Compensation of stress intensity factors in hollow cylinders containing several cracks under torsion by electro-elastic coating

In this article, a formulation for a hollow cylinder reinforced with an electroelastic layer is investigated. The hollow cylinder and its electro-elastic coating are under the Saint-Venant torsional loading. First, the solution to the problem containing a Volterra-type screw dislocation is obtained by using the Fourier transform. The problem is then reduced to a set of Cauchy singular integral equations by the distributed dislocation method. Finally, several examples are presented to show the effect of the electro-elastic coating on the reduction of the stress intensity factors at the crack tips.

In-situ measurement of elastic modulus for ceramic top-coat at high temperature

The ceramic thermal barrier coatings (TBCs) play an increasingly important in advanced gas turbine engines because of their ability to further increase the engine operating temperature and reduce the cooling, thus help achieve future engine low emission, high efficiency and improve the reliability goals. Currently, there are two different processes such as the plasma spraying (PS) and the electron beam-physical vapor deposition (EB-PVD) techniques. The PS coating was selected to test the elastic modulus. Using the nanoindentation and resonant frequency method, the mechanical properties of ceramic top-coat were measured in-situ. According to the theory of the resonant frequency and composite beam, the testing system was set up including the hardware and software. The results show that the accurate characterization of the elastic properties of TBCs is important for stress-strain analysis and failure prediction. The TBCs systems are multi-layer material system. It is difficult to measure the elastic modulus of top-coat by tensile method. The testing data is scatter by nanoindentation method because of the microstructure of the ceramic top-coat. The elastic modulus of the top-coat between 20?1 150 ℃ is obtained. The elastic modulus is from 2 to 70 GPa at room temperature. The elastic modulus changes from 62.5 GPa to 18.6 GPa when the temperature increases from 20 ℃ to 1 150 ℃.

Biaxial tensile properties and elastic constants evaluation of envelope material for airship

This paper presents an experimental study to determine the tensile properties of the envelope fabric Uretek3216L under biaxial cyclic loading.First the biaxial cyclic tests were carefully carried out on the envelope material to obtain the stress-strain data and the corresponding nonlinearity and orthotropy of the material were analyzed. Then for some determination options with different stress ratios the least squares method minimizing the strain terms was used to calculate the elastic constants from the experimental data.Finally the influences of the determination options with different stress ratios and the reciprocal relationship on the elastic constants were discussed.Results show that the orthotropy of the envelope material can be attributed to the unbalanced crimp of their constitutive yarns in warp and weft directions and the elastic constants vary noticeably with the determination options as well as the normalized stress ratios.In real design practice it is more reasonable to use constants determined for specific stress states in particular stress ratios depending on the project＆#39;s needs.Also calculating the structures with two limitative sets of elastic constants instead of using only one set is recommendable in light of the great variety of the constant＆#39;s values.

Micro mechanical properties of n-Al2O3/Ni composite coating by nanoindentation

A new type of nano test system was introduced, the test principle and the indentation data analysis method were described. It was used to test the micro mechanical properties, such as hardness, elastic modulus and indentation creep property of n-Al2O3/Ni composite coating on steel prepared by brush plating, and the variety of mechanical properties with coating thickness was researched. The results show that the mechanical properties are basically identical within the whole coating, the hardness and modulus decrease in the defect fields, especially within the dendritic crystals, whereas the mechanical properties are not influenced greatly at the interspaces among dendritic crystals. The average hardness and elastic modulus of n-Al2O3/Ni coating are 6.34 GPa and 154 GPa respectively, and the hardness is 2.4 times higher than that of steel and the indentation creep curve of n-Al2O3/Ni coating is similar to that of the uniaxial compression creep, and the creep rate of steady-state is about 0. 104 nm/s. These results will supply useful data for process improvement, new type material development and application expansion.

Evaluation of properties and thermal stress field for thermal barrier coatings

In order to get thermal stress field of the hot section with thermal barrier coating (TBCs), the thermal conductivity and elastic modulus of top-coat are the physical key properties. The porosity of top-coat was tested and evaluated under different high temperatures. The relationship between the microstructure (porosity of top-coat) and properties of TBCs were analyzed to predict the thermal properties of ceramic top-coat, such as thermal conductivity and elastic modulus. The temperature and stress field of the vane with TBCs were simulated using two sets of thermal conductivity data and elastic modulus, which are from literatures and this work, respectively. The results show that the temperature and stress distributions change with thermal conductivity and elastic modulus. The differences of maximum temperatures and stress are 6.5% and 8.0%, respectively.

INFLUENCE OF FIBER COATING ON TENSILE BEHAVIOR OF UNIDIRECTIONAL C/Mg COMPOSITES

The mechanical properties and deformation mechanisms of unidirectional carbon fiber reinforced magnesium composites under tensile loading are studied. Two different materials are used as fiber coatings: a single silica and a gradient C/SiC/SiO[sb 2]. The results show that, under the same preparation conditions, composite with the former coating is broken in a non-cumulative mode and its failure stress is rather low. Conversely, the latter coating demonstrates much better efficiency and the corresponding composite is broken in a cumulative mode.

雅赛尔11.8 tex弹力包芯纱生产实践

为了提高雅赛尔纤维弹力纱纺纱质量,以纺雅赛尔11.8 tex弹力包芯纱为例,介绍雅赛尔、氨纶弹力丝的性能指标及工艺流程;详细分析纺纱各生产工序采取的技术措施、工艺配置及注意事项;通过对细纱、筒纱质量指标的测试,说明雅赛尔11.8 tex弹力包芯纱成纱指标良好、质量稳定。指出:提高雅赛尔纤维品种强力、减少其成纱毛羽、控制氨纶丝包覆质量是保证成纱质量的关键;生产过程中,要优选各工序工艺,明确控制要点及参数,合理配置相关器材和车间温湿度,加强各工序过程控制和设备维护保养。

基于原位冷冻界面聚合法的纱线传感器制备及其应变传感性能

为解决传统传感器柔性差、制备成本高等问题,以涤纶包氨纶纱为基材,通过聚多巴胺修饰和聚吡咯的原位冷冻界面聚合制备了具有快速响应、稳定的电力学性能和循环耐用传感性能的柔性纱线应变传感器。利用扫描电子显微镜、X射线能谱分析仪、傅里叶红外光谱仪对导电纱的微观形貌和化学结构进行表征,探究了不同拉伸应变下导电纱的电阻变化性能。结果显示:在吡咯单体与三氯化铁的量比为1的最佳配比下,在不同的拉伸范围、拉伸速度下,纱线传感器电阻变化稳定,拉伸形变小于6%时,灵敏度达4.039;在10%应变下,响应时间为166.67 ms;此外,纱线循环拉伸1000次后仍具有优异的稳定性。导电纱可通过编织、针织或刺绣等方式与织物相结合,实时监测人体关节活动,广泛应用于人体运动识别和远程医疗服务等领域。

一种声学覆盖层用弹性防护涂层的制备及性能研究

以液化MDI、端氨基聚醚、胺类扩链剂等原材料制备了一种用于橡胶类声学覆盖层表面的弹性聚脲防护材料,并对该材料进行阻燃性能改性。考察了该喷涂聚脲材料的力学性能、声学性能、耐环境性能以及阻燃性能。结果表明,该材料力学性能和耐环境性能优异,阻燃改性后材料的氧指数可以达到27。在配合专用底漆后,该材料与声学覆盖层的附着力良好,可以对声学覆盖层提供有效防护。

防覆冰涂料及其抗结冰性能表征方法的研究进展

介绍了防覆冰材料表面的防覆冰机理,并对国内外亲水型、疏水型和弹性3大类防覆冰涂料的研究现状和优缺点进行了阐述,对涂层表面疏水性和防覆冰性的表征方法与手段进行了总结和介绍。最后,指出弹性疏水涂料将是未来防覆冰涂料领域的研究重点,另外在防覆冰涂料产品的推广应用、系统评价以及通用标准的建立方面,国内仍需要进一步优化与完善。

Adhesion strength of tetrahydrofuran hydrates is dictated by substrate stiffness

Understanding the hydrate adhesion is important to tackling hydrate accretion in petro-pipelines.Herein,the relationship between the Tetrahydrofuran(THF)hydrate adhesion strength(AS)and surface stiffness on elastic coatings is systemically examined by experimental shear force measurements and theoretical methods.The mechanical factor-elastic modulus of the coatings greatly dictates the hydrate AS,which is explained by the adhesion mechanics theory,beyond the usual factors such as wettability and structural roughness.Moreover,the hydrate AS increases with reducing the thickness of the elastic coatings,resulted from the decrease of the apparent surface elastic modulus.The effect of critical thickness for the elastic materials with variable elastic modulus on the hydrate AS is also revealed.This study provides deep perspectives on the regulation of the hydrate AS by the elastic modulus of elastic materials,which is of significance to design anti-hydrate surfaces for mitigation of hydrate accretion in petro-pipelines.

直升机旋翼前缘弹性耐砂蚀涂料的制备和性能研究

为提高直升机旋翼前缘的耐砂石侵蚀能力,采用弹性树脂作为基料树脂,碳化硅、聚四氟乙烯粉料为耐磨填料,制备了弹性耐砂蚀涂料的A组分,采用弹性固化剂作为耐砂蚀涂料的B组分。重点讨论了不同基料树脂、固化剂、n(—NCO)∶n(—OH)、耐磨填料以及耐磨填料的用量对弹性耐砂蚀涂料性能的影响。结果表明:所制备的弹性耐砂蚀涂料的耐磨损失为10 mg,拉伸强度达到26.3 MPa,断裂伸长率为278%,同时还具有优异的耐砂蚀性,能满足直升机旋翼前缘不锈钢件的防护要求。

PHA改性防水涂料在卫生间防水中的应用

卫生间防水一直是住宅装修中的一个重要难题,若防水做得不到位,将严重影响住宅的使用体验,因此,如何选择一种既能有效防水又具有较好弹性的防水材料成为了当前亟待解决的问题。以某住宅建筑卫生间防水施工为背景,介绍一种改性防水涂料的应用,并通过与传统防水涂料进行性能对比,从有害物含量、力学性能、耐老化性能等方面阐释其诸多优势,将有利于解决当前防水难题,提高住宅卫生间的使用质量。

水性有机硅高弹涂层胶FS-855K的合成及应用

以线性体羟基硅油、乳化剂、硅烷偶联剂为主要原料,加水乳化后,在30~40 MPa压力下经匀质制成硅乳液。采用低温催化聚合反应制成基础硅树脂,经中和、增稠后,加入交联及催化组分,即得到一种织物用水性有机硅高弹涂层胶。考察了乳化剂用量、偶联剂用量、交联及催化体系对织物涂层后的弹性、抗皱性及牢度的影响。结果表明,水性有机硅高弹胶具有良好的弹性,涂层后可以有效提升织物的回弹性、抗皱性能。

抗静电天冬聚脲弹性耐磨自洁地坪涂料的研制

介绍了一种抗静电天冬聚脲弹性耐磨自洁地坪涂料的研制及抗静电涂层设计方案,对电子、医药、物联网等领域提供了一种有效的抗静电地坪材料。该涂层由导电的底漆、天冬聚脲中涂及天冬聚脲面漆组成,表面电阻值3.0×10^(6)Ω,具有抗静电、弹性、耐磨、自洁、耐黄变等诸多优点,在高端地坪领域显示出良好的应用前景。

Elastic Modulus of 304 Stainless Steel Coating by Cold Gas Dynamic Spraying

304 stainless steel coating was deposited on the IF steel substrate by cold gas dynamic spraying （CGDS）, and the elastic modulus of the 304 stainless steel coating was studied. The elastic modulus of cold sprayed 304 stain- less steel coating was measured using the three-point bend testing and the compound beam theory, and the other me- chanic parameters （such as the equivalent flexural rigidity and the moment of inertia of area） of the coatings were also calculated using this compound beam theory. It is found that the calculated results using the above methods are accu- rate and reliable. The elastic modulus value of the cold sprayed 304 stainless steel coating is 1. 179 X 105 MPa, and it is slightly lower than the 304 stainless steel plate （about 2 X 105 MPa）. It indicates that the elastic modulus of the cold sprayed coatings was quite different from the comparable bulk materials. The main reason is that the pores and other defects are existed in the coatings, and the elastic modulus of the coatings also depends on varies parameters such as the feed stock particle size, porosity, and processing parameters.

Evaluating high temperature elastic modulus of ceramic coatings by relative method

The accurate evaluation of the elastic modulus of ceramic coatings at high temperature(HT)is of high significance for industrial application,yet it is not easy to get the practical modulus at HT due to the difficulty of the deformation measurement and coating separation from the composite samples.This work presented a simple approach in which relative method was used twice to solve this problem indirectly.Given a single-face or double-face coated beam sample,the relative method was firstly used to determine the real mid-span deflection of the three-point bending piece at HT,and secondly to derive the analytical relation among the HT moduli of the coating,the coated and uncoated samples.Thus the HT modulus of the coatings on beam samples is determined uniquely via the measured HT moduli of the samples with and without coatings.For a ring sample(from tube with outer-side,inner-side,and double-side coating),the relative method was used firstly to determine the real compression deformation of a split ring sample at HT,secondly to derive the relationship among the slope of load-deformation curve of the coated ring,the HT modulus of the coating and substrate.Thus,the HT modulus of ceramic coatings can be evaluated by the substrate modulus and the load-deformation data of coated rings.Mathematic expressions of those calculations were derived for the beam and ring samples.CVD-SiC coatings on graphite substrate were selected as the testing samples,of which the measured modulus ranging from room temperature to 2100℃demonstrated the validity and convenience of the relative method.

非均布约束刚度下硬涂层圆柱壳自由振动的半解析建模及分析

为有效模拟圆柱壳服役过程的螺栓连接失谐情况,提出了一种周向离散非均布弹性约束模型。在此基础上,利用Rayleigh-Ritz法建立非均布约束刚度下硬涂层圆柱壳自由振动半解析模型。以涂敷NiCoCrAlY+YSZ硬涂层材料的薄壁圆柱壳为例,通过理论与试验和有限元结果对比验证了该模型的合理性。同时,进一步探讨了螺栓连接失谐对硬涂层圆柱壳复合结构振动特性的作用规律。结果表明,在不同螺栓数量下,随着约束刚度失谐参数的增加,结构固有频率整体呈现逐渐增加的变化趋势其变化速率逐渐减小。随着螺栓数量的增加,约束刚度失谐参数对硬涂层圆柱壳复合结构固有频率的显著影响整体上逐渐由低周向波数转向高周向波数。

弹性约束硬涂层圆柱壳自由振动的半解析模型

为准确描述弹性约束下硬涂层圆柱壳复合结构的自由振动行为,本文在考虑弹性约束的基础上,以硬涂层圆柱壳为研究对象,采用Rayleigh-Ritz法对弹性约束硬涂层圆柱壳的自由振动进行半解析建模,提出一种离散非均布刚度弹性约束模型以有效模拟实际螺栓连接。以涂敷NiCoCrAlY+YSZ的硬涂层圆柱壳结构为例,将半解析计算和测试结果进行对比分析。结果表明,固有频率的半解析值与实验值基本一致,最大和最小偏差分别为4.57%和0.03%,验证了弹性约束硬涂层圆柱壳自由振动半解析模型的合理性;与经典固支约束条件对比模态振型结果,进一步验证该弹性约束模型的适用性。

添加Mo对AlTiN涂层组织结构和力学性能的影响

采用阴极电弧离子镀技术在硬质合金基体上分别沉积AlTiN和AlTiMoN两种涂层。采用扫描电镜、能谱仪、X射线衍射仪表征两种涂层的微观组织,并通过纳米压痕仪和摩擦磨损试验机测试分析涂层的硬度、弹性模量及摩擦磨损性能。结果表明,阴极多弧离子镀制备的两种涂层表面都有液滴的缺陷,且呈柱状生长;添加Mo元素后AlTiMoN涂层向(111)面的择优取向更加明显;AlTiMoN涂层比AlTiN涂层具有更加优异的力学性能,Mo的添加使涂层硬度从27.98GPa提高到30.27GPa,弹性模量从284.42GPa提高到368.33GPa,摩擦系数从0.85降到0.6,且涂层的耐磨性也得到提升。