Chapter 1

Interfaces: the Physics, Chemistry and Mechanics of Heterogeneous Continua

Of what does an interface between two solids consist? What qualifying or quantitative physical or chemical parameters must we specify to define it? What general considerations can we set out about the mechanical behavior of an interface in a heterogeneous solid? These are the basic questions that this chapter proposes to answer as an introduction to the following chapters, focusing on more specific points.

1.1. Definition and terminology

Strictly speaking, an interface can be defined as the two-dimensional border area between two dissimilar materials. These two materials may differ in their physical state (such as in the case of solid–liquid or solid–gas interfaces); their chemical composition (such as an interface between two immiscible liquids in an emulsion); their structure (such as a residual martensite/austenite interface in quenched steel); their relative orientation (such as the twin boundaries or grain boundaries in a polycrystal or the interface between layers in a multilayer composite); or even by their relative translation (such as a stacking fault surface in a crystal). In this book, as the title indicates, we will focus on the case of interfaces between two solid materials.

The geometric aspect of a solid–solid interface can prove extremely variable, depending on the scale at which it is observed. Abrupt interfaces, in which the physical and chemical characteristics change suddenly ...

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