Dimensional Variation Analysis of Compliant Sheet Metal Assembly

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.

This paper describes the effects of the clamping force and the pre-clamping force on the fatigue strength of bolt-connection. The results obtained are as follows:(1) The types of load-deflection diagrams of bolt-connection with the clamping force were classified into cross-type and un-cross-type.(2) And also, theoretical expressions of the optimum clamping force and the pre-clamping force were inducted to the both types of the diagrams.(3) The theoretical values of the optimum clamping force nearly fitted to the experimental values.(4) The experimental values of the fatigue limits on the optimum clamping force for the M 5 bolt of bolt-connection increased about 40% against the conventional value, at mean stress σm = 30 kg/mm2.(5) The effects of the pre-clamping force on the bolt-connection were inducted with the improvements on the compressive residual stress in bolt-connection and the optimum clamping force.

At present, the puncture clamp has been widely used in the cable branching technology. However, due to the complicated installation process, the clamping force is too large during installation, resulting in cable damage and reduced life. If the clamping force is too small, it may cause poor contact or even cause fire. In this paper, the 3D solid model of the puncture clamp is established by using SolidWorks 3D software. Then the finite element analysis model of the puncture clamp is established in the finite element analysis software ANSYS Workbench, and the static analysis and exploration of the puncture clamp are obtained. The results show that the puncture blade and the conductor on the puncture clamp have the greatest contact stress and the maximum amount of deformation of the bolt, while the bolt meets the required strength. The results can be used to further optimize the structural design of the puncture clamps, refine the installation specifications and guide the installation.

In order to study the influence of clamping force and friction coefficient on the stress distribution of drill pipe joint during the buckling process, the nonlinear contact problem and elastoplastic mechanical properties of Φ139.7mm × 9.17mm drill pipe were simulated by finite element analysis method in this paper, and the stress distribution and size of drill pipe joint during the buckling process were obtained. And the effect of clamping force and friction coefficient on the joint of drill pipe. It is found that the stress of drill pipe joint is mainly concentrated in the contact position of drill pipe and the stress value of drill pipe joint shows a trend of increasing. When the friction coefficient is 0.15 and the clamping force is 600KN, although there is stress concentration in the contact position between the clamp teeth and the drill pipe joint, it does not exceed the yield limit of the drill pipe joint, and no plastic deformation occurs. Through the simulation calculation, it is found that the maximum clamping force and the maximum torque are 1200KN and 81.9KN.m respectively. When the torque is fixed, the change of friction coefficient has a great influence on the maximum clamping force of drill pipe joint. With the increase of friction coefficient, the maximum clamping force of drill pipe joint decreases continuously, and the friction coefficient is inversely proportional to the maximum clamping force. The research in this paper enriches the understanding of the buckling process of punching pliers and provides a reference for the rational buckling of pipe string.

Lap joints are commonly used as a method of connecting structural parts. This includes parts that are made by 3D printing technology. Structural simulation using the finite element (FE) method can be used for lap joint analysis purposes. There are two approaches to use for the analysis of lap joints: actual bolt connection, and virtual bolt connection. Although an actual bolt connection is ideal to use, however in some cases it is impractical, for example when the number of joints and number of fasteners is huge. It is necessary to understand the behavior of these two different approaches for 3D printed lap joints. The modeling comparison of 3D printed PLA lap joint of these two different connections was studied using FE analysis. FE analysis was carried out using CATIA software to determine the Von Misses Stress value and displacement for each type of connection. Comparison between virtual bolt and actual bolt connections showed that actual bolts have higher Von Misses Stress value, while both connections models are having similar displacements. Different pre-tensions on bolts bring small changes to the Von Misses Stress values.

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.

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.

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

A typical aircraft panel is the assembly consisting of a multitude of thin and lightweight compliant parts. In panel assembly process, part-to-part locating scheme has been widely adopted in order to reduce fixtures. By this locating scheme, a part is located onto the pre-fixed part/subassembly by determinant assembly (DA) holes, and temporary fasteners (e.g., spring pin) are used for joining these DA hole-hole pairs. The temporary fasteners can fasten DA hole-hole pairs in the axial and radial directions of DA holes. The fastening in the radial directions is realized by the expansion of temporary fasteners. Although the usage of temporary fasteners helps reduce the positional differences between hole-hole pairs, their clamping forces thereby may lead to elastic deformation of compliant parts/subassemblies. Limited research has been conducted on such elastic deformation produced by temporary fastener and its influence on assembly dimensional quality. This paper proposes a novel rigid-compliant variation analysis method for aircraft panel assembly, incorporating the deformation in part-to-part locating process. Based on the kinematic theory and linear elasticity deformation assumption, the variation propagation through the locating process, as well as the entire assembly process of an aircraft panel, is formulated. Then, the statistical variation analysis is performed with Monte Carlo (MC) simulation. Finally, the proposed method is validated by a case study. The result shows the deformation in the part-to-part locating process significantly impacts the assembly variations, and our method can provide a more accurate and reliable prediction.

The effect of tightening again on bolt loosening under transverse load: Experimental and finite element analysis

Both experimental investigation and finite element analysis were conducted to explore the mechanisms for the early stage self-loosening of bolted joints under transverse cyclic loading. The nuts were glued to the bolts using a strong thread locker in the self-loosening experiments to ensure that no backing-off of the nut occurred. Depending on the loading magnitude, the clamping force reduction ranged from 10% to more than 40% of the initial preload after 200 loading cycles. Three-dimensional elastic-plastic finite element analysis was conducted with the implementation of an advanced cyclic plasticity model. The finite element results revealed that the local cyclic plasticity occurring near the roots of the engaged threads resulted in cyclic strain ratcheting. The localized cyclic plastic deformation caused the stresses to redistribute in the bolt, and the result was the gradual loss of clamping force with loading cycles. The finite element results agreed with the experimental observations quantitatively. When the two clamped plates started to slip and the slip displacement was controlled, both experiments and finite element simulations suggested that the friction between the clamped plates has an insignificant influence on the early stage self-loosening.

Existing artificial anal sphincter studies have shown that biomechanical compatibility problem between artificial anal sphincter and rectum caused by long-term morphological changes of the tissue surrounding the implanted prosthesis can lead to device failure or tissue ischemic necrosis. In this article, a mechanical artificial anal sphincter with constant force clamping is designed based on the superelasticity of shape memory alloys, which improved the biomechanical compatibility of implantable artificial anal sphincter. Firstly, the anatomical structure and the biomechanical properties of the rectum are analyzed to obtain the size parameters and material parameters of the rectal model. Secondly, a novel artificial anal sphincter with constant force is designed to improve the biomechanical compatibility between the artificial sphincter and the rectum. Thirdly, the static analysis of artificial anal sphincter is carried out by finite element analysis. The simulation results show that the artificial anal sphincter can maintain a constant clamping force of 4N within a certain variation range of intestinal tissue thickness, which verifies the constant force characteristic of the artificial anal sphincter. The constant clamping force of the artificial anal sphincter to the rectum is 4N that is greater than the clamping force 3.99 N required to close the rectum, which verifies the effectiveness the artificial anal sphincter. The surface contact stress and the minimum principal stress of the rectum in the clamping state are less than the pressure threshold, which verifies the safety of the artificial anal sphincter. The novel artificial anal sphincter has better biomechanical compatibility and improves the mechanical match between artificial sphincter and intestinal tissue. This study may provide more reasonable and effective simulation data for in vivo experiments of artificial anal sphincter in future, which may provide theoretical and technical support for further research about clinical application of artificial anal sphincter.

: Finite element computer techniques were used to study the linear and nonlinear structural response of bonded and weldbonded lap joints. Although the techniques used are applicable to either single-lap or double-lap joints, the emphasis was on the single-lap joint problem with the attendant complication of joint bending. Nonlinear algorithms were developed to account for nonlinear stress-strain charcteristics of the adhesive, and the joined metal sheet, weld- heat softening of the metal sheet, progressive debonding of the adhesive, and nonlinear cyclic loading. The nonlinear modes of response were simulated by sequences of linear solutions. Eight different single-lap joint configurations, designed so as to constitute an experimental parameter study, were studied in a laboratory testing program. Representative specimens were subjected to quasi- static tensile strength and cyclic-load tests and to tensile fatigue tests. The quasi-static and fatigue data generally plot into clear S-N patterns that are in a reasonable relationship to the lap joint design parameters. For the most part, strains measured on the surfaces of the test specimens were in reasonably good agreement with those computed by finite element analysis, provided out-of-plane bending effects were accounted for. The dominant failure modes were consistent with the computer analyses. (Author)

Feasibility analysis of composite fuselage shape control via finite element analysis