Obviously, the primary factors governing productivity of geothermal heat extraction are high temperature, existence of sufficient geothermal fluid and path of fluid-flow. Thus the establishment of highly reliable technology for recovering the abundant geothermal energy is critical for solving the global energy problems. In addition to these advantages, the estimated amount of geothermal energy in the earth’s crust is abundant.
It is renewable and is almost free from global environmental problems such as global warming. It has been recognized that geothermal energy has the potential to be an alternative energy to fossil-fuel.
As a typical example, a series of studies, which are part of the frontiers of fracture technology, on the electromigration failure of metal lines, will be cited. The fracture phenomenon in such components is much different from those for cracks shown in the bold line.
The crack usually is microns to several tens microns in size.Įngineering structures of today generally include the combination of a mechanical and electronic and/or microelectronic components. A stable crack may extend perpendicular to the fiber axis when it is sufficiently small and extend in an unstable manner when it grows to its critical size. The treated optical glass fiber has a diameter of 125 μm. The first example is a lifetime prediction of an optical glass fiber. The fracture phenomenon of a minute part of engineering structures is generally difficult to evaluate using the bulk material. This discipline is referred to as Crustal Rock Fracture Mechanics. The sizes of cracks considered are as long as several kilometers. The cracks are artificially induced for use as heat exchange surfaces, through which water is circulated from the ground surface to the underground rock ( Fig. 1.Ĭrack/defect size with wider range and Fracture Technology.Ī typical example for a large crack problem is the geothermal energy extraction from hot, dry rock mass. However these studies will not be reviewed since our major interest of this review is outside the bold line in Fig.
Two of our major studies are shown in Fig. 1, say of from several hundred microns to at most several tens of centimeters. The sizes of cracks in engineering structures appearing in those papers are mostly shown in the bold line in Fig. Fracture mechanics has widely been applied to the design of engineering structures and also for integrity assessments. A great many papers on fracture mechanics have been published in the past several decades. This paper is confined to fracture starting from cracks and/or defects. 4) The author acknowledges that fracture mechanics is a subset of the Yokobori concept. An outstanding and historical work was done by Professor Takeo Yokobori and his first book was published more than half a century ago. 2), 3) An understanding of the strength and the fracture of materials, however, needs more interdisciplinary studies with their synthetical views. The original work of the widely used fracture mechanics is the Griffith theory 1) which is extended and applied to metals. Fracture mechanics is generally applied by equating combinations of stress and crack size to the measurement of resistance, which is geometrically independent, for crack extension.
Fracture mechanics is a subject of science-based engineering, and it is being used to assess the safety of engineering structures containing crack-like defects.