共查询到20条相似文献,搜索用时 31 毫秒
1.
One of the most important requirements for finding new applications for cellular metals is to integrate them in complex technical structures. The metal foams have to be joined to each other, or to sheet materials, by suitable joining techniques. The main topics of this paper are the ultrasonic torsion welding of cellular metallic materials to sheet metals and the investigation of the mechanical properties of the joints. The basic materials of foams and sheet metals were different aluminum and iron alloys. Depending on the materials used, weldings with tensile shear strengths of up to 25 MPa were realized. Using aluminum foam sandwich (AFS) and sheet metals, successful weldings were performed before and after the foaming process. Furthermore, it was possible to perform a successful foaming process with the unfoamed AFS/sheet metal joints. Microscopic investigations showed that the ultrasonic welding technique allows the joining of the metal foams with sheet metals without significant deformation of the joining partners. The temperatures during the welding process in the interface were below the melting point of the foams and the sheet metals. 相似文献
2.
The application of fusion welding process is restricted to certain grades of alloys and materials. Solid-state joining process offers greater advantages over fusion welding process such as fumeless and effective joining, minimum or no preparation time, environment friendly, etc. One such solid-state joining process is friction stir welding (FSW), which uses a non-consumable rotating tool. This rotating tool joins the two faying surfaces of the workpiece by forging them. This joining technique successfully joins metals, alloys and metal matrix composite (MMC), which are considered as difficult to join using conventional processes. The present study is an endeavor to review a specific domain of FSW, i.e. joining of MMCs. The initial part of the study provides a detailed introduction about the FSW process, and along with it, an overview of the published literature related to FSW of alloys has been presented. The later part of the study pays specific attention to macrostructure, microstructure, joint properties and residual stresses in welded joints along with wearing of tool during welding of MMC. The observations of this study provide a basis for future research in the specified domain. 相似文献
3.
Numerical and experimental investigations on the residual stresses of the butt-welded joints 总被引:5,自引:0,他引:5
Welding is a reliable and efficient joining process in which the coalescence of metals is achieved by fusion. Localized heating during welding, followed by rapid cooling, can generate residual stresses in the weld and in the base metal. Estimating the magnitude and distribution of welding residual stresses is important. This study applies thermal elasto-plastic analysis, using finite element techniques, to analyze the thermomechanical behavior and evaluate the residual stresses in butt-welded joints. The residual stresses at the surface of the weldments were measured by X-ray diffraction. The results of finite element analysis were compared with experimental residual stress data to confirm the accuracy of the method. The aim is to present data that may confirm the validity of currently employed fabrication processes in welded structures and even improve them. 相似文献
4.
PH. P. DARCIS H. KATSUMOTO M. C. PAYARES-ASPRINO S. LIU T. A. SIEWERT 《Fatigue & Fracture of Engineering Materials & Structures》2008,31(2):125-136
Arc welding typically generates residual tensile stresses in welded joints, leading to deteriorated fatigue performance of these joints. Volume expansion of the weld metal at high temperatures followed by contraction during cooling induces a local tensile residual stress state. A new type of welding wire capable of inducing a local compressive residual stress state by means of controlled martensitic transformation at relatively low temperatures has been studied, and the effects of the transformation temperature and residual stresses on fatigue strength are discussed. In this study, several LTTW (Low Transformation‐Temperature Welding) wires have been developed and investigated to better characterize the effect of phase transformation on residual stress management in welded joints. Non‐load‐carrying cruciform fillet welded joints were prepared for measurement of residual stresses and fatigue testing. The measurement of the residual stresses of the three designed wires reveals a compressive residual stress near the weld toe. The fatigue properties of the new wires are enhanced compared to a commercially available wire. 相似文献
5.
H.C. Schmidt W. Homberg A.G. Orive G. Grundmeier B. Duderija I. Hordych S. Herbst F. Nürnberger H.J. Maier 《Materialwissenschaft und Werkstofftechnik》2019,50(8):924-939
The cold pressure welding of metals is a joining by forming technique capable of joining both similar and dissimilar metals in their solid state. In this article collective research on the cold pressure welding of metals with the aim of increasing both the overall weld strength and the weld‐ability is presented. The application of innovative strategies based on electrochemical methods for an optimized conditioning of metal surfaces is investigated. The results account for a noticeable increase in the weld strength of steel‐aluminum joints after a surface activation consisting of either an electrochemical roughening or electrodeposition of a bifunctional organosilane thin film. In addition to the surface activation process regimes for the pre‐ and post‐welding heat treatment is investigated. Both weld strength and weld ability are improved due to heat treatments of steel sheets with various coatings and uncoated aluminium. The cold pressure welding is hereby done by incremental rolling, a new design process that allows for the manufacture of linear and curved joints between sheet metal blanks. 相似文献
6.
Fiber laser beam welding has always been a user‐friendly and flexible method to join dissimilar materials despite differences in thermal coefficient. Many industrial applications such as automotive has replaced the conventional joining methods towards this because of the flexibility and reduction in time consumption. In the present study, dissimilar titanium alloy; Ti6Al4 V and aluminum alloy; AA2024‐0 were laser welded through a lap joint technique using a low power Yb‐fiber laser without any additional filler. The influence of welding speed on weld morphology was investigated using optical microscopy (OM) and scanning electron microscope (SEM). The cross‐section of the joints revealed that the fusion zone (FZ) and heat affected zones (HAZ) are wider when welding speed decreases with lower laser power. This result shows that the low power fiber laser has sufficient energy to melt the base materials, forming a liquid bridge to facilitate the smooth flow of molten metal between the top and bottom layer. Therefore, at lower welding speeds with constant low laser power, it was shown that there are possibilities of laser welding between two non‐ferrous metals. 相似文献
7.
Current demands on light weight constructions lead to an increasing use of light weight metals such as aluminum or magnesium alloys as well as fiber reinforced polymers (FRP). Suitable welding methods are necessary to join these dissimilar material groups and to integrate them in engineering structures. At the Institute of Materials Science and Engineering the ultrasonic metal welding technique was successfully applied to realize aluminum sheet/carbon‐fiber‐reinforced polymer (CFRP) ‐ joints. The welding during this process occurs in two steps: First the ultrasonic shear waves lead to a softening and displacement of the polymer matrix out of the welding zone. In the second step a direct weld between the load bearing carbon fibers of the CFRP and the aluminum alloy sheet is generated. A welding time of less than 5 s and no damage of the carbon fibers are important advantages of the process. Actually tensile shear strengths of about 30 MPa were achieved for the joints. By means of light microscopic and SEM investigations the bonding mechanisms can be described in detail. Possible application fields of such welds can be seen in the automotive or in the aircraft industry. 相似文献
8.
Y. Dong Y. Garbatov C. Guedes Soares 《Fatigue & Fracture of Engineering Materials & Structures》2018,41(8):1823-1837
The impact of residual stresses on the fatigue crack initiation life of welded joints is evaluated by the finite element method. The residual stresses of nonload‐carrying cruciform joints, induced by welding and ultrasonic impact treatment, are modelled by initial stresses, using the linear superposition principle. An alternative approach of using modified stress‐strain curves in the highly stressed zone is also proposed to account for the residual stress effect on the local stress‐strain history. An evaluation of the fatigue crack initiation life of welded joints based on the local strain approach is carried out. The predicted results show the effect of residual stresses and agree well with published experimental results of as‐welded and ultrasonic impact treated specimens, demonstrating the applicability of both approaches. The proposed approaches may provide effective tools to evaluate the residual stress effect on the fatigue crack initiation life of welded joints. 相似文献
9.
焊缝匹配影响焊接残余应力的研究 总被引:3,自引:0,他引:3
采用有限元法对相同温度场的焊缝与母材强度和线膨胀系数匹配影响焊接残余和的规律进行了数值模拟,计算结果表明:等强度等匹配的焊缝区纵向残余应力水平高达母材的屈服强度, 相似文献
10.
By using a “GLEEBLE-3800” complex, we perform the experimental investigations of the dynamics of changes in the yield strength
of the metal of the heat-affected zone (HAZ) in low-carbon high-strength steels for various rates of cooling of the welded
joints. The influence of the rate of energy input and thermal welding cycles on the formation of residual stresses in welded
joints of steels with different chemical compositions and properties is determined both experimentally and numerically. The
relationship between the residual stresses, modes of heat input, and the period of holding of the HAZ metal at temperatures
above the point AC3 is established. 相似文献
11.
Brazing Al2O3 to sintered Fe-Ni-Co alloys 总被引:2,自引:0,他引:2
R. M. Do Nascimento A. E. Martinelli A. J. De A. Buschinelli A. N. Klein 《Journal of Materials Science》1999,34(23):5839-5845
Active metal brazing has been widely used to join ceramics to metals, as sound joints are usually achieved in a single step process without special equipment. However, residual stresses may be a potential problem especially upon joining ceramics to alloys with relatively high thermal expansion coefficients. This work investigates the brazing behavior of Alumina (Al2O3) to a sintered Fe-Ni-Co alloy, specially designed to match its coefficient of thermal expansion to that of the ceramic counterpart. The results indicate the presence of an interfacial zone whose microstructure depends on the filler alloy employed. A relationship was established between the microstructure of the interface and the flexural strength of the joints. 相似文献
12.
In a mobile world weight reduction is a predominant target of innovative products. In this context appropriate joining techniques are necessary for the integration of lightweight metals in complex mechanical components. Friction stir welding (FSW) is a newly established well suited process to realize high‐quality lightweight metal joints in solid state. In a research project of WKK the friction stir weldability of similar joints using die casted AZ91‐Mg‐alloy and MRI‐Mg‐alloys was investigated. Additionally the joining of hybrid joints between AZ91 and AA5454 aluminum alloy was performed. To describe and optimize the FSW‐process the welding temperatures and welding forces were recorded online during the process. The investigations of the monotonic properties of AZ91/AZ91‐joints and MRI/MRI‐joints yielded in tensile strength values at the level of the parent materials. For dissimilar joints an extreme increase of the nugget hardness was measured. By SEM investigations and EDX element mappings it could be proved that this is caused by intermetallic phases positioned as thin interlayers in the contact area between the Mg‐ and the Al‐alloy. As a consequence, in hybrid joints failures occur predominantly along these interlayers. Finally, for similar and dissimilar welds corrosion experiments in 5 mass% NaCl solution were carried out. The investigations showed that the nugget area was more susceptible to corrosion then the base material. To understand the corrosion behavior the affected areas were analyzed using SEM and EDX. 相似文献
13.
C. Barbatti Dr. J. Garcia G. Liedl A. Pyzalla 《Materialwissenschaft und Werkstofftechnik》2007,38(11):907-914
Welding of dissimilar materials such as steel and cemented carbides (hardmetals, cermets) is particularly challenging e.g. because mismatches in their thermal expansion coefficients and thermal conductivities result in residual stress formation and because of the formation of brittle intermetallic phases. Laser beam welding of cemented carbides to steel appears as an attractive complementary technique to conventional brazing processes due to its high precision, high process speed, low heat input and the option of welding without filler. Here a laser welding process including pre‐heat treatment and post‐heat treatment was applied successfully to joining as‐sintered and nitrided hardmetals and cermets to low alloyed steel. The microstructure and mechanical properties of the welds are investigated by microscopy, X‐ray diffraction, microhardness measurements, and bending tests. The results reveal that the three‐step laser beam welding process produced crack‐free and non‐porous joints. Nitridation of the cemented carbides results in a significant reduction of the amount of brittle intermetallic phases. The mechanical properties of the joints are competitive to those of the conventional brazed steel‐cemented carbide joints. 相似文献
14.
《材料与设计》2015
Manufacturing process of pressure vessels used in high-temperature applications normally needs employing dissimilar metal welds (DMWs) between austenitic and ferritic steel. However, high amount of thermal stresses at the welds are induced due to differences in coefficient of thermal expansion between the types of steel. This study investigates the evaluation of welding residual stresses in a pressure vessel manufactured by DMW of 316 L stainless steel shell to A106 carbon steel caps as well as similar welding of stainless steel shells. By using longitudinal critically refracted (LCR) ultrasonic waves, the residual stresses are experimentally measured. The ultrasonic method is based on acoustoelasticity law by which the ultrasonic wave velocity could be connected to the material stress. By changing the frequency in which the ultrasonic transducers are working, the LCR waves are able to penetrate in various depths of the material in order to measure the sub-surface residual stresses. Hence, four main aspects are considered in this study: (I) stress evaluation of the DMW; (II) sub-surface stress measurement; (III) stress evaluation of longitudinal weld and (IV) stress measurement in cross weld. It is demonstrated that the residual stresses of the DMW pressure vessel could be comprehensively evaluated by using the LCR method. 相似文献
15.
Chao Chang Gesheng Xiao Erqiang Liu Jinbao Lin Xuexia Zhang Xu Long 《Materials Science & Technology》2019,35(8):986-992
Owing to the microstructural inhomogeneities and residual stresses that are generated during welding, welded joints are the weakest parts of structures. Nanoindentation, a non-destructive technique, is commonly used to analyse the local mechanical properties and residual stresses in welded joints. However, the pile-up effect is often neglected during the nanoindentation procedure, which results in inaccurate measurements. In this study, an alternative procedure, based on a previous study, was used to measure the local mechanical properties and residual stresses in metal inert gas (MIG) welded joints. Moreover, a new equation is proposed for estimating the residual stresses. 相似文献
16.
Yashar Javadi Khaled Azari Seyed Mahmoud Ghalehbandi M. J. Roy 《Research in Nondestructive Evaluation》2017,28(2):101-122
Fusion welding is a joining process widely used in the industry. However, undesired residual stresses are produced once the welding process is completed. Post-weld heat-treatment (PWHT) is extensively employed in order to relieve the welding residual stresses. In this study, effect of PWHT time and temperature on the residual stresses of a ferritic stainless steel is investigated. Residual stress distributions in eight welded specimens were measured by using an ultrasonic method. Ultrasonic stress measurement is a nondestructive method based on acoustoelasticity law, which correlates mechanical stresses with velocity of an ultrasonic wave propagating within the subject material. The ultrasonic wave employed could be longitudinal or shear wave produced by the longitudinal (normal) or transverse (shear) transducers, respectively. Ultrasonic stress measurements based on longitudinal waves use longitudinal critically refracted (LCR) waves in this direction, while shear wave methods use an ultrasonic birefringence phenomenon. The results show that the effect of PWHT can be successfully inferred by both longitudinal and shear wave methods, but the former is found to be more sensitive to stress variation. Furthermore, the distribution of subsurface residual stresses is found to be more distinguishable when the LCR method is employed. 相似文献
17.
Ultrasonic welding of thermoplastic composites is a very interesting joining technique as a result of good quality joints, very short welding times and the fact that no foreign material, e.g. a metal mesh, is required at the welding interface in any case. This paper describes one further advantage, the ability to relate weld strength to the welding process data, namely dissipated power and displacement of the sonotrode, in ultrasonic welding of thermoplastic composite parts with flat energy directors. This relationship, combined with displacement-controlled welding, allows for fast definition of optimum welding parameters which consistently result in high-strength welded joints. 相似文献
18.
Using examples from the adhesive bonding and ultrasonic welding technique shows how various methods of vacuum‐assisted analysis can contribute to explain joining mechanisms and derive optimization potentials for strength and durability of composites. Employing Time‐of‐Flight Secondary Ion Mass Spectrometry (ToF‐SIMS) to characterize epoxy‐adhesives, locally resolved and quantitative structural informa‐tions can be achieved. Multivariate data analysis methods prove to be very helpful here. Analytical investigations with high spatial resolution at the interface of ultrasonic welded aluminium joints provide structural and chemical data and allow the characterization of the bonding zone in detail. Thus the physical and chemical processes occurred during the welding process can be reconstruct. The increase of strength and longterm durability of ultrasonic‐ or induction welded hybrid joints (aluminium and carbon‐fibre reinforced thermoplastics) can be attributed to micromechanical interlocking of the CF‐matrixpolymer with Al‐oxide‐layer. 相似文献
19.
《Engineering Failure Analysis》2001,8(1):15-27
Micro-crack development in welds, including repair welding, of the tube to tube-sheet region of industrial boilers is not an uncommon problem. Often such cracking is exacerbated by stress corrosion cracking or thermal fatigue, in which the residual stresses associated with welding can play a major role. In this paper, a custom built, but robust, air abrasive centre hole drilling facility was used; which induced negligible machining stresses. This system was modified to attach to the (vertical) tube sheets of boilers on site, and to sample residual stresses in the tube to tube-sheet welds, of both conventional circumferential fillet welds of protruding tubes as well as recessed ‘J’ configuration type. The experimental test programme evaluated transverse and circumferential profiles of the residual stresses. Global post-weld heat treatment (PWHT) of a whole boiler, indicated substantial (75%) reductions in the tensile peak residual stress. A localised PWHT technique, using a 1 kW incandescent light source inserted into the tube, easily achieved the requisite temperatures and heating rates, but led to significant increases in local residual stresses. The implications of such localised PWHT techniques on residual stress and consequent service life, are therefore of vital importance with regard to plant integrity and safety. 相似文献
20.
M. TAKAHASHI N. OKABE X. ZHU K. KAGAWA 《Fatigue & Fracture of Engineering Materials & Structures》2003,26(5):391-398
ABSTRACT Residual stresses generated by the mismatch of thermal expansion coefficients of ceramics and metals affect the strength of ceramic–metal joints. An interlayer metal can be inserted between the ceramic and metal in order to relax this stress. An analysis was carried out of the residual stresses produced during joint‐cooling and in 4‐point bending tests. The effects of interlayer thickness on ceramic–metal joint strength were then studied by considering a superimposed stress distribution of the residual stress and the bending stress. Finally, joint strength was estimated from fracture mechanics and strength probability analysis by considering the residual stress distribution, defect size and position of pre‐existing defects in the ceramic parts. As a result of this study, we suggest an optimum material selection and interlayer thickness for ceramic–metal joint structures. This approach is generally suitable for the design of electrical and mechanical structures. 相似文献