidirectional and laminated composites is nonlinear at high strain levels). Experimental results reveal little interaction between longitudinal compression and transverse stresses as long as matrix-dominated modes such as transverse cracking and delamination are suppressed.

Buckling-load interaction in tailored composite plates

The concept of stiffness tailoring is investigated for improved buckling resistance of rectangular composite plates subject to general in-plane combined loading. The tailoring approach involves the piecewise-uniform redistribution of a portion of the given material with given orientations to create beneficial stiffness distributions across the planform of the plate. The resulting local nonuniformities in thickness and in membrane and bending stiffnesses combine to change the buckling response of the plate. Finite element models are used to calculate the prebuckling stress distribution and the buckling loads. The weight and average membrane shear stiffness are essentially unaffected by the tailoring. Optimum tailoring geometries are determined for a wide range of shear and transverse tension and compression loadings combined with longitudinal compression loading. Maximum improvements in the buckling loads of over 700% are shown possible with tailoring for some loading combinations compared with uniform plates. In general, the benefit of tailoring is greatest with low shear loads and high transverse tensile loads.

Mechanical Behavior of Respirable Fibrils of Kevlar Aramid Fibre, Glass, and Asbestos

The deformation of equivalent size and shape glass, asbestos and Kevlar∗aramid fibrils, when subjected to bending or longitudinal compressive loads, was estimated based on published mechanical properly data and established mechanical analysis. Based on this analysis, Kevlar fibrils are expected to deform more easily than glass or asbestos fibrils. This behavior is a direct result of the lower compressive modulus and compressive yield strength of Kevlar fibres. Among the Kevlar fibres studied, those with higher molecular orientation and crystalline perfection (Kevlar 149 > Kevlar 49 > Kevlar 29) were more flexible and deformed more easily. Compressive yielding may occur more easily in fibrils stripped from the spun filament surface and also may promote fibril breakdown through chemical degradation.

Device for longitudinally compressing single pulp fibers

Paper and paperboard products are often subjected to edgewise compression loads in use. The basic component of paper and paperboard is the individual pulp fiber. Observance of external changes on the fiber wall should provide information as to how and why pulp fibers fail under compressive load. A fiber compression device was designed for use in the specimen chamber of a scanning electron microscope. This device permits observation of changes in the cell walls of individual pulp fibers while the fiber undergoes longitudinal compressive loading.

Compressive loads in the lumbar vertebral column during normal level walking

The longitudinal compressive load acting on the L3-L4 spinal motion segment was investigated during normal level walking for a range of speeds of progression. Forces were predicted using experimental data from photogrammetric measurements of upper body segmental motion and inertial properties, along with a biomechanical model of the trunk. A partial validation of the results was obtained using records of the electrical activity of the trunk muscles and intradiscal pressure information available in the literature. Experiments were carried out in five normal young male subjects. Results showed that the L3-L4 motion segment is subjected to cyclic compressive loads. The maximum and minimum values of this load vary with walking speed from approximately 1.0 to 2.5 and from 0.8 to 0.2 times body weight, respectively. Relevant peaks occur with a frequency ranging approximately from 1.3 to 2.5 Hz. Muscular action is mostly concentrated in the trunk extensors, which show a burst of activity at the time of ipsilateral toe-off.

Analysis and Performance of Fiber Composites

Analysis and Performance of Fiber Composites

Stability Design Criterion for Vessels Subjected to Concurrent External Pressure and Longitudinal Compressive Loads

This paper presents a design procedure for determining the maximum allowable compressive stress and the maximum allowable external pressure for cylindrical vessels subjected to loadings which produce both longitudinal and circumferential stresses simultaneously. Although the ASME Pressure Vessel Code Section VIII [1] mentions the combinations of loadings as a factor in determining the thickness of vessels, the Code procedures (UG-23) for longitudinal compressive stress and (UG-28) for external pressure do not consider the interaction of these two buckling loads when acting concurrently. Calculations of typical vessels subjected to these conditions reveal that adherence to the Code rules without inclusion of these effects may yield results which fall below the safe design limits established by the Code. The design procedure developed herein extends the existing Code formulations as applicable; and incorporates established elastic stability data as necessary.

Elastic Stability of Simply Supported Flat Rectangular Plates Under Critical Combinations of Longitudinal Bending, Longitudinal Compression, and Lateral Compression

A theoretical investigation was made of the buckling of simply supported flat rectangular plates under critical combinations of longitudinal bending, longitudinal compression, and lateral compression. Interaction curves for these loadings are presented for various plate aspect ratios. Also included are curves of critical buckling constants for simply supported flat rectangular plates under combined unsymmetrical bending and lateral compression. The results indicate that the reduction in the allowable bending stress due to the addition of lateral compression is greatly magnified by the further addition of only a small longitudinal compressive load. INTRODUCTION IN THE DESIGN OF STRESSED-SKIN STRUCTURES, consideration must sometimes be given to the critical stress of a plate under combined longitudinal bending, longitudinal compression, and lateral compression. Box-beams webs, for example, are subjected to these loading conditions due to the bending moments alone. Also in beams having unsymmetrical distributions of cross-sectional area, the webs are subjected to unsymmetrical longitudinal bending stresses and lateral compression (crushing) stresses due to the applied moment. In the present paper, the critical stress coefficients are found for the plate loading shown in Fig. la. Critical stress coefficients have been calculated by other investigators for certain boundary values of the more general loading case assumed here. Some of these are: longitudinal bending and compression, Fig. lb ; longitudinal bending and lateral compression, Fig. lc; and compression in two directions,? 4 Fig. Id. The results of these papers were used to aid in the construction of the interaction curves presented herein. SYMBOLS a ~ length of plate in ^-direction an = Fourier coefficients b = width of plate in ^-direction D = plate flexural rigidity, Et/12(1 /x) E — Young's modulus of elasticity kb = critical longitudinal bending stress coefficient kbx = critical stress coefficient for longitudinal bending and compression combined kx = critical longitudinal compressive stress coefficient ky = critical lateral compressive stress coefficient m — number of half waves in x-direction Nb = longitudinal bending force per unit length acting on plate middle plane = maximum compressive value of Nb at edge of plate = longidutinal compressive force per unit length acting on plate middle plane = lateral compressive force per unit length acting on plate middle plane Nbx = sum of longitudinal loadings Nx and JV& R = stress ratio T = external work of applied forces t — thickness of plate V = internal energy of deformation w = deflection of buckled plate normal to middle plane iVo Nx Nv