Unidirectional Compression Research Articles

The properties of copper foams with negative Poisson's ratio via resonant ultrasound spectroscopy

The Poisson's ratios of re-entrant Cu foams with different initial relative densities were studied by resonant ultrasound spectroscopy (RUS). Slight anisotropy in foam was detected by RUS and removed by a small unidirectional compression. The transformation into the re-entrant foam was accomplished by applying a sequence of permanent triaxial compression deformations. The Poisson's ratio first decreases and then increases with increasing compression strain. A minimum in Poisson's ratio of approximately −0.7 for all initial densities was achieved with an appropriate permanent compression strain, compared with −0.6 at similar density determined earlier via optical methods. Foams with higher values of initial density attained minima in Poisson's ratio at lower permanent volumetric compression. The shear modulus increased with increasing volumetric compression ratio, and showed a small hump near the point corresponding to Poisson's ratio minimum.

Advanced Composites with Multi-Functionality Enhanced by Nanoparticles

Continuous fibre (carbon or glass) composite laminates with an epoxy matrix modified by nanoparticles (nanosilica of 25 nm or nanocarbon of 35 nm) were fabricated using a vacuum assisted resin infusion technique, aided by hot pressing, that produces high performance composites of a fibre fraction over 60 vol%. The presence of nanoparticles enhances fibre-matrix adhesion, the transverse tensile strength, the unidirectional compression strength, and mode I interlaminar fracture toughness. In particular, the GF/EP composites with the conductive nanoparticles allow the in-situ monitoring of damage (e.g. delamination) growth and impact damage assessment using a novel method of electrical resistivity tomography.

First-principles calculations on elastic, electronic and optical properties for the alkaline platinum hydrides A2PtH6 (A=K, Rb and Cs)

The alkaline platinum hydrides are considered the most promising as hydrogen storage materials. The alloying ability of crystal, elastic constants and related parameters, electronic and optical properties have been studied using pseudo-potential plane–wave method based on the density functional theory. The investigated compounds show a weaker resistance to compression along the principal a-axis and their resistance to shear deformation is lower than the resistance to the unidirectional compression. The band structure indicates that A2PtH6 (A=K, Rb and Cs) are X–X direct gap semiconductors. The effective electron mass at equilibrium has been predicted towards X–Γ, X–W and L–W directions. The strong hybridization between Pt-d and H-s states in the upper valence band translates the existence of covalent bonding character in these compounds. The static optical dielectric constant is inverse proportional to the fundamental gap.

Compression behaviors of magnetorheological fluids under nonuniform magnetic field

This work is concerned with an experimental and theoretical study on compression properties of magnetorheological fluids under the nonuniform field. Experimental tests of unidirectional monotonic compression were firstly carried out under constant area operation using a commercial plate–plate magneto-rheometer where the magnetic field radial distribution was nonuniform. Normal forces increased with decreasing of the gap distance, and two regions were found through the normal force versus gap distance curves: elastic deformation and plastic flow. High normal forces could be obtained in the case of high magnetic field, high compression velocity, low initial gap distance, high volume fraction, and high medium viscosity. In the plastic flow region, the normal force with the gap distance could be fitted with a power law relation $F_{\textrm {N}} \propto h^n$ , and the index n was around well in the range (−3, −2). Taking nonuniform magnetic field into account, the theoretical modeling in the plastic flow was then developed to calculate the normal force under compression based on the continuum media theory. Compared to the uniform field, there existed a magnetic field gradient-induced normal force under nonuniform field. Considering the sealing and squeeze strengthening effect, the gap distance-dependent shear yield stress was proposed, and a good correspondence between the theoretical and experimental results was obtained.

Deterministic and probabilistic assessment of the critical buckling strength of ships’ grillages (gross panels)

An analytical method for control of the strength of a grillage (gross panel) under unidirectional in-plane axial load is proposed. It allows us to solve the following tasks: (i) calculation of the critical stiffness of transverse girders, (ii) calculation of the maximum unidirectional in-plane compression load when the structure's scantlings are known (iii) and calculation of the required structure's scantlings when the unidirectional in-plane compression load is given. The proposed procedure is helpful in the application of probabilistic methods without employing specialised computer programmes, which is an advantage when fast (although approximate) evaluation is needed for the grillage critical buckling strength (e.g. ship's deck structure) before applying the finite-element method (FEM) analysis. Results of analytical approach are compared and confirmed using FEM data. A probabilistic method for control of the strength of ship's deck structure under unidirectional in-plane axial load is proposed. It allows us to assess the effect of deterioration due to corrosion on the deck's buckling strength while avoiding the use of specialised computer programmes.

Uniaxial tension and compression characterization of hybrid CNS–glass fiber–epoxy composites

In this work, unidirectional multi-scale, carbon nanostructure (CNS)–glass fiber–epoxy, composites were manufactured using a novel in-line continuous production scalable chemical vapor deposition based CNS manufacturing process. The processing parameters peculiar to the growth system, specifically growth chamber temperature, catalyst concentration and line speed, were varied to observe the effect on the CNS growth and parent filament degradation. Unidirectional tension and compression tests were conducted to measure the strength and modulus in the filament direction and failure mechanisms of the hybrid materials identified. Based on the results of tensile tests, gains in tensile strength and tensile modulus are achieved through a uniform coverage of short CNS. The greatest increases in CNS-enhanced composite compressive strength can be achieved through the combination of low weight percent CNS on the fiber and minimal parent filament environmental degradation. For stiffness governed applications, these CNS-enhanced composites may not provide the ideal solution. However, applications which demand significant deformation prior to failure or damage tolerance can benefit from the properties afforded by these CNS–fiber–epoxy composites.

Experiments on centimeter-sized dust aggregates and their implications for planetesimal formation

The first macroscopic bodies in protoplanetary disks are dust aggregates. We report on a number of experimental studies with dust aggregates formed from micron-size quartz grains. We confirm in laboratory collision experiments an earlier finding that producing macroscopic bodies by the random impact of sub-mm aggregates results in a well-defined upper-filling factor of 0.31 \pm 0.01. Compared to earlier experiments, we increase the projectile mass by about a factor of 100. The collision experiments also show that a highly porous dust-aggregate can retain its highly porous core if collisions get more energetic and a denser shell forms on top of the porous core. We measure the mechanical properties of cm-sized dust samples of different filling factors between 0.34 and 0.50. The tensile strength measured by a Brazilian test, varies between 1 kPa and 6 kPa. The sound speed is determined by a runtime measurement to range between 80 m/s and 140 m/s while Young's modulus is derived from the sound speed and varies between 7MPa and 25MPa. The samples were also subjected to quasi-static omni- and uni-directional compression todetermine their compression strengths and flow functions. Applied to planet formation, our experiments provide basic data for future simulations, explain the specific collisional outcomes observed in earlier experiments, and in general support a scenario where collisional growth of planetesimals is possible.

On the validity of continuous media theory for plastic materials in magnetorheological fluids under slow compression

In this manuscript, we address the long-standing question of whether a single theory for model plastic fluids is suitable to deal with the unidirectional compression problem in magnetorheological (MR) fluids. We present an extensive experimental investigation of the performance of MR fluids in slow-compression, no-slip, constant-volume squeeze mode under different magnetic field strengths (0–354 kA/m), dispersing medium viscosities (20–500 mPa·s) and particle concentrations (5–30 vol%). Normal force versus compressive strain curves reasonably collapse when normalizing by the low-strain normal force. Deviations from the squeeze flow theory for field-responsive yield stress fluids are associated to microstructural rearrangements under compression in good agreement with the so-called squeeze strengthening effect. Yield compressive stresses are found to scale as \(\sim \eta^{0.33\, }\phi ^{2.0\, }\)H2.0.

Squeeze flow magnetorheology

This paper is concerned with an investigation of the rheological performance of magnetorheological fluids under squeeze flow. Preliminary results on Newtonian fluids are first compared to Stefan’s equation. Then, unidirectional monotonic compression tests are carried out in the presence of uniaxial external magnetic fields at slow compression rates under constant volume operation. Results are compared to Bingham plastic, biviscous, and single chain micromechanical squeeze flow models. Measurements using combined deformation modes (compression+small-strain oscillatory shear) suggest a compression-induced shear strengthen effect up to strains of ∼0.5. Particle-level dynamic simulations are in qualitatively good agreement with experimental observations.

A multi-region model for numerical simulation of micro bulk forming

Due to the small billet size in micro forming, each grain, especially that on the surface layer, has direct influence on the deformation behavior of the billet. The multi-region model was proposed for simulating the micro bulk forming process in this paper. The object in the model is divided into three different regions: the inner polycrystal region, the grain interior of the surface region and the grain-boundary layer in the surface region. Each surface grain has different orientation. Depending on the Hall–Petch formula, which is applicable to describe polycrystal materials, and introducing scale parameters, the constitutive equation of each region is deduced based on the unidirectional compression tests data of the copper specimen. Using the multi-region model, the coining process with micro feature is simulated to investigate the size effect in micro forming. Moreover, an experiment of coining process with micro-feature is performed to verify the correctness of the multi-region simulation model. The experimental results show a good agreement with those in numerical simulation.

High Resistance Porous Pieces Obtained by PM, Reinforced with Metallic Yarns

The paper presents the results of the experiment in the fields of new technologies of obtaining PM reinforced with metallic yarns pieces. This type of high resistance porous pieces are made from a base part from recovered low alloyed steel or iron powder reinforced in the border zone with high alloyed steel yarns. For the reinforcing have been used solid yarns Φ 0,3 mm and mixed yarns Φ 0,45 mm. There have been obtained parallelipipedic samples reinforced with four yarns placed as in fig.1.1. The samples have been pressed at 300-600 MPa pressure. The pressing has been made orthogonal onto the placement direction of the yarns. The compacting has been made in an unidirectional compression mould with section of 7x51mm. The sintering was made at 1200 degree Celsius in an argon medium. The sintered samples have densities of 5,72g/cm3 (pressed at 300MPa) and 6,72 g/cm3 (pressed at 600MPa). There have been made mechanical bending tests. There were obtained bending strengths σi=490…800 MPa. From the things previously presented it can be observed that this type of reinforced with yarns pieces have high bending strength, though they have high porosity (low density).

Microstructural Aspects of Grain Boundary Bulge in a Dynamically Recrystallized Mg-Al-Zn Alloy

Microstructural features of grain boundary bulging have been studied in a dynamically recrystallized (DRXed) Mg-Al-Zn alloy. Unidirectional compression was used to deform the specimens to different strains at 473 K (200 °C). Microstructural characterization of the deformed specimens was performed by using both scanning electron microscopy and transmission electron microscopy (TEM). From the present results, it is suggested that in AZ31 Mg alloy, the DRXed grain is developed from grain boundary bulging. After a grain boundary segment starts to bulge, a bridging dislocation wall forms and anchors the bulged grain boundary. During further deformation, the misorientation of this bridging wall gradually increases, then transforms into a grain boundary, and a DRXed grain forms. Electron backscattered diffraction was used to study the orientation relationship between bulges/DRXed grains and the parent grains, and no special orientation relationship was found between them.

Numerical Simulation and Press Molding of Glass Micro Devices

Many kinds of optical glass devices are needed in various fields such as optics, biotechnology, medical care and so on. If an optical device such as an aspheric lens does not have a simple shape, and/or its size is micro-/nanometer scale, press molding should be carried out at a higher temperature than the glass transition temperature (Tg) to reduce cost and increase productivity. However, the most suitable conditions for glass molding are generally determined by performing many experiments. Consequently, it is useful to be able to predict the most suitable molding condition by numerical simulation. Press molding experiments and numerical simulation using finite element analysis, in relation to micro press molding of the borosilicate glasses Pyrex and D263, were carried out. Thermo-viscoelastic properties of the glasses were estimated using unidirectional compression creep testing according to traditional thermo-viscoelastic theory. Glass micro press molding was carried out with a glassy carbon die with a line and space pattern machined by a dicing saw. The optimum molding temperatures for accurate transcription of the die profile to the glass were investigated. Numerical simulation of micro press molding of the glass was carried out by the finite element method using universal FEM code (ANSYS ver.11.0). Experimental and numerical simulation results for the cross-section shape and the height of the groove profile were in approximate agreement.

ガラスマイクロプレス成形に関する数値シミュレーション

In the present paper, some experiments for press molding and numerical simulation about micro press molding of glass devices using finite element method is investigated. Thermo-viscoelastic properties of the glass materials were estimated using unidirectional compression creep test based on traditional thermo viscoelastic theory. In this study, Pyrex and D263 were used as glass materials. Glass micro press molding was carried out with Glass-like Carbon (GC) mold given to Line & Space patterns machined by dicing. The adaptive condition of the molding temperature which given appropriate transcription profile of the glass was investigated. Moreover, numerical simulation for micro press molding of the glass was carried out by finite element method using universal FEM code (ANSYS ver. 11.0). As a result of comparing experimental results with numerical ones, the cross section shape and the height of groove profile obtained by FEM simulation approximately agree with experimental value.

Deliberation of Effect to Glass Imprinting Analysis by Williams-Landel-Ferry Equation

The Mems-ONE is well known software which simulates thermo-viscoelastic properties in the conduct of nanoimprinting. Assuming the glass materials to be viscoelastic body, the relaxation shear modulus was measured by the creep test, Williams-Landel-Ferry (WLF) equation is applied for expressing the temperature dependence of liquid viscosity. We compared experimental with analytic results used by Mems-ONE with the condition of fixed pressure and time. Thermo-viscoelastic properties of the glass materials were estimated using unidirectional compression creep test based on traditional thermo viscoelastic theory. Glass was Borosilicate Glass (D263, Schott). Glass imprinting was carried out on Glassy Carbon (GC) mold with line & space10 μm patterns fabricated by dicing saw. The machining accuracy is most important thing as the evaluation mold. The glass imprinting temperature consulted thermo-viscoelastic properties of the glass materials. The numerical simulation was carried out on the small portion of mold and glass. The constant value of WLF equation fitting in high temperature translates the master curve of D263 with a high degree of accuracy. It caused the accuracy improvement of analysis result. In addition, we confirm that WLF equation intended to resin can use to the glass imprinting.

Elastic Langmuir Layers and Membranes Subjected to Unidirectional Compression: Wrinkling and Collapse

We apply the two-dimensional elastic continuum model to describe the wrinkling of elastic Langmuir layers (membranes) subjected to unidirectional compression. The effects of the dilatational, shear, and bending elasticities are taken into account. Among the numerous solutions of the generalized Laplace equation, corresponding to different membrane tensions, we determine the membrane shape as the profile that minimizes the energy of the system. In the case of small deformations, the problem can be linearized. Its solution predicts a wavelike shape of the compressed membrane. At negligibly small bending elasticity, the energy of the system is minimal for a sinusoidal profile, whose amplitude and wavelength tend to zero. In the opposite limiting case, where the effect of bending elasticity prevails over the effect of gravity, the membrane has a half-wave profile. When the two effects are comparable, the membrane shape exhibits multiple periodic wrinkles (ripples). An expression is derived for calculating the bending elasticity (rigidity) from the wavelength, and reasonable values are obtained from available experimental data. To determine the membrane shape at larger out-of-plane deformations, we solved numerically the respective nonlinear problem. Depending on the values of the physical parameters, the theory predicts various shapes: nonharmonic oscillations, toothed profiles, and profiles with two characteristic wavelengths. The results can be used for determining the bending elastic modulus of Langmuir films (membranes) as well as for the interpretation of buckling and collapse of monolayers.

Characterization of the Thermo-Viscoelastic Property of Glass and Numerical Simulation of the Press Molding of Glass Lens

A measurement technique for obtaining the thermo-viscoelastic properties of glass with high accuracy is discussed. An unidirectional compression creep test was employed to measure the relaxation modulus of the glass specimens. The creep function derived from the experimental creep test is approximated by a generalized Voigt model, and then converted into a relaxation modulus expressed by a generalized Maxwell model using the Laplace transform and its inversion. Relaxation moduli and shift factors of the glass specimens BK-7 and TaF-3 were estimated according to the presented procedure, and the accuracy of the relaxation modulus was verified by a numerical demonstration using finite element analysis. A fundamental numerical simulation of the press molding of glass lenses was carried out to illustrate the validity of the thermo-viscoelastic properties obtained by the presented approach. Residual stresses under processing conditions were estimated, and the optimal conditions for residual stress minimization are discussed.

The interplay of fold mechanisms and basement weaknesses at the transition between Laramide basement-involved arches, north-central Wyoming, USA

Horizontally-shortened, basement-involved foreland orogens commonly exhibit anastomosing networks of bifurcating basement highs (here called arches) whose structural culminations are linked by complex transition zones of diversely-oriented faults and folds. The 3D geometry and kinematics of the southern Beartooth arch transition zone of north-central Wyoming were studied to understand the fold mechanisms and control on basement-involved arches. Data from 1581 slickensided minor faults are consistent with a single regional shortening direction of 065°. Evidence for oblique-slip, vertical axis rotations and stress refraction at anomalously-oriented folds suggests formation over reactivated pre-existing weaknesses. Restorable cross-sections and 3D surfaces, constrained by surface, well, and seismic data, document blind, ENE-directed basement thrusting and associated thin-skinned backthrusting and folding along the Beartooth and Oregon Basin fault systems. Between these systems, the basement-cored Rattlesnake Mountain backthrust followed basement weaknesses and rotated a basement chip toward the basin before the ENE-directed Line Creek fault system broke through and connected the Beartooth and Oregon Basin fault systems. Slip was transferred at the terminations of the Rattlesnake Mountain fault block by pivoting to the north and tear faulting to the south. In summary, unidirectional Laramide compression and pre-existing basement weaknesses combined with fault-propagation and rotational fault-bend folding to create an irregular yet continuous basement arch transition.

Mechanical Behaviour of Ceramic Beads Used as Medium for Hydroforming at Elevated Temperatures

The need of light weight construction for high efficient vehicles leads to the use of new materials like aluminium and magnesium alloys or high strength and ultra high strength steels. At elevated temperatures the formability of steel increases as the flow stresses decrease. Forming high complex geometries like chassis components or components of the exhaust system of vehicles can be done by hydroforming. The hydroforming process by oils is limited to temperatures of approximately 300 °C and brings disadvantages of possible leakage and fouling. Using granular material like small ceramic beads as medium could be an approach for hydroforming of ultra high strength steels like MS W1200 and CP W800 at temperatures up to 600 °C. The material properties of granular material are in some points similar to solid bodies, in other points similar to liquids. For understanding and simulation of the behaviour of the medium a basic characterisation of ceramic beads with different ball diameters is necessary. Powder mechanics and soil engineering give ideas for experimental setups. For the conversion of these approaches on the one hand the behaviour of the ceramic beads itself has to be characterized, on the other hand the contact between a blank and the beads have to be investigated. For the tests three different kinds of spheres with a diameter between 63 microns and 850 microns are used. In unidirectional compression test compressibility, pressure distribution in compression direction and transversal compression direction and the effect of bead fracture are investigated. The tests are carried out at different compression velocities and for multiple compressions. For determination of friction coefficients between blank and beads and determination of shear stress in bulk under compression a modified Jenike-Shear-Cell for use in universal testing machines with the possibility of hydraulic compression of the beads is built up. The gained data can be used for material modelling in ABAQUS using Mohr-Coulomb or Drucker-Prager model.

Comparison of Microstructural Changes in a SIMA Processed A356 Aluminum Alloy after Unidirectional Compression and Rolling: Effect of Pressure Depth

In this study, in order to compare effect of unidirectional compression and rolling on final microstructure of strain induced melt activated (SIMA) A356 aluminum alloy, rectangular samples with dimensions of 3cm×5cm in area and 1cm in thickness and cylindrical specimens with 2.5cm in diameter and 1cm in length, have been prepared for rolling and compressing processes, respectively. Then, these samples were plastically deformed at a same strain in ambient temperature. Afterward, the strained samples were cut into equal quarters. In the next stage, to produce globular microstructure, these specimens were partially remelted in 580°C for different times. Results obtained from light microscopy showed that specimen's thickness and so, its strain affected zones influence on the globulization of dendrites. In addition, it was seen that at a given strain and constant diameter, increase of H/D ratio led to increase of needed time for reaching a certain sphericity in cylindrical samples. Also, it was showed that microstructural evolutions during SIMA processing of both rolled and unidirectional compressed samples were relatively identical. However, at a same condition, ultimate size of globulized dendrites in the rolled samples was smaller than those of compressed ones.