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Sandra J Shultz - One of the best experts on this subject based on the ideXlab platform.
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contribution of knee flexor and extensor strength on sex Specific Energy Absorption and torsional joint stiffness during drop jumping
Journal of Athletic Training, 2010Co-Authors: Randy J Schmitz, Sandra J ShultzAbstract:Abstract Context: Lower extremity injury often occurs during abrupt deceleration when attempting to change the body's direction. Although sex-Specific biomechanics have been implicated in the greater risk of acute knee injury in women than in men, it is unknown if sex differences in thigh strength affect sex-Specific Energy Absorption and torsional joint stiffness patterns. Objective: To determine sex differences in Energy Absorption patterns and joint stiffnesses of the lower extremity during a drop jump and to determine if these sex differences were predicted by knee extensor and flexor strength. Design: Cross-sectional study. Setting: Laboratory environment. Patients or Other Participants: Recreationally active, college-aged students (41 women: age = 22.1 ± 2.9 years, height = 1.63 ± 0.07 m, mass = 59.3 ± 8.0 kg; 40 men: age = 22.4 ± 2.8 years, height = 1.77 ± 0.1 m, mass = 80.9 ± 14.1 kg). Intervention(s): Participants performed knee flexor and extensor maximal voluntary isometric contract...
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Contribution of knee flexor and extensor strength on sex-Specific Energy Absorption and torsional joint stiffness during drop jumping.
Journal of athletic training, 2010Co-Authors: Randy J Schmitz, Sandra J ShultzAbstract:Lower extremity injury often occurs during abrupt deceleration when attempting to change the body's direction. Although sex-Specific biomechanics have been implicated in the greater risk of acute knee injury in women than in men, it is unknown if sex differences in thigh strength affect sex-Specific Energy Absorption and torsional joint stiffness patterns. To determine sex differences in Energy Absorption patterns and joint stiffnesses of the lower extremity during a drop jump and to determine if these sex differences were predicted by knee extensor and flexor strength. Cross-sectional study. Laboratory environment. Recreationally active, college-aged students (41 women: age = 22.1 ± 2.9 years, height = 1.63 ± 0.07 m, mass = 59.3 ± 8.0 kg; 40 men: age = 22.4 ± 2.8 years, height = 1.77 ± 0.1 m, mass = 80.9 ± 14.1 kg). Participants performed knee flexor and extensor maximal voluntary isometric contractions followed by double-leg drop-jump landings. Lower extremity joint energetics (J × N(-1) × m(-1)) and torsional joint stiffnesses (Nm × N(-1) × m(-1) × degrees(-1)) were calculated for the hip, knee, and ankle during the initial landing phase. Body weight was measured in newtons and height was measured in meters. Sex comparisons were made and sex-Specific regressions determined if thigh muscle strength (Nm/kg) predicted sagittal-plane landing energetics and stiffnesses. Women absorbed 69% more knee Energy and had 36% less hip torsional stiffness than men. In women, greater knee extensor strength predicted greater knee Energy Absorption (R(2) = 0.11, P = .04), and greater knee flexor strength predicted greater hip torsional stiffness (R(2) = 0.12, P = .03). Sex-Specific biomechanics during the deceleration phase of a drop jump revealed that women used a strategy to attempt to decrease system stiffness. Additionally, only female strength values were predictive of landing energetics and stiffnesses. These findings collectively demonstrated that the task may have been more difficult for women, resulting in a different movement strategy among those with different levels of thigh strength to safely complete the task. Future researchers should look at other predictive factors of observed sex differences.
Randy J Schmitz - One of the best experts on this subject based on the ideXlab platform.
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contribution of knee flexor and extensor strength on sex Specific Energy Absorption and torsional joint stiffness during drop jumping
Journal of Athletic Training, 2010Co-Authors: Randy J Schmitz, Sandra J ShultzAbstract:Abstract Context: Lower extremity injury often occurs during abrupt deceleration when attempting to change the body's direction. Although sex-Specific biomechanics have been implicated in the greater risk of acute knee injury in women than in men, it is unknown if sex differences in thigh strength affect sex-Specific Energy Absorption and torsional joint stiffness patterns. Objective: To determine sex differences in Energy Absorption patterns and joint stiffnesses of the lower extremity during a drop jump and to determine if these sex differences were predicted by knee extensor and flexor strength. Design: Cross-sectional study. Setting: Laboratory environment. Patients or Other Participants: Recreationally active, college-aged students (41 women: age = 22.1 ± 2.9 years, height = 1.63 ± 0.07 m, mass = 59.3 ± 8.0 kg; 40 men: age = 22.4 ± 2.8 years, height = 1.77 ± 0.1 m, mass = 80.9 ± 14.1 kg). Intervention(s): Participants performed knee flexor and extensor maximal voluntary isometric contract...
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Contribution of knee flexor and extensor strength on sex-Specific Energy Absorption and torsional joint stiffness during drop jumping.
Journal of athletic training, 2010Co-Authors: Randy J Schmitz, Sandra J ShultzAbstract:Lower extremity injury often occurs during abrupt deceleration when attempting to change the body's direction. Although sex-Specific biomechanics have been implicated in the greater risk of acute knee injury in women than in men, it is unknown if sex differences in thigh strength affect sex-Specific Energy Absorption and torsional joint stiffness patterns. To determine sex differences in Energy Absorption patterns and joint stiffnesses of the lower extremity during a drop jump and to determine if these sex differences were predicted by knee extensor and flexor strength. Cross-sectional study. Laboratory environment. Recreationally active, college-aged students (41 women: age = 22.1 ± 2.9 years, height = 1.63 ± 0.07 m, mass = 59.3 ± 8.0 kg; 40 men: age = 22.4 ± 2.8 years, height = 1.77 ± 0.1 m, mass = 80.9 ± 14.1 kg). Participants performed knee flexor and extensor maximal voluntary isometric contractions followed by double-leg drop-jump landings. Lower extremity joint energetics (J × N(-1) × m(-1)) and torsional joint stiffnesses (Nm × N(-1) × m(-1) × degrees(-1)) were calculated for the hip, knee, and ankle during the initial landing phase. Body weight was measured in newtons and height was measured in meters. Sex comparisons were made and sex-Specific regressions determined if thigh muscle strength (Nm/kg) predicted sagittal-plane landing energetics and stiffnesses. Women absorbed 69% more knee Energy and had 36% less hip torsional stiffness than men. In women, greater knee extensor strength predicted greater knee Energy Absorption (R(2) = 0.11, P = .04), and greater knee flexor strength predicted greater hip torsional stiffness (R(2) = 0.12, P = .03). Sex-Specific biomechanics during the deceleration phase of a drop jump revealed that women used a strategy to attempt to decrease system stiffness. Additionally, only female strength values were predictive of landing energetics and stiffnesses. These findings collectively demonstrated that the task may have been more difficult for women, resulting in a different movement strategy among those with different levels of thigh strength to safely complete the task. Future researchers should look at other predictive factors of observed sex differences.
Peter Dimbylow - One of the best experts on this subject based on the ideXlab platform.
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FDTD calculations of Specific Energy Absorption rate in a seated voxel model of the human body from 10 MHz to 3 GHz.
Physics in medicine and biology, 2006Co-Authors: R P Findlay, Peter DimbylowAbstract:Finite-difference time-domain (FDTD) calculations have been performed to investigate the frequency dependence of the Specific Energy Absorption rate (SAR) in a seated voxel model of the human body. The seated model was derived from NORMAN (NORmalized MAN), an anatomically realistic voxel phantom in the standing posture with arms to the side. Exposure conditions included both vertically and horizontally polarized plane wave electric fields between 10 MHz and 3 GHz. The resolution of the voxel model was 4 mm for frequencies up to 360 MHz and 2 mm for calculations in the higher frequency range. The reduction in voxel size permitted the calculation of SAR at these higher frequencies using the FDTD method. SAR values have been calculated for the seated adult phantom and scaled versions representing 10-, 5- and 1-year-old children under isolated and grounded conditions. These scaled models do not exactly reproduce the dimensions and anatomy of children, but represent good geometric information for a seated child. Results show that, when the field is vertically polarized, the sitting position causes a second, smaller resonance condition not seen in resonance curves for the phantom in the standing posture. This occurs at ~130 MHz for the adult model when grounded. Partial-body SAR calculations indicate that the upper and lower regions of the body have their own resonant frequency at ~120 MHz and ~160 MHz, respectively, when the grounded adult model is orientated in the sitting position. These combine to produce this second resonance peak in the whole-body averaged SAR values calculated. Two resonance peaks also occur for the sitting posture when the incident electric field is horizontally polarized. For the adult model, the peaks in the whole-body averaged SAR occur at ~180 and ~600 MHz. These peaks are due to resonance in the arms and feet, respectively. Layer Absorption plots and colour images of SAR in individual voxels show the Specific regions in which the seated human body absorbs the incident field. External electric field values required to produce the ICNIRP basic restrictions were derived from SAR calculations and compared with ICNIRP reference levels. This comparison shows that the reference levels provide a conservative estimate of the ICNIRP whole-body averaged SAR restriction, with the exception of the region above 1.4 GHz for the scaled 1-year-old model.
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Resonance behaviour of whole-body averaged Specific Energy Absorption rate (SAR) in the female voxel model, NAOMI
Physics in medicine and biology, 2005Co-Authors: Peter DimbylowAbstract:Finite-difference time-domain (FDTD) calculations have been performed of the whole-body averaged Specific Energy Absorption rate (SAR) in a female voxel model, NAOMI, under isolated and grounded conditions from 10 MHz to 3 GHz. The 2 mm resolution voxel model, NAOMI, was scaled to a height of 1.63 m and a mass of 60 kg, the dimensions of the ICRP reference adult female. Comparison was made with SAR values from a reference male voxel model, NORMAN. A broad SAR resonance in the NAOMI values was found around 900 MHz and a resulting enhancement, up to 25%, over the values for the male voxel model, NORMAN. This latter result confirmed previously reported higher values in a female model. The effect of differences in anatomy was investigated by comparing values for 10-, 5- and 1-year-old phantoms rescaled to the ICRP reference values of height and mass which are the same for both sexes. The broad resonance in the NAOMI child values around 1 GHz is still a strong feature. A comparison has been made with ICNIRP guidelines. The ICNIRP occupational reference level provides a conservative estimate of the whole-body averaged SAR restriction. The linear scaling of the adult phantom using different factors in longitudinal and transverse directions, in order to match the ICRP stature and weight, does not exactly reproduce the anatomy of children. However, for public exposure the calculations with scaled child models indicate that the ICNIRP reference level may not provide a conservative estimate of the whole-body averaged SAR restriction, above 1.2 GHz for scaled 5- and 1-year-old female models, although any underestimate is by less than 20%.
Che Husna Azhari - One of the best experts on this subject based on the ideXlab platform.
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Energy Absorption and load carrying capability of woven natural silk epoxy–triggered composite tubes
Composites Part B: Engineering, 2015Co-Authors: R.a. Eshkoor, A. U. Ude, Abu Bakar Sulong, Rozli Zulkifli, Ahmad Kamal Ariffin, Che Husna AzhariAbstract:Abstract This study investigated the Energy Absorption response and load carrying capability of woven natural silk/epoxy–triggered composite rectangular tubes subjected to an axial quasi-static crushing test. The rectangular composite tubes were prepared by hand lay-up technique. The tubes consisted of 12, 24, and 30 layers of natural woven silk/epoxy laminate and were 50, 80, and 120 mm long. The crashworthiness of the tubes was evaluated by measuring the Specific Energy Absorption in quasi-static axial compression. Specific Energy Absorption was obtained from the load–displacement curve during testing. The failure mode of the tubes was analyzed from high resolution photographs obtained. Overall, the tube with 50 mm length and 30 layers showed the best crashworthiness among the tubes. The failure morphology showed that the specimens failed in two distinct modes: local and mid-length buckling. The triggered composite tubes exhibited progressive failure.
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Failure mechanism of woven natural silk/epoxy rectangular composite tubes under axial quasi-static crushing test using trigger mechanism
International Journal of Impact Engineering, 2014Co-Authors: R.a. Eshkoor, A. U. Ude, Abu Bakar Sulong, Rozli Zulkifli, Ahmad Kamal Ariffin, Simin Ataollahi Oshkovr, Che Husna AzhariAbstract:Abstract This study investigates the Energy Absorption response of rectangular woven natural silk/epoxy composite tubes when subjected to an axial quasi-static crushing test using a trigger mechanism. The resulting deformation morphology of each failure region was captured using high resolution photography. The rectangular composite tubes were prepared through the hand lay-up technique, in which 24 layers of silk fabric were used, each with a thickness of 3.4 mm and tube lengths of 50, 80, and 120 mm. The parameters measured were peak load, Energy Absorption, and Specific Energy Absorption as functions of the tube lengths. Specific Energy Absorption values decreased with increased length of the composite specimen, whereas total Energy Absorption increased with the increased length of the composite specimen. The deformation morphology showed that the failure mechanism proceeded in two stages, namely, (i) onset of tear and (ii) propagation of tear, which included progressive buckling and delamination. The composite tubes only exhibited progressive but not catastrophic failure.
Dirk Mohr - One of the best experts on this subject based on the ideXlab platform.
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smooth shell metamaterials of cubic symmetry anisotropic elasticity yield strength and Specific Energy Absorption
Acta Materialia, 2019Co-Authors: Colin Bonatti, Dirk MohrAbstract:Abstract Shell-lattices consist of a single, periodic, non-intersecting shell of uniform wall thickness that separates two intertwined void phases. To obtain a comprehensive overview on their small and large strain response, three families of shell-lattices are derived from Simple-Cubic (SC), Face-Centered Cubic (FCC) and Body-Centered Cubic (BCC) tube-lattices using a parameterized surface-smoothening functional. Each family's central element is an approximation of a Triply Periodic Minimal Surface (TPMS). Detailed finite element simulations are carried out for more than 800 shell-lattices covering relative densities ranging from 1% to 80%. It is found that the TMPS-like structures exhibit highly anisotropic elastic and plastic properties that depend on the type of cubic symmetry. However, when averaging the mechanical properties over all possible directions of loading, the performance of the SC, FCC and BCC shell-lattices turns out to be similar, with all structures providing substantially higher stiffness and strength than optimal truss-lattices of equal mass. They also exhibit high Specific Energy Absorption for large strain compression. It is found that the macroscopic deformation mode changes from foam-like crushing (for relative densities below 10%) to bulk-like positive strain hardening (for relative densities above 20%). The spectrum of anisotropic structures obtained through varying the bias parameter of the surface-defining functional also includes elastically-isotropic shell-lattices. The Young's modulus of the isotropic shell-lattices of FCC and BCC symmetry is slightly higher than the average modulus of their TPMS-like counterparts, while the opposite holds true for SC structures. Compression experiments are performed on additively-manufactured stainless steel 316L specimens to validate the conclusions drawn from numerical simulations.
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Stiffness and Specific Energy Absorption of additively-manufactured metallic BCC metamaterials composed of tapered beams
International Journal of Mechanical Sciences, 2018Co-Authors: Thomas Tancogne-dejean, Dirk MohrAbstract:Abstract Periodic beam networks of Body-Centered Cubic (BCC) symmetry belong to the same family of cubic metamaterials as the well-known Face-Centered Cubic (FCC) octet truss lattice. Analytical closed form expressions are derived to compute their homogenized macroscopic moduli as a function of the relative density. Detailed finite element simulations are performed to confirm the analytical results. The large strain compression response of BCC lattices is also investigated numerically, showing that for any relative density, their crushing response is stable in the sense that the engineering stress-strain curve increases monotonically until densification. Both theoretical considerations and numerical simulations demonstrate that the tapering of the beam cross-sections leads to higher Specific mechanical properties, with increases in the effective Young's modulus and Specific Energy Absorption of up to 70% and 45%, respectively. To validate the Specific Energy Absorption estimates, static compression experiments are also performed on specimens of 10%, 20% and 30% relative density and minimum beam diameter of 300 µm made from stainless steel 316 L through selective laser melting. In addition, dynamic compression experiments at strain rates of about 500/s are performed on a Hopkinson pressure bar system revealing a dynamic increase factor of 1.3 for the BCC metamaterials, which is comparable to that of the basis material. The comparison of the BCC and FCC lattice materials shows that the BCC Young's modulus for the stiffest material direction is higher than that for the FCC truss lattice, while the opposite holds true for the softest directions.
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additively manufactured metallic micro lattice materials for high Specific Energy Absorption under static and dynamic loading
Acta Materialia, 2016Co-Authors: Thomas Tancognedejean, Adriaan B Spierings, Dirk MohrAbstract:Abstract An octet truss lattice material is designed for Energy Absorption purposes featuring an exceptionally high Specific Energy Absorption, a constant plateau stress between initial yield and densification, and zero plastic Poisson’s ratio. It is demonstrated through detailed finite element simulations that the meso-structural response of metallic lattice materials under compression changes from an unstable twist mode to a stable buckling free mode at a relative density of about 0.3. Furthermore, it is found that the nature of the macroscopic stress-strain curve changes from mildly-oscillating to monotonically-increasing as the meso-structural deformation mode changes, while a stress-plateau is observed at relative densities above 0.3. Since the Specific Energy Absorption is a monotonically increasing function of the relative density, lattice materials of relative densities around 0.3 feature both a plateau stress and a high Specific Energy Absorption capability. Prototype materials are built from stainless steel 316L using Selective Laser Melting. The basic building element of the micro-lattices are 2.2 mm long beams with a 500 μm diameter cross-sections. Detailed micro- and meso-structural analysis including tomography, microscopy and EBSD analysis revealed substantial local material property variations within the lattice structure. Compression experiments are performed under static and dynamic loading conditions confirming the anticipated exceptional Energy Absorption material characteristics for strain rates of up to 1000/s.
