“夹部牙”光弹实验及临床应用

本文提出三维牙颌光弹模型的制作方法,该方法制作的模型可以满足各种有关牙齿的三维光弹应力分析的需要.同时提出新型的“夹部牙”.临床应用及光弹性实验证明它是设计合理的.     

光弹性粘结材料的试验研究

在三维光弹性试验中，为模拟具有软弱夹层或由不同岩土构成的复杂地基问题，需用粘结材料将各种不同弹模的型材粘结成组合模型。本文提出三种新型光弹性粘结材料，并通过试验阐明其光学和力学性能，分析比较了它们的主要特点和差异，同时探讨了其粘结应力的作用与效果。     

变弹模成层岩基受预锚荷载作用的三维光弹性实验研究

本文介绍了变弹模成层岩基受预锚荷载作用的三维光弹性实验过程。求出了岩基在锚固应力作用下锚根附近的应力场,并和电测成果、理论计算成果进行了比较,结果非常相近.为进一步探讨这些问题提供了可靠的依据.     

地质构造应力的分布与煤和瓦斯突出关系的光弹试验研究

煤和瓦斯突出是一种复杂的矿井动力现象,是矿井生产的一大灾害。本文介绍了某矿区在水平地质构造应力作用下构造应力场的变弹模光弹模拟实验,并在实验结果分析的基础上指出了地质构造应力的...     

固体火箭发动机燃烧室光弹性分析

本文运用光弹性法研究了某型固体火箭发动机燃烧室内端燃型药柱和星柱型药柱两种形状的固体复合推进剂的残余应力场,测定了光弹材料的弹性模量、泊松比、线胀系数、材料条纹值和冻结温度,获得了光弹材料在压应力和温度应力下的等差线条纹图,分析了应力分布情况.     

三维光弹模型内部应力全场分析的进一步研究

本文对目前广泛采用的三维光弹性应力分析“冻结”切片法作了扼要的讨论,并提出以“冻结”法为基础,采用一种连续切片法,可将对切片一次正射所获得的实验数据,与弹性理论基本方程和本文所导出的方法相结合,进行三维模型内部应力全场分析,通过电子计算机进行数值计算,获得了满意的成果,且为今后三维光弹性应力分析自动化提供新的途径。     

一种动光弹模型材料的制作方法及其应用

基于#618环氧树脂、甲基六氢苯酐、促进剂DMP-30、环氧树脂消泡剂四种原料,提出制作光弹性模型的新配方和新方法,并利用单轴压缩实验、电测法和动态光弹法分别测定了制作的光弹模型的动态力学参数。新方法工艺简单,制作周期短,对人体无害。制作的光弹模型初始应力小,表面光洁,质地均匀,透光性好,光学灵敏度高,具有良好的机械加工和切削性能。通过三点弯曲梁冲击实验,得到了清晰的光弹等差条纹图像,验证了该配方和方法制作的模型可以应用于动态光弹性实验。     

用光弹和光弹贴片法研究爆炸应力波

本文借助于光弹和光弹贴片法及沙丁照相机,用透明的环氧树脂板和带有双折射贴片的大理石板模拟无限平面,研究了炸药爆炸后介质中应力波传播的特征。借助于动态二维应力光学定律和应变光学定律得出了无限平面中炮孔周围应力场的定量分析结果。     

应用新型动光弹系统研究某设备受冲击载荷作用

结构受到冲击时,其应力分布与在静荷载作用下完全不同.本丈应用新型动光弹实验系统研究了某设备在冲击载荷作用下其内部动态应力分布情况.该系统由部分传统的动光弹实验装置、高速摄影系统和数字光弹图像处理系统组成,并且采用激光光源、落锤冲击载荷加载装置.加工制作了该设备模型的光弹性模型,应用到冲击载荷作用下的实验研究中,得到了该...     

散斑光弹性干涉法

全息干涉法和普通光弹性法相结合产生了全息光弹性法。与此类似,本文建议将散斑干涉法和光弹性相结合形成具有一定特点的散斑光弹干涉法。近十几年来,散斑干涉法得到了很快的发展,可以获得面内或离面位移,错位散斑干涉法则可获得位移梯度场。本文建议将光弹性透明模型置于双光束散斑干涉光路中,通过两次曝光法可以获得模型的应力条纹图案。但和全息光弹性法相比,只要选择合适的漫反射器,用散斑光弹干涉法可以获得不受等差线干扰的、单纯的等和线条纹图。同样的理由,也可以获得三维应力模型冻结切片的等和线条纹图。更有意义的是采用双光片散光穿透模型的散斑光弹性干涉法将有可能获得整体三维应力模型内部的绝对光程应力条纹图,这将为三维应力分析提供一种新的实验方法。     

软弱地基上拱形围堰的光弹性研究

介绍目前水利水电工程设计中常遇到的软弱地基上拱形围堰的光弹性试验研究.其中包括异弹模组合模型浇制与粘结、水砂压荷载模拟及主要试验成果. 文中分析了在上述荷载作用下拱堰的受力特点和工作状态,探讨了低弹模基础和边界条件不对称性对堰体内力的作用和影响,提出了进一步改善应力和稳定条件的途径和措施.     

Hollow sphere of randomly bonded material subjected to internal pressure

A hollow sphere of an elastic binding material of slight stiffness, bonded randomly by “fiber” segments of a stiffer material, is considered. Polymer material, for example, can be the binder. Such a bonding permits obtaining a material with improved properties, where the material on the whole is quasi-isotropic [1]. The stress distribution in a hollow sphere is obtained.     

Effects of chemical structures of para-halobenzoates on micelle nanostructure,drag reduction and rheological behaviors of dilute CTAC solutions

Counterion chemical structure and counterion to cationic surfactant molar ratio, ξ, control counterion binding, micelle nanostructures, drag reduction (DR) effectiveness and rheological behavior of quaternary ammonium surfactant systems. The effects of chemical structures of four sodium para-halobenzoate (F, Cl, Br, I) counterions with different ξ values on these properties were compared for dilute solutions of cetyltrimethylammonium chloride (CTAC). Counterion binding was determined by zeta-potential and ¹H NMR measurements. Nanostructures were determined by ¹H NMR and cryo-TEM imaging. Nanostructures, drag reduction effectiveness measured over a range of temperatures and Reynolds numbers, shear viscosities and first normal stress differences N1 were related to the chemical structures of the four counterions and their molar ratios to CTAC.     

双层滑片回转运动机构的力学特性

建立双层滑片运动机构的力学模型，并全面分析其力学特性，通过分析发现，与机械摩擦损失相比，双层滑片之间相对运动产生的粘性磨擦损失很小，可以忽略不计，采用双层滑片能够明显改善滑片端部的密封效果，减轻滑片的磨擦磨损，但滑片应力有所增加，强度有所降低，厚度比对双层滑片的受力及摩擦磨损影响很小，只对强度产生较大影响，从增加强度和便于加工的角度考虑，优化出双层滑片机构厚度的比的适宜值。     

皮肤的力学性能概述

鉴于皮肤的力学性能对于临床和日用化妆品的重要性,人们已经对在体和离体皮肤的力学性能进行了长期的研究.本文对皮肤力学的近期发展进行了全面的回顾,总结了在体和离体实验的方法和仪器,概述了皮肤的主要力学性能,包括杨氏模量、泊松比、压缩系数、强度、韧性、初应力和初张力、热膨胀系数、约束力/层离能、摩擦系数,以及这些性能的各向异性,并以表格形式收集了现有文献中的有关数据.最后,讨论了有关皮肤力学的一些特殊领域中的未来研究方向.      

Morphological Responses of Vascular Endothelial Cells Induced by Local Stretch Transmitted Through Intercellular Junctions

It has been well established that mechanical stimuli including fluid shear stress and cyclic stretch play a key role in endothelial cell (EC) remodeling. However, in contrast to global remodeling to these mechanical stimuli, little is known of how local mechanical forces are transmitted through cells to induce cell remodeling leading to alteration in cell functions. In this study, we demonstrated that EC remodeling can be exerted by local tension generated in a neighboring EC. In this technique, a glass microneedle was used to apply local stretch in an EC in confluent monolayer and the resulting tension is transmitted to a neighboring EC across intercellular junctions. Local stretch induced reorientation and elongation of ECs parallel to the direction of stretch associated with reorganization of stress fibers. In addition, recruitment of Src homology 2-containing tyrosine phosphatase-2, binding to intercellular adhesion molecules platelet-endothelial cellular adhesion molecules-1, was selectively observed at the force-transmitted intercellular junctions after application of local stretch. These findings suggest that intercellular junctions can not only transmit but also sense local forces, and are potentially involved in EC mechanotransduction pathways.     

Effects of the pH on the mechanical behavior of articular cartilage and corneal stroma

Electro-chemo-mechanical couplings in articular cartilages and corneal stroma are due to the presence of electric charges on proteoglycans. In addition, at non-physiological pH, collagen molecules become charged as well. Variation of the pH of the electrolyte has strong implications on the electric charge of these tissues, and by the same token, on their transport and mechanical properties. Indeed, articular cartilages and corneal stroma swell and shrink depending on the composition of the electrolyte, they are in contact with.Emphasis is laid here on the combined effects of pH, ionic strength, calcium and chloride binding on mechanical properties.The tissues are viewed as three-phase multi-species porous media. The constitutive framework is phrased in the theory of thermodynamics of deformable porous media. Acid–base reactions, as well as ion binding, are embedded in this framework. Although, macroscopic in nature, the approach accounts for a number of biochemical details defining collagen and proteoglycans.The model is used to simulate laboratory experiments where specimens of articular cartilages and corneal stroma are put in contact with a bath of controlled chemical composition. Chemical loadings, where the ionic composition and pH of the bath are varied, are intermingled with mechanical loadings. The variations of the stress and strain are observed to depend strongly on the ionic strength and ion type present in the bath: sodium chloride leads to a stiffer response than calcium chloride and hydrochloric acid. Moreover, when the bath changes from basic to acidic, the change of sign of the fixed charge across the isoelectric point has definite mechanical implications, and it gives rise to non-monotonous evolutions of the stress, strain and chemical content.While the chemo-mechanical effect is a key phenomenon that governs the behavior of tissues with fixed charges, the converse mechano-chemical effect is significant in corneal stroma due to its low stiffness.     

A stochastic approach to the internal damage in a structure solid: Part 1: Theoretical model

The material system is considered as heterogenous medium of actual microstructural elements. These elements exhibit random geometric and physical characteristics and are further disturbed by a latitude of randomly oriented, second phase particles. A stochastic model is presented for the occurring damage process due to the nucleation and growth of microvoids under external loading. From a micromechanical point of view, the nucleation of a void at a partile-matrix interface is considered to be associated with the cut-off of the interfacial binding potential. The growth of an elemental void is seen, then, to follow a random walk of the discrete Markov type. The latter is associated with the build-up of strain in front of the tip of the advancing void and the redistribution of local stress. As the void reaches the boundary between neighbouring elements, a dicrete inter-elemental fracture process is examined in relation to the intensities of transformation within the elemental boundary.     

Effect of intrinsic stress gradient on the effective mode-I fracture toughness of amorphous diamond-like carbon films for MEMS

The influence of intrinsic stress gradient on the mode-I fracture of thin films with various thicknesses fabricated for Microelectromechanical Systems (MEMS) was investigated. The material system employed in this study was hydrogen-free tetrahedral amorphous diamond-like carbon (ta-C). Uniform gauge microscale specimens with thicknesses 0.5, 1, 2.2, and 3 μm, containing mathematically sharp edge pre-cracks were tested under mode-I loading in fixed grip configuration. The effective opening mode fracture toughness, as calculated from boundary force measurements, was 4.25±0.7 MPa√m for 0.5-μm thick specimens, 4.4±0.4 MPa√m for 1-μm specimens, 3.74±0.3 MPa√m for 2.2-μm specimens, and 3.06±0.17 MPa√m for 3-μm specimens. Thus, the apparent fracture toughness decreased with increasing film thickness. Local elastic property measurements showed no substantial change as a function of film thickness, which provided evidence for the stability of the sp²/sp³ carbon binding stoichiometry in films of different thicknesses. Detailed experiments and finite element analysis pointed out that the dependence of the effective fracture toughness on specimen thickness was due to the intrinsic stress gradient developed during fabrication and post-process annealing. This stress gradient is usually unaccounted for in mode-I fracture experiments with thin films. Thicker films, fabricated from multiple thin layers, underwent annealing for extended times, which resulted in a stress gradient across their thickness. This stress gradient caused an out-of-plane curvature upon film release from its substrate and, thus, combined bending and tensile mode-I loading at the crack tip under in-plane forces. Since the bending component cannot be isolated from the applied boundary force measurements, its contribution, becoming important for thick films, remains unaccounted for in the calculation of the critical stress intensity factor, thus resulting in reduced apparent fracture toughness that varies with film thickness and curvature. It was concluded that in the presence of a stress gradient, accounting only for the average intrinsic stresses could lead in an overestimate of the fracture resistance of a brittle film. Under these considerations the material fracture toughness of ta-C, as determined from specimens with negligible curvature, is K_IC=4.4±0.4 MPa√m.     

EXPERIMENTAL INVESTIGATIONS OF STRENGTH,TOUGHNESS AND FAILURE MECHANISM OF THE METAL/EPOXY/METAL ADHESIVE SYSTEM

本文系统地开展了金属/环氧/金属胶结体系的强韧机理及失效行为实验研究,针对铝合金圆棒与铝合金圆棒通过环氧树脂胶层的各种斜截面方向粘结,实验观测了该体系的拉伸变形和失效行为,测量了界面失效载荷对胶层厚度和粘结界面倾斜角的依赖关系;通过引入胶结界面平均正应力、平均剪应力、平均正应变、平均剪应变等概念,可对界面失效强度进行测量,获得界面强度与界面粘结角度以及胶层厚度的关系,进而获得了铝合金/环氧胶层/铝合金体系的强度失效面以及胶结界面的断裂能和胶结体系的能量释放率.上述研究结果为深入认识金属胶结体系的强韧性能和失效机制提供了科学依据,对金属胶结体系的优化设计和性能评判具有重要指导意义.研究结果表明,铝合金/环氧胶层/铝合金体系的拉伸失效总体呈弹脆性破坏特征,失效表现为胶层粘结界面的断裂,失效强度和界面断裂能在胶层厚度为百微米量级时表现出强烈的尺度效应：界面粘结强度随着胶层厚度的减小而显著增大,临界状态的平均正应力和平均剪应力在强度破坏面上近似位于同一圆上,界面断裂能随着胶层厚度的减小而显著减小;与此同时,界面失效强度和界面断裂能也密切依赖于界面粘结角度.