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08 February 2010, Volume 32 Issue 1
Application study
2010, 32(1):  68-71.  doi:10.6052/1000-0879-2008-139
Abstract ( 1163 )   PDF (632KB) ( 442 )
Based on the existing string mechanical model, the mechanical model of washover-string is built with its structure features (big diameter, thin-wall). After washover-string inflexion condition and contact force are analyzed, friction resistance of washover-string is calculated and analyzed.
Education Study
2010, 32(1):  81-82.  doi:10.6052/1000-0879-2008-364
Abstract ( 1120 )   PDF (269KB) ( 605 )
A simple solution of the classic dog-and-dog pursuit problem is presented, which emphasizes the use of concepts of relative motion and, therefore, can be used in introductory mechanics course.
Interesting mechanics story
2010, 32(1):  91-97.  doi:10.6052/1000-0879-2008-379
Abstract ( 1181 )   PDF (2697KB) ( 923 )
Application study
2010, 32(1):  20-23.  doi:10.6052/1000-0879-2008-448
Abstract ( 1249 )   PDF (803KB) ( 531 )
It is difficult to isolate the signal with messages of structure's mini-faults in vibration detection methods. This paper proposes a method of wavelet analysis and modern spectrum estimation technology to extract the weakness elastic wave signal that represents structure's cracks characteristics. For a specimen with crack, the experimental results show that this method can improve the accuracy of the crack identification from the vibration signal. It will be used in the non-damage detection technology for mini-faults in engineering practice.
Education Study
2010, 32(1):  82-83.  doi:10.6052/1000-0879-2008-464
Abstract ( 940 )   PDF (580KB) ( 572 )
Application study
2010, 32(1):  24-28.  doi:10.6052/1000-0879-2008-492
Abstract ( 1271 )   PDF (1903KB) ( 479 )
Based on elasto-plastic damage theory of rock materials, the failure and fracture processes of rock slopes are numerically simulated with the site response of the rock slope under strong seismic loading, including the local damage evolution and the development of failure area. Two independent damage variables are introduced into the constitutive model to control the tension and compression behaviors of the rock materials. Although the characteristics of initial micro-cracks inherent in the rock materials are not considered in the constitutive model, their influence on the properties of rock materials is taken into consideration by reducing the corresponding moduli and strength. The interfacial characteristics between large cracks such as faults are considered as in the interface contact. The numerical simulation by finite element method is carried out for the failure of a practical rock slope on the left bank of a river with a large hydraulic power station under a strong seismic loading (in 100-year recurrent period and over a probability of 2{\%}). The mechanism of landslide for such kind of fractured rock slope is analyzed. Some advices are proposed for prevention and treatment of the landslide according to the simulation results.
2010, 32(1):  29-32.  doi:10.6052/1000-0879-2008-541
Abstract ( 1170 )   PDF (696KB) ( 643 )
The deformation of porous media is visco-elasto-plastic, with the elastic deformation as the main-body deformation, the viscous deformation as the structure deformation and the plastic deformation as the damage deformation. Based on the concept of effective stresses and the principle of damage mechanics, this paper studies the properties of effective stresses of porous media. Assuming that the grain is in compression, and the grains can have a local failure, with an increase of the effective stresses and the supporting capacity of grains, the damage effective stresses are considered in the calculation, which would show the complex properties of deformation of porous media more accurately.
2010, 32(1):  60-63.  doi:10.6052/1000-0879-2008-542
Abstract ( 1387 )   PDF (1090KB) ( 602 )
The effect of residual stress on the structural design of high temperature MEMS shear stress sensor is analyzed both theoretically and numerically. It is found that under the condition of constant electrode width and electrode gap, the increase of electrode number and the decrease of electrode length will effectively reduce the electrostatic-force induced stress and deformation. The residual stress originated from MEMS fabrication, however, shows much stronger influence on the stress and deformation than that of electrostatic force. Therefore, the residual stress must be seriously considered for the reliability of the structure. The analytical results can be a reference for the structural design of this innovative high temperature MEMS shear stress sensor.
Discussion
2010, 32(1):  89-90.  doi:10.6052/1000-0879-2008-563
Abstract ( 1671 )   PDF (274KB) ( 534 )
Based on velocity composition theorem and acceleration composition theorem，while the rigid pure rolling upon fixed surfaces，calculated formulas on velocity and acceleration of contact point is deduced .The method is easy to understand.
2010, 32(1):  88-89.  doi:10.6052/1000-0879-2008-572
Abstract ( 1447 )   PDF (276KB) ( 567 )
Application study
2010, 32(1):  33-36.  doi:10.6052/1000-0879-2008-576
Abstract ( 1202 )   PDF (633KB) ( 485 )
The concrete gravity dam's displacement caused by foundation seepage volume forces was studied based on the elastic theory and a porous continuum model. Stresses and displacements in the isotropic foundation with seepage volume forces are obtained. Some conclusions are drawn: (1) With the upstream foundation subsidence and the downstream foundation elevation by the seepage volume forces, the dam has an upcurrent displacement. (2) The displacement caused by the foundation area force is larger than that cansed by the foundation seepage volume force, but these loads all lead to the dam upcurrent displacement.
2010, 32(1):  41-45.  doi:10.6052/1000-0879-2008-601
Abstract ( 1187 )   PDF (780KB) ( 540 )
Based on the twin shear unified strength theory and for materials with different elastic moduli in tension and compression, this paper derives unified solutions for the stress and displacement fields in a thick spherical shell in expansion. The influences of several factors are analyzed, including different elastic moduli in tension and compression, different parameters in models and the development of plastic zone. The results show that the elastic ultimate expansion pressure, stress and displacement fields depend on the elastic moduli, and the model parameters. If $\alpha$ is less than 1, the elastic limit pressure ($p_e$) can be increased significantly. The plastic ultimate pressure $(p_r)$ is not related with elastic moduli, it depends on parameter $(\eta)$ in models, and increases first and then decreases with the increasing $\eta$. Large errors may be resulted if the classical elastic theory and the single model are adopted and the strain-softening properties are neglected.
2010, 32(1):  64-67.  doi:10.6052/1000-0879-2008-616
Abstract ( 1051 )   PDF (1035KB) ( 602 )
The paper introduces the principle of a synchronous trigger based on PVDF film. With the input of fast PVDF film and probe, the trigger can reach the precision of one microsecond. When it is used in metal cleavage experiment, the flash X-ray digital imaging system can be made synchronous, to obtain the X-ray images of metallic chippings at different instants.
2010, 32(1):  37-40.  doi:10.6052/1000-0879-2008-629
Abstract ( 1312 )   PDF (633KB) ( 917 )
Since the classic 4th order compact scheme requires nine points for 2D Poisson equation, the boundary conditions make the scheme difficult to be implemented, especially when the equations need to be solved by a multi-grid method. A new 4th order accurate scheme is derived. First, a predictive solution is obtained by using the classic 2nd order five-point scheme. Then, the solution is corrected by considering the residual term. Finally, the scheme combines the predictive and the corrective solutions to achieve 4th order accuracy. In each step, the classical 2nd order scheme is used and the boundary conditions are easy to be treated. Although the scheme costs twice of the computational time as compared with the 2nd order scheme, it is much more accurate than the 2nd order scheme. Moreover, the boundary conditions are quite simple and it is easier to code for this new scheme. The numerical simulations confirm that the new scheme has the same accuracy as the classic 4th order compact scheme. This provides a new approach to turn a lower order scheme in to a high order scheme.
Education Study
2010, 32(1):  86-87.  doi:10.6052/1000-0879-2008-639
Abstract ( 1140 )   PDF (357KB) ( 519 )
Review
2010, 32(1):  10-15.  doi:10.6052/1000-0879-2009-052
Abstract ( 1508 )   PDF (2051KB) ( 640 )
The granular matter is a large assemblage of dense packing particles. The interparticle forces are usually dominant in comparison with drag forces from interstitial fluid, and are transmitted through heterogeneous force chains. This paper studies the multiscale structures and rate-dependent processes involved in granular materials, and shows that the granular matter is a typical multiscale mechanical system. Three length scales are identified, particle, force chain and granular system in micro- meso- and marco scales, respectively, and with three related characteristic time scales. The correlation of particle-force chain, force chain-system would be the major problem in the multiscale analysis of granular materials.
Application study
2010, 32(1):  16-19.  doi:10.6052/1000-0879-2009-060
Abstract ( 1528 )   PDF (695KB) ( 455 )
The elastic interaction between a wedge disclination dipole and a wedge crack is investigated. The closed form solutions of complex potentials and stress fields are obtained by using complex potential theory. The stress intensity factor at the tip of the wedge crack is also obtained. The shielding or anti-shielding effects of the wedge disclination dipole on the stress intensity factor is evaluated. The results indicate that the shielding or anti-shielding effects on the stress intensity factor increase sharply when the wedge disclination dipole approaches the tip of the crack. Under certain conditions, the disclination dipole may weaken the stress intensity near the crack tip. If the center of the dipole is fixed, there always exists a critical value of the angle of the dipole arm for the shielding or anti-shielding effects to be maximal. In addition, the wedge angle of the crack and the length of the dipole arm have a significant influence on the stress intensity factor.
2010, 32(1):  54-59.  doi:10.6052/1000-0879-2009-078
Abstract ( 1754 )   PDF (3416KB) ( 789 )
The herringbone buckling(double rib buckling) of strip was a serious flatness defects, and its mechanism of production was still unknown. A new explanation about herringbone buckling was put forward in this paper, and based on Airy stress function and S.Timoshenko’s principle of least work, a new mechanical model of herringbone buckling was established, and the stress field in strip prebuckling was obtained in this paper, the mathematic model of critical buckling stress was also achieved by Galerkin’s principle of virtual displacement, the path generation of post-buckling was found with Perturbation-Variational Solution, and the mode of post-buckling was in good accordance with the buckling mode of Finite Element Method. The results of the analysis could play a important role in prediction of herringbone buckling and its angle of inclination on strip rolling line.
Review
2010, 32(1):  1-9.  doi:10.6052/1000-0879-2009-103
Abstract ( 1395 )   PDF (2557KB) ( 606 )
Glycocalyx on the surface of vascular endothelial cells is of a hair-like structure composed of various proteoglycans and glycoproteins and is a barrier with selective permeability for the vascular wall. It has been known that glycocalyx can assist red blood cells in their motion through capillaries, prevent the adhesion of blood cells and participate in signal communications. It has been well documented that glycocalyx may also take part in shear stress sensing and transduction. This article briefly reviews the physiological functions of glycocalyx with particular emphases on its roles in mechanotransduction.
Education Study
2010, 32(1):  78-79.  doi:10.6052/1000-0879-2009-141
Abstract ( 1256 )   PDF (443KB) ( 695 )
This paper has introduced several methods determining the secure parabola of projectiles, and discussed its properties of geometry and mechanics from different point of views.
2010, 32(1):  76-77.  doi:10.6052/1000-0879-2009-198
Abstract ( 877 )   PDF (450KB) ( 481 )
Application study
2010, 32(1):  46-53.  doi:10.6052/1000-0879-2009-224
Abstract ( 1320 )   PDF (1983KB) ( 499 )
Both nodes of reduced beam section and widened beam section can make the plastic hinge shift away from the beam and column interface to relieve the stress concentration in the connections, to avoid brittle fracture in weld. 3-D finite element models were used to analyze the mechanical properties of nodes of reduced beam section and widened beam section and ordinary nodes using ANSYS. The analysis results show that the bearing capacity of nodes of the reduced beam section is reduced due to weakened beam flanges, however, the bearing capacity of nodes of the widened beam section is enhanced due to widened beam flanges. Moreover, a scopes of design parameters of the nodes are given, for seismic design of steel frames.
Interesting mechanics story
2010, 32(1):  102-104.  doi:10.6052/1000-0879-2009-342
Abstract ( 1319 )   PDF (433KB) ( 797 )
Education Study
2010, 32(1):  72-75.  doi:10.6052/1000-0879-2009-357
Abstract ( 1633 )   PDF (1238KB) ( 793 )