Innovation for forming aluminum alloy thin shells at ultra-low temperature by the dual enhancement effect

Integral thin shells made of high strength aluminum alloys are urgently needed in new generation transportation equipment. There are challenges to overcoming the co-existing problems of wrinkling and splitting by the cold forming and hot forming processes. An innovative technology of ultra-low temperature forming has been invented for aluminum alloy thin shells by the new phenomenon of ‘dual enhancement effect’. That means plasticity and hardening are enhanced simultaneously at ultra-low temperatures. In this perspective, the dual enhancement effect is described, and the development, current state and prospects of this new forming method are introduced. This innovative method can provide a new approach for integral aluminum alloy components with large size, ultra-thin thickness, and high strength. An integral tank dome of rocket with 2 m in diameter was formed by using a blank sheet with the same thickness as the final component, breaking through the limit value of thickness-diameter ratio.

ANALYSES ON NONLINEAR COUPLING OF MAGNETO-THERMO-ELASTICITY OF FERROMAGNETIC THIN SHELL—II:FINITE ELEMENT MODELING AND APPLICATION

Based on the generalized vaxiational principle of magneto-thermo-elasticity of a ferromagnetic thin shell established （see, Analyses on nonlinear coupling of magneto-thermo- elasticity of ferromagnetic thin shell--I）, the present paper developed a finite element modeling for the mechanical-magneto-thermal multi-field coupling of a ferromagnetic thin shell. The numerical modeling composes of finite element equations for three sub-systems of magnetic, thermal and deformation fields, as well as iterative methods for nonlinearities of the geometrical large-deflection and the multi-field coupling of the ferromagnetic shell. As examples, the numerical simulations on magneto-elastic behaviors of a ferromagnetic cylindrical shell in an applied magnetic field, and magneto-thermo-elastic behaviors of the shell in applied magnetic and thermal fields are carried out. The results are in good agreement with the experimental ones.

NONLINEAR DEFORMATION THEORY OF THIN SHELL

The exact relation between strain and displacement is given for nonlinear deformation of thin shell. The! fundamental formula of large deformation when the deflection is on the same class with the thickness of the shell is derived after simplified rationally. The fundamental formula of large deformation when the deflection is art the same class with the length of the shell is derived exactly for cylinder shell deformed cylindrical shaped.

A simple analytical model of laser direct-drive thin shell target implosion

A high-neutron yield platform imploded by a thin shell target is generally built to probe nuclear science problems,and it has the advantages of high neutron yield,ultrashort fusion time,micro fusion zone,isotropic and monoenergetic neutron.Some analytical models have been proposed to interpret exploding-pusher target implosion driven by a long wavelength laser,whereas they are imperfect for a 0.35 μm laser implosion experiment.When using the 0.35 μm laser,the shell is ablated and accelerated to high implosion velocity governed by Newton’s law,ablation acceleration and quasi-adiabatic compression models are suitable to explain the implosion of a laser direct-drive thin shell target.The new analytical model scales bang time,ion temperature and neutron yield for large variations in laser power,target radius,shell thickness,and fuel pressure.The predicted results of the analytical model are in agreement with experimental data on the ShenguangIII prototype laser facility,100 kJ laser facility,Omega,and NIF,it demonstrates that the analytical model benefits the understanding of experiment performance and optimizing the target design of high neutron yield implosion.

Analysis of the Eccentric Cylindrical Thin Shell

The present paper gives the approximate equations of the eccentric cylindricalthin shell under small deflections. Br means of the analytical method, we solved theequations. Thus the relations between the stress, the displacement and the eccentricityof the eccentric cylindrical thin shell are obtained.

An Overview of 3D Thin Shell Textile Preforms

The automobiles, aircraft, and lightweight industries continuously demand thin near-net-shape preforms just out-of-machine as close to the final shape. This study addresses the possibilities of 3D thin shell textile preform as the solution of lightweight reinforcement in various applications. Investigation into the development of 3D thin shells has led to different manufacturing processes. However, 3D thin shell preforms are mostly made by weaving and knitting, but nonwoven, winding, and/or layup techniques have been reported for over a decade. Owing to the complex thin shell manufacturing processes, they are not similar to the conventional methods. The different 3D thin shell preforms can extend the opportunities for new applications in various technical fields. This study presents existing research gaps and a few potential issues to be solved regarding 3D thin shell preforms in the near future.

An Overview of 3D Thin Shell Textile Preforms

The automobiles, aircraft, and lightweight industries continuously demand thin near-net-shape preforms just out-of-machine as close to the final shape. This study addresses the possibilities of 3D thin shell textile preform as the solution of lightweight reinforcement in various applications. Investigation into the development of 3D thin shells has led to different manufacturing processes. However, 3D thin shell preforms are mostly made by weaving and knitting, but nonwoven, winding, and/or layup techniques have been reported for over a decade. Owing to the complex thin shell manufacturing processes, they are not similar to the conventional methods. The different 3D thin shell preforms can extend the opportunities for new applications in various technical fields. This study presents existing research gaps and a few potential issues to be solved regarding 3D thin shell preforms in the near future.

Asymptotically Confirmed Hypotheses Method for the Construction of Micropolar and Classical Theories of Elastic Thin Shells

In the present paper asymptotic solution of boundary-value problem of three-dimensional micropolar theory of elasticity with free fields of displacements and rotations is constructed in thin domain of the shell. This boundary-value problem is singularly perturbed with small geometric parameter. Internal iteration process and boundary layers are constructed, problem of their jointing is studied and boundary conditions for each of them are obtained. On the basis of the results of the internal boundary-value problem the asymptotic two-dimensional model of micropolar elastic thin shells is constructed. Further, the qualitative aspects of the asymptotic solution are accepted as hypotheses and on the basis of them general applied theory of micropolar elastic thin shells is constructed. It is shown that both the constructed general applied theory of micropolar elastic thin shells and the classical theory of elastic thin shells with consideration of transverse shear deformations are asymptotically confirmed theories.

Shell stand:Stable thin shell models for 3D fabrication

A thin shell model refers to a surface or structure,where the object’s thickness is considered negligible.In the context of 3D printing,thin shell models are characterized by having lightweight,hollow structures,and reduced material usage.Their versatility and visual appeal make them popular in various fields,such as cloth simulation,character skinning,and for thin-walled structures like leaves,paper,or metal sheets.Nevertheless,optimization of thin shell models without external support remains a challenge due to their minimal interior operational space.For the same reasons,hollowing methods are also unsuitable for this task.In fact,thin shell modulation methods are required to preserve the visual appearance of a two-sided surface which further constrain the problem space.In this paper,we introduce a new visual disparity metric tailored for shell models,integrating local details and global shape attributes in terms of visual perception.Our method modulates thin shell models using global deformations and local thickening while accounting for visual saliency,stability,and structural integrity.Thereby,thin shell models such as bas-reliefs,hollow shapes,and cloth can be stabilized to stand in arbitrary orientations,making them ideal for 3D printing.

Thin-Shell Wormholes Admitting Conformal Motions in Spacetimes of Embedding Class One

This paper discusses the feasibility of thin-shell wormholes in spacetimes of embedding class one admitting a one-parameter group of conformal motions. It is shown that the surface energy density σis positive, while the surface pressure is negative, resulting in , thereby signaling a violation of the null energy condition, a necessary condition for holding a wormhole open. For a Morris-Thorne wormhole, matter that violates the null energy condition is referred to as “exotic”. For the thin-shell wormholes in this paper, however, the violation has a physical explanation since it is a direct consequence of the embedding theory in conjunction with the assumption of conformal symmetry. These properties avoid the need to hypothesize the existence of the highly problematical exotic matter.

Isogeometric cohesive zone model for thin shell delamination analysis based on Kirchhoff-Love shell model

We present a cohesive zone model for delamination in thin shells and composite structures.The isogeometric(IGA)thin shell model is based on Kirchhoff-Love theory.Non-Uniform Rational B-Splines(NURBS)are used to discretize the exact mid-surface of the shell geometry exploiting their C 1-continuity property which avoids rotational degrees of freedom.The fracture process zone is modeled by interface elements with a cohesive law.Two numerical examples are presented to test and validate the proposed formulation in predicting the delamination behavior of composite structures.

Finite element corotational formulation for geometric nonlinear analysis of thin shells with large rotation and small strain

Based on the consistent symrnetrizable equilibrated （CSE） corotational formulation, a linear triangular flat thin shell element with 3 nodes and 18~ of freedom, constructed by combination of the optimal membrane element and discrete Kirchhoff trian- gle （DKT） bending plate element, was extended to the geometric nonlinear analysis of thin shells with large rotation and small strain. Through derivation of the consistent tangent stiffness matrix and internal force vector, the corotational nonlinear finite element equations were established. The nonlinear equations were solved by using the Newton-Raphson iteration algorithm combined with an automatic load controlled technology. Three typical case studies, i.e., the slit annular thin plate, top opened hemispherical shell and cylindrical shell, validated the accuracy of the formulation established in this paper.

Energy conserving and decaying algorithms for corotational finite element nonlinear dynamic responses of thin shells

On the basis of the finite element corotational formulation for geometric nonlinear static analysis of thin shells with large rota- tion and small strain established before and from the generalized-a time integration algorithm, the energy conserving and de- caying algorithms for corotational formulation nonlinear dynamic response analysis of thin shells are established in this paper. Responses are solved by means of a predictor-corrector procedure. In the case of ignoring the structural damping, the conserv- ing or decaying total energy of structure and the controllable numerical damping for high frequency responses can ensure the numerical stability of the algorithm. The inertial parts are linearly interpolated directly in the fixed global coordinate system by using the element nodal displacement in the global coordinate system for obtaining the constant mass matrix, while the elastic parts adopt the corotational formulation. Hence, the whole formulation obtained in this paper is element independent. Through three typical numerical examples, the performances of the algorithm in this paper were compared with those of the classical Newmak and HHT-a algorithms to indicate that the algorithm in this paper could accurately solve nonlinear dynamic respons- es of thin shells with large displacements and large rotations.

A DONNELL TYPE THEORY FOR FINITE DEFLECTION OF STIFFENED THIN CONICAL SHELLS COMPOSED OF COMPOSITE MATERIALS

A Donnell type theory is developed for finite deflection of closely stiffened truncated laminated composite conical shells under arbitrary loads by using the variational calculus and smeared-stiffener theory. The most general bending-stretching coupling and the effect of eccentricity of stiffeners are considered. The equilibrium equations, boundary conditions and the equation of compatibility are derived. The new equations of the mixed-type of stiffened laminated composite conical shells are obtained in terms of the transverse deflection and stress function. The simplified equations are also given for some commonly encountered cases.

Method to calculate interior sound field of arbitrary-shaped closed thin shell

The concept of covering-domain means that an arbitrary-shaped closed shell can be approached by a series of closed spherical shells. Based on it, the interior scattering sound field of the arbitrary-shaped closed shell is given. According to the reciprocity theory, the radiating sound field of the elastic surface due to the action of external force is presented. The method presented can also be used to calculate the interior sound fields of arbitraryshaped closed thin shells of which the thickness are either equal or unequal. It is verilied to be correct by corresponding test.

Finite element modeling of power spinning of thin-walled shell with hoop inner rib

A 3D elasto-plastic finite element(FE)model of power spinning of thin-walled aluminum alloy shell with hoop inner rib was established under software ABAQUS.Key technologies were dealt with reasonably.The reliability of the FE model was verified theoretically and experimentally.The forming process was simulated and studied.The distribution of the thickness and stress,and the variations of spinning force were obtained.The workpiece springback was analyzed with ABAQUS/Standard.The results show that the FE model considering elastic deformation can not only be used to analyze the workpiece springback in the complex spinning process,but also serve as a significant guide to study the local deformation mechanism and choose the reasonable parameters.

Analytical solution for cylindrical thin shells with normally intersecting nozzles due to external moments on the ends of shells

The stress analysis based on the theory of a thin shell is carried out for cylindrical shells with normally intersecting nozzles subjected to external moment loads on the ends of shells with a large diameter ratio(ρ 0 ?0. 8). Instead of the Donnell shallow shell equation, the modified Morley equation, which is applicable toρ 0(R/T)1/2 ?1, is used for the analysis of the shell with cutout. The solution in terms of displacement function for the nozzle with a nonplanar end is based on the Goldenveizer equation. The boundary forces and displacements at the intersection are all transformed from Gaussian coordinates (α, β) on the shell, or Gaussian coordinates (ζ, θ) on the nozzle into three-di-mensional cylindrical coordinates(ρ,θ, z). Their expressions on the intersecting curve are periodic functions ofθ and expanded in Fourier series. Every harmonic of Fourier coefficients of boundary forces and displacements are obtained by numerical quadrature. The results obtained are in agreement with those from the three-dimensional finite element method and experiments.

Amendment on the strain measurement of thin-walled human skull shell as intracranial pressure changes

The human skull, composed of tabula extema, tabula intema, and a porous diploe sandwiched in between, is deformed with changing intracranial pressure （ICP）. Because the human skull＇s thickness is only 6 mm, it is simplified as a thin-walled shell. The objective of this article is to analyze the strain of the thin-wailed shell by the stress-strain calculation of a human skull with changing ICP. Under the same loading conditions, using finite element analysis （FEA）, the strains of the human skull were calculated and the results were compared with the measurements of the simulative experiment in vitro. It is demonstrated that the strain of the thin-walled shell is totally measured by pasting the one-way strain foils on the exterior surface of the shell with suitable amendment for data. The amendment scope of the measured strain values of the thin-walled shell is from 13.04% to 22.22%.

Numerical Simulation and Experiment on Thin-Shell Object Separation from Aircraft

The unsteady aerodynamic loads generated by the thin-shell object separating from aircraft affects flying safety.To investigate the loads,a method combining numerical simulation and experiment is proposed.Firstly,the motional tendency of the thin-shell object separating from aircraft is calculated,and then the high-speed air blowing test on ground is designed.Thereafter,the external store is employed to avoid colliding with the thin-shell object in air.Finally,the hanging and flight test is conducted by a high-speed unmanned aerial vehicle(UAV),and the feasibility of the thin-shell object separating from aircraft at high speed is proved.Consequently,the separating problem of a thin-shell object with an unconventional aerodynamic configuration is solved,and the collisions with aircraft is prevented.

Neumann＇s method for boundary problems of thin elastic shells

The possibility of using Neumann＇s method to solve the boundary problems for thin elastic shells is studied. The variational statement of the static problems for the shells allows for a problem examination within the distribution space. The convergence of Neumann＇s method is proven for the shells with holes when the boundary of the domain is not completely fixed. The numerical implementation of Neumann＇s method normally requires significant time before any reliable results can be achieved. This paper suggests a way to improve the convergence of the process, and allows for parallel computing and evaluation during the calculations.