Densification effects on the fracture in fused silica under Vickers indentation

This study investigates the effects of densification on the deformation and fracture in fused silica under Vickers indentation by both the finite element analysis (FEA) and experimental tests. A refined elliptical constitutive model was used, which enables us to investigate the effects of the evolution of yield stress under pure shear and elastic properties with densification. The densification distribution was predicted and compared with experiments. The plastic deformation and indentation stress fields were used to analyze the initiation and morphology of various crack types. The formation mechanism of borderline cracks was revealed for the first time. This study reveals that the asymmetry of the densification distribution and elastic-plastic boundary significantly influences the cracking behavior. Under the Vickers indentation, conical cracks have the largest penetration depth. When these cracks emerge from a region far from the impression, they extend with constant radii to form circles on the sample surface. Otherwise, they tend to be initiated at the centers of the indenter-material contact edges before propagating towards the impression corners with increasing radii. Therefore, the borderline cracks consisting of successive partial conical cracks can form at a low load and makes them the first type of crack to appear.     

常压等离子射流表面改性超高模量聚乙烯纤维

利用常压等离子射流(APPJ)方法对超高模量聚乙烯(UHMPE)纤维进行表面改性处理。研究了处理前后UHMPE纤维的力学性能、表面形貌、化学成分、表面粘结性能的变化。结果表明,常压等离子射流处理后,UHMPE纤维的强度未发生显著变化,纤维表面粗糙度增加,表面氧元素的含量增加,表面极性基团增加,纤维与环氧树脂之间的粘结性能得到显著的改善。     

Study on wettability improvement and its uniformity of wool fabric treated by atmospheric pressure plasma jet

The influence of processing parameters on wettability improvement and its uniformity of wool fabric treated by atmospheric pressure plasma jet (APPJ) was explored. A woven wool fabric was treated by APPJ under various treatment conditions such as different treatment time, different oxygen flow rate, and different jet‐to‐substrate distance. The water absorption time of wool fabric was measured to determine wettability improvement. The diffusion photo of water droplet on wool fabric surface was taken by digital camera to reflect wettability uniformity. After APPJ treatment, SEM observation showed that the scales on the wool fiber surface directly facing plasma jet pores were destroyed than those on the other fiber surface. XPS analysis showed that the carbon concentration substantially decreased. The concentration of oxygen and nitrogen significantly increased and but the concentration of sulfur and silicon did not obviously changed. With the addition of oxygen gas, more polar groups such as hydroxyl and carboxyl produced on wool fiber surface. The water absorption time of wool fabric greatly reduced indicating wettability improvement. The diffusion of water droplet on wool fabric surface was also larger and more homogenous suggesting uniform plasma treatment. It was concluded that the wettability improvement and its uniformity of the treated wool fabric increased and then decreased with the increasing oxygen flow rate and jet‐to‐substrate distance, and increased with the increasing treatment time. Therefore to achieve reasonable wettability and its uniformity of the wool fabric treated by APPJ, plasma treatment conditions have to be carefully chosen. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Surface modification of ultra high modulus polyethylene fibers by an atmospheric pressure plasma jet

To improve their adhesion properties, ultra high modulus polyethylene (UHMPE) fibers were treated by an atmospheric pressure helium plasma jet (APPJ), which was operated at radio frequency (13.56 MHz). The surface properties of the fibers were investigated by X‐ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and contact angle measurement. The surface dyeability improvement after plasma treatments was investigated using laser scanning confocal microscopy (LSCM). The adhesion strengths of the fibers with epoxy were evaluated by microbond tests. In addition, the influence of operational parameters of the plasma treatment including power input and treatment temperature was studied. XPS analysis showed a significant increase in the surface oxygen content. LSCM results showed that the plasma treatments greatly increased fluorescence dye concentrations on the surface and higher diffusion rate to the fiber center. The tensile strength of UHMPE fiber either remained unchanged or decreased by 10–13.6% after plasma treatment. The contact angle exhibited a characteristic increase in wettability, due to the polar groups introduced by plasma treatment. The microbond test showed that the interfacial shear strengths (IFSS) increase significantly (57–139%) after plasma treatment for all groups and the optimum activation is obtained at 100°C and 5 W power input. SEM analysis showed roughened surfaces after the plasma treatments. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2008     

Oxygen vacancy levels on gadolinia-doped ceria interlayer deposited by atmospheric pressure plasma jet for solid oxide fuel cells

The oxygen vacancy levels as a factor on different gadolinia-doped ceria interlayer (GDCi) films deposited on yttria stabilized zirconia (YSZ) electrolyte substrates by an atmospheric pressure plasma jet (APPJ) via precursor solution of nitrate salts are investigated. Focusing on the effect of carrier gases, scanning electron microscopy (SEM), Raman, and X-ray diffraction (XRD) are implemented for the materials characterization of the as-deposited GDCi films and sintered-GDCi films at various temperatures. The higher level of oxygen vacancies in GDCi films adhered on 8YSZ electrolyte are evidently analyzed using Ar as the carrier gas during the deposition, of which the interdiffusion resulted in the formation of (GDC + YSZ) solid solution for sintering over 1300?°C degraded the total conductivity. The deposition of GDCi films on 8YSZ by APPJ method using O₂ carrier gas significantly improved the total conductivities of the whole electrolyte layers. Moreover, this study provides the useful insight into the oxygen vacancy levels on GDC films as interlayer (GDCi) to improve the values of open circuit voltage in LSM/GDCi/YSZ/Pt full-cell, as well as offering the efficiency of APPJ as one step deposition process.     

常压等离子体改善合成纤维吸湿性的研究

用氦气作为等离子体的气体源、对涤纶、锦纶6、高强度聚乙烯纤维,Twaron 1000芳纶4种合成纤维进行常压等离子体处理,改善纤维的吸湿性能。结果表明:常压等离子体处理,对涤纶和锦纶6的表面有一定的刻蚀作用,但对高强度聚乙烯纤维、Twaron 1000芳纶的表面没有明显影响;经常压等离子体处理后,合成纤维表面氧、氮有所增加,吸湿性能得到提高,强度没有显著变化。     

常压等离子体射流对聚乙烯醇薄膜性能的影响

用常压等离子体射流处理不同含水率聚乙烯醇（PVA）薄膜,通过扫描电镜（SEM）观察薄膜表面形态,并用红外光谱测试仪（FTIR）、X光电子能谱（XPS）、X射线衍射仪（XRD）分析了等离子体处理前后含水率为1.85%MC及41.33%MC两种 PVA化学结构及结晶结构的变化。试验结果表明:水分可加速氦气/氧气等离子体对PVA刻蚀及氧化,其中刻蚀速率达0.68μm/min,氧含量从30.8%提高到34.8％;同时,经过处理的薄膜结晶度增加了48％。     

Experimental investigation into the effect of adhesion properties of PEEK modified by atmospheric pressure plasma and low pressure plasma

High performance polymer, Polyether Ether Ketone (PEEK) (service temperature ?250°C to +300°C, tensile strength: 120 MPa) is gaining significant interest in aerospace and automotive industries. In this investigation, attention is given to understand adhesion properties of PEEK, when surface of the PEEK is modified by two different plasma processes (i) atmospheric pressure plasma and (ii) low pressure plasma under DC Glow Discharge. The PEEK sheets are fabricated by ultra high temperature resistant epoxy adhesive (DURALCO 4703, service temperature ?260°C to +350°C). The surface of the PEEK is modified through atmospheric pressure plasma with 30 and 60 s of exposure and low pressure plasma with 30, 60, 120, 240, and 480 s of exposure. It is observed that polar component of surface energy leading to total surface energy of the polymer increases significantly when exposed to atmospheric pressure plasma. In the case of low pressure plasma, polar component of surface energy leading to total surface energy of the polymer increases with time of exposure up to 120 s and thereafter, it deteriorates with increasing time of exposure. The fractured surface of the adhesively bonded PEEK is examined under SEM. It is observed that unmodified PEEK fails essentially from the adhesive to PEEK interface resulting in low adhesive bond strength. In the case of surface modified PEEK under atmospheric pressure plasma, the failure is entirely from the PEEK and essentially tensile failure at the end of the overlap resulting in significant increase in adhesive bond strength. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Improvement of Vickers hardness measurement on SWNT/Al2O3 composites consolidated by spark plasma sintering

Dense alumina composites with different carbon nanotube content were prepared by colloidal processing and consolidated by Spark Plasma Sintering (SPS). Single-wall carbon nanotubes (SWNTs) were distributed at grain boundaries and also into agglomerates homogeneously dispersed. Carrying out Vickers hardness tests on the cross-section surfaces instead of top (or bottom) surfaces has shown a noticeable increase in the reliability of the hardness measurements. This improvement has been mainly attributed to the different morphology of carbon nanotube agglomerates, which however does not seem to affect the Vickers hardness value. Composites with lower SWNT content maintain the Vickers hardness of monolithic alumina, whereas it significantly decreases for the rest of compositions. The decreasing trend with increasing SWNT content has been explained by the presence of higher SWNT quantities at grain boundaries. Based on the results obtained, a method for optimizing Vickers hardness tests performance on SWNT/Al₂O₃ composites sintered by SPS is proposed.     

高压水除鳞喷嘴射流边界的分析

目前国内多把除鳞喷嘴的高压水射流边界当作直线来进行估测,但实验数据表明由此计算出来的轧制方向射流宽度与实际值的差距比较大。从垂直喷射高度H与轧制方向射流宽度L的试验拟合曲线可知,射流边界近似为抛物线。     

Differences in indentation and wear behaviors between the two sides of thermally tempered soda lime silica glass

Thermal tempering is an industrial process widely used to make soda lime silica (SLS) glass panels stronger and tougher. During the tempering process, the upper and bottom sides of the glass may experience different cooling rates, and thus, their properties could be different. This study characterized changes in surface composition and subsurface glass network structures as well as indentation and wear resistance properties of the air- and tin-sides of 6-mm-thick SLS window panels faced toward the upper and sliding roller sides during thermal tempering. The results showed that although the chemical and structural differences detected with X-ray photoelectron spectroscopy and specular reflection infrared spectroscopy are subtle, there are large differences in nanoindentation behaviors and mechanochemical wear properties of the SLS glass surface. The findings of this study provide further insights into the performance difference between the air- and tin-sides of the SLS glass panel treated with thermal tempering.     

Tailoring the O2 reduction activity on hydrangea-like La0.5Sr0.5MnO3 cathode film fabricated via atmospheric pressure plasma jet process

An atmospheric-pressure plasma jet (APPJ) is applied to prepare porous perovskite materials, particularly of lanthanum strontium manganite La_0.5Sr_0.5MnO₃ (LSM551) oxide powder and film. LSM nano powder around 50.0?nm is obtained, and characterized by X-ray diffraction, scanning electron microscopy, and high-resolution transmission electron microscope. A spherical morphology with hydrangea-like shape is observed as associates to the pure tetragonal phase. LSM film is deposited onto yttria-stabilized zirconia (YSZ) electrolyte-support substrate as cathode layer for the operation in a solid oxide fuel cell at 600–900?°C operating temperatures. A series of symmetrical cells possessing high exchange current density of 30.12?mA/cm² at 800?°C. The prepared samples are assessed as an object to discover the diffusion mechanism of oxygen pathways for LSM/YSZ system based on the microstructural (particles size, and porosities) and electrochemical (kinetic and impedance) data. The mechanism of oxygen pathways is directly associated with the triple phase boundary lengthiness, in which the surface and bulk pathways occurring in APPJ-prepared LSM layer on YSZ lead to an increasing in activity of oxygen reduction reaction. Moreover, a fabrication of desirable ternary metal oxide, LSM, with highly porous structure via an advance-innovative APPJ preparation is outlined.     

等离子体射流载气流量大小对玻璃纤维改性效果影响的研究

通过大气压等离子体射流在玻璃纤维（GF）表面沉积氧化硅（SiOx）纳米颗粒的方法改善玻璃纤维增强聚丙烯（GFRP）复合材料的界面结合性能,利用扫描电子显微镜、原子力显微镜和X射线光电子能谱等表征分析了改性纤维的表面形貌、化学成分、润湿性能和复合材料的界面结合性能,并考察了等离子体射流载气流量大小对GF改性效果的影响。结果表明,当载气流量为40 mL/min时,GF的改性效果最好,且此时GF的表面能相比对照组提高了43.18%,GFRP复合材料的层间剪切强度提高了30.79%;经过等离子体处理后,GF的表面粗糙度增大,极性官能团增多,复合材料的界面结合性能提升。     

Environmentally friendly flame‐retardant materials produced by atmospheric pressure plasma modifications

The objective of this work was to investigate plasma modification of viscose for environmentally friendly flame‐retardant cellulosic materials. Sodium silicate layers were predeposited onto viscose and cotton flannel substrates and grafted/crosslinked using atmospheric pressure plasma. The modified cellulosic fabrics tested with the automated 45° angle test chamber showed significant improvement in their flame‐retardant properties. Analysis conducted by TGA and DSC exhibited enhanced thermal stability of the treated fabrics. Furthermore, the surface analysis (XPS and SEM) confirmed the presence of the SiO₂ network attached to the substrate even after intense ultrasound washes. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

蒸汽射流压力振荡主频研究

在稳定射流区,对饱和蒸汽在过冷水中浸没射流凝结引起的压力振荡特性进行了研究,测量得到了不同汽水参数下的压力振荡特性。通过FFT方法得到了压力振荡的主频,并分析了蒸汽质量流率和水温对压力振荡主频的影响规律,蒸汽射流凝结换热特性决定了压力振荡主频随着蒸汽质量流率和水温的增大而降低。同时,利用先前学者提出的公式并引入量纲为1的蒸汽质量流率和凝结势给出了计算主频的实验关联式,结果表明在本实验参数范围内计算值与实验值具有相同的变化趋势,且吻合的较好,误差在±8%以内。     

Surface characterization of PET nonwoven fabric treated by He/O2 atmospheric pressure plasma

The surface of polyethyleneterephthalate (PET) nonwoven fabric was modified by He/O₂ atmospheric pressure plasma treatment, varying plasma exposure time. The plasma treated PET surfaces have been analyzed to investigate the chemical nature and morphology of surface by X‐ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM), respectively. The change of wettability was measured depending on plasma exposure time. XPS results indicated the presence of oxygen‐based functional groups on the PET nonwoven fabric surface after plasma treatment and oxygen content increased as exposure time increased. The mean roughness increased after 30 s exposure and further increase in exposure to 60 s led to decrease of the roughness and then again increase. The root mean square roughness followed the similar trend to mean roughness. The average difference in height, Rz, increased after plasma exposure for 30 s, while it slightly decreased after 60 s exposure. Despite of redeposition, the Rz of 90 s exposed sample increased more than two times compared with those of 30 and 60 s exposed. Wettability increased progressively up to 10 times after 90 s exposure compared with the untreated. It is attributed to the increases of hydrophilicity and surface roughness. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Properties and in vitro assessment of ZrO2-based coatings obtained by atmospheric plasma jet spraying on biodegradable Mg-Ca and Mg-Ca-Zr alloys

Magnesium (Mg)-based biodegradable alloys have gained a major interest in the biomedical field. The advantages of Mg alloys are depicted by their high biocompatibility, easy biodegradation and satisfactory mechanical properties. However, one major disadvantage of these alloys is represented by their low corrosion resistance in physiological environment. Coatings are considered to be a viable alternative used to improve corrosion, mechanical and cell viability properties of Mg- based metallic alloys. In this paper, two types of ceramic coating materials ZrO₂-Y₂O₃ and ZrO₂-CaO were deposited on Mg-Ca and Mg-Ca-Zr substrates by the atmospheric plasma jet technique. The two types of the deposited coatings exhibit similar Young modulus and a hardness in the range of 0.2–0.4 GPa. Values of the elastic modulus for the layers were measured to be in the range of 11–27 GPa for ZrO₂-Y₂O₃ and of 16–31 GPa for ZrO₂-CaO. The corrosion rate for the ZrO₂-CaO coating has superior values than that for the ZrO₂-Y₂O₃ one. The ZrO₂-CaO coated samples present a better adhesion to the substrate. The MTT colorimetric tests (3-(4,5-dimethyl-thiazol–2-yl)-2,5-diphenyl tetrazolium bromide) did not reveal significant differences in cytocompatibility between the two types of coatings, presenting a moderate cell viability.     

常压等离子体改善高性能纤维粘结性的研究

以氦气为载气,氧气为反应气体,对高强度聚乙烯和Twaron 1000芳纶两种高性能纤维进行常压等离子体处理,来改善纤维的粘结性能;采用单纤维抽拔实验测定等离子体处理前后纤维与环氧树脂之间的界面剪切力;利用原子力显微镜和X射线光电子能谱仪分析等离子体处理前后纤维表面形态和化学成分的变化。结果表明:高强度聚乙烯纤维和芳纶经常压等离子体处理后,纤维表面粗糙度增加,纤维表面碳元素含量下降,羟基、羧基等含氧或氮的极性基团增加,纤维粘结性能得到提高,但其强度无明显变化。     

常压等离子体处理芳砜纶的结构与性能研究

分别采用氦气和氦气/氧气对芳砜纶进行常压等离子体处理。采用滴水吸收实验测定处理前后纤维表面的润湿性,利用扫描电子显微镜和X射线光电子能谱仪分析处理前后纤维表面形态和化学成分的变化。结果表明:经常压等离子体处理后芳砜纶表面粗糙度增加,纤维表面碳元素含量下降,羟基、羧基等含氧或氮的极性基团增加,芳砜纶纱线的润湿性能提高,纱线强度没有明显变化,氦气/氧气等离子体处理比氦气等离子体处理效果更好。     

纤维素在等离子体射流水平床内热解气化特性

采用新型等离子体射流水平床反应器,以羟丙基甲基纤维素(HPMC)为实验物料,考察了进料速率对热解气体产物组成、原料组成元素气相转化效率、气体产率和气体热值的影响,并进行了热解气化过程的能量转化规律研究。结果表明:等离子体热解气化产物主要为可燃气及少量固体残碳,无焦油存在;气体产物中以化学合成气(H2和CO)为主。随进料速率的增加,组成元素的气相转化率、气体产率均减小,而热解气热值增加。在进料速率为0.11 g/s时,氢元素气相转换效率可达93%,热解气中H2和CO体积分数之和可达95%,气体产率为1.37 L/g。在等离子体热解气化HPMC的过程中,电能主要转化为热解气和系统冷却水的显热,并未转化成热解产物的化学能,但等离子体射流为气化过程提供了高温、高焓、高升温速率的反应环境。