Radial Compressions Research Articles

Compressive behavior and energy absorption analysis of casting skin-wrapped aluminum foams

The mechanical properties are an indispensable factor affecting the energy absorption capability of aluminum foam. In the past few decades, various aluminum foam sandwich structures, including casting skin-wrapped aluminum foams (CWFs), have been developed and proven to be effective in enhancing the integral mechanical properties. This study investigates how adding casting skin affects the compressive behavior and energy absorption of closed-cell aluminum foam. The aluminum foams were produced using the melt route and then used as the core material for manufacturing CWFs through counter-gravity casting solution after pre-heating. Axial and radial compressions were applied to columnar CWFs with pores falling within two size ranges and three ratios (D/T) of outer diameter to casting skin thickness. The failure mode of CWFs was dominated by brittle fracture of casting skin and progressive crush of foam core. Adding casting skin significantly enhanced the mechanical properties in axial compression, while it had no significant effect in radial compression, with both types of compression varying depending on D/T values. Samples with smaller pore sizes exhibited better overall performance. The influence of the addition of mass on the specific energy absorption should be considered in the design of lightweight crashworthy components.

Bulk moduli of two-dimensional Yukawa solids and liquids obtained from periodic compressions

Langevin dynamical simulations are performed to determine the bulk modulus in two-dimensional (2D) dusty plasmas from uniform periodic radial compressions. The bulk modulus is calculated directly from its physical definition of the ratio of the internal pressure/stress to the volume strain. Under various conditions, the bulk moduli obtained agree with the previous theoretical derivations from completely different approaches. It is found that the bulk moduli of 2D Yukawa solids and liquids are almost independent of the system temperature and the external compressional frequency.

Assessment of in situ properties of municipal solid waste with a large-diameter borehole method.

A Municipal Solid Waste Borehole Assessment (MBA) was developed to assess in situ geotechnical properties of municipal solid waste (MSW) during the boring of gas extraction well construction. A Large-Diameter Borehole Caliper (LDBC) was lowered into the borehole to measure the diameter and record the condition of the wall by time-lapse video photography. The results indicated that the borehole experienced significant radial compression with depth following completion. Radial compressions amounted to approximately 7.5% at 9.14 m, 10% at 21.3 m and 11% at 27.4 m below ground surface. The bulk modulus was estimated by using the captured volumetric strains and reported lateral earth coefficients, and the results showed that it increases with increasing depth. For MSW, the bulk modulus increased up to 13.4 MPa in a linear trend with depth. The unit weights of MSW were obtained using three diameter readings from LDBC, auger barrel outside diameter and outer cutting bit outside diameter. The results showed that the diameter based on outer cutting bit yielded realistic unit weights (5.08-9.68 kN m-3) due to unrealistic calculated saturations by other two assumed diameters. The borehole assessment with LDBC was shown to be an efficient and valuable means for characterising MSW and effectively designing gas extraction wells. The research provided a means to assess the waste mass with accuracy at great depths by directly observing and measuring borehole condition.

Analytical investigation on the nonlinear postbuckling of functionally graded porous cylindrical shells reinforced with graphene nanoplatelets

The objective of this study is an analytical investigation on the nonlinear postbuckling of functionally graded porous cylindrical shells reinforced with graphene nanoplatelets (GNPs). It is assumed that the GNP and porous distribution patterns vary smoothly through the thickness. Three distribution schemes are considered for GNP and porous media distributions. The effective material properties are calculated via a micromechanical method. By considering the geometric nonlinearity, the energy functional of the considered system under the combined axial and radial compressions is obtained based on the classical sell theory. Then, an analytical solution procedure based on the Ritz method and Airy function is used to obtain the nonlinear postbuckling behavior of considered system with simply supported boundary conditions. Finally, the effect of different parameters such as porous distribution, GNP scheme, porosity coefficient, GNP weight fraction and geometry on the nonlinear buckling loads, and postbuckling behavior is studied.

Contact Pressure and Strain Energy Density of Hyperelastic U-shaped Monolithic Seals under Axial and Radial Compressions in an Insulating Joint: A Numerical Study

In insulation joints, elastomeric U-shaped monolithic seals (UMSs) are replacing O-ring systems because of their enhanced sealing capabilities for the oil and gas industries. UMSs are compressed axially during assembly and radially when pressurized in operation. The reliability of UMSs due to the displacement imposed during assembly and the internal pressure in operation is influenced by the axial compression ratio, thickness ratio (TR), and geometric complexity. In this study, the hyperelastic behavior of elastomeric UMSs under axial and radial compressions is investigated using axisymmetric finite-element analysis. Twelve examples of UMSs with three geometric restraints (open grooves on both sides (type 1), an open groove on one side only (type 2), and no groove (type 3)) and four thickness ratios (TR = 0.25, 0.50, 1.00, and 1.50) are evaluated. To analyze nonlinear elastomeric materials, neo-Hookean constitutive equations are applied and the UMSs are considered as being a nearly incompressible hyperelastic material with a Poisson’s ratio of 0.499. The failure and detachment risks of UMSs are analyzed in terms of the equivalent stress, gap distance, contact pressure, and strain energy density. It is advantageous that the smaller the TR, the smaller the stress distribution. However, the generation of broader detachment regions is observed. Type 1 symmetrically shows the lowest stress distribution and the smallest detachment region, whereas type 3 symmetrically shows the highest values. Type 3 (TR = 0.25) shows the broadest detachment region in the arc-length range from −15.7 to 15.7 mm, whereas the largest gap of 0.7 mm is observed in type 2 (TR = 0.5). For all types, the detachment region disappears completely at TR = 1.0 or higher, which implies that full sealing is occurring. The average contact pressure increases exponentially during axial compression (in assembly) and linearly during radial compression (in operation). The largest contact pressure of 31.5 MPa is observed in type 3 (TR = 1.5), while the lowest is observed in type 1 (TR = 0.25). As for the strain energy density, type 3 at TR = 0.25 shows the largest increase in the strain energy density with 1.75 MJ/m3, while type 1 shows the most stable values of all cases. In conclusion, the lowest risk of failure of a nonlinear hyperelastic UMS was investigated numerically with minor equivalent stress and detachment region with higher contact pressure, which can be taken into account to ensure the reliability of the UMS.

Surface free energy effects on the postbuckling behavior of cylindrical shear deformable nanoshells under combined axial and radial compressions

In the traditional continuum mechanics, the effects of surface free energy are generally ignored. However, this cannot be the case for nanostructures because of their high surface to volume ratio; surface energy plays an important role in the mechanical responses. In the present study, the nonlinear buckling and postbuckling characteristics of cylindrical nanoshells subjected to combined axial and radial compressions are investigated in the presence of surface energy effects. To this end, Gurtin–Murdoch elasticity theory is implemented into the classical first-order shear deformation shell theory to develop an efficient size-dependent shell model incorporating surface free energy effects. Subsequently, a boundary layer theory is employed including surface effects in conjunction with the nonlinear prebuckling deformations, the large postbuckling deflections and the initial geometric imperfection. Finally, a solution methodology based on a two-stepped singular perturbation technique is utilized to obtain the size-dependent critical buckling loads and equilibrium postbuckling paths corresponding to the both axial dominated and radial dominated loading cases. It is observed that for the both axial dominated and radial dominated loading cases, surface free energy effects cause to increase the both critical buckling load and critical end-shortening of shear deformable nanoshell made of silicon.

Experimental validation of more realistic computer models for stent-graft repair of abdominal aortic aneurysms, including pre-load assessment.

Although the endovascular repair of abdominal aortic aneurysms is a less invasive alternative than classic open surgery, complications such as endoleak and kinking still need to be addressed. Numerical simulation of endovascular repair is becoming a valuable tool in stent-graft (SG) optimization, patient selection and surgical planning. The experimental and numerical forces required to produce SG deformations were compared in a range of in vivo conditions in the present study. The deformation modes investigated were: bending as well as axial, transversal and radial compressions. In particular, an original method was developed to efficiently account for radial pre-load because of the pre-compression of stents to match the graft dimensions during manufacturing. This is important in order to compute the radial force exerted on the vessel after deployment more accurately. Variations of displacement between the experimental and numerical results ranged from 1.39% for simple leg bending to 5.93% for three-point body bending. Finally, radial pre-load was modeled by increasing Young's modulus of each stent. On average, it was found that Young's modulus had to be augmented by a factor of 2. Copyright © 2016 John Wiley & Sons, Ltd.

Compression Responses of Bio-Cellular Luffa Sponges

Crushing behaviors of luffa sponges were studied through mechanical experiments. Controlled by four-order hierarchical and anisotropic structures, luffa sponges exhibit anisotropic responses along axial, radial, and circumferential directions. The ultra-thin but stiff inner surface layer dominates the crushing behavior, endowing the axially compressed luffa cylinder with structural integrity, enhancing the elastic deformation and yielding strength. In radial, circumferential, and lateral compressions, after removing the inner surface layer, luffa sponges are compliant and have large quasi-linear deformation before densification, without a plateau characterized by yielding and deformation. Immersed into water, crushed luffa sponge cylinders recover their geometry completely. However, compression strength is only partially restored. Gradual damage of the inner surface layer in water immersing/drying cycles greatly weakens the compression strength. In the case of removal of the inner surface layer, crushed luffa sponge cylinders completely restore their quasi-linear deformation ability during the water immersing/drying cycles.

Surface stress effects on the postbuckling behavior of geometrically imperfect cylindrical nanoshells subjected to combined axial and radial compressions

Because of surface free energy effects at nanoscale, study of the mechanical behavior of nanostructures including surface stress effects is a topic of substantial interest. Herein, the nonlinear buckling and postbuckling characteristics of geometrically imperfect cylindrical nanoshells under combined axial and radial compressive loads are investigated in the presence of surface stress effects. An efficient size-dependent shell model is proposed based on Gurtin–Murdoch elasticity theory and von Karman–Donnell-type of kinematic nonlinearity. On the basis of variational approach using the principle of virtual work, the non-classical governing differential equations are derived. Afterwards, a boundary layer theory is employed incorporating surface stress effects in conjunction with nonlinear prebuckling deformations, initial geometric imperfections and large postbuckling deflections. Then a two-stepped singular perturbation methodology is put to use in order to solve the size-dependent nonlinear problem corresponding to axial dominated and radial dominated loading cases. It is shown that in the case of radial dominated loading, the combination of hydrostatic pressure with axial compression causes to decrease approximately the effect of surface stress compared to the absence of axial load. However, for the axial dominated loading case, in comparison with no applied radial load, the surface stress effects is more significant in the presence of hydrostatic pressure.

Nonlinear buckling and postbuckling behavior of cylindrical nanoshells subjected to combined axial and radial compressions incorporating surface stress effects

In the present study, the Gurtin-Murdoch elasticity theory, as a theory capable of capturing size effects, is implemented to predict the nonlinear buckling and postbuckling response of cylindrical nanoshells under combined axial and radial compressive loads in the presence of surface stress effects. For this purpose, a size-dependent shell mode containing geometric nonlinearity is proposed within the framework of the classical shell theory. Because it is necessary to satisfy balance conditions on the surfaces of nanoshell, it is assumed that the normal stress component of the bulk varies linearly through the shell thickness. On the basis of a variational formulation using the principle of virtual work, the non-classical governing differential equations are derived. Subsequently, a boundary layer theory is employed including the nonlinear prebuckling deformations and the large deflections in the postbuckling regime. Then a two-stepped perturbation methodology is utilized to obtain the size-dependent critical buckling loads and the postbuckling equilibrium paths of nanoshells corresponding to the axial dominated and radial dominated loading cases. It is revealed that in the radial dominated loading case, a positive value of surface elastic constants leads to increase the critical buckling load but decrease the critical end-shortening of nanoshell. However, in the axial dominated loading case, surface elastic constants with positive sign causes to increase the both critical buckling load and critical end-shortening of nanoshell.

Evidence of Multiwall Carbon Nanotube Deformation Caused by Poly(3-hexylthiophene) Adhesion

We show that when a soft polymer like poly(3-hexyl-thiophene) wraps multiwall nanotubes by coiling around the main axis, a localized deformation of the nanotube structure is observed. High resolution transmission electron microscopy shows that radial compressions of about 4% can take place, and could possibly lead to larger interlayer distance between the nanotube inner walls and reduce the innermost nanotube radius. The mechanical stress due to the polymer presence was confirmed by Raman spectroscopic observation of a gradual upshift of the carbon nanotube G-band when the polymer content in the composites was progressively increased. Vibrational spectroscopy also indicates that charge transfer from the polymer to the nanotubes is responsible for a peak frequency relative downshift for high P3HT-content samples. Continuously acquired transmission electron microscopy images at rising temperature show the MWCNT elastic compression and relaxation due to polymer rearrangement on the nanotube surface.

Power law scaling of lateral deformations with universal Poisson’s index for randomly folded thin sheets

We study the lateral deformations of randomly folded elastoplastic and predominantly plastic thin sheets under the uniaxial and radial compressions. We found that the lateral deformations of cylinders folded from elastoplastic sheets of paper obey a power law behavior with the universal Poisson’s index = 0.17 0.01, which does not depend neither the paper kind and sheet sizes thickness, edge length nor the folding confinement ratio. In contrast to this, the lateral deformations of randomly folded predominantly plastic aluminum foils display the linear dependence on the axial compression with the universal Poisson’s ratio e = 0.33 0.01. This difference is consistent with the difference in fractal topology of randomly folded elastoplastic and predominantly plastic sheets, which is found to belong to different universality classes. The general form of constitutive stress-deformation relations for randomly folded elastoplastic sheets is suggested.

Radial Compressive Properties of the Biodegradable Braided Regeneration Tubes for Peripheral Nerve Repair

Different regeneration tubes braided from biodegradable material poly (glycolide-co-L-lactide) (PGLA) for peripheral nerve repair and their radial compressive properties are presented. The influences of the braided structure and braiding angle are discussed. The results have shown that the nerve tube braided with the triaxial structure and the braiding angle at 60 has a higher ability to resist the radial compressions.

Dynamics of a high-power aluminum-wire array Z-pinch implosion

Annular Al-wire Z-pinch implosions on the Saturn accelerator [D. D. Bloomquist et al., Proceedings, 6th Pulsed Power Conference (Institute of Electrical and Electronics Engineers, New York, 1987), p. 310] that have high azimuthal symmetry exhibit both a strong first and weaker second x-ray burst that correlate with strong and weaker radial compressions, respectively. Measurements suggest that the observed magnetic Rayleigh–Taylor (RT) instability prior to the first compression seeds an m=0 instability observed later. Analyses of axially averaged spectral data imply that, during the first compression, the plasma is composed of a hot core surrounded by a cooler plasma halo. Two-dimensional (2-D) radiation magnetohydrodynamic computer simulations show that a RT instability grows to the classic bubble and spike structure during the course of the implosion. The main radiation pulse begins when the bubble reaches the axis and ends when the spike finishes stagnating on axis and the first compression ends. These simulations agree qualitatively with the measured characteristics of the first x-ray pulse and the overall energetics, and they provide a 2-D view into the plasma hydrodynamics of the implosion.

Stochastic stability and nonstability of a linear cylindrical shell

The regions of almost sure stochastic stability and nonstability of a uniform elastic cylindrical shell subjected to radial and axial stochastic compressions are investigated. Both radial and axial loadings are assumed to be correlated ergodic Gaussian random processes. The stability and nonstability regions are determined as functions of intensities of the acting loadings and the external damping coefficient. The problem is solved by means of Liapunov functionals method.

Method of Active Charge and Current Neutralization of Intense Ion Beams for ICF

Intense ion beam neutralization by sufficiently cold, co-moving and co-injected electrons is crucial to Light Ion and important to Heavy Ion Inertial Confinement Fusion (ICF) drivers for the ballistically focused propagation onto ~ 5 mm radius targets located some 10 m downstream. Methods of generating the beam neutralization electrons with required properties are given in the context of a Light Ion Fusion Experiment (LIFE) designed accelerator. Recently derived envelope equations for neutralized and ballistically focused intense ion beams are applied to the LIFE geometry in which 10 MeV He+ multiple beamlets coalesce and undergo 45:1 radial compression while beam pulses experience a 20:1 axial compression in the propagation range of 10 m. For these representative conditions, the theoretical analysis produces a requirement of the initial electron temperature neutralizing the ions as Teo ≤ 35 eV where also the initial ion temperature T <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">io</sub> is correlated. Both active and auto <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sup> -neutralization methods are examined and found to produce initial electron temperatures consistent with the requirement of the envelope equation for both radial and axial adiabatic beam pulse compressions. The stability of neutralized beam propagation is also examined concerning the Pierce type electrostatic instability and for the case of LIFE beams it is found to have insignificant effect. A scaled experimental setup is presented which can serve to perform near term tests on the ballistically focused propagation of neutralized light ion beams.

Multi-Stage Intense Ion Beam Electrostatic Accelerator for ICF

The design of a multi-aperture, channel focused, multi-stage low 8 electrostatic accelerator is made to produce well controlled intense light ion beams as drivers of Inertial Confinement Fusion (ICF) targets. Unlike the case of diode accelerators, the Light Ion Fusion Experiment (LIFE) accelerator system contains separate-function elements to launch 3 to 10 MeV, 23 kA accelerated current, He+ beams in 400 ns pulses where 20:1 axial pulse compression would occur during the neutralized and ballistically focused transport. Each beam line would impart 50 kJ implosion energy in ~ 20 ns on 5-6 mm radius targets located 10 m downstream and a system of 40 beam lines would deliver 2 MJ. Methods of producing beam neutralization with initial electron temperature Teo, satisfying analytically derived constraints for both radial (45:1) and axial (20:1) pulse compressions during transport are given separately. Also, the development of a pulsed intense cold plasma ion source capable of producing 1 A/cm2 and Ti ~ 0.15 eV He+ beamlets over large extraction surfaces which is suitable for this application is presented in these proceedings.