When solid materials break under impact loading, fast propagating cracks often appear and propagate at a speed more than several hundred m/s. The fast propagating cracks have been studied from the point of view to guarantee the safety of huge infrastructures in our society. One of the keys to understand the behavior of fast propagating cracks is to measuring dynamic stress intensity factor of the cracks. Since the crack speed is high, only the optical methods are available to measure the dynamic stress intensity factor. The present article describes those optical methods from the point of view of measurement accuracy based on the structure of the crack tip and its stress field.
A non-contact full-field surface shape measurement method capable of expanding the measurement region with maintaining high accuracy and high spatial resolution was constructed in order to precisely capture dynamic behavior of the flexible object surface. The constructed measurement method incorporates a connection measurement method into a sampling moiré method with two reference planes. Utilizing the advantage of the high spatial resolution of the sampling moiré method, a wiener filter is spatially applied to remove a white Gaussian noise appearing on the measured data. A surface shape measurement of the vibrating membrane was conducted by the constructed measurement system with two synthesized digital cameras, and two measured data were connected to reproduce the full-field surface shape of the vibrating membrane. The results showed that the constructed measurement system can appropriately capture the mode shape as well as the full-field surface shape of the vibrating membrane with high spatial resolution. This paper offers an effective method to capture a high-resolution surface shape of the vibrating flexible objects.
In this study, to investigate the influence of the measuring frequency on thermo-viscoelastic properties of polymers, dynamic mechanical analyses (DMA, 0.01-0.1 Hz and 0.5-10 Hz) and immersion ultrasonic testing (1-5 MHz) were carried out. In the ultrasonic testing, loss tangent (tan δ) was derived from the phase velocity and attenuation coefficient. The frequency dispersion curves of tan δ measured at several temperatures were incorporated in a single curve (the master curve) by shifting datasets parallel to the logarithmic frequency axis. That is, it was able to estimate the thermo-viscoelastic properties of a soft epoxy resin by applying the time-temperature superposition principle. As a result of comparing both master curves of tan δ obtained by the ultrasonic testing and DMA testing, they were identical qualitatively, but the difference appeared in the viscosity behavior.
In this study, a dynamic mechanical analysis (DMA) using a thermomechanical analyzer was applied to determine the thermo-viscoelastic properties (shift factors and a master curve) of a borosilicate glass (IWAKITE-32) under various frequencies and temperatures. It was confirmed that the storage elastic moduli decreased with increasing temperature in 575℃ to 770℃ and decreasing frequency in 0.001 Hz to 0.1 Hz. The shift factors and master curve in the glass sample were derived using datasets of the storage elastic moduli. The shift factors for the glass obtained by DMA test agreed well with those by a static creep test. However, the master curve of relaxation modulus estimated by each test was different. That is, stress relaxation behavior of glass indicates nonlinearity, and it was suggested that the master curves of relaxation moduli are different depending on measurement methods.
It is necessary to evaluate the mechanical properties at wide range of strain rates, since the general materials have the strain rate dependence of strength. In high strain rate (impact strain rate: 102~104 s-1) test, split Hopkinson pressure bar (SHPB) or direct-impact Hopkinson pressure bar (DHPB) methods are used. However, these methods cannot be compatible with load equilibaium evaluation and large deformation. In addition, these methods only evaluate the mechanical properties at the impact strain rate. From the viewpoint of development of constitutive equation including strain rate effect, evaluation at dynamic strain rate (100~101 s-1), which is intermediate strain rate between quasi-static and impact strain rates, is important factor. In this study, we developed new compressive test, dynamic and impact load-measuring apparatus with opposite load-cells, which can resolve above problems. In order to measure large deformation at dynamic and impact deformation, universal rate range load-cell, which can reduce the influence of the reflected stress wave, was used. In addition, load equilibrium can evaluate using opposite load-cells which consist of movable and stationary load-cells. It was confirmed that this new apparatus have utility through the evaluation of strain rate dependence of strength for pure aluminum and impact deformation for porous aluminum.
The interlaminar interfacial stiffnesses and the ply complex elastic constants of carbon/epoxy composite laminates were evaluated nondestructively from the ultrasonic wave transmission characteristics. Using the through-transmission immersion technique, the energy transmission coefficient of longitudinal wave was measured for unidirectional, quasi-isotropic, and cross-ply composite laminates made of the same UD prepregs for various frequencies and incident directions. The results were then fitted to the theoretical ones calculated by the stiffness-matrix approach with the thin interlaminar resin-rich regions modeled as interfaces with normal and tangential springs in order to identify the interlaminar interfacial stiffnesses as well as the anisotropic viscoelastic constants of the ply constituting the laminates. The validity of the evaluation method was verified on the basis of the experimental results. The evaluated ply complex moduli were found to have comparable values irrespective of the stacking sequence of the laminate. On the other hand, the interlaminar interfacial stiffnesses were found to be smaller when the neighboring plies had the different fiber orientation angles.
The purpose of this study is to develop a universal rate range load-cell (URR load-cell) that can measure the compressive properties of large deformation at wide strain rate range. In the previous studies of other researchers, the impact test methods with reduction technique of reflected stress wave have been proposed for the large deformable cellular materials. However, stress wave propagation behavior in load-cells has not been analyzed in detail. In addition, it has been known that the disturbance of stress wave occurred due to the characteristic vibration of the load-cell. First, we investigated the propagation of the stress wave behavior inside the load-cell by finite element analysis. The result showed that responsiveness could be improved by shortening the length of stress detection part. Second, in order to suppress the characteristic vibration, the optimal URR load-cell shape was investigated. It was revealed that reducing characteristic frequency was effective for suppressing vibration. We confirmed that URR load-cell could measure applied load for a longer time than the split Hopkinson pressure bar method.
History of the experimental mechanics in Republic of Croatia begins in 1920 when Stepan Prokopovych Timoshenko established the Department for testing materials at the Zagreb Polytechnic Institute. Although in the past Croatia was a federal unit of Yugoslavia, in 1992 became an independent country and nowadays the member of European Union. The development of experimental mechanics in Croatia is related to the establishment of Croatian Society of Mechanics and activities and connections to the central European countries through the Danubia-Adria Society of Experimental Methods in Solid Mechanics (DAS). Intensive international cooperation in the framework of the DAS and benefits of development of experimental methods that are used today are suitable for development and research in a number of Croatian laboratories. The paper is divided into three parts: history, creation and development of Danubia-Adria Society and review recent experimental methods and research involving the author: damaging process analysis and experimental analysis in fracture mechanics, application of the object grating method by using 3D image correlation photogrammetry system, the application of the optical method of caustics, structural life management by the survey of different parts of structures and monitoring their integrity over time, biomechanical studies of mechanical testing of bones and ligaments and the application of experimental mechanics in food industry.
This paper presents the development of a new step-climbing mechanism for heavy load carrier. The basic design of the proposed mechanism is illustrated, and its prototype is manufactured. Measured impact acceleration using the prototype. The results from several experiments demonstrate that this prototype is able to drive over the target step 10mm effectively. It is, therefore, shown that the proposed mechanism is effective for driving over a step. However, it was revealed that large impact acceleration occurred to the carrier when descending the step. Thus, the characteristic of shock acceleration when getting down from the step was clarified. Then it was found out that it is able to be reduced the maximum shock acceleration by using rotational dumper.
The aim of this study is to visualize Judo accident using the reconstruction analysis for the medical field, and propose an injury risk assessment system based on detailed statistical analysis of the past cases for calling medical field’s attention. In the assessment system, the mechanical input caused by the accident is obtained from replication of the motion called as Waza in Judo based on game video by using whole body numerical simulation, then the obtained acceleration response of the head was input to a human head finite element model to evaluate the injury risk by using the calculated mechanical parameter inside the skull. In this study, the replicated motion based on the video was verified by comparing the movement loci of the player’s head analyzed by a three-dimensional motion analysis system experimentally. In this paper, two concussion suspected accident cases were analyzed by using the purposed evaluation system, and the concussion was evaluated by seven mechanical parameters generated inside the skull caused by the collision. The injury risk evaluated by the parameters belonged to the dangerous range that may cause concussion. The brain injury risk can be successfully estimated by the reconstructed simulation of the game video and FE analysis.
August 28, 2017 There had been a service stop from Aug 28‚ 2017‚ 1:50 to Aug 28‚ 2017‚ 10:08(JST) (Aug 27‚ 2017‚ 16:50 to Aug 28‚ 2017‚ 1:08(UTC)) . The service has been back to normal.We apologize for any inconvenience this may cause you.
July 31, 2017 Due to the end of the Yahoo!JAPAN OpenID service, My J-STAGE will end the support of the following sign-in services with OpenID on August 26, 2017: -Sign-in with Yahoo!JAPAN ID -Sign-in with livedoor ID * After that, please sign-in with My J-STAGE ID.
July 03, 2017 There had been a service stop from Jul 2‚ 2017‚ 8:06 to Jul 2‚ 2017‚ 19:12(JST) (Jul 1‚ 2017‚ 23:06 to Jul 2‚ 2017‚ 10:12(UTC)) . The service has been back to normal.We apologize for any inconvenience this may cause you.
May 18, 2016 We have released “J-STAGE BETA site”.
May 01, 2015 Please note the "spoofing mail" that pretends to be J-STAGE.
Edited and published by : The Japanese Society for Experimental Mechanics Produced and listed by : Academic Publication and Printings(Vol.10 No.3) Hokuyou Business From Co.,Ltd(Vol.10 No.Special_Issue-) Academic Publication and Printings(Vol.10 No.2) Hokuyou Business From Co.,Ltd(Vol.9 No.Special_Issue-Vol.10 No.1) The Japanese Society for Experimental Mechanics(-Vol.9 No.4)