Theoretical estimation of dwell and consolidation times in rotary tablet machines

Knowledge of the time-dependent mechanical properties of pharmaceutical materials is critical to understanding of the compaction of tablets. In effort to determine the time-scale involved during compaction, equations for the dwell time and the consolidation time are proposed in this paper. Expressions for the consolidation time are obtained from generally accepted equations for punch displacement and separation between punch tips. These equations are deduced for rotary tablet machines with pressure rollers of the same and of different sizes. Specifically, the equations are applied to calculate the dwell and consolidation times for Manesty Betapress and Korsch Pharmapress Rotary tablet machines. The results are graphically presented.     

Theoretical estimation of dwell and consolidation times in rotary tablet machines

Abstract

Knowledge of the time-dependent mechanical properties of pharmaceutical materials is critical to understanding of the compaction of tablets. In effort to determine the time-scale involved during compaction, equations for the dwell time and the consolidation time are proposed in this paper. Expressions for the consolidation time are obtained from generally accepted equations for punch displacement and separation between punch tips. These equations are deduced for rotary tablet machines with pressure rollers of the same and of different sizes. Specifically, the equations are applied to calculate the dwell and consolidation times for Manesty Betapress and Korsch Pharmapress Rotary tablet machines. The results are graphically presented.     

Life prediction of stainless steels by cyclic and stable hysteresis curves

Abstract

This study develops an analytical expression to describe the cyclic stress‐strain curve obtained from a series of fully‐reversed fatigue tests. A set of stress‐strain relationships is proposed to simulate the tensile branch of the stable hysteresis loop. The complete shape of the stable hysteresis loop is then constructed and the associated theoretical plastic work calculated by integrating the area within the enclosed curve. The theoretical plastic work is employed to predict the fatigue lives of the investigated materials on the basis of their respective stable plastic work per cyclelife curves. In this paper, the current mathematical derivations are based upon the endochronic theory of plasticity. The accuracy of the proposed set of stress‐strain relationships is verified by conducting fully‐reversed constant strain amplitude fatigue tests on AISI 316 and AISI 304 stainless steels. The experimental and simulation results are found to be in good agreement, hence confirming the accuracy of the proposed analytical stress‐strain relationships. Again, comparing the obverted and predicted fatigue lives, a good agreement is found between the two sets of results.     

Failure mode transition in ceramics under dynamic multiaxial compression

An experimental technique based on the Kolsky pressure bar has been developed to investigate the behavior of ceramics under dynamic multiaxial compression. Experimental results for aluminum nitride (AlN), together with data available in the literature, indicate that a Mohr-Coulomb criterion and the Johnson–Holmquist model fit the experimental data for failure in a brittle manner, whereas the ceramic material exhibited pressure insensitive plastic flow at high pressures. A failure surface is constructed which represents the material failure behavior, including brittle failure, brittle/ductile transition and plastic flow, under various pressures. The effect of various material properties on the failure behavior was investigated. The Poisson's ratio is found to be a measure of brittleness for ceramic materials with low spall strength under shock wave loading conditions. Lower value of Poisson's ratio indicates that the material will fail in a brittle manner through axial splitting even under uniaxial strain loading; whereas materials with higher Poisson's ratio may be expected to deform plastically beyond the Hugoniot Elastic Limit (HEL). The applicability of the proposed failure surface to a range of ceramics is explored and the limitations of the model are outlined. This revised version was published online in July 2006 with corrections to the Cover Date.     

Potential consolidation-induced NAPL migration from coal tar impacted river sediment under a remedial sand cap

Subaqueous sediment, if capped for remediation purposes, may undergo consolidation due to the increased effective weight of the capping material. The standard Atterberg limits test and a modified drained three-dimensional consolidation test (DTCT) were performed on sediment collected from a river adjacent to a former manufactured gas plant site that contains high concentrations of coal tar. The plastic limit of five sediment samples ranged between 72 and 89%, and the liquid limit ranged between 123 and 194%. The plasticity index ranged from 51 to 122%, with the values among the sediments correlating with the coal tar content (r(2)=0.93). DTCT experiment was performed on 5 cm sediment overlain with 5 cm sand to a maximum applied effective cell pressure of 41.4 kPa. Consolidation increased almost linearly at lower pressures (<13.8 kPa); however, as higher pressures were imposed, the ratio of consolidation per applied pressure decreased. The results of this study suggest that porewater advection, resulting from sediment consolidation, will occur from the sediment to the capping material. Because this water will contain numerous polycyclic aromatic hydrocarbons, measures, such as adding sorptive materials, should be taken to reduce the flux of these compounds.     

材料力学性能的微型杯突试验评述

评述了新型的材料力学性能的微型杯突试验法，它采用微型薄片试样，依据试验的载荷-变形参量，建立微型杯突试验的力学性能指标与常规力学性能试验的力学性能指标之间相关联的定量关系，从而形成了适用范围广泛的新型的材料力学性能试验法。在国外，它用于受辐照材料脆化的评定，材料强度、塑性、韧-脆转折温度、断裂韧度、持久强度、蠕变等的测试，现役材料剩余寿命的评估和失效分析等。用它研究的材料有核电材料、各种金属和合金、复合材料、高分子材料、陶瓷材料、生物材料等。所应用的领域有核工业、电力、化工、机械、医疗等。它独特的试验方法和取样优势使其获得了愈来愈多的重视。基于该试验方法的优势和广泛的应用领域，建议建立微型杯突试验标准，以利于实验数据和信息的共享和工程应用。     

Small punch testing and its numerical simulations under constant deflection force conditions

A comparison of results of small punch tests on miniaturized discs under a constant force with their simulation by means of FEM is presented. A heat-resistant steel of type CSN 41 5313 (EN 10CrMo9-10) was selected for our investigations. The small punch tests as well as the necessary conventional creep tests on massive specimens were performed at 873 K. For simulations, the Norton power-law and the exponential relationships were applied in the FEM model of the SPT arrangement. Parameters of both relationships were derived from stress dependences of minimum creep rate obtained from the conventional creep tests. While at higher loads the Norton power-law yields results more comparable with those obtained from experiments, at lower loads the exponential relationship gives better results. The investigation also confirms the simple relation between stress in conventional tests and force in small punch tests resulting in identical time to fracture of both types of tests. __________ Translated from Problemy Prochnosti, No. 1, pp. 32–35, January–February, 2008.     

A damage-tolerant glass

Owing to a lack of microstructure, glassy materials are inherently strong but brittle, and often demonstrate extreme sensitivity to flaws. Accordingly, their macroscopic failure is often not initiated by plastic yielding, and almost always terminated by brittle fracture. Unlike conventional brittle glasses, metallic glasses are generally capable of limited plastic yielding by shear-band sliding in the presence of a flaw, and thus exhibit toughness-strength relationships that lie between those of brittle ceramics and marginally tough metals. Here, a bulk glassy palladium alloy is introduced, demonstrating an unusual capacity for shielding an opening crack accommodated by an extensive shear-band sliding process, which promotes a fracture toughness comparable to those of the toughest materials known. This result demonstrates that the combination of toughness and strength (that is, damage tolerance) accessible to amorphous materials extends beyond the benchmark ranges established by the toughest and strongest materials known, thereby pushing the envelope of damage tolerance accessible to a structural metal.     

Compaction Properties of Acrylic Resin Polymers with Plastic and Brittle Drugs

Abstract

Tensile strengths of compacts consisting of acrylic resin polymers in combination with a plastic drug (theophylline) and a brittle drug (sodium sulfathiazole) were investigated. The polymers studied included Eudragit RS PM, RL PM, S 100, L 100, and L 100-55. All compacts were compressed to a solid fraction of 0.81. The solid fraction, rather than compression force, was kept constant in order to account for the differences in packing characteristics and elastic and plastic deformational properties of different materials (1). Tensile strength profiles for the blends of the Eudragit S 100 and RL PM polymers with sodium sulfathiazole included approximately linear relationships between pure drug and pure polymer. The Eudragit L 100-55 exhibited a large peak in the tensile strength of compacts containing 20% sodium sulfathiazole. Significant differences between the physical-mechanical properties of the methacrylate ester and methacrylic acid copolymers were observed where the latter proved to be much stronger at all concentrations. The differences between the two categories of polymers were greater in compacts containing the plastic drug, theophylline. Peaks in tensile strengths were seen for both drugs with all three of the methacrylic acid copolymers, while the methacrylate ester copolymers maintained approximately linear relationships for all ratios of drug and polymer.     

Compaction Properties of Acrylic Resin Polymers with Plastic and Brittle Drugs

Tensile strengths of compacts consisting of acrylic resin polymers in combination with a plastic drug (theophylline) and a brittle drug (sodium sulfathiazole) were investigated. The polymers studied included Eudragit RS PM, RL PM, S 100, L 100, and L 100-55. All compacts were compressed to a solid fraction of 0.81. The solid fraction, rather than compression force, was kept constant in order to account for the differences in packing characteristics and elastic and plastic deformational properties of different materials (1). Tensile strength profiles for the blends of the Eudragit S 100 and RL PM polymers with sodium sulfathiazole included approximately linear relationships between pure drug and pure polymer. The Eudragit L 100-55 exhibited a large peak in the tensile strength of compacts containing 20% sodium sulfathiazole. Significant differences between the physical-mechanical properties of the methacrylate ester and methacrylic acid copolymers were observed where the latter proved to be much stronger at all concentrations. The differences between the two categories of polymers were greater in compacts containing the plastic drug, theophylline. Peaks in tensile strengths were seen for both drugs with all three of the methacrylic acid copolymers, while the methacrylate ester copolymers maintained approximately linear relationships for all ratios of drug and polymer.     

Deformation and Mechanical Characteristics of Compacted Binary Mixtures of Plastic (Microcrystalline Cellulose), Elastic (Sodium Starch Glycolate), and Brittle (Lactose Monohydrate) Pharmaceutical Excipients

This work studies the tensile strength, coherence, elastic, and plastic energy of single and bi-component compacted tablets consisting of (i) microcrystalline cellulose (MCC) PH 102 as a plastic material, (ii) (SSG) as an elastic material, and (iii) alpha lactose monohydrate as a brittle material by direct compression. Compacted tablets were studied with various mass ratios formed at an ultimate compaction stress of 150 MPa. The loading and unloading stages of the compaction process for the single and binary tablets were evaluated based on the energies derived from the force-displacement data obtained. The resulting tablet quality was measured in terms of the tensile strength. Material that exhibit predominantly plastic deformation (MCC) shows a dominant property over elastically deforming sodium starch glycolate (SSG) and brittle (lactose) materials during the loading and unloading stages of the compaction process. In conclusion, the tensile strength of the formed tablets depends directly on the plastic energy and indirectly on the elastic energy and is negatively affected by the presence of a brittle material.     

Mechanical behaviour of polycrystalline BeO,Al2O3 and AlN at high pressure

The mechanical behaviour of various types of BeO, Al₂O₃, and AlN have been investigated at confining pressures up to 1.25 GPa, at 25° C, and at strain rates of 3 to 7×10^–5 sec^–1. The stress-strain data taken in uniaxial compressive-stress loading indicate the BeO aggregates undergo a transition from brittle fracture at low pressures to plastic flow at high pressures. Depending on the fabrication process, this transition pressure in BeO occurs at 0.4 to 0.7 GPa. Concurrently, the ultimate compressive strength of BeO increases from 1.0 to 1.9 GPa at 0.1 MPa pressure to over 4.0 GPa at 1.O GPa. Alumina remains brittle at all pressures up to 1.25 GPa; its strength increases from 4.5 GPa at 0.1 MPa pressure to over 6.0 GPa at 1.25 GPa. Aluminium nitride behaves similarly to BeO, having a brittle-ductile transition at 0.55 GPa. Its ultimate strength increases from 3.2 GPa at 0.1 MPa pressure to 4.7 GPa at 0.8 GPa. The distortional strain energy (proportional to the area under the stress-strain curve) absorbed by each material during compression at pressure was calculated and compared to available data from the literature. Alumina shows a degraded energy absorption with pressure, but both BeO and AlN yield a strongly enhanced performance at moderate pressures. Beryllium oxide and AlN thus appear to be promising structural materials for certain applications where high strengths and ductilities are required at moderate pressures.     

Fatigue of brittle materials—A critical appraisal

Recent demands for high performance ceramics and glass for various applications from bioceramics to cutting tools under fluctuating stress conditions has focussed attention of the scientific community towards fatigue behaviour of brittle solids. Attention to fatigue phenomena in alumina ceramics phenomenological to metals, having an endurance dependent on applied stress with a limit at around 50% of the single cycle fracture stress, was first drawn by the author in late sixties. Slip assisted fatigue process was not considered to be dominant in ceramic materials due to the absence of appreciable crack tip plasticity. With the background of this general survey of fatigue behaviour some fatigue studies based on mode of testing, theoretical and experimental analyses and fractographic evidence have been presented. Studies have shown that there is a dormant period between each successive crack advancement during which the residual stress and a plastic component is built up in a cumulative manner leading to eventual failure. During fatigue (plastic) and (residual stress) components are predominant for ductile metals and brittle glass/ceramics respectively. It is also apparent that dislocation assisted plastic component as a contributing factor in the failure of brittle materials under fatigue cannot be ruled out.     

Thermal conversion efficiency of an ideal thermoelastic marmem cycle

The thermal conversion efficiency of an ideal stress-strain-temperature cycle based on the mechanical shape memory effect associated with a thermoelastic martensite transformation (thermoelastic marmem cycle) has been studied. A relationship between the upper limit of the thermal efficiency and a set of materials properties has been derived. It is shown that a higher thermoelastic marmem efficiency and a closer approach to the corresponding Carnot efficiency are favoured by: (1) higher yield stress of the high-temperature phase, (2) larger recoverable strain, (3) smaller transformation temperature range and thermal hysteresis associated with the transformation, and (4) smaller transformation latent heat. The thermal efficiency has been calculated for a cycle utilizing a Ti-50.4 at % Ni alloy. The highest efficiency for this particular alloy was found to be about 9%; this amounts to 45% of the corresponding Carnot efficiency. Thus it is concluded that efficiencies can be obtained which are comparable with those of cycles operating at small temperature differences with fluids as working media.Marmem is derived from martensite memory [21].     

A constitutive model for unsaturated soils: thermomechanical and computational aspects

This paper first presents a complete formulation of a constitutive model that deals with the irreversible behaviour of unsaturated soils under various loading and drying/wetting conditions. A standard form of incremental stress-strain relations is derived. The constitutive model is then cast into the thermodynamical theories and verified using the thermomechanical principles. It is shown that hydraulic hysteresis does not contribute to the plastic dissipation, though it contributes to the plastic work. All plastic work associated with a plastic increment of the degree of saturation is stored and can be recovered in a reversed plastic increment of saturation. The incremental constitutive equations are also reformulated for implementation in finite element codes where displacements and pore pressures are primary unknowns. Qualitative predictions of the constitutive model show that incorporating two suction related yield surfaces and non-associated flow rules into the Barcelona Basic Model opens a full range of possibilities in modelling unsaturated soil behaviour.     

Effective stresses in cyclic deformation

Stress relaxation measurements showed that the relative magnitude of the effective stresses increases with cycling. For the explanation of these results, the mechanism associated with edge dislocation exhaustion and increasing screw dislocation activity is suggested. Stress relaxation measurements around various points of the hysteresis loop showed that the effective stresses are completely absent during the plastic deformation immediately after stress reversal. This is taken as an indication that dislocation gliding is strongly assisted by the back stresses. As the applied load increases after stress reversal, the effective stresses increase in absolute value as well as relative to the applied load. The suggested explanation of this is that plastic strain along the hysteresis loop is derived from mobile dislocations which change in number and also in character with increasing stresses.     

Flexural strength analysis of brittle materials

The relation between flaw density and strength of ceramic or brittle materials were derived and applied to a commonly used testing method of four-point bending for determining the strengths of ceramic or brittle materials. Previous analysis failed to include the failures outside or at the inner loading positions for four-point test data. The present approach elevates such a constrain so that the relation applies to failures occurs at any points between the outer loading positions for four-point test data.     

Fracture criterion on the basis of uniformity of plastic work of polycrystalline ductile materials under various stress states

Studies on the fracture criterions of structural materials would be of great significance to the service security of engineering structures. This note proposes a novel criterion on the basis of the uniformity of plastic work under various stress states. In order to realize abundant stress states, modified Arcan fixtures were designed and integrated with a self-made in situ tensile device. Accordingly, by changing the stress ratio of tensile to shear components, true stress–strain relationships of a typical polycrystalline ductile material (Gr-4 titanium alloy) specimens on the basis of various stress states were obtained and piecewisely fitted. By, respectively, adopting linear and polynomial fitting in the elastic and plastic deformation stages, the plastic work, namely the envelope areas of true \({\sigma_{\rm t}}\)–\({\varepsilon_{\rm t}}\) curves, was quantitatively calculated. Approximate uniformity of plastic work was verified as no correlation between plastic work and stress state was observed. Moreover, the evolution behavior of microvoids inside a single grain and the equivalent average slip distance of polycrystalline ductile materials during trans-granular fracture process were also analyzed theoretically to explain the uniformity. The trans-granular slip and fracture behavior of Gr-4 titanium alloy specimen and orientations of crack propagation of extruded AZ61B magnesium alloy specimens were also examined experimentally.     

Pb-GF挤压包覆间隙的数值计算及实验研究

铅包覆玻璃纤维属于塑性材料包覆脆性材料,包覆条件是建立在玻璃纤维不发生变形的情况下,为此,入丝模芯顶端与挤压模口之间的间隙即包覆间隙的优化选择是成形工艺的关键问题.本文采用上限法对包覆挤压过程建立了数值模型,从能量的角度对包覆挤压过程进行了数值计算,将包覆间隙作为一变量引入功的表达武中,并通过数值计算软件给出了数值解,得出包覆间隙的最佳理论值.通过大量的实验证明了数值计算结果与实验结果基本吻合.运用本文结果可以确定不同规格的复合丝材成形时包覆间隙的大小,指导模具设计和工艺参数确定,具有工程意义.     

塑料药物包装材料可提取物全景分析方法概述

目的 对国内常用的塑料药物包材的挥发性、半挥发性、非挥发性物质及金属元素等提取物质的检测和分析方法进行总结,为塑料药物包材可提取物质全景分析和安全性评价提供参考。方法 通过检索国内外相关文献,对塑料药物包材中不同可提取物的分析方法进行总结和归纳。结果 目前,国内塑料药物包材日益更新,但可提取物的分析手段单一、检测分析方法不全面,缺乏相应的数据库。结论 药物包材的相容性研究在国内起步不久。针对目前存在的塑料包材可提取物的分析手段单一、不全面,缺乏相应的数据库等问题,现阶段亟需构建分辨率和灵敏度高、特异性强、筛查范围广的方法,对药物包材可提取物质进行全景分析,减少因包材安全性不良引起的医疗事故。