Abstract: Carbon fiber is a fiber material, so the tension must be kept constant in the placement process. The attitude of carbon fiber placement head will change with the change of a placement path. Focusing on the problem of tension fluctuation caused by the attitude of carbon fiber placement head, gravity balance characteristic of symmetrical objects is adopted to propose a tension control method for eliminating the tension fluctuation and tension measuring error caused by gravity. In this way, the tension is kept constant depending on tension feedback control. Mathematical model and theoretical analysis show that the tension control method with gravity balance can eliminate the gravity influence on tension and make the tension keep constant.
Abstract: The aim of this study is to discuss the plastic shakedown and true stress of the cyclically loaded pressure vessel. A thin-walled cylinder pressure vessel is made according to actual working state and a water pressure test system is built. The vessel is loaded to different strain levels of plastic deformation first. Then it is loaded cyclically to shakedown state. The relationship between plastic strain and shakedown range is given based on numerous experiments. The constitutive model of the true stress-true strain of the vessel is obtained. The experimental results show that the ratcheting obviously occurred when the vessel is cyclically loaded to plastic deformation. The true stress-strain constitutive model which is presented in this paper can show appropriately the constitutive relation of the vessel when it is under multi-axial stress state. The application of uniaxial shakedown constitutive model has been demonstrated in this study.
Abstract: Bamboo is a fiber-reinforced bio-composite with superior structural behavior. For the purpose of analyzing the correlations between the mechanical properties of bamboo and fiber volume fraction, tensile tests were performed on bamboo test specimen, and the corresponding volume fractions of fiber and parenchymatous ground tissue were measured. Linear and curvilinear regressions were done from tested data of elastic modulus, tensile strength and volume fractions of fiber. The results display that there is an obvious correlation between bamboo tensile properties and fiber volume fraction. In order to analyze the effects of fiber gradient distribution on bamboo structural behavior, models composed of fiber and parenchymatous tissue were built based on different fiber distribution for comparative analysis. The analysis results show that the maximum deformation of 4 layers model is 3.86% less than 1 layer model, and the maximum deformation of 8 layers model is 8.87% less than 4 layers model. In the part of maximum axial stress, the maximum axial stress of 4 layers model is 3.27% less than 1 layer model, and the maximum axial stress of 8 layers model is 8.90% less than 4 layers model. Conclusion can be drawn from the comparison that the strength and stiffness of the model appear to be growing with the degree of fiber gradient distribution deepening from 1 layer model to 4 layers model, and 4 layers model to 8 layers model.It can be concluded that the mechanical properties of bamboo structure are significantly improved because of fiber gradient distribution.
Abstract: Low-frequency acoustic method, studies of viscoelastic properties of polymers tetrazolecontaining. It was shown that the introduction of modifiers KCl and KNO3 has a different effect on the dynamic and mechanical characteristics tetrazolecontaining polymers. It is noted that such changes are related to the restructuring of the molecular organization of cross-linked polymers.
Abstract: The inertial effects of the components in the transmission device have both advantages and disadvantages and can not be unavoidable, it has direct influences on starting, braking, energy consumption and the equipment service life, it is one of the important problems need to be discussed carefully. Using the mechanics principle, this paper analyzed the calculation method of inertial effect in gear, and obtained the torque expression of the different sections in the transmission chain and the power factor of inertia effect, the results of the given numerical example show the correctness of the conclusions/
Abstract: The traditional elastic theory believes that there exists normal stress in pure bending body (PBB) and shear stress in pure torsion body (PTB). However, the author proved that there is no normal stress but ‘Bent Point Moment’ (BPM) in PBB. And it also concluded that there is no shear stress but ‘Shear Point Moment’ (SPM) in PTB. This article overturns the preliminary theorems of the Elasticity Theory, which believes that the value of the moment (Bending moment & Torsion moment) on a unit area converges to zero. Just as the completely different natural frequencies of the forced vibration can lead to completely different resonant conditions. Besides, this theory has also been validated in the Damage Mechanics National Key Laboratory of Tsinghua University. Therefore, it is significant to avoid destruction produced by resonance.
Abstract: The current theory of elasticity persisted in the standpoint that normal stress exists in pure bending and shearing stress exists in pure torsion, which has been negated by the non-zero point force moment elasticity theory .The mentioned new theory proved that bending point moment exists in pure bending and torsional point moment exists in pure torsion, which debunk the current theory of elasticity that the limit moment acting on the unit area is zero. As a consequence, the causation of fatigue should be revised as point moment instead of stress. By using theory of stress and the new theory to analyze fatigue of non-slender rod, safety factor worked out by the former one is much bigger, which suggests that theory of stress cannot ensure safety. Undoubtedly, that is the fundamental causation of frequent occurrence of fatigue rupture. Thus, the new theory is of great significance in the prevention of unexpected fatigue rupture in the field of aerospace, navigation, transportation and mechanical engineering, etc.
Abstract: In order to forecast the sailing response of planing craft at high speed rapidly and accurately, CFD code Fine/Marine solver was used to calculate the resistance and sailing attitude of a high-speed planing craft, then the numerical results were compared with experimental results and empirical formula results. The results showed that resistance error calculated by Fine/Marine was between 5% and 10%, trim and heave results were in good agreement with experimental results, and had greater accuracy compared with the empirical formula results. The feasibility of this numerical simulation method was validated and this method provided an effect performance evaluation method for new designing planing crafts.
Abstract: In this study the effects of viscous and pressure forces on trimming moments of Series 60 (CB = 0.6) hull form are calculated at different Froude numbers by employing computational methods. The grid generator GAMBIT was used for meshing hull and computational domain. The Simulations are carried out using commercial CFD code ANSYS Fluent 13. The SIMPLE (Semi-Implicit Methods for Pressure-Linked Equations) algorithm is used for pressure-velocity coupling. The volume of Fluid (VOF) formulation is employed. The computed resistance, wave profile and trim of series 60 hull are compared with experimental values and found in reasonable agreement.