Micro-cracking and incipient shear microstructures at low-strain deformation of Opalinus Clay: Insights from triaxial testing and broad-ion-beam scanning-electron-microscopy (BIB-SEM)

Abstract. A microphysics-based understanding of mechanical and hydraulic processes in clay shales is required for developing advanced constitutive models, which can be extrapolated to long-term deformation. Although many geomechanical laboratory tests have been performed to characterize the bulk mechanical, hydro-mechanical and failure behaviour of Opalinus Clay, important questions remain about microphysics: How do microstructural evolution and deformation mechanisms control the 15 complex rheology over time scales not accessible in the laboratory. In this contribution, Scanning Electron Microscopy (SEM) was used to image microstructures in an Opalinus Clay sample deformed in an unconsolidated-undrained triaxial compression test at 4 MPa confining stress followed by Argon Broad Ion Beam (BIB) polishing. Axial load was applied (sub-) perpendicular to bedding until the specimen failed. The test was terminated at an axial strain of 1.35 %. Volumetric strain measurements showed bulk compaction throughout the compression test. Observations on the cm- to μm-scale showed that deformation 20 localized by forming a network of μm-thick fractures. In BIB-SEM at the grain scale, incipient deformation zones show dilatant inter- and intragranular micro-cracking, granular flow, plastic deformation and bending of phyllosilicate grains, and pore collapse in fossils. Outside these zones, no deformation microstructures were observed indicating localized damage. Thus, microphysics of deformation appear to be controlled by both brittle and ductile processes along preferred orientations. Anastomosing networks of deformation bands develop into the main deformation bands along which the sample fails. 25 Microstructural observations and the stress-strain behaviour were integrated into a deformation model with three different stages of damage accumulation representative for the deformation of the compressed Opalinus Clay sample. Results on the microscale explain how the sample locally dilates while bulk measurement shows compaction, with an inferred major effect on permeability evolution. Comparison with the microstructure of highly strained Opalinus Clay in fault zones shows minor similarity and suggest that during long-term deformation additional solution-precipitation processes operate.

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Micromechanisms leading to shear failure of Opalinus Clay in a triaxial test: a high-resolution BIB–SEM study

Solid Earth ◽

10.5194/se-12-2109-2021 ◽

2021 ◽

Vol 12 (9) ◽

pp. 2109-2126

Author(s):

Lisa Winhausen ◽

Jop Klaver ◽

Joyce Schmatz ◽

Guillaume Desbois ◽

Janos L. Urai ◽

...

Keyword(s):

Compression Test ◽

Shear Failure ◽

Ion Beam ◽

Triaxial Compression ◽

Volumetric Strain ◽

Opalinus Clay ◽

Deformation Model ◽

Clay Sample ◽

Deformation Bands

Abstract. A microphysics-based understanding of mechanical and hydraulic processes in clay shales is required for developing advanced constitutive models, which can be extrapolated to long-term deformation. Although many geomechanical tests have been performed to characterise the bulk mechanical, hydro-mechanical, and failure behaviour of Opalinus Clay, important questions remain about micromechanisms: how do microstructural evolution and deformation mechanisms control the complex rheology? What is the in situ microstructural shear evolution, and can it be mimicked in the laboratory? In this contribution, scanning electron microscopy (SEM) was used to image microstructures in an Opalinus Clay sample deformed in an unconsolidated–undrained triaxial compression test at 4 MPa confining stress followed by argon broad ion beam (BIB) polishing. Axial load was applied (sub-)perpendicular to bedding until the sample failed. The test was terminated at an axial strain of 1.35 %. Volumetric strain measurements showed bulk compaction throughout the compression test. Observations on the centimetre to micrometre scale showed that the samples exhibited shear failure and that deformation localised by forming a network of micrometre-wide fractures, which are oriented with angles of 50∘ with respect to horizontal. In BIB–SEM at the grain scale, macroscale fractures are shown to be incipient shear bands, which show dilatant intergranular and intragranular microfracturing, granular flow, bending of phyllosilicate grains, and pore collapse in fossils. Outside these zones, no deformation microstructures were observed, indicating only localised permanent deformation. Thus, micromechanisms of deformation appear to be controlled by both brittle and ductile processes along preferred deformation bands. Anastomosing networks of fractures develop into the main deformation bands with widths up to tens of micrometres along which the sample fails. Microstructural observations and the stress–strain behaviour were integrated into a deformation model with three different stages of damage accumulation representative for the deformation of the compressed Opalinus Clay sample. Results on the microscale explain how the sample locally dilates, while bulk measurement shows compaction, with an inferred major effect on permeability by an increase in hydraulic conductivity within the deformation band. Comparison with the microstructure of highly strained Opalinus Clay in fault zones shows partial similarity and suggests that during long-term deformation additional solution–precipitation processes operate.

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Ultrastructural Features of Normal and Diseased Hair Revealed by Ion Beam Etching and Freeze Fracture

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100115419 ◽

1975 ◽

Vol 33 ◽

pp. 358-359

Author(s):

M. Spector ◽

A. C. Brown

Keyword(s):

Electron Microscopy ◽

Scanning Electron Microscopy ◽

Ectodermal Dysplasia ◽

Ion Beam ◽

Freeze Fracture ◽

Ion Current ◽

Ion Beam Etching ◽

Pili Torti ◽

Argon Ion ◽

Scanning Electron

Ion beam etching and freeze fracture techniques were utilized in conjunction with scanning electron microscopy to study the ultrastructure of normal and diseased human hair. Topographical differences in the cuticular scale of normal and diseased hair were demonstrated in previous scanning electron microscope studies. In the present study, ion beam etching and freeze fracture techniques were utilized to reveal subsurface ultrastructural features of the cuticle and cortex.Samples of normal and diseased hair including monilethrix, pili torti, pili annulati, and hidrotic ectodermal dysplasia were cut from areas near the base of the hair. In preparation for ion beam etching, untreated hairs were mounted on conducting tape on a conducting silicon substrate. The hairs were ion beam etched by an 18 ky argon ion beam (5μA ion current) from an ETEC ion beam etching device. The ion beam was oriented perpendicular to the substrate. The specimen remained stationary in the beam for exposures of 6 to 8 minutes.

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Microscopy Methods for Biofilm Imaging: Focus on SEM and VP-SEM Pros and Cons

Biology ◽

10.3390/biology10010051 ◽

2021 ◽

Vol 10 (1) ◽

pp. 51

Author(s):

Michela Relucenti ◽

Giuseppe Familiari ◽

Orlando Donfrancesco ◽

Maurizio Taurino ◽

Xiaobo Li ◽

...

Keyword(s):

Electron Microscopy ◽

Scanning Electron Microscopy ◽

Ion Beam ◽

Ruthenium Red ◽

Variable Pressure ◽

Sem Images ◽

Advantages And Disadvantages ◽

Pros And Cons ◽

Microscopy Techniques ◽

Scanning Electron

Several imaging methodologies have been used in biofilm studies, contributing to deepening the knowledge on their structure. This review illustrates the most widely used microscopy techniques in biofilm investigations, focusing on traditional and innovative scanning electron microscopy techniques such as scanning electron microscopy (SEM), variable pressure SEM (VP-SEM), environmental SEM (ESEM), and the more recent ambiental SEM (ASEM), ending with the cutting edge Cryo-SEM and focused ion beam SEM (FIB SEM), highlighting the pros and cons of several methods with particular emphasis on conventional SEM and VP-SEM. As each technique has its own advantages and disadvantages, the choice of the most appropriate method must be done carefully, based on the specific aim of the study. The evaluation of the drug effects on biofilm requires imaging methods that show the most detailed ultrastructural features of the biofilm. In this kind of research, the use of scanning electron microscopy with customized protocols such as osmium tetroxide (OsO4), ruthenium red (RR), tannic acid (TA) staining, and ionic liquid (IL) treatment is unrivalled for its image quality, magnification, resolution, minimal sample loss, and actual sample structure preservation. The combined use of innovative SEM protocols and 3-D image analysis software will allow for quantitative data from SEM images to be extracted; in this way, data from images of samples that have undergone different antibiofilm treatments can be compared.

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