Formula Home Mechanics of Materials Stress Strain Hooke's Law Orthotropic Material Transverse Isotropic Isotropic Material Plane Stress Plane Strain Finding E and n Finding G and K Applications Pressure Vessels Rosette Strain Gages Failure Criteria Calculators Stress Transform Strain Transform Principal Stress Principal Strain Elastic Constants Resources Bibliography
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more free publications       Shear Modulus from Pure Shear When a specimen made from an isotropic material is subjected to pure shear, for instance, a cylindrical bar under torsion in the xy sense, sxy is the only non-zero stress. The strains in the specimen are obtained by, The shear modulus G, is defined as the ratio of shear stress to engineering shear strain on the loading plane, where . The shear modulus G is also known as the rigidity modulus, and is equivalent to the 2nd Lamé constant m mentioned in books on continuum theory. Common sense and the 2nd Law of Thermodynamics require that a positive shear stress leads to a positive shear strain. Therefore, the shear modulus G is required to be nonnegative for all materials, G > 0 Since both G and the elastic modulus E are required to be positive, the quantity in the denominator of G must also be positive. This requirement places a lower bound restriction on the range for Poisson's ratio, n > -1
 Bulk Modulus from Hydrostatic Pressure When an isotropic material specimen is subjected to hydrostatic pressure s, all shear stress will be zero and the normal stress will be uniform, . The strains in the specimen are given by, In response to the hydrostatic load, the specimen will change its volume. Its resistance to do so is quantified as the bulk modulus K, also known as the modulus of compression. Technically, K is defined as the ratio of hydrostatic pressure to the relative volume change (which is related to the direct strains), Common sense and the 2nd Law of Thermodynamics require that a positive hydrostatic load leads to a positive volume change. Therefore, the bulk modulus K is required to be nonnegative for all materials, K > 0 Since both K and the elastic modulus E are required to be positive, the following requirement is placed on the upper bound of Poisson's ratio by the denominator of K, n < 1/2
 Relation Between Relative Volume Change and Strain For simplicity, consider a rectangular block of material with dimensions a0, b0, and c0. Its volume V0 is given by, When the block is loaded by stress, its volume will change since each dimension now includes a direct strain measure. To calculate the volume when loaded Vf, we multiply the new dimensions of the block, Products of strain measures will be much smaller than individual strain measures when the overall strain in the block is small (i.e. linear strain theory). Therefore, we were able to drop the strain products in the equation above. The relative change in volume is found by dividing the volume difference by the initial volume, Hence, the relative volume change (for small strains) is equal to the sum of the 3 direct strains.
Glossary  Selecting the Right 3D Printer

Discover how to choose the right 3D printer for your needs and the key performance attributes to consider. Injection Molding Design Guide

Guide for high quality and cost-effective plastic injection molding. 3D Scanners

A white paper to assist in the evaluation of 3D scanning hardware solutions. Mechanical Engineers Outlook

Guide for those interested in becoming a mechanical engineer. Includes qualifications, pay, and job duties.