The Experts below are selected from a list of 315 Experts worldwide ranked by ideXlab platform
Rene M Castelein - One of the best experts on this subject based on the ideXlab platform.
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posteriorly directed Shear Loads and disc degeneration affect the torsional stiffness of spinal motion segments a biomechanical modeling study
Spine, 2013Co-Authors: Jasper Johan Homminga, Anne M Lehr, Gerdine Meijer, Michiel M A Janssen, Tom P C Schlosser, Gijsbertus Jacob Verkerke, Rene M CasteleinAbstract:Study Design. Finite element study. Objective. To analyze the effects of posterior Shear Loads, disc degeneration, and the combination of both on spinal torsion stiffness. Summary of Background Data. Scoliosis is a 3-dimensional deformity of the spine that presents itself mainly in adolescent girls and elderly patients. Our concept of its etiopathogenesis is that an excess of posteriorly directed Shear Loads, relative to the body's intrinsic stabilizing mechanisms, induces a torsional instability of the spine, making it vulnerable to scoliosis. Our hypothesis for the elderly spine is that disc degeneration compromises the stabilizing mechanisms. Methods. In an adult lumbar motion segment model, the disc properties were varied to simulate different aspects of disc degeneration. These models were then loaded with a pure torsion moment in combination with either a Shear load in posterior direction, no Shear, or a Shear load in anterior direction. Results. Posteriorly directed Shear Loads reduced torsion stiffness, anteriorly directed Shear Loads increased torsion stiffness. These effects were mainly caused by a later (respectively earlier) onset of facet joint contact. Disc degeneration cases with a decreased disc height that leads to slackness of the annular fibers and ligaments caused a significantly decreased torsional stiffness. The combination of this stage with posterior Shear loading reduced the torsion stiffness to less than half the stiffness of a healthy disc without Shear Loads. The end stage of disc degeneration increased torsion stiffness again. Conclusion. The combination of a decreased disc height, that leads to slack annular fibers and ligaments, and posterior Shear Loads very significantly affects torsional stiffness: reduced to less than half the stiffness of a healthy disc without Shear Loads. Disc degeneration, thus, indeed compromises the stabilizing mechanisms of the elderly spine. A combination with posteriorly directed Shear Loads could then make it vulnerable to scoliosis.
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The role of posteriorly directed Shear Loads acting on a pre-rotated growing spine: a hypothesis on the pathogenesis of idiopathic scoliosis.
Studies in health technology and informatics, 2010Co-Authors: Michiel M A Janssen, Jan-willem M. Kouwenhoven, Rene M CasteleinAbstract:Despite years of extensive research, the etiology of idiopathic scoliosis still has not been resolved. A hypothesis on the role of posteriorly directed Shear Loads was studied in several biomechanical and imaging studies. So far, it has been shown that: on the human erect spine these posteriorly directed Shear Loads act; these Loads decrease the rotational stability of the spine vitro and in vivo; once rotation occurs, it logically follows an already built-in vertebral rotational pattern, that is pre-existent in the human spine; this pre-existent rotational pattern is related to organ anatomy, and not to handedness; certain areas in the female spine are more subject to posteriorly directed Shear Loads as certain areas in the female spine are more backwardly inclined. Although it is appreciated that the cause of idiopathic scoliosis is multi-factorial, we believe that the delicate upright spinal sagittal balance and the unique posteriorly directed Shear Loads acting on the erect human spine play a crucial role in the rotational stability of the human spine, and thus in the pathogenesis of idiopathic scoliosis.
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Effects of dorsal versus ventral Shear Loads on the rotational stability of the thoracic spine: a biomechanical porcine and human cadaveric study
Spine, 2007Co-Authors: Jan-willem M. Kouwenhoven, Theo H. Smit, Albert J. Van Der Veen, Idsart Kingma, Jaap H. Van Dieën, Rene M CasteleinAbstract:STUDY DESIGN. A biomechanical in vitro study on porcine and human spinal segments. OBJECTIVE. To investigate axial rotational stability of the thoracic spine under dorsal and ventral Shear Loads. SUMMARY OF BACKGROUND DATA. Idiopathic scoliosis is a condition restricted exclusively to humans. An important difference between humans and other vertebrates is the fact that humans ambulate in a fully erect position. It has been demonstrated that certain parts of the human spine, more specifically the dorsally inclined lower thoracic and high lumbar parts, are subject to dorsally directed Shear Loads. It has been hypothesized that these dorsal Shear Loads reduce the rotational stability of the spine, thereby increasing the risk to initiate idiopathic scoliosis. METHODS. Fourteen porcine and 14 human thoracic functional spinal units (FSUs) with intact costotransverse and costovertebral articulations were used for biomechanical testing. In both dorsal and ventral directions, Shear Loads were applied to the upper vertebra of the FSU in the midsagittal plane (centrally), and at 1 cm to the right and to the left (eccentrically), resulting in a rotary moment. Vertebral rotation was measured at 3 incremental Loads by an automated optoelectronic 3-dimensional (3D) movement registration system. RESULTS. The results of this study showed that eccentrically applied Shear Loads induce vertebral rotation in human as well as in porcine spinal segments. At the mid-thoracic and lower thoracic levels, significantly more vertebral rotation occurred under dorsal Shear Loads than under ventral Shear Loads. CONCLUSION. These data show that, in humans and in quadrupeds, the thoracic spine is less rotationally stable under dorsal Shear Loads than under ventral Shear Loads. © 2007 Lippincott Williams & Wilkins, Inc.
Tamara Reid Bush - One of the best experts on this subject based on the ideXlab platform.
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quantifying the effects of external Shear Loads on arterial and venous blood flow implications for pressure ulcer development
Clinical Biomechanics, 2013Co-Authors: Abinand Manorama, Ronald A Meyer, Robert W Wiseman, Tamara Reid BushAbstract:Abstract Introduction Forces applied to the skin cause a decrease in regional blood flow. This decrease in blood flow can cause tissue necrosis and lead to the formation of deep, penetrating wounds called pressure ulcers. These wounds are detrimental to individuals with compromised health, such as the elderly and spinal-cord injured. Although surface pressure is known to be a primary risk factor for developing a pressure ulcer, a seated individual rarely experiences pressure alone but rather combined loading which includes pressure as well as Shear force on the skin. However, little research has been conducted to quantify the effects of Shear forces on blood flow. Methods Fifteen men were tested in a magnetic resonance imaging scanner under no load, a normal load, and a combination of normal and Shear Loads. Changes in arterial and venous blood flow in the forearm were measured using magnetic resonance angiography phase-contrast imaging. Findings The blood flow in the anterior interosseous artery and basilic vein of the forearm decreased with the application of normal Loads, and decreased further with the addition of Shear Loads. Marginal to significant differences at a 90% confidence level (P = 0.08, 0.10) were observed, and medium to high effect sizes (0.3 to 0.5) were obtained. Interpretation Based on these results, Shear force is an important factor to consider in relation to pressure ulcer propagation and prevention, and hence, future prevention approaches should also focus on mitigating Shear Loads.
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blood perfusion and transcutaneous oxygen level characterizations in human skin with changes in normal and Shear Loads implications for pressure ulcer formation
Clinical Biomechanics, 2010Co-Authors: Abinand Manorama, Seungik Baek, Joseph Vorro, Alla Sikorskii, Tamara Reid BushAbstract:Abstract Background Decubitus ulcers (pressure ulcers) are localized areas of tissue breakdown in the skin and the underlying regions. Decubitus ulcers affect approximately 3 million people in the USA every year, including seniors, individuals with diabetes, and those who spend long periods in wheelchairs. Experimental studies demonstrate that static or dynamic normal Loads cause blood occlusion in the skin, while prolonged loading conditions can result in skin damage. However, few studies report the effects of ‘normal and Shear’ combined loading on blood perfusion. The goal of this research was to study alterations of transcutaneous oxygen levels and blood perfusion in human skin when both normal and Shear Loads were applied. Methods Fifteen human subjects were evaluated under seven different conditions for changes in transcutaneous oxygen and blood perfusion levels during applications of normal and Shear loading on the forearm. Transcutaneous oxygen levels and blood perfusion were continuously measured using a Laser Doppler system, while applied forces were quantified with a multi-axis load cell. Findings Transcutaneous oxygen and blood perfusion levels decreased when Shear Loads were applied in addition to normal Loads. Further, blood perfusion during recovery periods increased gradually from the first to the last test condition. Interpretation Results indicate that adding Shear Loads decreased transcutaneous oxygen and blood perfusion levels in the skin. Based on these findings, Shear force may play a role in skin damage, and both Shear and normal Loads should be considered when trying to prevent ulcer development.
Jacques Lamon - One of the best experts on this subject based on the ideXlab platform.
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Modelling of the stress/strain behaviour of a carbon/carbon composite with a 2.5 dimensional fibre architecture under tensile and Shear Loads at room temperature
Composites Science and Technology, 1999Co-Authors: Olivier Siron, Jérôme Pailhès, Jacques LamonAbstract:The paper presents a macroscopic model of the non-linear stress/strain behaviour and the ultimate failure of a needled, woven carbon/carbon (C/C) composite, under tensile and Shear Loads parallel to the plies. The model is based upon continuum damage mechanics concepts for the description of damage evolution, and the approach to plasticity for the description of inelastic strains induced by matrix damage, according to the general approach developed by Ladeveze for composites. Modelling was guided by the experimental data on the matrix damage modes obtained from extensive microscopy examination of the test specimens under load. The model involves three scalar damage parameters including two tensile parameters, and one Shear parameter resulting from a combination of the tensile ones. Identification of the damage parameters requires one off-axis (at 45° in the plane of the plies), and two on-axis (parallel to tow directions) uniaxial tensile tests. The model was validated with tensile stress/strain curves measured from various off-axis tests. The ultimate failure was predicted by the use of damage accumulation criteria.
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damage and failure mechanisms of a3 directional carbon carbon composite under uniaxial tensile and Shear Loads
Acta Materialia, 1998Co-Authors: O Siron, Jacques LamonAbstract:Abstract The mechanical behavior of a three-directional carbon/carbon (C/C) composite under tensile and Shear Loads is investigated in relation with the failure mechanisms and, the fiber architecture. This three-directional C/C composite was produced by Chemical Vapor Infiltration of a needled fiber preform of multiple layers of satin woven tows. The C/C composite exhibited several interesting features including an essentially non-linear stress–strain behavior and permanent deformations. Three families of matrix cracks were identified under tensile and Shear Loads, including microcracks in the tows, intertow delamination and cracks across the longitudinal tows. It was found that the delamination cracks affect preponderantly the stress–strain behavior and the mechanical properties. Similar features in the mechanical behavior and the failure mechanisms were highlighted under tension and under Shear loading.
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Damage and failure mechanisms of a3-directional carbon/carbon composite under uniaxial tensile and Shear Loads
Acta Materialia, 1998Co-Authors: O Siron, Jacques LamonAbstract:Abstract The mechanical behavior of a three-directional carbon/carbon (C/C) composite under tensile and Shear Loads is investigated in relation with the failure mechanisms and, the fiber architecture. This three-directional C/C composite was produced by Chemical Vapor Infiltration of a needled fiber preform of multiple layers of satin woven tows. The C/C composite exhibited several interesting features including an essentially non-linear stress–strain behavior and permanent deformations. Three families of matrix cracks were identified under tensile and Shear Loads, including microcracks in the tows, intertow delamination and cracks across the longitudinal tows. It was found that the delamination cracks affect preponderantly the stress–strain behavior and the mechanical properties. Similar features in the mechanical behavior and the failure mechanisms were highlighted under tension and under Shear loading.
Lei Zhang - One of the best experts on this subject based on the ideXlab platform.
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design of vertically stiffened steel plate walls under combined uniaxial compression and Shear Loads
Structures, 2020Co-Authors: Zhaoyu Xu, Genshu Tong, Lei ZhangAbstract:Abstract Elastic buckling of stiffened steel plate walls (S-SPWs) under combined compression and Shear was studied focusing on the stiffness demand on stiffeners to implement subpanel’s buckling mode. Flat-bars and closed form stiffeners were considered. Threshold stiffness of stiffeners is presented for elastic buckling of subpanels of S-SPWs in pure compression, pure Shear and combined compression and Shear. The effect of stiffeners’ torsional stiffness has been included. Then the elastic–plastic (E-P) buckling of S-SPWs under combined compression and Shear was studied. A criteria was established to identify the E-P Shear buckling stress under a prescribed compression stress for S-SPWs with given stiffness of stiffeners. Threshold stiffness of stiffeners was taken on the buckling stress – stiffness curve at the transition point as the E-P buckling Shear stress reaches a plateau. The demand of keeping stiffeners straight when stiffeners are compressed simultaneously has been incorporated in such defined threshold stiffness. Equations for threshold stiffness of flat-bars and closed form stiffeners are proposed separately and comparisons with finite element results show good accuracy.
Jeom Kee Paik - One of the best experts on this subject based on the ideXlab platform.
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ultimate strength of perforated steel plates under combined biaxial compression and edge Shear Loads
Thin-walled Structures, 2008Co-Authors: Jeom Kee PaikAbstract:Abstract The present paper is a sequel to the author's papers [Paik JK, Ultimate strength of perforated steel plates under edge Shear loading. Thin-Walled Structures 2007; 45: 301–6, Paik JK Ultimate strength of perforated steel plates under axial compressive loading along short edges. Ships Offshore Struct, 2007; 2(3): (in press)]. In contrast to the previous papers with the focus on edge Shear or uniaxial compressive Loads, the aim of the present study is to investigate the ultimate strength characteristics of perforated steel plates under combined biaxial compression and edge Shear Loads, which is a typical action pattern of steel plates arising from cargo weight and water pressure together with hull girder motions in ships and ship-shaped offshore structures. The plates are considered to be simply supported along all (four) edges, keeping them straight. The cutout is circular and located at the center of the plate. A series of ANSYS nonlinear finite element analyses (FEA) are undertaken with varying the plate dimension (thickness). Based on the FEA results obtained, closed-form empirical formulae of the ultimate strength interaction relationships of perforated plates between combined Loads, which can be useful for first-cut estimations of the ultimate strength in reliability analyses or code calibrations, are derived.
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ultimate strength of dented steel plates under edge Shear Loads
Thin-walled Structures, 2005Co-Authors: Jeom Kee PaikAbstract:Abstract The aims of this paper are to investigate the ultimate Shear strength reduction characteristics of steel plates due to local impacts, and also to develop the ultimate Shear strength design formulae of dented steel plates. The ANSYS nonlinear finite element code is used to investigate the effects of shape, size (depth, diameter), and location of the denting on the ultimate strength behavior of simply supported steel plates under edge Shear Loads. A closed-form expression for predicting the ultimate Shear strength of dented steel plates is derived by the regression analysis based on the computed results. The results and insights developed from the present study will be very useful for damage tolerant design of steel plated structures with local denting.
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ultimate Shear strength of plate elements with pit corrosion wastage
Thin-walled Structures, 2004Co-Authors: Jeom Kee Paik, Jaemyung LeeAbstract:Abstract The aim of the present paper is to investigate the ultimate strength characteristics of steel plate elements with pit corrosion wastage and under in-plane Shear Loads. A series of the ANSYS nonlinear finite element analyses for plate elements under in-plane Shear Loads are carried out, varying the degree of pit corrosion intensity and the plate geometric properties. Closed-form design formulae for the ultimate strength of pitted plates under edge Shear, which are essentially needed for the ultimate limit state based risk or reliability assessment of corroded structures, are derived by the regression analysis of the computed results. The insights developed from the present study will be very useful for damage tolerant design of plated structures with pit corrosion wastage.
