Diode-laser-to-waveguide butt coupling

A diode-laser-to-waveguide butt-coupling model is described. The model takes into consideration the Fabry-Perot reflection and transmission of the étalon formed by the laser front facet and the waveguide entrance facet. The model predicts coupling efficiency and the coupled-power fluctuations that occur versus the separation between the laser and the waveguide. Calculations performed for Fabry-Perot-laser-to-KTP waveguide coupling show that the transverse and the angular alignment tolerances of the waveguide can be increased when the waveguide entrance facet is antireflection coated. The longitudinal alignment tolerance of the waveguide can be increased by use of an index-matching gel between the laser and the waveguide.     

Friction stir welded butt joints optimization

Friction stir welding is an emergent technique that still lacks optimization studies in the literature. Optimum parameters are of prime importance for future investigations, as it will allow for consistent and sound welds. This is of even greater relevance for industrial applications, as for friction stir welding to become a mainstream joining technology. This paper presents an optimization study of friction stir welded butt joints through the Taguchi method. The most influent welding parameters and their trends were identified. The process optimization for the selected aluminium alloy was achieved and the best parameters combination to accomplished quality welds was selected. The parameters combination that lead to higher mechanical stiffness were: 1000 min^–1, 290 mm/min, 0.15 mm from the probe to the root surface and a shoulder/probe diameters ratio of 2 (shoulder diameter of 12 mm). Equations to estimate joint properties were derived by multiregression.     

Life prediction of butt welds containing welding defect

In the present study, the welding defects are divided into two types, i.e. the crack-like defect and the uncrack-like defect, based on the experimental and analytical results, and the criterion for distinguishing the defect type is tentatively proposed. The life predicting methods are given to accurately compute the fatigue life of butt welds containing different types of defect. The computation and the experiments show that the fatigue crack propagation life of the butt welds containing the crack-like defect is approximately equal to the total fatigue life and the fatigue crack initiation life can be neglected. Therefore, the fatigue life of this kind of welds is greatly decreased. On the other hand, the fatigue life of the butt welds containing uncrack-like defect consists of two phases, i.e. the fatigue crack initiation life and the fatigue crack propagation life and the fatigue crack initiation life occupies a greater portion, which cannot be neglected. In order to accurately predict the fatigue life of welded elements, not only the defect size but also the defect type should be determined. Consequently, the technology and the equipment for the nondestructive detection need to be highly developed.     

Finite element analysis of laser beam-welded butt joints

Thermal distortion of tailored blanks (TBs) during welding usually leads to a poor formability in the subsequent plastic deformation of TBs, and the welding distortion becomes especially serious in TBs consisting of different thickness plates. In this investigation, finite element method was applied to investigate the welding distortion of TBs with different thickness plates produced by laser beam welding. At the beginning, a 3D heat source model was built and verified by experimental results. Then, the following simulation results showed that the residual stresses generated in the thick plate side of the TBs were higher than those in the thin one. The varied reduction of heat input along the thickness direction for those two base plates can explain for this.     

Crack resistance of homogeneous and inhomogeneous butt welded joints

We describe the methods used for the evaluation of strength of butt welded joints according to their crack resistance both by the axial tension of small-sized cylindrical specimens with circular cracks and three-point bending of beam specimens with lateral cracks induced in low-or medium-strength surfacings welded into the high-strength bases of these specimens. We perform the comprehensive investigation of the near-weld zone of butt welded joints, where the lowest crack resistance is exhibited by the metal of the zone of fusion and the highest crack resistance is detected for the source material independently of the type of tested specimens. Metals of the weld and the heat-affected zone are characterized by higher values of crack resistance than the zone of fusion and lower values of crack resistance than the source material. By analyzing, as an example, the case of axial tension of a tubular specimen with internal circular crack in the surfacing, we study the crack resistance of seven types of inhomogeneous welded joints depending on the mode of thermal treatment of 35 and St. 3 steels after normalization and 09G2S, 20Kh, and 30KhGSA steels after hardening, medium tempering, and normalization. __________ Translated from Problemy Prochnosti, No. 4, pp. 62–76, July–August, 2007.     

闪光对焊技术研究现状及发展趋势

详细介绍了闪光对焊工艺和设备的研究及其应用现状,探讨了闪光对焊的机理,并分析了闪光焊接过程产生的主要缺陷,讨论了其预防措施.最后着重介绍了闪光对焊技术的发展趋势.     

Fatigue performance characterization of a composite butt joint configuration

Fatigue performance characterization of a composite butt joint configuration was studied. The study focused on failure mode, damage evolution, and tensile stiffness degradation analyses. Effects of surface ply orientation, doubler thickness, joint attachment, and defect on the joint fatigue performance were evaluated. The bonded-bolted joints with two-row fasteners installed in each overlap section had an extremely high fatigue performance. For such a bonded-bolted joint configuration with thick doubler, a minor disbond defect improved, rather than reduced, the joint fatigue performance. This outcome was examined using the corresponding joint tensile stiffness degradation curves, and a dominant failure mechanism was identified based on damage characteristics. The study showed that the butt joint made using appropriate elements, such as a thick doubler with two-row fasteners installed in each bonded overlap section, could have very good fatigue performance regardless of the presence of a minor disbond defect.     

Diode-laser-to-waveguide butt coupling: extremely short external cavity

An ultrashort composite cavity (相似文献   

Prediction of welding distortion in butt joint of thin plates

This paper investigates distortions and residual stresses induced in butt joint of thin plates using Metal Inert Gas welding. A moving distributed heat source model based on Goldak’s double-ellipsoid heat flux distribution is implemented in Finite Element (FE) simulation of the welding process. Thermo-elastic–plastic FE methods are applied to modelling thermal and mechanical behaviour of the welded plate during the welding process. Prediction of temperature variations, fusion zone and heat affected zone as well as longitudinal and transverse shrinkage, angular distortion, and residual stress is obtained. FE analysis results of welding distortions are compared with existing experimental and empirical predictions. The welding speed and plate thickness are shown to have considerable effects on welding distortions and residual stresses.     

An experimental investigation on flash butt welded rails

In this paper, experimental studies performed for flash butt welded rails used in Turkish railways network having 49E1 and 60E1 rail sections are presented. These studies comprise of full-scale laboratory tests such as four point bending fatigue and three-point slow bending tests, as well as related instrumentation of test specimens and data measurement. Fatigue and bending tests are prepared and carried out in accordance with EN 14587-2 standard. The fracture surfaces of the welded samples are examined to identify the associated failure modes. The fatigue test results are superimposed on a S–N diagram derived from earlier results reported as a part of the European Commission steel rails research project. A best fit curve following an exponential function is derived to describe the load deflection behavior of the weld under the slow bend testing conditions. It is shown that a single component of the equation defining the best fit curve is the factor controlling the scattering in the non-linear part of the load deflection curve, and hence control of this parameter can also be used to impart consistency to the welding process.     

Flash butt resistance welding for duplex stainless steels

Duplex stainless steels were welded using flash butt resistance welding with temperature controlling system. Flash butt resistance welding is consisting of two stage processes of flash action and contact resistance. First stage is flashing action. The specimen produced flashing or arcing across the interface of the two butting ends of the specimens. Fine particles of metals near the surface were burned out towards the opposing surface of the specimen irregularity and then the melted particles were deposited on the surface. The second stage is resistance welding. The solid state bonding was performed in the region around the deposited particles. The cross-sectional microstructure of the weld bond region was observed using microscopy. The microstructure showed two types of a deposited fine particles region and a solid state bonding region. The grain growth was hardly observed in the weld region and the heat-affected zone. The tensile strength and the impact energy increased with increasing heating time up to 1373 K because of increasing fine grained deposited metal.     

Novel approach to the impact testing of butt fusion-welded joints

Charpy impact tests have been carried out on specimens removed from the joint region in butt fusion-welded polyethylene pipe. In order to ensure that crack initiation occurs precisely at the weld line, a novel method of notching has been used. G _c data have been derived from these tests, which were conducted at temperatures of – 150 and 23 °C. Results obtained from pendulum impact and instrumented falling weight tests show consistent differences, probably attributable to the speed of impact. Data have also been obtained for the parent unwelded material.     

铝/钢搅拌摩擦焊对接焊缝组织及机理研究

为了提高Q235钢板和6082-T6铝合金对接的连接强度,采用搅拌摩擦焊进行对接焊接.研究了不同尺寸和形状的搅拌头、转速、焊接速度和偏移量等对铝钢对接焊缝组织的影响,进而优化了搅拌摩擦焊工艺.实验结果表明:不同形状的搅拌头影响接头"钉子"形状,接头的不同位置处由于受到不同热循环和搅拌导致晶粒尺寸不同,从而影响接头的力学性能.当搅拌针旋转速度260 r/min,焊接速度16 mm/min,针头偏向铝侧0.2 mm时,所得焊缝的拉伸强度为141.204 MPa,为最佳工艺参数.在此最优参数下获得过渡层的厚度约为8μm,界面的主要成分是Fe Al3.     

Resistance upset butt welding of austenitic to martensitic stainless steels

In this research, joining austenitic to martensitic stainless steels and effect of welding power on microstructure and mechanical properties of the joint were investigated. Microstructure of the weld was studied using optical microscopy (OM) and scanning electron microscopy (SEM). Energy dispersive spectroscopy (EDS) linked to SEM was used to determine chemical composition of phases and distribution of chromium (Cr), nickel (Ni) and iron (Fe) at the joint interface. Microhardness and tensile strength tests were performed. Finally fracture surface of samples were studied by SEM. Results showed that an interlayer composed of 80% ferrite and 20% martensite has formed at the joint interface and there were three different zones in the heat affected zone (HAZ) of two steels. Different forms of austenite phase including widmanstatten austenite (W_γ), allotriomorphic austenite (A_γ) and intergranular austenite (I_γ), delta ferrite (δ-ferrite) and chromium carbide (Cr₂₃C₆) have formed in the HAZ of austenitic stainless steel. Fractography of tension samples indicated that in all samples fracture occurred in austenitic stainless steel HAZ. The strength and hardness of the joint increased and HAZ length decreased with increasing of welding power.     

Strength of vibration-welded modified polyphenylene oxide structural foam butt joints

Tensile tests on 120 Hz vibration-welded butt joints of specimens cut from 6.35 mm thick plaques of modified polyphenylene oxide (M-PPO) structural foam have shown that 5% and 25% density reduction M-PPO structural foams weld well. This has been shown to be true for both foam-to-foam and skin-to-foam welds. The weld process phenomenology for these foams is shown to be identical to that for all neat resins: the penetration-time curve exhibits the four phases associated with vibration welding. The effect of weld pressure is not as significant as for solid M-PPO, for which increases in weld pressure are known to cause large decreases in weld strength.     

Surface residual stress evaluation in double-electrode butt welded steel plates

Surface residual stress evaluation for double-electrode welding was studied. The stresses were monitored after each operational step: positioning, implementing of constraints, welding and constraints removal. The measurements were performed at the deposited metal, heat affected zone, base metal close to the weld joint and along the plate using the X-ray diffraction method. It was observed differences in the stress evaluations for double-electrode welding which resulted in lower bending distortions and higher values of surface residual stresses, compared with single-electrode welding. This behavior is associated with the stress distribution just after the welding processes in both heat affected zone and base metal close to the fillet for double-electrode welding. The main results from the laboratorial tests indicated lower values of the bending distortions for double-electrode welding compared with the single-electrode. In relation to the residual stress, the double-electrode welding generated, in general, higher stress values in both longitudinal and transversal directions.     

Fatigue tests of notched specimens made from butt joints at steel

The weld toe as well as the weld root of joints acts as a geometrical notch, which decreases the fatigue strength of welded components. Local approaches used for fatigue assessment account for the local stress concentration when referring to the notch stress as a fatigue parameter. This applies also to the approaches based on the notch stress intensity factor like, for example, the averaged strain energy density, neglecting the actual notch radius and considering a sharp notch as a simplification. A uniform S‐N curve valid for different types of welded joints and failure locations was derived from re‐analyses of fatigue test results as documented in literature. The fatigue tests described in this paper aimed at validating that energy‐based S‐N curve by dedicated tests on artificially notched specimens. At first, four parameters were investigated in order to estimate their influence on the fatigue strength and to select appropriate notch geometries for the final step of the test campaign. The advantages of these tests are that both the exact notch geometry and the local stress range at the notch, including misalignment effects, were identified and considered in experimental data analysis. This paper presents the results of the rather comprehensive testing activities and comparisons with the design‐S‐N curve mentioned, yielding unexpected fatigue behaviour. This can be explained by the short crack propagation life.     

Static strength of a composite butt joint configuration with different attachments

The static failure behaviour of a composite single-strap joint configuration using three different attachments was studied experimentally. The attachments used were: adhesive bonding; mechanical bolting; and bonded-bolted joining. The dimensions of the composite butt joint used were determined based on actual joint configurations in aircraft structures, such that the test results would be beneficial to both the academic exploration and practical engineering application for advanced composite joint design and analysis. A damage evolution process was presented for the bonded-bolted butt joints based on the observed stress versus displacement curves and associated failure modes from all the related butt joints with the three attachments. An approach was then proposed for estimating the ultimate tensile strength in the bonded-bolted joints.     

Reliability against fracture of butt welds as inferred from inspection data

Butt welds under static stress may suffer fracture due to a crack growing quickly from some defect in the weld. Nondestructive inspection for defects needs a rational criterion for acceptance of a weld. The paper demonstrates that recent results in structural reliability theory applied to defect fracture systems may constitute a basis for a criterion for highly reliable welds. It takes into account uncertainty from several sources. Essential uncertainty is due to the high degree of idealization of the widely used standard fracture mechanical criterion of crack initiation. Also the indirect measurement of the defect sizes contributes significantly. Finally the statistical uncertainty due to small sample sizes cannot be neglected. Besides the distribution of defect sizes the number of defects in the weld has importance. Only an estimate is needed of the mean number of defects. Statistical uncertainty of this estimate has very low importance for the total reliability of the weld.