Showing papers on "Shell (structure) published in 1995"

A continuum-based shell theory for non-linear applications

Abstract: The paper introduces a non-linear shell theory, which provides a complete three-dimensional state of stress. Since the theory is derived from simple three-dimensional continuum mechanics, it is very easy to understand. As an example, the theory is applied to quadrilateral shell elements, which provide only displacement degrees of freedom located at nodes on the outer surfaces and one degree of freedom at the middle surface. It is proposed to eliminate this degree of freedom on element level, so that the elements have the same layout as the equivalent brick elements, but have a better behaviour in bending, have stress resultants and are cheaper with respect to computational effort. The advantages with respect to implementation in a finite element program, as well as in special applications, are obvious. However, well-known conditioning problems in thin shell applications must be expected. Therefore emphasis is put on this issue in the example problems. It is shown that the elements can give acceptable answers in engineering applications and offer a potential for material non-linear applications, which will be considered in a forthcoming paper.

An assumed strain approach avoiding artificial thickness straining for a non‐linear 4‐node shell element

Abstract: A quadrilateral degenerated C° shell element is presented which relies on extensible director kinematics and which incorporates unmodified three-dimensional constitutive models. It is shown that the direct interpolation of the extensible director field causes severe locking behaviour in the case of thin shell structures. An assumed strain interpolation is proposed to overcome the thin-shell defect. Due to this modification the shell element is able to accommodate large rotations without a rotation tensor, even for very thin shells. Several large deformation examples confirm that the developed shell element is competitive with more elaborate formulations which use rotational degrees of freedom.

A coupled analysis method for structures with independently modelled finite element subdomains

Abstract: A new method for analysing plate and shell structures with two or more independently modelled finite element subdomains is presented, assessed, and demonstrated. This method provides a means of coupling local and global finite element models whose nodes do not coincide along their common interface. In general, the method provides a means of coupling structural components (e.g., wing and fuselage) which may have been modelled by different analysts. In both cases, the need for transition modelling, which is often tedious and complicated, is eliminated. The coupling is accomplished through an interface for which three formulations are considered and presented. These formulations are: collocation, discrete least-squares, and hybrid variational. Several benchmark problems are analysed and it is shown that the hybrid variational formulation provides the most accurate solutions.

The modeling of piezoceramic patch interactions with shells, plates, and beams

Abstract: General models describing the interactions between a pair of piezoceramic patches and elastic substructures consisting of a cylindrical shell, plate and beam are presented. In each case, the manner in which the patch loads enter both the strong and weak forms of the time-dependent structural equations of motion is described. Through force and moment balancing, these loads are then determined in terms of material properties of the patch and substructure (thickness, elastic properties, Poisson ratios), the geometry of the patch placement, and the voltages into the patches. In the case of the shell, the coupling between banding and inplane deformations, which is due to the curvature, is retained. These models are sufficiently general to allow for potentially different patch voltages which implies that they can be suitably employed when using piezoceramic patches for controlling system dynamics when both extensional and bending vibrations are present.

Process for bonding a shell to a substrate for packaging a semiconductor

Abstract: A process for manufacturing a vacuum enclosure for a semiconductor device formed on a substrate with leads extending peripherally. Assembly of the enclosure is compatible with known batch fabrication techniques and is carried out at pressures required for optimal device operation. In a first embodiment, an intrinsic silicon shell is sealed to the substrate via electrostatic or anodic bonding with the leads diffusing into the shell. In a second embodiment, a thin interface layer of silicon or polysilicon is deposited on the substrate prior to electrostatic bonding a glass shell thereon. In a third embodiment, tunnels are formed between a lower peripheral edge of the shell and the substrate, allowing leads to pass thereunder. The tunnels are sealed by a dielectric material applied over the enclosure.

A simple finite element formulation for a laminated composite plate with piezoelectric layers

Abstract: A simple finite element formulation for a composite plate with laminated piezoelectric layers is presented. Classical laminate theory with electromechanical induced actuation and variational principles are used to formulate the equations of motion for a Mindlin plate element based upon uniformly reduced numerical integration and hourglass stabilization. The equations of motion are discretized with four-node, 24 degree of freedom quadrilateral shell elements with one electrical degree of freedom per piezoelectric layer. Performance of the finite element formulation developed here has been tested and compared to the experimental and analytical results documented in literature.

Earth boring drill bit with shell supporting an external drilling surface

Abstract: A method for making an earth boring drill bit which includes an outer shell having an external surface adapted to carry cutting elements and a unitary shank and bit core which is fitted into the outer shell. The shell and bit core are threadably engaged with one another or are interferingly engaged. The shell and bit core may be welded, secured with brazing alloys or with high temperature adhesives. In one embodiment, a ridge formed on the shank is received in a groove formed on an interior surface of the shell to prevent relative rotational movement of the shank and shell during drilling. In another embodiment, the shell is formed using matrix infiltration techniques. After the shell is formed, it is heated to braze cutters thereto. While still hot from the brazing process, the shell and shank are fitted together. After cooling the shell contracts to form heat shrink connection between the shell and the shank.

Shielded electrical connector

Abstract: A connector (11) which is of a duplex type, having an insulative housing (12) enclosed by two shells (40, 46) except its bottom face. The housing (12) includes the upper section and the lower section each defining a cavity (14, 16) with a plate (18) horizontally extending therein. Each sections includes therein a plurality of contacts (90) projecting into the corresponding cavity (14, 16). The housing (12) includes plural recesses (76, 78, 80) extending rearward around each cavity (14, 16) for snugly receiving a corresponding number of tangs (56, 64, 70) which project in a backward folded manner from the front edges around the corresponding opening (52, 54) in the front shell (40). Some of such tangs (56, 64, 70) include embossments (84) or kinks (86) thereon for functions as retention means (70) and/or grounding means (56). A pair of spring grounding tangs (47) forward projecting out of the mating face (20) of the connector (11). The front shell (40) includes fastening means (41) to secure to the housing (12) and the rear shell (46) has locking means (55) to be securely fixed to the front shell (40), and thus the housing (12), the front shell (40) and the rear shell (46) form an assembled unit (11).

An efficient assumed strain element model with six DOF per node for geometrically non‐linear shells

Abstract: The present paper describes an assumed strain finite element model with six degrees of freedom per node designed for geometrically non-linear shell analysis. An important feature of the present paper is the discussion on the spurious kinematic modes and the assumed strain field in the geometrically non-linear setting. The kinematics of deformation is described by using vector components in contrast to the conventional formulation which requires the use of trigonometric functions of rotational angles. Accordingly, converged solutions can be obtained for load or displacement increments that are much larger than possible with the conventional formulation with rotational angles. In addition, a detailed study of the spurious kinematic modes and the choice of assumed strain field reveals that the same assumed strain field can be used for both geometrically linear and non-linear cases to alleviate element locking while maintaining kinematic stability. It is strongly recommended that the element models, described in the present paper, be used instead of the conventional shell element models that employ rotational angles.

A Neumann-Neumann Domain Decomposition Algorithm for Solving Plate and Shell Problems

Abstract: We present a new Neumann-Neumann type preconditioner of large scale linear systems arising from plate and shell problems. The advantage of the new method is a smaller coarse space than earlier method od the authors, which improves parallel scalability. A new abstract framework for Neumann-Neumann preconditioners is used to prove optimal convergence properties of the method. The convergence estimates are independent of the number of subdomains, coefficient jumps between subdomains, and depend only polyogarithmacally on the nember of the elements per subdomain. We formulate and prove an approximate parametric variationa; principle for Reissner-Mindlin elements as the plate thickness approaches zero, which makes the results applicable to a large class of non-locking elements in everyday engineering use. The theoretical results are confirmed

On implementation of a nonlinear four node shell finite element for thin multilayered elastic shells

Abstract: A simple non-linear stress resultant four node shell finite element is presented. The underlying shell theory is developed from the three dimensional continuum theory via standard assumptions on the displacement field. A model for thin shells is obtained by approximating terms describing the shell geometry. In this work the rotation of the shell director is parameterized by the two Euler angles, although other approaches can be easily accomodated. A procedure is provided to extend the presented approach by including the through-thickness variable material properties. These may include a general non-linear elastic material with varied degree of orthotropy, which is typical for fibre reinforced composites. Thus a simple and efficient model suitable for analysis of multilayered composite shells is attained. Shell kinematics is consistently linearized, leading to the Newton-Raphson numerical procedure, which preserves quadratic rate of asymptotic convergence. A range of linear and non-linear tests is provided and compared with available solutions to illustrate the approach.

Pressure vessel and process for producing the same

Abstract: The pressure vessel of the present invention comprises an inner shell capable of serving as a gas barrier and a pressure resistant outer shell provided to cover the inner shell, said outer shell being made of an FRP comprising reinforcing fibers and a resin and is 35 GPa or more in tensile modulus and 1.5% or more in tensile breaking strain. The present invention can provide a pressure vessel not only light in weight, but also excellent in retaining its internal pressure against repetitive impacts and also excellent in reliability. The process for producing a pressure vessel of the present invention comprises the step of forming a pressure resistant outer shell made of an FRP comprising reinforcing fibers and a resin and is 35 GPa or more in tensile modulus and 1.5% or more in tensile breaking strain, around an inner shell capable of serving as a gas barrier, by a filament winding method or a tape winding method. The present invention can produce a pressure vessel excellent in retaining its internal pressure, excellent in reliability, and light in weight at a low cost.

A study of fabric deformation using nonlinear finite elements

Abstract: Fabric deformation characterized by large displacements and rotations but small strains is analyzed using a geometric nonlinear finite element method. The fabrics are modeled by shell/plate elements. Special considerations for applying the finite element method to fabric analysis are discussed and several examples of fabric deformation presented. The results from the finite element model are compared with experimental data and are in good agreement.

Plateau De Bure Observations of IRC+10216: High Sensitivity Maps of SiC2, SIS, and CS

Abstract: We have obtained high angular resolution ~ 3”), and high sensitivity maps of IRC+10216. SiC2 is found both in a spherical shell and in the very central region, indicating it is formed both in the inner envelope close to the star, and in the outer shell. The molecules SiS and CS are mostly found in the inner parts of the envelope, but are still detectable in the outer region (r ~ 15”) where the products of photochemistry are found. The maps show that IRC+10216 has a very clumpy envelope, with strong departures from spherical symmetry; an axis oriented NS-SW (P.A. 20°) can be seen in all maps. The radial brightness distribution of CS has secondary maxima, at the radius where the SiC2 shell has its peak emission. A preliminary map shows CN in the same shell, but also in a still larger outer shell. Time variations in the mass loss rate, could be invoked to explain the multiple shell structure of this envelope.

Continuous Gradient Index and Shell Models of the human Lens

Abstract: Because of the complexity of tracing rays through a gradient refractive index medium, the human eye’s lens is sometimes approximated by a shell structure with constant refractive index within shells. In the shell model, power arises from a combination of an axial variation in index and the curvatures of the shell surfaces. We develop an equation which gives the power due to the gradient index of the lens, and use this to choose shell models that have the same power as the continuous gradient index model. Some types of shell models are described and evaluated.

Vibration Control of a Cylindrical Shell Using Distributed Piezoelectric Sensors and Actuators

Abstract: This paper presents a study on vibration control of a cylindrical shell using distributed piezoelectric sensors and actuators which are parts of the shell wall. Modal expansion method is used in establishment of the state equation of the system. The robust control including JO. control theory and A-synthesis method are applied to the design of the controller which satisfies given control performance and robust stability. Simulation and experiment are carried out when the shell is excited at the resonance frequency of a controlled mode. The results show good agreement between simulation and experiment, as well as the effectiveness of the method using distributed sensors and actuators, and qK0. control theory and t-synthesis method.

Breathable shell for outerwear

Abstract: A shell for outerwear comprising an outer closely woven synthetic fabric, a relatively high-tensile-strength stratum printed on the inner face thereof and covering from 10 to 90% of the surface of the inner face, and fluorocarbon impregnation thereof.

Load floor lining having integrated sound insulation

Abstract: There is provided a one-piece, removable load floor lining having sound insulation properties, for motor vehicles, having an upper shell (2) and a lower shell (1). The upper shell (2) is substantially flat and is hingeably connected with the lower shell (1) which is adapted to the contours of the trunk region, so that a complete unit is obtained which because of the double-wall principle achieves a large acoustic effect. The upper shell (2) further includes coverings (19, 20) which can be folded open by means of hinge means, whereby together with the contour-following configuration of the lower shell (1) there are provided closed hollow spaces (4, 5, 6, 7) of different depths, in particular as storage compartments for receiving accessory parts, baggage or the like, such as e.g. a so-called active noise control system.

Fluid filter assembly

Abstract: A snap-together, all-plastic filter assembly for filtering fluids includes a generally cylindrical injection molded plastic outer shell which has a closed base and an open opposite end and which defines a hollow interior which receives a filtering element and an integral injection molded plastic endplate/centertube member. The outer shell is injection molded with a pair of concentric, generally cylindrical, inner annular walls which are integral with the closed based and extend part way toward the open end of the outer shell. The filtering element which has a hollow interior fits down within the outermost of the two concentric annular walls and the centertube of the endplate/centertube member extends through the center of the filtering element and snaps in place by means of snap-fit projections which snap into snap-fit pockets disposed within the inner most of the two concentric annular walls. The filter assembly is designed as a spin-on filter and is threadedly engaged and positioned onto a mounting base thereby completing the fluid flow path. In related embodiments the filtering element is preassembled to the endplate/centertube member as a replaceable cartridge.

Universal joint prosthesis

Abstract: The universal joint prosthesis has a cap which has an outer shell, an inner shell, a calotte-shaped, smooth outer surface formed by the outer shell and an inner surface formed by the inner shell and having projections distributed along the circumference. At least some projections have undercuts and/or are provided with through holes. The outer material forming the outer shell has, with the same surface characteristics, a smaller coefficient of friction than the inner material forming the inner shell. On the other hand, the inner material permits a firmer bond with a bone than the outer material. The universal joint prosthesis also has perforated sleeves projecting from the cap. The universal joint prothesis can usually be attached firmly to a bone without a binder, the undercuts and/or holes helping to provide a permanent connection between the cap and the bone.

Pressure vessel and method of manufacturing same

Abstract: A pressure vessel according to the invention has a feature comprising an inner shell having a gas barrier property and a pressure outer shell provided in a manner to cover the inner shell, the outer shell being composed of FRP containing a reinforcing fiber and a resin and having a tensile elastic modulus of 35 GPa or more and a tensile rupture strain of 1.5 % or more. It is possible to provide a pressure vessel which has a good pressure withstanding property against repeated shocks and a good reliability, not to mention a light weight. Also, a method of manufacturing a pressure vessel, according to the invention, has a feature comprising forming a pressure outer shell, which is composed of FRP containing a reinforcing fiber and a resin and has a tensile elastic modulus of 35 GPa or higher and a tensile rupture strain of 1.5 % or larger, around an inner shell, which has a gas barrier property, by means of a filament winding method or a tape winding method. It is possible to produce a pressure vessel which is low in cost and has a good pressure withstanding property and a good reliability, and is lightweight.

Discrete crack growth analysis methodology for through cracks in pressurized fuselage structures

Abstract: A methodology for simulating the growth of long through cracks in the skin of pressurized aircraft fuselage structures is described. Crack trajectories are allowed to be arbitrary and are computed as part of the simulation. The interaction between the mechanical loads acting on the superstructure and the local structural response near the crack tips is accounted for by employing a hierarchical modelling strategy. The structural response for each cracked configuration is obtained using a geometrically non-linear shell finite element analysis procedure. Four stress intensity factors, two for membrane behaviour and two for bending using Kirchhoff plate theory, are computed using an extension of the modified crack closure integral method. Crack trajectories are determined by applying the maximum tangential stress criterion. Crack growth results in localized mesh deletion, and the deletion regions are remeshed automatically using a newly developed all-quadrilateral meshing algorithm. The effectiveness of the methodology, and its applicability to performing practical analyses of realistic structures, is demonstrated by simulating curvilinear crack growth in a fuselage panel that is representative of a typical narrow-body aircraft. The predicted crack trajectory and fatigue life compare well with measurements of these same quantities from a full-scale pressurized panel test.

Vehicle assembling method

Abstract: A vehicle assembling method includes the steps of assembling a lower body shell a including underbody portion having a front floor and front body portion, assembling an upper body shell, including a roof member and right and left body side panels, and assembling the upper body shell and the lower body shell, moving rearward the lower body shell relative to the upper body shell, and engaging transverse opposite side ends of the lower body shell with lower end portions of the upper body shell to join the lower body shell with the upper body shell. The under body portion can be readily joined with the upper body shell, improving the workability of the joining operation. The structure of joint portion thereof can be simplified with a desirable sealing.