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131.
用多试样阻力曲线法和剖面法测定了球罐钢ＢＰ４６０ＮＬＩ焊接接头的裂纹尖端张开位移特征值，得出了裂尖伸张区达到饱和时的启裂值δｉｓ在母材，焊缝，熔合线和热影响区中的分布，并用金相显微镜和扫描电镜观察了焊接接头各区的显微组织和断裂形态。 相似文献
132.
海洋泊链用钢大尺寸试样CTOD试验研究 总被引：1，自引：0，他引：1
设计制作了大尺寸试样裂纹尖端张开位移(CTOD)试验用低温环境箱和相关的卡具。依据英国BS7448断裂韧性试验标准，分别对海洋泊链用钢母材及焊缝进行了一20℃的CTOD试验。结果表明，母材试样的CTOD特征值δm普遍很高，均在0．77mm以上；所有焊缝试样都发生了脆性断裂，其中，两块试样的P-V曲线图及其所对应的宏观断口异常，另两块焊口试样在弹性区就发生了脆性断裂，导致了它们的CTOD特征值δc小于设计指标0．15mm的要求。试验分析结果为评价焊接工艺及焊后热处理规范提供了依据。 相似文献
133.
V. V. Chaudhari D. M. Kulkarni 《Fatigue & Fracture of Engineering Materials & Structures》2015,38(7):851-859
Fracture tests of extra deep drawn steel sheet were carried out at ambient temperature to investigate the effect of loading rate on fracture toughness. To determine fracture limits, fracture tests and finite‐element cohesive zone model simulation tool are used. Fracture tests are conducted at various loading rates (0.1–2.5 mm min?1). An alternative constant traction separation law is used to account for maximum load and large load line displacements. Experimental findings, as well as cohesive zone model, show that the loading rate has no significant effect on fracture toughness till 0.4 mm min?1; however, there is a sharp decrease in fracture toughness beyond 0.4 mm min?1. 相似文献
134.
Microstructural and mechanical properties of laser welded sheets of magnesium AZ31‐HP with and without filler wires This paper describes Nd:YAG laser beam welding experiments carried out on rolled 2.5 mm thick magnesium sheet AZ31‐HP. For the butt welds in flat position, filler wires AZ31X and AZ61A‐F were used, diameter 1.2 mm. The microstructure and mechanical properties of the different laser beam welded joints were examined and compared with one another. The obtained results show that the laser beam welding of AZ31‐HP sheet is possible without hot crack formation, both without and with filler wires. The determined tensile strength, ductility, fracture toughness and microhardness of laser beam welded joints without filler wire were not effected by AZ31X nor AZ61A‐F. By use of these filler wires loss of zinc was minimized and the shape of weldments was optimized. The values of fracture strength, yield strength and microhardness of the joints and base material are quite similar. It is found that the ductility of the joints is lower than the base materials due to the heterogeneous microstructure of the fusion zones and geometrical notches of the weld seams. Both, weld and base material of AZ31‐HP, showed stable crack propagation. Furthermore, for base material slightly lower fracture toughness values CTOD than for the joints were determined. 相似文献
135.
V. V. CHAUDHARI D. M. KULKARNI R. PRAKASH 《Fatigue & Fracture of Engineering Materials & Structures》2011,34(4):260-269
The crack tip opening displacement (CTOD) evaluation from CMOD values using compact tension (CT) specimen geometry and plastic hinge model (PHM) is well standardized in the literature. However, the model is found to be conservative for the general yielding situation. Moreover, the knowledge of the location of apparent axis of rotation which in turn depends on plastic rotational factor, rpl, is essential for the conversion from CMOD to CTOD. In the present investigation, the ‘crack flank opening angle’ (CFOA) method has been suggested for the evaluation of plastic CTOD. This approach has facilitated the exact determination of apparent axis of rotation. The effect of the specimen thickness and notch root radius on CTOD has been investigated using the PHM and CFOA method. These results have been compared with finite element analysis results. Results achieved point out that the CTOD obtained from the traditional PHM are underestimated for the general yield situation. 相似文献
136.
WeeLiam Khor 《Fatigue & Fracture of Engineering Materials & Structures》2019,42(7):1622-1630
Crack tip opening displacement (CTOD) from national and international standards was shown to give different values. This paper investigates the feasibility of CTOD determined based on the concept of rigid rotational factor in single‐edge notched bend (SENB) specimens. Based on validated modelling methods, finite element (FE) models were simulated for crack ratios 0.3 ≤ a0/W ≤ 0.7 and yield‐to‐tensile ratio 0.44 ≤ σys/σuts ≤ 0.98. This covers cases of shallow to deeply cracked specimens and a wide range of strain hardening properties. CTOD obtained from the FE models was used as the basis of a newly implemented strain hardening corrected rotational factor, which considers the effects of crack tip blunting due to strain hardening, rp sh. An improved equation considering strain hardening was implemented based on the rp sh. The equation gives accurate estimation of CTOD from the FE models compared with the equation from BS 7448‐1, ASTM E1820, and WES 1180. 相似文献
137.
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139.
叶运勤;苗张木;张步爱 《机械强度》2015,37(3):562-566
随着海洋工程的发展,探索海洋油气的项目增多,天然气、石油的输送工程也日渐发展起来。UOE生产工艺下的高强X70钢被广泛运用到油气输运工程中,然后强度越高的钢其断裂韧度越低,需对这种高强钢的断裂韧度值进行确定。材料断裂韧度大小可以用临界裂纹尖端张开位移CTOD(crack tipopening displacement)来度量。临界CTOD是弹塑性断裂力学中重要的参数,其大小直接反映了裂纹尖端材料抵抗开裂的能力,临界CTOD值越大表示材料抗开裂性能越好,反之抗开裂性能越差,确定临界CTOD值意义重大。首先依据BS7448规范对X70钢断裂韧度临界CTOD值进行了测试,然后利用Ansys软件从CTOD定义出发对X70钢临界CTOD进行了计算,实现了试验与模拟的对比分析,可供压力容器和管道生产和结构安全性评估企业借鉴。 相似文献
140.
断裂韧性作为评估管道结构完整性的一个重要参数,对其进行尺寸效应研究具有重要的科学意义和工程价值。当前对金属材料断裂韧性尺寸效应的研究主要集中于线弹性断裂参数应力强度因子K,且大多仅考虑试件厚度的影响。为建立试件尺寸对高强度高韧性管道钢材料断裂韧性的系统影响规律,基于Gurson-Tvergaard-Needelman (GTN)模型对单边切口梁(SENB)试件三维断裂过程进行模拟,选用裂纹尖端张开位移(CTOD)与裂纹尖端张开角(CTOA)对其断裂韧性进行表征,分析两者沿试件厚度的分布规律,并研究裂纹深度与试件厚度对其影响。同时选取应力三轴度对试件约束水平进行评估,以此解释断裂韧性尺寸效应存在的原因。研究结果表明:断裂韧性在试件厚度方向一定范围内基本保持不变,在自由表面处取得最大值;裂纹深度对断裂韧性几乎没有影响,而试件厚度越大,断裂韧性越低,且临界CTOA比临界CTOD更能反映断裂韧性的变化规律。 相似文献