Thin Liner Research Articles

General Kinematical Solution to the Motion of an Explosively Driven Liner

AbstractIt is shown that the motion of an explosively driven smooth thin liner, obeys, whenever the material forces are negligible, the following equation: where V is the liner velocity, ∂Vl/∂t is the time derivative of the velocity component along the liner direction and l is the Lagrangian coordinate measuring the length of the liner contour (formation line). The transformation from the rest to moving coordinate system is calculated, as well as a very accurate approximation to the liner elongation. Under the assumption of an exponential acceleration a closed form for the liner elongation is obtained. The influence of the liner curvature on the projection angle δ is also found. The comparison of the obtained solution with two dimensional Lagrangian code calculations shows a very good agreement. Finally, some predictions of the model are discussed for demonstrating its applicability to various problems.

A new method for sealing composite resin contraction gaps in lined cavities.

Composite resin restorations are often applied in cavities where cervical margins are left unetched, resulting in poorer adaptation in this area. Recent experiments have indicated the possibility of impregnating with resin the gap caused by polymerization contraction. Cavities were prepared in vitro and in vivo. A thin liner was applied inside and outside the cavity. Except for the cervical wall, enamel margins were bevelled and acid-etched, and the cavities restored with Concise Enamel Bond and Composite. In another series, cavities with unetched enamel were restored. Since the liner was placed outside the cavity margins, excess material could be removed without blockage of the air-filled gap. Enamel Bond with a fluorescent additive was applied to various margins. Ground sections were prepared, and the penetration of this resin into the gap was examined with a microscope. In most teeth, the resin penetrated from 0.5 to 2 mm from the cervical margins. Similar penetration was seen from unetched margins, except for the occlusal one. No penetration was seen at acid-etched margins. By impregnating gaps with low-viscous resin after the filling has cured, one can obtain an improved seal at unetched margins.

Spherical Kevlar 49/Epoxy Vessels with 430-MPa (62-ksi) Burst Pressures

A development program for spherical composite pressure vessels with burst pressures as high as 430 MPa (62.5 ksi) is described. Vessels were fabricated by filament-winding Kevlar 49/epoxy over thin seamless copper liners. Two configurations of stainless steel fill stems were evaluated both experimentally and analytically. Finite-element techniques were used to compute stress concentrations produced in the liner and composite shell as a result of the fill-stem geometry. An analytical model was used to estimate vessel pressure-strain response and predict burst pressure as a function of composite and liner properties, composite fiber volume fraction vf, and the composite shell's outer to inner radius ratio β. This model predicts a nonlinear relationship between the burst pressure and β, and at a given β a strong dependence of burst pressure on vf. Experimental data confirmed the predicted dependence of burst pressure on fiber volume fraction. In addition, predicted values of surface strain and burst pressures were in fair agreement with experimental data.

Morphology and chemistry of projectile residue in small experimental impact craters

Small‐scale impact craters (5‐7 mm in diameter) were produced with a light gas gun in high purity Au and Cu targets using soda lime glass (SL) and man‐made basalt glass (BG) as projectiles. Maximum impact velocity was 6.4 km/s resulting in peak pressures of approximately 120–150 GPa. Copious amounts of projectile melts are preserved as thin glass liners draping the entire crater cavity; some of this liner may be lost by spallation, however. SEM investigations reveal complex surface textures including multistage flow phenomena and distinct temporal deposition sequences of small droplets. Inasmuch as some of the melts were generated at peak pressures >120 GPa, these glasses represent the most severely shocked silicates recovered from laboratory experiments to date. Major element analyses reveal partial loss of alkalis; Na2O loss of 10–15% is observed, while K2O loss may be as high as 30–50%. Although the observed volatile loss in these projectile melts is significant, it still remains uncertain whether target melts produced on planetary surfaces are severely fractionated by selective volatilization processes.

Crack extension caused by internal gas pressure compared with extension caused by tensile stress

Explosive loading in borehole configurations has been investigated to assess the relative importance of internal gas pressurization and stress-wave-induced circumferential tensions for extending radial cracks originating at the borehole walls. Simple calculations of an extending crack (with and without confining pressure) were performed to estimate an upper bound on crack length resulting solely from internal pressurization for comparison with the crack length resulting solely from tensile stresses. These calculations indicated that a internal gas pressure could increase the crack length by a factor of 10 to 100 (no confining pressure) or 3 to 25 [6.9-MPa (1000-psi) confining pressure] compared with the tensile stresses acting alone. Simple laboratory experiments were performed using 3.2 × 10−3m diameter (1/8in.) by 1.52 × 10−1m long (6 in.) borehole charges centered in a 1.3 × 10−2m diameter (1/2in.) borehole in transparent Plexiglas cylinders 3 × 10−1m in diameter by 3 × 10−1m long (12in. by 12in.) to verify these computational results. Two tests were performed: one with a thin (5.08 × 10−4m) steel liner to contain the explosive gases and one without a liner so that the explosive gases could enter and pressurize the fractures. A confining pressure of 6.9 MPa (1000 psi) was applied to the Plexiglas cylinders in both experiments to better simulate field conditions and to contain the cracks within the cylinder; all other experimental conditions were identical. These experiments indicated that the primary effect of the explosive gases was to increase crack length by a factor of five to ten compared with the tensile stresses acting alone, in approximate agreement with the predictions.

Polymerization of acrylamide using the hydrogen peroxide–hydroxylamine couple

AbstractThe large heat of polymerization for acrylamide makes the measurement of conversion by temperature rise in an adiabatic system quite convenient. The initial monomer concentration in the reaction medium ranged from 0.2 to 0.8 mol/kg while the concentration of the two initiator components was varied from 1 to 100 mmol/kg. The adiabatic reactor was an aluminum beaker with a thin internal organic liner. The reactor was insulated and shielded. Approximate reactor charge was 200g. Iron has a pronounced accelerating effect on the rate. The predominant reaction appears to be the iron‐catalyzed decomposition of hydrogen peroxide in the presence of small amounts of hydroxylamine hydrochloride. At hydroxylamine to peroxide ratios greater than about 1:2, there seems to be no further benefit from hydroxylamine additions. The activation energy is lowered by the addition of iron decreasing from 18.7 kcal/mol with no added iron to 4.5 kcal/mol when the system contains 1 ppm iron.

Experimental study of a new mechanism of magnetic flux cumulation by the propagation of shock-compressed conductive region in silicon

A new mechanism of magnetic flux compression proposed by one of the authors has been experimentally proved promising for the generation of ultrahigh pulsed fields. A cylindrical implosion type device is used here, and the thin metal liner normally used is replaced by a solid cylinder of crystalline or powdery silicon. As predicted by the theory, the field compression factor depends strongly on the initial density of the silicon, on the explosive, and on the scale. A typical value of the field multiplication factor is 17.8 for a 45-mm-diam silicon cylinder of density 1.1 g/cm3.

Interaction of a cylindrical cavity with a periodically supported thin shell liner

The coupled axisymmetric problem of a periodically supported circular cylindrical shell bonded to a cylindrical cavity in an infinite isotropic, homogeneous elastic body is investigated. Explicit expressions for the resulting Fourier coefficients are obtained and convergence of the solution is established. Numerical results for two different shell materials in contact with a typical geologic formation are presented.

Elementary catastrophe theory modelling of an end-loading ring in a rigid cavity

The gas-tight integrity of the thin steel cylindrical liner shells of containment vessels is an important problem in nuclear engineering. To ensure the liner's integrity, it is required that buckling or deformation be avoided. Consequently, in order to estimate the load carrying capacity of the liner the load-displacement response must be investigated. To examine the instabilities of a circumferential slice of the liner shell, subjected to compressive end loading forces, elementary catastrophe theory (ECT) is used. ECT is a recently developed mathematical tool that provides conceptual insight into systems exhibiting discontinuous behavior changes. An ECT model for an elastic ring in a ridgid cavity is developed and a discussion of experimental data supporting the model is presented.

28. Vacuum developments for fusion plasma experiments

Summary The vacuum design of a proposed large toroidal pinch experiment and some of the development work undertaken is described. The system comprises four main parts. A thin inconel bellows liner (surface area 160 m 2 ) contains the plasma and is bakeable to achieve uhv. This liner is protected by a guard vacuum to relieve it of atmospheric pressure load and the consequences of pinhole formation. The guard region also gives thermal and electrical insulation. A gas admittance system is used to pulse fill the liner with 0.1 to 10 mtorr of H 2 , D 2 or He with tracer gases. Criteria for choosing the pumping speed (7000 l s −1 at the liner) and other vacuum parameters (e.g. maximum permitted leakage) have been developed to minimize impurities in the plasma. Contamination by low mass number elements Data obtained from tests of several materials (including perflouroelastomer) likely to be used in vacuum and plasma diagnostic components will be given.

Buckling of a stud-supported thin cylindrical liner shell encased in concrete

The problem of a point-supported liner shell encased in a rigid cylindrical cavity is studied. The large displacement equations are developed, and the resulting non-linear equations are solved in closed form for an assumed buckling wave. The analytical model is specialized to the case of the ring or infinite cylinder under circumferential strain, and is compared to published results. Complete load displacement curves are presented for the ring or cylinder with a predominate circumferential strain, and for the axisymmetric response or cylindrical shells under an axial load. The results of this study can be used to determine the spacings of point supports for cylindrical liner shells.

The stability of a uniformly compressed ring surrounded by a rigid circular surface

As a first step in the study of the stability of the thin steel liner of a prestressed concrete pressure vessel, the states of equilibrium of a uniformly compressed elastic ring placed inside a rigid circular cylinder are analysed. It is shown that there is no critical load as defined by classical theory, but that there is a state of unstable equilibrium which can be reached by small displacements only from the unbuckled position and a state of stable equilibrium which necessitates large displacements. Work must always be done to displace the ring from the unbuckled state, but this is reduced as the uniform compression is increased. Buckling apparently takes place when some random disturbance occurs which is large enough to provide the effort needed.

The stabilisation of the steel liner of a prestressed concrete pressure vessel

The thin steel liner of a nuclear reactor concrete pressure vessel is likely to buckle inward as the concrete is prestressed. This paper deals with the case of a hollow cylinder of infinite length. After analysis of the equilibrium states of the shell it is concluded that buckling can be suppressed by anchoring the shell to the concrete with the anchors spaced circumferentially at S p = 2.5 t/√ ϵ, where t is the thickness of the shell and ϵ is the circumgerential strain imposed by prestressing. The maximum value of ϵ for which no pegging is needed is given by ϵ 0 = 0.5( t/ R) 1.2, where R is the radius of the vessel. The analysis has been verified experimentally.

Explosively Loaded Metallic Cylinders. I

Recent experiments using thin-walled metal cylinders internally loaded with high explosives have been performed in an effort to show that the casing velocity vector bisects the angle formed by the expanding cylinder and the undisturbed portion. This relation, which was first derived by Sir Geoffrey Taylor, can be expressed by the equation δ=θ/2, where δ is the angle between the velocity vector and the normal to the undisturbed casing, and θ is the angle formed by the normals to the moving and undisturbed portions of the casing. Although this relation forms a part of most theories pertaining to the acceleration of thin liners by high explosives, direct experimental verification of the relation has been difficult. In an attempt to verify Taylor's relation, values of δ were determined by inspecting the fragmentation patterns produced on cylindrical witness targets surrounding the charges. The values of δ determined in this manner are within the range of recent measurements by Singh using similar charges. Values of θ were independently determined from Kerr Cell photographs of the expanding cylinders. The experimental observations are in good agreement with the relation δ=θ/2.

Vacuum Treatment of Parkes’ Process Crusts On a Pilot-Plant Scale

Parkes’ process crusts were vacuum distilled using a shortened Pidgeon retort. Zinc was effectively removed below 800°C and re-covered as a zinc sheet easily stripped f rom the furnace liner. Lead distillation required about 950°C and the resulting lead condensate tended to stick to the thin metal liner. Final purity of residue is limited only by nonvolatile metals such as copper.