Nomenclature Physical Terms Creep. A slow incremental crack increase under a constant or slowly varying load that is below that of the the Griffith criterion. Critical dynamic stress intensity factor KID. The value that if the stress intensity factor is larger than it, dynamic (fast) fracturing would continue. KID is usually larger than KIC (see Eq. 1.137). Critical or post critical conditions. Are associated with crack growth at KI = KIC. Critical stress intensity factor. A material-dependent property KIC. When KI = KIC, the Griffith criterion is fulfilled and fracturing can commence. Effective saturation. An assumption that beyond a certain value, crack density increases very slowly (logarithmically) with load increase. Fatigue. Material failure by cracking under periodic or repeated stresses. Flaws. General name for small heterogeneities in rocks (fossils, concretions, pores) that may initiate crack growth. Griffith criterion. A necessary condition for fracturing of materials: The stress intensity factor KI, becomes equal to the critical stress intensity factor KIC. Griffith flaws. Flaws in brittle material (glass) that have an effective length of ≈2 µm (Lawn 1993, p. 13), while in rocks they may range up to lengths of grain boundaries. Linear elastic fracture mechanics (LEFM). The framework theory for linearly calculating stress fields in different configurations and deducing KI values. Very valuable for static fracture problems, but fails for dynamic or extremely slow fracturing. Saturation of crack spacing. An assumption that the crack spacing (No. of cracks per unit length) is limited. Once the spacing reaches this value, no increase is possible under any load. Stable crack growth. Occurs under loads in which KI decreases with the increase in crack length, and the crack arrests when the load is removed (also termed ‘controlled’). Stress concentration. A situation where near to an abrupt geometrical change in the mate- rial, such as a flaw, crack, pore, vacancy, etc., a local increase of stress occurs in the stress field. Sress intensity factor KI. A measure of the ratio of the maximal stress concentration near σ a flaw to the nominal stress. In an infinite plate under remote tension, 0, having a sharp σ π ½ flaw of length c, expressed as KI = 0( c) . 530 Nomenclature Sub-critical conditions. Are associated with crack growth below the critical stress inten- sity factor KIC. Time to failure. The time interval from the minute of application of a load, smaller than that needed for instantaneous fracture, until the sample breaks. Unstable crack growth. Occurs ‘catastrophically’ at KI = KIC even when unloaded (also termed ‘uncontrolled’). v vs. KI diagrams. Correlate the changes in the instantaneous crack velocity v with values of the instantaneous tensile stress intensity factor KI. Nomenclature of Main Fractographic Features Arrest marks. Ripple marks that form on the fracture surface and signify slow crack propa- gation down to arrest, or crack restarting growing. Barbs. See plumes. Dynamic mirror plane. Forms when fractured primarily by high tensile stresses; it propa- gates rapidly and exhibits characteristic morphological features. En echelon-fringe. A fringe populated by en echelon cracks. En echelon segmentation. Cracks that systematically relate to each other in a ‘shingle-like’ arrangement and are confined to the fringe. Fractography. The branch of science that analyses fracture surface morphology and re- lated features and their causes, as well as mechanisms, in technological materials. Fringe. A zone that surrounds the mirror plane and contains cracks that display rough morphologies. Hackle cracks. A series of cracks that relate to each other three dimensionally in various directions and are confined to the fringe. Hackle-fringe. A fringe populated by hackle cracks. Mirror boundary. A narrow morphological rim separating the mirror from the fringe. Mirror plane. The crack surface that contains the initial flaw, the critical flaw, the striae (plume) and the ripple marks. Oscillating cracks. Bends of the mirror plane around the axis normal to the direction of crack propagation. Plumes. Form by slow fracture on the mirror plane due to stress fields which rotate the fracture front about the axis of the direction of crack propagation, and often are identified by their dendrite-like morphologies consisting of many splayed barbs. Quasi-static mirror plane. Forms when fractured under low stresses; it propagates sub- critically and exhibits characteristic morphological features. Ripple marks. Form on the mirror plane due to stress fields that intermittently bend the crack front around the axis normal to the direction of propagation, when both axes are on the fracture surface. Two types of ripple marks occur, undulations and arrest marks. Nomenclature 531 Striae. Form by rapid fracture on the mirror plane due to stress fields which rotate the fracture front about the axis of the direction of crack propagation, and often are identified by sharp, continuous cuts in the material (glass or rock). Undulations. Ripple marks that form on the fracture surface and signify crack propaga- tion in various velocities. Nomenclature of Joints Burial joints, or subsidence joints. Form during the sedimentation and diagenetic pro- cesses, and often are single-layer joints. They may form in great depths. Cooling joints. Form during various cooling stages of the pluton (or volcanic rock). Crack. In the present text is almost synonymous with fracture. It is generally applied to small fractures. These are general terms, regardless of loading mode. Cross-fold joints. Form sub-orthogonal to fold axes. Cross-joints. A set of younger, nonsystematic joints that arrest at earlier, systematic, single- layer joints, seen in plan view (Gross 1993). Dihedral angle. Produced between two genetically linked fractures or fracture sets (joints or faults) that maintain a conjugate relationship. Fault. Of a primary nature, that originated by slip(s), which resulted in lost cohesion in the rock. Of a secondary nature, that formed by slip(s) on an existing joint. Fractography. Fracture markings that describe the surface morphology that forms essentially by an opening mode. Every such surface (joint) has a unique fracto- graphy. Group. This term is occasionally applied (rather than set or system) when fracture affinities are debatable. Joint. A surface on which the rock has lost cohesion and does not show a discernible lateral slip. Joint set. Consists of a series of joints of similar strikes that exhibit similar fracture sur- face morphologies (if present). This similarity often reflects on the same fracture condi- tions, even if in different fracture episodes. Joint system. Consists of various joint sets that probably are genetically linked. Multi-layer joints. Cut many layers, often dissecting the entire outcrop. They are widely and irregularly spaced. Orthogonal joint sets. Form perpendicular to each other (in a map), but may deviate up to 10° from this relationship. Post uplift joints. Post uplift fractures that form in association with erosion. Single-layer joints. Cut vertically individual layers (or less commonly, two layers) but ar- rest at the layer boundaries. They maintain small, regular spacing. Strike joints, or strike-parallel joints. Form sub-parallel to fold axes. 532 Nomenclature Surface joints. Recent fractures that are confined to the upper layer, below the soil cover. Syntectonic joints. Form during intense deformation, occasionally associated with fault- ing. They may form in great depths. Tectonofractography. The application of joint fractography to the interpretation of tectonophysical processes. Uplift joints. Form during uplift. They can be both single-layer and multi-layer fractures and form in shallow depths. Selected Supplementary Parameters Skewness. The degree of asymmetry, or departure from symmetry, of a distribution. If the frequency curve of a distribution has a longer “tail” to the right of the central maxi- mum than to the left, the distribution is said to be skewed to the right or to have positive skewness. If the reverse is true, it is said to be skewed to the left or to have negative skew- ness (Spiegel 1961). Kurtosis. The degree of peakedness (between high and flat-topped peaks) of a distribu- tion, usually taken relative to a normal distribution (Spiegel 1961). Statistics of extremes. The statistics of the largest (or smallest) members of a population, e.g., the severest earthquakes, the highest waves, etc. FSI. The fracture spacing index, defined as the slope of the best-fit line when joint spacing is plotted versus layer thickness (Narr and Suppe 1991). FSR. The fracture spacing ratio defined as the layer thickness divided by the median joint spacing for an individual bed (Gross 1993). L / S. The ratio of joint length to joint spacing (Bahat 1991a, p. 309; Wu and Pollard 1995). References Abraham FF, Brodbeck D, Ridge WE, Xu X (1997) A molecular dynamics investigation of rapid frac- ture mechanics. J Mech Phys Solids 45:1595–1619 Abraham FF, Walkup R, Gao HJ, Duchaineau M, De la Rubia TD, Seager M (2002) Simulating materi- als failure by using up to one billion atoms and the world’s fastest computer: Brittle fracture. Proceedings of the National Academy of Sciences of the United States of America 99:5777–5782 Acocella V, Gudmundsson A, Funiciello R (2000) Interaction and linkage of extension fractures and normal faults: Examples from the rift zone of Iceland. 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