非接触检测中螺纹图像牙型边界修正研究

利用图像的非接触检测螺纹是一种高效的检测方法。检测中,精准的获取到螺纹图像的牙型边界是检测的关键,而现有的图像处理技术并不能消除由于螺纹旋线对螺纹图像的影响。针对螺纹图像中牙型边界被遮挡的问题,从圆锥螺纹的几何空间关系分析图像产生误差的原因,建立圆锥螺纹数学模型,得到误差的方程。最后再设计了图像检测系统,根据误差方程修正螺纹图像、提取参数,经验证,此方法可以提高螺纹的检测精度,且通用在圆锥螺纹与圆柱螺纹中。     

高体分SiC_p/Al复合材料螺纹性能的测试

从SiCp/Al复合材料性能分析着手,讨论了预置件法、焊接法和粘接法等在空间遥感器研制中常用的联接方法的优缺点,提出了在高体积分数(体分)SiCp/Al复合材料上直接加工螺纹,并加装钢丝螺套的方法来改善螺纹联接性能。对在某高体分SiCp/Al复合材料上加工的M4、M5螺纹进行了拉伸测试,结果表明:加装钢丝螺套前,复合材料螺纹有被拉脱现象;加装钢丝螺套后,M4螺纹、螺杆在3 000～4 000 N被拉断;M5螺纹、螺杆在8 000～9 000 N被拉断,测试后两种规格的螺纹状态良好,可以满足实际应用对该材料拉伸强度的要求,其已应用于工程项目中。     

高体分SiC_p/Al复合材料螺纹性能的测试

从SiCp/Al复合材料性能分析着手,讨论了预置件法、焊接法和粘接法等在空间遥感器研制中常用的联接方法的优缺点,提出了在高体积分数（体分）SiCp/Al复合材料上直接加工螺纹,并加装钢丝螺套的方法来改善螺纹联接性能。对在某高体分SiCp/Al复合材料上加工的M4、M5螺纹进行了拉伸测试,结果表明：加装钢丝螺套前,复合材料螺纹有被拉脱现象;加装钢丝螺套后,M4螺纹、螺杆在3 000～4 000 N被拉断;M5螺纹、螺杆在8 000～9 000 N被拉断,测试后两种规格的螺纹状态良好,可以满足实际应用对该材料拉伸强度的要求,其已应用于工程项目中。     

目镜螺纹的测量和加工

本文根据目镜螺纹和量针的接触原理,按照其精确关系给出接触点处的作用直径、螺纹沟槽宽、压力角、针倾斜角、跨针尺寸、最大和最小三针直径、最佳三针直径。为了减少三针尺寸数量,笔者为只用一种尺寸的三针测量所有的目镜螺纹提供了依据。笔者认为目镜螺纹铣削刀具轮廓和磨削砂轮轮廓的精确形状应以螺纹的法向面形为依据。为此,可以用上述参数来评价铣刀和砂轮的外形,从而达到指导加工的目的。     

内螺纹管管型结构对管内流动阻力特性的影响

对不同结构的内螺纹管内空气-水两相流动的阻力特性进行了实验研究,从实验方面得出了影响内螺纹管阻力特性的主要几何参数(螺纹高度,螺纹升角,螺纹宽度等)对内螺纹管阻力特性的影响规律。结合实验现象,引入了研究内螺纹管阻力特性的并联管路模型,最终得出适用于不同结构内螺纹管的阻力特性半理论经验公式。通过该公式可以较好地反映出各个几何参数对内螺纹管阻力特性的影响规律。     

刻螺纹对Nd：YAG晶体棒输出功率影响的实验研究

针对Nd：YAG棒刻螺纹是否能改善激光器的输出，理论上分析了Nd：YAG晶体棒内热传导过程及影响其冷却效果的因素。给出了表面刻上螺纹后，Nd：YAG晶体棒表面积的变化结果和其对表面冷却换热方式的改变。对使用螺纹棒的激光器输出进行了实验研究，与普通棒的实验结果对比发现：用螺纹棒比用普通棒时平均功率大了23．2％，发散角小了3mrad。说明激光棒的表面刻槽可以提高冷却效果，有效地提高了激光器的输出。     

机器视觉螺纹图像评价方法北大核心CSCD

为了提高机器视觉螺纹的测量精度,建立了基于螺纹图像质量的评价方法。通过对螺纹灰度图像的行灰度分布情况和螺纹光学成像特点的分析,揭示出由于螺旋升角造成螺纹图像牙廓边缘失真的机理。在分析多种螺纹图像评价方法性能的基础上,采用基于螺纹边缘的评价算法L-yakuo,计算多幅不同物距螺纹图像的评价值。最后,通过对机器视觉求取的M14×2、M20×2.5牙型角和接触测量仪得到的牙型角进行实验对比分析。实验结果表明:采用L-yakuo算法得到最清晰的牙廓图像后再进行机器视觉螺纹牙型角求取,规格M14×2、M20×2.5的螺纹牙型角精度平均提高9′33′′。借助L-yakuo算法能够灵敏地反映螺纹牙廓清晰度,基本满足了螺纹图像清晰度的评价需求,评价值的变化和牙型角相对误差的变化基本一致,且该评价值具有精度高、易计算的特点。     

螺纹管内污垢热阻的对比实验研究

本文对一冷却塔中的7根螺纹管进行了长时间污垢实验研究.螺纹管几何参数范围:螺纹数18～45,螺纹角25°～45°,螺纹高0.33～0.55 mm.污垢是颗粒污垢和析晶污垢的混合物.本文基于普朗特类比,引入修正因子β(β=(A_w/A_(wp))/(A_c/A_(cp)),A_w为润湿面积,A_c为截面积,下标p表示光管),对半经验污垢预测模型进行修正,证明了螺纹管内参数对污垢热阻的形成影响很大,并建立了不同结构参数的螺纹管的统一结垢模型,对工程实际有一定指导意义.     

机器视觉螺纹螺距的测量与评定北大核心CSCD

为实现螺纹螺距的高效测量与合理评定,在分析现有机器视觉螺纹螺距测量方法的基础上,提出了一种基于面积法求解螺纹螺距的测量与评定方法。首先对螺纹图像进行旋转矫正,然后以螺纹轴截面上牙廓区域投影面积等几何关系,获取螺纹中径点,再使用最小二乘法拟合中径线,最后结合包容原则获得被测螺纹螺距。以螺纹塞规为对象进行对比实验,数据表明:面积法与接触式综合测量仪、工具显微镜所测螺距平均值相当,标准差0.9μm略大于综合测量仪所测螺距的标准差0.6μm,但远小于工具显微镜所测螺距的标准差9.6μm;测量效率上面积法是综合测量仪的1.9倍,是工具显微镜的2.5倍。     

目镜螺纹中径的优化测量

在光学精密机械里,目镜采用一种特殊螺纹,即目镜螺纹。在通过其轴的截面内呈现三角形的螺纹轮廓;在垂直其轴的截面内呈现阿基米德螺旋线的横向螺纹轮廓。它们的螺纹线数(或者头数)N一般较大,有的达20。这样,它们的导程角(或者螺纹升角)相应也大,有的高达12°。     

Damping sources in wood structures

Damping in wood structures is either associated with the material itself or with the joining devices. An experimental study indicates that material damping is relatively independent of wood type and constant in a given environment. Nailed joints can provide additional damping which can be further augmented by special nailing devices. Such devices increase the total damping by more than an order of magnitude. The damping of glued joints depends upon the characteristics of the adhesive. The adhesive can double the damping provided by the wood alone.     

Adhesive bonding of composite aircraft structures: Challenges and recent developments

In this review paper,the challenges and some recent developments of adhesive bonding technology in composite aircraft structures are discussed.The durability of bonded joints is defined and presented for parameters that may influence bonding quality.Presented is also,a numerical design approach for composite joining profiles used to realize adhesive bonding.It is shown that environmental ageing and pre-bond contamination of bonding surfaces may degrade significantly fracture toughness of bonded joints.Moreover,it is obvious that additional research is needed in order to design joining profiles that will enable load transfer through shearing of the bondline.These findings,together with the limited capabilities of existing non-destructive testing techniques,can partially explain the confined use of adhesive bonding in primary composite aircraft structural parts.     

Measuring the critical energy release rate in mode II of tough,structural adhesive joints using the tapered end-notched flexure (TENF) test

This paper shows and discusses results of the Tapered End-Notched Flexure (TENF) test, investigating the fracture behaviour of high-strength structural adhesive joints under shear loading. The TENF test has been previously applied to brittle joints by different authors and has been re-designed to be applicable to ductile adhesives in the presented work. Furthermore, the tests are performed at two velocities, a quasi-static and a dynamic one, to investigate rate effects on the fracture behaviour of the joint. All experimental work has been performed using the structural adhesive DOW Betamate 1496V.     

Effect of ultrasonic vibration on adhesive enhancement of plasma-modified nickel surface

Poor adhesion of nickel surface limits its further application in the aerospace field. In this study, plasma modification was conducted on the surface of the nickel plate pretreated by sandblasting, and then ultrasonic vibration was applied during the adhesively bonding process of the CFRP(Carbon fibre-reinforced polymer)/Ni joints. The bonding strength of the joints was increased by 65%. The adherend surface and the bonding interface were analyzed from microstructure, element distribution and chemical bonding to study the strengthening mechanism. By the sandblasting, irregular pits were formed on the nickel surface, effectively increasing the surface roughness. The plasma modification could introduce active functional groups including hydroxyl, amino and carbonyl on the nickel surface, which improved the surface wettability macroscopically. However, at a microscopic level, the adhesive with high viscosity and poor fluidity did not form a compact interface with the nickel. The ultrasonic application could promote the filling of the adhesive in irregular micro-scale pits on the surface, thereby strengthening the mechanical anchoring effect. Furthermore, the ultrasonic application produced dynamic impingement at the interface, enhancing the contact between the adhesive and the nickel plate. The adhesive molecules could fully collide and react with the active functional groups introduced on the nickel surface to form more chemical bonds, thus effectively improving the bonding strength of the CFRP/Ni joints.     

Kinetics of adhesive contact formation between thermoplastic melts and solid surfaces: Effect on bond strength

Formation of an adhesive contact between a polymer melt (or solution) and reinforcing fibers is considered from the viewpoint of kinetics. A two-stage model of this process has been proposed, and an expression for the interfacial bond strength as a function of time and temperature is derived. Experimental data on bond strength in adhesive joints between thermoplastic polymers and reinforcing fibers formed under various conditions were obtained, and the concept of activation energy was used to analyze them. Since the process is controlled by the stage having the larger activation energy, the adhesive contact formation between fibers and polymer solutions is governed by the rate of adhesive bonding, whereas that between fibers and polymer melts is governed by the rate of the melt spreading.     

The role of alumina nanoparticles in epoxy adhesives

Both untreated and calcined fumed alumina nanoparticles were dispersed into an epoxy-based adhesive at various percentages. The glass transition temperature of the nanofilled adhesives increased up to an optimal filler loading and then decreased, probably due to concurrent and contrasting effects of chain blocking and reduction of the crosslinking degree. Tensile modulus, stress at break, and fracture toughness of bulk adhesive were positively affected by the presence of untreated alumina nanoparticles at an optimal filler content. Mechanical tests on single-lap aluminum bonded joints indicated that untreated alumina nanoparticles markedly improved both the shear strength and fatigue life of the bonded joints. In particular, the shear strength increased by about 60% for an optimal filler content of 1 vol.%, and an adhesive failure mechanism was evidenced for all the tested specimens. Concurrently, a relevant decrease of the equilibrium contact angle with water was observed for nanofilled bulk adhesives. In summary, alumina nanoparticles can effectively improve the mechanical performances of epoxy structural adhesives, both by increasing their mechanical properties and by enhancing the interfacial wettability with an aluminum substrate.     

Propagation of ultrasonic guided waves in lap-shear adhesive joints: case of incident a0 Lamb wave

This paper deals with the propagation of ultrasonic guided waves in adhesively bonded lap-shear joints. The topic is relevant to bond inspection by ultrasonic testing. Specifically, the propagation of the lowest-order, antisymmetric a0 mode through the joint is examined. An important aspect is the mode conversion at the boundaries between the single-plate adherents and the multilayer overlap. The a0 strength of transmission is studied for three different bond states in aluminum joints, namely a fully cured adhesive bond, a poorly cured adhesive bond, and a slip bond. Theoretical predictions indicate that the dispersive behavior of the guided waves in the multilayer overlap is highly dependent on bond state. Experimental tests are conducted in lap-shear joints by a hybrid, broadband laser/air-coupled ultrasonic setup in a through-transmission configuration. The Gabor wavelet transform is employed to extract energy transmission coefficients in the 100 kHz 1.4 MHz range for the three different bond states examined. The cross-sectional mode shapes of the guided waves are shown to have a substantial role in the energy transfer through the joint.     

Experimental studies of the mechanical and thermal stability of a polymer-substrate interface

The use of mass spectrometry to study the mechanisms of formation and fracture of polymer adhesive joints is considered. The factors affecting the joint strengths are analyzed, and the possible development of mass spectrometry for destruction processes in solids is discussed.     

有限元仿真兰姆波评价胶接接头界面弹性模量的研究

金属薄板检测中,声-超声检测方法可激发多模式的兰姆波,兰姆波能够评价金属胶接后结构质量,正确认识兰姆波传播特性与胶接接头弹性模量的关系是有效应用该技术的基础。本文采用有限元仿真法分析这种关系,得出随着胶层弹性模量的降低,各模式兰姆波通过胶接接头后能量有不同程度的衰减,频率为0.5 MHz和1 MHz时,兰姆波主要模式A₀、S₀能量值与接头弹性模量具有一定的线性关系。实验结果表明,低频时随着胶接接头的人工老化,接头中主要模式兰姆波能量均发生一定程度的衰减,其能量变化曲线与有限元仿真结果趋势一致。本方法能为实验研究、实际检测提供有效参考依据。     

Ultrasonic testing of anaerobic bonded joints

The paper deals with ultrasonic testing of adhesive joints between sheets of thickness greater than 1 mm, bonded by a "zero thickness" layer of anaerobic adhesive. In the case of equally thick sheets, interference phenomena can arise that make impossible the use of the "decay method" (a method previously developed by the authors for the case of non-zero adhesive thickness). Consequently an alternative method, termed "first peak", has been proposed. In order to evaluate the applicability of the two methods, a series of tests has been carried out on specimens having geometry suitable for both types of inspection. Also two different levels of surface roughness have been considered. The results allow for evaluating the defect detection capability of each method, accounting for the roughness effect, and give information on the suitable control procedures.