ねじ締結体の疲れ強さに及ぼす締付力および予締付力の影響

Recently, highly porous metal foams have been used to replace the traditional open-flow channels to improve gas transport and distribution in the cells. Deformation of flow plate, gas diffusion layer (GDL), and metal foam may occur during assembling. When the cell size is small, the deformation may not be significant. For large area cells, the deformation may become significant to affect the cell performance. In this study, an assembling device that is capable of applying uniform clamping force is built to facilitate fuel cell assembling and alleviate the deformation. A compressing plate that is the same size of the active area is used to apply uniform clamping force before surrounding bolts are fastened. Therefore, bending of the flow plate and deformation of GDL and metal foam can be minimized. Effects of the clamping force on the microstructures of GDL and metal foam, various resistances, pressure drops, and cell performance are investigated. Distribution of the contact pressure between metal foam and GDL is measured by using pressure sensitive films. Field-emission scanning electron microscope is used to observe the microstructures. Electrochemical impedance spectroscopy analysis is used measure resistances. The fuel cell performance is measured by using a fuel cell test system. For the cell design used in this study, the optimum clamping force is found to be 200 kgf. Using this optimum clamping force, the cell performance can be enhanced by 50%, as compared with that of the cell assembled without using clamping plates. With appropriate clamping force, the compression force distribution across the entire cell area can approach uniform. This enables uniform flow distribution and reduces mass transfer resistance. Good contact between GDL and metal foam also lowers the interface resistance. All these factors contribute to the enhanced cell performance.

The effects of frictional damping on the dynamic response of a beam structure have been investigated. The frictional damping was contributed from the slip mechanisms in a ‘pseudo’ joint, that is a joint that did not take any static load. Using pseudo joints for vibration control has significant advantages over using joints that are designed both to take static load and to introduce frictional damping; because there is almost no restriction on the configuration of the pseudo joint, the undesirable side effects related to the frictional damping such as fretting corrosion of contact surfaces and loss of static stiffness are zero if the frictional damping from a pseudo joint is utilized. An ‘optimum’ clamping force was found which minimized the magnitude of the frequency response function (FRF) of the structure under excitation. A reduction of about 20 dB in the amplitudes of the FRFs was achieved by adjusting the clamping force at the joint. Frictional damping was found to be significant over the measured frequency range of 20-2000 Hz, and it was particularly effective over the range of 20-1000 Hz. The magnitudes of the FRFs of the structure were determined by the ratio of clamping force to excitation force. They were insensitive to the change of clamping force near its optimum value; also the optimum clamping force was not sensitive to small modifications to the structure. Therefore, utilizing frictional damping in pseudo joints is an effective technique for vibration control.

Fixture design is a critical step in machining. An important aspect of fixture design is the optimization of the fixture, the primary objective being the minimization of workpiece deflection by suitably varying the layout of fixture elements and the clamping forces. Previous methods for fixture design optimization have treated fixture layout and clamping force optimization independently and/or used nonlinear programming methods that yield sub-optimal solutions. This paper deals with application of the genetic algorithm (GA) for fixture layout and clamping force optimization for a compliant workpiece. An iterative algorithm that minimizes the workpiece elastic deformation for the entire cutting process by alternatively varying the fixture layout and clamping force is proposed. It is shown via an example of milling fixture design that this algorithm yields a design that is superior to the result obtained from either fixture layout or clamping force optimization alone.

Machining accuracy of thin-walled parts is easily affected by clamping and cutting deformation due to its poor stiffness. In this paper, synchronous optimization method of clamping force and cutting parameters is presented based on GA and FEM. The optimization objective is to minimize the maximum deformation and to improve the machining efficiency. GA is used to optimize cutting parameters and clamping force, and FEM is used to predict the machining deformation of the thin-walled workpiece. Finally, taking a titanium alloy thin-walled part with irregular shape as an example, the optimal clamping force and cutting parameters at every cutting position are obtained to demonstrate the feasibility of the method.

Fixture Layout Design (FLD) determines the specific position of locators and clamps to orient and holds the workpiece with respect to a machine tool. The FLD approaches that use Finite Element Analysis (FEA) have been widely used in previous works and have become computationally expensive and specific to a particular problem. Further, the FLD and clamping force optimization were often performed separately by ignoring their interdependence. In the present work, the locators' contact forces are uniformly distributed by suitably varying the fixture layout and clamping force to maximize the part dimensional and form quality. The parametric rigid body model is used to depict the behaviour of the workpiece-fixture system, and it is incorporated with the genetic algorithm to optimize the design variables. A prismatic workpiece with pocket milling operation is considered to validate the proposed methodology. Stability criterion and tool-fixture interference are considered constraints. Subsequently, FEA is used to verify the integrity of the proposed approach. The results infer that the uniform distribution of maximum elastic deformation is achieved due to the uniform distribution of contact forces. The suggested approach is proven effective for designing a milling fixture to manufacture components with high dimensional and form precision.

The simultaneous improvement of injection molding process efficiency and product quality, as required by Industry 4.0, is a complex, non-trivial task that requires a comprehensive approach, which involves a combination of sensoring and information techniques. In this study, we investigated the suitability of in-mold pressure sensors to control the injection molding process in multi-cavity molds. We have conducted several experiments to show how to optimize the clamping force, switchover, or holding time by measuring only pressure in a multi-cavity mold. The results show that the pressure curves and the pressure integral are suitable for determining optimal clamping force. We also proved that in-channel sensors could be effectively used for a pressure-controlled SWOP. In the volume-controlled method, only the sensors in the cavity were capable of correctly detecting the end of the filling. We proposed a method to optimize the holding phase. In this method, we first determined the integration time of the area under the pressure curve and then performed a model fit using the relationship between the pressure integral and product mass. The saturation curve fitted to the pressure data can easily determine the gate freeze-off time from pressure measurements.

In order to assure the dimensional quaLity of compLiant sheet metal assembly, it is quite necessary to use the numerical method to simulate and analyze the assembly process before real assembly. In this paper, the finite element analysis of the whole compLiant sheet metal assembly process is reaLized in two steps: clamping force calculation and joining and springing back simulation. Clamping force is optimized so that the initial gap between parts can be closed. The joints of the two parts are simulated by DOF coupLing in ANSYS. Spring-back force, which is assumed to be equal to the optimum clamping force, is appLied on the joint points. Large displacement static analysis is run in ANSYS to calculate the displacement distribution of both clamped part and compLiant sheet metal assembly. An example of compLiant sheet metal assembly by lap joints is studied to demonstrate the finite element analysis process in this paper.

Off-line modelling and planning of optimal clamping forces for an intelligent fixturing system

The stress corrosion cracking(SCC) of austenitic stainless steel and nickel-based alloy is a primary concern for stable operation in Boiling Water Reactors(BWRs) and Pressurized Water Reactors (PWRs). Laser peening is one of the promising technologies for prevention of SCC initiation to induce compressive residual stress near the surface region. However, the compressive residual stress by laser peening is likely affected due to applied stress. In this study, the effect of mechanical loading on the compressive residual stress by laser peening was investigated. The specimens of low carbon austenitic stainless steel (Type316L), nickel-based alloy (Alloy600) and their weldments were prepared, and several levels of cyclic loading were applied to their specimens. The surface residual stress at surface was measured by X-ray diffraction method before and after loading. The relaxation behaviour of the compressive surface residual stress by laser peening was evaluated at the base metal and heat affected zone (HAZ) of the weldment. It was confirmed that compressive surface residual stress remained after stress loading which corresponds to 0.2% proof stress, and that the relaxation of the surface residual stress remarkably observed after initial loading during cyclic loading test. These relaxation behaviour were similar in Type316L, Alloy600 and their HAZ.

Optimization of residual stress field in ultrasonic assisted burnishing process

The benefits of applied compressive residual stress on fatigue properties of materials is a well-known phenomenon, but not well described in all respects. The fatigue life and the fatigue limit could be improved by targeted created compressive residual stress in the surface layers therefore, diversified surface compressing methods are developed and used in the engineering industry. The relaxation of the compressive residual stress state during a cyclic and static load is determinative for the life time of a componenet. Compressive stress relaxation was experimentally determined during the cyclic and static load. The compressive residual stress was induced by shot penning on the surface of stainless steel, micro alloyed high strength steel and hardened steel specimens. The residual stress state was investigated nondestructively by X-ray diffraction method then these specimens were load. After a certain number of cycles the fatigue load was stopped and the residual stress state was recorded again and again until fracture. To investigate the relaxation process during static load a four-point bending bench was used. The compressive residual stress relaxation was correlated to the applied fatigue stress level, the cycle number the quality of alloys.

Residual weld stresses in stiffener-to-deck plate weld of an orthotropic steel deck

Microstructural evolution and performance analysis of WC-11Co reinforced iron matrix composites

Tensile residual stresses at the surface of welded components are known to compromise fatigue resistance through the accelerated initiation of microcracks, especially at the weld toe. Inducement of compression in these regions is a common technique employed to enhance fatigue performance. Transformation plasticity has been established as a viable method to generate such compressive residual stresses in steel welds and exploits the phase transformation in welding filler alloys, that transform at low temperature to compensate for accumulated thermal contraction strains. Neutron and X-ray diffraction have been used to determine the stress profiles that exist across the surface of plates welded with low transformation temperature welding alloys, with a particular focus on the stress at the weld toe. For the first time, near-surface neutron diffraction data have shown the extent of local stress variation at the critical, fusion boundary location. Compression was evident for the three measurement orientations at the fusion boundaries. Compressive longitudinal residual stresses and tensile trans- verse stresses were measured in the weld metal.

Abrasive waterjet peening (AWJP) is a new mechanical surface treatment where particles are delivered by a waterjet to induce plastic deformation and achieve surface strengthening effects on a workpiece. Although fatigue strength can be improved by inducing compressive residual stress, the prediction of residual stress distribution remains challenging because particle–workpiece interaction occurs with randomicity, superposition, and overlapping. In this paper, a theoretical model is proposed for predicting workpiece plastic deformation and compressive residual stress by analysing i) the non-uniform energy distribution of the AWJP beam caused by the non-uniformity of the abrasive size, spatial distribution, and impact velocity; ii) material hardening among multiple impacts by abrasive particles; and iii) overlapping traces induced by the changing position of the AWJP beam. The AWJP experiments were conducted in single-pass/multiple-pass/multiple-overlapping footprints with different pump pressures, traverse speeds, and jet centre distances of the adjacent traces to validate the model. The results showed good agreement with the predicted surface roughness and compressive residual stress. Compressive residual stress increased with the pump pressure, whereas the effect of pump pressure change rate decreased when the pump pressure was increased; further, residual stress is nearly constant with the variation in traverse speed and jet centre distance of the adjacent traces when it decreases to a certain value. These results can act as references for the control of residual stress and the prediction model can aid industrial manufacturing in AWJP parameter optimisation (e.g. pump pressure, traverse speed, surface roughness, compressive residual stress, and centre distance between two adjacent traces).