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Crack healing as a function of pOH- and fracture morphologyFallon, Jessica Anne 17 February 2005 (has links)
Crack healing in quartz has been investigated by optical microscopy and interferometry
of rhombohedral ( 1 1 10 ) cracks in polished Brazilian quartz prisms that were annealed
hydrothermally at temperatures of 250°C and 400°C for 2.4 to 240 hours, fluid pressure
Pf = Pc = 41 MPa, and varying pOH- (from 5.4 to 1.2 at 250°C for fluids consisting of
distilled water and NaOH solutions with molalities up to 1). Crack morphologies before
and after annealing were recorded for each sample in plane light digital images. Crack
apertures were determined from interference fringes recorded using transmitted
monochromatic light (l = 598 nm). As documented in previous studies, crack healing is
driven by reductions in surface energy and healing rates are governed by diffusional
transport; sharply defined crack tips become blunted and split into fluid- filled tubes and
inclusions. A rich variety of fluid inclusion geometries are also observed with nonequilibrium
shapes that depend on initial surface roughness.
Crack healing is significant at T=400°C. Crack healing is also observed at T=250°C for
smooth cracks with apertures <0.6 mm or cracks subject to low pOH-. The extent of
crack healing is sensitive to crack aperture and to hackles formed by fine-scale crack
branching during earlier crack growth. Crack apertures appear to be controlled by
hackles and debris, which prop the crack surfaces open. Upon annealing, crack
apertures are reduced, and these reduced crack apertures govern the kinetics of
diffusional crack healing that follows. Hackles are sites of either enhanced or reduced
loss of fluid-solid interface, depending on slight mismatches and sense of twist on
opposing crack surfaces. Hackles are replaced either by healed curvilinear quartz
bridges and river patterns surrounded by open fluid-filled crack, or by fluid- filled tubes
surrounded by regions of healed quartz. For a given temperature, aperture and anneal
time, crack healing is enhanced at low pOH- ( £ 1.2) either because of changes in the
hydroxylated quartz- fluid interface that enhance reaction rates or because of increased
rates of diffusional net transport of silica at high silica concentrations.
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Comparative biomechanics of two non-invasive mandibular fracture repair techniques in dogsKitshoff, Adriaan Mynhardt 04 June 2013 (has links)
Dissertation (MSc)--University of Pretoria, 2012. / Companion Animal Clinical Studies / MSc / Unrestricted
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The effect of scale on the morphology, mechanics and transmissivity of single rock fracturesFardin, Nader January 2003 (has links)
This thesis investigates the effect of scale on themorphology, mechanics and transmissivity of single rockfractures using both laboratory and in-situ experiments, aswell as numerical simulations. Using a laboratory 3D laserscanner, the surface topography of a large silicon-rubberfracture replica of size 1m x 1m, as well as the topography ofboth surfaces of several high-strength concrete fracturereplicas varying in size from 50mmx50mm to 200mm x 200mm, werescanned. A geodetic Total Station and an in-situ 3D laser radarwere also utilized to scan the surface topography of a largenatural road-cut rock face of size 20m x 15m in the field. Thisdigital characterization of the fracture samples was then usedto investigate the scale dependency of the three dimensionalmorphology of the fractures using a fractal approach. Thefractal parameters of the surface roughness of all fracturesamples, including the geometrical aperture of the concretefracture samples, were obtained using the Roughness-Lengthmethod. The results obtained from the fractal characterization ofthe surface roughness of the fracture samples show that bothfractal dimension, D, and amplitude parameter, A, for aself-affine surface are scale-dependent, heterogeneous andanisotropic, and their values generally decrease withincreasing size of the sample. However, this scale-dependencyis limited to a certain sizedefined as the stationaritythreshold, where the surface roughness parameters of thefracture samples remain essentially constant beyond thisstationarity threshold. The surface roughness and thegeometrical aperture of the tested concrete fracture replicasin this study did not reach stationarity due to the structuralnon-stationarity of their surface at small scales. Although theaperture histogram of the fractures was almost independent ofthe sample size, below their stationarity threshold both theHurst exponent, Hb, and aperture proportionality constant, Gb,decrease on increasing the sample sizes. To investigate the scale effect on the mechanical propertiesof single rock fractures, several normal loading and directshear tests were performed on the concrete fracture replicassubjected to different normal stresses under Constant NormalLoad (CNL) conditions. The results showed that both normal andshear stiffnesses, as well as the shear strength parameters ofthe fracture samples, decrease on increasing the sample size.It was observed that the structural non-stationarity of surfaceroughness largely controls the contact areas and damage zoneson the fracture surfaces as related to the direction of theshearing. The aperture maps of the concrete fracture replicas ofvarying size and at different shear displacements, obtainedfrom numerical simulation of the aperture evolution duringshearing using their digitized surfaces, were used toinvestigate the effect of scale on the transmissivity of thesingle rock fractures. A FEM code was utilized to numericallysimulate the fluid flow though the single rock fractures ofvarying size. The results showed that flow rate not onlyincreases on increasing the sample size, but also significantlyincreases in the direction perpendicular to the shearing, dueto the anisotropic roughness of the fractures. <b>Key words:</b>Anisotropy, Aperture, Asperity degradation,Contact area, Finite Element Method (FEM), Flow analysis,Fractals, Fracture morphology, Heterogeneity,Stress-deformation, Surface roughness, Roughness-Length method,Scale dependency, Stationarity, Transmissivity, 3D laserscanner.
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The effect of scale on the morphology, mechanics and transmissivity of single rock fracturesFardin, Nader January 2003 (has links)
<p>This thesis investigates the effect of scale on themorphology, mechanics and transmissivity of single rockfractures using both laboratory and in-situ experiments, aswell as numerical simulations. Using a laboratory 3D laserscanner, the surface topography of a large silicon-rubberfracture replica of size 1m x 1m, as well as the topography ofboth surfaces of several high-strength concrete fracturereplicas varying in size from 50mmx50mm to 200mm x 200mm, werescanned. A geodetic Total Station and an in-situ 3D laser radarwere also utilized to scan the surface topography of a largenatural road-cut rock face of size 20m x 15m in the field. Thisdigital characterization of the fracture samples was then usedto investigate the scale dependency of the three dimensionalmorphology of the fractures using a fractal approach. Thefractal parameters of the surface roughness of all fracturesamples, including the geometrical aperture of the concretefracture samples, were obtained using the Roughness-Lengthmethod.</p><p>The results obtained from the fractal characterization ofthe surface roughness of the fracture samples show that bothfractal dimension, D, and amplitude parameter, A, for aself-affine surface are scale-dependent, heterogeneous andanisotropic, and their values generally decrease withincreasing size of the sample. However, this scale-dependencyis limited to a certain sizedefined as the stationaritythreshold, where the surface roughness parameters of thefracture samples remain essentially constant beyond thisstationarity threshold. The surface roughness and thegeometrical aperture of the tested concrete fracture replicasin this study did not reach stationarity due to the structuralnon-stationarity of their surface at small scales. Although theaperture histogram of the fractures was almost independent ofthe sample size, below their stationarity threshold both theHurst exponent, Hb, and aperture proportionality constant, Gb,decrease on increasing the sample sizes.</p><p>To investigate the scale effect on the mechanical propertiesof single rock fractures, several normal loading and directshear tests were performed on the concrete fracture replicassubjected to different normal stresses under Constant NormalLoad (CNL) conditions. The results showed that both normal andshear stiffnesses, as well as the shear strength parameters ofthe fracture samples, decrease on increasing the sample size.It was observed that the structural non-stationarity of surfaceroughness largely controls the contact areas and damage zoneson the fracture surfaces as related to the direction of theshearing.</p><p>The aperture maps of the concrete fracture replicas ofvarying size and at different shear displacements, obtainedfrom numerical simulation of the aperture evolution duringshearing using their digitized surfaces, were used toinvestigate the effect of scale on the transmissivity of thesingle rock fractures. A FEM code was utilized to numericallysimulate the fluid flow though the single rock fractures ofvarying size. The results showed that flow rate not onlyincreases on increasing the sample size, but also significantlyincreases in the direction perpendicular to the shearing, dueto the anisotropic roughness of the fractures.</p><p><b>Key words:</b>Anisotropy, Aperture, Asperity degradation,Contact area, Finite Element Method (FEM), Flow analysis,Fractals, Fracture morphology, Heterogeneity,Stress-deformation, Surface roughness, Roughness-Length method,Scale dependency, Stationarity, Transmissivity, 3D laserscanner.</p>
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