indentation site
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Author(s):  
Spencer P. Lake ◽  
Victor H. Barocas

The mechanical behavior of connective soft tissues depends largely on their structural organization, particularly of the collagen network. Previous studies have utilized polarized light imaging techniques to quantify collagen organization and fiber kinematics under tensile load (e.g., [1–2]). Many native tissues function in non-tensile loading environments, however, and the microstructural response to such loads is poorly understood. For example, fiber-reinforced soft tissues can be subjected to indentation in vivo (e.g., supraspinatus tendon in shoulder, flexor tendons that wrap around bones), resulting in a complex combination of compressive (near indentation site) and tensile forces (away from indentation site) being applied to the tissue. In order to understand and predict a tissue’s response to such loading, the respective roles of the collagen and non-fibrillar matrix must be elucidated. In particular, how do the properties of the collagen network (e.g., density/organization) and non-fibrillar matrix (e.g., type/quantity) modulate behavior under load? In order to address these questions, our group has utilized type I collagen gel tissue-equivalents (TEs) as a simplified model system to evaluate properties and relationships of tissue components. TEs are particularly useful because organizational and compositional properties can be controlled during formulation (e.g., mold geometry altered to induce changes in collagen fiber alignment [3]). While our other work has used co-gel tissue analogs to evaluate the contribution of non-fibrillar matrix to indentation [4], the purpose of this study was to evaluate the role of initial collagen organization on tissue behavior in indentation using cell-compacted TEs as a model system.


2000 ◽  
Vol 649 ◽  
Author(s):  
B.J. Inkson ◽  
H.Z. Wu ◽  
T. Steer ◽  
G. Möbus

ABSTRACTA new method has been developed to map cracks in 3D using focused ion beam (FIB) microscopy. Using the FIB, many parallel 2D slices are cut in the specimen. Imaging each 2D slice down several directions enables the 3D co-ordinates of features in the slice to be determined. Computer alignment and reconstruction of the 2D slices generates a 3D data set of the analysed zone. The 3D mapping method has been applied to the analysis of the cracks around an indentation site in a Al2O3-5vol.%SiC nanocomposite. This reveals the 3D location and morphology of radial and deep lateral cracks at the indent periphery, surface localised crack clusters, and a crack deficient zone close to the indent centre.


1997 ◽  
Vol 51 (9) ◽  
pp. 1405-1409 ◽  
Author(s):  
Michael Bowden ◽  
Derek J. Gardiner

The microline focus spectrometer (MiFS) Raman imaging process is described and is used to investigate stress and structure defect patterns in micro-indented single-crystal silicon. Raman intensity, frequency, and bandwidth images are reported with 0.3-μm pixel resolution, which reveal residual compressive stress distributions around the indentation site and areas of tensile stress at the crack tips. A previously unreported annular structural defect region, remote from the indent site, is observed in images where the indenter tip edges are aligned with the 110 direction of the silicon crystal.


1994 ◽  
Vol 9 (5) ◽  
pp. 1199-1207 ◽  
Author(s):  
Byong-Taek Lee ◽  
Kenji Hiraga

Crack propagation and deformation behavior of a pressureless-sintered Al2O3-24 vol. % ZrO2 composite have been studied by transmission electron microscopy on Vickers-indented specimens from room temperature to 1200 °C. Hardness of the composite gradually decreases with increasing temperature, whereas the ratio of indent to crack lengths, which corresponds to the apparent toughness of materials, decreases up to about 1000 °C and then quickly increases with increasing temperature. In the samples indented at room temperature and 1000 °C, most of the cracks propagate along Al2O3/ZrO2 interfaces and Al2O3 grain boundaries, but a few monoclinic ZrO2 grains are transgranularly fractured. These fractured grains are heavily deformed and produce a marked reduction of the driving force for propagation of cracks at room temperature. In the sample indented at 1200 °C, cracks are hardly observed, but on the other hand, formation of subgrain boundaries, elongation of grains, and grain boundary sliding are observed both in the Al2O3 and ZrO2 grains located around the indentation site.


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