Advanced Materials Research Vols. 189-193

Abstract: Soft fingers contribute to dexterous grasping on account of the area contact and high friction involved. This paper presents a novel approach in modeling of soft contacts between soft fingertip and object using viscoelastic material and analyses its characteristics employing BondGraph Methods (BGM). The fingers are made viscoelastic by using springs and dampers. Detailed bond graph modeling of the contact phenomenon with two soft-finger contacts considered to be placed against each other on the opposite sides of the grasped object as is generally the case in a manufacturing environment is presented. The stiffness of the springs is exploited in order to achieve the stability in the soft-grasping which includes friction between the soft finger contact surfaces and the object. It is shown in the paper that the system stability depends on the viscoelastic material properties of the soft interface. Method of root locus is used to analyze this phenomenon. The paper shows how the weight of the object moving downward is controlled by the friction between the fingers and the object during the application of contact forces by varying the damping and the stiffness in the soft finger.

Abstract: The face gear drive is a gear meshing drive with cylindrical gear and bevel gear. Because of its small space, high contact ratio, large transmission torque, low vibration and noise, not sensitive to the axial phase error of the worm and so on, face gear transmission is widely applied. In the traditional gear transmission dynamic contact analysis (TCA), first, simulate the meshing equation; second, calculate the contact trajectory that is formed by the adherent point; last, solve each of the instantaneous contact areas and solve tooth contact region in meshing process. But it can’t solve the tail, diamond and other high contact defects. In the real mesh transmission, tooth meshing is very complex, including edges contact, multi-tooth engagement and many other issues. With the progress of the times, using finite element analysis software ANSYS, it will be able to simulate the dynamic contact analysis of the gear. In this paper, the offset face gear as the research object, with MATLAB program, Solidworks and ANSYS software, establish the mathematical model of the orthogonal offset face gear, simulate its geometric model in the three-dimensional software. Finally, implement the simulation of its dynamic contact meshing in the finite element analysis software.

Abstract: Commercially pure titanium (CP Ti), grade II, is subjected to hot compression at temperatures ranging from 673 to 973 K with 50 K intervals and strain rates of 0.001, 0.01, 0.1 and 1s^-1 up to 60% height reduction. By analysing work hardening rate vs. flow stress, the deformation behaviour can be divided into three groups, viz. three-stage work hardening, two-stage work hardening and flow softening. By plotting the data in a T vs. logε diagram, the present and previous data fall into three distinct domains which can be separated by two distinct values of the Zener-Hollomon parameter.

Abstract: The wave force spectrum expressed in terms of Morison's equation was deduced by ocean wave theory and spectral analysis theory, and the spectral analysis of wave force were analyzed with the finite element method which was applied to the leg of the offshore wind power installation vessel, the natural frequencies and the vibration model were accomplished with boundary conditions. The dynamic response of the leg were studied in different conditions, it can be concluded that the wave force of the leg is only related with geometric shape and working depth of truss legs.

Abstract: The first-order kinetic models were used in the article to study the effect of the addition of gum acacia (A₁), the ratio of core material and wall material, the ratio of maltodextrin and starch, and the gel types on the release properties of pellets in distilled water. The results showed that the sucrose release rate (K values) of slow-release pellets slowed down gradually with the increase of A1 amount, larger ratio of wall material resulted in smaller K values, the ratio of starch increased from 2:1 to 1:1, K values at different water temperatures increased significantly, additional starch might result in the blocking of elution tube by pellets and smaller K values of the pellets, K values of the pellets prepared with gum acacia (A₂) was the maximum and that with A₁ was the minimum, and the compound of A₁ and A₂ could control the release rate of the pellets. The release process of the pellets in the static distilled water system showed that the pellet diameter (D1) expanded rapidly in the early period, then the pellet wall surface eroded, pellet size expansion slowed down until insoluble starch circle was left. The pellet core diameter (D2) changed a little in the early period and decreased faster after a period of time until it was completely dissolved. The release process of pellets in the static distilled water supposed that there were two stages of sucrose release from the pellets, and the model fitting results showed: the K values in the first stage was significantly higher than those of the second stage.

Abstract: The monolithic flexible joint is introduced as a novel component of inertial guidance instrument. The angular stiffness of the joint is investigated by employing theory of flexure hinges considering the key part of the joint is a variation of the common circular flexure hinge. Closed-form equation is formulated to unify the typical angular stiffness equations developed by other authors in terms of the circular hinge, and the main variables of the formulation are also discussed. Finite element models of the monolithic joint are built to confirm the analytical model predictions. A measuring system controlled by computer is also developed to evaluate the angular stiffness of the monolithic flexible joint. Checked against finite element analysis and experimental measurement data, the analytical model predictions are within 7% error margins. The study results indicate that the angular stiffness is more sensitive to the minimal thickness of hinge and less sensitive to the notch angle and the oblique angle of hinge.

Abstract: Flexible pipes with helical reinforcement are widely used in the marine engineering and tissue engineering because of their low bending stiffness. Through appropriate design, they could also meet the strength requirement. All studies on this kind of structures regard the pitch angle of helical wires, strips or fibers as a vital parameter influencing the mechanical properties. In this study, we compare the tensile property of pipes with helical reinforcements braided in different initial pitch angles. Contact pressure is taken into consideration and eliminated by using deformation compatibility equation. The pitch angle changes under axial tension which induces the geometric nonlinearity. It is noted that when the pitch angle is larger than a critical value, even if there is no internal or external pressure, helixes will contact with the core under axial tension. But the initial pitch angle can not be too large since the contact pressure will induce partial buckling of the flexible pipe.

Abstract: Due to the length of the mill, accurate modelling of stationary solution of continuous cold roll forming by the finite element method using the classical Lagrangian formulation usually requires a very large mesh leading to huge CPU times. In order to model industrial forming lines including many tools in a reasonable time, the sheet has to be shortened or the element size has to be increased leading to inaccurate results. On top of this, applying loads and boundary conditions on this smaller sheet is usually more difficult than in the continuous case. Moreover, transient dynamic vibrations, which are unnecessarily computed, may appear when the sheet hits each tool, decreasing the convergence rate of the numerical simulation. Beside this classical Lagrangian approach, an alternative method is given by the Arbitrary Lagrangian Eulerian (ALE) formalism which consists in decoupling the motion of the material and the mesh. Starting from an initial guess of the sheet geometry between the rolls, the numerical simulation is performed until the stationary state is reached with a mesh, the nodes of which are fixed in the rolling direction but are free to move on perpendicular plane, following the geometrical boundary of the sheet. The whole forming line can then be modelled using a limited number of brick and contact elements because the mesh is only refined near the tools where bending and contact occur. In this paper, ALE results are compared to previous Lagrangian simulations and experimental measurement on a U-channel, including springback.

Abstract: In order to find the distribution law of coal fragmentation, mathematic model of size distribution was built according to fractal theory. Based on this, the experiments of impactive crash were carried out under different impact rate and different Protodikonov's hardness. The comparison between Weibull distribution and fractal distribution was done so as to find the relationship between the influence parameters and the coal fragmentation characteristic index, the coal fragmentation degree coefficient and the fractal dimension. The results indicate that both two types of distribution functions are suitable for the distribution discipline of coal fragmentation, but the relationship of the coal fragmentation degree and impact parameter is not reacted correctly by the coal fragmentation characteristic index and coal fragmentation degree coefficient in the Weibull distribution while the coal fragmentation degree could be expressed by the fractal dimension in fractal distribution. The relationships between the fractal dimension and the rate, the Protodikonov's hardness of coal are linear.

Abstract: The spherical impact is a common phenomenon in mechanical engineering. The elasto-plastic impact is more complicate than the elastic impact. The elasto-plastic impact loads are investigated for the different contact stiffness and the different impact velocity by the nonlinear finite element method. The accuracy and reliability of the finite elements model are verified by comparing the numerical results of the elastic impact with the Hertz results. The elasto-plastic impact simulation shows that the impact loads have a negative exponential relation with the contact stiffness as well as a linear relation with the impact velocity. The contact time decrease with the increase of the contact stiffness and the impact velocity. The comparison between the influence of the contact stiffness and the impact velocity indicates that the impact velocity has a significant influence on the impact load and the contact stiffness has a big influence on the contact time.