摘要 :
Dynamic FEM and DEM simulations are carried out to investigate dynamic penetration of a projectile into a target of granular medium. Spatial distribution and time dependence of ejecta are clarified together with their trajectories...
展开
Dynamic FEM and DEM simulations are carried out to investigate dynamic penetration of a projectile into a target of granular medium. Spatial distribution and time dependence of ejecta are clarified together with their trajectories in medium. Highly densified region is generated just ahead of the projectile and propagates leaving rarefied regions. Force on the projectile is fully discussed in connection with dynamic behavior of granular target.
收起
摘要 :
It is well known that electromagnetic phenomena are often observed preceding earthquakes. However, the mechanism by which these electromagnetic waves are generated during the fracture and deformation of rocks has not been fully id...
展开
It is well known that electromagnetic phenomena are often observed preceding earthquakes. However, the mechanism by which these electromagnetic waves are generated during the fracture and deformation of rocks has not been fully identified. Therefore, in order to examine the relationship between the electromagnetic phenomena and the mechanical properties of rocks, uniaxial compression and three-point bending tests for two kinds of rocks with different quartz content, granite and gabbro, have been carried out at quasi-static and dynamic rates. Especially, in the bending tests, pre-cracked specimens of granite were also tested. Using a split Hopkinson pressure bar and a ferrite-core antenna in close proximity to the specimens, both the stress– strain (load–displacement) curve and simultaneous electromagnetic wave magnitude were measured. It was found that the dynamic compressive and bending strengths and the stress increase slope of both rocks were higher than those observed in static tests; therefore, there is a strain-rate dependence in their strength and stress increase rate. It was found from the tests using the pre-cracked bending specimens that the intensity of electromagnetic waves measured during crack extension increased almost proportionally to the increase of the maximum stress intensity factor of specimens. This tendencywas observed in both the dynamic and quasi-static three-point bending tests for granite.
收起
摘要 :
A series of three-point bending tests for granite consisting of quartz, plagioclase, alkali feldspar and biotite was carried out at quasi-static and dynamic rates to examine the relation between its mechanical properties and elect...
展开
A series of three-point bending tests for granite consisting of quartz, plagioclase, alkali feldspar and biotite was carried out at quasi-static and dynamic rates to examine the relation between its mechanical properties and electromagnetic phenomena during fracture. The output of ferrite-core antenna, which was located close to the specimen in a shielding box made of Permalloy plates, was measured through a band-pass filter. The dynamic bending strength was larger than the static one, i.e. the positive strain-rate dependence was observed in the strength of granite. It was also found that the intensity of electromagnetic waves measured in dynamic tests was much greater than that observed in static tests. This means that the electromagnetic phenomenon strongly depends on the loading rate, too.
收起
摘要 :
Historical review of research and development of the SHPB method in Japan is outlined. After introduction of the SHPB in early 1960s, various kinds of compression, tension, torsion and bending tests have been performed in Japan an...
展开
Historical review of research and development of the SHPB method in Japan is outlined. After introduction of the SHPB in early 1960s, various kinds of compression, tension, torsion and bending tests have been performed in Japan and are presently shown together with special techniques such as the strain rate change test and the ramped wave method. Applications of the SHPB method to characterize dynamic response of materials from various points of view are also described in connection with its flexibility and simplicity. Current activities related to the SHPB method are briefly explained.
收起
摘要 :
To characterize damage and deformation in an impacted area of structure caused by flying foreign objects, it is fundamentally needed to measure the acting force and its distribution over the area. In the present experiments, it wa...
展开
To characterize damage and deformation in an impacted area of structure caused by flying foreign objects, it is fundamentally needed to measure the acting force and its distribution over the area. In the present experiments, it was attempted toidentify visually the impact force using the pressure sensitive paper 'Prescale'. A split Hopkinson pressure bar method was used to evaluate the sensitivity of the paper under impact loading. It is found that the pressure sensitive paper instantaneouslyresponds even for the impact loading of which duration is several hundred microseconds, while the sensitivity is significantly reduced when compared to the quasi-static loading. Hertzian impact tests were tried to visually evaluate pressure distributionsusing the pressure sensitive paper, and the experimental results were discussed.
收起
摘要 :
In this study, the behaviour of elastic stress wave propagating two connected cylindrical bodies was examined using dynamic finite element method (FEM). They consist of two bodies with different cross-sectional area, different You...
展开
In this study, the behaviour of elastic stress wave propagating two connected cylindrical bodies was examined using dynamic finite element method (FEM). They consist of two bodies with different cross-sectional area, different Young’s modulus and identical mechanical impedance. It was found that when an incident wave passes through the boundary step between two different cross-sectional areas, a pair of reflected waves which has the same amplitude and opposite sign was observed, despite the same mechanical impedance. This phenomenon appears to be caused by the loading and unloading the boundary section due to the arrival and the passage of incident wave. It was also found that a connection manner to insert the smaller diameter cylinder into the other cylinder with a little length is quite effective for the reduction of the reflected wave, because of the superposition of waves from two edges and control of local deformation. This phenomenon was verified by a series of impact experiments using two cylindrical bodies connected by interference fit.
收起
摘要 :
The foamed film as the shock absorption material has attracted much attention because it is thin (100?μm ～ 400?μm) and has a closed cell structure. However, the dynamic mechanical properties have not been reported in the foamed...
展开
The foamed film as the shock absorption material has attracted much attention because it is thin (100?μm ～ 400?μm) and has a closed cell structure. However, the dynamic mechanical properties have not been reported in the foamed film. The purpose of this study is to elucidate the compressive behavior of the foamed polyethylene film at the wide strain rate range. First, the new compressive test apparatus for the dynamic strain rate, the drop-weight testing machine with opposed load cell, was developed, which can be also evaluated the dynamic stress equilibrium of the specimen. It is confirmed that the compressive flow stress increased with increasing the strain rate, regardless of the film thickness. The foamed polyethylene film has the high strain rate sensitivity in the quasi-static deformation. On the other hand, there is almost no change of the strain rate sensitivity in the dynamic and the impact deformation. In order to investigate the mechanism of strain rate dependence, the foamed polyethylene film was observed by X-ray computed tomography scanner before and after compressive test. The fracture of the closed cell only occurred in the quasi-static deformation. It was clarified that the strain rate sensitivity of the foamed film depends strongly on that of the construction material, polyethylene.
收起
摘要 :
In this study, the effect of strain rate on the strength and the absorbed energy of polylactic acid resin foam (PLA-foam), which is generally known as one of carbon-neutral and environmentally-friendly polymers, were examined by a...
展开
In this study, the effect of strain rate on the strength and the absorbed energy of polylactic acid resin foam (PLA-foam), which is generally known as one of carbon-neutral and environmentally-friendly polymers, were examined by a series of compression tests at various strain rates from 0.001 to 750 s~(-1). For the measurements of the impact load and the displacement of specimen, a special load cell and a high-speed video camera were used, respectively. The flow stress of the PLA-foam strongly depends upon not only strain rate but also density of specimens. Thus, a new technique to eliminate the effect of the difference in the specimen density was proposed and successfully applied. It was also found that the strain-rate dependency of PLA-foam can be expressed by a simple power law.
收起
摘要 :
In order to evaluate dynamic deformation behaviors under high strain rates, Kobe Steel has developed and applied a Split-Hopkinson Bar (SHB) apparatus. This paper discusses the validity of the strain measurements and strain rates ...
展开
In order to evaluate dynamic deformation behaviors under high strain rates, Kobe Steel has developed and applied a Split-Hopkinson Bar (SHB) apparatus. This paper discusses the validity of the strain measurements and strain rates measured by this SHB apparatus. The strain waves that propagated in the incident and transmitted bars and the specimen are captured using a highresolution type high-speed photography in detail. The strain wave propagated many times in the incident and transmitted bars and the specimen when the specimen was not broken. The amount of the deformation of the specimen decreases with the propagation frequency of the incident wave. On the other hand, to improve accuracy at the strain and strain rate calculated by the one-dimensional stress wave theory, Young's modulus, the longitudinal wave speed, and the density were accurately determined. It was understood that the calculation value showed the strain and strain rate captured with the high-speed photography are a good agreement. As a result, the validity of the measurement accuracy of this SHB could be shown.
收起
原文获取