Effects of Feed per Tooth and Radial Depth of Cut on Amplitude Parameters and Power Spectral Density of a Machined Surface

Surface topography and roughness significantly affect the functional properties of engineering parts. In this study, a mathematical model simulating the surface topography in end milling is presented and verified by milling experiments. The three dimensional (3D) surface amplitude parameters (arithmetic average deviation S_ba and root mean square deviation S_q) of the milled surface were calculated by using the model and the effects of the product (p) and ratio (r) of radial depth of cut a_e and feed per tooth f_z on amplitude parameters were researched. To evaluate the lateral characteristics of the milled surface, one dimensional (1D) power spectral densities (PSD) along both feed and step-over direction were calculated and investigated. It was found that f_z affects 1D PSD along both directions, whereas a_e affects 1D PSD along the step-over direction. An angular spectrum, derived from the area power spectral density (APSD), was employed to research the spatial distribution of spectral energy on the milled surface. Furthermore, the influences of p and r on the PSD properties were researched. It was found that r is the significant factor that influences the direction of surface energy spectrum distribution.

Three dimensional microstructural network of elastin, collagen, and cells in Achilles tendons

Similar to most biological tissues, the biomechanical, and functional characteristics of the Achilles tendon are closely related to its composition and microstructure. It is commonly reported that type I collagen is the predominant component of tendons and is mainly responsible for the tissue's function. Although elastin has been found in varying proportions in other connective tissues, previous studies report that tendons contain very small quantities of elastin. However, the morphology and the microstructural relationship among the elastic fibres, collagen, and cells in tendon tissue have not been well examined. We hypothesize the elastic fibres, as another fibrillar component in the extracellular matrix, have a unique role in mechanical function and microstructural arrangement in Achilles tendons. It has been shown that elastic fibres present a close connection with the tenocytes. The close relationship of the three components has been revealed as a distinct, integrated and complex microstructural network. Notably, a "spiral" structure within fibril bundles in Achilles tendons was observed in some samples in specialized regions. This study substantiates the hierarchical system of the spatial microstructure of tendon, including the mapping of collagen, elastin and tenocytes, with 3-dimensional confocal images. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:1203-1214, 2017.

High-resolution study of the 3D collagen fibrillary matrix of Achilles tendons without tissue labelling and dehydrating

Knowledge of the collagen structure of an Achilles tendon is critical to comprehend the physiology, biomechanics, homeostasis and remodelling of the tissue. Despite intensive studies, there are still uncertainties regarding the microstructure. The majority of studies have examined the longitudinally arranged collagen fibrils as they are primarily attributed to the principal tensile strength of the tendon. Few studies have considered the structural integrity of the entire three-dimensional (3D) collagen meshwork, and how the longitudinal collagen fibrils are integrated as a strong unit in a 3D domain to provide the tendons with the essential tensile properties. Using second harmonic generation imaging, a 3D imaging technique was developed and used to study the 3D collagen matrix in the midportion of Achilles tendons without tissue labelling and dehydration. Therefore, the 3D collagen structure is presented in a condition closely representative of the in vivo status. Atomic force microscopy studies have confirmed that second harmonic generation reveals the internal collagen matrix of tendons in 3D at a fibril level. Achilles tendons primarily contain longitudinal collagen fibrils that braid spatially into a dense rope-like collagen meshwork and are encapsulated or wound tightly by the oblique collagen fibrils emanating from the epitenon region. The arrangement of the collagen fibrils provides the longitudinal fibrils with essential structural integrity and endows the tendon with the unique mechanical function for withstanding tensile stresses. A novel 3D microscopic method has been developed to examine the 3D collagen microstructure of tendons without tissue dehydrating and labelling. The study also provides new knowledge about the collagen microstructure in an Achilles tendon, which enables understanding of the function of the tissue. The knowledge may be important for applying surgical and tissue engineering techniques to tendon reconstruction.

Confocal arthroscopy-based patient-specific constitutive models of cartilaginous tissues - II: prediction of reaction force history of meniscal cartilage specimens

The theoretical framework developed in a companion paper (Part I) is used to derive estimates of mechanical response of two meniscal cartilage specimens. The previously developed framework consisted of a constitutive model capable of incorporating confocal image-derived tissue microstructural data. In the present paper (Part II) fibre and matrix constitutive parameters are first estimated from mechanical testing of a batch of specimens similar to, but independent from those under consideration. Image analysis techniques which allow estimation of tissue microstructural parameters form confocal images are presented. The constitutive model and image-derived structural parameters are then used to predict the reaction force history of the two meniscal specimens subjected to partially confined compression. The predictions are made on the basis of the specimens' individual structural condition as assessed by confocal microscopy and involve no tuning of material parameters. Although the model does not reproduce all features of the experimental curves, as an unfitted estimate of mechanical response the prediction is quite accurate. In light of the obtained results it is judged that more general non-invasive estimation of tissue mechanical properties is possible using the developed framework.