In daily life, we often use earphone to listen sound and music. However kanal type earphone like earplug shape shuts off the sound of surroundings, thus, is not preferable to use in jogging or driving. Bone conductive speaker is alternative to hear sound from surroundings and player simultaneously. However conventional ones based on piezoelectric material or voice coil are large size, difficult to equip, and amplifier necessary due to the low output force. Here, we propose functional earphone using magnetostrictive vibrator. The device consists of magnetostrictive rod (Galfenol) and magnetic yoke constructing unimorph structure, winding coil, bias magnet and vibration plate. The ring shape vibrator with hole to pass air-conductive sound is easy to equip on ear hole and can generate sufficient sound without additional amplifier. In this study, we fabricate several prototypes to evaluate static and dynamic characteristics to verify the principle and advantages.

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In this study, quasi-isotropic (QI) laminates were fabricated using two types of PA6/CF thin-ply prepregs with different fiber/matrix interfacial properties, and Charpy impact tests and falling weight impact tests were conducted. The effects of layer thickness of prepreg and interfacial properties on the impact energy absorption performance were investigated by clarifying the fracture mode and propagation during impact. The layer thickness of each ply was set to 40, 80 and 120 μm by using thin-ply prepreg with the thickness of about 40 μm made by tow-spreading technology. Charpy impact values were higher for PA6/CFsmooth, where interface fracture was dominant, the values significantly increased as the layer thickness of the prepreg increased. On the other hand, the Charpy impact values of PA6/CFrough, where cohesive fracture is dominant, did not change significantly with increasing prepreg layer thickness. The results of the drop-weight impact test indicate that the layer thickness of the prepregs changing the fracture mode depends on the fiber/matrix interfacial properties. It is clear that the layer thickness at which the "thin-ply effect = reduced delamination" induced by changes in the layer thickness constituting the QI material is affected by the fiber/matrix interfacial properties. From the viewpoint of impact energy absorption, similar to the results of the Charpy impact test, it was shown that more impact energy can be absorbed when large scale delamination occurred.

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The effect of the layer thickness of prepreg on the tensile properties and failure behavior of quasi-isotropic (QI) laminates of thermoplastic CFRP consisting of carbon fiber and polyamide 6 was investigated. The layer thickness of each ply was set to 40, 80 and 120 μm by using thin-ply prepreg with the thickness of approximately 40 μm made by tow-spreading technology. As a result, that so-called "Thin-ply Effect" reported for thermosetting CFRP was not remarkable in this study of thermoplastic CFRP composed of CF/PA6. The tensile stress linearly increased with tensile strain up to the maximum tensile stress independent of the layer thickness. The tensile strength and modulus hardly changed with the layer thickness, although the delamination was interestingly inhibited with decrease of layer thickness. However, although the effect of the layer thickness of the prepreg was slight until the maximum tensile stress was reached, the failure behavior at the final breaking was significantly different depending on the layer thickness. Thinner layers inhibited delamination, and as the layer thickness increased, delamination became the dominant failure mode. Therefore, it was clarified that the effect of the layer thickness of prepreg appeared in the fracture behavior at the final failure after reaching the maximum tensile stress in the QI laminates of CF/PA6.

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The effect of layer thickness of prepreg on the static and dynamic flexural properties of quasi-isotropic carbon fiber reinforced polyamide 6 laminates were investigated. The layer thickness of each ply was set to 40, 80 and 120 μm by using thin-ply prepreg with a thickness of about 40 μm made by tow-spreading technology. Four-point flexural tests were carried out to evaluate the static flexural properties of the laminated materials. The results showed that the flexural strength and modulus did not change much as the layer thickness change. The delamination at interlaminar was interestingly inhibited with decrease of layer thickness. Charpy impact strength evaluated as the dynamic flexural properties was affected by the layer thickness depending on the impact direction. In the impact test where the applied load was parallel to the laminates (edgewise test), the Charpy impact strength was almost unaffected by the layer thickness change. In contrast, Charpy impact strength increased with increasing layer thickness where the applied load was normal to the laminates (flatwise test). In the observation of the fracture appearance after edgewise test, the fiber fractures were observed independent of the layer thickness. Meanwhile, the occurrence of the cracking and delamination at interlaminar were effectively suppressed with decrease of layer thickness in the specimen after flatwise test. The delamination at interlaminar progressed in the in-plane direction with increasing layer thickness, resulting in large-scale delamination. As a result, a large amount of fracture energy could be absorbed. In conclusion, the layer thickness of the laminate is an important material design factor for controlling the impact properties of the composite materials.

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This study presents the effects of fiber characteristics of carbon fiber diameter and surface sizing agents, etc. on the mechanical properties and failure modes of carbon fiber reinforced thermoplastic (CFRTP) laminates. In the study, 90° tensile tests of unidirectional laminates, 3-point bending tests, and CAI tests of quasi-isotropic laminates employing three types of carbon fibers were carried out. Furthermore, the correlation between the failure modes of the laminates under both static and impact loading was also investigated. The 3-point bending tests clarified that increasing the fiber diameter suppressed buckling on the compressive side and improved the flexural properties of the laminates. However, in the case of thick fiber, the interfacial adhesion was decreased and the extent of damage caused by impact loading was larger than that in the case of static loading due to reduction in the number of filaments per unit cross-sectional area. Even when the fiber diameter was increased, the interfacial adhesion, and hence the CFRTP failure modes, were found to be dependent on the sizing agent. Moreover, the failure modes were independent of the loading modes (static or impact) in each carbon fiber/PA6 combination.

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