Clamping Points Research Articles

Strong Localization Induced by One Clamped Point in Thin Plate Vibrations

We discover a strong localization of flexural (bi-Laplacian) waves in rigid thin plates. We show that clamping just one point inside such a plate not only perturbs its spectral properties, but essentially divides the plate into two independently vibrating regions. This effect progressively appears when increasing the plate eccentricity. Such a localization is qualitatively and quantitatively different from the results known for the Laplacian waves in domains of irregular boundary. It would allow us to control the confinement of mechanical vibrations in rigid plates and of eddies in the slow Stokes flow.

Clamping modelling: state‐of‐the‐art and future trends

PurposeThe purpose of this paper is to clarify the relationship between automated assembly and mass production environments such as the manufacture of cars, airplanes and white goods and methods of modelling and simulation. Even in this environment high‐level automated assembly is restricted to the original equipment manufacturers where production volumes are high and flexibility and the ability to quickly reconfigure systems are not major drivers. It proposes modelling of the fixing/assembly process and outlining why and how new methods are important throughout the manufacturing process. The paper aims to expand the domain of co operation of different research institutes, universities and companies.Design/methodology/approachThe paper focuses on typically, fixture design, which involves the identification of clamp, locator, and support points, and the selection of corresponding fixture elements for their respective functions. In addition, the automation of fixture design activities in manufacturing is an important research area, which aims to achieve the integration of design and manufacturing. The most commonly used methods are pointed out.FindingsThe paper summarizes the main modelling and simulation methods applied to new fixing and assembly processes.Research limitations/implicationsBecause of the chosen research approach, the paper is more general.Practical implicationsThe paper includes implications for the development of a powerful new fixing method applied in the automotive and aerospace industry, which is important for stability and easy change in a rough manufacturing environment.Originality/valueThis paper fulfils an identified need to study how new fixing methods can improve motorcar and aerospace manufacturing.

Relation between mechanical properties and microstructure of human fetal membranes: An attempt towards a quantitative analysis

Objective We sought to measure the mechanical baseline behavior of fetal membranes in order to determine constitutive mechanical model parameters for fetal membranes, and to examine their relation to molecular correlates for mechanical function, i.e. collagen and elastin. Study design The uniaxial stress–strain response of nine human term fetal membranes was measured. Methods of nonlinear continuum mechanics were applied for the analysis of the stress–strain curves. Thickness of amnion and chorion were determined from histologic sections for each fetal membrane sample. Complementary biochemical analysis was performed to quantify the soluble collagen and soluble elastin components for each sample. Results We report a straightforward histologic modality for measurements of amnion and chorion thickness. Average thickness of the amnion and chorion layers were 111 ± 78 μm, and 431 ± 113 μm, respectively, which are about twice larger than previously reported. The average content of acid-soluble elastin was 2.1% of wet weight and the one of pepsin/acetic acid-soluble collagen was 10.5% of dry weight. Our data show an inverse proportionality between soluble elastin and soluble collagen content. The low strain elastic modulus ranged between 10 and 25 kPa. Correlations were found between biochemical data and mechanical parameters: there is clearly a direct proportionality between small strain elastic modulus and elastin content. Further, a (less pronounced) direct correlation was observed also between soluble collagen content and the parameter governing the increase in stiffness at larger strains in the nonlinear mechanical model. The mechanical tests revealed a relatively low variability for samples from the same membrane but a large variation between donors. The proposed nonlinear model provides a good fit of the experimental data, with a coefficient of determination, R 2, typically in the range of 0.94. Membranes failure originated at the clamping points thus impairing the quantification of ultimate stress and strain. Thus, no correlation was found between maximum stress and collagen or elastin content. Conclusions This study provides a starting point for comprehensive quantitative analysis of the relationship between fetal membranes microstructure and their nonlinear deformation behavior. These insights could become useful in identifying potential medical interventions to prevent membranes rupture.

Virtual optimisation of car passenger seats: Simulation of static and dynamic effects on drivers’ seating comfort

The virtual investigation of static and dynamic effects on seating comfort requires the application of an adequate human model. An appropriate seat model considering static and dynamic properties of the structure, the foam and the trim is needed to perform an optimisation for a lower load level on the driver. The evaluation of the seating comfort must be divided into a static and a dynamic part. For the computation of the relevant physical quantities with the human model CASIMIR and a detailed seat model, the finite-element solver ABAQUS (ABAQUS Inc., http://www.abaqus.comwww.abaqus.com) is used. To reflect a real driving situation, in the first step the human model is adapted to the right posture, which is given by the inclination of the cushion and the backrest. The seating process is then computed by the load due to gravity. The static comfort is mainly evaluated by the seat pressure distribution. Results such as the H-point and the meat-to-metal value can give additional important informations for the ergonomic and structural design of the seat. As the model reflects the nonlinear properties and the finite-element solver considers the effects out of finite displacements and contact, a good correlation with measurement is achieved. The dynamic simulation is carried out by a unit excitation of the seat slides at the clamping points. To consider frequency-dependent properties of foam, structure and the human body, the computation uses an implicit solver. Therefore the model is linearised after the nonlinear static seating process. Dynamic comfort is evaluated by the seat-transfer function. The presented numerical method leads to a good correlation with the measurements. Superposing the results with real excitation signals enables the estimation of the dynamic loads as muscle or intervertebral disc forces on the driver. Altogether this method, in an early state of the development enables the user to optimise a car passenger seat structure due to the static and dynamic comforts. Considering boundary conditions as higher load amplitudes and accelerations, the advantages of virtual development can also be applied for construction vehicle seats. Relevance to Industry The present method allows the evaluation of static and dynamic comforts in a virtual phase of seat development. Besides the reduction of time and costs, the application of the simulation enables the testing of new materials and ways of construction with low investment.

Immobilization check for fixture design

Fixture design contributes highly to manufacturing safety and quality. Computer aided fixture design (CAFD) facilitates more cost effective and efficient workholder design. However, heuristic and case-based approaches are still common. This paper addresses CAFD using the computational geometry approach. The correctness of a fixture design will be determined through vector-theoretic immobilization checking of the fixture points (i.e. location and clamping points) proposed. Details of the translational and rotational immobilization checking theory are explained, which are also applicable to general three-dimensional shapes. In real life, perfect geometry does not exist. As contemporary CAFD systems cannot cater for non-ideal geometry satisfactorily, the paper also develops an interval analysis scheme for toleranced immobilization checks. A real-life case study is presented to demonstrate the procedure.

Fixturing Feature for Determining Optimum Clamping Points. Concept of Fixturing Feature and Its Application to 2-D Workpiece Models.

In manufacturing process, engineers often estimate deformation of clamped workpieces from their features, and select clamping points with minimum deformation. In this paper, fixturing features which composed of the compliance feature and deformation pattern feature are proposed in order to determine optimum points for clamping a workpiece. And the effects of the method of deciding best clamping points applying this concept are confirmed for two-dimensional workpieces.

A Clamping Design Approach for Automated Fixture Design

in this paper, an innovative clamping design approach is described in the context ofcomputer-aided fixture design activities. The clamping design approach involves identification of clamping surfaces and clamp points on a given workpiece. This approach can be applied in conjunction with a locator design approach to hold and support the workpiece during machining and to position the workpiece correctly with respect to the cutting tool. Detailed steps are given for automated clamp design. Geometric reasoning techniques are used to determine feasible clamp faces and positions. The required inputs include CAD model specifications, features identified on the finished workpiece, locator points and elements.

308 フィクスチュアリングフィーチャに基づく工作物最適クランプ位置の決定 : フィクスチュアリングフィーチャの概念と 2 次元モデルへの適用

In the manufacturing process, engineers often estimate the deformation of clamped workpieces from their features, and select clamping points with minimum deformation. In this paper, the fixturing features which composed of the form features, the compliance features and deformation features are proposed in order to determine the optimum points for clamping a workpiece. And the effects of the method of deciding the best clamping points applying this concept are confirmed for two-dimensional workpieces.

A computational geometry approach to optimum clamping synthesis of machining fixtures

Automatic fixturing configuration is an important task to be addressed in manufacturing. An optimum clamping planning approach for arbitrarily shaped workpieces based on computational geometry of contacting wrenches is developed. A clamping analysis algorithm drawing on the metric of force closure is presented, in which all feasible clamping points are automatically found by examining whether the convex hull of bounding wrenches associated with constraining contacts contains the origin. Optimal clamping points are then chosen from the feasible clamping regions according to a proposed criterion based on the radius of the maximal inscribed hypersphere centred at the origin within the convex hull. The clamping sequence is in turn decided by the feasible clamping area where the clamps are situated. A clamping equilibrium criterion is also proposed so that robust clamping layout can be generated. Case studies are included to demonstrate the effectiveness and capabilities of the developed methodology.

Stretching DNA with optical tweezers

Force-extension (F-x) relationships were measured for single molecules of DNA under a variety of buffer conditions, using an optical trapping interferometer modified to incorporate feedback control. One end of a single DNA molecule was fixed to a coverglass surface by means of a stalled RNA polymerase complex. The other end was linked to a microscopic bead, which was captured and held in an optical trap. The DNA was subsequently stretched by moving the coverglass with respect to the trap using a piezo-driven stage, while the position of the bead was recorded at nanometer-scale resolution. An electronic feedback circuit was activated to prevent bead movement beyond a preset clamping point by modulating the light intensity, altering the trap stiffness dynamically. This arrangement permits rapid determination of the F-x relationship for individual DNA molecules as short as -1 micron with unprecedented accuracy, subjected to both low (approximately 0.1 pN) and high (approximately 50 pN) loads: complete data sets are acquired in under a minute. Experimental F-x relationships were fit over much of their range by entropic elasticity theories based on worm-like chain models. Fits yielded a persistence length, Lp, of approximately 47 nm in a buffer containing 10 mM Na1. Multivalent cations, such as Mg2+ or spermidine 3+, reduced Lp to approximately 40 nm. Although multivalent ions shield most of the negative charges on the DNA backbone, they did not further reduce Lp significantly, suggesting that the intrinsic persistence length remains close to 40 nm. An elasticity theory incorporating both enthalpic and entropic contributions to stiffness fit the experimental results extremely well throughout the full range of extensions and returned an elastic modulus of approximately 1100 pN.

Development of passive microvalves by the finite element method

The combination of a stiff titanium membrane and a flexible polyimide membrane was used to form a check valve for a micropump. This work is concerned with calculating the performance of such a microvalve and modifying its design so that instead of acting as an inlet valve, it functions as an outlet valve. It will be demonstrated here by application of the finite element method how design solutions can be found to this problem. Both the deflection behavior of the microvalve membrane exposed to the pressure and the stresses generated at the clamping points of the membrane structures have been calculated.

Vibration of Triangular Plates: Point Supports, Mixed Edges and Partial Internal Curved Supports

A numerical method, which is a hybrid form of the Rayleigh-Ritz method and the Lagrangian multiplier method, is presented in this paper for the vibration analysis of general triangular plates with complicated supported conditions. These support conditions include internal clamped or simple point supports, mixed periphery boundary conditions and partial internal curved supports. Several plate examples are used to illustrate the method. Apart from the limiting cases of some of these triangular plates with point supports where existing results are available for comparison, the frequency parameters presented in this paper are new. They should be valuable to designers in some industrial applications.

Air flow measurement by vortex shedding from multimode and monomode optical fibres

Wind tunnel experiments to investigate flow-induced vibration by vortex shedding from both multimode and monomode optical fibres are described, covering Reynolds numbers from 30 to 240. The fibre vibration frequency was a linear function of air flow speed over the range 2 to 8 m s-1. Multimode fibre vibration was detected by the modulated bend loss at the fibre clamping points. A fibre Mach-Zehnder interferometer enabled the strain, and hence vibration amplitude, of a monomode fibre to be determined under similar flow conditions. It was thus shown that for vortex shedding flowmeters with fibre sensing elements, interferometric techniques offer no significant performance advantage over simpler bend loss modulated devices.