Key Engineering Materials Vols. 297-300

Abstract: In order to investigate the effect of a confinement condition on the damage induced by a spherical impact, an experimental setup that can impact contact pressure to the specimen through a pressing die was composed. The steel and the WC balls in 3mm diameter impacted to the soda-lime glass specimen with dimension of 33×33×8m in the impact velocity range of 30m/s to 200m/s. Three different conditions are given for the impact damage investigation, which are the case without a pressing die and the cases of p=0MPa and p=200MPa with a pressing die. The stress distribution in the glass specimen by impacting the particle was also evaluated using MARC s/w system. The particle impact produced various kinds of the damage such as the ring and the cone cracks, the radial cracks and the craters. The contact pressure applied to the specimen changed stress fields in the specimen. The damage zones of the specimen without a pressing die increased as the impact velocity increased. The damage extents in the specimen with the contact pressure of 200MPa were reduced as compared with the case of those without a pressing die.

Abstract: The damage behaviors induced in a SiC by a spherical particle impact having a different material and size were investigated. Especially, the influence of the impact velocity of a particle on the cone crack shape developed was mainly discussed. The damage induced by a particle impact was different depending on the material and the size of a particle. The ring cracks on the surface of the specimen were multiplied by increasing the impact velocity of a particle. The steel particle impact produced the larger ring cracks than that of the SiC particle. In the case of the high velocity impact of the SiC particle, the radial cracks were generated due to the inelastic deformation at the impact site. In the case of the larger particle impact, the morphology of the damages developed were similar to the case of the smaller particle one, but a percussion cone was formed from the back surface of the specimen when the impact velocity exceeded a critical value. The zenithal angle of the cone cracks developed into the SiC decreased monotonically as the particle impact velocity increased. The size and material of a particle influenced more or less on the extent of the cone crack shape. An empirical equation was obtained as a function of impact velocity of the particle, based on the quasi-static zenithal angle of the cone crack. This equation will be helpful to the computational simulation of the residual strength in ceramic components damaged by the particle impact.

Abstract: In this study, a bar impact test of low velocity was carried out to gain an insight into the damage mechanism and sequence induced in alumina plates during quasi-static impact conditions. An experimental setup which could measure directly the impact force applied to the specimen and supply a compressive pre-stress to the specimen by utilizing an long bar impact was devised. During the bar impact testing, the influence of the pre-stress applied to the specimen along the impact direction on the fracture behavior was investigated. The measured impact force profiles explained well the damage behavior induced in alumina plates. The application of higher pre-stress to the specimen led to less damage due to the suppression of radial cracks which was caused by the increase in the apparent stiffness of the plate. The observed results showed the following sequence in damage development: The development of cone crack at the impact region, the formation of radial cracks from the rear surface of plate depending on the plate thickness, and the occurrence of crushing or fragmentation within the cone envelope.

Abstract: Brain damage by the impact force was evaluated by the numerical analysis with a three dimensional Finite Element (FE) model. The FE model was constructed from the MRI data of a subject, and visco-elastic behavior for constitutive equation was applied to the brain tissue. From the FE simulation, brain damage and deformation of the frontal head impacted by a steel impactor were analyzed. The variations of head acceleration and Intra-Cranial Pressure (ICP) during the impact were analyzed in order to evaluate Traumatic Brain Injury (TBI). In addition, relative displacement between the skull and the brain due to head impact was investigated. And, pathological severity was evaluated according to Head Injury Criterion (HIC) from the FE simulation. The analytic results of brain damage showed a good agreement with those of the cadaver test performed by Nahum et al. (1977) and other medical reports. And then, the variation of the HIC value was evaluated according to various impact conditions. This study would provide useful data and methodology in the field of biomechanics for analyzing the brain damage by head impact.

Abstract: In this paper, the energy absorption characteristics on extruded aluminum box-section strengthened with carbon-fiber-reinforced plastics (CFRP) laminates and/or foam material were investigated under impact loading. Impact tests using a pneumatic impact tester were conducted with the specimens in three-point bending flexure with consideration given to the side-door impact beams in vehicles. The absorbed energy to the specimen during the impact was determined from the loaddisplacement curve, which was obtained from the strain gauge attached to the impactor and the laser displacement transducer. From the results, it was found that the strengthening by externally bonding with CFRP laminates improved the impact-induced energy absorption. Also, the effect of the improvement was clearly seen in the case of the use of filling form material in the aluminum extrusion together with attaching CFRP laminates.

Abstract: In this paper, the energy absorption characteristics on extruded aluminum box-section strengthened with carbon-fiber-reinforced plastics (CFRP) laminates and/or foam material were investigated under impact loading. Impact tests using a pneumatic impact tester were conducted with the specimens in three-point bending flexure with consideration given to the side-door impact beams in vehicles. The absorbed energy to the specimen during the impact was determined from the loaddisplacement curve, which was obtained from the strain gauge attached to the impactor and the laser displacement transducer. From the results, it was found that the strengthening by externally bonding with CFRP laminates improved the impact-induced energy absorption. Also, the effect of the improvement was clearly seen in the case of the use of filling form material in the aluminum extrusion together with attaching CFRP laminates.

Abstract: The package used to transport radioactive materials, which is called by cask, must maintain the structural integrity for the requirements of hypothetical accident conditions, 9m free drop of the thick plate impact. These requirements for the cask design should be verified through test or finite element analysis to confirm the regulatory guide. In this paper, three dimensional impact analysis using ABAQUS/Explicit code under 9m free drop of the thick plate impact condition for the KSC-4 cask is performed. As the results, maximum stress intensity on each part of the cask and deformation shape of the cask is calculated and the structural intensity of the cask is evaluated by NRC Regulatory Guides.

Abstract: The impact fracture behavior of Zr-based bulk metallic glass was investigated by an instrumented impact tester using subsize Charpy specimens. Influences of loading rate and notch shape on the fracture behavior of amorphous Zr-Al-Ni-Cu alloy were examined. As a result, the maximum load and absorbed fracture energy under impact loading were lower than those under quasi-static loading. A large part of the absorbed fracture energy in the Zr-based BMG was consumed in the process for crack initiation and not for crack propagation. In addition, fractographic characteristics of BMGs were investigated. Fractured surfaces under impact loading are smoother than those under quasi-static loading. The absorbed fracture energy appeared differently depending on the appearance of the shear bands developed. It can be found that the fracture energy and fracture toughness of Zr-based BMG are closely related with the extent of shear bands developed during fracture.

Abstract: Slipping characteristic on the contacts between the tubes and the supports is investigated to study the fretting wear of a vibratory tube. Tests were carried out to simulate the vibration of the fuel rods supported by the springs and dimples. A tube was forced to vibrate with 30Hz. The supporting condition was varied artificially: positive contact force or gap existence. During the tube vibration, amplitudes were measured continuously in the vicinity of the supports. Simple equations were derived to evaluate the slip displacement on the contacts. As a result, it was found that the supporting condition affected the vibration characteristic near the contacts. In the positive contact condition, the phase difference of the vibration signals at both sides of the contact was 180 degrees. It is altered in the gap condition and the higher frequency components than 30Hz appeared. The severer wear in the case of the gap existence is discussed with the evaluated slip distance per cycle.

Abstract: Hydroxyapatite (HA) powders were directly synthesized in simulated body fluid (SBF) at 37°C, without the need for high-temperature calcified. These powders were found to contain trace amount of CO32-, Cl-, Na+ and K+ impurities, originated from the of SBF solutions during their deposition. The characterizations of the synthesized HA powders were performed by X-ray diffraction (XRD), Fourier-transformed infra-red spectroscopy (FTIR) and Transmission electron microscope (TEM). The experimental results showed that the HA synthesized by the SBF route might be more close to that human bone in structure and compositions. Furthermore, the processes flow for HA synthesis was optimized and the synthesized mechanism was also discussed.