共查询到20条相似文献,搜索用时 203 毫秒
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《江苏科技大学学报(社会科学版)》2017,(6)
利用疲劳试验机,研究了残余元素Sn对20Cr Mn Ti钢疲劳裂纹扩展速率以及疲劳寿命的影响,同时利用扫描电镜分析断口形貌,结果表明:当ΔK33.35 MPa·m1/2、w(Sn)为0.05%时裂纹扩展速率稍高,当ΔK33.35 MPa·m1/2、w(Sn)为0时裂纹扩展速率稍高,然而两者扩展速率总体差别不大,可认为一致;w(Sn)为0或0.05%时,疲劳裂纹扩展断口形貌均为准解理断裂+少量韧窝,无明显差别.不含Sn及含0.05%Sn时,疲劳寿命分别为4.0×104周次、4.1×104周次,断口分析表明,疲劳源区均在试样表面,疲劳区均未出现疲劳条纹,瞬断区均呈韧窝状断口形貌,无明显区别.即当w(Sn)≤0.05%时,对20Cr Mn Ti钢疲劳性能没有明显影响. 相似文献
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针对6061铝合金采用TIG、MIG和FSW的焊接方法所得到的焊接接头性能进行试验研究,测试了3种方法得到的焊接接头的抗拉强度σb和延伸率δ,并对接头的微观组织和断口形貌进行了观察和分析,结果表明:搅拌摩擦焊接头的综合力学性能最好,MIG焊的接头强度要高于TIG焊接头的强度;搅拌摩擦焊接头的组织比母材细小,而熔化焊接头的晶粒中弥散着大量的析出相质点;TIG焊试样断口的韧窝比较浅,在韧窝附近有类似于准解理断裂的光滑平台,而MIG焊试样断口的韧窝也要比TIG焊试样断口的韧窝深,而FSW焊缝区的断口的韧窝尺寸要比TIG焊接头的韧窝小而深,许多小韧窝集聚成尺寸较大的韧窝。 相似文献
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铝合金表面状态对搅拌摩擦焊接头组织和性能的影响 总被引:1,自引:0,他引:1
研究了铝合金表面状态对搅拌摩擦焊焊接接头组织和性能的影响。试验结果表明:试板表面油污的存在使得焊接接头强度下降为母材的60%左右,同时显著降低接头的塑性;试板表面的氧化膜和油污还会造成焊核区及焊缝前进侧的残余间混结合线缺陷。对焊接接头拉伸断口进行扫描电镜观察发现:拉伸试样的断口中存在油污和A l2O3的聚集物,这些聚集物会成为拉伸时的裂纹源。断口和力学性能综合分析表明:铝合金表面的油污和氧化膜都会降低搅拌摩擦焊接头的强度和塑性。 相似文献
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狗骨形试样具有中间等截面段试验有效区。采用悬链线代替圆弧线的轮廓方程,获得了狗骨形试样的解析计算方法。分析结果表明,试样初始尺寸在一定范围内取值时轮廓方程代替所引起的误差控制在3%以内。可通过增大变截面段长度或粗、细端的半径比来缩短试样长度,但增大变截面长度会降低试样位移应力系数。尽管狗骨形试样的位移应力系数不如沙漏形试样,但狗骨形比沙漏形更节省试验材料,而且其位移应力系数也足够满足试验要求。铝合金6063的超声疲劳试验表明,狗骨形试样的设计等式是可行的。铝合金6063的S-N曲线呈现持续下降的趋势,其疲劳裂纹扩展以剪切方式进行,并且呈现裂纹表面萌生机制。疲劳源区与裂纹扩展区之间存在明显的台阶。 相似文献
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对某船用柴油机活塞销断裂故障进行了分析研究。金相观察及断口的宏观和微观观察表明,活塞销的破坏属疲劳断裂,疲劳裂纹在表面渗碳层的网状碳化物萌生,进而扩展引发断裂。改进渗碳工艺,杜绝网状碳化物析出是防止活塞销疲劳破断的有效途径。 相似文献
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钢纤维混凝土是拉应力敏感材料,在外荷载作用下,裂纹端部会产生微裂纹形成微裂区。这一特征使线弹性断裂力学不能直接分析钢纤维混凝土的断裂。同时钢纤维混凝土开裂后,钢纤维在开裂区通过提供拉应力,限制裂纹的扩展。针对钢纤维混凝土这两个特征,本文用理论和实验的方法,对钢纤维混凝土I型断裂的裂纹产生和裂纹扩展进行了研究,并得到可用有效裂纹长度代替真实裂纹长度和用闭合力等效钢纤维阻裂作用的结论。最后用线弹性断裂力学方法计算钢纤维混凝土I型断裂的临界应力强度因子和钢纤维拉应力。 相似文献
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为研究试样厚度对船用钢疲劳裂纹扩展速率的影响,设计并实施两组不同厚度的紧凑拉伸试样进行疲劳裂纹扩展速率试验,同时建立了三维疲劳裂纹扩展有限元模型,分别基于线弹性理论和弹塑性理论对应力强度因子进行了计算,并分析了试样厚度对裂纹扩展速率的影响。试验与计算结果的综合分析表明:相同应力水平下,薄试样裂纹尖端的塑性区明显大于厚试样,且裂纹尖端应力强度因子值大于理论经验计算结果可达23.25%,因此,在材料裂纹扩展速率试验前,特别是试样厚度尺寸较小时,应充分考虑试样的厚度效应,参考基于弹塑性理论计算得到的应力强度因子结果,同时有必要针对当前试样及材料进行专门的裂纹扩展速率试验,以得到准确裂纹扩展参数结果。 相似文献
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Yoichi Sumi Hiroshi Yajima Masahiro Toyosada Takao Yoshikawa Shuji Aihara Koji Gotoh Yoshitaka Ogawa Toshiyuki Matsumoto Kazuhiro Hirota Hideyuki Hirasawa Masanobu Toyoda Yasushi Morikage 《Journal of Marine Science and Technology》2013,18(4):497-514
The rapid enlargement of the size of container ships has led to the application of extremely thick plate in the deck structures, which may grow concerns about the fracture toughness at the butt-weld with large amount of heat input, and the arrest toughness of brittle crack propagation in the base metal of such thick plates. Also, slam-induced whipping stresses might affect the fatigue crack propagation and the initiation of a brittle crack in a container ship. In order to prevent the catastrophic failure of deck structures by brittle fracture, national joint research projects, which focused on the safety-related issues of extremely thick steel plate applied to hull of large container ships, were formed from April 2007 to March 2011 organized by the Japan Ship Technology Research Association (JSTRA) supported by the Japanese Government in collaboration with universities, national research institute, classification societies and relevant industries including shipbuilding, steel manufacturing and shipping companies. The joint research projects have carried out the investigations on crack initiation toughness of the weld, fatigue crack propagation under seaway loading, the potential of defect detection by ultrasonic testing, and the crack-arrest methods after brittle crack propagation. Practical recommendations to prevent brittle fracture of large container ships were proposed based on these comprehensive investigations. The essential parts of the above research activities are presented in this paper. 相似文献
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裂纹尖端张开位移(CTOD)是研究大范围屈服的低周疲劳破坏的重要参数之一,其值可反映结构材料抵抗低周疲劳裂纹形成和扩展的能力,是评估结构材料韧性的重要参量以及分析低周疲劳破坏引起裂纹扩展的主要控制参量。文章基于弹塑性断裂力学理论,从循环J积分着手,以裂纹尖端累积塑性应变为重要参量,建立循环载荷下船体板CTOD理论模型,并在有限元模拟中分析了应力比、应力幅等相关因素影响。将本模型结果与有限元计算结果进行了比较,发现结果吻合良好。结果表明:在考虑累积塑性影响下,该模型能较好地反映在循环载荷下船体板CTOD的变化规律,同时也为正确评估循环载荷下船体板低周疲劳破坏与累积塑性破坏两种破坏模式耦合作用的总体断裂破坏提供了途径。 相似文献
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This study reports a deformation limit for the initiation of ductile fracture failure in fatigue-cracked circular hollow section (CHS) X-joints subjected to brace in-plane bending. The proposed approach sets the deformation limit as the calculated crack driving force in a fatigue crack at the hot-spot location in the tubular joint reaches the material fracture toughness measured from standard fracture specimens. The calibration of the proposed approach and the numerical procedure utilizes two large-scale X-joint specimens with fatigue generated surface cracks. The subsequent numerical investigation covers X-joints with two different brace-to-chord intersection angles, a wide range of geometric parameters and a practical range of material parameters. The development of the deformation limit includes a non-dimensional material toughness, which covers both the geometric parameters and material properties. The lower-bound deformation limit thus developed exhibits a linear relationship with respect to the crack depth ratio and indicates consistent values among X-joints with different brace-to-chord intersection angles. 相似文献
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Chemical analysis, tensile, Charpy, DW NDT and fracture mechanics toughness data are presented for a grade A steel plate from the Kowloon Bridge, a sister ship of Derbyshire. The plate is shown to have poor toughness under dynamic loading conditions. The results leave open the possibility that brittle fracture could have contributed to a structural failure in the Derbyshire even at the high temperature of +30°C which is reported to have existed at the time of the ship's disappearance. The results are felt to support the proposition that present classification society rules need tightening to reduce the risk of brittle fracture in ships. 相似文献
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Fatigue crack propagation under the biaxial tensile loading, which loading directions are normal and parallel to the initial crack position, is highlighted in this study. Most of in-service structures and vessels are subjected to many types of loading. Generally, these loadings have different axial components with different phases. However, the structural integrities of structures and vessels are evaluated according to design codes based on theoretical and experimental investigations under a uniaxial loading condition. Most of these codes are based on the S–N curves approach. An approach that does not use S–N curves has been favored by researchers, with the fracture mechanics approach preferred for evaluating the fatigue life of structures. An advanced fracture mechanics approach was developed based on the Re-tensile Plastic zone Generating (RPG) stress criterion for fatigue crack propagation. In this study, fatigue crack propagation tests under biaxial loading with six different phase and loading conditions are performed and the effect of the phase difference under biaxial loading is evaluated. A numerical simulation method of fatigue crack propagation based on the RPG stress criterion under different biaxial loading phase conditions is presented and compared to measured data. 相似文献
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