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Recently, shipbuilding design techniques is developing so fast. As a result, vessels and plant became large, and is required arctic vessel for polar resource development. However, steel show brittle nature at reduce temperature. So research of character is increased under low temperature. In this study, thick plate has been used to measure the fracture toughness to evaluate at low temperature, using AIS3000 indentation tester and impact tester. And micro structure analysis for fracture surface has been observed by SEM.
Since the ceramic and metal are joined at high temperature, the residual stress will develop when it is cooled from bonding temperature due to remarkable difference of thermal expansion coefficient between ceramic and metal. Moreover, the edge of jointed interface makes singular stress field and this singular sσess field influences on the strength of joints. In this study. The effects of residual stress, mechanical load and repeat thermal cycle were estimated in the ceramic/metal joints. The change of singular stress field due to these effectswas analyzed. The results are as follow : 1) Strength of jcints was evaluated by the sσess singularity index λ and the intensity K of singular stress field. 2) The stress singularity index λ and the intensity K of singular stress field also increase as temperature of thermal cycle and its number of cycle increase. 3) In the case of mechanical load, the effect of residual stress reduces since the difference(Δλ) of stress singular index between existence and inexistence of residual stress decreases in proportion to the increasing of tensile load.
Fracture toughness is an important parameter in designing structure applied in low temperature. The huge tesging machine and manufacturing of the testing specimen are the main shortages of the CTOD and FCG testing methods. Therefore, in this study the indentation tester AIS 3000 is applied to measure the fracture toughness. The experiment was conducted at RT, 0℃, -20℃ and -45℃, respectively. Furthermore, the fracture surface was observed by SEM. Through the results we can see that the fracture toughness was reducing through the temperature drop, and the highest fracture toughness in base metal and weld zone was measured at room temperature though there were a little peak at -20℃. As we expected, the highest fracture toughness in th HAZ was observed at -20℃ for procedding less brittle fracture at low temperature.
Non destructive test is applied to revise mechanical strength and assume material strength or defect of material, equipment and structure, instead of fracture test. Especially, ultrasonic test has the characteristics such as an excellent permeability, high-sensitiveness to fine defect and an almost exact measurement for position, size and direction of inner defect, which differ from other non destructive tests. In this study, the program is developed to evaluate optimal testing condition, to distinguish obstacle echo and defect position. This program on the basic of Ray-Tracing model shows generation and processing of ultrasonic pulse. The simulation is compared with testing in the 3 cases of an oblique angle transducer like 45°, 60° and 70°. The test result for all conditions is well compared with simulation result when relative error is within 0.1~7.2%. And the course of several echos is simply assumed through simulation.
Kecently, shipbuilding design tectruques is developing so fast. As a result, vessels and plant became large, and is required arctic vessel for polar resource development. However, steel show brittle nature at reduce temperature So research of character is increased under low temperature. In this study, thick plate has been used to measure the fracture toughness to evaluate at low temperatue, using AIS3000 indentation tester and impact tester. And micro structure analsysis for fracture surface has been observed by SEM.
Recently, the production at shipbuilding and offshore plant industries, with a trend toward large structures, has led to an increased use of high strength ultra-thick plates. The use of ultra-thick plates increases the welding tasks, and the welding process generates distortion and residual stress in the weldment because of the rapid heating and cooling. Welding distortion and residual stress in the welded structure resulte in many troubles such as deformation and life deterioration. In particular, the welding residual stress has an important effect on welding deformation, fatigue, buckling strength, brittleness, etc. The purpose of this study was to evaluate the residual stress at a multi-pass weldment using an experimental method for EH36 high-tension steel. In this experimental method, AlS3000 was used to measure the residual stress of a welded part, HAZ, and base metal; EPMA and XRD were used to study the material properties.