织构对CVD自支撑金刚石薄膜残余应变的影响

计算了薄膜试样不同方向的弹性模量,研究了织构和甲烷浓度对CVD自支撑金刚石薄膜的宏观残余应变的影响.结果表明,织构使CVD金刚石薄膜的弹性模量和宏观残余应变呈现各向异性.甲烷浓度的升高导致织构组分密度水平变化,使薄膜的弹性模量增大,从而降低残余应变;另一方面,杂质浓度的升高增大宏观残余应变.改变薄膜沉积工艺参数可调整织构,从而调节薄膜的残余应力.     

Oxygen gas permeability and the mechanical properties of poly (n-butylamino)-(di-n-hexyamino) phosphazene Membranes

Poly (n-butylamino)-(di-n-hexylamino)-phosphazene was prepared by the reaction of poly (dichlorophosphazene), di-n-hexylamine and n-butylamine using tetrahydrofuran (THF) solvent and triethylamine at room temperature. To increase the mechanical properties of polymer films, cross-linking agents, such as neopentyl glycidyl diether and trimethylol propane triglycidyl diether, were added to the original polymer. The original and agent-added polymer films were prepared by a casting method. The films with cross-linking agents were heated at 60 and 120 °C, and then transparent films were prepared. The oxygen gas permeability and the mechanical properties of the original and the cross-linked films were determined. It was found that the oxygen gas permeability and the mechanical properties, such as Young's modulus, of the cross-linked films were greater than for the original film.     

Wrinkled liquid-crystalline microparticle-enhanced photoresponse of PDLC-like films by coupling with mechanical stretching

Photoresponsive behaviors are studied in hybrid liquid-crystalline (LC) films prepared with light-responsive LC polymer microparticles as dopants using photoinert polymers as a host material. Upon mechanical stretching, both topological shape change and mesogenic alignment occur in the LC polymer microparticles, enabling the polymer-dispersed LC (PDLC)-like films to bend toward a light source upon UV irradiation. The rough morphologies of the hydrophobic LC microparticles enhance their interactions with hydrophilic polymer substrates. The bilayer-like structures of the hybrid film formed in the fabrication processes are responsible for the photomechanical behavior, which is reversibly controlled by combing light irradiation with the stretching processes.     

Dynamic features of the photoinduced plasticity kinetics in glassy semiconductors

The photoinduced variation of plasticity (photoplastic effect) in glassy semiconductor films was studied for the first time on a nanoscale level using a nanoindentation technique. It is shown that an increase in Young’s modulus and a decrease in the nanohardness for such films in the initial stage of their exposure to light with a wavelength in the vicinity of the fundamental absorption edge is a characteristic feature of the photomechanical response kinetics. The photoplastic after-effect has been observed, whereby the state of film softening (as compared to the initial dark state) is retained for some time after the light switch-off, and the length of this period is dependent on the conditions of exposure.     

基于细观力学的大开孔层合板缝合补强力学性能计算的新方法基于细观力学的大开孔层合板缝合补强力学性能计算的新方法

从细观力学的角度出发,考虑了面内纤维弯曲及富树脂缺陷,建立了大开孔层合板缝合补强孔边针脚损伤的单胞模型。建立了纤维弯曲函数,推导了纤维弯曲区域的纤维体积分数及纤维弯曲角度。基于复合材料力学分析方法,计算得出了单胞的材料弹性常数。研究表明:缝合导致单胞面内纤维最大弯曲角不超过20°,单层板纵向杨氏模量减小,横向杨氏模量、剪切模量及泊松比均增大,变化幅度均在-8%~20%之间;且对于大开孔层合板缝合补强而言,针距变化引起的材料性能变化相对边距大许多。由上述计算结果,建立了一种缝合补强大开孔层合板力学性能计算的新方法,同时引入针孔模拟针脚处的应力集中现象,结果表明:缝合会造成层合板面内力学性能降低,并且对面内的压缩性能影响大于对面内拉伸性能的影响。      

The influence of poly(acrylic acid) molar mass and concentration on the properties of polyalkenoate cements Part II Young''s modulus and flexural strength

The Young's modulus and flexural strength were determined for glass polyalkenoate cements as a function of poly(acrylic acid), PAA molar mass, concentration, glass volume fraction and cement ageing time. The Young's modulus was independent of PAA molar mass. The Young's modulus increased dramatically with the PAA concentration of the cement until concentrations greater than 50% m/m were reached. The modulus increased with time for nearly all the cements investigated consistent with a continuing ionic cross-linking process in the cement matrix. The modulus increased with an increase in the volume fraction of the higher modulus glass phase. Increasing the glass volume fraction provides more surface area for acid attack resulting in a more cross-linked polysalt matrix, as well as increasing the volume fraction of residual glass particles. Flexural strength was highly dependent on molar mass of the PAA and its concentration. The molar mass dependence of the flexural strength was greatest at higher PAA concentrations.     

Light-induced optical activity in optically ordered amorphous side-chain azobenzene containing polymer

Abstract

We report the appearance of circular birefringence (optical activity) in amorphous side-chain azobenzene polymer films on illumination with circularly polarized light. The effect is observed only if an optical axis is previously created in the film with the help of linearly polarized light. The photoinduced optical activity is believed to be due to changes in the polymer structure initiated by a circular momentum transfer from the circularly polarized light to the azobenzene chromophores.     

Evaluation of Young＇s Modulus and Residual Stress of NiFe Film by Microbridge Testing

Microbridge testing was used to measure the Young＇s modulus and residual stress of metallic films. Samples of freestanding NiFe film microbridge were fabricated by microelectromechanical systems. Special ceramic shaft structure was designed to solve the problem of getting the load-deflection curve of NiFe film microbridge by the Nanoindenter XP system with normal Berkovich probe. Theoretical analysis of load-deflection curves of the microbridges was proposed to evaluate the Young＇s modulus and residual stress of the films simultaneously. The calculated results based on experimental measurements show that the average Young＇s modulus and residual stress for the electroplated NiFe films are 203.2 GPa and 333.0 MPa, respectively, while the Young＇s modulus measured by the Nano-hardness method is 209.6：1：11.8 GPa for the thick NiFe film with silicon substrate.     

Effect of the pressure of sputtering atmosphere on the physical properties of amorphous aluminum oxide films

Amorphous aluminum oxide films were prepared by rf-sputtering at various values of the pressure of sputtering atmosphere, and their density, refractive index, Young's modulus and internal stress were measured. The physical properties of the present films depended on the pressure of sputtering atmosphere. The density, refractive index, and Young's modulus decreased with the pressure below about 6.5 Pa, beyond which they increased. The compressive stress and tensile stress were induced in the films depending upon the pressure of sputtering atmosphere, and the tensile stress reached a maximum at the pressure of 6.5 Pa and then decreased as the pressure increased. From the results of the energy-dispersive X-ray analysis (EDX), it was found that the pressure of sputtering atmosphere gave a large influence to the chemical composition (the atomic ratio, O/Al) of the film. The pressure dependence of the physical properties was successful to be explained by the change of chemical compositions of the films. The presence of OH group in the films was verified by using FT-IR, and their microstructure was investigated by SEM study.     

Evaluation of Young''''s Modulus and Residual Stress of NiFe Film by Microbridge Testing

Microbridge testing was used to measure the Young's modulus and residual stress of metallic films. Samples of freestanding NiFe film microbridge were fabricated by microelectromechanical systems. Special ceramic shaft structure was designed to solve the problem of getting the load-deflection curve of NiFe film microbridge by the Nanoindenter XP system with normal Berkovich probe. Theoretical analysis of load-deflection curves of the microbridges was proposed to evaluate the Young's modulus and residual stress of the films simultaneously. The calculated results based on experimental measurements show that the average Young's modulus and residual stress for the electroplated NiFe films are 203.2 GPa and 333.0 MPa, respectively, while the Young's modulus measured by the Nano-hardness method is 209.6±11.8 GPa for the thick NiFe film with silicon substrate.     

Measurement of Young''s modulus and residual stress of copper film electroplated on silicon wafer

The Young's modulus and residual stresses of electroplated copper film microbridges were measured. Special ceramic shaft structure was designed to solve the problem of getting the load-deflection curves of the microbridges from a nanoindentation system equipped with a normal Berkovich probe. Theoretical analysis of the load-deflection curves of the microbridges is proposed to evaluate the Young's modulus and residual stress of the copper films simultaneously. The calculated results based on the experimental measurements showed that the average Young's modulus and residual stress of the electroplated copper films are 115.2 GPa and 19.3 MPa, respectively, while the Young's modulus measured by the nanoindenter for the same copper film with silicon substrate is 110±1.67 GPa.     

Surface effect on the elastic behavior of static bending nanowires

The surface effect from surface stress and surface elasticity on the elastic behavior of nanowires in static bending is incorporated into Euler-Bernoulli beam theory via the Young-Laplace equation. Explicit solutions are presented to study the dependence of the surface effect on the overall Young's modulus of nanowires for three different boundary conditions: cantilever, simply supported, and fixed-fixed. The solutions indicate that the cantilever nanowires behave as softer materials when deflected while the other structures behave like stiffer materials as the nanowire cross-sectional size decreases for positive surface stresses. These solutions agree with size dependent nanowire overall Young's moduli observed from static bending tests by other researchers. This study also discusses possible reasons for variations of nanowire overall Young's moduli observed.     

The influence of hydroxyapatite: Zinc oxide ratio on the setting behavior and mechanical properties of polyalkenoate cements

The influence of hydroxyapatite (HA) content on the setting behavior and mechanical properties of hydroxyapatite-zinc oxide-poly(acrylic acid) (HA-ZnO-PAA) composite cements were investigated as a function of HA content. The working time increased with HA content up to 45 wt % HA and then decreased whilst the setting time increased with increasing HA content. Mechanical properties were determined after storage in water at 37 degrees C for 1, 7 and 28 days. Young's moduli and compressive strength go through a maximum at approximately 30 and 45 wt % HA. Young's modulus increases with time, which is consistent with an ongoing crosslinking reaction.     

Using thin film stress to produce precision, figured X-ray optics

We are studying the possibility of producing precision, aspherical mirrors for X-rays and visible light. Our study examines the use of ultrastructure processing to replace mechanical methods of material removal. The method starts with a chemically-mechanically polished, flat silicon wafer. The aim is to preserve atomic scale smoothness of the surface wafer while the wafer is bent to a desired figure. We report measurements of the mechanical properties of various stressing layers. This involves measuring the deformation of several thin silicon wafers coated with chemically vapor deposited nickel and boron films of known thickness. We have found that, under normal conditions, the film does not add to the microroughness of the substrate on either the front or the back surfaces. Film and substrate thicknesses, however, vary by as much as 10%. This is the present limit on figure accuracy. We have developed a model that describes bending of B/Si and Ni/Si structures. The model relates stress and Young's modulus to the measured thickness of the film, and the thickness and curvature of the substrate. This approach is used to measure the stress and Young's modulus for boron and nickel films. The Young's modulus E_f was 3.05 x 10¹² Pa for the boron films and 1.4 x 10¹⁰ Pa for the nickel films. From the relationship developed and verified for predicting the radii of curvature of the substrate, if may be possible to define a film thickness pattern which would provide a desired optical figure.     

Polarization holographic gratings in side-chain azobenzene polyesters with linear and circular photoanisotropy

We investigate thin phase polarization holographic gratings recorded with two waves with orthogonal linear polarizations in materials in which illumination with linearly/circularly polarized light gives rise to linear/circular birefringence. The theoretical analysis shows that the presence of circular photoanisot-ropy changes significantly the diffraction characteristics of the gratings. The intensities of the waves diffracted in the +1 and -1 orders of diffraction and their ratio depend substantially on the reconstructing-wave polarization. Experiments with films of side-chain liquid-crystalline azobenzene polyester that is a photoanisotropic material of the considered type confirm the unusual polarization properties. It is shown that polarization holography may be used for real-time simultaneous measurement of photoinduced linear and circular birefringence.     

Structural and mechanical properties of Al–Si alloys obtained by fast cooling of a levitated melt

Data on the structure and mechanical properties of cast Al–Si alloys in a wide compositional range from hypo-to high hyper-eutectic composition are scares. These properties depend on many factors during solidification of the alloys. In the present work, samples were obtained by rapid cooling of levitated melts of various compositions from 11.5 to 35 wt.% Si. The measurements revealed linear concentration dependences of density and Young's modulus. The average temperature coefficient of Young's modulus in the range from room temperature to 500 °C and the yield point for bending both had maxima at about 20 wt.% Si. The hysteresis of the temperature dependence of Young's modulus had a minimum at about 20 wt.% Si as well. Changing Young's modulus temperature coefficient and Young's modulus hysteresis as a function of the Si content are connected with the creation of the Guinier–Preston zones. Values of the yield point are explained by the plasticity of components of the eutectic structure, primary crystals and grain boundaries. The extrema of the concentration dependences of the mechanical properties occurred for the fine-grained structure arisen from coupled eutectic-like growth. Solidification at other conditions led to formation of primary crystals of solid solution or primary Si crystals.     

Photoinduced anisotropy measurements in liquid-crystalline azobenzene side-chain polyesters

Reversible photoinduced anisotropy in a series of liquid-crystalline azobenzene side-chain polyesters is investigated as a function of intensity of the write beam and the sample temperature. Measurements reveal that the erasing takes place at a temperature much higher than the glass transition temperature. Induced anisotropy can be erased by heating the polyesters to approximately 80 °C.     

Investigations into the fracture mechanics of acetylsalicylic acid and lactose monohydrate

The fracture mechanics of acetylsalicylic acid (ASS) and lactose monohydrate (LM) were studied using three-point beam bending experiments and compared with conventional tabletting performance. ASS was found to have an unusual behaviour in terms of its Young's modulus and tensile strength when determined with beams of different porosities. The Young's modulus as a function of beam porosity showed two exponential parts separated by a constant region and the tensile strength as a function of the porosity followed a non-exponential law. Tabletting experiments revealed that ASS undergoes different deformation mechanisms at the different compaction pressures associated with the porosity ranges covering the different regions. The different deformation mechanisms might have caused different crack and flaw patterns or different crack lengths, in particular at the beam surfaces, which are under maximum tensile stress during the tests. The unusual findings were, however, not reflected in experiments to determine the critical stress intensity factor as a function of beam porosity, because here crack propagation is controlled via a notch introduced into the beams. In contrast to ASS, LM behaved like the majority of materials i.e. Young's modulus, tensile strength and critical stress intensity factor were found to relate to the beam porosity exponentially.     

Modelling the Young''s modulus of platelet reinforced thermoplastic sheet composites

Particulate reinforced polymers is a mature field and many models are available to predict the Young's modulus of such composites. However, most existing models have a common flaw; they all predict that the composite modulus equals that of the reinforcing agent when the polymer content approaches zero. This implies, in this limit, a monolithic reinforcement whereas, in fact, it is composed of discrete particles with very little interaction. This is a serious drawback and therefore this study focussed on deriving an improved model for the prediction of the Young's modulus. The porosity of the present samples was correlated with the volume fraction binder and the maximum packing density of the pure reinforcement. A theoretical model for Young's modulus was derived along the lines of the Padawer and Beecher modified Cox model. However, it includes the effect of composite porosity on the composite's mechanical properties. In contrast to other available models, it correctly predicts the loss of material stiffness and strength in the limit of zero binder content. Good agreement was found between the predictions of this model and experimental measurements.     

Liquid‐Crystalline Dynamic Networks Doped with Gold Nanorods Showing Enhanced Photocontrol of Actuation

A near‐infrared‐light (NIR)‐ and UV‐light‐responsive polymer nanocomposite is synthesized by doping polymer‐grafted gold nanorods into azobenzene liquid‐crystalline dynamic networks (AuNR‐ALCNs). The effects of the two different photoresponsive mechanisms, i.e., the photochemical reaction of azobenzene and the photothermal effect from the surface plasmon resonance of the AuNRs, are investigated by monitoring both the NIR‐ and UV‐light‐induced contraction forces of the oriented AuNR‐ALCNs. By taking advantage of the material's easy processability, bilayer‐structured actuators can be fabricated to display photocontrollable bending/unbending directions, as well as localized actuations through programmed alignment of azobenzene mesogens in selected regions. Versatile and complex motions enabled by the enhanced photocontrol of actuation are demonstrated, including plastic “athletes” that can execute light‐controlled push‐ups or sit‐ups, and a light‐driven caterpillar‐inspired walker that can crawl forward on a ratcheted substrate at a speed of about 13 mm min^‐1. Moreover, the photomechanical effects arising from the two types of light‐triggered molecular motion, i.e., the trans–cis photoisomerization and a liquid‐crystalline–isotropic phase transition of the azobenzene mesogens, are added up to design a polymer “crane” that is capable of performing light‐controlled, robot‐like, concerted macroscopic motions including grasping, lifting up, lowering down, and releasing an object.