Hisashi Naoi

Effects of Mandrel Shape and Dimension on Deformation Behavior for Hot Mandrel Bending

Elbows, which belong to butt-welded steel pipe joints, are used in piping of various plants. Elbows are mainly manufactured by hot mandrel bending. In hot mandrel bending, short straight pipes are inserted into an inner tool of mandrel and are bent at specified bending radius, while they are compressed by pusher from one end of pipes and their outer diameter are expanded. Elbows manufactured by this bending process have small deviation in wall thickness and also high accuracy in roundness, even when they are processed into short bending radius. Shape and dimension of mandrel are designed by trial and error through many experimental tests. However, there are a few research works on hot mandrel bending. We focus on expansion ratio and bending radius ratio of mandrel, which are main variables, and greatly affect deformation behavior of hot mandrel bending. And we conducted experiment and numerical analysis using mandrels which have several kinds of expansion ratio and bending radius ratio. Following items are clarified by this research work: At extrados, axial strain decreases slightly, when expansion ratio increases. As a results, neutral axis of bending moves from extrados toward intrados by increasing of expansion ratio. And at intrados, wall thickness strain at intrados decreases, when expansion ratio increases. Wall thickness strain at intrados decreases, when bending radius ratio increases. Forming load increases, when expansion ratio increases and with bending radius ratio decreases. When experimental conditions do not coincide with optimized expansion ratio and bending radius ratio, deviation of wall thickness occurs in elbow.Copyright

Study on Deformation Behavior of the Buried Pipes for Cables of Electricity at Ground Subsidence

In this study, we have an object to investigate the piping system buried in the ground at ground subsidence. Therefore, we conduct bending test of bellows pipes for buried piping using experimental equipment which is simulator for assumed ground subsidence. Grade of bellows pipe is stainless steel. We measure load and displacement and calculated stress and strain appeared at bellows pipe. We conduct bending test at four kinds of experiment conditions for outer surface of bellows pipe, that conditions are non-restraint, soil or gypsum are filled around outer surface of bellows pipe, buried piping system is set in the box in which soil is filled. By analyzing these experimental results, we clarify deformation characteristic of bellows pipes for buried piping at ground subsidence, and we verify the application of bellows pipe to buried piping.Copyright

Deformation Behavior of Bellows Pipes for Laying Cables Under Ground by Axial Load and Bending Moment

Recently, electricity demand is rising steeply with advance of science. Additionally quantity of cables such as telephone and optical fiber is rising with communications development and increase of residence. These cables are untidily wired in the air with telephone pole. They impair cityscape and disturb pedestrian safety. Therefore improvement of procedures installing cables is requested. In order to solve it, the plan [1] which buries cables protected in pipes under ground is progressing. They are called buried pipes and consist of straight pipe made from stainless steel or plastic. However there is concern that the buried pipe is crushed and broken by the complex load due to earthquake and ground subsidence. Thus, it is necessary to develop the buried pipe with function of flexibly against damage or rupture. We focus attention to U-type bellows pipe with function of flexibly. In this study, we conduct tensile, compressive, bending test and numerical analysis of those tests using finite element method. From result, we investigate for the relationship between mechanical characteristic and deformation behavior. We study application of bellows pipe to buried pipe. In this study, we examined and analyzed deformation behavior when axial load and bending moment were given to specimens. Examinations items are as (1) we measured load, elongation bending radius by using are experimental device which modeled ground subsidence. (2) We obtained deformation behavior by numerical analysis by using constituted equations of solid mechanics. (3) We conducted simulation analysis of models constructed by finite element method. By comparing these three items, the deformation behavior is clarified.Copyright

Shape Recovery Characteristics of Pipes With Heavy Wall Thickness Made by Ferrous Shape Memory Alloy

Recently, ferrous shape memory alloys have been developed. Shape recovery strains of ferrous shape memory alloys are smaller than those of Ti-Ni shape memory alloys[1,2] . Strength, ductility and workability of the former alloy are higher than those of the latter alloy. Therefore, ferrous shape memory alloys are tried to apply for several kinds of pipe joints, as an example, joints of support pipes in the tunnel[3] . One of the other applications, the alloys is used as the material of simulation model to analyze the deformation behavior of the core tube in the fast breeder reactor. In this study, we investigated the shape recovery characteristics of pipes with heavy wall thickness made by ferrous shape memory alloy. Chemical compositions of this alloy are Fe, 28%Mn, 6%Si and 5%Cr. The alloy is melted, and round bars are manufactured by rolling, and pipes are machined from them. Tensile strength is 1100MPa, and yield strength is 320MPa. Ratios of wall thickness to central diameter of pipes are 10, 15, 20 and 25%. We insert tapered punch in the pipe, and expanded it by test machine. Then the circumferential strain of the center diameter of the pipes is 7%. And finally, the heat treatment is conducted at 350 degrees C in order to induce the shape recovery strain, and the pipe diameter decreases by means of austenitic transformation. The results obtained by the experiment are shown as follows. As the value of ratios of wall thickness to center diameter decreases, shape recovery strain increases and seems to approach the shape recovery strain obtained by uni-axial tension test, which was conducted in the past time.Copyright

Deformation Behaviors of Aluminum Pipes Compressed in the Direction of Pipe Axis

Recently there are strong demands for reduction of carbon dioxide exhausted from cars on the viewpoint of global warming prevention. And, improvement in safety of cars is needed with increase of its speed. The main method to satisfy the former demand is to reduce the mass of cars, and main procedure to solve the latter subjects is to protect lives of crews in the head-on collision of automobiles. Lightweight members to absorb the energy at the collision have been installed in the engine room in order to satisfy abovementioned both demands. The purpose of this study is to optimize cross sectional size and shape of the aluminum pipe as the lightweight members for energy absorption.(1)(2)(3) In this report, the specimens are aluminum pipes whose shapes are hexagon and octagon. And ribs that connect one corner to opposite corner of the specimens in order to increase the energy absorption at the collision are installed inside the hexagonal and octagonal pipes. We also prepared the other specimens where the ribs are removed from the pipes. These specimens are compressed in the direction of the pipe axis, and deformation behaviors are observed. We investigate the effect of cross sectional shape on the performance of energy absorption, being measured from the force-displacement diagram obtained by compressive test. The results are as follows. (1) The plastic deformation by compressive test of the aluminum pipes starts from initiations machined at the vicinity of the pipe end then the folds results one after another in the pipes. (2) When we start to compress the pipe from which the ribs are removed, compressive force reaches at its maximum value, thereafter the force rapidly and greatly drops with large plastic deformation. And the force moves repeatedly up and down at its lower values with the progress of folds. (3) When we start to compress the pipes in which the ribs are installed, the drop of the force is smaller than that of the pipes without ribs and the force moves repeatedly up and down at its higher values. (4) The amounts of energy absorption at the octagonal pipe are bigger than those of the hexagonal pipe. And, the amounts of energy absorption of the pipes in which the ribs are installed are bigger than those of the pipes from which the ribs are removed.Copyright

Deformation Behavior of Intrusion Bending for Steel Pipes

We have investigated the intrusion bending for steel pipes for several years. The bending machine consists of three parts. They are called pusher, guide cylinder and gyro. The aim of this investigation is to reveal the effect of size and strength of materials, pushing forces and so on. That we study in this report are as follows: (1) The effect of bending radius ratio on ovality of outer diameter and eccentricity of wall thickness, and (2) the effect of ratio of wall thickness to outer diameter on ovality of outer diameter and eccentricity of wall thickness. The conclusions of this study are summarized as follows. (1) The ovality of outer diameter and the eccentricity of wall thickness increase as the bending radius ratio decreases. (2) The ovality of outer diameter decreases and the eccentricity of wall thickness increase as thickness outside diameter ratio increases.© 2003 ASME

Investigation of Shape Recovery Characteristics on Ferrous Shape Memory Alloy

Aims of this study are to clarify the shape recovery characteristics on ferrous shape memory alloy in order to utilize one as a many kinds of mechanical components. In this study, Fe-Mn-Si-Cr shape memory alloy is used. The fundamental characteristics and the shape recovery characteristics are investigated in this alloy. From the result of this investigation, shape recovery strain without training process reaches to maximum value of 2% at the amount of 5∼7% work-strain. That with the training process reaches 3.5% in the maximum, which is 1.8 times of that without training process. In addition, the shape recovery characteristic under constant stress which is given during the heating process is investigated. The microstructure of the deformed material is observed. The Widmanstatten structure is generated. This structure is attributed to the transformation from austenite to e-martensite. In order to enable the prediction analysis of the shape recovery behavior, the relationship between shape recovery strain and work-strain is formulated by the regression analysis in cubic equation.Copyright