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神宮, 利夫 ; 石坂, 純一 ; 羽鳥, 勲
概要:
application/pdf<br />Journal Article<br />Experience has shown that loosening occurs, when stress wave and vibration are emitted to the screw fastening system, even if the tightening is sufficient. In order to clarify the cause of
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the looseness, the stress wave emitted from bolt shank which constitutes the screw fastening system is made to impinge to engagement conjunction of screw thread, and the problem of the loseness has been studied experimentally. It was proven that seperating the engagement of screw thread of the bolt and nut by the stress wave was one of the causes of the loseness. This paper studies the looseness by emitting stress wave from both of the bolt and the nut. Noticing that soft materials have buffer effect for the impact, the prevention of the looseness is studied by using the soft washer in the screw fastening system.
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| 2.
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神宮, 利夫
概要:
application/pdf<br />Journal Article<br />Experience has shown that a bolt-nut assembly system properly tightened can be loosened under vibrating load or impact. This paper experimentally investigates the loosening response of an
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assembly when a stress wave is transmitted from a gross area of a bolt, a face of a circular disk, or a screw thread of the thick circular disk assembly fastened by the bolt-nut unit. When a falling bar strikes the opposite side of a threaded rod fastened to the circular disk, or a falling circular pipe collides with the circular disk or with the anvil attached to the end of a screw, a stress wave propagating from the collision interface is transmitted into the assembly. The axial stress of a bolt tightened by a hexagonal nut in conjunction with a plain washer is measured, while a number of incident waves are impinged into the assembly. The shift of axial stress due to the stress wave transmitted from the portion of the screw thread is the largest. The cause of the loosening is investigated by observing the stress waves transmitted into the circular disk assembly system.
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神宮, 利夫 ; 松本, 浩之
概要:
application/pdf<br />Journal Article<br />When a hard steel sphere over a range of impact velocities (80-100 m/s) and im
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pact angles (15-90°) is projected obliquely onto three ductile metal targets, the shapes of the plastic craters and the softening or hardening of the craters were measured. Their variations with impact angle were experimentally obtained. It is observed that a pronounced lip is formed at the end of the crater for an impact angle of 45°in the three targets. It can be assumed that such a large lip will be easily detached during abrasive grit-blasting. The hardness at the crater periphery except for the lip and the interior of the crater were measured by means of a micro-vickers hardness tester. The hardness of a mild steel crater at an impact angle of 15°is less for the residual tensile deformation due to the tangential component of the oblique impact than for the virgin specimen. The hardness of the craters of other soft metal targets except for steel increase with the impact angle. Cracks in the piling-up were observed using SEM. The impact and rebound angles of the sphere projectile were also measured using a CCD camera.
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| 4.
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神宮, 利夫
概要:
application/pdf<br />Journal Article<br />When a bar falling or moving at any speed strikes the opposite side of threaded rod fastening a thick circular disk, stress wave propagating from the collision interface is transmitted into the
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assembly system, tightening the thick circular disk by the bolt-nut unit. This paper experimentally studies the relationship between the loosening response of bolt-nut fastening assembly system and stress wave modes (tension or compression) along the direction of propagation. The technique of observing the loosening of a bolt-nut assembly system by monitoring the configuration of stress waves reflected from the surface of a thick circular disk is presented. The axial stress of a bolt tightened by a hexagonal nut in conjunction with a plain washer, a spring washer or a flanged nut is measured, when a number of incident waves are impinged into the assembly system. The shift of axial stress due to tightening by flanged nut is the smallest.
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| 5.
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神宮, 利夫
概要:
application/pdf<br />Journal Article<br />This paper describes the transient response of a robotic arm which rebounds from a wall or is interrupted by the wall, after the free end of the arm comprising a beam attached to a hub gyrating
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about an axis, strikes the surface of a rigid wall. Two integro-differential equations are produced to use Hamilton's principle, providing the variational method upon which the finite-element weak form is built. The flexure energy of the beam is derived by using the Bernoulli-Euler beam theory. The kinetic energy caused by the moment of inertia of the hub is also taken into account. The finite-element method is used to discretize the equations of motion. The results of simulation are compared to time histories of bending strain measured by a strain gage. The variations of bending strain consist of the basic frequency mode and other frequency modes. The time histories of the simulated bending strain is in agreement with that from experiment, except in high-frequency modes.
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神宮, 利夫 ; 川端, 一司
概要:
application/pdf<br />Journal Article<br />The misalignment of the flat anvil of a testing machine with the end of a circular rod specimen causes local crushing due to the stress concentration and bending moment, which must be avoided in
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compression tests. When very hard material, such as fine ceramics, is tested using the compression split Hopkinson bar, the hard specimen may be indented into the incident and transmission bars. In this paper, the insertion of a thin metal plate between the bar-specimen interface in the conventional compression split Hopkinson bar system was examined to prevent indentation. The stress pulse in the incident and transmission bars is measured using the thin steel plate (thickness 0.4 and 1 mm), copper (1 mm) and aluminium (1 mm) , and the pulse profile is investigated. The configuration of the wave observed using the thin steel plate (0.4 mm) is the sharpest, and is similar to that without the plate. The rise of pulses using the steel plate (1 mm) is ramplike. With use of a copper plate and aluminium, the two-step profile appears. The stress-strain relationship evaluated from these stress pulses was compared with that obtained in the static test. The dynamic strength of ceramics is less than about half the static strength.
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| 7.
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神宮, 利夫
概要:
application/pdf<br />Journal Article<br />The strength of unidirectionally reinforced carbon/epoxy composites (CFRP) subjected to the compressive impact load was measured by the Split Hopkinson Pressure Bar Method (S. H. P. B. M),
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then the effect of fiber orientation on the compressive impact strength was investigated. Stress of the specimen, caused by multiple reflected stress waves at its ends in contact with the incident bar and transmitter, was analysed based on one-dimensional stress wave theory. The resulting formulation can be used to evaluate either the linear or nonlinear stress-strain relation. The strength of a specimen of zero-degree fiber is the greatest. The strain of a specimen of 45-degree fiber is the largest. A split fracture parallel to the fiber appeared in the specimen of zero-degree fiber. Inclination of the fracture surface of specimens of 30-, 45- and 60- degree fiber is in alignment with the fiber orientation. Tat of 90 degrees is not. The impact strength is about 80 MPa larger than the static strength. In contrast, the dynamic elongation is smaller than the static elongation.
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神宮, 利夫 ; 永倉, 和郎
概要:
application/pdf<br />Journal Article<br />The fracture strength of the adhesive butt joint of a round steel bar bonded by cyano-acrylate for tensile stress waves and alternating waves was measured experimentally. The tensile stress wave
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initiates in the round bar with the adhesive butt joint as the anvil attached at the end of the bar is struck by the dropping a circular cylinder. The alternating stress waves, which change from compressive to tensile, repeatedly propagate in the longer bar, as two bars of unequal length coaxially collide into each other. The location of the joint is designed to agree with the position at which the intermittent or serial alternating stress waves are observed. The fracture strength of the adhesive decreases as the acting period of waves increases. The fracture strength for intermittent waves is larger than for serial waves. The dynamic fracture strength was compared with the result for static fracture strength.
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| 9.
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神宮, 利夫 ; 永倉, 和郎
概要:
application/pdf<br />Journal Article<br />A robotic manipulator is simplified by numerous beams with pinjoints between them and an anchor pinjoint at the base. The beams under impact loading are allowed to rotate about the axis of the
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pinjoint. The dynamic response of a vertical chain for a transverse load suddenly applied along every beam is theoretically analysed. The angular and linear acceleration of the mass center of beams, reaction force at the pinjoints, shearing force and bending moment along the beams is presented as a function of impact load. As the vertical chain consisting of one plaster beam and one steel beam, or two with a pinjoint between them, is subjected to the collision of the flier steel rod accelerated by the air gun, the location of the fracture of the plaster beam is measured experimentally. The validation of the theory is confirmed by comparison of the location of the critical bending moment with the position of the fracture of the beam.
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| 10.
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神宮, 利夫 ; 永倉, 和郎
概要:
application/pdf<br />Journal Article<br />When a striker of finite mass impinges on the end of bar which is imperfectly fixed at its distal end, the impact stress of striker and bar is analysed by accounting for reflection coefficient
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of stress wave at the striker-bar interface and terminal end of bar. The reflection coefficients of stress wave in this case are determined in the same way with the evaluation of reflection and transmission of wave passing through shafts having discontinuous cross-sectional area or interface of dissimilar materials. The results of analysis are compared with impact stress of bar perfectly fixed and experiment. The impact stress of bar imperfectly fixed is about 60%-80% of perfectly. The period of impact stress acting in imperfect fixing bar is shorter than in perfect fixing bar. Although the magnitude of impact stress predicted by the analysis is in agreement with the experiment, the shape of wave is a little difference. It is shown that the impact stress of striker-bar interface can be indirectly determined by evaluating the stress caused in striker.
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