Types of Mechanical Forces

A force exerted on a body can cause a change in either the shape or the motion of the body. The unit of force in SI system is the newton (N) and Dyne. The unit of force in USCS is pound-force. No solid body is perfectly rigid and when forces are applied to it, changes in dimensions occur. Such changes are not always perceptible to the human eye since they are negligible. For example, the span of a bridge will sag under the weight of a vehicle and a spanner will bend slightly when tightening a nut. It is important for civil engineers and designers to appreciate the effects of forces on materials, together with their mechanical properties of materials.

Lateral torsional buckling of anisotropic laminated thin-walled simply supported beams subjected to mid-span concentrated load

H. Ahmadi, H.A. Rasheed

Abstract

In this paper, a generalized semi-analytical approach for lateral-torsional buckling of simply supported anisotropic, thin-walled, rectangular cross-section beams under concentrated load at mid-span/mid-height was developed using the classical laminated plate theory as a basis for the constitutive equations. A closed form buckling expression was derived in terms of the lateral, torsional and coupling stiffness coefficients of the overall composite. These coefficients were obtained through dimensional reduction by static condensation of the general 6x6 constitutive matrix mapped into an effective 2 × 2 coupled weak axis bending-twisting relationship. The resulting two coupled stability differential equations are manipulated to yield a single governing differential equation in terms of the twisting angle. This differential equation with variable coefficients, subjected to applicable boundary conditions, was solved numerically using Mathematica. The resulting solution was found to correlate with the effective lateral-flexure, torsional and coupling stiffness coefficients to yield a general semi-analytical solution. An analytical formula was possible to extract, which was verified against finite element buckling solutions using ABAQUS for a wide range of lamination orientations showing excellent accuracy. The stability of the beam under different geometric and material parameters, like length/height ratio, layer thickness, and ply orientation, was investigated

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Lateral-torsional buckling of simply supported anisotropic steel-FRP rectangular beams under pure bending condition

H.A.Rasheed, H. Ahmadi and A. Abouelleil

Abstract

In this paper, a generalized analytical approach for lateral-torsional buckling of simply supported anisotropic hybrid (steel-FRP), thin-walled, rectangular cross-section beams under pure bending condition was developed using the classical laminated plate theory as a basis for the constitutive equations. Buckling of such type of hybrid members has not been addressed in the literature. The hybrid beam, in this study, consists of a number of layers of anisotropic fiber reinforced polymer (FRP) and a layer of isotropic steel sheet. The isotropic steel sheet is used in two configurations, (i) in the mid-depth of the beam sandwiched between the different FRP layers and (ii) on the side face of the beam. A closed form buckling expression is derived in terms of the lateral, torsional and coupling stiffness coefficients of the overall composite. These coefficients are obtained through dimensional reduction by static condensation of the 6 × 6 constitutive matrix mapped into a 2 × 2 coupled weak axis bending-twisting relationship. The stability of the beam under different geometric and material parameters, like length/height ratio, ply orientation, and layer thickness, was investigated. The analytical formula is verified against finite element buckling solutions using ABAQUS for different lamination orientations showing excellent accuracy. Link to full text.

Lateral torsional buckling of anisotropic laminated composite beams subjected to various loading and boundary conditions

H. Ahmadi

Abstract

Thin-walled structures are major components in many engineering applications. When a thin-walled slender beam is subjected to lateral loads, causing moments, the beam may buckle by a combined lateral bending and twisting of cross-section, which is called lateral-torsional buckling. A generalized analytical approach for lateral-torsional buckling of anisotropic laminated, thin-walled, rectangular cross-section composite beams under various loading conditions (namely, pure bending and concentrated load) and boundary conditions (namely, simply supported and cantilever) was developed using the classical laminated plate theory (CLPT), with all considered assumptions, as a basis for the constitutive equations.

Buckling of such type of members has not been addressed in the literature. Closed form buckling expressions were derived in terms of the lateral, torsional and coupling stiffness coefficients of the overall composite. These coefficients were obtained through dimensional reduction by static condensation of the 6x6 constitutive matrix mapped into an effective 2x2 coupled weak axis bending-twisting relationship. The stability of the beam under different geometric and material parameters, like length/height ratio, ply thickness, and ply orientation, was investigated. The analytical formulas were verified against finite element buckling solutions using ABAQUS for different lamination orientations showing excellent accuracy. Link to the source.

Temperature Effects on Strain Gage Measurement

Introduction

The strain measurement is a very straight forward method in experimental stress analysis. The strains obtained from an experiment at room temperature are considered to be accurate, and actually it is accurate with some minor errors if it is performed at unchanged environmental condition. The case arises when the temperature changes, and the specimen is subjected to a different temperature during performing the test. In this case, the strain reading will be affected by several factors that cause error in the reading. When the temperature changes, the specimen will expand, and this expansion causes and increases or decreases in strain reading. The temperature change also affects the gage itself, and the gage can’t read correctly.

Solution for two layer laminate +/-[45]T composite plate with a given propertis

A Summary of Yarn Structure and Measurement

Here is a brief review of yarn structure and measurement methods

A)     Linear density designation of yarn:

1)      Direct system: based on measuring weight/unit length of a yarn

Tex -> weight  in gram of 1000 meters = 10 decitex (SI unit)

Denier -> weight in grams of 9000 meters...