Assessment of the Mechanical Properties of Carbon-Fiber Heating Cables in Snow and Ice Melting Applications

The use of carbon-fiber heating cables(CFHC)to achieve effective melting of snow and ice deposited on roads is a method used worldwide.In this study,tensile and compressive tests have been conducted to analyze the mechan-ical properties of the CFHC and assess whether the maximum tensile and compressive strengths can meet the pavement design specifications.In order to study the aging produced by multiple cycles of heating and cooling,in particular,the CFHC was repeatedly heated in a cold chamber with an ambient temperature ranging between-20℃ and+40℃.Moreover,to evaluate how the strength of the pavement is affected by its presence,the CFHC was embedded at different depths and concrete blocks with different curing ages were subjected to relevant com-pression and splitting tensile tests.Numerical simulations based on the ANSYS software have also been performed and compared with the outcomes of the static loading tests.The results show that the CFHC embedded in the concrete does not affect the compressive splitting tensile strengths of the pavement.Overall,the CFHC meets the conditions required for continued use in road ice melting applications.

Weld Joint Efficiency of the Kazakhstani Constructional Steel

In the Republic of Kazakhstan, the regulatory framework in construction based on Eurocodes has been in force since 2015. However, Kazakhstani produced steel has not been studied for compliance with the requirements of Eurocode 1993. This has resulted in limited use of Kazakhstani structural steel in construction. The feasibility of using structural steel in welded joints has been experimentally investigated. To verify the application of such joints in construction, including earthquake engineering, experimental studies of welded joints made of structural steel produced by Arcelor-Mittal in Temirtau have been carried out. In total, 7 types of structural steel of various thicknesses were selected. Five specimens have been used in each series of tests. The Brinell hardness values of the weld joint, yield strength of steel and tensile strength, relative rupture strain were determined. It was found that for all types of structural steel, the quality of weld joints complied with the requirements of Eurocode 1993—a sample rupture appeared along the plates (main body of the metal), not along the weld joints. It has been established that structural steel produced in the Republic of Kazakhstan fully complies with the requirements of Eurocode 1993. The studies on the dependence of Brinell hardness values of weld joint steel on the yield strength, tensile strength and relative rupture strain have been carried out. The correlation dependences between the values of yield strength of steel and tensile strength, relative rupture strain and BH Brinell hardness were studied. The results of work will allow for significantly increasing the use of Kazakhstani structural steel in seismic and conventional areas of the Republic of Kazakhstan.

Experimental investigation on tensile strength of butt welded joint post high temperatures

In order to investigate the laws of variation on tensile strength of butt welded joint post high temperatures, the wide plate tension tests for butt welded joint were conducted after cooling down from different high temperatures. The tests indicate that specimens appear ductile fracture at the steel plate during the tension tests after cooling down. The maximum temperatures undergone and the cooling pattern are major factors influencing tensile strength of butt welded joint post high temperatures. The tensile strength mostly reduces by 8% within 900℃. Based on the experimental results, the paper proposes the calculation formulas of tensile strength of butt welded joint post high temperatures. The conclusions of the paper supply references for evaluation damage and reinforcement of steel structure post fire.

Investigation on Hardness and Tensile Strength of Welded Joint of 6061 Aluminum Alloy for Highspeed Railway Vehicle

Investigations are carried out on the hardness, the tensile strength, the elongation and porosity of welded joints of 2.5 mm thick 6061 aluminum alloy sheets. The welded joints are prepared by MIG welding process with a commercial filler metal SAlSi-1. Experimental results of the hardness distribution across the welded joint show that: in the HAZ, there is an overaged zone in which the failure usually occurs, and natural ageing do not show significant improvement of the situation. The heat input of welding has an effect upon the porosity in the weld. A feasible application of the welded aluminum alloy joint is proposed.

Characteristics of structural loess strength and preliminary framework for joint strength formula

The strength of structural loess consists of the shear strength and tensile strength. In this study, the stress path, the failure envelope of principal stress （ Kf line）, and the strength failure envelope of structurally intact loess and remolded loess were analyzed through three kinds of tests： the tensile strength test, the uniaxial compressive strength test, and the conventional triaxial shear strength test. Then, in order to describe the tensile strength and shear strength of structural loess comprehensively and reasonably, a joint strength formula for structural loess was established. This formula comprehensively considers tensile and shear properties. Studies have shown that the tensile strength exhibits a decreasing trend with increasing water content. When the water content is constant, the tensile strength of the structurally intact soil is greater than that ofremolded soil. In the studies, no loss of the originally cured cohesion in the structurally intact soil samples was observed, given that the soil samples did not experience loading disturbance during the uniaxial compressive strength test, meaning there is a high initial structural strength. The results of the conventional triaxial shear strength test show that the water content is correlated with the strength of the structural loess. When the water content is low, the structural properties are strong, and when the water content is high, the structural properties are weak, which means that the water content and the ambient pressure have significant effects on the stress-strain relationship of structural loess. The established joint strength formula of structural loess effectively avoids overestimating the role of soil tensile strength in the traditional theory of Mohr-Coulomb strength.

Microstructure and tensile properties of friction stir welded dissimilar AA6061-AA5086 aluminium alloy joints

The fusion welding of dissimilar heat treatable and non-heat treatable aluminium alloy faced many problems related to solidification. The difficulties can be overcome to achieve the combined beneficial properties of both aluminium alloys using friction stir welding(FSW). The microstructural features and tensile properties of friction stir welded(FSW) similar and dissimilar joints made of AA6061 and AA5086 aluminium alloys were investigated. The microstructures of various regions were observed and analyzed by means of optical and scanning electron microscopy. Microhardness was measured at various zones of the welded joints. The tensile properties of the joints were evaluated and correlated with the microstructural features and microhardness values. The dissimilar joint exhibits a maximum hardness of HV 115 and a joint efficiency of 56%. This was attributed to the defect free stir zone formation and grain size strengthening.

Effect of tool pin profile on microstructure and tensile properties of friction stir welded dissimilar AA 6061e AA 5086 aluminium alloy joints

Joints between two different grades of aluminium alloys are need of the hour in many light weight military structures.In this investigation,an attempt has been made to join the heat treatable(AA 6061) and non-heat treatable(AA 5086) aluminium alloys by friction stir welding(FSW)process using three different tool pin profiles like straight cylindrical,taper cylindrical and threaded cylindrical.The microstructures of various regions were observed and analyzed by means of optical and scanning electron microscope.The tensile properties and microhardness were evaluated for the welded joint.From this investigation it is founded that the use of threaded pin profile of tool contributes to better flow of materials between two alloys and the generation of defect free stir zone.It also resulted in higher hardness values of 83 HV in the stir zone and higher tensile strength of 169 MPa compared to other two profiles.The increase in hardness is attributed to the formation of fine grains and intermetallics in the stir zone,and in addition,the reduced size of weaker regions,such as TMAZ and HAZ regions,results in higher tensile properties.

Damage Failure Analysis of Z-Pins Reinforced Composite Adhesively Bonded Single-Lap Joint

In order to study themechanical properties of Z-pins reinforced laminated composite single-lap adhesively bonded joint under un-directional static tensile load,damage failure analysis of the joint was carried out bymeans of test and numerical simulation.The failure mode and mechanism of the joint were analyzed by tensile failure experiments.According to the experimental results,the joint exhibits mixed failure,and the ultimate failure is Z-pins pulling out of the adherend.In order to study the failure mechanism of the joint,the finite element method is used to predict the failure strength.The numerical results are in good agreement with the experimental results,and the error is 6.0%,which proves the validity of the numerical model.Through progressive damage failure analysis,it is found that matrix tensile failure of laminate at the edge of Z-pins occurs first,then adhesive layer failure-proceeds at the edge of Z-pins,and finally matrix-fiber shear failure of the laminate takes place.With the increase of load,the matrix-fiber shear failure expands gradually in the X direction,and at the same time,the matrix tensile failure at the hole edge gradually extends in different directions,which is consistent with the experimental results.

Interfacial microstructure and properties of YG11C/42CrMo joint brazed with BCu64MnNi filler metal

Brazing hard alloy to high strength steel, incomplete atomic diffusion and excessive brittle reaction product precipitation at the faying interface are usually suffered because of incomplete understanding the process of the initial interface disappearing and diffusion layer forming and evolving. In this paper , hard alloy YG11C （ WC-11wt. %Co） and high strength steel 42CrMo were picked up as base metals and BCu64MnNi as filler metal to clarify the interfacial microstrncture evolution. The process parameters of dwell time were set as 30 s, 60 s, 120 s, and 300 s and braze temperature were set as 950 ℃, 970 ℃, 990 ℃, 1 010 ℃, the effect of which on the evolution of interfacial microstructure, tensile strength, integrated with fracture morphology analysis, were conducted. The results showed that increasing brazing temperature from 950 ℃ to 970 ℃, no signifwant difference existed in the joint interface, whereas brazed at 990 ℃, the binder phase erosion occurred, i. e. the liquid filler metal etched into Co binder phase of WC-Co base metal, which caused WC particles debonding from the base metal surface and formed an micro-anisotropic zone.. Increase temperature to 1 010 ℃, severe binder erosion happened so as to micropores appear. Through the parameters optimization, the tensile strength can reach to the maximum 589 MPa at temperature of 970 ℃. The dwell time showed similar effect on tensile strength because longer dwell time also caused erosion and porosity owing to long-time diffusion and reaction.

Interfacial Stress Analysis on Skutterudite-based Thermoelectric Joints under Service Conditions

In thermoelectric(TE)devices,the interfacial reliability greatly influenced devices’durability and power output.For skutterudites(SKD)devices,TE legs and electrodes are bonded together with diffusion barrier layer(DBL).At elevated temperatures,DBL react with SKD matrix or electrode to generate complex interfacial microstructures,which often accompanies evolutions of the thermal,electrical and mechanical properties at the interfaces.In this work,a finite element model containing the interfacial microstructure characteristics based on the experimental results was built to analyze the interfacial stress state in the skutterudite-based TE joints.A single-layer model was applied to screen out the most important parameters of the coefficient of thermal expansion(CTE)and the modulus of DBL on the first principle stress.The multilayer model considering the interfacial microstructures evolution was built to quantitively simulate the stress state of the TE joints at different aging temperatures and time.The simulation results show that the reactive CoSb2 layer is the weakest layer in both SKD/Nb and SKD/Zr joints.And by prolonging the aging time,the thickness of the reaction layer continuously increased,leading to a significant raising of the interfacial stress.The tensile testing results of the SKD/Nb joints match the simulation results well,consolidating accuracy and feasibility of this multilayer model.This study provides an important guidance on the design of DBL to improve the TE joints’mechanical reliability,and a common method to precisely simulate the stress condition in other coating systems.

Fracture mechanism of QFP micro-joints soldered with Sn-Pb and SnAgCu solders

Tensile strengths of QFP micro-joints with different pitches were tested by means of micro-joints tester. On the basis of those results, the effects of QFP pitches’ numbers on the mechanical properties were studied and the microstructures of cracks of micro-joints were analyzed based on facts of SEM and EDS. The results indicate that of tensile strengths micro-joint of 48 pitches are lower than that of 100 pitches and the tensile strength of soldered joint is higher than that of solder itself. The fracture mechanism of QFP soldered joint with Sn-Pb solder acts as the interface cavity impair ductile rupture while the fracture mechanism of QFP soldered joint with lead-free solder shows trans-crystalline toughness rupture which belongs to micro-holes coalescence fracture.

冻融循环作用下约束浆锚搭接连接性能试验研究

为了研究冻融环境下约束浆锚搭接试件的连接性能,以灌浆料种类(高强水泥基灌浆料、环氧树脂灌浆料、地聚物灌浆料)和冻融循环次数(0次、50次、100次)为主要试验参数,进行27个约束浆锚搭接试件的单向拉拔试验,分析试件的外观变化,破坏形态、极限荷载、荷载-位移曲线及荷载-应变曲线。结果表明:常温下和冻融50次后,试件均发生钢筋拉断破坏;100次后试件发生劈裂破坏。常温下和冻融50次后三种灌浆料的约束浆锚搭接试件的连接性能均可靠;冻融循环次数达到100次,极限荷载大幅降低。试件的极限粘结强度随着冻融循环次数的增加逐渐降低。约束浆锚搭接连接性能可靠,三种灌浆料均能满足锚固要求。

Q460高强钢管柱-H形梁焊接节点循环拉伸性能试验研究

为研究Q460高强钢管柱-H形梁焊接节点在地震作用下的力学行为,对11个梁翼缘板与柱段焊接组成的节点进行了低周循环拉伸性能试验,研究了梁翼缘板与钢管宽度比α、厚度比β以及钢管宽厚比λ等参数对节点破坏模式、承载力、延性和耗能能力的影响规律。结果表明:在循环拉伸荷载作用下,Q460高强钢管柱-H形梁焊接节点的失效模式主要分为连接处焊缝断裂、连接处钢管面板断裂或梁翼缘板被拉断三种;高强钢梁翼缘板与钢管宽度比、钢管柱宽厚比对焊接节点的受力行为影响较大,当宽厚比α由25.0减小到18.75时,节点的应变能减小了134%;当节点破坏时,具有新型焊接通过孔构造的焊接节点极限位移超过传统构造节点近2倍,前者延性性能较好。研究成果可为高强钢管柱与梁焊接节点的抗震设计以及进一步的理论研究提供依据。

装配式建筑用聚合物乳液改性套筒灌浆料的制备及性能研究

本文利用醋酸乙烯酯-乙烯共聚乳液(EVA)、丙烯酸酯乳液(PAE)分别对装配式水泥基套筒灌浆料进行改性,制备了2种聚合物乳液改性套筒灌浆料。研究了聚合物乳液对套筒灌浆料流动度、抗压强度、吸水率、膨胀率、耐久性、拉伸性能和微观结构的影响,并进行了成本核算。结果表明:掺入聚合物乳液能显著改善灌浆料的流动度、抗压强度、吸水率、抗硫酸盐侵蚀和抗冻融侵蚀性能,而且PAE改性的套筒灌浆料的综合性能优于EVA改性;PAE改性能增强灌浆料整体内聚力和密实度,使得灌浆料的膨胀率基本无负面影响且无泌水现象,同时可以增强灌浆料接头的拉伸性能、抗拉强度以及黏结强度。当PAE掺量在0.3%~1.0%(质量分数)时,PAE改性灌浆料性能均满足相应国家标准要求,且制备成本较低。

基于IPOA-BP算法的焊接接头抗拉强度预测模型

为了更加快捷方便的获得X80管线钢管环焊缝焊接接头抗拉强度,通过IPOA-BP算法构建了X80管线钢管环焊缝焊接接头抗拉强度预测模型,引入Logistic混沌映射、反向差分进化和萤火虫算法来提高POA算法的寻优能力。模型选择焊接电流、焊接电压、焊接热输入、保护气体流量、焊接速度、送丝速度作为焊接工艺输入参数,接头抗拉强度作为输出参数。把IPOA-BP模型和POA-BP模型以及BP神经网络模型进行对比,通过训练集对模型进行训练、测试集对模型进行验证,用均方误差、平均绝对百分比误差和R^(2)来评价模型。最终结果表明,IPOA-BP算法模型预测更加精准,拟合程度更高。

球墨铸铁管道新型抗震接口力学性能试验及数值模拟

有效的管线接口抗震措施是优化城市供水管网抗震性能和震后功能恢复能力的关键。为此,基于机械自锚设计和自变形补偿等思想,提出一种球墨铸铁管道新型自锚式抗震接口。开展普通承插式接口和新型抗震接口的轴向拉伸拟静力试验及抗震接口精细化三维有限元数值模拟,研究新型管道接口的抗拉承载能力、初始抗拉刚度、抗变形能力和极限破坏状态等力学特性。结果表明:0.2 MPa以内的水压变幅对普通承插式接口的轴向力学性能和破坏方式的影响不大,接口初始漏水至功能失效状态的过渡变形约为2.5 mm;新型自锚式抗震接口具备良好的承载能力和抵抗大变形能力,其抗拉力学性能曲线分为3个阶段,即胶圈受力阶段、卡环受力阶段和卡环失效破坏,其中,在卡环变形量为9 mm左右时,达到峰值承载力330 kN左右。

大跨度混凝土拱桥金属构件焊接接头抗拉强度测试

针对大跨度混凝土拱桥金属构件焊接接头焊接区域容易出现裂纹问题,提出大跨度混凝土拱桥金属构件焊接接头抗拉强度测试方法。通过处理接头抗拉强度,得到标准化处理后的正常测试点,消除测试变量之间的差异影响。选择与抗拉强度密切相关的组分含量作为输入特征,基于对组分含量的相互作用,建立金属构件焊接接头抗拉强度的测试参数,对其求解得出抗拉强度测试参数值。利用Jmatpro软件进行参数计算和优化,得到拱桥金属构件焊接接头的抗拉强度值。实验结果表明,在测试不同焊接速度、搅拌头转速与轴肩压深时,所提方法测试结果与真实值大致相同,且测试最大值误差仅为2 MPa。

双组分新型施工缝界面剂性能研究

通过对比不同界面剂(水泥基渗透结晶防水涂料、聚合物乳液、双组分新型施工缝界面剂HBA)在施工缝处粘结强度和抗渗性方面的差异,评估了双组分新型施工缝界面剂HBA的性能。结果表明,相同试验条件下双组分新型施工缝界面剂HBA粘结强度更高、抗渗性更好;该界面剂中的聚合物和胶凝材料含量较高,聚合物膜与水化产物相互交织,形成网状结构,有效提高了界面的密实度与粘结作用。

一种速生材椅类家具接合点增强方法

为缓解优质木材资源短缺,扩大速生材的利用途径,提高速生材的利用价值,提出了一种用速生杨木作构件,用榉木作两构件的接合点,采用椭圆形榫接合,适用于椅类家具节点的接合增强方法。并对接点增强杨木T试件、全榉木T型试件、全杨木T型试件分别进行了抗拔与抗弯性能测试。结果表明:接点增强杨木T型试件抗拔强度比全杨木T型试件增加了1 999.56 N,提高了47.71%;比全榉木T型试件仅低175.8 N,仅低2.76%。接点增强杨木T型试件抗弯强度比全杨木T型试件增加了487.85 N,提高了93.07%;比全榉木T型试件增加了143.84 N,提高了16.56%。证明用该增强方法制作的接合结构适用于速生杨木椅类家具。

大斜度井举升工艺技术在M油田的试验

为有效解决大斜度井有杆泵举升存在的问题,M油田开展敷缆连续油管无杆举升工艺技术试验。室内实验,总伸长量4.41‰,外部承压25 MPa,空载抗拉强度300 kN,满载抗拉强度255 kN,力学性能优良。现场试验2口井,连续油管无杆举升可下到指定深度并可通过一定井斜变化率位置,单井产能提高;明确清蜡点为电动机电流的80%,合理清蜡参数为“对内置加热电缆进行连续5 h加热”;评价能耗与效率,与游梁式抽油机相比,2口井平均单耗降低11.059 kWh/t,节能率为64.05%,系统效率高23.83个百分点。敷缆连续油管无杆举升工艺技术应用于大斜度井初步适应性较好,但应用时间较短,应持续跟踪其井下工具的使用寿命,为技术的推广应用提供有力支撑。