Plastic Shell Research Articles

Mechanism of buckling development and strain reversal occurrence in elastic–plastic cylindrical shells under axial impact

In order to clarify the mechanism of loading and unloading, buckling growth, and strain-reversal occurrence in elastic–plastic cylindrical shells that are impacted axially, non-linear dynamic equations in incremental form are derived and solved by using the finite difference method. The validity of the developed theory is verified by comparing theoretical and experimental results. From the calculation results, it is found that, at the initial stage of the impact process, the effective stress related to the middle-surface stresses in the part near the impacted end rises with time, and exhibits plastic loading. The radial restraints on the impacted end have obvious influence on the strain reversal occurrence at an early stage of the impact process. The effective modulus controls the post-buckling deformation of the shell, which contrasts with the situation for the bar to be impacted axially.

Initial experiments on the shock-ignition inertial confinement fusion concept

Shock ignition is a two-step inertial confinement fusion concept where a strong shock wave is launched at the end of the laser pulse to ignite the compressed core of a low-velocity implosion. Initial shock-ignition technique experiments were performed at the OMEGA Laser Facility [T. R. Boehly et al., Opt. Commun. 133, 495 (1997)] using 40-μm-thick, 0.9-mm-diam, warm surrogate plastic shells filled with deuterium gas. The experiments showed a significant improvement in the performance of low-adiabat, low-velocity implosions compared to conventional “hot-spot” implosions. High areal densities with average values exceeding ∼0.2g∕cm2 and peak areal densities above 0.3g∕cm2 were measured, which is in good agreement with one-dimensional hydrodynamical simulation predictions. Shock-ignition technique implosions with cryogenic deuterium and deuterium-tritium ice shells produced areal densities close to the 1D prediction and achieved up to 12% of the predicted 1D fusion yield.

Enhanced Direct-Drive Implosions with Thin High-ZAblation Layers

New direct-drive spherical implosion experiments with deuterium filled plastic shells have demonstrated significant and absolute (2x) improvements in neutron yield when the shells are coated with a very thin layer ( approximately 200-400 A) of high-Z material such as palladium. This improvement is interpreted as resulting from increased stability of the imploding shell. These results provide for a possible path to control laser imprint and stability in laser-fusion-energy target designs.

Characterizing the Expansive Deformation of a Bioresorbable Polymer Fiber Stent

Polymeric vascular stents must employ other strategies than malleable deformation, as generally practiced with metal stents, to expand and withstand compressive stresses in situ. The stent expansion strategy must further consider induced flow perturbations and wall stresses that may injure the vessel wall and promote thrombogenesis. Analyzing the stresses furled stents undergo during balloon-assisted expansion is an important first step in achieving a better understanding of stent-wall mechanical interactions, thereby to improve stent function. To this end, we performed finite element (FE) analysis of the balloon-induced unfurling of an internally coiled, bioresorbable polymeric stent employing a 3D FE solid model of a 120 degrees symmetric stent segment and a large deformation finite strain formulation. Uni-axial tensile testing of stent fiber elastic to plastic yielding provided the mechanical property information, and the von Mises criterion was employed to establish the elastic-plastic transition in the FE model. The model was validated with pressure and deformation measurements obtained during stent expansion tests. The internal coils of this inner coil-outer coil design twisted as the stent expanded, leading to plastic yielding at the point of tangency of the inner and outer coils. The remaining stent fiber portions underwent elastic bending. Cross-sections revealed only the outside surface layer of the coiled fiber underwent plastic yielding. The interior elastic fiber was supported by this plastic shell. The analysis suggests that during balloon-induced expansion, local plastic yielding in torsion "sets" the stent fibers, imparting high radial collapse resistance. The results further suggest that the stent exerts non-uniform mechanical forces on the vessel wall during expansion.

Paraplegia of late onset in adolescents with healed childhood caries of dorsal spine: A cause of pressure on the cord and treatment

Background:Paraplegia of late onset in adolescents with caries of dorsal spine is considered to be due to the reactivation of infection. Internal salient at the level of acute kyphotic deformity of the dorsal spine is formed by posterior cartilaginous remains of grossly destroyed vertebral bodies. The author presents a study of eight adolescent patients with paraplegia of late onset associated with severe kyphotic deformity of dorsal spine with observations on the cause of paraplegia, the final neurological outcome following anterior decompression and its prevention.Materials and Methods:Eight adolescent patients mean age 14.4 yrs 6 males and 2 females with healed childhood caries of dorsal spine, having a mean kyphotic angle of 80° (range 60°–140°) presented with paraplegia of late onset. Of these patients, two had medical research council grade 0 muscle power; four had grade 2 muscle power, and two others had grade 3 muscle power in the lower limbs and were unable to walk unaided. One patient with 140° kyphoscoliotic deformity with grade 3 muscle power had post-polio residual paralysis (PPRP) in addition. All patients were subjected to thorough anterior spinal decompression through transthoracic, transpleural thoracotomy from the left side.Results:In six of the eight patients, the spine at the site of deformity being very rigid, the deformity could not be corrected and the intervertebral gap was bridged with appropriate autogenous tricortical cortico cancelluous bone graft. In one patient (case 4), the kyphotic deformity could be corrected by 50%. In one patient with 140° kyphosis and PPRP, the gap after the decompression of cord, could not be bridged with bone graft and was given a custom made, well molded plastic black shell to wear while walking and, in particular, while traveling in a vehicle. In all seven patients, bone grafts took six months for bridging the intervertebral gaps. All patients recovered to grade 4 muscle power 6–12 months after surgery.Conclusion:In adolescents with healed caries of dorsal spine with acute kyphosis and paraplegia, the treatment of choice is anterior surgical decompression of the cord and bridging the gap thus created with bone graft.

An insecticidal refuge trap to control adult small hive beetle, Aethina tumida Murray (Coleoptera: Nitidulidae) in honey bee colonies

SummaryThe establishment of the small hive beetle in eastern Australia and its subsequent economic impact on bee keeping prompted research into the insecticidal control of adult beetles inside the hive. A refuge trap comprising a two piece rigid plastic shell encasing a fipronil-treated corrugated cardboard insert was developed. The precise dimensions of the harbourage entrance slots allow beetles to enter but prevent bee access or contact with the insert. Mean fiprole (fipronil plus its toxic metabolites) residues in honey ripened in research hives over one month while the devices were in place did not exceed 1 μg kg−1 and no ill effects on the bees were observed. A field trial was conducted at three western Sydney apiaries during autumn 2007 when beetle numbers were naturally increasing. Results demonstrated that deployment of a single harbourage on the bottom board of 26 infested hives caused an estimated 62% overall beetle mortality within 6 weeks and reduced mean live adult beetle numbers by 96%.

Stability of orthotropic elastic–plastic open conical shells

The paper presents a derivation of the stability equation and the solution method of the problem for an orthotropic elastic–plastic open conical shell. The use is made of the constitutive relations of incremental plastic flow theory, elastic compressibility of the material, and Shanley concept of increasing load are taken into account in the consideration. A variation, strain energy method is used to derive the stability equation for bilayered open conical shell with nonuniform pre-critical stress distribution. The shell is free supported at the edges and the load acting the shell, in the form of longitudinal force and lateral pressure, is active one, i.e. unloading is not considered.

Hydrodynamics studies of direct-drive cone-in-shell, fast-ignitor targets on OMEGA

Experiments have been performed on the OMEGA Laser Facility [T. R. Boehly et al., Opt. Commun. 133, 495 (1997)] to study the hydrodynamics of directly driven cone-in-shell, fast-ignitor targets. A 35° or 70° opening-angle gold cone was inserted into spherical plastic shells of ∼24-μm thickness and ∼870-μm diameter, which were imploded with up to 21kJ of 351-nm laser light. A backlighter was used on some experiments to compare the fuel assembly of targets with or without a high-pressure fill gas. The shock breakthrough to the inside of the cone, where the ultrafast laser propagates in integrated fast-ignitor experiments, was studied using a streaked optical pyrometer. No plasma was seen inside the cone before the assembled core reached peak compression.

Nonlinear stability of cylindrical shells subjected to axial flow: Theory and experiments

This paper, is concerned with the nonlinear dynamics and stability of thin circular cylindrical shells clamped at both ends and subjected to axial fluid flow. In particular, it describes the development of a nonlinear theoretical model and presents theoretical results displaying the nonlinear behaviour of the clamped shell subjected to flowing fluid. The theoretical model employs the Donnell nonlinear shallow shell equations to describe the geometrically nonlinear structure. The clamped beam eigenfunctions are used to describe the axial variations of the shell deformation, automatically satisfying the boundary conditions and the circumferential continuity condition exactly. The fluid is assumed to be incompressible and inviscid, and the fluid–structure interaction is described by linear potential flow theory. The partial differential equation of motion is discretized using the Galerkin method and the final set of ordinary differential equations are integrated numerically using a pseudo-arclength continuation and collocation techniques and the Gear backward differentiation formula. A theoretical model for shells with simply supported ends is presented as well. Experiments are also described for (i) elastomer shells subjected to annular (external) air-flow and (ii) aluminium and plastic shells with internal water flow. The experimental results along with the theoretical ones indicate loss of stability by divergence with a subcritical nonlinear behaviour. Finally, theory and experiments are compared, showing good qualitative and reasonable quantitative agreement.

Springback Compensation Based on Finite Element for Multi-Point Forming in Shipbuilding

Flame bending has been widely used for forming hull plates of marine vessels, Since it is difficult to estimated the amount of residual deformation after applying the flame heat, flame bending has been carried out by skilled workers without automatic facility. A mechanical bending such as multiple-piston pressing forming has been studied as an alternative to the flame bending. However, springback is a major problem in the press forming process. Present paper presents a combination of FEM (Finite Element Method) and springback compensation algorithm to calculate the compensated stroke of pressing points. In order to calculate the springback, the process is modeled by an elastic plastic material and shell elements. Combination of global scale factor and local scale factors is suggested to adjust the amount of strokes through an iterated numerical calculation. In each iteration, shape deviation between object surface and processed shape is minimized to reach the designed shape. The shape deviations due to springback are compensated using the residual shape estimated by FEM.

Critical load of a bilayered orthotropic elastic–plastic conical shell with the change of the shell basic surface location

The paper presents the derivation of stability equations and the comparison of critical loads for an orthotropic elastic–plastic conical shell with proper location of the shell basic surface. Prandtl–Reuss plastic flow theory is accepted in the analysis. To derive the stability equations the variational method was accepted and Ritz method was used to solve the equations. Numerical results were obtained by the use of a special iterative algorithm of the elastic–plastic analysis implemented on the PC.

Blast response of a lined cavity in a porous saturated soil

The paper proposes a comprehensive approach to simulate the blast response of a lined cavity in a porous soil. To calculate the soil–structure contact pressure, the coupled Godunov-variational-difference approach was developed. The lining is modeled by a Timoshenko elastic–plastic shell with kinematic linear hardening. To solve the problem in the lining domain, the variational-difference method is applied. The soil is modeled by the Lyakhov three-phase model that takes into account both bulk and shear elastic–plastic behavior, including the effect of soil pressure on the yield strength for the stress tensor deviator. The problem of blast wave propagation within the soil medium is solved by the Godunov method. The coupled approach to calculate the soil–lining contact pressure is based on the relationships on the shock and rarefaction waves with finite-difference equations of the shell motion using a simple iteration method. It allows the reduction of the contact problem to the self-similar symmetric Riemann problem. Solution of the problem of an explosion in a porous medium, and analysis of the soil–obstacle interaction under the blast action using the proposed method show good correspondence with available experimental results. Also, the plane problem of blast response of the circular cavity lined by a thin steel lining was solved. The effect of the gas volumetric content in the soil on the incident shock wave pressure as well as on the contact pressure and lining meridian strain was studied.

On post-buckling analysis and experimental correlation of cylindrical composite shells with Reissner–Mindlin–Von Kármán type facet model

In this paper post-buckling analysis of carbon fibre reinforced plastic cylindrical shells under axial compression is considered. Reissner–Mindlin–Von Kármán type shell facet model is used in the computations. The effect of geometric imperfection shape and amplitude on nonlinear analysis results is discussed. Numerical–experimental correlation is performed using the results of experimental buckling tests found in the literature. Results show that bringing the diamond shape geometric imperfection in the model significantly improves the correlation and gives good accuracy in simulating cylindrical shell post-buckling behaviour.

Investigations to Remove Domes from Plastic Shells by Polishing

A problem often observed for thick wall plastic targets is the presence of surface domes. We have been successful in applying mechanical polishing to remove isolated surface domes from thick wall 2 mm shells during a preliminary investigation. The background surface roughness for polished shells was dramatically improved with final values typically around 10 nm RMS as measured by WYKO patch surface profiles. The polishing sequence applied was also examined using AFM spheremapper data that was obtained for shells after each polishing step. A two-step polishing approach was able to produce shells that had significant improvement in all AFM power modes except for modes (3.10). Further polishing development is needed to reduce AFM low and mid power modes for shells. Polishing of otherwise target quality 2 mm shells that have domes could be a future treatment for NIF targets.

A Way to Reach the Cryogenic’s Temperature and Roughness Requirements for the Laser Megajoule Facility

Smooth solid DT layer inside a plastic spherical shell are needed in order to achieve the ignition on the Laser MegaJoule (LMJ) facility. This paper follows our previous one1 and presents the up to date results concerning the quenching and breathing techniques. New analysis software has been made which allowed us to update the results already obtained for the breathing technique. New experiments done on quenching have leaded to obtain a smooth layer for the higher mode down to 2.3 K below the triple point. The time where the roughness NIF specifications are obtained while the temperature is 1,5 K below the triple point is around 6 seconds using the quenching technique. Roughness analyses are made on one axis view. We also discuss other experimental aspects, such as shadowgraphy and redistribution process.

Mass Production Methods for Fabrication of Inertial Fusion Targets

The High Average Power Laser (HAPL) Program is a national program to develop Inertial Fusion Energy with lasers (http://aries.ucsd.edu/HAPL/), direct drive targets and solid wall chambers. General Atomics is currently constructing and will operate a Mass Production Layering Experiment (MPLX) System. The MPLX System will demonstrate the filling and layering of approximately 700 plastic spherical targets (4 mm diameter plastic shells) simultaneously in a fluidized bed as a batch process in less than a day. In addition the system will be able to characterize a single deuterium filled and layered cryogenically-cooled target. This paper details hardware being developed and tested for the building of this system.

Nuclear measurements of fuel-shell mix in inertial confinement fusion implosions at OMEGA

Direct drive spherical implosions on the OMEGA laser system [T. R. Boehly et al., Opt. Commun. 133, 495 (1997)] have shown that increased capsule convergence results in increased susceptibility to fuel-shell mix. Mix results from saturation of the Rayleigh-Taylor instability, leading to small-scale, turbulent eddies and atomic-level mixing of the high-density compressed shell with hot, low-density fuel from the core. To sensitively probe the extent of mix, nuclear yields were measured from implosions of capsules filled with pure He3. The plastic capsule shell contains a deuterated plastic (CD) layer either on the inner surface or offset from the inner surface by 1μm. Mixing of D from the shell with hot He3 in the core is necessary to produce 14.7MeV DHe3 protons in such capsules. DHe3-proton spectral measurements have been used to constrain the amount of mix at shock time, to demonstrate that some of the fuel mixes with the offset CD layer, and that capsules with a higher initial fill density or thicker shell are less susceptible to the effects of mix.

Stability and initial postbuckling behavior of anisotropic cylindrical shells under external pressure

A solution is obtained to describe the stability and initial postbuckling behavior of cylindrical shells made of composites with one plane of symmetry. The solution is based on the Donnell-Mushtari-Vlasov nonlinear theory of anisotropic shells and Koiter’s theory of buckling and postbuckling behavior. Calculated results are presented for boron plastic shells with reinforcement of different types under external pressure. It is shown that the conventional model of a composite as an orthotropic material is erroneous for many types of reinforcement

Internal blast loading in a buried lined tunnel

The paper presents a comprehensive approach to simulate an explosion occurring inside a buried axisymmetric lined cavity. The approach considers all the stages of the process: detonation of the internal charge; the shock wave propagation in the internal gas and its following interaction with the cavity's shell lining including multiple reflections; soil–structure dynamic interaction, including multiple gap opening/closure and wave propagation in the surrounding medium. The cavity's lining is modeled as a Timoshenko elastic plastic shell. The soil is modeled by the Grigoryan model that takes into account both bulk and shear elastic plastic behavior, including the effect of soil pressure on the yield strength for the stress tensor deviator. The gas-dynamics problem is solved by the modified Godunov method, based on a fixed Eulerian mesh with the so-called mixed cell. The variational difference method is applied to solve the problem in the soil and in the shell domains. The contact pressures acting on the lining due to both the detonation products on the internal side and the soil on its outer side are computed by solving the coupled system of finite differences equations of gas, shell and soil dynamics using a simple iteration method. The problems of a blast-hole charge and of a periodical system of spherical blast charges that are placed at equal distances from each other were solved. The explosion occurs within a cylindrical steel pipeline, surrounded by an elastic plastic loess soil. The effect of the soil elastic plastic pressure-density behavior and its shear properties on the soil–structure interaction (including the gap opening/closure process) was studied.

Incorporation of silver/carbon nanoparticles into poly(methyl methacrylate) via in situ miniemulsion polymerization and its influence on the glass‐transition temperature

AbstractSilver/carbon nanoparticles (9 nm) were incorporated, as reinforcements, into a matrix of poly(methyl methacrylate) via in situ miniemulsion polymerization. It was found by differential scanning calorimetry that the glass‐transition temperature of the poly(methyl methacrylate) showed an improvement of 14 °C with only 0.5 wt % nanoparticles in comparison with a pure poly(methyl methacrylate) control, which was also obtained by miniemulsion polymerization under the same conditions. This increase was related to a polymer chain mobility restriction due to a combination of bound plastic and joint plastic shell effects at the interphase and the surrounding regions. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 511–518, 2007.