The Critical Energy Release Rate of Welded Joints Between Fiber-Reinforced Thermoplastics and Metals When Thermal Residual Stress is Considered

Thermal effects on welded joints between fiber-reinforced thermoplastics (FRTPs) and metals have been investigated theoretically and experimentally. Because FRTPs use thermoplastics as the matrix resin, they have advantages over fiber-reinforced thermoset plastics (FRPs or FRSPs), including the ability to be welded. When dissimilar materials are welded together, however, thermal stress occurs due to the different thermal expansions of the materials and affects the energy release rate of the joint. Therefore, a method for evaluating the true energy release rate, including the effect of thermal stress, is necessary for strength evaluation tests. Although several theories that compensate for the thermal stress and evaluate the true energy release rate have already been proposed, they require parameters that are difficult to measure. Therefore, it is difficult to apply them in experimental investigations. In this article, a theoretical method with easily measurable parameters is proposed to calculate the energy release rate of welded double cantilever beam (DCB) joints. The effect of the thermal stress on the critical energy release rate is discussed in terms of the experimental results of a welded DCB specimen composed of a FRTP and an aluminum alloy.     

Interrelationships between welding parameters of hot‐gas welded polypropylene

In case of hot‐gas welding, the parameters of welding influence the strength of the welded joint. A welding portal was designed and built to make the welding parameters of manual hot‐gas welding controllable and independent of human factors. Large series of experiments were performed with the automatic welding station to explore the effect of welding parameters (welding temperature, flow rate, welding speed, and welding force). The strength of the welded joints was determined in a standard tensile test carried out according to ISO 527–3. Using two‐way analysis of variance it was concluded that all four parameters influence the strength of the welded joint significantly, and the strength of the welded joint exhibits a complex dependence on all four parameters. Based on a thermodynamic approach the welding energy was determined. The measured tensile strength values were plotted against the welding energy and the welding force and it was found that the results can be approximated by a quadratic surface function well. POLYM. ENG. SCI. 46:1173–1181, 2006. © 2006 Society of Plastics Engineers.     

The study of linear vibrational welding of moso bamboo

Moso bamboo (Phyllostachys pubescens) linear-vibration welded joints with three different combinations between the inner and outer surfaces were studied in this paper. The tensile-shear strength, the microstructures and welded layer thickness observed by SEM and the density profiles measured by X-ray densitometer of the welded samples have been considered and compared. The maximum average tensile-shear strength of outer-outer, inner-inner and outer-inner welded joints were 5.91, 7.15 and 6.24 MPa, respectively. And only the inner-inner welded joints have the bamboo failure after the shear test. The welded joint is composed of a lot of bamboo fibers entangled in the molten and flown intercellular materials which decide the final mechanical performance of the welded joints. The thickness of the outer-outer welded layer is the smallest and the inner-inner welded layer is the highest. However, the maximum density reached in the inner-inner welded joint is smaller than in the outer-outer welded joint owing to the different vascular distribution in the cross section of the moso bamboo. The relative density can be used to reflect the tensile-shear strength of the welded joints. The natural structure of bamboo really do have significant influences on the welded interface.     

Shrink-Fitting and Dowel Welding in Mortise and Tenon Structural Wood Joints

Shrink-fitting, a common bonding technique in metal assemblies, was used for mortise and tenon wood joints. The joints had considerable strength. Shrink-fitting yielded joint strengths comparable to those obtained by using several welded dowels. Increasing the number of welded dowels, however, produced joints of higher strength than those bonded just by shrink-fitting. Combining in the same joint both dowel welding and shrink-fitting yielded joint strengths higher than those obtained by the individual techniques alone, and at the same time allowing decreasing the number of welded dowels needed.     

纤维增强树脂基复合材料的搅拌摩擦焊研究

利用搅拌摩擦焊实现了纤维增强树脂基复合材料的焊接,获得了焊接接头力学性能并分析了接头形成和断裂机制。结果表明,由于搅拌摩擦焊过程中搅拌针的摩擦剪切及对塑化材料的挤压作用,使树脂基体发生塑化并带动碳纤维迁移形成焊接接头,在搅拌头旋转速度950 r/min,焊接速度38 mm/min时,接头拉伸强度可以达到52.43 MPa,接近母材强度的51%,焊接接头的断裂机制主要为基体剪切断裂和纤维-基体界面脱粘。     

Wood Welding: Chemical and Physical Changes According to the Welding Time

Wood welding using linear friction is a technique that has been developed in the past five years. The goal of this study was to analyze the microstructure development in the interphase enabling the wood-to-wood adhesion without any adhesive. Chemical and physical analyses have been carried out using infrared thermography, mechanical shear tests, transmitted light microscopy and X-ray densitometry. They have been considered as efficient to qualify the characteristics of the welded joints. The aim of this paper is to present a study using these analysis methods to observe the physical modifications of the wood in the interphase according to the welding time. The welding process of beech wood (Fagus sylvatia) with a welding time between 0 and 11 s could be divided into three different phases. The first phase describes changes in the physical and chemical characteristics of the wood. Densification and anatomical modifications occur in this phase. The second phase represents stabilization of the welded joint. The last phase of the cycle is a conditioning phase. All phases are controlled by the heat spread in the interphase and the time of heat exposure. Various parameters such as welding time, shear strength, temperature and width of the welded joint have been correlated and a hypothesis on the chemical reactions occurring in the interphase has been put forth. This study allowed discovering a window of parameters in which the quality of the welded joint is quite stable. Improving the quality of manufactured welded wood products without adhesive can now be done more easily due to this method.     

焊接接头断裂驱动力参量的数值研究

采用有限元方法对焊接接头的断裂参量Ｊ积分进行了系统计算。结果表明，焊缝区存在裂纹的焊接接头其周边母材的材料性能变化对整个接头的Ｊ积分断裂参量有很大影响。在同一载荷作用下，焊缝材料不变时，高屈服强度母材焊接接头的裂纹驱动力明显小于低屈服强度母材焊接接头的驱动力，高硬化母材则对整个焊接接头驱动力有明显的加速作用。     

Vibration welding of heat-treated wood

Vibration welding of wood that has been preheated according to an industrial two-step process indicates that such wood can be welded and can yield welded joints of good strength. The joint strength is, however, markedly lower than obtained when welding non-heat-treated timber. In general, weld strength of the timber is poor if welding is done on hydrothermolyzed wood. The strength results are instead much better if welding is done at the end of the complete heat treatment process, i.e., after the dry heat step. The weld lines of heat-treated wood show entangled cells where there is none or very little of the molten matrix intercellular material usually observed in welded timber. Furthermore, in weldlines obtained after hydrothermolysis an increase in rigidity and brittleness of the wood cells is observed. Hence, the wood cells are not entangled at all or very little. Both observations indicate that heat treatment has affected the main melting region of the wood, namely the intercellular material. As most of this material is already either lost or heavily cross-linked during heat treatment, only little of it is now available to melt and bind the wood surfaces during vibrational wood welding.     

聚乙烯管道热熔焊接技术研究进展

简述了聚乙烯（PE）管道热熔焊接接头的影响因素,对国内外热熔接头可靠性测试方法的研究进展进行了综述。总结了焊接参数对接头质量的影响规律,并分析了接头的失效机理。焊接参数的改变能显著影响热熔接头的性能,选择最优焊接参数能提高接头乃至整个管道系统的可靠性。分别从力学性能、有限元模拟和无损检测3个方面总结了热熔接头相关研究,期待未来建立一种全面的热熔焊接接头力学性能评价标准,能减少实验时间、降低测试成本。随着材料的创新和科技手段的发展,未来有限元模拟和无损检测技术有望代替力学实验,成为热熔接头可靠性检测的主要方法。     

过载拉伸对焊接接头应力集中区域力学行为的影响

本文以弹塑性有限元为基础,建立了过载拉伸对焊接接头应力集中区域的力学数值计算模型,得出了在不同载荷下板材的应力集中区域的应力分布情况,单元屈服以及卸载后的残余应力分布情况。结果表明:过载拉伸时,在应力集中处会首先发生屈服,并伴有一定的拉伸塑性变形;卸载后,在构件中会产生由于不均匀塑性变形引起的残余应力,在应力集中处发生拉伸塑性变形的区域将产生压缩应力,该压缩应力对结构是有益的。     

Performance of Dowel-Welded Wood Furniture Linear Joints

Comparison of three types of furniture joints such as scarf joints, step butt joints and dovetail joints held together either by one or two welded dowels, glued dowels and steel nails showed that the dowels always gave better shear strength and greater stiffness than the steel nails. The results of welded dowels and glued dowel joints were found to be comparable. The application of the welded joint technique to joints where the number of dowels is limited by the narrow space in which they can be applied, such as in furniture, can give results comparable to those obtained by gluing the same dowels.     

Rechnerunterstützte Gestaltung und Kostenerkennung von Schweißkonstruktionen

Computer-assisted design and cost assessment of welded constructions. Newly developed functions permit modelling of welded joints in 3D CAD systems. The designer identifies the welding zone and the CAD system suggests appropriate forms and dimensions of welded seams at an early design stage. The user can then correct the proposal if necessary. Detailed information about the welding process can be added later by another specialist or with the aid of an expert system. On utilising the CAD-assisted selection of raw materials, the costs of the welded joint can be calculated automatically in very detailed form.     

Some Characteristics of Ultrasonic Welding of Polymers

Ultrasonic mechanical vibrations are usually introduced perpendicular to the welded surfaces, which coincides with the direction of the clamping force. The characteristics of the physical processes in ultrasonic welding (USW) of polymers cause heating of the parts to occur primarily at the site of their contact. For this reason, it is possible to form a high-quality weld at a lower temperature than with other kinds of welding. In some cases, USW of polymer parts is even possible at a temperature below their pour point (melting point), which allows obtaining welded articles made from different polymers and welding polymers whose degradation temperature is comparable to or lower than the melting point [fluoroplastic, poly(ethylene terephthalate)]. One of the most important characteristics of USW is the possibility of forming a high-quality weld at a relatively large distance from the site of introduction of mechanical energy, which allows obtaining sufficiently strong welded joint in articles of very complicated design. The possibility of manufacturing welded joints of polymers with contaminated surfaces significantly expands the range of application of USW, as it can be used for hermetic sealing of polymer containers filled with finished products. USW allows industrial production of nonwoven cloth both from purely thermoplastic polymer fibers and from blends with natural or other chemical fibers.     

铂重整加热炉炉管的焊接与标注

介绍了铂重整加热炉U型炉管的焊接与焊缝标注方法。对焊接、检验人员及炉管和焊材必须有专门的要求 ,应建立相应的施焊管理制度。所有焊缝均应进行热处理、X射线探伤和硬度测定 ;施焊位置应标注炉管号、焊缝号、焊工号。     

Accelerating vs Constant Rate of Insertion in Wood Dowel Welding

Dowel insertion rates whether accelerating or constant are determining parameters for the tensile strength of welded dowel joints. Dowel insertion at acceleration up to 4–7 m/s² appears to yield the best results at the lower dowel insertion speed, characteristic of welding by manual drills. Strength results for dowel welded joints of 24 mm depths of up to 2700 N/mm² have been obtained. Constant dowel insertion rates appear instead to yield best results when the insertion rate is much higher and can be better controlled, as it is the case for a computer controlled dowel insertion equipment. Strength results for dowel welded joints of 24 mm depths of up to 4700 N/mm² have been obtained for insertion rates of 18–20 mm/s and welding time as short as 1.2 s. The results indicate that at low to medium insertion rates, the greater is the acceleration the better are the results. At fast insertion rates the acceleration has only little effect. The predominant effect is that a short welding time yields a high strength joint.     

Comparative potential of alternative wood welding systems,ultrasonic and microfriction stir welding

Two alternative welding systems were evaluated for wood welding. Ultrasonic welding produces joints of good strength but it appears to be applicable only to thin wood pieces. It does not appear that further possible process improvement could bring the joint strength to a structural level. Microfriction stir welding does show potential for welding continuously wooden plates without any limitation on length of wood pieces. The strength of the weld obtained was low due to the limited depth of the weldline. Optimisation of parameters is necessary. A drawback at present appears to be the limited thickness of the wooden pieces that can be welded. X-ray micro densitometry, scanning electron microscopy and optical microscopy showed that the main difference compared to the other techniques is that in the microfriction stir weld, there is a veritable welded line of molten material. This molten material comes from the wood in contact with the rotating steel cylinder, which has flowed down in the micro gap between the two pieces of timber where it has bonded by solidifying.     

Molekülanordnungen in Fetten mit trikliner Kristallstruktur

Molecular Arrangements in Fats with Triclinic Crystal Structure Apart from their stable β-form the saturated mono-acid triglycerides are found to occur in four other modifications with triclinic crystal structure which differ from each other by the angle of chain tilt of the molecules. This fact, of little consideration in literature so far, could be confirmed and evidence could be given of it, partially for the first time, by means of X-ray diffraction of the even-numbered triglycerides trilaurin till tristearin. Based on several hypotheses, e. g. a nearly constant triclinic subcell, a theoretic structure model could be elaborated in which all experimental results of the five triclinic crystal forms may be classified. In addition, mathematic relations were found which allow a complete build-up of the β-unit cell from the subcell. It was found from electron and X-ray diffraction studies that an homologous isomorphism of the triglycerides studied does not exist in the strict sense. The cause may be seen in a slight but characteristic shrinkage of the subcell with increasing molecular length.     

Joining of wood layers by friction welding

A welding technique has been developed to join wooden work pieces by frictional heat without any wood glue. During the welding process 'melting' of the surfaces, resulting from the influence of pressure and frictional heat, was observed. Solidification and bond formation between the welded pieces happened during cool down of the heat-affected zone. The solidification of the heat-affected zone is explained. Tests were carried out to determine the resistance of the joint as a function of the interfacial temperature and the solidification time. The results show that after 20 s of cooling, the shear strength of the welded bonds amounted to 70% of the ultimate shear strength of the connection after 15 min of solidification. This behaviour allows continuous welding of multilayered wood laminates. Due to the use of natural materials only, the welded products are environmentally compatible. In case of disposal, the welded components can be burned in the same way as natural wood without the evolution of toxic compounds.     

2(1/4)Cr1Mo钢及其焊接接头缺陷失效评定曲线

通过对 2 14Cr1Mo钢及其焊接接头在常温和高温下应力 -应变关系曲线的分析 ,用塑性多段幂次法描述材料的本构关系。基于弹塑性有限元法和工程评定方法建立 2 14Cr1Mo钢及其焊接接头的失效评定曲线 (FAC) ,并将计算结果与R6通用曲线进行了比较 ,为 2 14Cr1Mo钢制压力容器缺陷的安全评定提供技术支持     

夹套管封板角焊缝裂纹原因分析及对策

本文针对夹套管封板角焊缝裂纹原因产生机理进行了分析,通过应力计算,指出因结构不合理是造成裂纹产生的根本原因,同时提出了解决问题的办法.