Key Engineering Materials Vols. 353-358

Abstract: High purity alumina/stainless steel joints were produced via activated molybdenummanganese (Mo-Mn) route using 72Ag-28Cu solder. Microstructures of the metallized ceramic and joint sections were observed by scanning electron microscopy. Joint strength was tested by shear-loading method. Some process factors were characterized and analyzed, which include temperature, holding time and heating and cooling rate in ceramic metallization process. The effects of Ni plating and succedent annealing were also investigated. Experimental results show that, migration of glassy phases is the main mechanism of the ceramic metallization. Glass migration direction is from metallizing layer to ceramic side. In the ranges of temperature and holding time of metallization, joint strength firstly increases and then falls with temperature raising and time extending. More fully sintered metallizing layer can be obtained while the temperature increases from 1200oC to 1500oC, and the time prolongs from 30min to 60min. Over-sintering of the metallizing layer will take place with metallizing temperature of 1600 oC and overlong holding time of 70min, which reduces the joint strength. The slower heating and cooling rate, and the annealing after Ni plating both help enhance the seal strength, due to relieving or eliminating interlayer residual thermal stress. However, too slow heating and cooling rate, such as 5 oC /min, is equivalent to overlong holding time and finally also decline the strength. A thin Ni coating helps solder wet metallizing surface, and stops solder erode metallizing layer.

Abstract: This paper conducted the outer constraint test of Coffin thermal fatigue and studied the deformation behaviors of microstructure for two kinds of welding deposited metals, they are 3Cr2W8 and HM3. The experimental results show that the thermal fatigue deformation belongs to multiple slip systems and the heterogeneous deformation mainly concentrates around the second phase particles. Moreover, it is found that the cracking initiation relates to the separation between the second phase particles and base body, void and micro-cracking formation.

Abstract: The design of small-sized single pass boilers is usually based on the construction code for small-sized boilers, in Japan. Design methods in this construction code and other country codes have not been clearly defined, although most of small-sized boiler’s headers are constructed from two concentric circular shells and cover plates. Therefore, Finite Element Analysis (FEA) with a PC and measurement by strain gauges are mainly used in strength design of these boilers. A T type welded joint of SS400 was adopted for the header of small-sized single pass boilers was studied. The stress concentration was evaluated by the FEA, and S-N curves were re-drawn using maximum elastic stress, Ktσmax.

Abstract: The hot spot stress or the notch strain alleviates the welding detail dependency of S-N curve to some extent. This paper suggests a new stress model which alleviates the dependency further, thus the fatigue strengths of several welding details of same material can be evaluated with the S-N curve of the base material. A stress at the hot spot of a weld joint is decomposed into two components; linear rising one, and rapid rising one which is inversely proportional to the distance from the hot spot. For the stress decomposition, a formula is proposed with which the configuration of stress distribution near a hot spot is fitted exactly. The new stress model makes use of a geometric characteristic of the stress distribution curve by the formula. The stress model is applied to five different weld joints. As the result, the experimental fatigue data are plotted very closely to the S-N curve of the base material

Abstract: In an early stage of design process for the lower arm in automobile suspension module, an easy and fast FE modeling, static and durability analysis supported by parametric study considering its geometric changes are required. The FE modeling support system has been developed, which is implemented on the platform of MSC.Patran. The CAD file produced by taking into account of automatic 3D parametric model in CATIA V5 can be transferred to this system. For the process automation of various design activities including the parametric study, human interactions are excluded practically, in which all processes are dealt with the XML-wrapper, and in- and output data are linked each other and treated in the engineering data management. The developed FE modeling support system reduces time and cost to design and analyze engineering problems.

Abstract: Two types of load carrying fillet weldment, which are typical weld joints in ship structures, were examined under out-of-plane bending load by using structural stress approach. Finite element analyses using both solid and shell elements models have been performed for the assessment of fatigue strength. Basis for the derivation of structural stress method is discussed in detail. The calculated structural stress values for the fatigue strength evaluation of load carrying fillet weldments are independent of mesh size. In this study, drawbacks and doubts associated with applying the structural method such as the guidance of virtual node method and the application of three-dimensional equilibrium condition for solid model have been discussed accompanied by various case studies. In order to solve the problem of the solid model, the alternative method for solid model by using the equilibrium condition of the nodal force has been introduced.

Abstract: This study performed tensile test using small-size flat specimen and ball indentation test at room temperature to characterize the local tensile properties of bi-metallic weld joints. The weld specimens used were fabricated by joining between SA508 Gr.3 ferritic steel and Type 316 stainless steel with Alloy 82 buttering on the ferritic steel side and Alloy 82/182 weld metal. The test results showed that yield stress (YS) of weld metal was slightly higher than that of Type 316 and smaller than that of SA508 Gr.3, and ultimate tensile stress (UTS) of weld metal was similar as those of Type 316 and SA508 Gr.3 base metals. Also, the values of YS and UTS of buttering layer (Alloy 82) were nearly same as those of weld metal. Heat-affected-zones (HAZs) showed higher YS and UTS values compared to their base metals. Especially, the strengths of SA508 Gr.3 were significantly higher than those of surrounding materials. Also, it was known that the ball indentation test reasonably measured the local YS and UTS of bi-metallic weld joints.

Abstract: During the welding process to make welded joints, residual stress is inevitably generated and weld metal is used. Welding Residual stress is influenced on the behavior of welded joints under monotonic and cyclic loading. And the weld metals used in welding process have different mechanical characteristics than structural steels. Therefore, to accurately predict the hysteretic behavior of welded joints, the effect of residual stress and weld metal must be investigated. In this paper, the residual stress distribution in a welded tubular T-joint was investigated by carrying out three-dimensional non-steady heat conduction analysis and three-dimensional thermal elastic-plastic analysis. To consider a effect of base metal(SM490) and weld metal(E71T-1), a cyclic plasticity model was formulated based on monotonic and cyclic loading tests. And the formulated model was applied to three-dimensional elastic-plastic finite element analysis. The effect of residual stress and weld metal on hysteretic behavior of a welded tubular T-joint was investigated by carrying out numerical analyses considering residual stress and cyclic plasticity model of base metal and weld metal respectively.

Abstract: This paper proposes a new semi-rigid detail used high-strength bolts for use in earthquake resistant structures. These specimens were single-side beam-to-column assemblies that are representative of exterior beam-to-column connections, and they were composed of identical beam and column but had the different connection details, respectively. All beam-to-column assembly required no welding. Specimen 1 (TSD) was standard Top-Seat-Double-web-angle but specimen 2 (MTSD) was made by modified shape. Two high-strength bolted steel semi-rigid connections were prepared and cyclic load was applied to each test specimen using displacement control. The cyclic load and displacements, moment-rotation plots, and the deformation pattern or failure modes for all the test cases are presented. The strength, stiffness, energy, and ductility of the tested connections are compared to each other.

Abstract: In this paper, the welding residual stress state and the distribution of 5A06 aluminum alloy welded plate were determined before and after tension loading by means of hole-drilling method. Results show that the applied load can reduce the residual stress obviously and drive it to an even state. But the local strain near the weld is higher than other positions far from the welding central line relatively.