Influence of tool pin profile on the interface migration of friction stir lap joints＊

Friction stir lap joints of LY12 aluminum alloy plates with a thickness of 3 mm were fabricated using several tools with different pin profiles. The effects of tool pin profile on the interface migration of friction stir lap joints were investigated with the comparison of weld morphologies. The results show that the screw thread of the pin plays an important role in the migration of weld interface in the thickness direction. The interface between the sheets will move upwards to the top of the plate when the pin with left hand thread was used. Conversely, the interface will move downwards to the tip of the pin when the pin with right hand thread was used： As for a stir pin with smooth surface was used, the upward or downward migration of the weld interface was largely reduced, but the extension of weld interface to the weld center line from the retreating side becomes more serious. By analyzing the force on the pin according to the sucking-extruding theory for the weld formation, the obtained results have been well explained.

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.

Effect of pin penetration depth on double-sided friction stir welded joints of AA6061-T913 alloy

Friction stir welding (FSW) of aluminum alloys is currently utilized in several modern industries. The joints must have sufficient elastic?plastic response and formability levels similar to that of the base metal. In this work, double-sided FSW of AA6061 sheet was compared with its conventional single-sided one. An adjustable tool with different pin lengths (50%?95% of the sheet thickness) was used to perform the double-sided welds. Macro- and micro-structures, strength, and hardness of the joints were investigated to determine the optimum pin penetration depth. The best results were obtained for a double-sided joint made by a pin length equal to 65% of the sheet thickness, which showed an increase of 41% in the ultimate tensile strength compared with the single-sided joint.

EFFECT OF Z-PINS’ DIAMETER,SPACING AND OVERLAP LENGTH ON CONNECTING PERFORMANCE OF CMC SINGLE LAP JOINT

The effect of through-thickness reinforcement by composite pins （Z-pins） on the static tensile strength and failure mechanisms of the joints made from ceramic matrix composite （CMC） is investigated. Overlap length of the single lap joint is 15 mm, 20 mm, 23 mm, 37 mm, and 60 mm, respectively. The experimental results indicate that the final failure modes of the joints can be divided into two groups, （a） the bond-line stops debonding until crack encounters Z-pins; and then the adherends break at the location of Z-pins, when overlap length is more than 20 mm; （b） the bond-line detaches entirely and Z-pins are drawn from adherends, when overlap length is equal to 15 mm. A simple efficient computational approach is presented for analyzing the benefit of through-thickness pins for restricting failure in the single lap joints. Here, the mechanics problem is simplified by representing the effect of the pins by tractions acting on the fracture surfaces of the cracked bond-line. The tractions are prescribed as functions of the crack displacement, which are available in simple forms that summarize the complex deformations to a reasonable accuracy. The resulting model can be used to track the evolution of complete failure mechanisms, for example, bond-line initial delamination and ultimate failure associated with Z-pin pullout, ultimate failure of the adherends. The paper simulates connecting performance of the single lap joints with different Z-pins＇ diameter, spacing and overlap length; the numerical results agree with the experimental results; the numerical results indicate enlarging diameter and decreasing spacing of Z-pins are in favor of improving the connecting performance of the joints. By numerical analysis method, the critical overlap length that lies between two final failure modes is between 18 mm and 19 mm, when Z-pins＇ diameter and spacing are 0.4 mm, 5 mm, respectively.

搭接长度对Z-pins增强陶瓷基复合材料接头连接性能的影响

本文对搭接长度分别为15mm,20mm,23mm,37mm,60mm的Z-pins增强陶瓷基复合材料接头在单向载荷作用下的连接性能进行了试验研究和数值模拟。试验结果表明接头的最终失效形式有两种:(1)搭接长度大于、等于20mm的接头由搭接板断裂而失效;(2)搭接长度等于15mm的接头由搭接面的脱胶而失效。在搭接长度为20mm^60mm之间,接头的最大破坏载荷与搭接长度之间呈线性关系变化。采用有限元的方法对搭接接头的破坏过程进行了数值模拟,模拟结果与试验结果吻合较好,进而得到了介于上述两种破坏模式之间的搭接接头的搭接长度。

复合材料z-pinning技术的应用与发展

简单介绍了z-pin的种类和复合材料z-pin的拉挤工艺。重点综述了利用热压罐和UAZ两种z-pinning技术及z-pinning在复合材料层板、结构件连接及泡沫夹层复合材料中的应用,同时,提出了当前发展z-pinning技术的对策和建议。

Z-pins增强陶瓷基复合材料单搭接接头的裂纹尖端能量释放率

对典型Z-pins增强陶瓷基复合材料单搭接接头的裂纹尖端能量释放率进行了数值模拟,重点研究Z-pins在不同直径和间距下裂纹尖端能量释放率随裂纹扩展的变化规律。研究发现能够形成桥联的Z-pins具有一定抑制开裂的能力,形成桥联后,Z-pins的直径对于裂纹尖端能量释放率的影响较大,而Z-pins的间距对于裂纹尖端能量释放率也有影响,但当间距小到某一限度时,再减小间距裂纹尖端能量释放率基本保持不变。

Z-pin增强树脂基复合材料单搭接头弯曲性能

为了研究Z-pin对单搭接头弯曲性能的影响,制备了不同参数Z-pin增强单搭接头试样,研究了Z-pin单搭接头在三点弯曲载荷下连接性能。结果表明：Z-pin（直径0.5mm）体积分数从0%～1.5%时,弯曲载荷随Z-pin体积分数的增加而增加,体积分数在1.5%～3.0%范围内时,试样的弯曲载荷随Z-pin体积分数的增加而下降,Z-pin体积分数为1.5%时达到最大值1303.2N;Z-pin直径为0.3～0.7mm时（体积分数1.5%）,峰值载荷随着直径的增加而增加,0.7mm增强接头的弯曲载荷比0.3mm增强接头高出27.9%。Z-pin植入角度对单搭接头弯曲性能影响不大。另外,随着搭接长度的增加,单搭接头的弯曲性能提高。

基于黏聚区模型的Z-pin增强复合材料T型接头分层损伤研究

复合材料T型接头Z-pin增强就是将直径非常细的金属或复合材料pin针植入筋条-蒙皮截面,通过Z-pin的桥接牵引提高接头力学性能。采用ABAQUS有限元软件分别建立了T型接头与Zpin增强T型接头的三维数值计算模型。基于黏聚区模型,采用新的简化后Z-pin桥接牵引关系模拟Z-pin增强作用过程。模拟了T型接头的拉伸失效模式,计算了其拉伸强度和总耗散能,对比分析了有无Z-pin增强2种接头的载荷-位移曲线和损伤耗散能-位移曲线。数值计算结果与文献中数据符合较好。结果表明:Z-pin增强T型接头的极限载荷与极限位移相比于无增强T型接头分别提高了66%和304%;2种接头的载荷-位移曲线斜率相同,初始损伤载荷一致;Z-pin增强T型接头在拉伸破坏过程中相比于无增强接头吸收能量多13.74倍。

Z-pins对2D编织陶瓷基复合材料搭接接头连接性能的影响

对Z-p ins增强2-D编织陶瓷基复合材料搭接接头在单向载荷作用下的连接性能进行了试验研究。试验结果表明Z-p ins的加入能够改善2-D编织陶瓷基复合材料搭接接头的连接性能,反映在载荷-位移曲线的后半段,载荷变化出现了波动不大的起伏区域。产生此区域的原因为Z-p ins从搭接接头拔出的过程中,与复合材料形成桥联,消耗了部分本该作用在开裂尖端的能量。利用有限元的方法模拟了有、无Z-p ins,Z-p ins在不同直径和间距下搭接接头的失效过程,并与试验结果相比较,吻合较好。

Z-pin增强复合材料加筋构件连接性能研究

通过横向三点弯曲试验研究Z-pin直径和体积分数对复合材料加筋类简化构件连接性能的影响。随着Z-pin体积分数的增加,Z-pin增强试件相比于空白对照试件,有效载荷提升48.41%~96.97%,总能量耗散提升661.88%~748.72%,本试验组研究结果表明高Z-pin体积分数可以有效提高加筋试件的承载能力。在Z-pin体积分数同为0.4%的情况下,Z-pin直径为0.5 mm的试验组的承载能力略高于Z-pin直径为0.3 mm的试验组的承载能力,但Z-pin直径为0.3 mm的试验组具有更好的稳定性。试验结果表明Z-pin的植入能够提高复合材料加筋类简化构件的有效载荷及能量耗散,很大程度上提高了加筋试件的连接性能。

并联PiN二极管的温度频率特性建模与分析

针对风电变流器等应用场景,随着功率等级的不断提升,硅PiN二极管的并联使用问题日益突出。然而,并联硅PiN二极管器件的静态参数具有分散性,并联器件间的线路布局存在不均衡性,这些因素都导致并联器件间的电流分布不均,进而引起器件间的损耗和发热不一致,使并联PiN二极管工作于不同的结温。相应地,结温差异会对二极管的反向恢复过程产生影响,并进一步影响并联器件间的电流和结温分布,甚至危害器件和变流器的安全稳定。该文以硅PiN二极管分立器件为研究对象,计及温度影响,建立正向导通损耗和反向恢复损耗的数学模型,以阐释温度对并联PiN二极管电–热平衡的调节机制。然后,针对大注入电流的运行工况,基于导通损耗与反向恢复损耗对温度所呈现出的相反趋势,结合二极管开关频率和工作结温之间的内在制约机制,提出决定并联二极管结温差异发展趋势的“零温度–频率特性”概念。最后,利用实验展示不同温度、不同电流等级下的温度–频率特性,验证该特性的正确性。通过构建并联二极管开关频率与热稳定极限的关系,可为硅PiN二极管的并联设计和使用提供参考,并为模块封装中的结温在线监测提供方法。

Z-pin增强对自动铺丝复合材料T型接头拉脱、剪切性能影响的试验研究及数值模拟

针对自动铺丝复合材料T型接头,开展了Z-pin增强对结构件拉脱以及剪切性能影响的试验研究及数值模拟,拉脱试验和剪切试验分别在电子拉伸试验机(CMT5504)和MTS大吨位疲劳系统上进行。试验研究了Z-pin增强和非增强两种试件,绘制了位移-载荷曲线图。拉脱试验结果表明:Z-pin增强可显著提高拉脱承载能力,同时,与非增强T型接头相比,Z-pin增强明显延缓了掉载。试验件的破坏位置都在中间层和蒙皮之间;剪切试验结果表明;Z-pin增强可显著提高剪切承载能力,Z-pin增强试验件的破坏位置在筋条和中间层之间,非增强的试验件的破坏位置在中间层和蒙皮之间。在此基础上建立了T型件拉脱以及剪切有限元模型,采用内聚力模型模拟界面的破坏情况,在分层的部位建立添加非线性弹簧来模拟Z-pin的增强作用,模拟结果与实验结果比较吻合,验证了模型的有效性。

Shaking table test and numerical analysis of a 1:12 scale model of a special concentrically braced steel frame with pinned connections

This paper describes shaking table tests of a 1：12 scale model of a special concentrically braced steel frame with pinned connections, which was fabricated according to a one-bay braced frame selected from a typical main factory building of a large thermal power plant. In order to investigate the seismic performance of this type of structure, several ground motion accelerations with different levels for seismic intensity Ⅷ, based on the Chinese Code for Seismic Design of Buildings, were selected to excite the model. The results show that the design methods of the members and the connections are adequate and that the structural system will perform well in regions of high seismicity. In addition to the tests, numerical simulations were also conducted and the results showed good agreement with the test results. Thus, the numerical model is shown to be accurate and the beam element can be used to model this structural system.

Z-pin增强复合材料T型接头拉伸数值模拟与参数分析

利用内聚力模型建立了Z-pin增强复合材料T型接头拉伸破坏过程的数值分析模型,并对Z-pin的分布进行参数分析.通过Z-pin桥联试验得到Z-pin拔出的位移-载荷曲线,再将该曲线转化为Z-pin所在区域的界面单元属性,从而模拟Z-pin对T型接头性能的增强效果.通过静力拉伸试验验证了该模型的可靠性.在此基础上分析了不同Z-pin分布对T型接头拉伸性能的影响,结果表明:Z-pin列距越小则拉脱载荷及极限位移越大,Z-pin行距的变化对结构承载能力影响较小,而Z-pin与中轴面的距离增大会使拉脱载荷呈线性减小的变化趋势.

Influence of tool pin design on properties of dissimilar copper to aluminum friction stir welding

Dissimilar friction stir welding （FSW） of copper and aluminum was investigated by nine different tool designs, while the rest of the process parameters were kept constant. Mechanical and metallurgical tests such as macrostructure, microstructure, tensile test, hardness, scanning electron microscope and electron X-ray spectrographs were performed to assess the properties of dissimilar joints. The results exhibited that, the maximum joint strength was achieved by the tool of cylindrical pin profile having 8 mm pin diameter. Besides, the fragmental defects increased as the number of polygonal edges decreased, hence the polygonal pin profiles were unsuitable for dissimilar FSW butt joints. Furthermore, the tensile strength increased as the number of polygonal edges increased. Stir zone of polygonal pin profiles was hard and brittle relative to cylindrical tool pin profiles for same shoulder surface. Maximum hardness of HV 283 was obtained at weld made by the polygonal square pin profile. The hard and brittle intermetallic compounds （IMCs） were prominently presented in the stir zone. Phases of IMCs such as CuAl, CuAl2, Cu3Al and Cu9Al4 were presented in the stir zone of dissimilar Cu-Al joints.

RTM成型Z-Pin增强复合材料T型元件拉脱性能研究

采用RTM工艺制备了复合材料Z-Pin增强与未增强的T型元件,并进行了拉脱破坏对比试验,结果表明,Z-Pin增强的T型元件的拉脱破坏载荷较未增强的提高了64.8%,本文从试验现象和破坏模式上分析了这种情况产生的原因。

Cable-pin系统和克氏针张力带治疗尺骨鹰嘴骨折临床分析

目的探讨尺骨鹰嘴骨折治疗中Cable-pin系统和克氏针张力带(tension band wiring,TBW)两种内固定方法的临床效果。方法尺骨鹰嘴骨折病人36例,根据所使用内固定种类的不同分为Cable-pin系统治疗的Cable-pin组(19例)和克氏针张力带治疗的TBW组(17例),对每组病人术中情况、远期效果及并发症发生率等情况进行比较。结果所有病人均获随访,随访时间12~25个月,平均(13.00±4.68)个月。Cable-pin组在骨折愈合时间、术后优良率及并发症发生率分别为(12.2±2.3)周、78.9%和10.5%,TBW组分别为(16.0±2.2)周,58.8%和,35.3%,两组比较差异有统计学意义(P<0.05);Cable-pin组在手术出血量、术中耗时分别为(66.4±11.0)ml和1.5±0.6)小时,TBW组分别为(71.6±9.8)ml和(1.6±0.5)小时,两组比较比较,差异无统计学意义(P>0.05)。结论治疗尺骨鹰嘴骨折时,Cable-pin系统利于骨折愈合,固定可靠及并发率低。

Subtalar joint pigmented villonodular synovitis misdiagnosed at the first visit:A case report

BACKGROUND Pigmented villonodular synovitis(PVNS)is an uncommon disease that usually occurs in large joints,and involvement of the subtalar joint is rare.The lack of comprehensive knowledge of subtalar joint PVNS could lead to misdiagnosis.CASE SUMMARY We present a 64-year-old woman who,at her first visit,complained of discomfort in the right ankle when she walked.Based on the physical signs and X-ray report,the physician failed to make the suspected diagnosis of PVNS.Eighteen months later,the patient returned with a complaint of a mass in her right lateral malleolus with intermittent blunt pain.The X-ray presented an osteophyte formation and soft tissue calcification at the margin of the subtalar joint.The laboratory tests were normal,whereas magnetic resonance imaging(MRI)showed a low-intensity area on both T1-and T2-weighted images.A suspected diagnosis of PVNS was made and later confirmed by postoperative pathology.Subsequently,the patient received radiotherapy with 32 Gy in 16 fractions.At 6 mo postoperatively,the patient only complained of discomfort after walking three blocks.The American Orthopedic Foot and Ankle Society Ankle-Hindfoot score was 97.CONCLUSION MRI is necessary for the diagnosis of PVNS.Early soft tissue calcification and painless joint swelling should be of concern.

Fracture-Dislocations of Lisfranc Joint in Lomé(Togo)

Introduction: The purpose of this prospective study was to describe the clinic pathological varieties of fracture-dislocations of Lisfranc joint and outcome of treatment. Patients and Methods: This study was conducted on 21 cases of fracture-dislocations of the Lisfranc joint treated in our orthopedics trauma unit from 2010 to 2013. We selected middle foot pure dislocations or associated with Lisfranc joint bone fractures. Classification of Myerson was used to characterize the lesions. The results assessment criteria were clinical and radiological for foot and Massari score. Results: Fourteen (14) patients were male. The average age was 34.7 years. Five (5) clinic pathological forms were met by relying on the classification of Myerson;4 cases of type A;5 cases of type B1;B2, 6 cases;4 cases of type C1 and 2 cases of type C2. There were eight cases of pure dislocation and 13 dislocations were associated with fractures (metatarsal in 11 patients, cuneiform in 5 patients, cuboid bone in 2 patients and enucleation fracture of the medial cuneiform in 2 patients). It was noted 10 cases of skin openings. Treatment consisted on open reduction in all patients and stabilization by pin complemented by a foot plaster for 6 weeks. Four (4) immediately arthrodeses were made. All patients were followed up 7 month to 4 years (mean, 30 month). According to the criteria of Massiri, treatment outcomes were excellent in 19% of cases, good in 28%, fair in 30% and poor in 23%. Conclusion: In our context, these lesions are often open and associated with fractures of Lisfranc joint skeleton and treated after a period more or less long and sometimes, we face lesions totally old. Immediately arthrodesis can be a lasting solution and should not be overlooked.