Effect of Lubrication and Forging Load on Surface Roughness, Residual Stress, and Deformation of Cold Forging Tools

Cold forging is a metal forming that which uses localized compressive force at room temperature. During the cold forging process, the tool is subjected to extremely high loads and abrasive wear. Lubrication plays an important role in cold forging to improve product quality and tool life by preventing direct metallic contact. Surface roughness and residual stress also greatly affects the service life of a tool. In this study, variations in surface roughness, residual stress, and specimen deformation with the number of cold forging cycles were investigated under different forging conditions. Specimens that were made of heat-treated SKH51 (59-61 HRC), a high-speed tool steel with a polished working surface, were used. The specimens were subjected to an upsetting process. Compressive residual stress, surface roughness, and specimen deformation showed a positive relationship with the number of forging cycles up to a certain limit and became almost constant in most of the forging conditions. A larger change in residual stress and surface roughness was observed at the center of the specimens in all the forging conditions. The effect of the magnitude of the forging load on the above discussed parameters is large when compared to the effect of the lubrication conditions

目白大学看護学部看護学科と人間学部人間福祉学科とのIPEの取り組み

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The discovery and follow-up of four transiting short-period sub-Neptunes orbiting M dwarfs

Sub-Neptunes with radii of 2–3 R⊕ are intermediate in size between rocky planets and Neptune-sized planets. The orbital properties and bulk compositions of transiting sub-Neptunes provide clues to the formation and evolution of close-in small planets. In this paper, we present the discovery and follow-up of four sub-Neptunes orbiting M dwarfs (TOI-782, TOI-1448, TOI-2120, and TOI-2406), three of which were newly validated by ground-based follow-up observations and statistical analyses. TOI-782 b, TOI-1448 b, TOI-2120 b, and TOI-2406 b have radii of Rp = 2.740 +0.082-0.079 R⊕, 2.769+0.073-0.068 R⊕, 2.120 ± 0.067 R⊕, and 2.830+0.068-0.066 R⊕ and orbital periods of P = 8.02, 8.11, 5.80, and 3.08 days, respectively. Doppler monitoring with the Subaru/InfraRed Doppler instrument led to 2σ upper limits on the masses of <19.1 M⊕, <19.5 M⊕, <6.8 M⊕, and <15.6 M⊕ for TOI-782 b, TOI-1448 b, TOI-2120 b, and TOI-2406 b, respectively. The mass–radius relationship of these four sub-Neptunes testifies to the existence of volatile material in their interiors. These four sub-Neptunes, which are located above the so-called "radius valley," are likely to retain a significant atmosphere and/or an icy mantle on the core, such as a water world. We find that at least three of the four sub-Neptunes (TOI-782 b, TOI-2120 b, and TOI-2406 b), orbiting M dwarfs older than 1 Gyr, are likely to have eccentricities of e ∼ 0.2–0.3. The fact that tidal circularization of their orbits is not achieved over 1 Gyr suggests inefficient tidal dissipation in their interiors.Peer reviewe

Correlation on Scatter Between Torque Coefficient and Bolt Preload in Pipe Flange Connection

In this paper, a mechanism of variation in axial bolt force in pipe flange connection during bolt tightening process is investigated. Especially, Correlation between torque coefficient and bolt preload is investigated. The actual pipe flange connection is tightened by a wrench due to the torque control method. Axial bolt forces were measured in the tightening process. The three types of gasket are chosen in this paper. As a result the good relationships are seen between torque coefficient and axial bolt force. The effect of gasket material on the relationships between torque coefficient and bolt preload is not seen.</jats:p

Thermal Stress Analysis and the Sealing Performance Evaluation of Bolted Flange Connection at Elevated Temperature

In designing bolted flange connections under heat conduction conditions and internal pressure, the characteristics such as the contact gasket stress are important factors from reliable design standpoint. They must be examined analytically and experimentally. In this paper, in order to examine the above characteristics, thermal stress of bolted flange connections subjected to internal pressure and heat conduction conditions is analyzed using the theory of elasticity and FEM calculations. The effects of gasket properties and nominal diameter of flanges on the above characteristics are examined numerically. In the experiments, the amount of helium gas leakage in the connection was measured. Using the obtained gasket stress at elevated temperature, a method for estimating the amount of gas leakage is proposed. The analytical results of the above characteristics are compared with the experimental results, with reasonable agreements. The results reveal that the sealing performance increases due to the gasket properties as the temperature increases in this study.</jats:p

Effect of Scatter in Axial Bolt Force on the Sealing Performance of 20” Inch Pipe Flange Connections With CSG Under Internal Pressure

Since a scatter in axial bolt force exists in assembling the pipe flange connections, it is important to evaluate the effect of scatter in axial bolt force on the sealing performance of pipe flange connection. The FE and experimental analyses were done to evaluate the effect of scatter in axial bolt force on the sealing performance of pipe flange connection with 20 “nominal diameter. The results revealed that the large diameter pipe flange connection was sensitive to the scatter in axial bolt force. Besides, the large diameter pipe flange affected more by flange rotation when internally pressurized. As a result, a larger diameter pipe flange connection with scattered bolt preload showed poor sealing performance. The experimentally obtained scatter in axial bolt force as assembled was taken into account in FE analyses and the effect of the scatters on the contact gasket stress distributions was shown numerically. FE results show that the sealing performance is reduced due to the distributed gasket stress and bolt force scatter in the axial direction.</jats:p

New Design Formula for Bolted Joints Under Tensile Loads

In designing a bolted joint, it is important to estimate an increment in axial bolt force when an external tensile load is applied to an assembly. The ratio of the increment Ft in the axial bolt force to the external tensile load W is called the load factor φ(= Ft/w). The formula φ = Kt/(Kt+Kc) proposed by Thum has been applied for estimating the value of the load factor φ, where Kt is the spring constant of bolt-nut system and Kc is the compressive spring constant of clamped parts. It has been found that the value of the load factor varies with the position of load application to the assembly. Then, a method to compensate Thum’s formula was proposed. However, this compensation is made empirically and the theoretical background is not made clear. In this paper, the concept of the tensile spring constant Kpt for clamped parts is introduced newly when an external load is applied to the outer circumference of clamped parts (hollow cylinders) and a method for estimating the value of the load factor exactly is proposed by using Kpt. The value of Kpt is analyzed using an axisymmetric theory of elasticity. For verification of the proposed method, experiments were carried out to measure the load factor. A fairly good agreement is seen between the analytical and the experimental results of the values of the load factor while the values of the load factor obtained from Thum’s formula were so different with the experimental results. The reason why the difference in the values of the load factor is substantial between values and the values obtained from Thum’s formula is elucidated. It is found that the value of the load factor decreases as the outer diameter of the hollow cylinder increases and the as thickness of the clamped parts decreases. In addition, FEM calculations for the load factor are carried out. The FEM results are in a fairly good agreement with the theoretical results.</jats:p

Axi-Symmetrical Stress Analysis and Sealing Performance Evaluation of a Pipe Flange Connection Under Elevated Temperature and Internal Pressure

The pipe flange connections have been widely used in mechanical structures and these are mainly used under internal pressure and elevated temperature. Some investigations have been performed on mechanical behaviors such as the contact gasket stress distribution of pipe flange connection under internal pressure. However, the effects of elevated temperature on the sealing performance and mechanical behavior in the pipe flange connection have not been analyzed exactly. To design a pipe flange connection, it is necessary to know the effect of elevated temperature and the detailed flange strength for the hub and the contact gasket stress distributions in the connection. In this paper, the stress analysis of a pipe flange connection under elevated temperature and internal pressure is carried out taking into account a non-linearity and hysteresis of the gasket using the axi-symmetric theory of elasticity. The contact gasket stress distributions at the interfaces, the hub stress, in the pipe flange connection under elevated temperature and internal pressure are analyzed. Using the obtained contact gasket stress distributions, the amount of gasket leakage (He gas) is estimated. Leakage tests of the pipe flange connections were also conducted and the temperature of pipe flange connection was measured using thermoelectric couples. As a result, the difference of temperature between inner and outer is about 10%. The contact gasket stress was increased as the heated temperature was increased.</jats:p