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The renaissance of continuum mechanics
Wei-qiu Chen
Journal of Zhejiang University-SCIENCE A (Applied Physics & Engineering), 2014, 15(4): 231-240.
https://doi.org/10.1631/jzus.A1400079
Continuum mechanics, just as the name implies, deals with the mechanics problems of all continua, whose physical (or mechanical) properties are assumed to vary continuously in the spaces they occupy. Continuum mechanics may be seen as the symbol of modern mechanics, which differs greatly from current physics, the two often being mixed up by people and even scientists. In this short paper, I will first try to give an illustration on the differences between (modern) mechanics and physics, in my personal view, and then focus on some important current research activities in continuum mechanics, attempting to identify its path to the near future. We can see that continuum mechanics, while having a dominating impact on engineering design in the 20th century, also plays a pivotal role in modern science, and is much closer to physics, chemistry, biology, etc. than ever before.
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Undrained anisotropy and non-coaxial behavior of clayey soil under principal stress rotation
Jian Zhou, Jia-jia Yan, Zheng-yi Liu, Xiao-nan Gong
Journal of Zhejiang University-SCIENCE A (Applied Physics & Engineering), 2014, 15(4): 241-254.
https://doi.org/10.1631/jzus.A1300277
In this study, a series of undrained tests were conducted on both intact and reconstituted clay using an automatic hollow cylinder apparatus. Monotonic shearing tests with fixed principal stress directions were carried out, pure and cyclic principal stress rotation tests were also performed. The non-coaxiality, defined as the non-coincidence of the principal plastic strain increment direction and the corresponding principal stress direction, of clayey soil was studied experimentally. The effects of the intermediate principal stress, shear stress level, and inherent anisotropy were highlighted. Clear non-coaxiality was observed during pure principal stress rotation, in both intact and reconstituted clay. The influence of the intermediate principal stress parameter, shear stress level, and inherent anisotropy on the non-coaxial behavior of the clayey soil was found to be insignificant when compared with the sand. The non-coaxial behavior of the clayey soil depended more on the stress paths. Under undrained conditions, the contribution of elastic strain to the direction of the total principal strain increment cannot be ignored.
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A modified creep index and its application to viscoplastic modelling of soft clays
Qi-yin Zhu, Ze-xiang Wu, Yan-ling Li, Chang-jie Xu, Jian-hua Wang, Xiao-he Xia
Journal of Zhejiang University-SCIENCE A (Applied Physics & Engineering), 2014, 15(4): 272-281.
https://doi.org/10.1631/jzus.A1300331
Conventional consolidation tests on reconstituted specimens of numerous natural soft clays show a decreasing of creep index Cαe with increasing soil density. Based on all selected and conducted experimental results, a modified creep index Cαe* defined in double logarithmic plane lge-lgt, was plotted for various clays, from which Cαe* can be assumed as a constant for different soil densities. Then, the modified creep index was applied to a newly developed elastic viscoplastic model. In this way, the modified creep index Cαe* can naturally take into account the nonlinear Cαe revealing the influence of soil density in the soil assemblies without additional parameters. Finally, the enhanced model was incorporated into the finite element code ABAQUS and used to simulate a consolidation test and a test embankment. The improvement of simulations by the modified creep index was highlighted by comparing simulations using the conventional creep index Cαe.
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Evolution laws of strength parameters of soft rock at the post-peak considering stiffness degradation
Zeng-hui Zhao, Wei-ming Wang, Xin Gao
Journal of Zhejiang University-SCIENCE A (Applied Physics & Engineering), 2014, 15(4): 282-290.
https://doi.org/10.1631/jzus.A1300314
To evaluate the strength attenuation law of soft rock in the western mining area of China, we established an evolution model for the strength parameters of soft mudstone at the post-peak stage by employing a tri-linear strain softening model. In the model, a stiffness degradation coefficient ω and a softening modulus coefficient α were introduced to take into account the stiffness degradation, and the subsequent yield surfaces at post-peak stage were all assumed to meet the Mohr-Coulomb yield criterion. Furthermore, attenuation laws of stiffness and strength parameters of soft mudstone were analyzed according to an engineering case. Finally, the model’s accuracy was verified by comparison of results from numerical calculation and tri-axial compression tests. Results showed that the attenuation of the friction angle was dominated mainly by the instantaneous stress states and damage features, while the attenuation law of cohesion was also related to the plastic behavior. The degradation rates of strength parameters decreased with increasing confining pressure and the friction angle tended towards its initial value. Residual strengths were also enhanced with increasing confining pressure. The results indicate that the evolution model can accurately describe the strain softening behavior of soft rock.
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Drivability improvements for a single-motor parallel hybrid electric vehicle using robust controls
Hu Zhang, Cun-lei Wang, Yong Zhang, Jun-yi Liang, Cheng-liang Yin
Journal of Zhejiang University-SCIENCE A (Applied Physics & Engineering), 2014, 15(4): 291-301.
https://doi.org/10.1631/jzus.A1300356
For a single-motor parallel hybrid electric vehicle, during mode transitions (especially the transition from electric drive mode to engine/parallel drive mode, which requires the clutch engagement), the drivability of the vehicle will be significantly affected by a clutch torque induced disturbance, driveline oscillations and jerks which can occur without adequate controls. To improve vehicle drivability during mode transitions for a single-motor parallel hybrid electric vehicle, two controllers are proposed. The first controller is the engine-side controller for engine cranking/starting and speed synchronization. The second controller is the motor-side controller for achieving a smooth mode transition with reduced driveline oscillations and jerks under the clutch torque induced disturbance and system uncertainties. The controllers are all composed of a feed-forward control and a robust feedback control. The robust controllers are designed by using the mu synthesis method. In the design process, control- oriented system models that take account of various parameter uncertainties and un-modeled dynamics are used. The results of the simulation demonstrate the effectiveness of the proposed control algorithms.
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7 articles
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