EFFECTS OF LEAD WIDTHS AND PITCHES ON RELIABILITY OF QUAD FLAT PACKAGE(QFP)SOLDERED JOINTS

The finite element method（FEM） is used to analyze the effects of lead widths and pitches on reliability of soldered joints. The optimum simulation for QFP devices is also researched. The results indicate that when the lead pitches are the same, the maximum equivalent stress of the soldered joints increases with the increasing of lead widths, while the reliability of the soldered joints reduces. When the lead widths are the same, the maximum equivalent stress of the soldered joints doesn＇t decrease completely with the increasing of lead pitches, a minimum value of the maximum equivalent stress values exists in all the curves. Under this condition the maximum equivalent stress of the soldewed joints is relatively the least, the reliability of soldered joints is high and the assembly is excellent. The simulating results indicate the best parameter： The lead width is 0.2 mm and lead pitch is 0.3 mm （the distance between two leads is 0.1 mm）, which are benefited for the micromation of QFP devices now. The minimum value of the maximum equivalent stress of soldered joints exists while lead width is 0.25 mm and lead pitch is 0.35 mm （the distance between two leads is 0.1 mm）, the devices can serve for a long time and the reliability is the highest, the assembly is excellent. The simulating results also indicate the fact that the lead width is 0.15 mm and lead pitch is 0.2 mm maybe the limit of QFP, which is significant for the high lead count and micromation of assembly.

Pushover analysis of reinforced concrete frames considering shear failure at beam-column joints

Since most current seismic capacity evaluations of reinforced concrete （RC） frame structures are implemented by either static pushover analysis （PA） or dynamic time history analysis, with diverse settings of the plastic hinges （PHs） on such main structural components as columns, beams and walls, the complex behavior of shear failure at beam-column joints （BCJs） during major earthquakes is commonly neglected. This study proposes new nonlinear PA procedures that consider shear failure at BCJs and seek to assess the actual damage to RC structures. Based on the specifications of FEMA-356, a simplified joint model composed of two nonlinear cross struts placed diagonally over the location of the plastic hinge is established, allowing a sophisticated PA to be performed. To verify the validity of this method, the analytical results for the capacity curves and the failure mechanism derived from three different full-size RC frames are compared with the experimental measurements. By considering shear failure at BCJs, the proposed nonlinear analytical procedures can be used to estimate the structural behavior of RC frames, including seismic capacity and the progressive failure sequence of joints, in a precise and effective manner.

Seismic Behaviour of Beam-Column Joints of Precast and Partial Steel Reinforced Concrete

A beam-column joint of precast and partial steel reinforced concrete( PPSRC) is proposed for precast reinforced concrete frames. The PPSRC consists of partial steel and reinforced concrete. The partial steel is located in the core joint region and the connections between concrete members. This paper presents an experimental study of a series of PPSRC specimens. These specimens are tested under low cyclic loading.Experimental results demonstrate that the bearing capacity of the PPSRC specimens is 3 times that of the ordinary reinforced concrete( RC) beam-column joints. The strength and stiffness degradation rates are slower compared with that of the RC beam-column joints. In addition,the strength of the core joint region and the connections is higher than other parts of the PPSRC specimens. Beam failure occurs firstly for the PPSRC specimens,followed by column failure and connections failure. The failure of the core joint region occurs finally.Test results show that the seismic performance of the PPSRC is better than that of the ordinary RC beam-column joints.

基于Flatjoint接触模型的岩石单轴压缩和巴西劈裂颗粒流模拟研究

基于颗粒流平台,选择Flatjoint接触模型作为岩石模拟的基本模型,用单轴压缩和巴西劈裂数值试验测试岩石宏观参数,对数值试验进行正交设计,采用多因素方差分析和回归分析研究宏细观参数之间的关系。在此基础上,提出了基于岩石单轴压缩和巴西劈裂数值试验的细观参数匹配方法。以灰岩的室内试验为基础,对灰岩细观参数进行了标定,实现了灰岩单轴压缩和巴西劈裂的颗粒流模拟,模拟结果与试验结果相接近,验证了本文方法的有效性。

Seismic performance of steel reinforced ultra high-strength concrete composite frame joints

To investigate the seismic performance of a composite frame comprised of steel reinforced ultra high-strength concrete （SRUHSC） columns and steel reinforced concrete （SRC） beams, six interior frame joint specimens were designed and tested under low cyclically lateral load. The effects of the axial load ratio and volumetric stirrup ratio were studied on the characteristics of the frame joint performance including crack pattern, failure mode, ductility, energy dissipation capacity, strength degradation and rigidity degradation. It was found that all joint specimens behaved in a ductile manner with flexural-shear failure in the joint core region while plastic hinges appeared at the beam ends. The ductility and energy absorption capacity of joints increased as the axial load ratio decreased and the volumetric stirIup ratio increased. The displacement ductility coefficient and equivalent damping coefficient of the joints fell between the corresponding coefficients of the steel reinforced concrete （SRC） frame joint and RC frame joint. The axial load ratio and volumetric stirrup ratio have less influence on the strength degradation and more influence on the stiffness degradation. The stiffness of the joint degrades more significantly for a low volumetric stirrup ratio and high axial load ratio. The characteristics obtained from the SRUHSC composite frame joint specimens with better seismic performance may be a useful reference in future engineering applications.

Seismic performance and global ductility of RC frames rehabilitated with retrofi tted joints by CFRP laminates

This paper presents a new FRP retrofi tting scheme to strengthen local beam-column joints in reinforced concrete(RC) frames.The new retrofi tting scheme was proposed following a preliminary study of four different existing retrofi tting schemes.A numerical simulation was conducted to evaluate the effectiveness of FRP-strengthened reinforced concrete frames by bridging behavior of local joints to the whole structure.Local confi nement effects due to varying retrofi tting schemes in the joints were simulated in the frame model.The seismic behavior factor was used to evaluate the seismic performance of the strengthened RC frames.The results demonstrated that the new proposed retrofi tting scheme was robust and promising,and fi nite element analysis appropriately captured the strength and global ductility of the frame due to upgrading of the local joints.

Mechanical properties of QFP micro-joints soldered with lead-free solders using diode laser soldering technology

Soldering experiments of quad flat package(QFP) devices were carried out by means of diode laser soldering system with Sn-Ag-Cu and Sn-Cu-Ni lead-free solders, and competitive experiments were also carried out not only with Sn-Pb eutectic solders but also with infrared reflow soldering method. The results indicate that under the conditions of laser continuous scanning mode as well as the fixed laser soldering time, an optimal power exists, while the optimal mechanical properties of QFP micro-joints are gained. Mechanical properties of QFP micro-joints soldered with laser soldering system are better than those of QFP micro-joints soldered with IR reflow soldering method. Fracture morphologies of QFP micro-joints soldered with laser soldering system exhibit the characteristic of tough fracture, and homogeneous and fine dimples appear under the optimal laser output power.

Finite Element Analysis (FEA) for the Beam-Column Joint Subjected to Cyclic Loading Was Performed Using ANSYS

This paper analyses the seismic performance of exterior beam-column joints strengthened with unconventional reinforcement detailing. The beam-column joint specimens were tested with reverse cyclic loading applied at the beam end. The samples were divided into two groups based on the joint reinforcement detailing. The first group (Group A) of three non-ductility specimens had joint detailing in accordance with the construction code of practice in India IS456-2000, and the second group (Group B) of three ductility specimens had joint reinforcement detailed as per IS13920-1993, with similar axial load cases as the first group. The experimental studies are proven with the analytical studies carried out by finite element models using ANSYS. The results show that the hysteresis simulation is satisfactory for both un-strengthened and ferrocement strengthened specimens. Furthermore, when ferrocement strengthening is employed, the strengthened beam-column joints exhibit better structural performance than the un-strengthened specimens of about 31.56% and 38.98 for DD-T1 and DD-T2 respectively. The analytical shear strength predictions were in line with the test results reported in the literature, thus adding confidence to the validity of the proposed models.

汽车组合仪表有意电磁干扰空时域联合分离系统设计

有意电磁波与汽车仪器电磁传输波产生的混合干扰,降低了汽车组合仪表的稳定运行能力,造成仪表设备失灵;为避免上述情况的发生,设计汽车组合仪表有意电磁干扰空时域联合分离系统;在步进电机驱动电路中,设置汽车组合仪表控制器、分离电源与PCB电路板、有意电磁干扰数字传感器;分配有意电磁波空时域源地址,通过计算干扰信号平坦度的方式,确定脉冲参数的取值范围,实现汽车组合仪表有意电磁的空时域干扰效应分析;估算有意电磁波干扰信号的数目,按照信号分解的处理原则,求解联合分离修正函数,实现电磁干扰的联合分离;在设置频率范围在100 MHz~1 GHz之间、幅度范围为0.5~5 V、脉冲宽度范围为10~100 ns区间后,通过实验结果表明,设计系统应用后可以在混合信号中,按照空域、时域标准的不同分离有意电磁波,且分离后的信号波长、信号频率依然在1.0μm、300 Hz左右,不会因混合干扰降低汽车组合仪表的稳定运行能力。

钢管混凝土扁柱-钢梁节点抗震性能有限元分析

为避免钢框架结构中梁柱节点凸出墙体,文章提出一种钢管混凝土扁柱与钢梁节点,采用ABAQUS有限元模拟软件建立4个不同连接位置的钢管混凝土扁柱-钢梁节点的有限元模型,分析节点在低周往复荷载下的破坏模式和抗震性能;结果表明,所提出的节点构造可以实现梁柱刚性连接,所有节点均发生梁铰破坏,抗震性能和耗能能力良好。进一步研究轴压比、竖向隔板厚度和连接构造对节点抗震性能的影响规律,结果表明:随着轴压比的提高,柱端峰值承载力随之下降;减小柱内竖向内隔板的厚度会导致柱端承载力的降低;将盖板连接改为竖向加劲肋连接后,能有效缓解节点处柱壁的应力集中现象。

缓倾层状岩体各向异性力学性能与破裂特征研究

为研究缓倾层状岩体结构特性对其各向异性力学性能和破裂演化特征的影响,本文考虑不同结构面间距、强度、倾角等结构特征参数及模型尺寸效应,开展缓倾层状砂泥岩多因素影响试验研究.基于颗粒流方法建立缓倾层状岩体数值力学模型,通过室内试验标定了层状砂泥岩参数,并验证了所建立模型的有效性.通过颗粒流数值力学试验,创新性地研究层状岩体结构面的裂纹发育速率,进而揭示缓倾层状砂泥岩强度各向异性及破裂演化特征,确立其力学特性与结构面间距、强度、倾角三个结构特性之间的关系.研究结论:(1)引入的平节理模型(FJM)与光滑节理模型(SJM)建立的离散元力学模型,能表征缓倾层状岩体强度各向异性力学特性与破裂演化过程;(2)缓倾层状岩体切线模量与强度,随层间距和层间强度的增大而增大,随结构面倾角的增大而减小,破裂特征受结构面的影响逐渐增大,基于单组结构面理论计算结构面发生剪切破坏的临界角度为24.5°;(3)结构面裂纹的发育速度,随结构面间距的增大而减小、随结构面倾角的减小而减小,随结构面强度的变化不明显.本文研究结果为缓倾层岩体隧道的力学行为与围岩稳定性研究提供了参考.

基于深度学习的腕关节DR成像质控模型的研究与应用

目的基于深度学习的方法建立腕关节直接数字平板X线成像系统(DR)自动质控模型生成系统,并对质控性能进行初步研究。方法采用人工智能深度学习的方法建立腕关节正位和侧位DR图像质控系统模型,回顾性收集重庆大学附属中心医院临床怀疑腕关节病变的1315张图像,按6︰4的比例划分训练集和验证集。在MobileNet V2分类模型和Global Universal U-Net(GU2Net)关键点检测模型上进行训练,然后分别使用模型准确率、精准度、召回率和曲线下面积(AUC),以及平均径向误差(MRE)和成功检出率(SDR)进行评估。结果根据验证数据集的实验所得到的伪影分类模型在伪影识别方面具有较高的性能,AUC=0.9701,95%可信区间(95%CI)0.9700~0.9703,其准确率、精准度、召回率分别为0.93、0.88和0.97。正位和侧位影像中关键点检测模型的MRE也在合理水平,分别达到(0.7944±3.2535)mm和(3.8134±7.4087)mm。距离10.0 mm下正位和侧位关键点检测模型的SDR分别为99.64%、92.51%。结论基于深度卷积神经网络开发的全自动腕关节DR质控系统模型,能够对腕关节正位和侧位片自动生成图像质量控制报告,且效果较好。

水平冷缝对大荷载无梁楼盖及类似结构的影响

首先,介绍了托板上水平方向施工冷缝对无梁楼盖顶板抗冲切承载力的不利影响,列举了3个不同地区地下车库坍塌的工程实例。其次,介绍了容易导致无梁楼盖顶板的托板或相似部位出现水平施工冷缝的3种情况。最后,给出了对投入使用的无梁楼盖结构加强日常检查的建议,一旦发现托板部位存在竖向折断裂缝,应立即采取应急措施以防止坍塌事故的发生。

基于置信水平的钢轨焊接接头设备状态评定方法

[目的]为解决我国无缝线路钢轨设备状态评定体系不完善的问题,需要建立基于置信水平的钢轨焊接接头设备状态评定方法。[方法]阐述了目前我国规定的高速铁路钢轨平直度允许偏差、焊接接头平直度允许偏差。以我国某条已开通运营13年的高速铁路为案例,对该线钢轨焊接接头平直度数据进行分析,认为钢轨接头平直度检测数据总体服从正态分布。根据正态分布及置信区间原理,对均值和标准差评定法、置信水平评定法进行对比,提出了基于置信水平的钢轨焊接接头设备状态评定方法,得到高速铁路钢轨设备状态的评定标准。[结果及结论]该方法能够客观、直观地反映出钢轨焊接接头的设备状态,可以准确地掌握钢轨设备状态。该方法可为分析钢轨设备变化规律,以及制定大中修的标准、计划及方案等提供很好的理论依据。

学龄期儿童柔韧性扁平足严重程度与步行平衡稳定性、关节协调运动功能相关性分析

目的集中对学龄期儿童柔韧性扁平足严重程度与步行平衡稳定性、关节协调运动功能的相关性进行分析。方法将2023年1月-12月期间常州市儿童医院收治的60例学龄期儿童柔韧性扁平足患儿作为研究对象,依照临床表现及影像学检查结果判定的病情严重程度将患儿分为轻度组(n=20)、中度组(n=20)、重度组(n=20);同时纳入20例健康儿童作为参比组。对4组患儿进行三维步态分析,并对分析数据进行对比。结果4组患儿步频对比,差异无统计学意义(P>0.05);4组支撑相时间比、步速、步长及步宽对比,差异有统计学意义(P<0.05);其中,轻度组、中度组、重度组支撑相时间比及步宽均大于参比组,步速及步长小于参比组,差异有统计学意义(P<0.05)。4组患儿左侧、右侧踝关节运动学参数矢状面、水平面、额状面对比,差异有统计学意义(P<0.05);其中,轻度组、中度组、重度组踝关节矢状面运动学参数、水平面运动学参数及额状面运动学参数均小于参比组,差异有统计学意义(P<0.05);同时轻度组、中度组、重度组踝关节矢状面运动学参数、水平面运动学参数及额状面运动学参数对比,轻度组>中度组>重度组,差异有统计学意义(P<0.05)。结论学龄期儿童柔韧性扁平足严重程度与步行平衡稳定性、关节协调运动功能具有相关性,其中,轻度患儿的不良关节协调运动功能表现显著多于中度及重度患儿。

失效铝合金平底无铆连接接头的原位固相修复方法

为了修复失效平底无铆连接接头并提高其力学性能,提出一种原位固相修复方法。通过对比研究平底无铆连接接头和修复接头的显微组织、力学性能和断裂失效行为,验证修复方法的可行性和有效性。结果表明,失效平底无铆连接接头的断裂颈部被成功地原位修复。焊核的显微组织被充分细化,使得修复接头的力学性能得到提升。转速和持续加热时间对修复接头的力学性能起着至关重要的作用。与平底无铆连接接头相比,冶金结合使修复接头的力学性能得到加强。修复接头的最大拉剪强度提高了409.90%,最大断裂伸长量提高了68.92%。断裂失效行为表明,修复接头的强度明显高于原始平底无铆连接接头,这说明失效平底无铆连接接头的修复方法是可行有效的。

Study on Strengthening of RC Beam Column Joint Using Hybrid FRP Composites

Beam-Column joints are critical zones in reinforced concrete structures which are most vulnerable to earthquake forces. Hence strengthening beam-column joint is vital to save the structure and its inhabitants in case of seismic forces. Numerous retrofitting works using fibre reinforced polymer (FRP) composites are being undertaken worldwide. This work aims to investigate the effectiveness of strengthening beam-column joints using natural and artificial fibres. In this study, basalt (natural fibres) as monolithic composite (BFRP) and as hybrid composite along with glass (artificial fibres) were used for strengthening of beam-column joints. Totally six specimens were prepared and tested under monotonic loading. Specimen details used were: two control specimen, two specimens for monolithic wrapping and remaining two specimens for hybrid wrapping. The test results were compared with control and rehabilitated specimens. The performance of the treated joints was studied using the following parameters: initial and ultimate cracking loads, energy absorption, deflection ductility and stiffness at ultimate. From the test results, it was found that the hybrid combination of Basalt and Glass FRPs were found to be more effective in the treatment of beam-column joints. The strong column weak beam concept was achieved by failure in beam portion which helped in preventing the catastrophic failure of the entire structure.

平直混凝土预制块半圆形榫接头静力学行为的数值模拟

建立带有半圆形榫接头的平直混凝土预制块受弯矩和剪切作用的三维有限元模型,并以硬接触和罚函数法分别模拟榫接头部位的法向和切向接触状态,分析平直预制块榫接头在弯矩和轴向压力作用下的抗弯和剪切特性,同时分析了榫接头几何参数对榫接头抗弯与剪切特性的影响,并基于混凝土塑性损伤因子,分析榫接头部位混凝土在弯矩和剪切作用下的损伤区域,给出了优化半圆型榫接头几何参数和提高接头抗弯刚度与剪切强度的途径。

核电厂钢板混凝土结构一字型连接节点研究

在核电厂房钢板混凝土结构设计中,SC-RC一字型对接节点是常用的构造形式。为研究该节点的受力性能,设计了4个足尺的节点试件,分析其传力机理、可靠性、破坏形态、极限承载力、极限变形能力及其在弯矩和面外剪力作用下的滞回特性,探究不同的连接构造对节点性能的影响。试验结果表明:在受力性能方面,SC-RC一字型对接墙连接节点性能取决于较弱一侧的RC构件性能;在构造措施方面,RC墙纵筋伸入SC墙40d的锚固长度是足够的,SC-RC交界面有无设置抗剪键对节点性能影响不大。

防水卷材搭接缝剥离强度及不透水性影响因素研究

通过对比试验研究了不同类型防水卷材搭接缝施工方式、卷材外观、胶层厚度以及搭接施工后热处理、浸水处理等因素对卷材搭接缝剥离强度和不透水性的影响。结果表明,不同类型防水卷材搭接缝剥离强度在热处理和浸水处理后有一定增长;改性沥青防水卷材热熔搭接只要严格按工艺要求施工,搭接缝不透水性均有保障;自粘聚合物改性沥青防水卷材搭接的平整度控制对于搭接缝不透水性至关重要;高分子自粘胶膜防水卷材的搭接缝不透水性受胶层厚度和搭接平整度的影响较大,背胶必不可少。