Mechanics of Solid Interfaces

Book Preface

When we observe the objects around us, wherever we look, we must search for a long time to find any that are made up of a homogeneous material, at either the macroscopic or microscopic level. The most common steel contains both ferrite and cementite; plastic materials are stiffened by mineral particles enrobed by a polymer matrix; the ceramic used in our daily pots combines crystallites bonded by a glassy phase. Mineral and organic glasses are frequently strengthened by a polycarbonate film or coated with an antiscratch, anti-fouling or photochromic film.

In advanced technology, the search for optimal material/ function matching has led to an increasingly frequent use of “multimaterials”, “hybrid materials”, composites, brazed or adhesive bonding, coatings, and structural or functional multilayers. Practically all high-performance metallic alloys are strengthened by precipitates of various sizes, which hinder the dislocation motion that goes along with plasticity, but localize damage and promote crack initiation at the same time. Microelectronics’ integrated circuits combine fine metal deposits, insulators and semiconductors of very different types. Depending on the intended application, various functional characteristics are expected of the solid–solid interfaces that these single block pieces or components contain, but they are all heterogeneous at different scales. In every case, an adequate fracture resistance of interfaces is required to maintain the principal function and integrity of the material.

The question of the mechanical behavior of the interfaces between two different materials is thus a critical challenge, as much from an applied perspective as from a fundamental one. The problems related to its characterization are far from being solved, which justifies active and multidisciplinary research in which the necessity of understanding bringsmechanics together with the physics of materials, the chemistry of solids, and the thermodynamics of multicomponent equilibria.

We therefore thought it would be useful to compile typical contributions towards the approach to this topic in a single book. Part 1 (Chapters 1 and 2) presents the basics of the mechanical and structural characterization of interfaces. Part 2 (Chapters 3 and 4) is specifically devoted to a description of the theoretical and experimental tools used to address the issue of the initiation and propagation of interfacial fractures. Part 3, containing Chapters 5, 6 and 7, illustrates the way in which, given the current state of knowledge, we address practical problems of interfacial adherence in various geometric and loading conditions, and attempt to handle them. Finally, Part 4 of this book (Chapters 8 and 9) is dedicated to the specific case of interfaces between thin films and substrates, which is of growing importance in current practical applications. Each chapter includes a bibliography that will help readers to further their knowledge in this subject.

We make no claim to have exhausted the subject; but have laid down some milestones: theoretical and experimental advances will follow on the heels of all these approaches, as will other aspects of interface mechanics that can profitably be associated with a presentation such as the one we have written. Here, we are particularly thinking of the numerical modeling of problems of adherence and interfacial fracture, which surely deserves further development; and of questions of surface and interface elasticity, the importance of which is just beginning to be realized with the advent of nano-objects and nanofilms in research laboratories. These same nanoobjects, as part of a matrix or confined by their free surface (paradoxically!) and the interface with their support, present unexpected deformation mechanisms that we are now just discovering. The approaches presented in this book are often illustrated by reference to inorganic materials, the field of activity for most of the contributors to this book; however, the ideas developed are common to all types of systems, and if we tie them in with the profusion of literature about the adherence of organic materials, their similarity becomes apparent. The older and more frequent topic of the mechanical behavior of mobile interfaces with relative sliding has not been addressed as it is well-documented thanks to specialists in wear and tribology.

We could not end this introduction without offering our deep gratitude to those who have helped us, particularly all the contributors who agreed to write a brief presentation on their area of scientific interest. Their names can be found in the various chapters they have written; this book belongs to them as well.

We wish you happy and fruitful reading.

Muriel BRACCINI
Michel DUPEUX
June 2012