Large Longitudinal Strain Research Articles

Using RBF-FD for calculation of hydroelastic vibrations of axisymmetric orthotropic shells of rotation

Geometrically nonlinear differential equations describing the dynamic deformation of axisymmetric shells of rotation are derived on the basis of general equations for solving functions in the global coordinate system. The equations take into account thinning/thickening at large longitudinal strains as well as transverse shear for thick shells. The motion and pressure of an ideal incompressible fluid is described by a displacement potential. To obtain the numerical solution, the finite difference method based on spline interpolation by polyharmonic radial basis functions is applied. The calculation method is implemented in software package. Good agreement of the calculated displacements with the results of modeling by different finite elements in ANSYS is obtained. The frequencies of the hydroelastic vibrations of the tanks are compared with those obtained by the finite element and boundary element method, as well as with results from published articles by other researchers.

Piezoelectric Fixing Direction effect on GRF test results in Wearable Shoe-Insole System

This article is about studying the placing direction effect of a piezoelectric sensor on the shoe insole in the GRF results. Where the sensors used in this research are in two directions, along and perpendicular to the foot midline. In the both cases the sensors were fixed on the shoe insole to sense the foot pressure. For the first set of sensors which are perpendicular to the foot midline the collected data has similar trend to the GRF collected from the force plate, as the small lateral strain in the shoe insole due to the patient weight and GRF is close to the GRF data collected from other measurement system. On the other hand, the collected data from the second set of sensors which are in a longitudinal direction with the foot midline will have different trend and values from the collected data from the force plate or any other GRF measurement system. This different in the results is due to the large longitudinal strain in the shoe insole due to the patient weight which produce dissimilar results from the force plate result data.

A Hybrid Gripper With Soft Material and Rigid Structures

Various robotic grippers have been developed over the past several decades for robotic manipulators. Especially, the soft grippers based on the soft pneumatic actuator (SPA) have been studied actively, since it offers more pliable bending motion, inherent compliance, and a simple morphological structure. However, few studies have focused on simultaneously improving the fingertip force and actuation speed within the specified design parameters. In this study, we developed a hybrid gripper that incorporates both soft and rigid components to improve the fingertip force and actuation speed simultaneously based on three design principles: first, the degree of bending is proportional to the ratio of the rigid structure; second, a concave chamber design is preferred for large longitudinal strain; and third, a round shape between soft and rigid materials increases the fingertip force. The suggested principles were verified using the finite element methods. The improved performance of the hybrid gripper was verified experimentally and compared with the performance of a conventional SPAs. The ability of the hybrid gripper to grasp different objects was evaluated and was applied in a teleoperated system.

Post-Buckling Failure Modes of X65 Steel Pipe: An Experimental and Numerical Study

In service pipelines exhibit bending loads in a variety of in-field situation. These bending loads can induce large longitudinal strains, which may trigger local buckling on the pipe's compressive side and/or lead to rupture of the pipe's tensile side. In this article, the post-buckling failure modes of pressurized X65 steel pipelines under monotonic bending loading conditions are studied via both experimental and numerical investigations. Through the performed full-scale bending test, it is shown that the post-buckling rupture is only plausible to occur in the pipe wall on the tensile side of the wrinkled cross section under the increased bending. Based on the experimental results, a finite element (FE)-based numerical model with a calibrated cumulative fracture criterion was proposed to conduct a parametric analysis on the effects of the internal pressure on the pipe's failure modes. The results show that the internal pressure is the most crucial variable that controls the ultimate failure mode of a wrinkled pipeline under monotonic bending load. And the post-buckling rupture of the tensile wall can only be reached in highly pressurized pipes (hoop stress no less than 70% SMYS for the investigated X65 pipe). That is, no postwrinkling rupture is likely to happen below a certain critical internal pressure even after an abrupt distortion of the wrinkled wall on the compressive side of the cross section.

1502 PNN-PT 系セラミックスの合成と電気機械的特性

Relaxor-type ferroelectric perovskites, (1-x)Pb(Ni_<1/3>Nb_<2/3>)O_3・xPbTiO_3 with x between 0.32 and 0.4,were prepared through process of heat treatment and then acid treatment of oxide mixtures containing PbO in amount greater than in the perovskite composition. The perovskite phases were crystallized without the formation of pyrochlore phase from the mixtures 5PbO+(1-x)NiO+(1-x)Nb_2O_5+3xTiO_2 at 950℃. By leaching with a 1N acetic acid solution to remove the excess PbO, the perovskite phases were obtained in discrete and cube-shaped particles of 1-5μm size. The ceramic sintering was made at 1180℃ for 3h. Relatively good dielectric and electromechanical properties were observed in the ceramics with x=0.34 to 0.39. The most remarkable was that the ceramic with x=0.36 showed a large longitudinal strain of 0.28% at 1600V/mm near room temperatures.

Novel electrostrictive poly(vinylidene fluoride-trifluoroethylene) copolymer actuators

Electroactive materials for applications in active noise and vibration control should possess a high displacement capability, high reliability, and be easily fabricated to conform to complicated surfaces and shapes. Apparently, almost all the current available materials cannot meet these requirements. It was discovered recently that a massive electrostriction (strain level ∼5%) can be achieved in specially treated P(VDF-TrFE) copolymers [Q. M. Zhang, Vivek Bharti, and X. Zhao, Science 280, 2101 (1998)]. More significantly, because of the high elastic modulus, the material also exhibits high elastic energy and power density, an order of magnitude higher than those from the conventional piezoceramic and magnetostrictive materials. In addition to the large longitudinal strain, the transverse strain can be tuned over a broad range by varying the processing and irradiation conditions, from near zero in unstretched samples to more than the longitudinal strain in stretched samples. In this paper, the electromechanical properties of this class of material and the performance under different external conditions will be presented. The results on the unimorph and multilayer actuator performance fabricated using the new electrostrictive polymers with different electrode materials will also be presented. [Work supported by ONR.]