钢材的冲击韧性对断裂韧性的影响分析(英语完全)

1、The Ninth International Symposium on Structural Engineering for Young Experts, August 18-21 2006, Fuzhou & Xiamen, China aaAnalysis on the Influence of Impact Toughness on Fracture Toughness for Structure SteelWang Xi, Yuan-Qing Wang, Yong-Jiu ShiDepartment of Civil Engineering, Key Laboratory o

2、f Structural Engineering and Vibration of China Education Ministry, Tsinghua UniversityBeijing, 100084, P.R. ChinaABSTRACT: Impact toughness and fracture toughness are the two important mechanical indexes of structure steel. This paper introduces the normal impact toughness index, impact absorption

3、work, which is widely applied in the steel structure design. Also the paper describes the definitions of steel impact toughness in the standards domestic and abroad and some data in the standards are enumerated. It is introduced that there are three criterions used to judge the fracture, K criterion

4、, J criterion and COD criterion. How to use the criterions is pointed out. At last, the correlation between impact toughness and fracture toughness is emphatically discussed based on the existing studies while some research results are enumerated. KEYWORDS: structure steel, impact toughness, fractur

5、e toughness, correlation1. INDEXES USED TO MEASURE THE IMPACT TOUGHNESS OF STEEL The impact toughness is an important mechanical index to measure the performance ability of steel, it reflects the plastic deformation and energy absorbing ability of steel in the three-dimensional stress state. There a

6、re two approaches to measure impact toughness, Charpy V-notch and U-notch tests, the former is widely used domestic and abroad.There are two index to measure the V-notch impact toughness, one is “Akv”, which is the absorbed energy in the impact test by the normal sample. The index has obvious physic

7、al meaning, its unit is “J”; the other is “akv”, which is the quotient derived from the Akv divided by the area at the notch section, it is merely the maths mean value of the impact work on the fracture section, the unit is “J/cm2”. Due to absence of physical meaning, the index “akv” is used less an

8、d less in the engineering practice. (None, 1994)2. APPLICATION OF IMPACT TOUGHNESS IN THE STEEL STRUCTURE DESIGNAs an important mechanical index of steel, Impact toughness is specified in the steel, press vessel and steel structure design standards domestic and abroad. In the Chinese steel standard

9、GB700-88 and GB/T 1591-94, factory technical conditions on impact toughness are definitely limited, the steel impact toughness values in the various temperatures are specified and it is defined that the sampling of impact samples must be lengthwise with V-notch.In the Chinese standard for the pressu

10、re vessel steel, it is defined that Charpy V-notch impact test must be taken at room temperature, sampling should be crosswise. GB6654-1996 specifies the impact toughness values of pressure vessel steel plate.Table 1 Clauses on impact toughness of steel in Chinese standards(Hou J.G. et al, 2001)Low

11、limit of impact workSerial numberSteel gradeSampling orientationTest temperature()Akv(J)GB700-88Q235BQ235CQ235Dlengthwise200-2027GB/T 1591-94Q345B，Q390BQ345C，Q390CQ345D，Q390Dlengthwise200-203420R16MnR15MnVRcrosswise203115MnNbRcrosswise-203420R16MnR15MnVRcrosswise2034GB6654-199616MnRcrosswise-2024GB1

12、50-1998JB4732-9507MnCrMoVR07MnNiCrMoVDRcrosswise-20-4047GB713-199720g16MngcrosswiseRoom temperature2716qcrosswiselengthwise-20343916Mnq15MnVqNot definite-4034YB/T10-8115MnVNqNot definite-4039In Chinese standard GB150-1998 and industry standard JB4732-95 for pressure vessel, it defined that the impac

13、t test samples of steel should be with Charpy V-notch and crosswise sampling. For the hardened and tempered steel plate or the plate for shell structure whose thickness is larger than 60mm, Charpy V-notch impact test should be taken on every plate. When the working temperature is lower than 0, the t

14、est should be taken on any piece or every piece out of every batch of steel. GB150-1998 and JB4732-95 enumerate the values of impact test on steel in low temperature.Chinese standard for boiler steel plate GB713-1997 and industry standard for bridge steel YB/T10-81 both limit the impact toughness va

15、lues of steel. In the standard GB50017-2003, it is defined that the impact toughness must be assured for the structure steel that needs fatigue checking at room temperature. when the structure working temperature is lower than 0, the standard definitely specifies the impact toughness of steel.In the

16、 American, Japanese, britannic and Germanic standard for steel or pressure vessel, the Charpy V-notch impact absorption work is used to measure the impact toughness of steel. American ASME pressure vessel standard defines the lowest impact work on the “nominal thickness-impact work”coordinates figur

17、e with the method that drawing the fold lines which joint the steel yield points at various temperatures. In the Japanese industry standard JIS G 3106-1995 for rolled steel of welded structure and JIS G 3128-1987 for high strength steel plate of welded structure, the Charpy V-notch impact absorption

18、 work of steel is defined. The Charpy U-notch impact test values are defined in the 前苏联 steel standard OCT 27772-88 for rolled construction steel.Table 2 Clauses on impact toughness of steel in Japanese industry standards(Hou J.G. et al, 2001)Low limit of impact workSerial numberSteel grade Sampling

19、 orientation Test temperature()Akv(J)JIS G 3106-1995SM400BSM400CSM490BSM490CSM490YBSM520BSM520CSM570lengthwise0000000-52747274727274747JIS G 3128-1987SHY685SHY685NSHY685NSlengthwise-20-20-40473. FRACTURE ANALYSIS CRITERIONS OF STEEL STRUCTUREFor the structural members with complex stress state, larg

20、e thickness and constraint or in the low temperature, the fractures usually happen while there is little plastic deformation but in the plasticity extent, and fracture tendency of structure can be understood through comparing the fracture toughness index KIC derived from the normal test and the stre

21、ss intensity factor derived from linear elastic analysis. For the fracture analysis which needs to consider plasticity development, the fracture criterion with COD test resisting force curve or the critical value of energy release rate at crack tip JIC is adopted.3.1 K CriterionIn the elastic extent

22、, if stress intensity factor at crack tip KI meets: KIKIC, KIC is the critical value, the crack may grow unstably. The K criterion is valid only when linear elastic state or small scall yield condition is satisfied.The K criterion is no longer valid when the plastic size of crack tip is large, it mu

23、st adopt J integral and crack opening displacement (COD) theories based on elastic-plastic analysis to study the fracture law.3.2 J CriterionIf J integral at the crack tip meets: JJIC, JIC is the critical value, the crack may develop.3.3 Crack Opening Displacement C (COD) CriterionComparing the inde

24、x C of steel and the real opening displacement under load, if C, the crack may develop.4. CORRELATION BETWEEN IMPACT TOUGHNESS AND FRACTURE TOUGHNESSFracture toughness criterion is based on fracture mechanics. Fracture criterion contact fracture toughness with the applied load and member flaw, and i

25、t is more representative than impact toughness. But fracture toughness test is expensive and difficult to carry out, so people are trying to find the correlation between impact toughness and fracture toughness to infer the fracture toughness of materials from impact toughness which is easier.4.1 Cor

26、relation between KIC and AkvThe scholars all over the world put forward many correlations between KIC and Akv, as shown table 3. (Li S.F. et al, 1999)The experiential correlations above are based on each independent experiment. Genfu Yuan etc. deduce the universal correlation between fracture toughn

27、ess and impact toughness under room temperature from the analysis of impact work. Under the same fracture law, there is a universal correlation between K1c and Akv. For specific steel under certain state, KIC2 and Akv meet: (Yuan G.F. et al, 1996)aAbk21vCKThe linear correlation nicely presents what

28、is in the table 3, so we can obtain the correlation between fracture toughness and impact work with regression method for the specific steel.4.2 Correlation between JIC and Akv The plasticity-brittleness transition curve of impact work is divided into upper mounting plate zone, plasticity-brittlenes

29、s transition zone and nether mounting plate zone. The fracture of materials is absolutely brittle in the nether mounting plate zone. In the plasticity-brittleness transition zone, the impact work and fracture toughness have different tendencies along with the change of temperature, so it is difficul

30、t to get the correlation between them in this zone. Here the discussions are concentrated on the upper mounting plate zone.The J criterion is usually used for normal carbon-manganese steel, but what we have known about the correlation is only between KIC and AKV. Under the plane strain and small sca

31、ll yield condition, KIC can be obtained by: (Zhu W.Y., 1979)CCJEK1211Then we can deduce the correlation between JIC and AKV through the correlation between KIC and AKV.Table 3 Correlations between KIC and Akv Correlation or figureScope of application05. 0A5k2ICysvysKWhere, Akv is the impact work at

32、80oF(foot-pound)KIC is the fracture toughness at 80oF(kilopound/inch3/2)ys is the yield strengthUpper mounting plate of Akvys =7581696MPa10002000300040005000600004080120160200240akv(J)K1C(N/mm3/2)s 470MPa,ferrite01223. 0A2 .5182 . 0k22 . 01vcKWhere, K1C is kgf/mm3/2Akv is kgfm/mm3/20.2 is kgf/mm2Upp

33、er mounting plate of Akv3/2k21A2vCEKTransition and low temperatures =2871765MPasvCKk21A300100Transition and low temperatureHT60,HT80 steel fusion-line2/1k1A5 .15vCKTransition and low temperatureA533B， A517F， A5422/1k1A900vscKTransition and low temperatureHT60,HT80 parent metal and welds where, A=4 o

34、r 5vCAEKk21ABridge steelKVKAABCT ,KA ,J300KV3000Figure 1 Akv becomes along with the temperatureJiangyang Qin etc. deduce two correlations between JIC and AKV based on the data in table 4. (Qin J.Y. et al, 2001)Table 4 16MnR series test results under low temperature36mm16MnR40mm16MnRtemperature()s(MP

35、a)AKV(J)JI(N/mm)s(MPa)AKV(J)JI(N/mm)6023150-20-30-40-50-60-703503643783813893974014065852464024201613107516443467.68.6284291303353317386347398635944342115106.34465897663747.37.7Rolfe-Novak-Barsom put forward the experiential formula below on the upper mounting plate zone of impact work:10 . 0A64. 0k

36、21ysvyscKIf E=2.1105MPa, =0.3, the correlation between JIC and AKV is:ysvyscCJ10 . 00029. 01Roberts and Newton commend a more conservative correlation based on more test data and study results:02. 0A52. 0k21ysvyscKThen another correlation between JIC and AKV is obtained:ysvyscCJ20 . 00024. 01The tes

37、t results of Jiangyang Qin etc. show that the impact work and fracture toughness have different tendencies along with the change of temperature. In the plasticity-brittleness transition zone, AKV becomes linearly larger while JIC gets slowly increase and then decrease rapidly along with the decrease

38、 of temperature. so the correlation in the plasticity-brittleness transition zone still needs to be studied.5. CONCLUSIONS It is simple and economical to measure the impact toughness of steel, and there is a lot of data reserved from much engineering practice, impact toughness is the necessary index

39、 to measure for steel in many countries.Fractures of steel structure members happen frequently. The study of steel fracture laws and approaches to avoid it always an important question in the engineering. Fracture toughness index nicely reflect the influence on fracture by fracture resisting force, plasticity and inner flaws. But it is expensive and difficult to machine and measure in tests, so studying the correlation between fracture toughness and impact toughness can help us derive fracture toughness from impact toughness.Kinds