Unidirectional Compression Research Articles

A Characterization for the Deformation Behavior of As-Cast P91 Alloy Steel and Utilization in Hot Extrusion Process

The constitutive models of as-cast P91 alloy steel were investigated by unidirectional thermal compression tests, which were conducted over a wide range of temperature and strain rate on Gleeble-3500 thermal simulation machine. The constitutive models were coupled with finite element method to simulate the hot extrusion process. Furthermore, the industrial hot extrusion experiment on actual pipe was conducted on 500 MN vertical extrusion machine and the load-displacement data during the extrusion were recorded. Comparisons between the numerical simulation and industrial experimental results were carried out and confirmed that the developed constitutive models can be used in the simulation and industrial research of compact hot extrusion process.

Sample Size Effect of Magnetomechanical Response for Magnetic Elastomers by Using Permanent Magnets

The size effect of magnetomechanical response of chemically cross-linked disk shaped magnetic elastomers placed on a permanent magnet has been investigated by unidirectional compression tests. A cylindrical permanent magnet with a size of 35 mm in diameter and 15 mm in height was used to create the magnetic field. The magnetic field strength was approximately 420 mT at the center of the upper surface of the magnet. The diameter of the magnetoelastic polymer disks was varied from 14 mm to 35 mm, whereas the height was kept constant (5 mm) in the undeformed state. We have studied the influence of the disk diameter on the stress-strain behavior of the magnetoelastic in the presence and in the lack of magnetic field. It was found that the smallest magnetic elastomer with 14 mm diameter did not exhibit measurable magnetomechanical response due to magnetic field. On the opposite, the magnetic elastomers with diameters larger than 30 mm contracted in the direction parallel to the mechanical stress and largely elongated in the perpendicular direction. An explanation is put forward to interpret this size-dependent behavior by taking into account the nonuniform field distribution of magnetic field produced by the permanent magnet.

Geometry-dependent compressive responses in nanoimprinted submicron-structured shape memory polyurethane.

High resolution surface textures, when rationally designed, provide an attractive surface engineering approach to enhance surface functionalities. Designing smart surfaces by coupling surface texture with shape memory polymers has garnered attention in achieving tunable mechanical properties. We investigate the structure-mechanical property relationships for programmable, shape-memorizing submicron-scale pillar arrays subjected to flat-punch compression. The geometrically-dependent deformation of structured surfaces with two different aspect ratios (250 nm-pillars 1 : 1 and 550 nm-pillars 2.4 : 1) were investigated, and their moduli were found to be lower than that of non-patterned surface. From finite element analysis, the pillar deformation is correlated to a mechanistic transition from a discrete, unidirectional compression of 250 nm-pillars to lateral constraints caused by interpillar contact in 550 nm-pillars. This lateral pillar-pillar contact in the 550 nm-pillars resulted in an increased and maximum strain-dependent modulus but lower elastic recovery and energy dissipation as compared with the 250 nm-pillars. Furthermore, the compressive responses of temporarily shaped pillars (programmed by stretching) were compared with the permanently shaped pillars. The extent of lateral constraints controlled by pillar shape and spacing in 550 nm-pillars was responsible for the modulus differences between the original and stretched patterns, whereas the modulus of 250 nm-pillars remained as a constant value with different levels of stretching. This study provides mechanistic insights into how the mechanical behavior can be modulated by designing the aspect ratio of shape memory pillar arrays and by programming the surface geometry, thus revealing the potential of developing ingenious designs of responsive surfaces sensitive to mechanical deformation.

Iron foams created by directional freeze casting of iron oxide, reduction and sintering

Iron foams with aligned, lamellar channels were created by directionally freeze-casting slurries of water and Fe2O3 nanopowders, sublimating the ice, and reducing and sintering under hydrogen the powders accumulated in the interdendritic spaces. Foam porosity decreases from 85 to 50% with Fe2O3 slurry fractions increasing from 14 to 23vol.%. For foams created from 18.5vol.% Fe2O3 slurries, with increasing sintering temperature from 900 to 1100°C, a decrease in porosity from 71 to 61% and an increase in unidirectional compression strength from 8 to 20MPa are observed.

First Principles Investigation of Fluorine Based Strontium Series of Perovskites

Density functional theory is used to explore structural, elastic, and mechanical properties of SrLiF3, SrNaF3, SrKF3 and SrRbF3 fluoroperovskite compounds by means of an ab-initio Full Potential-Linearized Augmented Plane Wave (FP-LAPW) method. Several lattice parameters are employed to obtain accurate equilibrium volume (Vo). The resultant quantities include ground state energy, elastic constants, shear modulus, bulk modulus, young's modulus, cauchy's pressure, poisson's ratio, shear constant, ratio of elastic anisotropy factor, kleinman's parameter, melting temperature, and lame's coefficient. The calculated structural parameters via DFT as well as analytical methods are found to be consistent with experimental findings. Chemical bonding is used to investigate corresponding chemical trends which authenticate combination of covalent-ionic behavior. Furthermore electron density plots as well as elastic and mechanical properties are reported for the first time which reveals that fluorine based strontium series of perovskites are mechanically stable and posses weak resistance towards shear deformation as compared to resistance towards unidirectional compression while brittleness and ionic behavior is dominated in them which decreases from SrLiF3 to SrRbF3. Calculated cauchy's pressure, poisson's ratio and B/G ratio also proves ionic nature in these compounds. The present methodology represents an effective and influential approach to calculate the whole set of elastic and mechanical parameters which would support to understand various physical phenomena and empower device engineers for implementing these materials in numerous applications.

Force reduction induced by unidirectional transversal muscle loading is independent of local pressure

Transversal unidirectional compression applied to muscles via external loading affects muscle contraction dynamics in the longitudinal direction. A recent study reported decreasing longitudinal muscle forces with increasing transversal load applied with a constant contact area (i.e., leading to a simultaneous increase in local pressure). To shed light on these results, we examine whether the decrease in longitudinal force depends on the load, the local pressure, or both. To this end, we perform isometric experiments on rat M. gastrocnemius medialis without and with transversal loading (i) changing the local pressure from 1.1–3.2Ncm−2 (n=9) at a constant transversal load (1.62N) and (ii) increasing the transversal load (1.15–3.45N) at a constant local pressure of 2.3Ncm−2 (n=7). While we did not note changes in the decrease in longitudinal muscle force in the first experiment, the second experiment resulted in an almost-linear reduction of longitudinal force between 7.5±0.6% and 14.1±1.7%. We conclude that the observed longitudinal force reduction is not induced by local effects such as malfunction of single muscle compartments, but that similar internal stress conditions and myofilament configurations occur when the local pressure changes given a constant load. The decreased longitudinal force may be explained by increased internal pressure and a deformed myofilament lattice that is likely associated with the decomposition of cross-bridge forces on the one hand and the inhibition of cross-bridges on the other hand.

Mechanisms of Thermo-Mechanical Process on Grain Boundary Character Distribution of 316L Austenitic Stainless Steel

Grain boundary engineering (GBE) was carried out on 316L austenitic stainless steel with Thermo-mechanical processing (TMP), which was performed by unidirectional compression and subsequent annealing. The effect of TMP parameters including the strain and annealing time on grain boundary character distribution (GBCD) and the corresponding mechanism was investigated in the study. The results showed that high fraction of low-Σ coincident-site lattice (CSL) grain boundaries (about 55%) associating with interrupted network of random boundaries was obtained through TMP of 5% cold compression followed by annealing at 1000 °C for 45 min. The fraction of low-Σ boundaries increased with increasing the annealing time under all the experiment strain, but the mechanisms were different between the low and medium above levels of strain. Grains rotation and reaction of migratory boundaries might be the reasons of low-Σ boundaries growth in the strain of 5% and in the strain greater than or equal to 10%, respectively.

Interfacial organization of achiral porphyrins via unidirectional compression: a general method for chiroptical porphyrin assemblies of selected chirality.

Porphyrins are considered to be important scaffolds bridging supramolecular chemistry and chiral chemistry, where chirality selection via physical effects such as directional stirring and spin-coating has aroused particular interest. Nevertheless, these protocols could only work on a limited number of achiral porphyrins. It still remains a formidable challenge to pave a general avenue for the construction of chiral assemblies using achiral porphyrins. By means of a unique Langmuir-Schaefer (LS) technique of a unidirectional compression configuration, we herein have demonstrated that a series of achiral porphyrins could be facilely organized to form chiral interfacial assemblies of controlled supramolecular chirality. It has been disclosed that such a fascinating chirality selection scenario is intimately related to the direction of the compression-generated vortex-like flow, while the compression speed, one of the most significant parameters of the Langmuir technique, contributes less to this issue. With regard to a surface-pressure-dependent chirality selection phenomenon, it is suggested that the directional vortex-like flow generated by lateral compression might play a role in promoting the preferential growth of chiral assemblies showing an enhanced yet controlled CD signal. Our protocol might be, to some extent, a general method for achieving chiral porphyrin assemblies of controlled chirality.

MULTIDIMENSIONAL OPEN SYSTEM FOR VALVELESS PUMPING

In this study, we present a multidimensional open system for valveless pumping (VP). This system consists of an elastic tube connected to two open tanks filled with a fluid under gravity. The two-dimensional elastic tube model is constructed based on the immersed boundary method, and the tank model is governed by a system of ordinary differential equations based on the work-energy principle. The flows into and out of the elastic tube are modeled in terms of the source/sink patches inside the tube. The fluid dynamics of this system is generated by the periodic compress-and-release action applied to an asymmetric region of the elastic tube. We have developed an algorithm to couple these partial differential equations and ordinary differential equations using the pressure-flow relationship and the linearity of the discretized Navier-Stokes equations. We have observed the most important feature of VP, namely, the existence of a unidirectional net flow in the system. Our computations are focused on the factors that strongly influence the occurrence of unidirectional flows, for example, the frequency, compression duration, and location of pumping. Based on these investigations, some case studies are performed to observe the details of the ow features.

Numerical Analysis of the Edge Effect in a Composite Laminate with Compressed Reinforcement Plies

A piecewise-homogeneous material model is used to numerically determine the edge effect length in a composite laminate with reinforcement plies subject to unidirectional longitudinal compression. Consideration is given to mixed boundary conditions (regularity of the material structure and symmetry of the surface load) on the sides of the composite specimen and boundary conditions for stresses on the stress-free sides of the specimen. The dependence of the edge effect length on the ratio of the mechanical characteristics of the composite components is studied

Distribution of Contact Pressure Between a Sealing Element and a Cylinder

The distribution of contact pressure between a sealing element and a cylinder depending on the dimensions and mechanical characteristics of the former when subject to unidirectional compression is studied. The axial load needed to ensure seal tightness is determined. The relationship between this load and the dimensions of the sealing element is established. It is shown that as the height of the element is decreased, the axial load increases substantially. The maximum height beyond which the contact pressure hardly depends on the axial load is determined

Modeling the Behavior of the Fiber Reinforced Concrete by Damage Mechanics

The damage mechanics allows a detailed modeling of reinforced concrete’s degradation phenomenon. The theory of isotropic damage leads to quite satisfactory results in the description of both in the local and the global behavior. It is within the scope of this work to provide a model of damage based on the non-linear mechanical behavior of fiber concrete. This model takes into account the ductile nature of the observed during testing of material and direct tension after cracking. The modeling will be done while checking the principles of damage mechanics using the fundamentals of continuous mechanics of materials to propose a law of damage variation in unidirectional compression and tension. Confrontations with experimental test results are established.

Modeling the Biaxial Behavior of Concrete by Damage Mechanics with Poisson’s Ratio Variable

A new model is introduced, for predicting the nonlinear behavior of the concrete until the rupture. The non-linear behavior of the concrete is taken into account under monotonic load verifying the principles of the mechanics damage [1] and the concepts of the mechanics of the fracture, using the foundations of the continuum mechanics of materials [2]. The nonlinear mechanical behavior of the concrete in unidirectional is described by two laws (Sargin [3] for the compression and Grelat [4] on the tension). By introducing two variables of damage applied in unidirectional respectively in tension and in compression (Y. Bouafia , R. Smahi, and al., (2014)) [5]. Their combination with the laws of the continuum mechanics of materials (Hooke’s low generalized) [2], and the theory of the mechanics damage (theory of the isotropy of the damage, and principle of the equivalent deformation), brings us to a law of variation of the damage in three-directional applied in bidirectional. In addition, if the variation of the Poisson’s ratio of concrete in unidirectional compression has attracted the interest of several researchers we can cites: (Sami, A., Klink, 1975 [6], Murray D.W. 1979 [7], Niels Saabye ottosen, (1980) [8], Atheel E. Allos., L.H.Martin, (1981) [9], Ramtani.S, Y. Berthaud , J. Mazars, (1992) [10] and Ferretti, E., (2004) [11]. For the three-dimensional, we can mention: Chen 1982 [12], Guo 1997 [13], Zhu 1998 [14], Hyuk-Chun Noh, Hyo-Gyoung Kwak 2006 [15] and Ding Faxing Yu Zhiwu 2006 [16]. Confrontations of the calculations with experimental results (behavior of the concrete in biaxial compression and tension) have allowed to describe and to follow the real behavior of the concrete.

Theoretical study of the structural, elastic, electronic and optical properties of XCaF3 (X = K and Rb)

The PLANE WAVE pseudo-potential method within density functional theory (DFT) has been used to investigate the structural, elastic, electronic and optical properties of XCaF3 (X = K and Rb) insulating. The studied compounds show a weak resistance to shear deformation compared to the resistance to the unidirectional compression. KCaF3 and RbCaF3 are considered ductile. The elastic constants and related parameters were predicted. The stiffness is more important in KCaF3, whereas, the lateral expansion is more important in RbCaF3. KCaF3 and RbCaF3 have R- Г indirect band gap. The main peaks in the imaginary part of the dielectric function correspond to the transition from the occupied state F−p to the unoccupied states Ca: s or K, Rb: p. At lower energies, KCaF3 and RbCaF3 show the same optical properties. Under pressure effect, the peaks of imaginary part of dielectric function were shifted toward high energy.

Generalization of the memory integer model for the analysis of the quasi-static behaviour of polyurethane foams

Polyurethane foam is a cellular material characterized by an interesting mechanical spectrum of properties: low density, capacity to absorb the deformation energy and low stiffness. This spectrum of properties makes polyurethane foam commonly used in many thermal, acoustic and comfort applications. Several models, such as memory, hyper-elastic and pseudo-elastic models have been developed in the literature to describe the mechanical response of polyurethane foam under quasi-static and dynamic test conditions. The main disadvantage of these models is the dependence of their parameters against the test conditions (strain rate, maximum compression level, etc). This affects the general character of their representativeness to the quasi-static and dynamic behaviours of polyurethane foam. The main goal of this article is to implement reliable mechanical model which is able to provide the quasi-static response of the polyurethane foam under different strain rates and large compressive deformation. The dimensional parameters of our model can be expressed by the product of two independent parts; the first contain only the test conditions and the second define the dimensionless and invariant parameters that characterize the foam material. The developed model has been proposed after several experimental studies allowing the apprehension of the quasi-static behaviour (through unidirectional compression tests). The polyurethane foam, under large deformations, exhibits a nonlinear elastic behaviour and viscoelastic behaviour. To assess the ability of our model to be a general representation, three industrial polyurethane foams have been considered.

Star-Shaped Surface Cracking during Inhibited Dealloying Controlled by Grain Crystallography

Nanoporous gold (npg) produced by dealloying of Au alloys has been recently proposed for many different applications from catalysis to bio-sensors. Historically, Au alloys constitute an important model system in the context of corrosion, dealloying, and stress corrosion cracking. While electrochemical dealloying in sulfuric acid produces homogeneous nanoporosity a thiol-modified starting surface results in surface cracks showing a nanoporous core with very fine ligament size [1]. The intact surrounding area exhibits the knowm ultrathin Au layer on top of the alloy stabilized by the self-assembled thiol film [2]. Adsorbed self-assembled monolayers of thiol molecules inhibit thus the dealloying reaction. On thiol-modified Cu-Au alloys dealloying finally proceeds in a localized reaction instead of a homogeneous process. Volume shrinkage during dealloying has been reported for Ag-Au alloys [3]. The forming cracks within the nanoporous defect regions indicate a volume shrinkage and stress accumulation also for Cu-Au alloys. Thiols can be also removed from Au surfaces and thus hierarchical structures may be formed by combining different potential treatments [4].The crystallographic orientation of the surface influences the number density of the formed cracks as well as the crack morphology. The crack density is on some grains of special surface orientations especially high, while others exhibit only few cracks. The morphology reveals a clearly crystallographic influence on the crack morphology. Especially on (001) and (111) oriented surfaces clear 4-fold (Fig.1) and 3-fold symmetries are observed, respectively. The crystallographic nature of the cracks formed under near-isotropic hydrostatic stress (Fig.2) is in contrast to uni-directional compression behavior, e.g. during nanoindentation [5]. With the possibility to control the initiation of dealloying by a controlled introduction of defects [6] in the self-assembled thiol film the here presented system offers an interesting approach to address the mechanical behavior of nanoporous material during a corrosion process.[1] A. Pareek, S. Borodin, A. Bashir, G. N. Ankah, G. A. Eckstein, M. Rohwerder, M. Stratmann, Y. Gründer, F. U. Renner, Initiation and Inhibition of dealloying of single crystalline Cu3Au (111) surfaces, J. Am. Chem. Soc. 133 (2011), 18264.[2] A. Pareek, G. N. Ankah, S. Cherevko, P. Ebbinghaus, K. J. J. Mayrhofer, A. Erbe, F. U. Renner, Effect of thiol self-assembled monolayers and plasma-polymer films on dealloying, RSC Advances 3 (2013), 6586.[3] S. Parida, D. Kramer, C. A. Volkert, H. Rosner, J. Erlebacher, J. Weissmuller, Phys. Rev. Lett. 97, 35504 (2006).[4] G. N. Ankah, A. Pareek, S. Cherevko, J. Zegenhagen, F. U. Renner, Hierarchical nanoporous films obtained by surface cracking on Cu-Au and ethanethiol on Au(001), Electrochimica Acta 2014.[5] A. Volkert, E. T. Lilleodden, D. Kramer and J. Weissmüller, Appl. Phys. Lett., 2006.[6] M. Valtiner, G. N. Ankah, A. Bashir and F. U. Renner, Atomic force microscope imaging and force measurement at electrified and actively corroding interfaces: Challenges and novel cell design, Rev. Sci. Instr. 82 (2011), 023703.

The Effect of Opening on Elastic Buckling of Plates Subjected to Unidirectional Compression Load

This paper has investigated the effect of hole shape, hole size and hole position on elastic buckling of square perforated plates by using the finite element method. According to the effect law of these three geometric factors on buckling bearing capacity, buckling coefficient was obtained by data fitting. The results show that: The plate with circular perforation has the greatest buckling bearing capacity of the three perforation shape plate; When the center perforations have the same area, the relationship between buckling coefficient and perforation size is exponential for the plate with circular hole or square hole, the relationship between buckling coefficient and perforation size is biquadratic for the plate with triangular hole and the greater the perforation size is, the less the buckling bearing capacity will be; For the plate with uniform circular perforation size, The relationship of buckling coefficient and the spacing between perforation center and structure center is quadratic and the greater the spacing is, the less the buckling bearing capacity will be. The results in this paper provide reference for perforation design of plate.

Ambient-pressure drying synthesis of large resorcinol–formaldehyde-reinforced silica aerogels with enhanced mechanical strength and superhydrophobicity

Silica aerogels generally exhibit poor mechanical properties, which seriously restrict their commercial use and makes it necessary to reinforce their structures to obtain materials strong enough to withstand mechanical stresses. The incorporation of polymers into silica aerogels is a promising approach due to the enhancement in mechanical strength afforded and the possibility of imparting the hydrophobicity of the polymers to the resulting aerogels. However, the processes typically employed to prepare polymer-reinforced silica aerogels are complex, arduous and costly, requiring multiple washing and soaking steps for the infiltration of the polymer precursors after gelation and supercritical drying. Additionally, diffusion problems can result in heterogeneity in aerogel monoliths due to the use of various cross-linked polymers and the autoclave-limited dimensions of aerogels. In this study, a facile sol–gel route was developed to fabricate a large (500 cm3) polymer–silica aerogel monolith that was stable under atmospheric conditions and suitable for machining. The synthesis of the polymer–silica aerogels began with a facile one-pot reaction involving resorcinol (R), formaldehyde (F), methyltrimethoxysilane (MTMS), and N-(β-aminoethyl)-γ-aminopropyl-trimethoxysilane (AEAPTES), followed by an ambient-pressure drying process. The resulting aerogels were characterised by nitrogen adsorption–desorption, scanning electron microscopy (SEM), contact angle, and thermal conductivity measurements, and the aerogel mechanical properties were evaluated by a unidirectional compression test. The Young's modulus of compression of the aerogels was observed to increase from 3.95 to 34.88 MPa with an increase in the density of the aerogels from 0.14 to 0.26 g cm−3. Simultaneously, the aerogels were observed to be superhydrophobic, with a contact angle as high as 168°, and exhibited low thermal conductivity (0.038 W m−1 K−1) and good absorption for organic liquids, which are critical characteristics for the practical application of aerogels, especially in energy-saving and oil-/chemical-cleanup practices.

An Approximate Method to Present the Buckling Strength of A Grillage in A Probabilistic Form – Technical Note

An approximate method for calculation in probabilistic terms of the buckling strength of a grillage under unidirectional in-plane compression is proposed. The geometric properties of longitudinals and transverses and the mechanical properties (yield stress and modulus of elasticity) of the material they are built from are treated as random parameters that may change over ship's service life. The cumulative distribution function of the grillage's critical buckling strength is calculated by using an analytical formula for multitude sets of input parameters while all of them having the same level of certainty. The assumption is that the critical buckling strength has the same (or very similar) level of certainty as that of the input parameters. The accuracy of the proposed approximate method is relatively high (the maximal error is around 2%). It is recommended for use when specialized computer programs for application of Monte Carlo simulation method are not available. The method does not require a complicated specialized computer program and can be run on EXCEL computer program.

Microstructure Evolution of Hypereutectic Al-Si Alloy in Semi-Solid Compression Deformation

The semi-solid microstructure evolution of hypereutectic Al-20Si-3Fe-1Mn-4Cu-1Mg alloy was studied by unidirectional compression deformation experiment, at a range of deformation temperature of 833K~873K and a range of strain rate of 0.1s-1~0.001s-1. The results showed that the microstructure of the reheating alloy was more spherical and fine than the microstructure of as-cast, the alloy was a positive strain rate sensitive material that the flow stress was decreased with increasing in deformation temperature and it was increased with increasing in strain rate. The mechanical properties of the alloy were hardly improved when the deformation temperature was too high to fracture the thick phase of the alloy.The lower strain rate was not only reducing the productivity but also reducing the plastic deformation. The microstructure of the alloy which the thick phase was broken fundamentally and the grain became further refinement can be obtained at 833K~853K, and at 0.1s-1~0.01s-1.It can be done that reducing the plastic deformation resistance and strengthening the fabrication procedure of the alloy.