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Metals & Mining
In view of the reduction in operational costs, container ships have become large-scaled so significantly that even larger ships of over 16,000 TEU have been designed and constructed in recent years. And these ships are applied heavy plates 70–90mm in thickness. The Kca ≧ 4,000–6,000 N/mm of arrestability in temperature-gradient ESSO tests (large scale crack-arrest test) is needed for arresting super-long brittle cracks (193 research committee of Japan Ship Research Association). Thus, in this paper, improvement in the arrestability of steel plates was achieved through investigating the effect of shear-lips. As a result, generating shear-lips at lower temperature and enhancing the propagating resistance of ductile cracks allowed us to improve arrestability. In addition, it is not practical for us to employ an ESSO test as a usual testing method for product inspection due to its large size. Accordingly, a Kca estimation method according to the combined use of a drop weight test together with a Charpy impact test was analyzed, and it was thus confirmed that said method had good accuracy regarding estimation. INTRODUCTION Figure1 shows ESSO specimen. The brittle crack forced to be initiated by wedging. Temperature gradient is 0.25–0.35°C/mm in standard ESSO test (ClassNK, Guidelines on Brittle Crack Arrest Design 2009) Figure 2 shows the relationship between 50%FATT (Fracture Appearance Transition Temperature:50% brittle, 50% ductile) of Chalpy impact test at 1/2t and at a Kca value obtained by ESSO test at 0°C for YP315 and YP355 N/mm E-grade steel plates. Chalpy is test for brittle crack initiation and ESSO is test for crack arrestability. However, there are mutual relation between Chalpy and ESSO test, because they strongly depend on grain size of steels. Therefore it is considered E-grade, best grade of ordinary ship steels in toughness, posses suitable or sufficient arrestability for prevention of brittle fracture.
- Materials > Metals & Mining > Steel (1.00)
- Transportation (0.93)
Evaluation Method For Crack Arrestability of Steel Plates Using Small-Scale Fracture Test Results
Ishikawa, Tadashi (Steel Research Laboratories, Nippon Steel Corporation) | Inoue, Takehiro (Steel Research Laboratories, Nippon Steel Corporation) | Funatsu, Yuuji (Plate Sales Division, Nippon Steel Corporation) | Otani, Jun (Oita works, Nippon Steel Corporation)
ABSTRACT The crack arrestability in a steel plate is determined by both its surface layer properties and its mid-section properties. Through investigation of the correlation between ESSO test results (as a large scale crack-arrest test) and NRL drop weight test results (as a small scale crackarrest test), it was found that crack arrestability can be estimated as a function of plate thickness using a proposed equation and the NDT temperatures of the NRL drop weight test obtained from both the surface layer section and the mid-section of a steel plate. Applying this concept to very thick EH47-class steel, it is shown that the crack arrestability can also be estimated using small scale test results, although the correlation factors should be determined independently for each steel plate manufacturing process. INTRODUCTION Large scale welded structures need to maintain their structural integrity against brittle fractures in order to avoid catastrophic failures and accidents. For large ships and low temperature storage tanks, the double integrity concept, which takes into account both the prevention of brittle fracture initiation and the arrest of brittle fractures in the case of an emergency, has been investigated (Machida, 1972) (Kanazawa, 1973). To realize the double integrity concept, high performance steel plates with improved crack arrestability have been developed, such as SUF (Surface layer with Ultra Fine grained microstructure) steel and EH47-class steel with sufficient crack arrestability. Such steel plates have already been used in the construction of important vessels, such as LPG carriers and mega-containerships. Recently, the significance of crack arrestability in steel plates for determining the structural integrity of mega-containerships has increased dramatically, because some ship classification societies are now considering and establishing new guide-lines or new standards concerning the crack arrestability of very thick, high-tensile steel plates.
Thickness Effect On the Brittle Crack Arrest Toughness Value (Kca) - Brittle Crack Arrest Design For Large Container Ships -6 -
Sugimoto, Kei (Nippon Kaiji Kyokai) | Hiroshi, Hiroshi (Nagasaki Institute of Applied Science) | Aihara, Shuji (Tokyo University) | Yoshinari, Hitoshi (National Maritime Research Institute) | Hirota, Kaszuhiro (Mitsubishi Heavy Industies, Ltd) | Toyoda, Masanobu (IHI Marine United Inc) | Kiyosue, Takaaki (Kawasaki Heavy Industries, Ltd) | Inoue, Takehiro (Nippon Steel Corporation) | Handa, Tsunehisa (JFE Steel Corporation) | Kawabata, Tomoya (SumitomoMetal Industries, Ltd) | Tani, Tokutaka (Kobe Steel, Ltd) | Usami, Akio (Nippon Kaiji Kyokai)
ABSTRACT: Brittle fracture of the hull structure has the possibility to cause serious structural damage and so it should be avoided. Therefore, it is important to ensure the hull structural integrity by preventing brittle cracks from being initiated and also by providing a proper means for arresting the brittle crack when the crack propagation occurs. In the last 4 papers of ISOPE 2010, the authors investigated a proper brittle crack arrest design for large container carriers by carrying out a number of large scale and middle scale fracture tests. The issue of the plate thickness effect on the required Kca has become a key concern with regards to the applicability of the proposed Kca. Since 2009, the authors conducted ultra-wide duplex ESSO tests with plate thickness from 25mm to 75mm, which had no structural influences on the test results, in order to investigate the thickness effect on the required Kca value. As a result, it was confirmed that plate thickness affects the required Kca value. INTRODUCTION As for the past researches related with brittle crack arrest toughness, the 193rd research committee of the shipbuilding Research Association of Japan (SR 193, 1985) investigated the arrestability of steel plates with 35 mm thickness and determined the necessary Kca value to be 4000N/mm3/2 (Fig.1). Fukui et al. (2003) investigated the necessary Kca value of steel plates with a thickness range from 25mm to 50mm and proposed 6000N/mm3/2 (Fig.2). Yamaguchi et al. (2010) researched the brittle crack arrest design for large container ships and proposed the necessary Kca value for brittle crack arrest to be 6000N/mm3/2 or over for steel plates exceeding 50mm in thickness, in which both brittle crack arrest toughness of steel plates and structural effects of the connection of Hatch side coaming and Upper deck were taken into account.
- Materials > Metals & Mining > Steel (0.99)
- Transportation > Marine (0.71)
- Transportation > Freight & Logistics Services > Shipping > Container Ship (0.61)
Numerical And Experimental Analysis of Brittle Crack Propagation And Arrest In Steels
Aihara, Shuji (The University of Tokyo) | Watabe, Yoshiyuki (The University of Tokyo) | Shibanuma, Kazuki (The University of Tokyo) | Inoue, Takehiro (Nippon Steel Corporation) | Koseki, Tadashi (Nippon Steel Technoresearch Corp.)
A new model for dynamic crack propagation and arrest in steel plates is proposed. The model is based on the local fracture stress criterion and incorporates the influence of plastic deformation on the tip of a dynamically propagating crack. The model explains anomalous data in temperature-gradient crack arrest test under high applied stress. The model also explains many aspects of crack propagation and arrest behaviors. The hypothesis that crack driving force is saturated at long crack propagation has been replaced by the present model. INTRODUCTION Prevention of brittle crack propagation as well as crack initiation is essentially important for ensuring double integrity in such steel structures as large containerships and offshore structures. Brittle crack initiation is prevented by controlling defects associated with welding practices and cracks associated with repeated loading during service and by selecting steel plates with high HAZ toughness and high toughness welding materials. On the other hand, brittle crack propagation must be prevented by adopting steel plates with high crack arrest toughness of base metal, together with proper crack arrest design. Nippon Kaiji Kyokai published the guidelines on Brittle Crack Arrest Design, (Nippon Kaiji Kyokai, 2009), in which fundamental procedures for preventing brittle crack propagation in containership hull structures. The guideline also addresses a testing method to measure brittle crack arrest toughness using temperature-gradient tests. Brittle crack propagation and arrest can be evaluated by fracture mechanics approach; a crack continues to propagate if crack driving force as expressed by stress intensity factor, K, exceeds crack arrest toughness, Kca, and vice versa. It has long been recognized, however, that a crack could be arrested in some of ultra-wide plate tests even if K exceeds Kca, (Machida and Aoki, 1972). Figure 1 shows their crack arrest test results of 30mm thick YP24 steel plates.
- Research Report > New Finding (0.50)
- Research Report > Experimental Study (0.40)
- Overview > Innovation (0.34)
- Transportation > Marine (1.00)
- Materials > Metals & Mining (1.00)
- Transportation > Freight & Logistics Services > Shipping > Container Ship (0.54)