Early Stage Of Compression Research Articles

Evolution Characteristics of the Strength and Dilation Parameters of Gas Hydrate-Bearing Sediments and a Modeling Study

Gas hydrate has gradually become a new potential energy resource. However, some engineering and environmental problems related to the mechanical properties of gas hydrate-bearing sediments (GHBS) during gas recovery may occur. Many studies have been carried out on the basic mechanical properties of GHBS samples based on laboratory tests, but their evolution characteristics and suitable models require further research. Based on a series of data analyses of published laboratory experimental results on GHBS samples with different hydrate saturations under various confining pressures, the evolution characteristics of strength and dilation parameters were investigated. It was found that cohesion (c) increases quickly to a peak value and then decreases gradually to a residual value with an increasing plastic shear strain, and the samples with higher hydrate saturations have higher initial values, peak values, and residual values of cohesion (c). The internal friction angle (φ) increases quickly with increasing plastic shear strain and then becomes stable at a residual value for all the samples with different hydrate saturations. The dilation angle (ψ) increases from negative to positive values with increasing plastic shear strain and then becomes stable at a residual value. These characteristics are likely to be related to the compaction occurring at the early stage of compression before expansion due to dilation. In this paper, a non-linearly fitted model is proposed considering the evolution of the mechanical parameters, and the verification tests show that the proposed model can simulate the stress–strain behaviors of the GHBS samples well. This model is also adopted in the stability analysis of submarine slopes containing hydrate reservoirs. The analytical approach is developed, accompanied by the strength reduction method.

Quantitative analysis of layered re-crushing of crushed coal particles during compression based on CT scanning

Due to the compaction of the overburden strata, the crushed coal in caved zone will be re-crushed. The compaction and re-crushing degree of crushed coal differ at different heights, which is called layered re-crushing. Quantitatively revealing the layered re-crushing characteristics of crushed coal particles is the key to elucidating pore structure evolution of caved zone and coalbed methane enrichment pattern in the gob. In this paper, quantitative characterization of layered re-crushing of coal particles during compression is achieved using self-designed CT visual compacting apparatus. The results showed that: (1) the degree of particle re-crushing decreased from the loaded side (the upper layer) to the fixed side (the lower layer). In the early stage of compression, the overall skeletal structure is looser, which is not conducive to the transfer of force chains. Thus, the stress has the greatest effect on the particles in the upper layer, with the proportion of particle increase reaching 49.3% from 0 Mpa to 2.14 Mpa. There was a pattern of becoming larger first and then smaller in the difference of average diameter among different layers, and the final average diameter decreased by about 60% in three layers. (2) The particle diameter distribution transferred to a smaller diameter fastest in the upper layer and slowest in the lower layer, which is due to the gradual transfer of external load from the top to the bottom. After compression, the number of particles smaller than 4 mm predominated in the upper layer (40.3%) and the number of particles larger than 5 mm predominated in the lower layer (47.1%). (3) With the increase of stress, the void volume gradually decreases regardless of the whole sample or the three layers, while the void number increases instead. And at both 2.14 MPa and 23.24 MPa, the void volume shows the law of upper layer < middle layer < lower layer.

On the compressive properties of aluminum and magnesium syntactic foams: Experiment and simulation

The influence of the materials of Al and Mg-based syntactic foams on the compressive behavior was investigated. Two different kinds of foams of cp-Al and cp-Mg in combination with ceramic hollow spheres (Al2O3 or Al2O3/SiO2/mullite) were manufactured by infiltration technique. A full-scale finite element model was established to explain the experimental results and to explore the effect of matrix and hollow sphere properties up to the peak strain. In this full-scale model, the ceramic hollow spheres’ effective elastic and fracture properties were used, determined from compression tests and micromechanical model of single hollow spheres. The finite element model predicted the compression curve with high precision in the investigated deformation range for the highly ductile foams with Al matrix, indicating that fracture becomes the dominant failure mode only near the peak stress. The model of Mg matrix syntactic foams showed that fracture in the early stage of compression did not change the strength of the material; however, it significantly lowered the stiffness in the case of Al2O3 hollow sphere having a diameter of ∼4 mm and thin (150 µm) wall. If significant reactions occurred between the matrix and hollow spheres during manufacturing, the model could estimate the formed complex interface’s effect on the syntactic foams’ strength.

β1-Blocker improves survival and ventricular remodelling in rats with lethal crush injury.

Crush injury/crush syndrome (CI/CS) is the second most common cause of death during earthquakes. Most studies of CI/CS have mainly focused on kidney injury after decompression. Few studies have focused on myocardial injury caused by crush injury and its potential mechanisms. We first verified cardiomyocyte injury during compression in rats with a crush injury. The survival rate, electrocardiographic results, histological results, catecholamine changes and cardiac β1-AR expression were evaluated. Next, we explored the effects of pretreatment with a selective β1-blocker (bisoprolol) with or without fluid resuscitation on rats with a crush injury. In addition to evaluating the survival rates, biochemical and histological analyses and echocardiographic measurements were also performed. Reduced heart rates, elevated ST segments, and tall-peaked T waves were observed in the rats with a crush injury. The changes in the myocardial enzymes and pathological results demonstrated that myocardial damage occurred during compression in rats with a crush injury. The levels of the catecholamine norepinephrine in both the serum and myocardial tissue were elevated during compression. Pretreatment with a selective β1-blocker combined with fluid resuscitation significantly improved the survival rates of the rats with lethal crush injury. The myocardial enzymes and pathological results showed that the combined therapy decreased myocardial damage. The echocardiography measurements showed that the rats that received the combined therapy exhibited decreased left ventricular mass (LVM), left ventricular volume at end-systole (LVVs) and left ventricular internal diameter (LVID) compared with the rats with a crush injury. Our findings demonstrated the presence of myocardial injury in the early stage of compression in rats with a crush injury. Pretreatment with a β1-blocker (bisoprolol) with fluid resuscitation significantly reduced mortality, decreased myocardial tissue damage, and improved ventricular remodelling in rats with a lethal crush injury.

Dual‐system tract pattern: Significance for foreland basin reservoir prediction (Jurassic, Central Junggar Basin, West China)

The Junggar Basin is a typical superimposed system characterized by multilateral steep thrusts and extrusions and one of the primary petroliferous basins in Western China. To date, geologists have been most interested in the basin's tectonic evolution and petroleum geology characteristics. Based on field outcrops, lithologic combinations, logging curves, and seismic reflection characteristics, we present a systematic study of the sequence stratigraphy pattern for the Jurassic central Junggar Basin. Herein, we identify the central Junggar area as having a “dual” characteristic sequence framework composed of a lowstand system tract (LST) and a transgressive system tract (TST), which is distinguishable from the traditional three system tract (LST, TST, and highstand system tract [HST]). In each third‐order sequence, the LST consists of conglomerate or pebbly sandstone deposits, displaying the characteristics of braided channel and fan delta. The TST consists of siltstone, argillaceous siltstone, and mudstone, displaying fine‐grained, shore‐shallow lacustrine deposits. It is considered that the combination of multiphasic thrust extrusion and subsequent, steady deposition is likely responsible for the dual‐system tract. The forming process of the dual‐system tract pattern could divide into four stages: the quiet stage of tectonic activity, the early stage of compression, the continuous stage of compression, and the rapid rebound stage. Additionally, two reservoir predictive models are proposed: the progradational predicting model on the edge of the depression and truncated and pinchout predicting model on the palaeo‐uplift. We conclude that the coarse clastic unit of the LST has bright prospects for oil and gas exploration within the superimposed system in Western China.

Compressive consolidation of strongly aggregated particle gels

The compressive yield stress of particle gels shows a highly nonlinear dependence on the packing fraction. We have studied continuous compression processes, and discussed the packing fraction dependence with the particle scale rearrangements. The 2D simulation of uniaxial compression was applied to fractal networks, and the required compressive stresses were evaluated for a wide range of packing fractions that approached close packing. The compression acts to reduce the size of the characteristic structural entities (i.e. the correlation length of the structure). We observed three stages of compression: (I) elastic-dominant regime; (II) single-mode plastic regime, where the network strengths are determined by the typical length scale and the rolling mode; and (III) multi-mode plastic regime, where sliding mode and connection breaks are important. We also investigated the way of losing the fractal correlation under compression. It turns out that both fractal dimension $D_{\mathrm{f}}$ and correlation length $\xi$ start to change from the early stage of compression, which is different from the usual assumption in theoretical models.

Effect of Silicification on the Tableting Performance of Cellulose II: A Novel Multifunctional Excipient

The effect of silicification on the tableting performance of microcrystalline cellulose II (MCCII) was assessed through coprocessing with fumed silica via spray drying and wet granulation at the 98:2, 95:5, 90:10 and 80:20 ratios. Compacts produced by spray drying and wet granulation rendered better tensile strength than MCCII. The Kawakita and Heckel models implied that silicification increased compressibility and decreased the plastic deforming behavior and densification by die filling at the early stage of compression for MCCII. It also decreased the sensitivity to hydrophobic lubricants such as magnesium stearate, especially for the spray-dried products due to the competing effect with magnesium stearate. Further, silicification decreased the high elastic recovery typical of MCCII due to the increase in specific surface area and fragmenting behavior which contributed to the formation of stronger compacts. Moreover, silicification did not affect the fast disintegrating properties and release rates of poorly soluble drugs such as griseofulvin formulated in tablets compared to those of Prosolv® SMCC 50 and Prosolv® SMCC 90. The new silicified materials are appropriate to formulate fast disintegrating tablets by direct compression.

Flow Stress Behavior of Al-Fe-V-Si Heat-Resistant Aluminum Alloy Prepared by Spray Forming under Hot-Compression Deformation

The behavior of the flow stress of Al-Fe-V-Si heat-resistant aluminum alloy prepared by spray forming during hot compression deformation was studied. The results show that the true stress-true strain curves of the spray forming Al-Fe-V-Si heat-resistant alloy are characterized by a high true stress occurrence at the early stage of compression, followed by a steady flowing due to recovery and strain softening because of dynamic recrystallization. The flow stress of the alloy decreases with increasing deforming temperature and increases with increasing strain rate. The flow stress of the spray forming Al-Fe-V-Si heat-resistant aluminum alloy during hot compression deforming can be described by constitutive equation in hyperbolic sine function．The deformation activation energy of the alloy during hot deformation by Sellars-Tegart equation is much higher than those of the conventional aluminum alloy. The deformation activation energy decreases with decreasing strain rate at the beginning, then increases with decreasing strain rate. Keywords：Al-Fe-V-Si alloy；heat-resistant aluminum alloy；hot compression deformation；flow stress

Constant Rate of Loading Test on Ultra-Soft Soil

Abstract The conventional consolidation test on ultra-soft soil takes a long time to complete due to the viscous effect in the early stage of compression. Instead of conducting the test until the end-of-primary (EOP) consolidation at each loading step, the testing time can be shortened if the test is carried out at a constant rate of loading (CRL). In this study the CRL tests were carried out at various loading rates. The settlement and pore pressure behavior were studied, and a suitable rate of loading (1 kPa/800 s) was determined. The proposed rate of loading is slightly slower than the rate of loading for natural clay suggested by others. The transition point between viscous stage and soil stage can be determined from the measured peak pore pressure. The compression indices, the large strain coefficient of consolidation, and the coefficient of permeability can also be determined from the CRL test with the proposed equations. This paper discussed the experimental test on ultra-soft soil at a CRL.

Effects of initial orientation, sample geometry and friction on anisotropy and crystallographic orientation changes in single crystal microcompression deformation: A crystal plasticity finite element study

The study presents crystal plasticity finite element simulations of cylindrical Cu single crystal micropillar compression tests. The aim is to study the influence of the stability of the initial crystal orientation, sample geometry (diameter-to-length ratio) and friction on the anisotropy and crystallographic orientation changes during such tests. Initial anisotropy (initial orientation) has a strong influence on the evolution of crystallographic orientation changes and also, to a minor extent, on the sample shape during compression. Pronounced orientation changes occur at an early stage of compression (at engineering strains of 0.2), entailing as a rule a large orientation spread within the initially uniformly oriented sample. A non-zero friction has a stabilizing effect on the course of the compression test even in cases where strong orientation changes occur. The evolution of orientation changes during compression is in part due to rigid body rotations (shape inclination due to buckling) rather than exclusively to crystallographic reorientation. Orientations that are crystallographically unstable and non-symmetric during compression tend to entail shape instability of the pillars at an earlier stage than observed for more stable cases.

Interactions of a Fluoroaryl Surfactant with Hydrogenated, Partially Fluorinated, and Perfluorinated Surfactants at the Air/Water Interface

A novel surfactant containing pentafluorophenyl moiety attached at the terminal position of undecanol (11,11-difluoro-11-(pentafluorophenyl)undecan-1-ol, abbr. PBD) was synthesized and employed for the Langmuir monolayer characterization and miscibility studies with a semifluorinated alkane (perfluorodecyleicosane, abbr. F10H20) and four alcohols differing in the degree of fluorination in their hydrophobic chains: octadecanol (C18OH), perfluorooctyldecanol (F8H10OH), perfluoroisononyldecanol (iF9H10OH) and 1H,1H-perfluorooctadecanol (F18OH). Pure monolayers of all of the investigated surfactants as well as their mixtures were investigated with surface pressure-area isotherms complemented by Brewster angle microscopy (BAM) images. PBD was found to form stable Langmuir monolayers of liquid-expanded character. Characteristic dendritic structures were formed at the very early stage of compression and remained up to the vicinity of collapse, where 3D crystallites appeared. 2D miscibility studies revealed that PBD forms mixed monolayers with the investigated semifluorinated alkane (F10H20) as well as with perfluorinated alcohol (F18OH) within the whole composition range, do not mix with octadecanol to the fully hydrogenated alcohol, whereas it is partially miscible (up to a certain surface pressure value) with the studied semifluorinated alcohols. The analysis of the miscibility derived from the surface pressure-area isotherms (collapse pressure vs composition dependencies) agrees well with BAM images. Molecular interactions in the investigated systems have been quantified with interaction parameter, alpha.

Dry granulation and compression of spray-dried plant extracts

The purpose of this research was to evaluate the influence of dry granulation parameters on granule and tablet properties of spray-dried extract (SDE) from Maytenus ilicifolia, which is widely used in Brazil in the treatment of gastric disorders. The compressional behavior of the SDE and granules of the SDE was characterized by Heckel plots. The tablet properties of powders, granules, and formulations containing a high extract dose were compared. The SDE was blended with 2% magnesium stearate and 1% colloidal silicon dioxide and compacted to produce granules after slugging or roll compaction. The influences of the granulation process and the roll compaction force on the technological properties of the granules were studied. The flowability and density of spray-dried particles were improved after granulation. Tablets produced by direct compression of granules showed lower crushing strength than the ones obtained from nongranulated material. The compressional analysis by Heckel plots revealed that the SDE undergoes plastic deformation with a very low tendency to rearrangement at an early stage of compression. On the other hand, the granules showed an intensive rearrangement as a consequence of fragmentation and rebounding. However, when the compaction pressure was increased, the granules showed plastic deformation. The mean yield pressure values showed that both granulation techniques and the roll compaction force were able to reduce the material's ability to undergo plastic deformation. Finally, the tablet containing a high dose of granules showed a close dependence between crushing strength and the densification degree of the granules (ie, roll compaction force).

Distribution of the Surfactant-Associated Protein C within a Lung Surfactant Model Film Investigated by Near-Field Optical Microscopy

Lung surfactant films at the air/water interface exhibit the particularity that surfactant molecules are expelled from the surface monolayer into a surface associated multilamellar phase during compression. They are able to re-enter the surface film during the following expansion. The underlying mechanism for this behavior is not fully understood yet. However, an important role is ascribed to the surfactant-associated protein C (SP-C). Here, we studied a model lung surfactant, consisting of dipalmitoylphosphatidylcholine (DPPC), dipalmitoylphosphatidylglycerol (DPPG), and SP-C, by means of scanning near-field optical microscopy (SNOM). Attaching a fluorescent dye to the protein allowed the localization of its lateral distribution at various surface pressures with high resolution. At an early stage of compression, the film appears demixed into a pure lipid phase and a protein-enriched phase. Within the latter phase, protein aggregations are revealed. They show a uniform density, having three times the fluorescence intensity of their surroundings. Across the phase boundary between the lipid phase and the protein-rich phase, there is a protein density gradient rather than an abrupt border. When the film is highly compressed, we observe the formation of multilamellar structures that are fluorescent. They are often surrounded by a slightly fluorescent monolayer. The fluorescence of the multilayer stacks (i.e., the protein content per unit area) is proportional to the height of the stacks.

The phase behavior of lipid monolayers containing pulmonary surfactant protein C studied by fluorescence light microscopy.

Three compounds of the pulmonary surfactant--dipalmitoylphosphatidylcholine (DPPC), dipalmitoylphosphatidylglycerol (DPPG), and the surfactant associated protein C (SP-C)--were spread at the air-water interface of a Langmuir trough as a model system to mimic the properties of natural surfactant. Fluorescence microscopical images of the film formed at the interface were obtained during compression using a fluorescence dye bound covalently either to phosphatidylcholine or to SP-C. The images were quantified using statistical methods in respect to relative areas and relative fluorescence intensities of the domains found. In the early stage of compression, film pressure rose slightly and was accompanied by a phase separation which could be recognized in the images by the formation of bright and dark domains. On further compression, after a steep increase of film pressure, a plateau region of constant film pressure started abruptly. During compression in the plateau region, fluorescence intensity of the bright domain formed in the early stage of compression increased. The increasing fluorescence intensity, the non-Gaussian intensity distribution of the bright domain, and the small mean molecular area of the film in the plateau region gave rise to the assumption that multilayer structures were formed in the late stage of compression. The formation of the multilayer structures was fully reversible in repeated compression-expansion cycles including the plateau region of the phase diagram. The ability of lipid/SP-C mixtures to form reversible multilayer structures during compression may be relevant to stability in lungs during expiration and inhalation.

Dynamic recrystallization of Nb 3Al produced from alloy powder

The deformation behaviour of Nb 3Al compressed at above 1300 K was studied using off-stoichiometric, single-phase Nb 3Al produced by consolidation of prealloyed and ball-milled powders. It was found that Nb 3Al was able to be deformed plastically above 1400 K and the stress-strain curves showed deformation softening after a peak stress. Transmission electron microscopic observations revealed that this deformation softening was caused by dynamic recrystallization. The amount of deformation softening decreases and steady state deformation occurs at an early stage of compression, as the compression temperature increases.

The influence of pressure on crystallisation of amorphous Zr 70Cu 30 alloy—I. Crystallisation temperature and the crystallisation phases

The pressure dependence of the crystallisation temperature of amorphous Zr 70Cu 30 alloy and the variation of its crystallisation phases under high pressure annealing were investigated by electrical resistivity measurement and X-ray diffraction method. The results show that pressurising generally raises the crystalisation temperature, but slightly decreases it at the early stage of compression. Evident changes in crystallisation phase in the alloy were also observed under high pressure annealing. At atmosphere pressure, the crystallisation products are CuZr 2 with a modicum of α-Zr, while at a pressure of 2 GPa, the alloy crystallises into a mixture consisting of CuZr 2, Cu 10Zr 7 and an appreciable amount of α-Zr. The origin of these observations is discussed.

Scaling of size/time/temperature — Part 2: Progressive damage in uniaxial compressive specimen

Having analyzed the thermal/mechanical behavior of a uniaxial tensile bar, Part 2 of this investigation is concerned with the same geometric configuration and loading rate but the load is reversed such that material elements are in compression. The cylindrical bar would tend to bulge in compression rather than necking. Time response of the stress and strain differed for the two loading cases. Compression gives rise to a much more stable change in deformation states in contrast to tension where the deformation tends to increase more rapidly with loads that are increased monotonically at the same rate. More time is available in compression to accumulate damage prior to global failure. Thermal changes also differed qualitatively and quantitatively. Macroheating is observed during the early stage of compression instead of cooling as in the case of tension. Distortion on the surface of the compressed specimen is the more dominant mode of deformation whereas dilatation in the center of tensile specimen is more critical. These differences attribute to the contrasting features of tensile and compressive failure. Cooling/heating associated with dilatation/distortion are assessed for different size elements. Although the behavior is highly oscillatory, it is unique and deterministic provided that the size, time and temperature for each element are synchronized. This is accomplished by application of the isoenergy density theory which assumes the interdependence of surface and volume energy and applies to nonequilibrium and irreversible physical processes. The same event referred to the atomic, microscopic and macroscopic scale can thus be interconnected though their behavior may appear different at each level. Precise characterization of material behavior is different because the response is sensitive to changes in load type and history. Even in the cases of uniaxial tensile and compressive specimen, the difference is dramatic when the results are compared with those reported in Part 1 [1].

Experimental analysis of the spinal cord compressed by spinal metastasis.

The purpose of the present study of experimental spinal metastasis, developed in rats by inoculation of tumor cells through the spinous process, was to find the factor that causes the initial damage to the cord in this disorder. In the early stage of paralysis, the degenerated posterior funiculus originated from a small hemorrhagic area in the posterior column of the involved cord. Using the scanning electron microscope, the hemorrhage was found to be from the intrinsic vein, resulting from the disturbance of venous drainage in the compressed portion. In the early stage of compression, extravasation of horseradish peroxidase was observed in the white matter, but histologic degeneration was not. A hemorrhage existed wherever degeneration of the funiculus was observed. Therefore, the trigger to induce the initial damage on the cord in spinal metastasis was not likely to be vasogenic edema, but instead the intrinsic venous hemorrhage.

Damage of the microcapsule wall during compression

Cellulose acetate phthalate microcapsule containing phenacetin was used as a model and the effect of compression force and characteristics of excipients on the damage of microcapsule wall during compression process were studied. Calcium citrate with different particle sizes and microcrystalline cellulose were used as excipients. The degree of damage of the wall was evaluated from the dissolution rate of phenacetin and results observed by scanning electron microscopy. When calcium citrate was used as an excipient, microcapsule wall was damaged remarkably in the early stage of compression (P=100 kg/cm2), and the degree of damage was affected by particle size of calcium citrate. The larger particles caused more remarkable damage. In the case of microcrystalline cellulose which showed high compressibility, the degree of damage under high compression force (P=1000 kg/cm2) was less than that of calcium citrate under low compression force (P=100 kg/cm2). From these results, it was considered that the magnitude and distribution of shear stress on the wall were affected by particle size and compressibility of excipients and that the degree of damage of microcapsule wall was different between calcium citrate and microcrystalline cellulose.

Preferred orientation of crystalline particles within tablets. III. Change in degree of preferred orientation of aspirin crystals during compression (author's transl)

The degree of preferred orientation of aspirin crystals in a tablet as a function of compression force was measured using the X-ray diffraction method. Preferred orientation took place during compression and the degree was affected by the size and morphology of the crystals. Thin, plate-like crystals had the strong tendency to orient preferentially at an early stage of compression, while pulverized crystals oriented gradually at over 100 kg/cm2 of the compression force. In addition, volume, specfic surface area, pore size distribution and breaking strength of the tablets were measured and the relationship among these factors was investigated.