Language：English   Publishing type：Research paper (international conference proceedings)  

The purpose of this study is to examine the dynamic properties for viscoelastic materials over the wide range of frequency by measuring the change of waveform propagating in the bar. The viscoelastic properties in the frequency up to around 15 kHz can be evaluated by the impact test that the striker bar collides with the specimen bar mechanically. The properties of the high frequency area are different from those of the low frequency area. However, the impact tests using the striker bar cannot determine the dynamic characteristics in the high frequency range. The propagation tests using the wave packet generated by the ultrasonic transducers were performed. The attenuation and dispersion properties were examined by using the ultrasonic transducers having several characteristic frequencies within 25-200 kHz. It was found that the dynamic properties in the low frequency range could be identified as a three-element model based on the elementary theory. On the other hand, a five-element model based on the three-dimensional theory had to be applied in the high frequency range. © The Society for Experimental Mechanics, Inc. 2014.

DOI： 10.1007/978-3-319-00852-3_4

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Japanese Society for Experimental Mechanics  

The use of viscoelastic materials has been increasing in various industries such as automotive and electronic industries because of their excellent impact resistance or damping capability. Precise knowledge of their dynamic properties are needed to further widen the applicability of viscoelastic materials. In the present study, attenuation and the dispersion properties of a polymethyl methacrylate (PMMA) bar were examined using both ultrasonic wave propagation experiments in the higher frequency range of 25 - 200kHz and longitudinal wave propagation experiments in the lower frequency range of up to 15kHz. Since the geometrical dispersion due to three-dimensional deformation was caused by higher frequency components involved in the ultrasonic waves, the three-dimensional wave theory was employed to analyze experimental data of wave propagation. Consequently, it was found that the dynamic properties in the lower frequency range can be identified as a 3-element viscoelastic model based on the elementary one-dimensional wave theory, while those in the higher frequency range must be identified as a 5-element viscoelastic model based on the three-dimensional wave theory.

DOI： 10.11395/jjsem.13.264

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Other Link： https://jlc.jst.go.jp/DN/JALC/10024570625?from=CiNii

Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：TRANS TECH PUBLICATIONS LTD  

This study aims to develop a system for golf clubhead to maximize the flying distance of a golf ball after impact. The procedure consists of a step of pre-design with a CAD software, a process of optimization performed by the combination of a general purpose FEM code and an optimization program developed by the authors, and a step of redesign. For the optimization process, the relation between eigen frequencies and the coefficient of restitution (COR) is verified numerically at first. Based on the results of numerical examination, an approach is proposed for the optimal design in impact problem with basis vector method. And the basis vectors are created by using the sensitivity functions of eigen frequencies obtained by modal analysis. A numerical example is given to demonstrate the validity of the developed system.

DOI： 10.4028/www.scientific.net/AMM.215-216.382

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：ELSEVIER SCIENCE BV  

Indirect impact method using fixed end reflection was newly proposed as the technique for evaluating the dynamic characteristic of viscoelastic materials. A cylindrical specimen is sandwiched between a viscoelastic input bar and a rigid wall, and is tested impacting the input bar. The reflection and the transmission at interfaces as well as the longitudinal wave propagation in viscoelastic bars were analyzed based on the elementary theory in the frequency domain. Some kinds of viscoelastic materials were tested using the proposed method, and the dynamic properties of the materials were evaluated within the frequency of about 15kHz. Moreover, the validity of the proposed method was examined by comparing with the conventional methods. Consequently, it is shown that the proposed method could easily decide the characteristic values of various materials in the elastic region with high accuracy. (C) 2011 Published by Elsevier Ltd. Selection and peer-review under responsibility of ICM11

DOI： 10.1016/j.proeng.2011.04.397

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：ELSEVIER SCIENCE BV  

For the design of impact sports products, for instance, the golf club, the efficiency of the energy transmission from impacting body to the impacted body is an important factor. A so-called concept of impedance matching has been proposed for this purpose. According to this theory, the coefficient of restitution reaches to the maximum when the first natural frequency of the impacting body is corresponding to that of the impacted body. However, it is derived based on a pair model of spring-mass system with a few degrees of freedom, and it is not clear in two or three dimensional problems and the boundary conditions. In this research, the impedance matching in Multi-dimensional problems is verified numerically. It is found that the number of eigen frequencies that should be taken into account increases as the number of dimensions increases. An approach is proposed for the optimal design of impact problem to maximize the coefficient of restitution. The basis vector method is applied to optimization process, and the basis vectors are created with the sensitivity functions of eigen values. (C) 2011 Published by Elsevier Ltd. Selection and peer-review under responsibility of ICM11

DOI： 10.1016/j.proeng.2011.04.543

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：The Japanese Society for Experimental Mechanics  

High polymers or composite materials with lightness and formability have widely been used in various industries. It is well known that these materials show the viscoelastic behavior; the deformation remarkably depends on the time or strain rate. It is, therefore, very important to understand the dynamic behavior technologically. To this end, the split Hopkinson pressure bar techniques using polymeric materials (polymeric SHPB technique) have been used as a method of evaluating the compressive impact characteristics of various viscoelastic materials. However, the accuracy of the method depends on the specimen geometry and mechanical properties of test materials. In this research, therefore, a method of calculating the experimental strain waveform obtained by the polymeric SHPB technique is proposed. The calculations of reflection and transmission at interfaces are considered based on the one-dimensional theory in the frequency domain. The amplitude of reflected strain pulse and the stresses at both interfaces of the specimen are analyzed by changing the mechanical impedance of the specimen. The uniform deformation within the specimen is required in the polymeric SHPB technique. Moreover, the appropriate amplitude of the reflected and the transmitted strain pulses should be measured. Next, polymeric SHPB tests are carried out by using some specimens. The complex compliances of the specimens, which are the ratio of the strain to stress in the frequency domain, are determined, and a mechanical model are identified. It is shown that the actual polymeric SHPB tests should be performed based on the appropriate impedance matching between the specimen and input/output bars studied by the numerical experiments.

DOI： 10.11395/jjsem.11.s227

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Publishing type：Research paper (scientific journal)  

DOI： 10.1007/978-1-4419-9794-4_14

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The examination of the accuracy for a split Hopkinson pressure bar method with viscoelastic input and output bars (viscoelastic SHPB method), which is one of the methods of evaluating the dynamic properties for viscoelstic materials, is executed. The key-point for accurately determining the dynamic properties of low impedance materials lies in how to measure the moderate size of reflected and transmitted waves. Moreover, the loading at both ends of the specimen should be equal each other in this method. Polymethyl methacrylate (PMMA) bars are used as the input and output bars. The viscoelastic properties of PMMA are approximated to a 3-element solid model in advance through preliminary wave propagation experiments. The same model is used as the mechanical properties of specimens, and the value of the instantaneous modulus is changed. The shape of waves at the boundary and the gage position of the input and output bars as well as the specimen are analyzed using the Elementary theory. The stress distribution in the specimen is also examined. It is found that the dynamic properties of viscoelastic materials can be evaluated with good precision by viscoelastic SHPB method when the ratio of the input/ output bars and the specimen of mechanical impedance is about 10-20%. Then, the viscoelastic SHPB tests are actually performed. The complex compliance of the specimens which represent the characteristics of materials is obtained. The dynamic properties of the specimen satisfied the condition obtained by the previously mentioned analysis can be evaluated with high accuracy. © 2010 Society for Experimental Mechanics Inc.

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：The Japanese Society for Experimental Mechanics  

A split Hopkinson pressure bar (SHPB) technique has been developed to study the dynamic behavior of materials having low characteristic impedance. To obtain better matching with low impedance specimens, polymethyl methacrylate (PMMA) bars are used as the input and output bars. The viscoelastic properties of PMMA are determined in advance through preliminary wave propagation experiments. In the present SHPB method, the wave analysis of the stress pulses is conducted in the frequency domain. The incident, reflected and transmitted pulses on the PMMA input and output bars obtained from a SHPB test are resolved into frequency components using the Fourier transform, and corrected to obtain the waveforms at the specimen-bar interfaces. The dynamic viscoelastic properties of the specimen are subsequently determined based on the corrected waveforms. The proposed SHPB technique is then applied determined the viscoelastic models for core and cover materials of a 2-piecegolf ball. The complex compliance for each material is determined as one of the viscoelastic properties in the frequency domain. Furthermore, it is verified through the FEM simulations on the impact of golf balls that the proposed SHPB method provides reasonable estimates of the dynamic behavior of low impedance materials.

DOI： 10.11395/jjsem.10.s174

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：日本実験力学会  

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Publishing type：Research paper (international conference proceedings)  

A split Hopkinson pressure bar (SHPB) technique has been developed to study dynamic behavior of materials having low characteristic impedance. To enable better matching of characteristic impedance with a specimen, polymethyl methacrylate (PMMA) bars are used as the input and output bars. The viscoelastic properties of PMMA are determined in advance through preliminary experiments. In the present SHPB method, the wave analysis of the stress pulses is executed in the frequency domain. Incident, reflected and transmitted pulses on the PMMA input and output bars resulting from a SHPB test are resolved into frequency components by the Fourier transform, and are corrected to be the waveforms at the specimen-bar interfaces. The dynamic properties of the specimen are subsequently determined based on the corrected waveforms. We apply the proposed SHPB technique to several low impedance materials. Some structural adhesives as well as golf ball materials are tested with a view to examining their dynamic viscoelastic properties. The complex compliance for each material is determined as one of the dynamic properties in frequency domain. Furthermore, by employing the FEM simulation on collision tests of a golf ball, it is found that the proposed SHPB method provides reasonable estimations on the dynamic behavior of materials having low impedance. ©2009 Society for Experimental Mechanics Inc.

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Publishing type：Research paper (international conference proceedings)  

Pochhammer-Chree theory was developed for viscoelastic bars of finite thickness in order to study geometrical effects on the attenuation and the dispersion properties. Applying the Fourier transformation to the theory, the attenuation and the dispersion characteristics were evaluated in the frequency region. Attenuation coefficient and phase velocity of Polymethyl Methacrylate(PMMA) with the various kinds of radius about the first, the second and the third mode were calculated over a wide range of frequencies. It was found that both attenuation coefficient and phase velocity indicated almost the same values in the case of dimensionless axis regardless of the mode. Moreover, stress distribution was analyzed. Phase differences generate and the nodes of the line which shows stress distribution appear as the frequency increases. The change of phase differences appears at each inflection point of attenuation coefficient. ©2009 Society for Experimental Mechanics Inc.

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The viscoelastic laws of polymethyl methacrylate (PMMA) and polyvinyl chloride (PVC) have been examined in the frequency domain at room temperature. Strain wave histories resulting from longitudinal impact tests on specimens of hollow cylinders are resolved into Fourier components in order to determine the complex tensile compliance. In a similar manner, the complex shear compliance is also obtained from the analysis of torsional impact tests. The experimental results reveal that 3-element viscoelastic model can be applied to the dynamic behavior of the materials both in tension and in shear in a frequency range 1∼10 kHz. By employing the corresponding relation between elasticity and viscoelasticity, the complex Poisson's ratio and the complex bulk modulus are determined from experimental data of tensile and shear compliances. It is found that the dilatational behavior may be approximated to be elastic as well as the relationship between axial and lateral response. The results suggests that viscous feature of the materials mainly arises from shear properties. © 2008 Society for Experimental Mechanics Inc.

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Publishing type：Research paper (international conference proceedings)  

The problems of the Viscoelastic Split Hopkinson Pressure Bar Method (Viscoelastic SHPB Method) are considered, and applicable conditions of this method are examined. When the loads on the both ends of the specimen are equal, the stress of a specimen is calculated by a transmitted wave and the strain of it is calculated by a reflected wave. It can be said that the reflected wave greatly influences the accuracy of characteristic evaluation of specimens because the peak value of this wave is smaller than that of the incident wave in Viscoelastic SHPB tests. The numerical experiments by the wave propagation analysis of the system that connected the stress bars and the specimen are conducted. The waveform in the stress bars and the specimen are analyzed, and an examination is made of the stress on both ends of the specimen. The waves measured on the strain gage are also predicted, and the peak values of each wave are examined. Appropriate experimental conditions are shown based on these results. The condition can be represented by the ratio of the characteristic values of the stress bars to that of the specimen. © 2008 Society for Experimental Mechanics Inc.

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Language：Japanese   Publisher：Maizuru National College of Technology  

Viscoelastic materials have the lightness and the damping characteristics, so they are widely used in the daily necessaries, the machine parts or the structural materials, etc. The development of plastics which use the materials of biodegradability has advanced in recent years. It is thought that they will be widely applied in various fields in the future. However, the method of evaluating the dynamic characteristics precisely has not been established. In this work, indirect impact method using fixed end reflection was newly proposed as the technique for evaluating the dynamic characteristic of viscoelastic materials. A cylindrical specimen is sandwiched between a viscoelastic input bar and a rigid wall, and is tested indirectly impacting the input bar. Firstly, the reflectivity at the interface between the specimen and the rigid wall was verified by using PMMA bar, and it could be considered that incident waves totally reflected at the rigid wall. Next, the devised indirect method was applied to he three kinds of material for the 3-piece golf ball considered to be difficult to evaluate by using the conventional methods. Consequently, these materials could be determined the dynamic properties at high strain rate.

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Two methods are newly proposed as the technique for evaluating the dynamic characteristics of viscoelastic materials. The first is a direct impact method in consideration of free end reflection. Compressive and tensile waves are generated alternately, propagate in the thin cylindrical specimen, and are superposed each other. Using Polymethyl Methacrylate (PMMA) specimens, accuracy of determined viscoelastic properties is confirmed by comparing the data resulting from an existing method. As an example of low impedance materials, the three kinds of material which consist a particular 3-piece golf ball are experimented by using the present method. The strain rate in the method shows about 101s-1. The second is an indirect impact method using fixed end reflection. A thin cylindrical specimen is sandwiched between a viscoelastic input bar and a rigid wall, and is tested indirectly by impacting the input bar. The same materials (3-piece golf ball) are experimented with the new indirect method and higher strain rates can be accomplished than those are given in the first method. By using proposed methods, the dynamic characteristics of low impedance materials can be reasonably determined at various strain rates.

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Publishing type：Research paper (international conference proceedings)  

The performance of a golf club is evaluated from various viewpoints, such as the flying distance of a golfball after impact, the size of sweet area and the sidespin, etc. Although there are some researches have been reported for the size, the parameter and the geometric optimization or golf club, the research on the detail design of the clubhead is still scarce. In this study, the optimal design of a clubhead is investigated for maximizing the distance of a flying ball. The thickness distribution of the clubface, the shape of clubhead and the mass distribution are set to be the design variables. Since the sensitivity of this kind of problem is difficult to be derived, the basis vector method which is a numerical approach is used. An approach to create the basis vectors using the eigenmodes obtained from modal analysis is presented. Another numerical approach of design of experiment is used to the optimal design of a multi-piece golfball for maximizing the flying distance and improving the feeling at impact. In this case, the thickness and material properties of each layer are design variables. Numerical examples are given to show that this approach is effective to the optimal design of golf clubhead and ball.

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：日本実験力学会  

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：日本実験力学会  

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In the rehabilitation of underground pipes, lining reinforcement is one of the most favored technologies. Deteriorated pipes under the ground are reinforced by spiral profile strips and mortar. From the experimental results of the conventional loading test for relined pipes, we can not observe significant effects of reinforcement. We simulate the fracture process and evaluate relations between load and displacement by a finite element method based on fracture mechanics. Since fracture of the renovated pipe starts from the interior of the mortar in tension, the actual underground condition in compression, can not be evaluated by the conventional loading test. We show that numerical results depend on construction conditions and the size of the pipe and the effect of reinforcement of underground pipes.

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Publishing type：Research paper (international conference proceedings)  

Polymers or composite materials are widely used because of their lightness and damping characteristics. It is important to determine their properties under dynamic loading precisely. Wave propagation is affected not only by the material factor but also by the geometrical factor. In this work, we expand Love-Rayleigh's theory and Pochhammer-Chree's theory of longitudinal waves' propagation in elastic bar into viscoelastic longitudinal waves, and study the influence of three-dimensional effects on the attenuation and the dispersion properties. Some experiments are performed on polymethyl methacrylate (PMMA) specimens, which are generally used in viscoelastic impact tests, with the view of assessing the analytical results. We evaluate the influence of three-dimensional effects on the attenuation and the dispersion by comparing our results with those of some impact tests on PMMA, and the adaptive limit of Elementary theory is discussed.

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：一般社団法人日本機械学会  

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Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

A viscoelastic split Hopkinson bar (SHB) technique is successfully applied to study dynamic behavior of a two-piece golf ball. Strain histories of the incident, reflected and transmitted waves on the input and output bars, resulting from SHB tests on cylindrical specimens of cover and core materials of the two-piece golf ball, are resolved into frequency components by Fourier transformation. Then, in frequency domain waveforms at measurement points are corrected to those at the interfaces between a specimen and bars. The complex compliance of each material is determined by calculating strain-stress ratio in the frequency domain, and 3-element viscoelastic models are subsequently identified based on variations of the complex compliances.

DOI： 10.1299/jsmesports.2004.0_134

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