It is supposed that a region within an isotropic elastic solid undergoes a spontaneous change of form which, if the surrounding material were absent, would be some prescribed homogeneous deformation. Because of the presence of the surrounding material stresses will be present both inside and outside the region. The resulting elastic field may be found very simply with the help of a sequence of imaginary cutting, straining and welding operations. In particular, if the region is an ellipsoid the strain inside it is uniform and may be expressed in terms of tabu­lated elliptic integrals. In this case a further problem may be solved. An ellipsoidal region in an infinite medium has elastic constants different from those of the rest of the material; how does the presence of this inhomogeneity disturb an applied stress-field uniform at large distances? It is shown that to answer several questions of physical or engineering interest it is necessary to know only the relatively simple elastic field inside the ellipsoid.

https://www.jstor.org/stable/pdfplus/100095.pdf

The Determination of the Elastic Field of an Ellipsoidal Inclusion, and Related Problems

Variational principles in the linear theory of elasticity, involving the elastic polarization tensor, have been applied to the derivation of upper and lower bounds for the effective elastic moduli of quasi-isotropic and quasi-homogeneous multiphase materials of arbitrary phase geometry. When the ratios between the different phase moduli are not too large the bounds derived are close enough to provide a good estimate for the effective moduli. Comparison of theoretical and experimental results for a two-phase alloy showed good agreement.

A variational approach to the theory of the elastic behaviour of multiphase materials

T he macroscopic elastic moduli of two-phase composites are estimated by a method that takes account of the inhomogeneity of stress and strain in a way similar to the Hershey-Kroner theory of crystalline aggregates. The phases may be arbitrarily aeolotropic and in any concentrations, but are required to have the character of a matrix and effectively ellipsoidal inclusions. Detailed results arc given for an isotropic dispersion of spheres.

A self-consistent mechanics of composite materials

Dislocation theory is used to invoke a strain gradient theory of rate independent plasticity. Hardening is assumed to result from the accumulation of both randomly stored and geometrically necessary dislocation. The density of the geometrically necessary dislocations scales with the gradient of plastic strain. A deformation theory of plasticity is introduced to represent in a phenomenological manner the relative roles of strain hardening and strain gradient hardening. The theory is a non-linear generalization of Cosserat couple stress theory. Tension and torsion experiments on thin copper wires confirm the presence of strain gradient hardening. The experiments are interpreted in the light of the new theory.

Strain gradient plasticity: Theory and experiment

The Classical Field Theories

Mit Hilfe des Begriffes der elastischen Polarisierbarkeit konnen die elastischen Konstanten des makroskopisch isotropen Vielkristalls aus den Einkristallkonstanten exakt ausgerechnet werden. Im Falle des Aggregats aus kubischen Kristalliten, in dem die Bestimmung des Kompressionsmoduls trivial ist, folgt der Schubmodul aus einer Gleichung 3. Grades [Gl. (22)], in der Kombinationen der Einkristallhauptkonstanten als Koeffizienten auftreten. Die experimentellen Vergleichswerte weichen von den berechneten etwas ab, was beweist, das die Experimente nicht den von der Theorie geforderten idealen Bedingungen genugt haben. Weitere Anwendungsmoglichkeiten der Methode werden besprochen.

Ekkehart Kröner

Papers

Berechnung der elastischen Konstanten des Vielkristalls aus den Konstanten des Einkristalls

Allgemeine Kontinuumstheorie der Versetzungen und Eigenspannungen

Kontinuumstheorie der Versetzungen und Eigenspannungen

Zur plastischen verformung des vielkristalls

Elasticity theory of materials with long range cohesive forces