POISSON’S RATIO BASIC INFORMATION AND TUTORIAL

POISSON'S RATIO TUTORIALS AND SAMPLE PROBLEM
What Is Poisson's Ratio? Sample Problem And Solution Using Poisson's Ratio


When a homogeneous slender bar is axially loaded, the resulting stress and strain satisfy Hooke’s law, as long as the elastic limit of the material is not exceeded.

In all engineering materials, the elongation produced by an axial tensile force P in the direction of the force is accompanied by a contraction in any transverse direction (Fig. 2.36).† In this section and the following sections (Secs. 2.12 through 2.15), all materials considered will be assumed to be both homogeneous and isotropic, i.e., their mechanical properties will be assumed independent of both position and direction.

It follows that the strain must have the same value for any transverse direction.\ Therefore, for the loading shown in Fig. 2.35 we must have Py 5 Pz. This common value is referred to as the lateral strain.

An important constant for a given material is its Poisson’s ratio, named after the French mathematician Siméon Denis Poisson (1781–1840) and denoted by the Greek letter n (nu). It is defined as

v = - lateral strain / lateral stress.

Sample Problem:


A 500-mm-long, 16-mm-diameter rod made of a homogenous, isotropic material is observed to increase in length by 300 mm, and to decrease in diameter by 2.4 mm when subjected to an axial 12-kN load. Determine the modulus of elasticity and Poisson’s ratio of the material.

Solution:

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FLY ASHES CIVIL ENGINEERING CONSTRUCTION PURPOSE BASICS AND TUTORIALS

FLY ASHES CIVIL ENGINEERING CONSTRUCTION PURPOSE BASIC INFORMATION
What Are Fly Ashes?


Fly ash meeting the requirements of ASTM C618, ‘‘Specification for Fly Ash and Raw or Calcined Natural Pozzolan for Use as a Mineral Admixture in Portland Cement Concrete,’’ is generally used as a cementitious material as well as an admixture.

Natural pozzolans are derived from some diatomaceous earths, opaline cherts and shales, and other materials. While part of a common ASTM designation with fly ash, they are not as readily available as fly ashes and thus do not generate the same level of interest or research.

Fly ashes are produced by coal combustion, generally in an electrical generating station. The ash that would normally be released through the chimney is captured by various means, such as electrostatic precipitators. The fly ash may be sized prior to shipment to concrete suppliers.

All fly ashes possess pozzolanic properties, the ability to react with calcium hydroxide at ordinary temperatures to form compounds with cementitious properties. When cement is mixed with water, a chemical reaction (hydration) occurs.

The product of this reaction is calcium silicate hydrate (CSH) and calcium hydroxide [Ca(OH)2]. Fly ashes have high percentages of silicon dioxide (SiO2). In the presence of moisture, the Ca(OH)2 will react with the SiO2 to form another CSH.

Type F ashes are the result of burning anthracite or bituminous coals and possess pozzolanic properties. They have been shown by research and practice to provide usually increased sulfate resistance and to reduce alkali-aggregate expansions.

Type C fly ashes result from burning lignite or subbituminous coals. Because of the chemical properties of the coal, the Type C fly ashes have some cementitious properties in addition to their pozzolanic properties. Type C fly ashes may reduce the durability of concretes into which they are incorporated.