屈曲試驗に關する研究

The VDA238-100 standard for tight radius bending (v-bending) of sheet materials has received widespread acceptance with automotive suppliers and material producers to characterize local formability. However, the test fixture and tooling in the v-bend test standard is not amenable to direct strain measurement and the operator cannot terminate the test at the onset of crack initiation as the outer bend surface is not visible. Consequently, fracture is identified using a load threshold and the bend angle estimated from an analytical formula based upon the punch displacement and tooling geometry. Bend angles are not directly transferable and must be interpreted relative to the sheet thickness and bend radius unlike a strain measurement. By obtaining an in-situ strain measurement on the surface using digital image correlation (DIC), the plane strain fracture limit can be accurately identified at the onset of cracking and remove ambiguity in translating the bend angles to practical forming operations and simulations. A novel inverted VDA test frame was developed to incorporate DIC strain measurement during the bend test and a variety of advanced high strength sheet materials were evaluated. It was observed that the VDA bend test creates a homogeneous strain state of plane strain across the width of the sample along with a proportional strain path to fracture without necking that is ideal for fracture characterization. A correlation is developed to relate the bend angle with the major strain for the materials considered and accounts for the sheet thickness and bend radius. A comparison of the bend angle obtained using the formula in the VDA standard based on the punch displacement was in very good agreement with manual measurements and an algorithm to measure the bend angle using DIC analysis was developed.

Investigation of the V-bending process with the effect of V-grooving insert geometries is performed through finite element analysis within ANSYS LS-DYNA. Different V-groover geometries are tested to evaluate the effect on the final bent angle and bent radius of the sheet metal part, with the objective of obtaining the minimized bent angle and bent radius results. It is also observed that the corner radius of the V-groover has a major influence on the bent angle and bent radius. Due to the removal of material in the bending region, which reduced the bending resistance, an increase in the corner radius results in a decrease in both the bent angle and radius. The shape of V-groover also affects the bending results, with variations in geometries leading to variations in both bent angle and radius. When the cutting cross-sectional area is kept constant, the bent angle shows minimal variation, while the bent radius steadily increases with the V-groover angle, reaching its maximum at 90 degrees.

Rotary bending is able to bend sheets with various bending radii and angles by controlling forming conditions. The effects of applied radial force and rotary angle on bending radius and angle are clarified to realize and a precise rotary bending system. The bending radius is determined by applied force and bending angle is determined by applied radial pressure and rotary angle. The feedback bending system for rotary bending is developed in that the bending conditions are determined by the previous measured value of bend sheets.

The development of intracranial internal carotid artery (ICA) stenoses may be associated with the morphology of the siphon. The aim is to quantitatively characterize the geometry of ICA, and develop a classifier of the ICA shape in relation to the location and incidence of stenoses. The ICA geometry from 74 subjects was analyzed by means of image-based computational techniques. The siphon was split into two bends, and was described in terms of curvature radius, radius of vessel, angle of bending, and length. Differences of geometry between ICA classes were assessed in control group, consisted of 30 subjects without stenoses. In stenosed group, the association between the ICA classes and the incidence of stenoses were investigated and validated by hemodynamic simulation. The curvature radius and angle of the posterior bend were significantly different between ICA classes, as well as the angle between the two bends. An innovative classifier was developed with the three geometric parameters. The ICA classification was found associated with the incidence of stenoses at the siphon. Geometric factors relative to the ICA were correlated with the location and incidence of stenoses at the siphon. The present work has potential implications in the quest for hemodynamic factors contributing to the initiation and progression of intracranial ICA stenoses.

As a hydraulic lifting pipeline structure widely used in deep-sea oil, gas transportation, and sediment dredging projects, the pipeline configuration is related to the improvement of transportation efficiency and pipeline safety. Particularly, the bending section consumes the most energy and withstands severe erosion. Understanding and predicting the conveying characteristics of two-phase flow in bends is therefore crucial. In this study, CFD-DEM (computational fluid dynamics-discrete element method) simulation method is employed to calculate various cases, considering five parameters: pipeline bending radius and angle, conveying velocity, particle diameter, and concentration, to explore the influence of these parameters on pressure drop and erosion rate of pipeline and result in a data set of hundreds of cases. Based on this data set, seven machine learning models are trained to predict pressure drop and erosion rate, respectively. To enhance model accuracy, the stacking method in ensemble learning is employed to combine multiple models with good performance. Additionally, the Optuna and SHAP (SHapley Additive exPlanation) methods are utilized to optimize hyperparameters and explain the degree to which parameters impact the predictions. The result demonstrates that pressure drop is almost unaffected by bending radius, while erosion rate initially decreases and then increases with bending angle, and both increase with other parameters. Among the evaluated models, artificial neural network, XGBoost, and random forest all demonstrate high prediction accuracy. The stacking model further improves the accuracy, with mean absolute error improving by 21.7% and 32.2%, and the SHAP method demonstrated good interpretability, which is basically consistent with CFD-DEM results.

Cover glass in commercial handheld devices is now evolving from flat (2D) to curved (3D) shapes. For example, some commercial devices have utilized sled-shape cover glass,[1] which partially covers long edges of the device. According to the patents published by key handheld manufacturers,[2, 3] we can expect more variety of 3D shaped cover glass for handheld devices in the market. In this study, we have focused on the reliability of 3D cover glass when it is dropped to a rigid surface. The key parameters under study are the corner/edge bend radius and angle of the cover glass, which determines the 3D shape of the cover glass. To achieve this goal, we developed a finite element model to simulate the drop[4-13] of a handheld device with 3D-shaped glass. The model uses explicit algorithm to simulate the high speed impact on the device during the drop test. The glass performance was evaluated based on contact force between the glass and the ground and maximum principal stress in the glass. We showed that to avoid severe damage because of first impact between the glass and the ground, the bend angle of 3D glass has to be in the range between 0 and 45°. For drop angles of 45° and higher, with the proposed glass bend angle, the impact can be taken over by the edge of the back cover of the device. In addition, we showed that optimum glass bend radius is in the range of 3.8 mm and larger. This is required to reduce stress in glass because of impact. The approach and conclusions from the current study can serve as a general guideline to improve the 3D cover glass reliability of a handheld device.

Optimization of Shock Loop for Least Stress in Hermetic Reciprocating Compressor

Interaction of low-frequency axisymmetric ultrasonic guided waves with bends in pipes of arbitrary bend angle and general bend radius

In this study, an intelligent tool system for flexible L-bending of sheet metals is developed. The punch and die are adaptively actuated by hydraulic cylinders incorporated in the punch and die, respectively. An adaptive structure with high stiffness and motion accuracy is designed and compared with a formerly developed one. The tool system can basically change the profile of the tools and pressure distribution along the workpiece during the L-bending process. The system is characterized by its capability to bend the workpiece to various bending radii and bend angles for different materials without tool change. Process control paths for obtaining desired bend radii and angles are determined off-line by a numerical simulation using the elasto-plastic model. The paths are stacked into a simulation database and used for real-time control of the L-bending process. The measured data from the sensors are input into a computer for controlling the actuators and learning the control model by comparing it with the simulated data. Several experiments have been carried out for obtaining various bend radii using two kinds of materials, SPC and aluminum alloy. The experimental results corresponded not only to various bending radii but also different materials. In addition, higher accuracy of the process control has been achieved by improving the structure of the tool system and learning the process control model. These results prove the validity and reliability of the proposed intelligent tool system.

To fabricate the precision V-bent parts, the bending angle, inner bending radius, and outer bending radius are strictly required. These requirements result in a processing difficulty especially for the difficult-to-bend material, such as high-strength steel. In the present study, the finite element method (FEM) and laboratory experiments were used to investigate the precision V-bending process. An innovation of sided coined-bead technique was proposed for preventing the spring-back and spring-go. The conventional coined-bead technique was also investigated. Based on the stress distribution analysis, the results revealed that the mechanism of the precision V-bending process, conventional coined-bead technique, and sided coined-bead technique were clearly identified. In the precision V-bending process, the conventional coined-bead technique could only prevent the spring-back. In contrast, the sided coined-bead could prevent both the spring-back and the spring-go by setting a suitable geometry and position. The FEM simulation results showed a good agreement with the experimental results with reference to the bending forces and bending angles.

Forming of the titanium elements by bending

In order to study the erosion and wear of elbows caused by solid-liquid two-phase flow, CFD numerical simulation of elbows with different geometric parameters was carried out based on hydrodynamics and tribology theory. The rules of geometric parameters and wear rate of elbows were summarized, and the wear mechanism of pipelines was analysed with related theories. The main conclusions are as follows: the maximum erosion rate decreases with the increase of the pipe diameter and bending angle and increases with the increase of the pipe length and bending radius. Among the above factors, the bending angle has the greatest impact on the maximum erosion rate of the pipeline.

Due to the particularity of the material and structure of the temperature control product ammonia axial channel thermotube on satellite, there are few researches on its forming at home and abroad at present. In the process of product development, defects such as cross section deformation, accuracy out of tolerance and springback will occur, which will reduce the quality and pass rate of the product and affect the progress of the product, laser induced bending forming method is adopted in this paper, and the technological parameters of laser induced bending forming are studied according to the bending radius and angle required by the designer.In actual research process, firstly, we utilize ABAQUE software to simulate the effect of the selection of process parameters and the forming mechanism of laser induced bending forming as well as observing the laser effect in the process of stress, strain and temperature changes as well as angle, referring to the result of simulation test. Finally, we get specific process parameters under bending radius and bending angle.

The transmission of 10.6-μm light in bent metal-walled waveguides of rectangular cross section is described both theoretically and experimentally. It is shown that the bending loss per angle of bend in these waveguides is explicitly independent of waveguide height, bend radius, and light wavelength, depending only on the reflectivity of the waveguide walls. In confirming experiments, guides with aluminum walls showed 95% transmission per radian of bend for radii in the range from less than 1 cm to 1 m.

We fabricated highly flexible Sr- and Ni-doped perovskite SmMnO3 thermistor film sensor arrays on an ultrathin (5 μm thick) and lightweight (21 mg) polyimide sheet for healthcare monitoring devices. The Ag nanowire and nanoparticle-impregnated carbon microcone array, which was prepared by precisely controlled surface laser carbonization of polyimide, showed sufficiently low resistance as a bottom electrode and good stability against sharp bending angles. The dot-shaped (diameter: 900 μm) perovskite thermistor film with a thickness of 900 nm was crystallized by pulsed ultraviolet laser irradiation of a precursor film printed with perovskite nanoparticle dispersion ink, and the film functioned well as the thermistor with a thermistor constant of 2820 K. The thermistor sensor sheet exhibited rapid responses to temperature variation and high stability in the temperature cycle tests over 1000 cycles between room temperature and 80 °C. The bending durability for a bending angle of 60° with a small bending radius (500 μm) was also high. During the bending test over 1000 cycles, the monitoring temperature variation was suppressed only within 0.1 °C. This ultrathin sensor array sheet can be mounted on surfaces with shape variations, and we used the sensor for real-time monitoring in healthcare to detect precise temperature variations on the human skin during physical exercise.