SIH, George C.
East China University of Science and Technology
Shanghai - China

TANG, X. S.

SPYROPOULOS,C. P.

UEDA, S. 

VU-KHANH, T.

NAIT ABDELAZIZ, M.

TU, S. T.

CHUE, C. H.

NOBILE, L.

JEONG, D.

Abstract
The traditional concept of structural and machine design has relied on the testing of small specimens for determining the material properties such that the data can be translated to the design of full scale structures. This philosophy has prevailed for centuries until the 1950s when the dramatic failure of large size structures has caused a great concern to the designers as well as the public at large. In particular, the unexpected loss of the Comet jet airliners and ships have indicated the need to consider the conditions under which a critical size (not necessarily the largest) defect can lead to catastrophic fracture. Such a concern has led to the development of the discipline of fracture mechanics. An initial defect in the form of a line crack has thus been adopted into material testing.
The recognition of energy saving and efficient use of materials has demanded a better understanding of the material micro- and nano-structure where non-homogeneity cannot be ignored. This trend has broadened the size scale of investigation from meters to microns, the size at which miniature electronics devices will be made. Their operational reliability must also be addressed. This raises the concern whether the same underlying physics and practice in technology at the macroscopic scale would remain valid for the smaller devices. The conventional material properties are based on the averages of the bulk and their association with the local properties where inhomogeneity plays a role is not precisely known. This calls for added attention for the transfer of information from one scale to the next possibly without substantial transient effects. Mesomechanics attempts to achieve this goal.
One of the difficulties is that scale shifting cannot be divorced from material damage. Stated more bluntly is that the damage also occurs between the macro- and micro-scale. The interim region shall be referred to as the mesoscopic zone and the corresponding discipline shall be known as Mesofracture Mechanics. This volume is devoted to the description of failure by cracking in the cross-scale region that is neither macroscopic nor microscopic. The size of this transition region can be large and small; it depends on the rate of load transfer, geometry and material. Since non-equilibrium mechanics is still beyond the common knowledge of the engineering community, each scale including the meso zone will be analyzed by equilibrium mechanics where the material properties are assumed to be measurable by performing tests under the adiabatic or reversible isothermal thermodynamic processes. The restrictions of these simplifying assumptions must be kept in mind because they will certainly be violated when the size and time scales are made smaller and smaller.
This volume on Mesofracture Mechanics contains twenty papers attempts to address material damage by cracking in materials and environments that would likely to be contained in the meso zone where the conventional fracture criteria may cease to be valid as they will yield unphysical results. Unlike the macroscopic scale where mechanical effects may dominate, other energy fields such electrical, magnetic or the combination may play a role, particularly when anisotropy and inhomogeneity must be considered. Moreover, the discrete character of the material microstructure takes precedent. The process of averaging the bulk material properties to which continuum mechanics relies on ceases to be valid. These fundamental issues are still in debate and will not be settled in the foreseeable future. Hence, Mesofracture Mechanics emphasizes the scale shifting aspects of fracture mechanics, particularly when the size is reduced and time is stepped up.