Mode I and mode II delamination properties of glass/vinyl-ester composite toughened by particulate modified interlayers

Various vinyl-ester (VE)/poly(acrylonitrile-butadiene-styrene) (ABS) blends were used for interlayer-toughening of a glass/VE composite to increase delamination resistance of the base material under mode I and mode II loading. Dry ABS powder was mixed with the liquid resin in four weight ratios: 3.5, 7, 11 and 15 phr (parts per hundred parts of resin) while the layer thickness was varied within the range of 150–500 μm. Firstly, mode I fracture toughness and tensile properties of the VE/ABS blends were assessed. By using the Raman Spectroscopy technique a chemical reaction was discovered which occurred during ABS–VE mixing: i.e. butadiene transition from the ABS particles to the VE. A butadiene saturation was discovered to occur in the VE beyond 7% ABS particle content. Both mode I and mode II fracture toughness were significantly improved with application of the interlayers. Mode I fracture toughness was found to be a function of layer thickness and particle content variations. The latter dominated G_Ic after the saturation point. On the other hand mode II fracture toughness was found to be independent of the layer thickness (within the used layer thickness range) and only moderately influenced by the particle content. Important Toughening mechanisms were plastic deformation and micro-cracking of the layer materials. Evidence of both mechanisms has been found using optical and scanning electron microscopy (SEM).     

Effect of ionomer thickness on mode I interlaminar fracture toughness for ionomer toughened CFRP

Effect of ionomer thickness on mode I interlaminar fracture toughness was investigated for the ionomer-interleaved CFRP. Laminates were fabricated with Toho UT500/111 prepregs. Ethylene-based ionomer, which has high ductility and good adhesion to epoxy resin, was used as an interleaf material in this study. Thickness of the ionomer film selected was 12, 25, 100 and 200 μm. EPMA analysis showed the existence of the interphase region between the interleaf film and the base prepreg lamina where ionomer and epoxy were mixed. Mode I fracture toughness tests were carried out using DCB specimens. Precracks were introduced into all of the specimens. Fracture toughness values were much improved by interleaving the ionomer films. The fracture toughness value increased sharply by inserting thin ionomer film; however, the additional increase with the increase of the ionomer thickness was smaller. The thickness effect of the ionomer interleaf differs from that of the other kinds of thermoplastic-interleaf. Microscopic observation revealed that the crack path depended on the thickness of the ionomer region. Crack propagated in the interphase/ionomer interfaces for thinner-ionomer-interleaved CFRP, and in the interphase region, at the interphase/base lamina interface and interphase/ionomer interface for thicker-ionomer-interleaved CFRP. Ionomer resin deformed largely only near the crack surfaces, and this fact is responsible for the nonlinear increase of the fracture toughness with the increase of the ionomer thickness.     

Optimization of single-gate carbon-nanotube field-effect transistors

The performance of Schottky-barrier carbon-nanotube field-effect transistors (CNTFETs) critically depends on the device geometry. Asymmetric gate contacts, the drain and source contact thickness, and inhomogenous dielectrics above and below the nanotube influence the device operation. An optimizer has been used to extract geometries with steep subthreshold slope and high I/sub on//I/sub off/ ratio. It is found that the best performance improvements can be achieved using asymmetric gates centered above the source contact, where the optimum position and length of the gate contact varies with the oxide thickness. The main advantages of geometries with asymmetric gate contacts are the increased I/sub on//I/sub off/ ratio and the fact that the gate voltage required to attain minimum drain current is shifted toward zero, whereas symmetric geometries require V/sub g/=V/sub d//2. Our results suggest that the subthreshold slope of single-gate CNTFETs scales linearly with the gate-oxide thickness and can be reduced by a factor of two reaching a value below 100 mV/dec for devices with oxide thicknesses smaller than 5 nm by geometry optimization.     

FRACTURE TOUGHNESS CALIBRATION OF THE Si3N4/Fe JOINT SYSTEM: A PARAMETRIC STUDY

Abstract— A fracture toughness calibration of the Si₃N₄/Fe joint system has been performed for various mixed-mode loading conditions and for different thicknesses of the metal interlayer. The asymmetric four-point-bend loading geometry was used. The values for the calibration function ( Y ) as well as the mode mixity (ψ)of the system increase on increasing the thickness of the metal. As the loading conditions change from mode II to mode I the dependence of both parameters on metal thickness is more intensive.     

The influence of patient thickness and imaging system on patient dose and physical image quality in digital chest imaging

The aim of this work was to study the influence of patient thickness, tube voltage and image detector on patient dose, contrast and ideal observer signal-to-noise ratio (SNR(I)), for pathological details positioned at different regions in the image in posterior-anterior (PA) chest radiology. A Monte Carlo computational model was used to compute measures of physical image quality (contrast, SNR(I)) and patient effective dose, E. Two metastasis-like details positioned in the central right lung and right lung near the spine, respectively, were studied. The tube voltage was varied between 100 and 150 kV and the patient thickness between 20 and 28 cm. Both, a computed radiography (CR) system and a direct radiography (DR) system, were investigated. The DR system provides both lower doses and better image quality compared with the CR system. The SNR(I)2/E is approximately 2.9 times higher for the DR system compared with the CR system.     

Characterization of delamination behavior of unidirectional graphite/PEEK laminates using cracked lap shear (CLS) specimens

Delamination failure criterion is an important tool for characterizing the fracture behavior of laminated composites under mixed loading. In this paper, a fracture envelope was built based on the energy release rate as a fracture criterion of graphite/PEEK laminates. Unidirectional cracked lap shear (CLS) specimens were employed to calculate mode I and mode II energy release rates (G_I, G_II. Static fracture tests were conducted using the specimens with two different lap to strap thickness ratios in order to obtain a wide range of G_I/G_II values. The G_I/G_II values for each thickness ratio were calculated numerically using finite element analysis. The results showed that as a delamination length changes, the G_I/G_II varies from 0.13 to 0.48 depending on the lap to strap thickness ratio. It was also found that a linear fracture envelope may be appropriate for a CLS composite specimen.     

Effect of ZnO layer thickness upon optoelectrical properties of NiO/ ZnO heterojunction prepared at room temperature

In this work, p-NiO/n-ZnO heterostructures were successfully prepared at room temperature using RF sputtering technique. The influence of ZnO layer thickness on the performance of the heterojunction was investigated. The deposited ZnO layers have a hexagonal Wurtzite structure with preferable growth orientations along (002) and (103) for thinner films. Increasing the thickness results in more crystallographic orientation randomness. The current–voltage measurements of the realized heterojunctions showed a clear rectifying behavior. The measured ideality factor varies from 2.5 to 1.6 according to the thickness of ZnO layer. The series resistance of the device is enlarged with increasing ZnO thickness. The deduced parameters from the I–V characteristics suggest that 200 nm is the optimal thickness of the ZnO layer according to our experimental conditions. We attribute the relatively better performance of this thickness to achieving reasonable compensation between serial resistance and ideality factor. The best heterojunction was tested and successfully used as a UV detector.     

Interface chemistry and bonding strength for diffusion-bonded Fe/Fe-FeO/Al2O3 systems

The samples for this study were made by oxidizing the interface region of an Fe/Al₂O₃ system containing either wüstite or Fe-FeO composite (I) as interlayer. The bonded materials of Fe/FeO/Al₂O₃ and Fe/I/Al₂O₃ were prepared by hot-pressing. For analysis of the boundary region electron probe microanalysis (EPMA), transmission electron microscopy and X-ray diffraction were used; at the FeO/Al₂O₃ and I/Al₂O₃ interfaces a newly formed reaction layer of about 6 m in thickness containing iron, aluminium and oxygen could be identified, but EPMA failed to reveal the Fe/FeO interface. Therefore, the interface of iron single crystals with FeO scale was investigated by Auger electron spectroscopy and X-ray photoelectron spectroscopy, and at the Fe/FeO interface formation of a transition layer with a thickness of several hundred nanometres was observed. Through the Fe/I interface, interdiffusion of iron occured. Fe/I/Fe and Al₂O₃/l/Al₂O₃ bonded materials had tensile strengths of 150 and 130 MPa, respectively, when an interlayer of Fe-25 mol% FeO was applied between both bonding pairs.     

橡胶夹层/复合材料粘接界面疲劳裂纹扩展行为的研究

用 型加载下的双悬臂夹层梁试样 ,以应变能释放率为裂纹扩展参量 ,研究橡胶夹层 /复合材料粘接界面疲劳裂纹的扩展行为。结果表明 ,循环载荷下的裂纹扩展速率对试验频率、载荷比、温度及橡胶夹层厚度反映较敏感。     

PEK-C膜层间增韧碳纤维/环氧树脂复合材料的力学性能

为探究热塑性酚酞基聚醚酮（Polyaryletherketone with Cardo,PEK-C）树脂薄膜及膜厚对层间增韧碳纤维/环氧树脂复合材料力学性能的影响,利用浸渍提拉法制备了三种不同厚度（分别约为1 μm、10 μm、30 μm）的PEK-C膜,通过热压成型制备了层间增韧碳纤维/环氧树脂复合材料层合板,对其进行了Ⅰ型层间断裂韧性、冲击后压缩强度、层间剪切及弯曲性能测试,并利用SEM观察微观形貌及AFM扫描微观相图。结果表明:不同PEK-C膜厚增韧碳纤维/环氧树脂复合材料的Ⅰ型层间断裂韧性、冲击后压缩强度及层间剪切强度有不同程度提高,Ⅰ型层间断裂韧性及层间剪切强度以膜厚为10 μm最佳,分别增大了157.17%和17.57%,冲击后压缩强度以膜厚为30 μm最佳,达到了186.67 MPa,这是由于PEK-C与环氧树脂在热压固化过程中形成了双相结构,改善了材料韧性;但弯曲性能持续下降,强度及模量由未增韧的1 551 MPa、106 GPa分别降至30 μm时的965 MPa、79 GPa,这是由于PEK-C树脂扩散进入环氧树脂中,降低了纤维体积分数及材料刚度。      

用双悬臂夹层梁试样研究复合材料与 橡胶粘接界面的断裂韧性

用Ⅰ 型加载下的双悬臂夹层粱试样, 借助于线弹性断裂力学和声发射技术研究橡胶/复 合材料的粘接界面的断裂韧性GIC与裂纹扩展阻力R 并探讨加载速率、试验温度及橡胶片厚度对 它们的影响。结果表明, 在本试验范围内, 低速加载或高温将会降低界面的断裂韧性, 增大橡胶片 厚度会使断裂韧性稍有提高。      

Effect of adhesive thickness on fatigue and fracture of toughened epoxy joints – Part II: Analysis and finite element modeling

The effect of bondline thickness on the fatigue and fracture of aluminum adhesive joints bonded using a rubber-toughened epoxy adhesive was studied using finite element analysis. The fatigue data of Part I examined the dependence of the fatigue threshold and cyclic crack growth rate on the adhesive thickness under both mode-I and mixed-mode loading. The fracture data of Part I illustrated the relation between the adhesive thickness and the quasi-static crack initiation and steady-state critical strain energy release rates. These experimental trends are explained in terms of the effects of the adhesive thickness and the applied strain energy release rate on the stress distribution in the bondline, the stress triaxiality at the crack tip, and the plastic zone size in the adhesive layer.     

Effect of mixed mode I/II on fracture behaviour of laminated metal matrix composites

Abstract

The effects of mixed mode loading (I/II) on the fracture toughness and fracture behaviour of both 6090/SiC/20_p-6013 diffusion bonded laminates and 2080/SiC/20_p-2080 adhesive bonded laminates tested in the crack arrester orientation were investigated. The effects of layer thickness and volume fraction ratio on the fracture behaviour under the mixed mode were also studied. The fracture behaviour under mode I/II of available similar discontinuously reinforced aluminium (DRA) materials was additionally compared to that of the laminates. The fracture behaviour of laminates under mode I/II was dependent on the volume fraction ratio and generally different from that of the monolithic and DRA. The increase in the fracture toughness of DRA by lamination with ductile layers under mode I changes somewhat under increasing load mixity, for 75/25 and 50/50 diffusion bonded laminate and 60/40 adhesive bonded laminate ABL. This results from extensive interfacial separation and delamination between the layers.     

CuPc/C60薄膜太阳能电池的制备及膜厚对其光电性能的影响

本文采用CuPc作为电子给体,C60作为电子受体制备了ITO/CuPc/C60/Al异质结太阳能电池。实验表明器件中活性层(CuPc/C60)对太阳能电池的光电性能有很大的影响。主要原因是有机物的激子扩散长度大约是十几纳米左右,产生的激子大多数在未到达异质结之前就已经复合。本文讨论了活性层(CuPc/C60)的厚度比,并获得其最优比例。     

复合型裂纹起裂角厚度效应的实验研究

完成了飞机结构铝合金LC4CS的2、4、8和14mm四种不同厚度试样在I+II复合加载条件下的复合型断裂实验,系统分析了厚度和复合载荷对裂纹起裂角的影响,揭示了常用复合型断裂准则的厚度适用范围,用三维断裂理论对结果进行了讨论。结果表明:复合型裂纹起裂角具有明显的厚度效应;最大周向应力准则能够准确预测薄试样和厚试样(厚度为2 mm 和14 mm)在各种复合加载条件下的起裂方向,但是不适用于中间厚度的试样,尤其是8 mm厚度的情况。最大三轴应力准则试图考虑裂纹尖端三维约束对裂纹起裂的影响,但是结果并不理想。最小应变能密度因子理论的预测结果与最大周向应力准则的预测结果非常接近,但同样不能预测8mm厚度试样的起裂方向。非常有必要建立一个普遍适用的三维复合型断裂准则。     

FRONT DEVELOPMENT OF A LONG FATIGUE CRACK DURING ITS GROWTH

Abstract— A 3-D elastic-plastic finite element analysis has been developed to simulate the deformation development along the front of a long mode I single edge crack in plates subjected to either monotonic or cyclic loading. Idealisations having both equal and unequal layers through the thickness of the plate were involved. Plane stress and plane strain 2-D finite element analyses were also performed and compared with the present 3-D solutions. The development of the monotonic and cyclic crack tip plastically deformed zones and opening displacements were traced and correlated to accommodate the effect of the plate thickness and the profile of the crack front. A previously developed crack tip deformation parameter was invoked to predict the effect of the specimen thickness on mode I fatigue crack growth and the associated change of crack front profile. Comparison of such a prediction and the experimental findings of the present work reflected the capability of that parameter in modelling fatigue crack growth through the plate thickness.     

The evolution of the structural, electrical and optical properties in indium-tin-oxide thin film on glass substrate by DC reactive magnetron sputtering

The evolution of the structural, electrical and optical properties in indium-tin-oxide (ITO) thin film on glass substrate prepared by DC reactive magnetron sputtering was investigated. The variation of the structural, electrical and optical properties could be largely divided into two regions of (i) the initial region I roughly up to the critical film thickness of 50 nm and (ii) the stable region II above the critical thickness. As the film thickness grew, X-ray diffraction (XRD) peak intensities of both (2 2 2) and (4 0 0) planes increased continuously and the film morphology became clear. The peak intensity ratio of I₂₂₂/I₄₀₀ decreased gradually with the thickness, implying a preferred orientation along the (4 0 0) plane at a higher thickness.In the region II over the critical film thickness of 50 nm, where the structural evolution was clearly observable, the carrier density also increased over 9.0×1020/cm³ and the specific resistivity was lower than 140 μΩ cm.     

50-nm fully depleted SOI CMOS technology with HfO/sub 2/ gate dielectric and TiN gate

In this paper, we demonstrate for the first time CMOS thin-film metal gate FDSOI devices using HfO/sub 2/ gate dielectric at the 50-nm physical gate length. Symmetric V/sub T/ is achieved for long-channel nMOS and pMOS devices using midgap TiN single metal gate with undoped channel and high-k dielectric. The devices show excellent performance with a I/sub on/=500 /spl mu/A//spl mu/m and I/sub off/=10 nA//spl mu/m at V/sub DD/=1.2 V for nMOSFET and I/sub on/=212 /spl mu/A//spl mu/m and I/sub off/=44 pA//spl mu/m at V/sub DD/=-1.2 V for pMOSFET, with a CET=30 /spl Aring/ and a gate length of 50 nm. DIBL and SS values as low as 70 mV/V nand 77 mV/dec, respectively, are obtained with a silicon film thickness of 14 nm. Ring oscillators with 15 ps stage delay at V/sub DD/=1.2 V are also realized.     

CoCrPtO-Based Granular Composite Perpendicular Recording Media

The effect of capping layer thickness (t_Cap) on media properties in CoCrPtO-based granular composite media is investigated. The CoCrPt-based capping layer with much less coercivity (H_c) and more exchange coupling than the bottom layer was used. Surprisingly, H_c increases from 4.9 to 5.9 kOe with increasing t_Cap from 0 to 3.8 nm (Zone I) and then decreases to 4.1 kOe at t_Cap=8.3 nm (Zone II). As t_Cap increases, the a axis lattice constant increases from 2.584 to 2.592 Aring, while the c axis lattice constant decreases from 4.213 to 4.192 Aring. Zone I exhibits relatively constant loop slope (alpha) at H_c and activation volume (Vact) for magnetic reversal, while Zone II shows the increase in alpha and V_act. This increase is confirmed by TEM images with less grain isolation and larger grain size. Angular dependence of H_cr in Zone II shows less coherent switching behavior compared to Zone I. Thermal stability factor continuously improves from 59 to 107 with increasing t_Cap. Simulation results reveal that the increase in H_c at Zone I is mostly due to the enhancement of thermal stability. The decrease in H_c at Zone II is understood as a dynamic tilted medium caused by the increase in lateral exchange coupling in the capping layer     

Fast-Disintegrating Sublingual Epinephrine Tablets: Effect of Tablet Dimensions on Tablet Characteristics

ABSTRACT

The purpose of this study was to evaluate the effect of changing dimensions on the hardness (H), disintegration time (DT), and wetting time (WT) of fast-disintegrating epinephrine tablets for sublingual administration as potential first aid treatment for anaphylaxis. Tablet formulations I and II, containing 0% and 10% epinephrine bitartrate, respectively, and weighing 150 mg were prepared by direct compression. Formulations were compressed at a range of forces using an 8/32″ die with concave punches (CP); a 10/32″ and an 11/32″ die with CP and flat punches (FP). Tablet weight variation, content uniformity, thickness, H, DT, and WT were measured. The 8/32″, 10/32″, and 11/32″ dies resulted in tablet thickness of ranges 0.25–0.19″, 0.17–0.1″, and 0.16–0.08″, respectively. The DT and WT using the 8/32″ die were ≤10 and ≤30 sec, respectively, at H ≤5.4 ± 0.2 kg for formulation I, and H ≤5.4 ± 0.3 kg for formulation II. The DT and WT were ≤10 and ≤30 sec, respectively, using 10/32″ die/CP, 10/32″ die/FP, 11/32″ die/CP, and 11/32″ die/FP at H ≤6.2 ± 0.6 kg, ≤6.8 ± 0.4 kg, ≤4.9 ± 0.1 kg, and ≤7.2 ± 0.3 kg, respectively, for formulation I. For formulation II, the DT and WT were ≤10 sec and ≤30 sec, respectively, when H < 4 kg. No difference in DT and WT was observed between concave and flat tablets. The 11/32″ and 10/32″ dies resulted in more ideal tablet dimensions for sublingual administration, but H must be maintained <4 kg to ensure rapid DT and WT.