Dynamic In-plane Research Articles

753 セル充填位置がアルミニウムハニカムの面内衝撃圧縮特性に与える影響(OS7-3 衝撃工学,OS7 先進材料および構造の力学特性評価)

753 セル充填位置がアルミニウムハニカムの面内衝撃圧縮特性に与える影響(OS7-3 衝撃工学,OS7 先進材料および構造の力学特性評価)

Cold-Start of a PEFC Visualized with High Resolution Dynamic In-Plane Neutron Imaging

Cold-starts of a polymer electrolyte fuel cell (PEFC), isothermally maintained at various subfreezing temperatures, were visualized using high resolution dynamic in-plane neutron imaging. The results obtained aim to bring new knowledge about the water accumulation mechanisms leading to the voltage drop usually observed in isothermal mode after a given working time, also called voltage failure. In particular, the data presented should be useful for comparison to simulation predictions provided by modeling studies. As main result, water in a condensed phase was observed to accumulate not only in the membrane-electrode-assembly (MEA), but also in the cathode gas diffusion layer (GDL) at −15°C and even in the cathode gas channels at −10°C. Moreover, approximately 400 cold-starts were realized without neutron imaging and revealed stochastic distributions of working times. The presence of water in super-cooled state is discussed and finally retained as only valid explanation of the results obtained. Additionally, the sudden freezing of super-cooled water is thought to cause the rapid water accumulation observed in the MEA during the voltage failure.

Dynamic in-plane resonant characteristics of piezoceramic and piezolaminated composite plates

Piezolaminated composite plates have received considerable attention in various industrial applications due to their intelligent characteristics. In this investigation, two experimental measurement techniques are used to determine the in-plane resonant vibration of angle-ply laminated composites embedded with a piezoceramic layer (piezolaminated plates) for different stacking angles. The first method is a full-field optical technique, which is called the AF-ESPI (amplitude-fluctuation electronic speckle pattern interferometry). This is the major experimental method. The AF-ESPI method is used to determine the in-plane resonant frequency and corresponding mode shape of a single-layer piezoceramic plate and piezolaminated plates with five different stacking angles. The second experimental technique, the impedance analyzer, is employed to determine the in-plane resonant frequency. Finally, numerical computations based on the finite element analysis are presented for comparison of the two experimental results. Excellent agreement between the experimentally measured data and the numerically calculated results are found for in-plane resonant frequencies and mode shapes. This study indicates that the dynamic characteristics of inplane resonant vibrations for piezolaminated plates with different stacking angles are quite different.

Aseismic retrofitting of unreinforced masonry walls using FRP

Many of existing unreinforced masonry (URM) buildings are seismically vulnerable and require retrofitting. This paper investigates in-plane seismic behaviour of URM walls before and after retrofitting using fiber-reinforced polymers (FRP). Dynamic in-plane tests were carried out on five half-scale specimens with two different effective moment/shear ratios namely 0.7 and 1.4. The specimens were retrofitted on a single side using different types and structures of FRPs. The test specimens were subjected to a series of synthetic earthquake motions on a uni-axial earthquake simulator. The retrofitting technique improved the lateral strength and stiffness of the URM walls. Moreover, the fundamental frequency and the initial stiffness of each specimen remained approximately constant before and after retrofitting. During the test, the slender specimens failed in flexural. For specimens failed in flexural, the measured FRP axial strains showed that the strain distributions along the specimens' cross-sections are approximately linear even at failure. Hence, the flexural strengths of the specimens were calculated using linear elastic approach. The measured lateral resistances of slender specimens are approximately 130% of the calculated flexural strength. This difference attributed to the difference in the nominal ultimate strains of FRPs and the real values at failure. The measured axial strains in FRPs during this test were approximately 50% of its nominal values. In addition, the shear strengths of the squat specimens were calculated using two different models. The calculated shear strengths approximately range from 99 to 177% of the measured lateral resistances.

A dynamic tyre model of vertical performance rolling over cleats

In the paper a dynamic tyre in-plane model of modal parameters is given. The tyre sidewall nonlinear characteristic is also taken into account. The static calculation results agree with the experimental data very well. The dynamic responses simulation of a tyre running over cleats with different speeds is carried out. The results agree with experiments well in both the time domain and the frequency domain in general and some questions are discussed.

Closed-form integration of singular terms for constant, linear and quadratic boundary elements. Part 2. SV-P wave propagation

Part I of these two related papers considered the analytical evaluation of singular integrals for anti-plane boundary elements, the results of which were then applied to the evaluation of scattering problems involving SH waves. This second part provides an extension of these results to the more complicated case of in-plane boundary elements, and presents their application to scattering problems involving SV-P waves. First, the singular integrals for constant, linear and quadratic boundary elements are evaluated a in closed form. Thereafter, the formulation is used to model cylindrical inclusions in a two-dimensional elastic medium illuminated by dynamic in-plane (plane-strain) line sources. The boundary element method (BEM) results are then compared with the known analytical solutions for these problems.

Theoretical analysis, numerical calculation and experimental measurement of transient elastic waves in strips subjected to dynamic loadings

In this study, the transient response of an elastic strip subjected to dynamic in-plane loadings on the surface is investigated in detail. One of the objectives of this study is to develop an effective analytical method for determining transient solutions in a strip. By applying Laplace transform, the analytical solution in the transformed domain is derived and expressed in matrix form. The solution is then decomposed into infinite wave groups in which the multiple reflected waves with the same reflection are involved. Each multi-reflected wave can be identified by a coding method and be verified by the theory of generalized ray. The inverse transform is performed by using the well-known Cagniard method. The transient solutions in time domain for stresses and displacements are expressed in a closed form and are discussed in detail by an example. The experimental results show that the early time transient responses of displacements on the surface agree very well with the numerical calculations based on the theoretical solutions.

MITIGATION OF THREE-DIMENSIONAL VIBRATION OF INCLINED SAG CABLE USING DISCRETE OIL DAMPERS — I. FORMULATION

Three-dimensional small-amplitude free and forced vibration problems of an inclined sag cable equipped with discrete oil dampers are formulated in this paper using a hybrid method. The hybrid method can readily consider cable sag, cable inclination, cable internal damping, damper direction, damper stiffness and others. Multi-pairs of oil dampers with either symmetric or unsymmetric arrangement can also be dealt with. From complex vibration analyses, the damping ratios of a cable, attributed to the installed oil dampers, in both in-plane and out-of-plane modes of vibration can be estimated. The dynamic in-plane and out-of-plane responses of the cable under harmonic excitation can also be determined in the frequency domain. The application of the derived formulae to sag cables in a real cable-stayed bridge is presented in part II of this paper with extensive parametric studies.

High-speed moire´ photography for studying dynamic properties in carbon fiber composites

A moire method for dynamic in-plane displacement measurement is used with the purpose of studying carbon fiber/epoxy composite specimens under tensile dynamic load. The displacement field is measured with a random noise level of less than 0.3 ?m and by using a high-speed camera, a framing speed of 1 million frames/s is achieved. Cracks propagating at speeds of 2000 m/s have been observed. To evaluate strain accurately from the displacement fields, a calibration for distortion in the high-speed image converter camera must be made. A method to measure the variable magnifications in the different frame areas of the camera back is described.

Analytical transient analysis of layered composite medium subjected to dynamic inplane impact loadings

In this study, the dynamic transient response of a layered composite with n layers under dynamic inplane impact loading on the surface is investigated in detail. One of the objectives of this study is to develop an effective analytical method for determining transient solutions. Complete solution of the contribution for each wave is expressed in an explicit form. These solutions will provide reliable solutions that can guide the development of numerical methods. In analyzing this problem, the waves reflected and refracted by the interfaces within the composite must be taken into account, which will generate infinite waves on each composite layer and make the problem extremely complicated to analyze. The problem is solved by using the Laplace transform method and the inverse transform is evaluated by means of Cagniard's method. The transient responses of stresses and displacement in the transform domain on each layer are expressed in a closed form. The equation for each wave front propagating in the layered composite is determined in this study. For the numerical investigation of the transient response of stress, a two layered composite medium is analyzed in detail.

Response and cyclic strain accumulation of pressurized piping elbows under dynamic in-plane bending

Eight pairs of carbon and stainless steel, long and short radius welding elbows were tested under conditions of steady internal pressure and in-plane, resonant dynamic moments that simulated seismic excitations. The elbows had an outside diameter of 60.3 mm and thicknesses of 3.91 and 5.54 mm. The material properties are reported, and the testing procedure and experimental programme fully described. The dynamic response of the comonents indicates that the stainless steel elbows behave differently from the carbon steel elbows. The cyclic strain accumulation for each component is assessed and ratios of applied to limit moments of the elbows at onset of ratcheting are given for each material. While the gross deformation range increased with level of input in testing, no permanent overall swelling or ovalization was recorded; this is contrasted with similar results reported in the general literature.

Automatic order-determination of transient in-plane displacement moire patterns

This paper presents a fringe-carrier method that eliminates sign ambiguity of transient moire fringes which can be used to automatically determine the relative orders. A fringe carrier is preset in the static state of the specimen and the dynamic in-plane displacements are recorded as the modulation to the frequency of the carrier fringes when the specimen is loaded by impact. According to a modulating criterion developed from the modulation degree, the fringes of the transient moire patterns keep monotonical in orders so that they can be automatically encoded in grey levels by a digital image system. The moire orders purely caused by dynamic loadings are evaluated by subtracting the grey-value of the unmodulated carrier image from that of the modulated carrier images encoded by their orders. With the subtracted moire orders the strain components can be obtained, and, correspondingly, the histograms of dynamic displacement moire images are shown with order variation by image-difference.

Dynamic In-Plane Motion of an X-Ray Mask Membrane Induced by Synchrotron Radiation Irradiation

In-plane motion of thermal distortion in an X-ray mask membrane has been investigated numerically by using a one-dimensional dynamic model. The difference between continuous multiple scanning (CMS) exposure and intermittent multiple scanning (IMS) exposure methods was compared in terms of thermal distortion behavior. Since a residual temperature field is formed by the CMS exposure method, a distorted membrane is not restored to the original state for every scan. For the IMS exposure method, a distorted membrane can be restored to the original state for every scan. Thermal stresses, not dependent on the scanning speed of the CMS exposure method, decrease with increasing scanning speed of the IMS exposure method.

Dynamic response of a ring fabricated from a non-linear elastic material

The study is concerned with the dynamic in-plane response of circular thin rings, fabricated from a non-linear elastic material. The governing displacement equations of motion are established and solved on the basis of the Galerkin procedure and the method of multiple scales. The results of the analysis of steady state forced vibration indicate that non-linear coupling induces motion not only of the excited mode, but also very strong response of certain other modes. In the case of a slowly increasing excitation frequency, a response similar to the beat phenomenon may develop under certain conditions.