• Transactions of Materials Processing
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• v.28 no.3
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• pp.145-153
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• 2019

The objective of this study is to analyze the mechanical splicing characteristic of the threaded bar according to the contact conditions of the transverse rib. In order to consider the contact conditions of the rib, selection of the main variables including the gap of the core diameter ($l_c$), rib angle (${\theta}$), and the number of contacts ($C_N$) of transverse rib was done. So as to analyze the splicing characteristic of the D51 threaded bar, a finite element (FE) simulation of the tensile test was conducted using the designed D51 threaded bar and coupler. Through FE simulation results, it was verified that the mechanical slicing characteristics varied based on the main design variables ($l_c$, ${\theta}$, and $C_N$). It was further confirmed that it was important to determine the $C_N$ in consideration of $l_c$. Additionally, the tensile test results of the D25 and D51 threaded bar combined with the couplers were similar to FE simulation results. Furthermore, to quantitatively evaluate FE simulation and test results, the calculation equation for the contacted projection area ratio (R) of the transverse rib was proposed. To secure a mechanical splicing joint of the threaded bar, it was established that the R calculated using the proposed equation had to be greater or equal to 40%.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.20 no.1
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• pp.49-59
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• 1984

Optimizing investigation of characteristics of underwater welding by a gravity type arc welding process was experimentally carried out by using six types of domestic coated welding electrodes for welding of domestic marine structural steel plates (KR Grade A-1, SWS41A, SWS41B,) in order to develop the underwater welding techniques in practical use. Main results obtained are summarized as follows: 1. The absorption speed of the coating of domestic coated lime titania type welding-electrode became constant at about 60 minutes in water and it was about 0.18%/min during initial 8 minutes of absorption time. 2. Thus, the immediate welding electrode could be used in underwater welding for such a short time in comparison with the joint strength of in-atmosphere-and on-water-welding by dry-, wet-or immediate-welding-electrode. 3. By bead appearance and X-ray inspection, ilmenite, limetitania and high titanium oxide types of electrodes were found better for underwater-welding of 10 mm KR Grade A-1 steel plates, while proper welding angle, current and electrode diameter were 6$0^{\circ}C$, above 160A and 4mm respectively under 28cm/min of welding speed. 4. The weld metal tensile strength or proof stress of underwater-welded-joints has a quadratic relationship with the heat input, and the optimal heat input zone is about 13 to 15KJ/cm for 10mm SWS41A steel plates, resulting from consideration upon both joint efficiency of above-100% and recovery of impact strength and strain. Meanwhile, the optimal heat input zone resulting from tension-tension fatigue limit above the base metal's of SWS41A plates is 16 to 19KJ/cm. Reliability of all the empirical equations reveals 95% confidence level. 6. The microstructure of the underwater welds of SES41A welded in such a zone has no weld defects such as hydrogen brittleness with supreme high hardness, since the HAZ-bond boundary area adjacent to both surface and base metal has only Hv400 max with the microstructure of fine martensite, bainite, pearlite and small amount of ferrite.