Yield Pressure Research Articles

Dynamic behaviors of calcareous sand under repeated one-dimensional impacts

Based on the background of the development of China's South China Sea, few studies can provide a reference for pile foundation construction in calcareous sand layers. In this paper, one-dimensional impact tests were conducted on three uniformly graded (0.25–0.50 mm, 0.50–1.00 mm, and 1.00–2.00 mm) and one mixed graded (0.075–2.00 mm) calcareous sand and silica sand specimens with the aid of a split Hopkinson pressure bar (SHPB) system, while several sets of mixed graded specimens with different moisture contents and relative densities were studied for comparison. Each specimen was impacted at least 10 times. The results of the tests based on the effect of the number of impacts, particle size, moisture content and relative density on the dynamic behavior of calcareous sand are summarized as follows. The dynamic apparent stiffness of calcareous sand is approximately 1/8–1/9 that of silica sand due to their different particle shapes and mineral compositions. The dynamic/bulk/shear apparent modulus of calcareous sand decreases with an increase in the mean diameter, d50. After repeated impact, the apparent modulus of specimens with different particle sizes continued to increase and decreased with an increase in d50. For calcareous sand, with increasing particle size, the compression index Cc increases, and the yield pressure is approximately 40% that of silica sand under the same conditions. Compared to silica sand, calcareous sand reaches a better energy absorption capacity at a lower stress. Under the same axial stress, the energy absorption efficiency increases with increasing particle size and decreases with an increase in the number of impacts.

Finite Element Modeling of a Mechanically Stabilized Earth Trial Wall

Polymer geogrid reinforced soil retaining walls have become commonplace, with routine design generally carried out by limiting equilibrium methods. Finite element analysis (FEA) is becoming more widely used to assess the likely deformation behavior of these structures, although in many cases such analyses over-predict deformation compared with monitored structures. Back-analysis of unit tests and instrumented walls improves the techniques and models used in FEA to represent the soil fill, reinforcement and composite behavior caused by the stabilization effect of the geogrid apertures on the soil particles. This composite behavior is most representatively modeled as enhanced soil shear strength. The back-analysis of two test cases provides valuable insight into the benefits of this approach. In the first case, a unit cell was set up such that one side could yield thereby reaching the active earth pressure state. Using FEA a test without geogrid was modeled to help establish appropriate soil parameters. These parameters were then used to back-analyze a test with geogrid present. Simply using the tensile properties of the geogrid over-predicted the yield pressure but using an enhanced soil shear strength gave a satisfactory comparison with the measured result. In the second case a trial retaining wall was back-analyzed to investigate both deformation and failure, the failure induced by cutting the geogrid after construction using heated wires. The closest fit to the actual deformation and failure behavior was provided by using enhanced fill shear strength.

Polymer-Ceramic Composite Membranes for Water Removal in Membrane Reactors.

Methanol can be obtained through CO2 hydrogenation in a membrane reactor with higher yield or lower pressure than in a conventional packed bed reactor. In this study, we explore a new kind of membrane with the potential suitability for such membrane reactors. Silicone–ceramic composite membranes are synthetized and characterized for their capability to selectively remove water from a mixture containing hydrogen, CO2, and water at temperatures typical for methanol synthesis. We show that this membrane can achieve selective permeation of water under such harsh conditions, and thus is an alternative candidate for use in membrane reactors for processes where water is one of the products and the yield is limited by thermodynamic equilibrium.

Study of Different Crystal Habits of Aprepitant: Dissolution and Material Attributes

In the present study, aprepitant (APT) was selected to find its suitable crystal habit, which can improve its existing poor dissolution and manufacturing processability. Solvents were screened out for solubility analysis of APT and further crystal habit modification. Solid-state characterization studies like powder X-ray diffraction (PXRD), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and Fourier infrared spectroscopy (FTIR) distinguished that tabular crystal habit was generated from acetone (APT-AC) and long tabular crystal habit was generated from ethyl acetate (APT-EA). Kawakita analysis and powder flow property studies showed that APT-EA is cohesive, has poor flow property and low bulk density compared to APT-AC (p < 0.05). Heckel plots reflected that APT-EA shows higher fragmentation and particle rearrangement during the initial stages as indicated by the higher intercept values. Higher slopes in APT-EA and APT-AC confirmed better plasticity but lower yield pressure in APT-AC proved good plastic deformation compared to APT-EA (p < 0.05). The dissolution profile of the APT-EA was found to be better than that of APT-AC. Overall, it can be concluded that APT-AC crystal habit has a better flow rate, tensile strength, and plasticity whereas APT-EA has better dissolution.

Indentation-derived mechanical properties of Ti-6Al-4V: Laser-powder bed fusion versus electron beam melting

Employing a depth-sensing indentation testing technique, the room temperature mechanical properties of Ti-6Al-4V (Ti64) alloy fabricated through laser powder-bed fusion (L-PBF) and electron beam melting (EBM) additive manufacturing processes were studied. Mechanical properties including nano-hardness (in GPa), reduced elastic modulus, yield pressure, elastic recovery, and wear resistance were extracted. The microstructure of the fabricated materials was correlated with the indentation-derived characteristics. It was observed that the nano-hardness and reduced elastic modulus values were 3.66 ± 0.06 GPa and 118 ± 3 GPa, for the L-PBF, and 3.43 ± 0.22 GPa and 136 ± 4 GPa, for the EBM materials, respectively. The higher strength of the L-PBF alloy is due to the finer microstructure of this alloy. While α laths with an average width of 3.61 ± 0.92 μm developed in the EBM-Ti64, the microstructure of L-PBF-Ti64 consisted of α′ martensite with an average width of 0.37 ± 0.10 μm.

LINX

The LINX device consists of a “bracelet” of magnetic beads in titanium cases, connected by individual wires placed noncompressively around the distal esophagus during laparoscopic surgery. This augments the native lower esophageal sphincter’s (LES) ability to resist reflux by increasing yield pressure and resisting shortening of the LES. Magnetic sphincter augmentation (MSA) was conceived as a safe, stomach sparing, minimally invasive, reversible implantable device for patients seeking an alternative to laparoscopic Nissen fundoplication. Though initially studied in patients with limited hiatal hernias, its use has expanded to include patients with large and even giant or paraesophageal hernias with excellent results. The author’s techniques of complete esophageal dissection, precise hiatal repair, current concepts on noncompressive sizing and placement of the MSA device are reviewed in this article. MSA can be considered first-line surgical therapy for GERD patients with adequate peristalsis regardless of hernia size.

Texture and surface feature-mediated striking improvements on multiple direct compaction properties of Zingiberis Rhizoma extracted powder by coprocessing with nano-silica

The study aims to markedly improve direct compaction (DC) properties of Zingiberis Rhizoma extracted powder (ZR) by modifying its texture and surface properties with nano-silica (NS). A wet coprocessing method was applied to evenly distribute up to 33.3% NS to ZR. To clarify uniqueness of NS, microcrystalline cellulose (MCC), a superior filler-binder in DC, was used as control. Coprocessed particles and physical mixtures (PMs) were comprehensively evaluated for surface features, micromeritic properties, and texture and compacting parameters. Compared to MCC, NS could more significantly modify the texture and surface features of ZR (e.g., hardness, cohesiveness, yield pressure, and nanoscaled surface roughness) via coprocessing, resulting in more striking improvements on multiple DC properties of ZR, including tabletability, flowability, lubricant sensitivity, hygroscopicity, etc. Especially, tensile strength (σt) of coprocessed ZR-NS (1:0.5) tablets was 4.62 and 3.22 times that of ZR and ZR-MCC counterparts pressed at 210 MPa, respectively. Moreover, percolation thresholds of σt enhancement were observed for ZR-NSs, but not for ZR-MCCs. Evaluation by the SeDeM expert system indicated that some ZR-NSs (but no ZR-MCCs) were qualified for DC. Collectively, coprocessing with NS by liquid dispersion appears to be a novel, effective, and pragmatic option for DC of drugs like ZR.

Application of modified SeDeM expert diagram system for selection of direct compression excipient for liquisolid formulation of Neusilin® US2

In the present investigations, the SeDeM expert diagram system, modified to include two important compression properties, i.e. mean yield pressure, Py, and compactibility parameter, σtmax, was used to identify a diluent most suitable for the direct compression of a liquisolid formulation of Neusilin® US2 (50NEU). The mean incidence values of 50NEU demonstrated that it had poor flowability and compactibility, and was highly hygroscopic. Three commonly used directly compressible tablet diluents, viz. lactose monohydrate, microcrystalline cellulose, and dibasic calcium phosphate, selected based on their index of good compressibility (IGC) values were evaluated for their usefulness for direct compression of 50NEU. Mathematical equations based on the linear and power mixing rules were used to calculate the percentage of diluent required for direct compression. The powder blends prepared using lactose monohydrate resulted in fragile tablets, dibasic calcium phosphate exhibited poor compactibility, however, powder blends containing microcrystalline cellulose resulted in tablets with acceptable compactibility. This demonstrated the significance of a rational selection of excipients based on their SeDeM parameters rather than the IGC values. Additionally, the study results showed that the modified SeDeM expert system was superior to the conventional SeDeM system for the selection of diluent for direct compression.

Understanding Deformation Behavior and Compression Speed Effect in Gabapentin Compacts.

Deformation mechanism and strain rate sensitivity of gabapentin powder was investigated in this work. Heckel analysis, specific surface area and indentation hardness measurements revealed an intermediate yield pressure and brittle fracture as the dominant type of deformation mechanism during consolidation. Strain rate sensitivity of gabapentin was studied by compressing it at 1mm/min and 500mm/min compression speeds. Gabapentin demonstrated an atypical strain rate sensitivity in compactibility profile (tensile strength vs. solid fraction). Compacts of gabapentin compressed at fast speed showed an increase in tensile strength when compared with those compressed at slow speed. To understand the effect of compression speed on gabapentin's compactibility, PXRD analysis, surface area analysis, indentation hardness measurements, and consolidation modeling were performed. PXRD analysis carried out on compacts revealed no effect of speed on the physical solid-state stability of gabapentin. Specific surface area of compacts made at fast speed was higher than that of compacts made at slow speed. Indentation measurements performed on gabapentin compacts showed higher values of hardness in the case compacts made at fast speed. It was identified that at the fast compression speed, gabapentin shows greater particle fragmentation and form compacts with smaller pores.

A data-driven approach for predicting the time-dependent settlement of embankments on soft soils

Models of soil behaviour, in situ and laboratory testing techniques and system models for describing the geometry and time-dependent processes involved in the settlement of embankments on soft soils have reached a level of maturity where reliable predictions for this problem should be readily achievable. Despite this, there is clear evidence to demonstrate engineering predictions of embankment behaviour can be inaccurate, resulting in construction cost and schedule overruns. One key reason for this is the significant influence that personal judgement plays in processing soil test data to derive engineering parameters. In this paper, a method that makes progress toward overcoming this is developed using oedometer test results directly in a data-driven approach, thus avoiding the need to evaluate profiles of compression indices and yield pressures. The method has been deployed as an easy-to-access cloud-based application and its use demonstrated with a comprehensive case history. Data used in this paper are freely available in electronic format.

A Dynamic expansion of a cylindrical cavity in a compressible elastic-plastic medium. The Analysis of medium resistance to dynamic penetration of a sharp-nosed impactor

This paper presents the solution of the problem related to the dynamic cylindrical cavity expansion in a compressible elastic-plastic medium. Finite strains, nonlinear compressibility and dependence of the yield stress versus pressure are taken into account in the problem formulation. The study targets at developing a new engineering model on the penetration of a sharp-nosed impactor in the range of middle impact velocities based on the problem analysis results of the cylindrical cavity expansion in a half-space (cylindrical cavity expansion approximation). Based on the analytical approach a model is obtained that determines the resistance of the medium to dynamic cavity expansion. The main parameters of the model depend on the mechanical properties of the medium. For these dependences we proposed approximating relations based on manipulation of the mechanical properties of a number of materials (some alloys and soils). To derive the dynamic penetration model the A.Ya. Sagomonyan assumption of the radial expansion of the hole is used. It is assumed that particles of the medium material move in a radial direction from the surface of the impactor penetrating into the shield. Such assumption can be applied for the class of impactors in the form of slender sharp-nosed bodies of revolution. Based on the assumptions we obtained a model of the medium resistance to the dynamic penetration of a slender sharp-nosed body of revolution. The new model, in addition to the "standard" strength and inertial components, contains the "attached mass", which changes during the penetration process. The experimental validation of the new penetration model using a series of experimental studies on the penetration of various forms of impactors into aluminum alloys is considered. The influence of the “attached mass” and inertial forces of the medium resistance to the penetration is estimated. The conditions of applicability of the new model are obtained: the penetration model is applicable for estimation of the resistance of a compressible medium to penetration of a thin sharp-nosed body of revolution at impact velocities of 200-800 m/s.

Spreading Kinetics of Herschel-Bulkley Fluids Over Solid Substrates

The spreading kinetics of Herschel-Bulkley fluids on horizontal solid substrates were theoretically studied. The equations of film thickness were derived in both gravitational and capillary regimes. The dynamic contact angle for the capillary regime was also derived. Finally, a limiting result for the case of τ0 = 0 was obtained, which was compared with the known solution for validation. The results show that the yield behavior of the fluids had a significant impact on the spreading kinetics in both cases. Only when stress was larger than the yield stress, would substantial flow occur. The spreading zone was divided into two parts by the yield surface: sheared zone and yield zone, which was completely different from common Newtonian fluids or power-law fluids. The thickness of the yield zone mainly depended on yield stress and pressure gradient along the z-direction. According to the final evolution, both the film thickness and dynamic contact angle were affected not only by the power-law index but also by the yield behavior.

Tableting of mini-tablets in comparison with conventionally sized tablets: A comparison of tableting properties and tablet dimensions

Mini-tablets are solid dosage forms with increasing interest for pharmaceutical industry due to clinical and biopharmaceutical benefits. But technological aspects on mini-tableting are not fully investigated. Therefore, the impact of punch size and tableting pressure for industrially relevant excipients like microcrystalline cellulose, lactose, isomalt and Ludiflash® are investigated using 8 and 11.28 mm punches for conventionally sized tablets and 1,2 and 3 mm punches for mini-tablets. For evaluation of the effect of tablet size on deformation behaviour and mechanical properties, compressibility, compactibility and tabletability plots are created and evaluated. Deformation behaviour is analysed by In-Die Heckel plot and modified Weibull function. Further, specific plastic energy (SPE) profiles are generated out of force-displacement plots. The effect of the adjustment of the aspect ratio towards 1 as in conventionally sized tablets on deformation behaviour and tabletability is analysed. The effect of tablet size on deformation behaviour mainly showed lower yield pressures for conventionally sized tablets, whereas comparable SPEs were obtained with all tablet sizes. Furthermore, mini-tablets indicate better compactibility, as (depending on the excipient) higher tensile strengths were obtained at lower solid fractions. However, no superior tabletability properties are obtained for mini-tablets compared to conventionally sized tablets.

An Algorithm for Evaluation of Mining Cycle Parameters and Analysis of Periodic Roof Weighting Using Monitored Longwall Shield Pressures and Shearer Location

Shield leg pressure data from all shields and shearer location with time stamp from a mechanized longwall face are monitored and recorded in a surface computer. These data contain random noise due to power failure, leakage of legs, bad sensor reading and other maintenance or geo-mechanical problems. An algorithm is developed to detect mining cycle parameters such as setting and final pressures and duration of the cycle from these data for the analysis of periodic roof weighting phenomena. The intensities and persistence of periodic roof weighting are the vital information to the mine management to take judicious decision on longwall operation. The paper presents details of the algorithm which identifies 96% of mining cycles from the noisy data belonging to consecutive 5 months or 410 m of face advancement. Based on this analysis, 2 types of periodic roof weighting phenomena are detected, namely, (i) normal type—having peak intensity of 75 to 90% of yield pressure, interval of occurrences of about 10 to 15 m with persistence of 3 to 4 m and (ii) severe type—peak intensity over 90% of yield pressure, interval of 25 to 40 m with persistence of over 10 m. It is envisaged that these phenomena have direct relationship with main roof thickness, its overhung length and material properties.

Structure-Property Relationship of Amorphous Maltitol as Tableting Excipient.

Maltitol shows interesting properties compared with mannitol or sorbitol, two other polyols, which are widely used as a pharmaceutical excipients for tablet compaction. For this study, the properties of an amorphous polyol, maltitol, were investigated using a tablet press simulator. The aim of this study was to evaluate the behavior of amorphous maltitol compared to SweetPearl® P 200, a pure product, and SweetPearl® P 300DC, a textured crystalline maltitol excipient for direct compression. The physicochemical and pharmacotechnical properties were compared, revealing a major change in properties after amorphization. The study of the tabletability, mean yield pressure, elastic properties, etc. shows that the compression behavior of amorphous powders has been significantly altered. The results showed specific properties of amorphous maltitol with good tabletability at low compaction pressure. The stability of the amorphous and the evolution of its behavior in compression were then studied, showing a direct link between its recrystallization and the change in its properties. The use of a stabilizing agent, maltotriitol, slowed down the recrystallization, maintaining the specific properties of the amorphous material in compression for a longer period of time.

The effects of spray drying, HPMCAS grade, and compression speed on the compaction properties of itraconazole-HPMCAS spray dried dispersions

Spray dried dispersions (SDDs) have the potential to dramatically improve the oral bioavailability of drugs with poor water solubility. However, SDDs tend to have material attributes, such as small particle size, low bulk density, and poor flowability, which are undesirable for downstream processing such as tableting. The objective was to perform a comprehensive compaction characterization of both physical mixtures and SDDs consisting of itraconazole (ITZ) and hypromellose acetate succinate (HPMCAS) to elucidate process and material influences on compressibility and compactibility. We fabricated SDDs with 20% ITZ as a model BCS Class 2 drug and 80% HPMCAS as a polymer carrier. Results indicate that SDDs, as well physical mixtures of ITZ and HPMCAS, were easily deformable with similar compressibility profiles across all compression speeds. Analysis of Heckel plots revealed that yield pressures were fairly low for both physical mixtures and SDDs (43.97-59.75 MPa), indicative of ductile materials. SDDs had a much greater propensity to laminate, especially at higher compression speeds, compared to physical mixtures. This difference is likely due to the higher elastic recovery of SDDs. However, for intact tablets, the mechanical strength of compacts from SDDs tended to be higher than those produced from physical mixtures, likely due to the much smaller particle size of the SDDs. Importantly, examination of the compacts with differential scanning calorimetry did not detect any drug crystallization as a result of compaction. In conclusion, while spray drying did not significantly alter the compressibility of binary mixtures ITZ and HPMCAS, it dramatically impacted compactibility and tabletability, increasing elastic recovery, and making the mixtures more prone to lamination. However, at low compression speeds, SDDs produced tablets with higher tensile strength than physical mixtures.

Evaluation of Lactose-Based Direct Tableting Agents' Compressibility Behavior Using a Compaction Simulator.

A compaction simulator (CS) is a single-punch instrument that records data during the powder compaction process. The aim of the study was to determine the behavior of lactose-based direct tableting agents (DTAs) by CS. The data recorded were used to evaluate the flowability and compressibility of powders. The focus of the study was on comparing the compressibility of StarLac® [alpha lactose monohydrate (85%) and white maize starch (15%)] and FlowLac®100 (spray-dried alpha lactose monohydrate) in order to make tablets containing poorly flowable paracetamol. Two lactose-based DTAs were used. Physical characterization of these powders was done by measuring bulk, tapped, and true densities alongside scanning electron microscopy analysis. Flow properties were then calculated by the angle of repose, Hausner ratio, and Carr's compressibility index. Force, in-die thickness, and punch displacement data produced by the CS were captured during in-die compression. Compressibility was calculated using the Heckel equation. The physical characterization test results showed no significant difference between the two DTAs. Hardness results revealed that tablet formulations containing FlowLac® had higher sensitivity to an increase in compression force in comparison with StarLac®. From the Heckel plots generated by the CS during the compression cycle, yield pressure (Py) values were calculated for FlowLac®100 and StarLac®. The Heckel parameter (Py) for FlowLac®100 and StarLac® was calculated as 87.5 MPa and 85.2 MPa, respectively, during the compaction cycle at 5 kN. These data indicated that both powders are compressible and have brittle behavior. StarLac® is less brittle, which was shown by its lower sensitivity to compression force. Py values obtained from the Heckel equation described the plasticity of particles, which gives distinct information on the compressibility of both DTAs in real time during the compaction cycle.

Polyglycerol esters of fatty acids as safe and stable matrix forming tableting excipients: A structure-function analysis

This work describes a novel approach for the development of extended release matrix tablets with stable performance via direct compaction. Selected molecules belong to polyglycerol esters of fatty acids (PGFAs) - a group of lipid-based excipients (LBE) with advanced solid-state stability - were used for developing extended release tablets. Metformin HCl as a freely water soluble API was used as model substance. Three PGFA compounds with a HLB range of 1.8–4.5 were selected as matrix forming agents. The deformation behavior of tableting blends with and without PGFAs and their flow properties studied. Blends composing PGFAs showed reduced yield pressure and decreased internal friction between particles, suggesting the tendency to plastic behavior of PGFAs and improved flow properties of their blends, respectively. The blends of selected lipids with API and filler were directly processable via direct compression without any pretreatment such as granulation. The resulted tablets showed desired tensile strength and friability. Application of PGFAs with different HLB allowed the tailoring of API release profile for different time periods with the same concentration of lipid in the tablet. The stable release profile was related to the stable solid state of lipids as matrix agent. No in vitro cytotoxic effect was observed by assessing the dehydrogenase activity.

Compression behaviour of granules produced via twin-screw melt granulation: Effect of initial particle size on granulation efficiency

This study focuses on the impact of initial particle size on the tabletability and the deformation behaviour (i.e. plasticity) of granules produced by twin-screw melt granulation (TSMG). As model substances, three different grades of anhydrous dicalcium phosphate (aDCP) were melt-granulated with polyethylene glycol 6000 (PEG) using a twin-screw granulator. Compaction performance of the granules and the corresponding physical mixtures (PM) was evaluated by in-die and out-of-die compaction analysis. A major impact on granules deformation behaviour was found for the relation of the specific surface area of the filler material to the binder content. A relative yield pressure (YP) was introduced to describe the enhancement in plastic deformation behaviour, defined as the plasticity performance factor (PPF). Furthermore, a modified Kawakita model was used to describe the granulation efficiency, compared to a calculated physical mixture model. Granules under investigation showed an increased plastic deformation, enhanced tabletability and reduced elastic recovery (ER). The binder was shown to be finely distributed and to fill the voids between the aDCP particles (image analysis of the carbon energy dispersive X-ray maps). A small initial particle size of filler material (DI-CAFOS® A7 and A12) was more efficient than a larger particle size (DI-CAFOS® A60). A very low particle size (DI-CAFOS® A7) required the addition of 1% (w/w) colloidal silicon dioxide to enable feeding of the material into the granulator. Moreover, due to the larger surface area of these particles, a higher amount of binder was necessary to achieve a low PPF and a high tensile strength (TS).

Compaction and tableting properties of composite particles of microcrystalline cellulose and crospovidone engineered for direct compression

BackgroundExcipients with improved functionality have continued to be developed by the particle engineering strategy of co-processing. The aim of this study was to evaluate the compaction and tableting properties of composite particles of microcrystalline cellulose (MCC) and crospovidone (CPV) engineered by co-processing.ResultsHeckel analysis of the compaction behavior revealed a decrease in plasticity of co-processed excipient (CPE) when compared to MCC due to an increase in Heckel yield pressure from 144 to 172 MPa. The compressibility-tabletability-compactibility (CTC) profile revealed a decrease in individual parameters for CPE when compared to MCC. CPE was found to be more sensitive to the lubricant effect of sodium stearyl fumarate (SSF) when compared to MCC and less sensitive to magnesium stearate (MST) when compared to MCC. A higher dilution potential was obtained for MCC (60%) compared to 44% for CPE when metronidazole was used as model drug. Tableting properties revealed that metronidazole tablets generated with CPE by direct compression disintegrated within 15 min and gave a rapid drug release when compared to MCC as a direct compression (DC) excipient.ConclusionThe compaction and tableting properties of CPE were characterized and yielded tablets with better disintegration and drug release profile when compared to MCC. This study, therefore, confirms the suitability of co-processing as a proven strategy in engineering the performance of excipients.