The Experts below are selected from a list of 52533 Experts worldwide ranked by ideXlab platform

Toshihiko Yamashita - One of the best experts on this subject based on the ideXlab platform.

  • three dimensional analysis of tarsal bone response to Axial Loading in patients with hallux valgus and normal feet
    Clinical Biomechanics, 2017
    Co-Authors: Kota Watanabe, Yasutoshi Ikeda, Takuma Kobayashi, Tomoyuki Suzuki, Atsushi Teramoto, Daisuke Suzuki, Toshihiko Yamashita
    Abstract:

    Abstract Background Patients with hallux valgus present a variety of symptoms that may be related to the type of deformity. Weightbearing affects the deformities, and the evaluation of the load response of tarsal bones has been mainly performed using two-dimensional plane radiography. The purpose of this study was to investigate and compare structural changes in the medial foot arch between patients with hallux valgus and normal controls using a computer image analysis technique and weightbearing computed tomography data. Methods Eleven patients with hallux valgus and eleven normal controls were included. Computed tomograms were obtained with and without simulated weightbearing using a compression device. Computed tomography data were transferred into a personal computer, and a three-dimensional bone model was created using image analysis software. The load responses of each tarsal bone in the medial foot arch were measured three-dimensionally and statistically compared between the two groups. Findings Displacement of each tarsal bone under two weightbearing conditions was visually observed by creating three-dimensional bone models. At the first metatarsophalangeal joint, the proximal phalanges of the hallux valgus group showed significantly different displacements in multiple directions. Moreover, opposite responses to Axial Loading were also observed in both translation and rotation between the two groups. Interpretation Weightbearing caused deterioration of the hallux valgus deformity three-dimensionally at the first metatarsophalangeal joint. Information from the computer image analysis was useful for understanding details of the pathology of foot disorders related to the deformities or instability and may contribute to the development of effective conservative and surgical treatments.

  • dynamic effect of the tibialis posterior muscle on the arch of the foot during cyclic Axial Loading
    Clinical Biomechanics, 2012
    Co-Authors: Tomoaki Kamiya, Eiichi Uchiyama, Kota Watanabe, Mineko Fujimiya, Daisuke Suzuki, Toshihiko Yamashita
    Abstract:

    Abstract Background The most common cause of acquired flatfoot deformity is tibialis posterior tendon dysfunction. The present study compared the change in medial longitudinal arch height during cyclic Axial Loading with and without activated tibialis posterior tendon force. Methods Fourteen normal, fresh frozen cadaveric legs were used. A total of 10,000 cyclic Axial Loadings of 500 N were applied to the longitudinal axis of the tibia. The 32-N tibialis posterior tendon forces were applied to the specimens of the active group ( n  = 7). Specimens of another group (non-active group, n  = 7) were investigated without the tibialis posterior tendon force. The bony arch index was calculated from the displacement of the navicular height. Findings The mean initial bony arch indexes with maximal weightbearing were 0.239 (SD 0.009) in active group and 0.239 (SD 0.014) in non-active group. After 7000 cycles, the bony arch indexes with maximal weightbearing were significantly greater in the active group (mean 0.214, SD 0.013) than in the non-active group (mean 0.199, SD 0.013). The mean bony arch indexes with maximal weightbearing after 10,000 cycles were 0.212 (SD 0.011) in the active group and 0.196 (SD 0.015) in the non-active group. Interpretation The passive supportive structures were inadequate, and the tibialis posterior muscle was essential to maintain the medial longitudinal arch of the foot in the dynamic weightbearing condition. The findings underscore that physical therapy and arch supportive equipments are important to prevent flatfoot deformity in the condition of weakness or dysfunction of the tibialis posterior muscle.

Dirk Mohr - One of the best experts on this subject based on the ideXlab platform.

  • Experiments and modeling of anisotropic aluminum extrusions under multi-Axial Loading – Part I: Plasticity
    International Journal of Plasticity, 2012
    Co-Authors: Matthieu Dunand, Audrey Maertens, Dirk Mohr
    Abstract:

    Abstract An extensive experimental program has been carried out to characterize the plastic behavior of 2 mm thick extruded aluminum AA6260-T6 sheets under large deformations. Using a newly-developed dual actuator system, combinations of normal and tangential loads are applied to a flat specimen to investigate the material response under more than 30 different multi-Axial stress states. The Yld2000-2d yield criterion with an associated flow rule and an isotropic hardening model has been successfully used to describe the initial yield surface and its evolution. The comparison between the experimental results and finite element simulations shows that this constitutive model provides very accurate predictions for the material response under multi-Axial Loading. A special extension of the Yld2000-2d yield function for general three-dimensional stress states is also presented. The yield function for three-dimensional stress states is chosen such that it reduces to the Yld2000-2d yield function under plane stress conditions and makes use of the same anisotropy coefficients.

  • experiments and modeling of anisotropic aluminum extrusions under multi Axial Loading part i plasticity
    International Journal of Plasticity, 2012
    Co-Authors: Matthieu Dunand, Audrey Maertens, Dirk Mohr, Meng Luo
    Abstract:

    Abstract An extensive experimental program has been carried out to characterize the plastic behavior of 2 mm thick extruded aluminum AA6260-T6 sheets under large deformations. Using a newly-developed dual actuator system, combinations of normal and tangential loads are applied to a flat specimen to investigate the material response under more than 30 different multi-Axial stress states. The Yld2000-2d yield criterion with an associated flow rule and an isotropic hardening model has been successfully used to describe the initial yield surface and its evolution. The comparison between the experimental results and finite element simulations shows that this constitutive model provides very accurate predictions for the material response under multi-Axial Loading. A special extension of the Yld2000-2d yield function for general three-dimensional stress states is also presented. The yield function for three-dimensional stress states is chosen such that it reduces to the Yld2000-2d yield function under plane stress conditions and makes use of the same anisotropy coefficients.

  • evaluation of associated and non associated quadratic plasticity models for advanced high strength steel sheets under multi Axial Loading
    International Journal of Plasticity, 2010
    Co-Authors: Matthieu Dunand, Dirk Mohr
    Abstract:

    Abstract The accuracy of quadratic plane stress plasticity models is evaluated for a dual phase and a TRIP-assisted steel. Both sheet materials exhibit a considerable direction-dependence of the r -ratio while the uniAxial stress–strain curves are approximately the same irrespective of the specimen direction. Isotropic and anisotropic associated as well as non-associated quadratic plasticity models are considered to describe this behavior. Using a newly-developed dual-actuator system, combinations of normal and tangential loads are applied to a flat specimen in order to characterize the sheet material response under more than 20 distinct multi-Axial Loading states. The comparison of the experimental results with the plasticity model predictions reveals that both the associated and non-associated quadratic formulations provide good estimates of the stress–strain response under multi-Axial Loading. However, the non-associated model is recommended when an accurate description of the thinning behavior is important. Moreover, a structural validation example is presented that demonstrates the higher prediction accuracy of the non-associated plasticity model.

  • ductile fracture of trip780 sheets under multi Axial Loading
    NUMIFORM 2010: Proceedings of the 10th International Conference on Numerical Methods in Industrial Forming Processes Dedicated to Professor O. C. Zien, 2010
    Co-Authors: Matthieu Dunand, Dirk Mohr
    Abstract:

    The Loading path to fracture in multi‐Axial experiments is determined through hybrid experimental‐numerical analysis. A series of multi‐Axial fracture experiments are carried out on specimens extracted from TRIP780 steel sheets. It involves three different types of full‐thickness specimens: notched tensile specimens, tensile specimens with central hole and disc specimens for punch testing. The experimental program characterizes the onset of fracture over a wide range of stress states between uniAxial tension and equi‐biAxial tension. Using an anisotropic Hill’48 plasticity model, the evolution of local stress and strain fields is evaluated through detailed finite element analysis of each experiment. The accuracy of this hybrid experimental‐numerical Loading history identification is evaluated by comparing the local digital image correlation measurements with the FE predictions. In particular, uncertainties affecting the identification of the state of Loading at the onset of fracture are quantified.

Matthieu Dunand - One of the best experts on this subject based on the ideXlab platform.

  • Experiments and modeling of anisotropic aluminum extrusions under multi-Axial Loading – Part I: Plasticity
    International Journal of Plasticity, 2012
    Co-Authors: Matthieu Dunand, Audrey Maertens, Dirk Mohr
    Abstract:

    Abstract An extensive experimental program has been carried out to characterize the plastic behavior of 2 mm thick extruded aluminum AA6260-T6 sheets under large deformations. Using a newly-developed dual actuator system, combinations of normal and tangential loads are applied to a flat specimen to investigate the material response under more than 30 different multi-Axial stress states. The Yld2000-2d yield criterion with an associated flow rule and an isotropic hardening model has been successfully used to describe the initial yield surface and its evolution. The comparison between the experimental results and finite element simulations shows that this constitutive model provides very accurate predictions for the material response under multi-Axial Loading. A special extension of the Yld2000-2d yield function for general three-dimensional stress states is also presented. The yield function for three-dimensional stress states is chosen such that it reduces to the Yld2000-2d yield function under plane stress conditions and makes use of the same anisotropy coefficients.

  • experiments and modeling of anisotropic aluminum extrusions under multi Axial Loading part i plasticity
    International Journal of Plasticity, 2012
    Co-Authors: Matthieu Dunand, Audrey Maertens, Dirk Mohr, Meng Luo
    Abstract:

    Abstract An extensive experimental program has been carried out to characterize the plastic behavior of 2 mm thick extruded aluminum AA6260-T6 sheets under large deformations. Using a newly-developed dual actuator system, combinations of normal and tangential loads are applied to a flat specimen to investigate the material response under more than 30 different multi-Axial stress states. The Yld2000-2d yield criterion with an associated flow rule and an isotropic hardening model has been successfully used to describe the initial yield surface and its evolution. The comparison between the experimental results and finite element simulations shows that this constitutive model provides very accurate predictions for the material response under multi-Axial Loading. A special extension of the Yld2000-2d yield function for general three-dimensional stress states is also presented. The yield function for three-dimensional stress states is chosen such that it reduces to the Yld2000-2d yield function under plane stress conditions and makes use of the same anisotropy coefficients.

  • evaluation of associated and non associated quadratic plasticity models for advanced high strength steel sheets under multi Axial Loading
    International Journal of Plasticity, 2010
    Co-Authors: Matthieu Dunand, Dirk Mohr
    Abstract:

    Abstract The accuracy of quadratic plane stress plasticity models is evaluated for a dual phase and a TRIP-assisted steel. Both sheet materials exhibit a considerable direction-dependence of the r -ratio while the uniAxial stress–strain curves are approximately the same irrespective of the specimen direction. Isotropic and anisotropic associated as well as non-associated quadratic plasticity models are considered to describe this behavior. Using a newly-developed dual-actuator system, combinations of normal and tangential loads are applied to a flat specimen in order to characterize the sheet material response under more than 20 distinct multi-Axial Loading states. The comparison of the experimental results with the plasticity model predictions reveals that both the associated and non-associated quadratic formulations provide good estimates of the stress–strain response under multi-Axial Loading. However, the non-associated model is recommended when an accurate description of the thinning behavior is important. Moreover, a structural validation example is presented that demonstrates the higher prediction accuracy of the non-associated plasticity model.

  • ductile fracture of trip780 sheets under multi Axial Loading
    NUMIFORM 2010: Proceedings of the 10th International Conference on Numerical Methods in Industrial Forming Processes Dedicated to Professor O. C. Zien, 2010
    Co-Authors: Matthieu Dunand, Dirk Mohr
    Abstract:

    The Loading path to fracture in multi‐Axial experiments is determined through hybrid experimental‐numerical analysis. A series of multi‐Axial fracture experiments are carried out on specimens extracted from TRIP780 steel sheets. It involves three different types of full‐thickness specimens: notched tensile specimens, tensile specimens with central hole and disc specimens for punch testing. The experimental program characterizes the onset of fracture over a wide range of stress states between uniAxial tension and equi‐biAxial tension. Using an anisotropic Hill’48 plasticity model, the evolution of local stress and strain fields is evaluated through detailed finite element analysis of each experiment. The accuracy of this hybrid experimental‐numerical Loading history identification is evaluated by comparing the local digital image correlation measurements with the FE predictions. In particular, uncertainties affecting the identification of the state of Loading at the onset of fracture are quantified.

Kota Watanabe - One of the best experts on this subject based on the ideXlab platform.

  • three dimensional analysis of tarsal bone response to Axial Loading in patients with hallux valgus and normal feet
    Clinical Biomechanics, 2017
    Co-Authors: Kota Watanabe, Yasutoshi Ikeda, Takuma Kobayashi, Tomoyuki Suzuki, Atsushi Teramoto, Daisuke Suzuki, Toshihiko Yamashita
    Abstract:

    Abstract Background Patients with hallux valgus present a variety of symptoms that may be related to the type of deformity. Weightbearing affects the deformities, and the evaluation of the load response of tarsal bones has been mainly performed using two-dimensional plane radiography. The purpose of this study was to investigate and compare structural changes in the medial foot arch between patients with hallux valgus and normal controls using a computer image analysis technique and weightbearing computed tomography data. Methods Eleven patients with hallux valgus and eleven normal controls were included. Computed tomograms were obtained with and without simulated weightbearing using a compression device. Computed tomography data were transferred into a personal computer, and a three-dimensional bone model was created using image analysis software. The load responses of each tarsal bone in the medial foot arch were measured three-dimensionally and statistically compared between the two groups. Findings Displacement of each tarsal bone under two weightbearing conditions was visually observed by creating three-dimensional bone models. At the first metatarsophalangeal joint, the proximal phalanges of the hallux valgus group showed significantly different displacements in multiple directions. Moreover, opposite responses to Axial Loading were also observed in both translation and rotation between the two groups. Interpretation Weightbearing caused deterioration of the hallux valgus deformity three-dimensionally at the first metatarsophalangeal joint. Information from the computer image analysis was useful for understanding details of the pathology of foot disorders related to the deformities or instability and may contribute to the development of effective conservative and surgical treatments.

  • dynamic effect of the tibialis posterior muscle on the arch of the foot during cyclic Axial Loading
    Clinical Biomechanics, 2012
    Co-Authors: Tomoaki Kamiya, Eiichi Uchiyama, Kota Watanabe, Mineko Fujimiya, Daisuke Suzuki, Toshihiko Yamashita
    Abstract:

    Abstract Background The most common cause of acquired flatfoot deformity is tibialis posterior tendon dysfunction. The present study compared the change in medial longitudinal arch height during cyclic Axial Loading with and without activated tibialis posterior tendon force. Methods Fourteen normal, fresh frozen cadaveric legs were used. A total of 10,000 cyclic Axial Loadings of 500 N were applied to the longitudinal axis of the tibia. The 32-N tibialis posterior tendon forces were applied to the specimens of the active group ( n  = 7). Specimens of another group (non-active group, n  = 7) were investigated without the tibialis posterior tendon force. The bony arch index was calculated from the displacement of the navicular height. Findings The mean initial bony arch indexes with maximal weightbearing were 0.239 (SD 0.009) in active group and 0.239 (SD 0.014) in non-active group. After 7000 cycles, the bony arch indexes with maximal weightbearing were significantly greater in the active group (mean 0.214, SD 0.013) than in the non-active group (mean 0.199, SD 0.013). The mean bony arch indexes with maximal weightbearing after 10,000 cycles were 0.212 (SD 0.011) in the active group and 0.196 (SD 0.015) in the non-active group. Interpretation The passive supportive structures were inadequate, and the tibialis posterior muscle was essential to maintain the medial longitudinal arch of the foot in the dynamic weightbearing condition. The findings underscore that physical therapy and arch supportive equipments are important to prevent flatfoot deformity in the condition of weakness or dysfunction of the tibialis posterior muscle.

Daisuke Suzuki - One of the best experts on this subject based on the ideXlab platform.

  • three dimensional analysis of tarsal bone response to Axial Loading in patients with hallux valgus and normal feet
    Clinical Biomechanics, 2017
    Co-Authors: Kota Watanabe, Yasutoshi Ikeda, Takuma Kobayashi, Tomoyuki Suzuki, Atsushi Teramoto, Daisuke Suzuki, Toshihiko Yamashita
    Abstract:

    Abstract Background Patients with hallux valgus present a variety of symptoms that may be related to the type of deformity. Weightbearing affects the deformities, and the evaluation of the load response of tarsal bones has been mainly performed using two-dimensional plane radiography. The purpose of this study was to investigate and compare structural changes in the medial foot arch between patients with hallux valgus and normal controls using a computer image analysis technique and weightbearing computed tomography data. Methods Eleven patients with hallux valgus and eleven normal controls were included. Computed tomograms were obtained with and without simulated weightbearing using a compression device. Computed tomography data were transferred into a personal computer, and a three-dimensional bone model was created using image analysis software. The load responses of each tarsal bone in the medial foot arch were measured three-dimensionally and statistically compared between the two groups. Findings Displacement of each tarsal bone under two weightbearing conditions was visually observed by creating three-dimensional bone models. At the first metatarsophalangeal joint, the proximal phalanges of the hallux valgus group showed significantly different displacements in multiple directions. Moreover, opposite responses to Axial Loading were also observed in both translation and rotation between the two groups. Interpretation Weightbearing caused deterioration of the hallux valgus deformity three-dimensionally at the first metatarsophalangeal joint. Information from the computer image analysis was useful for understanding details of the pathology of foot disorders related to the deformities or instability and may contribute to the development of effective conservative and surgical treatments.

  • dynamic effect of the tibialis posterior muscle on the arch of the foot during cyclic Axial Loading
    Clinical Biomechanics, 2012
    Co-Authors: Tomoaki Kamiya, Eiichi Uchiyama, Kota Watanabe, Mineko Fujimiya, Daisuke Suzuki, Toshihiko Yamashita
    Abstract:

    Abstract Background The most common cause of acquired flatfoot deformity is tibialis posterior tendon dysfunction. The present study compared the change in medial longitudinal arch height during cyclic Axial Loading with and without activated tibialis posterior tendon force. Methods Fourteen normal, fresh frozen cadaveric legs were used. A total of 10,000 cyclic Axial Loadings of 500 N were applied to the longitudinal axis of the tibia. The 32-N tibialis posterior tendon forces were applied to the specimens of the active group ( n  = 7). Specimens of another group (non-active group, n  = 7) were investigated without the tibialis posterior tendon force. The bony arch index was calculated from the displacement of the navicular height. Findings The mean initial bony arch indexes with maximal weightbearing were 0.239 (SD 0.009) in active group and 0.239 (SD 0.014) in non-active group. After 7000 cycles, the bony arch indexes with maximal weightbearing were significantly greater in the active group (mean 0.214, SD 0.013) than in the non-active group (mean 0.199, SD 0.013). The mean bony arch indexes with maximal weightbearing after 10,000 cycles were 0.212 (SD 0.011) in the active group and 0.196 (SD 0.015) in the non-active group. Interpretation The passive supportive structures were inadequate, and the tibialis posterior muscle was essential to maintain the medial longitudinal arch of the foot in the dynamic weightbearing condition. The findings underscore that physical therapy and arch supportive equipments are important to prevent flatfoot deformity in the condition of weakness or dysfunction of the tibialis posterior muscle.