QUARTERLY JOURNAL OF THE JAPAN WELDING SOCIETY
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PRINT ISSN: 0288-4771

QUARTERLY JOURNAL OF THE JAPAN WELDING SOCIETY Vol. 40 (2022), No. 4

  • A Novel Dissimilar Metal Joining Technology of Cu and Al Thin Plates Utilizing Eutectic Melting by Frictional Heat

    pp. 169-174

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    DOI:10.2207/qjjws.40.169

    A novel butt-joining technology of Cu and Al thin plates was developed, in which the edge of a Cu plate over the edge of an Al plate were pressed by the rotary tool with a truncated cone-shape in the atmosphere. Joining experiments were performed using 1mm thick C1020 plates and 1mm thick A1050 plates. The joint quality was investigated by observation and analysis of the joining interface and by tensile testing of dumbbell specimens fabricated with the Cu-Al joined bodies. The results clarified that the eutectic melting between Cu and Al was caused by pressure and frictional heat, and that the overlapped portion deformed into a butt joining shape while extruding the eutectic melt from the joining interface. A slant joining interface was formed between the C1020 and A1050 plates, and the film-like layer presumed to be consisted of CuAl2 and CuAl were generated at the entire joining interface. The thickness of the layer ranged from 0.6 to 1.3μm. The average ultimate tensile strength of the dumbbell specimens was 92MPa, and the section of A1050 approximately 2mm away from the joint fractured in the tensile testing. This indicates that the Cu-Al joint had a higher strength than 92MPa.
  • Simulation-Based Fracture Control Design of Knock-Off Bolts for Bridges

    pp. 175-185

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    DOI:10.2207/qjjws.40.175

    The purpose of this study is to develop a simulation method for predicting the effect of shape and dimension on shear strength, deformability and fracture behavior of knock-off bolts with circumferential notch and axial hole. Shearing tests for four types of knock-off bolts with various notch depth and axial hole diameter for constant cross-sectional area are conducted. Shear strength of these bolts is almost same value due to same cross-sectional area. On the other hand, the knock-off bolt with a shallower notch has larger deformability. Ductile cracking from notch of knock-off bolts unloaded at maximum load is observed. It is necessary for predicting shear strength and deformability of knock-off bolts to consider ductile crack initiation and growth. Stress states near notch tip of knock-off bolts depend on the angle to loading direction and are influenced by notch depth. The tensile/shear combined stress state dependent ductile damage model is proposed for predicting ductile crack initiation and growth from notch of knock-off bolts. The shear strength and deformability predicted by simulation based on the proposed ductile damage model present good agreement with experimental results. The effect of shape and dimension of knock-off bolt on shear strength and deformability is estimated by means of the developed simulation method. It is demonstrated that cross-sectional area and ratio of notch depth to bolt radius are dominant factor for shear strength and deformability, respectively.
  • Formulation of Effective Thickness for Predicting CTOD Value of Heavy Thickness Plates using Reduced Thickness CTOD Specimens

    pp. 202-209

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    DOI:10.2207/qjjws.40.202

    Demand for heavy thickness plate is increasing in offshore structure application and fracture toughness represented by CTOD is one of the most important properties for these heavy thickness plate. CTOD tests shall be conducted as full thickness of the material but it takes a lot of time and cost especially with the thickness exceeds 100mm. It is important to estimate the CTOD of full thickness plate using reduced thickness CTOD tests to accelerate material development in the laboratory. As a conventional estimating method for full thickness CTOD using the reduced thickness CTOD test, only the difference of crack driving force between full thickness and reduced thickness specimens have been considered. However, it is necessary to consider crack driving force in plate thickness direction for full thickness and reduced thickness specimens. As the first step, the influence of parameters on effective thickness considering crack driving force in plate thickness direction for the base metal is investigated in this study. Finally, formulation of effective thickness is proposed on the base of the influential parameters.
  • A method to determine surface tension for axisymmetric meniscus in gravity from positional coordinates and tangential angles of arbitrary two points on liquid surface

    pp. 210-215

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    DOI:10.2207/qjjws.40.210

    A method is proposed to evaluate surface tension for axisymmetric meniscus in gravity. The method requires positional coordinates and tangential angles of arbitrary two points on liquid surface. A theory of the liquid in gravity is used to derive a differential equation. All of the equations are normalized by a parameter determined from the gravity, the density, and the surface tension of the liquid. Numerical calculation is carried out to show that the present model expresses various kinds of axisymmetric meniscus. The present method is proposed based on the theory and investigated by the experiment using pure water with a borosilicate glass rod. The positional coordinates and the tangential angle of the surface points are obtained from a photograph of the meniscus. The method shows a successful evaluation of the surface tension. The present method is compared with conventional methods and discussed from a view point of minimum information required to evaluate the surface tension. It is expressed that the Hutzler’s method is a special case of the previous method and the previous method is a special case of the present method. The present method is suggested useful in various meniscus tests, such as sessile drop tests, pendant drop tests, Wilhelmy rod tests, wetting balance tests, meniscograph tests, etc., since it requires only information on meniscus shape, i.e., the position and the angle of arbitrary two point on it.
  • Effect of strength of steel sheets on tensile shear strength and failure mode of dissimilar joint of spot welds

    pp. 216-225

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    DOI:10.2207/qjjws.40.216

    Advanced high strength steel sheet (AHSS) is widely used in the automotive body for weight reduction and the improvement of crash performance. In general, weldability and formability of steel sheet tends to decline as steel strength increases. Hot stamping is a technique that achieves both formability and strength of steel sheet, and TS1500MPa class hot stamped steel sheet is applied to many vehicle models. On the other hand, since the joint strength characteristics of the spot weld are dominated by the melt-solidified zone and weld heat affected zone, there is a concern that performance of spot welded joints will decline as steel strength increases. In other words, in order to further expand the application of AHSS, it is very important to have knowledge about the characteristics of spot welded joints. In this report, we investigated the TSS of the TS1500MPa class hot stamped steel sheet, focusing on the characteristics of tensile shear joints. Then, we compared the joint strength and failure position of the same kind material joints and the dissimilar material joints with the TS1500MPa class hot stamped steel sheet in case of the plug failure. As a result, it was found that TSS of dissimilar material joints depend on base metal strength on lower strength steel side. However, fracture occurred on the TS1500MPa class hot stamped steel side except for joints with large difference of base metal strength. The mechanism is thought that the effect of strain concentration at the edge of nugget on the TS1500MPa class hot stamped steel side due to the increase of rotational deformation around the nugget.
  • Effect of strength of steel sheets on peel tensile strength and failure mode of dissimilar joint of spot welds

    pp. 226-237

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    DOI:10.2207/qjjws.40.226

    Advanced high strength steel sheet (AHSS) is widely used in the automotive body for weight reduction and the improvement of crash performance. Peel tensile strength of spot welds tends to decrease as the steel sheet strength increases. Therefore, in order to further expand the application of AHSS, technology to prevent fracture of spot welds is required. In order to achieve that, it is necessary to understand the characteristics of spot welded joints and clarify the controlling factors. However, most of the conventional joint strength evaluations have been conducted on the same kind material joints, and there are few systematic studies on the joint strength and fracture mode of dissimilar material joints that are often used in actual vehicles. Therefore, the purpose of this study is to obtain a guideline for grasping the characteristics of dissimilar joints in case of the plug failure.Using various joint shapes, we compared the peel tensile strength and failure position of the same kind material joints and the dissimilar material joints with the TS1500MPa class hot stamped steel sheet. As a result, it was found that the deformation behavior of the test piece affects the joint strength and fracture position of the dissimilar material joints. Specifically, in dissimilar material joints, cross tension joints and double cup-shape tension joints tended to break on the TS1500MPa class hot stamped steel side. On the other hand, L-shape tension joints broke on the lower strength material side. From these results, it is considered important to understand their deformation behavior in order to analyze and predict the fracture phenomenon of spot welds in actual vehicles and automotive parts.
  • Morphological Characteristics of Widmanstätten Austenite Formed in Laser Beam Welds of Lean Duplex Stainless Steels

    pp. 1WL-4WL

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    DOI:10.2207/qjjws.40.1WL

    The Widmanstätten austenite is well known precipitates at grain boundaries in duplex stainless steel welds, making the performance of welded joints degraded. That is affected by its morphology. However, the three dimensional microstructure has not been made abundantly clear. Almost all the studies on the morphology of Widmanstätten right now were based two dimensional only. In order to identify the morphology of Widmanstätten austenite, the three dimensional structure was observed by the serial sectioning three dimensional method. The Widmanstätten austenite in the same area observed on different cross-sections shows different morphologies and arrangements. And through the EBSD analysis, the relationship between part of the granular austenite in the ferrite grain and the Widmanstätten austenite precipitated at the grain boundary was determined.

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