J. L. Kelly

Bio: J. L. Kelly is an academic researcher from University of Texas at Austin. The author has contributed to research in topics: Lamb waves & Acoustic emission. The author has an hindex of 1, co-authored 1 publications receiving 792 citations.

Second-Order Elastic Deformation of Solids

Abstract: Expressions for the velocities of elastic waves in stressed solids are derived using Murnaghan's theory of finite deformations and third-order terms in the energy. For isotropic materials, in addition to the Lam\'e constants $\ensuremath{\lambda}$ and $\ensuremath{\mu}$, three additional constants, $l$, $m$, and $n$, are required to describe the material.By measuring the transmission time of elastic pulses through the material, the velocities of longitudinal and shear waves are determined as a function of applied stress. By subjecting the material to hydrostatic pressure as well as simple compression, it is found that seven functions of the three constants $l$, $m$, and $n$ can be measured and thus numerical values calculated. Results are given for polystyrene, iron, and Pyrex glass.

The non-linear field theories of mechanics

Abstract: Matter is commonly found in the form of materials. Analytical mechanics turned its back upon this fact, creating the centrally useful but abstract concepts of the mass point and the rigid body, in which matter manifests itself only through its inertia, independent of its constitution; “modern” physics likewise turns its back, since it concerns solely the small particles of matter, declining to face the problem of how a specimen made up of such particles will behave in the typical circumstances in which we meet it. Materials, however, continue to furnish the masses of matter we see and use from day to day: air, water, earth, flesh, wood, stone, steel, concrete, glass, rubber, ... All are deformable. A theory aiming to describe their mechanical behavior must take heed of their deformability and represent the definite principles it obeys.

The Elastic Constants of Crystals

Abstract: Publisher Summary This chapter discusses the elastic constants of crystals. The elastic properties of solid matter hold interest for both technology and basic research. In the first field applied elasticity is an important discipline for those fundamental considerations of engineering design which are usually included under the designation “strength of materials.” The treatment of structural materials requires semiempirical methods, because their compositions are complex and prior treatment has a pronounced effect. On the other hand, basic research into elastic properties is usually concerned with work on specimens in the simplest state which can be obtained reproducibly—for example, annealed single crystals. The complete tabulation of elastic constants for such specimens is valuable, not only for itself, but also because the data can be correlated with other physical measurements and thereby provide possible insight into the nature of the atomic forces in solid matter. The research aspect of elastic studies is of primary interest for this chapter. The case of the isotropic medium is important both for the chronological development of the subject of elasticity and also for its applicability to polycrystals and glasses.

Elastic Properties of Metals and Alloys, I. Iron, Nickel, and Iron-Nickel Alloys

Abstract: A comprehensive compilation is given of elastic properties of iron‐nickel alloys. When sufficient data exist, preferred values are recommended. This compilation covers, besides pure iron and pure nickel, the entire binary composition range, both b.c.c. and f.c.c. phases. Elastic constants included are: Young's modulus, shear modulus, bulk modulus (reciprocal compressibility), Poisson's ratio, and single‐crystal elastic stiffnesses, both second‐order and higher‐order. Data are compiled for variation of elastic constants with composition, temperature, pressure, magnetic field, mechanical deformation, annealing, and crystallographic transitions. An overview is given from the vantage points of the electron theory of metals, elasticity theory, and crystallographic theory. Also included are discussions of iso‐thermal and adiabatic elastic constants, interrelationships among engineering elastic constants, computation of the latter from single‐crystal elastic stiffnesses, and similar topics. Where key data have n...

Microcracks, and the static and dynamic elastic constants of annealed and heavily cold-worked metals

Abstract: The existence of sub-microscopic cracks in heavily cold-worked metals has been suggested in explanation of the very large discrepancies in dislocation densities estimated from changes in density and electrical resistivity, and release of stored energy on annealing such materials. It is shown that microcracks will produce changes in the elastic constants of a material comparable with - but somewhat larger than - the change in electrical resistivity, rather than with change in density. Measurements have been made, both statically and dynamically, of Young's modulus, the shear modulus and Poisson's ratio for annealed and heavily cold-worked aluminium, copper and nickel. No changes in moduli were found that could be ascribed to the presence of microcracks. An unexpected result is a very large and consistent difference between the bulk moduli, and Poisson's ratio, determined statically and dynamically - a difference very much greater than can be accounted for by the usual thermodynamic relationship between isothermal and adiabatic moduli.