几种β-胡萝卜素微胶囊干粉的压缩特性和成型机理

为了比较几种不同配方和生产工艺得到的β-胡萝卜素干粉的压缩特性和形成片剂的能力,考察了其干粉的粉体特征,以及在压缩过程中粉体的微观结构变化,并通过Heckel方程和Kawatika方程具体表征其压缩行为,分析其成型机理,结合加速实验时各片剂中β-胡萝卜素的保留率的变化,认为以明胶为壁材,通过淀粉床流化干燥技术得到的β-胡萝卜素微胶囊干粉在挤压时主要是通过塑性变形成型,而且其中的β-胡萝卜素稳定性好,这种干粉最适合于制成片剂。     

Cold densification and sintering of nanovaterite by pressing with water

While dissolution-precipitation, plastic deformation and fracture have been proposed to explain the compaction of carbonates in geological formations, the role of these mechanisms on the densification process of calcium carbonate nanoparticles in synthetic systems remains poorly understood. Here, we systematically investigate the effect of pH of the aqueous phase (1 ≤ pH ≤ 7), temperature (10 ≤ T ≤ 90 °C), and pressure (10 ≤ P ≤ 800 MPa) on the cold compaction of nanovaterite powder with water to shed light on the mechanisms underlying this unique densification. Compaction experiments reveal that the applied pressure plays a major role on the densification of vaterite nanopowder with water. Our experimental data thus suggest that plastic deformation or subcritical crack growth might be important densification mechanisms for vaterite nanoparticles. These findings provide a new perspective into the cold compaction of nanopowders with water and may open promising routes for the manufacturing of CO₂-based structural materials at mild processing conditions.     

Effect of Relative Humidity on the Viscoelastic and Mechanical Properties of Spray-Dried Powder Compacts

Spray-dried powder compacts exhibit viscoelastic properties such as stress relaxation, creep, and delayed elastic strain. This behavior is attributed to the organic binder, which forms bridges between the particles in spray-dried granules, thereby affecting their deformation characteristics. The viscosity and distribution of the binder within the powder compact can affect its mechanical and viscoelastic properties. In this study, the powder was conditioned at different ambient relative humidity (RH) levels, to vary the binder viscosity. Load deformation, stress relaxation, fracture strength, and fracture toughness behavior of ferrite powder compacts were studied as a function of ambient RH both before and after compaction. The loading rate was found to significantly affect the time-dependent response, and the relaxation times decreased at high humidity levels during compaction. It is proposed that increasing the humidity level during compaction increases the number of particle–particle contacts. This simple mechanism of binder redistribution led to slower relaxation times, increases in fracture strength, and elastic modulus of the green bodies, without significantly altering the fracture toughness when powders were compacted at high humidity to a given density.     

Structure and Properties of Explosively Compacted Copper–Molybdenum

The microstructure, deformation characteristics, and electric conductivity of composites produced by explosive compaction of a copper–molybdenum powder mixture were studied. It is shown that an increase in detonation velocity during explosive treatment leads to an increase in crystal lattice microstrains and dispersivity of the block structure. This favors the plastic deformation of the particles, mainly copper particles, activation and weldability of their boundaries, which increases the conductivity of the compacts produced. Optimal conditions of explosive compaction and heat treatment for production of composites with high conductivity are found. Key words: powder mixture, planetary mill, explosive compaction, heat treatment, electric conductivity, x-ray structural analysis.     

The interrelationship between the compaction behaviour and the mechanical strength of pure pharmaceutical tablets

This paper presents and analyses data obtained from the uniaxial compaction of pure pharmaceutical powders in terms of a number of mechanical properties, and correlates these data to some aspects of fracture mechanics. This includes seven different types of pharmaceutical drugs and excipients: alpha lactose, microcrystalline cellulose (Avicel PH 102), acetylsalicylic acid (Aspirin), dicalcium phosphate, magnesium carbonate, acetaminophen (Paracetamol) and starch. The powders were compacted to various ultimate normal stresses ranging between 25 and 246 MPa in an instrumented (force/displacement) single-ended axial compression in cylindrical die with planar punches. The results clearly demonstrate that, to some extent, the toughness of a tablet may be interpreted directly from some mechanical characteristics of its compliance response, i.e., the plastic work and the plasticity index, during the compaction process.     

Real time TEM observation of alumina ceramic nano-particles during compression

The behavior of alumina nano-particles taken from a commercial powder is investigated during in situ compression experiments in a transmission electron microscope (TEM). Small particles of 40 nm in diameter can undergo severe plastic deformation without failure, whereas brittle fracture is observed for 120 nm sized nano-particles. This is evidence of a critical size under which alumina, at least in the form of nano-particles, cannot be considered as brittle materials even at room temperature and a direct observation of the grinding limit generally observed during ball milling.     

A comparative study of fracture behavior between carbon black/poly(ethylene terephthalate) and multiwalled carbon nanotube/poly(ethylene terephthalate) composite films

Fracture behavior of amorphous poly(ethylene terephthalate) (PET) films added multiwalled carbon nanotube (MWCNT) has been compared with that of the PET films added with carbon black (CB) to elucidate the effects of the large aspect ratio of MWCNT. Fracture toughness has been evaluated using the essential work of fracture tests. Evolution of the crazes has been analyzed by conducting time‐resolved small‐angle X‐ray scattering measurements during tensile deformation of the films at room temperature using synchrotron radiation. CB and MWCNT increased the fracture toughness of the PET film by increasing the plastic work of fracture. This resulted from the effects of the fillers to prevent the localization of deformation upon the crazes formed at earlier stages of tensile deformation and to retard the growth of the fibrils in the crazes to a critical length. The CB particles provided a number of sites where the crazes were preferably formed due to stress concentration. In the case of MWCNT, on the other hand, the widening of the crazes formed at earlier stages was suppressed due to the bridging effect arising from the large aspect ratio of MWCNT. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Dynamic Compaction of Al2O3-ZrO2 Compositions

Shock compaction of Al₂O₃-ZrO₃ binary and ternary powder compositions resulted in dense, one-piece samples without visible cracks for pressures ≤12.6 GPa. Dynamic pressures were achieved by using a 6.5-m-long two-stage gas gun. It is believed that plastic deformation by dislocation slip of α-Al₂O₃ partially accommodates the tensile stresses created during the release of shock pressures. A fine and narrow particle size distribution is necessary to achieve high bulk densities, but the bulk structural integrity was not strongly related to the distribution. A high-pressure phase of ZrO₂, which was formed from the monoclinic polymorph, was found at and above shock pressure of 6.3 GPa. No evidence of the orthorhombic cotunnite structure was observed. Compaction of glassy and submicrocrystalline rapidly solidified starting materials showed good structural integrity, although the bulk density was relatively low. It is not clear what the densificationhonding mechanism is in these materials, although it appears not to be plastic deformation. Microstructural analysis showed that fine and uniform microstructures are retained after compaction at appropriate dynamic pressures for all compositions, with some interparticle cohesion present.     

The elastic relaxation of starch tablets during ejection

Tablets are invariably formed by uniaxial compression in rigid dies and the tablet mechanical integrity is highly dependent on its ability to withstand the physical dimensional changes resulting from the elastic relaxation due to the release of the elastic strains incurred during the tablet formation. Therefore, a complete understanding of the continuous tablet elastic relaxation behaviour will provide designers of the solid drug delivery system, important information on the probable mechanical performances of the designed tablets and the likelihood of failures at each stage in the tablet preparation process. This current work has successfully studied online Starch 1500 tablet elastic relaxation behaviour during ejection, which is one of the main stages in a tablet preparation through the use of novel non-contact laser measuring devices. The starch tablets were observed to undergo ‘recompression’ or height reduction in the early stages of ejection, followed by height expansion as they moved further towards the die exit and during emergence. Online diametrical measurements of the tablets during emergence indicated the existence of periodic diametrical expansions-contractions, which has been attributed to the diametrical elastic relaxation behaviour as well as the topographical nature of the circumferential tablet surface. The amplitudes of these expansion-contraction cycles, are believed to be dependent upon the corresponding stored elastic energy of that particular strip of circumferential surface in contact with the die walls. It is also found that the starch tablets formed at a lower compaction velocity predominantly dissipate the internal stored elastic energies by plastic flow and maintain its stored elastic energy during the ejection stage in relative to those formed at a higher compaction velocity.     

Multiscale Simulation of Indentation,Retraction and Fracture Processes of Nanocontact

The process of nanocontact including indentation and retraction between a large Ni tip and a Cu substrate is investigated using quasicontinuum (QC) method. The multiscale model reveals that significant plastic deformation occurs during the process of nanocontact between Ni tip and Cu substrate. Plastic deformation is observed in an area as large as 20 nm wide and 10 nm thick beneath Ni tip during the indentation and retraction. Also, plastic deformation at a deep position in the Cu substrate does not disappear after the neck failure. The analysis of generalized planar fault energy curve shows that there is a strong tendency for deformation twinning in Cu substrate. However, deformation twinning will be retarded during indentation due to the high stress intensity caused by stepped surface of Ni tip. The abrupt drop of load curve during tip retraction is attributed to the two different fracture mechanisms. One is atomic rearrangement near the interface of Ni tip and Cu substrate at the initial stage of neck fracture, the other is shear behavior of adjacent {111} planes at the necking point. A comparison of the critical load and critical contact radius for neck fracture is also made between theoretical values and our numerical results.     

Tensile properties of ultrathin double-walled carbon nanotube membranes

Direct tensile tests of double walled carbon nanotube (DWCNT) membranes with thickness of 40–80 nm were performed using a micro-stress-strain puller. The tensile strength and Young’s modulus are 4.8E2–8.4E2 MPa and 4.4–8.8 GPa, respectively. The deformation and fracture processes were analyzed using the stress vs. strain curves, and SEM observations of the fracture surface of a membrane. The membrane experienced elastic strain and plastic strain during tensile-loading to fracture, and the plastic process is due to the real plastic deformation of the membrane and the slippage between the DWCNT bundles. Cracks occur and spread during the tensile test which causes the membrane to be mangled. With these excellent mechanical properties, the DWCNT membranes can be used in nanotube-reinforced composites.     

PA6/CaCO3复合材料的单边缺口拉伸断裂研究

研究了尼龙6(PA6)/CaCO3复合材料的单边缺口拉伸断裂。结果表明,PA6/CaCO3复合材料在拉伸速率为0.1～300 mm/min的缺口拉伸实验中,裂纹扩展均为脆性断裂。断口主要分为塑性屈服变形区和弹性变形区两部分。塑性屈服变形区形貌是以缺口根部为底边的圆弧型,弹性变形区将塑性屈服变形区包围在里面。塑性屈服变形区面积到达临界尺寸后,材料瞬间断裂。断裂后观察到的塑性屈服变形区面积即为在该实验条件下的裂纹源面积。随着拉伸速率增加,其裂纹源面积减小,而弹性变形区域增加,弹性储存能的储存速度增加,在其裂纹源面积较小的情况下即可发生瞬间脆断。     

Fracture behaviour of a rubber nano-modified structural epoxy adhesive: Bond gap effects and fracture damage zone

This paper critically examined the fracture behaviour of a rubber-modified, structural epoxy adhesive with various bond gap thicknesses ranging from 0.05 mm to 6 mm. The main and very novel contribution is direct measurement of the fracture process zone, plastic deformation zone and intrinsic fracture energy dissipated in the fracture process zone. The shape and size of the fracture process zone and plastic deformation zone were identified using scanning electron microscopy, transmission electron microscope and transmission optical microscope. As the bond gap thickness increased, the fracture energy increased steadily from 2365 J/m² for 0.05 mm bond gap thickness to 6289 J/m² of 1.6 mm bond gap thickness, and then plateaued. The thickness and failure strain of the fracture process zone remained essentially constant, being approximately 0.052 mm and 0.55 respectively, for different bond gap thicknesses. The intrinsic fracture energy (dissipated in the fracture process zone) appeared to be a material property, which remained approximately 2738 J/m². The plastic deformation zone extended through the entire bond gap in thickness and occupied a significant length for all bond gap thicknesses. The effect of bond gap thickness on the fracture energy of the adhesive joints is hence directly attributed to the variation of the plastic deformation energy (dissipated in the plastic deformation zone) with bond gap thickness.     

尾矿砂改性混凝土的强度与声发射损伤特征研究

为了研究尾矿砂改性混凝土的受压损伤特征,对4组不同磷矿尾矿砂取代率的混凝土进行了单轴压缩-声发射监测试验。根据混凝土受压损伤时所释放的声发射(AE)信号,定量探讨了材料的损伤程度,并以AE指标为基础分析了混凝土损伤演化特征。结果表明:混凝土的应力-应变曲线可分为弹性变形、塑性变形、断裂破坏和残余变形4个阶段;随着尾矿砂含量增加,混凝土的抗压强度先增加后保持稳定,尾矿砂取代率为30%(质量分数)的改性混凝土峰值抗压强度最大;由AE信号提出了损伤因子,损伤因子-应变曲线表明普通混凝土的结构损伤主要在塑性变形阶段,而尾矿砂改性混凝土的结构损伤集中在塑性变形和断裂破坏阶段;一定比例的磷矿尾矿砂有助于提高水泥砂浆的密实度,从而增强抗压强度和变形性能。这为尾矿砂改性混凝土的研究提供了重要参考。     

Influence of the phase morphology on the molecular orientation at the crack tips in rubber‐modified nylon 6: A micro Fourier transform infrared study

Despite extensive efforts to understand the toughening mechanism of rubber‐modified semicrystalline polymers, the plastic deformation event at the crack tips with an extreme deformation gradient and its correlation with phase morphology is, thus far, poorly understood. In this study, micro Fourier transform infrared measurements were adopted to give direct evidence of plastic deformation at the crack tips by the molecular orientation in nylon 6/ethylene–propylene–diene terpolymer (EPDM) blends with a distinct phase morphology. Significant plastic deformation ahead of the crack tips, manifested by a high molecular orientation, was observed in the compatibilized nylon 6/EPDM blends with fine rubber particles. Moreover, the increased transverse crack‐propagation resistance due to high molecular orientation dramatically extended the plastic deformation into adjacent regions around the crack tips; this was responsible for enhanced energy dissipation during the fracture process. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

纳米结构陶瓷涂层精密磨削表面/亚表面的形貌

用扫描电镜对纳米(以n表示)结构WC／12Co(n-WC／12Co)和Al2O3／13TiO2(n-Al2O3／13TiO2)涂层经立式精密平面磨削后的磨削表面／亚表面的形貌进行观察，测量了n-WC／12Co和n-Al2O3／13TiO2涂层精密磨削的磨削力分力比、比磨削能。结果表明：在大多数磨削条件下，n-WC／12Co磨削的材料去除机理主要是非弹性变形方式，即以塑性变形为主，伴随一定的材料粉末化。材料较少以脆性碎裂去除。n-Al2O3／13TiO2陶瓷涂层磨削的材料去除机理主要是脆性去除，同时也存在一定的材料粉末化以及极少的显微塑性变形。     

A new approach to characterize scratch and mar resistance of automotive coatings

Mar damage is a major customer concern of the automotive coatings industry. Our study of mar performance can be separated into two distinct areas, a detailed understanding of the damage formation mechanism, and an investigation of the relationship between the damage morphology and appearance. We have developed a nanoscratch technique that can measure important physical quantities, such as penetration depth, normal force and tangential force during the formation of the scratch. Mar resistance of three coatings was evaluated and compared based on the damage mechanisms: plastic flow and fracture. The different deformation mechanisms result in different damage morphologies and a corresponding change in visual impact of the scratch. Statistical surveys of appearance of well-defined scratches indicate that in very short observation times, scratches where fracture has occurred are much more visible than those made by plastic deformation alone. However, with sufficient time and strong illumination a significant percentage of observers could see plastic deformation as well.     

PE-HD/PC/POE-g-MAH复合材料断裂性能的研究

采用基本断裂功(EWF)法评价了高密度聚乙烯(PE-HD)/聚碳酸酯(PC)/聚烯烃弹性体接枝马来酸酐(POE-g-MAH)复合材料处于平面应力与平面应变过渡状态下的断裂韧性和塑性功。研究不同PC含量对复合材料断裂行为的影响,并把宏观断裂参数的变化与复合材料的微观结构联系起来,从物质结构上寻求断裂功参数变化的原因。结果表明,随PC含量的增加,复合材料的比基本断裂功增加,比塑性功降低;复合材料的断裂韧性主要取决于屈服后材料抵抗裂纹扩展的能力,复合材料的塑性变形能力也更依赖于屈服后的行为;复合材料的缺口冲击强度随PC含量的增加而降低,缺口冲击强度高的材料比基本断裂功较小。     

Contact deformation and bonding criteria under impulsive loading

Conclusions It has been shown that the state of strain in the contact zone of dynamically interacting surfaces can be revealed by the recrystallization method. The interval of homologous temperatures for determining the state of strain of the joints and the intense plastic deformation zone R, a parameter related to the physical conditions of realization of bulk-atom interaction on the intracontact surface, has been found.It has been shown, with reference to the example of explosive-welded copper and nickel blanks, that for equivalent welding conditions the values of the intense plastic deformation zone are equal and for different materials amount to 0.8–1.5% of the thickness of the flyer plate depending on the roughness of the impact surfaces.Explosive welding and bond formation in powder compaction have both been shown to be primarily a consequence of deformation processes localized at the contacts, which introduce into the initial system a new structural level of plastic flow.There is two-orders difference between the powers of the localized plastic strain energy released at the contacts and required for strong bond formation in explosive welding and powder compaction respectively.Novosibirsk. Translated from Fizika Goreniya i Vzryva, Vol. 27, No. 3, pp. 103–117, May–June, 1991.     

聚丙烯纤维增强水泥砂浆力学性能试验研究

为研究聚丙烯纤维掺入量对不同养护龄期的水泥砂浆试件变形破坏规律的影响,对水泥砂浆试件进行单轴压缩实验,同时利用数字散斑相关方法(DSCM)、扫描电子显微镜(SEM)对试件侧向变形场、断口形貌进行细观观测.结果表明:试件养护龄期相同时,抗压强度随聚丙烯纤维掺量增加呈先增加后减小趋势,在设置的变量梯度范围内,纤维最优掺量为0.5%;掺入聚丙烯纤维的试件峰后表现出明显的塑性特征,峰后广义刚度系数变化量较大;试件侧向变形场演化过程分为四个阶段:均匀阶段、成核阶段、变形局部化阶段、破坏阶段;聚丙烯纤维与水泥砂浆的粘结强度弱于砂粒与水泥的粘结强度,含聚丙烯纤维的试件在破坏形态上表现出"裂而不断"的特点.提出了含聚丙烯纤维水泥砂浆的微观胶结接触模型,模型的力学关系较好的解释了聚丙烯纤维试件峰后塑性提高的特征.