石油化工油气管道焊接接头断裂韧性评定

评定了石油化工油气管道焊接接头断裂韧性，为今后石油化工油气管道质量提升、改进提供全新的研究思路。选取壁厚15,20,25 mm的石油化工油气管道常用X80等径管材，使用熔化极气体保护焊与双面多丝埋弧焊相结合的焊接方式，分别制备AJ-1,AJ-2,AJ-3 3种焊接接头试验试件。使用CTOD断裂韧性分别测定3个试件焊缝中心、熔合线、热影响区的裂纹顶端张开位移，并使用扫描电子显微镜观察各试件断裂微观形貌，分析各试件断裂韧性受裂纹扩展量影响情况。试验结果显示：裂纹扩展量会导致焊接接头裂纹顶端张开位移增大，影响焊接接头的韧性。3种焊接接头试件的不同区域裂纹顶端张开位移均>0.15 mm,断裂韧性较高；微观形貌结果显示，壁厚为15 mm的试件AJ-1热影响区韧窝较小，且出现较大解理面，脆性与韧性断裂特征都较为明显，该试件在焊缝中心与熔合线的韧窝较小，断裂韧性较低；壁厚为20 mm的试件AJ-2在热影响区存在准解理形貌，断裂韧性降低。在焊缝中心区的韧窝斜拉区断裂韧性升高，在熔合线出现较多剪切唇，断裂韧性并不理想；壁厚为25 mm的试件AJ-3在焊接接头各个区域均出现较多大韧窝，尤其焊缝中心的...     

陶瓷涂层断裂韧性的表征

由于陶瓷本身的脆性,陶瓷涂层的应用受到了极大的制约。断裂韧性是反映材料抵抗裂纹失稳扩展能力的力学性能指标,陶瓷涂层因为脆性和低维特点,对其断裂韧性的表征存在较大困难,目前主要有临界应力强度因子KⅠC、临界裂纹扩展能量释放率GⅠC和裂纹密度β三种表征方法。本文对上述方法进行了总结、分析。     

焊接方法对X90管道环焊接头断裂韧性的影响

为准确获取X90环焊接头的断裂韧性,采用改进的规则化法对X90环焊接头的低约束单边缺口拉伸试件进行断裂韧性测试,分别从手工焊、自保护药芯半自动焊和气保护药芯半自动焊焊接的X90管道环焊接头中提取测试试件,进行断裂韧性试验.结果表明,相同焊接方法下,浅裂纹试件所得阻力曲线比深裂纹试件所得阻力曲线低;热影响区的深裂纹试件具有最高的裂纹扩展阻力曲线,而热影响区的浅裂纹试件具有最低的裂纹扩展阻力曲线;焊缝区试件在试验中极易发生脆断,具有相对较差的断裂性能,并且受焊接方法影响较大,其中气保护药芯焊丝半自动焊的焊缝区试件全部发生脆断.因此,气保护药芯焊丝半自动焊在实际X90管道工程应用中作为参考方法需要优化,这对保持X90管道结构的完整性至关重要.     

蠕变断裂韧性对裂纹开裂和扩展的影响

本文研究了蠕变断裂韧性对二种低合金耐热钢蠕变裂纹开裂和扩展的影响。试验表明:随着蠕变断裂韧性提高,抗蠕变裂纹开裂和扩展能力增加。材料呈韧性或脆性状态时,蠕变裂纹萌生和扩展过程不同。韧性状态时,裂纹为穿晶和晶界二种混合形式:穿晶裂纹可在晶内碳化物处发生,或在晶界上形核后向晶内扩展,晶界裂纹仍是由晶界上空洞形成和相互连接而成,裂纹可沿晶界和晶内扩展,但不连续。脆性状态时,裂纹沿晶界发生,它是由晶界形成空洞和相互连接而成,扩展仅沿晶界发生。     

钛合金的断裂韧性

断裂韧性是材料对裂纹和其它尖锐缺陷扩展抗力的一种特性。在破断会产生严重后果的场合下所使用的钛合金和其它材料,断裂韧性是重要的。由于钛比其它许多结构材     

烧结NdFeB永磁合金的断裂韧性

用Zwick万能实验机测量了烧结NdFeB永磁合金样品的三点弯曲强度、断裂韧性KIC及弹性模量E。在三点弯曲试验中测得塑变功为0，而断裂功与最大消耗功相等，表明烧结NdFeB合金具有极大的缺口敏感性。缺口敏感的脆性材料用单边切口粱法（SENB）测量KIC时要求较高的抛光精度，以消除表面划痕的影响，比较而言，压痕法测量KIC简便迅速。但由于所用NdFeB合金为烧结复相材料，其微观结构的不均匀性使实验数据较为分散。本研究借助Palmqvist裂纹系统半椭圆裂纹模型HV-KIC的计算公式，采用开微缺口的单边缺口粱试样的KIC和压痕硬度及系列压痕裂纹参数，经回归分析确定了该公式中的经验常数，使之能够较为准确地表征烧结NdFeB永磁合金的断裂韧性。     

蠕变断裂韧性对Cr-Mo-V钢蠕变-疲劳交互作用下裂纹开裂和扩展的影响

本文研究了蠕变断裂韧性对三种低合金Cr-Mo-V钢在蠕变一疲劳交互作用下裂纹开裂和扩展的影响.试验表明,材料韧性对裂纹开裂和扩展起重要作用,脆性状态时,裂纹开裂时间比蠕变时短,二者间的裂纹扩展速度无明显差别;韧性状态时,裂纹开裂时间不仅比蠕变时短,而且其裂纹扩展速度比蠕变时大得多.此外,低合金Cr-Mo-V钢经蠕变一疲劳交互作用后有脆化倾向,其脆性程度取决于钢的原始韧性值.韧性状态时,蠕变-疲劳交互作用显著促使三种Cr-Mo-V钢由韧性向脆性转变;而在脆性状态时,这种脆性转变不明显。     

基于数字图像相关方法测试Cr12MoV钢的断裂韧性

将数字图像相关方法用于测量含Ⅰ型裂纹Cr12MoV钢的断裂韧性。搭建了数字图像相关方法非接触光学测试系统,通过进行三点弯曲试验,得到了Cr12MoV钢试件裂纹尖端的位移场。从位移场提取了裂纹嘴张开位移,并通过P-V曲线得到Ⅰ型裂纹Cr12MoV钢的断裂韧性。将实验结果与传统COD引伸计测试结果进行对比,误差不超过10%,证明该方法是准确的。     

用多次冲击法测定金属断裂韧性

多次冲击条件下裂纹尖端应力强度因子的表达式为K_I=(AE/BW)~(1/2)·F(a/W)。经柔度法标定,其临界值可用以度量材料的断裂韧性。所得结果相当于加载速率为k=10~5公斤/毫米~(3/2)/秒下的动态断裂韧性K_(Id)。断口上临界裂纹尺寸在(a/W)=0.36-0.6范围内,结果有效。多次冲击法较为简便,只需测出断口上的临界裂纹尺寸,便可在已绘好的曲线上直接查出材料的断裂韧性。在实际生产中可以作为一种筛选方法应用。     

粉末冶金材料断裂韧性的动态算法

引入等效表面能密度概念,建立了含微裂纹材料的断裂韧性计算法,并利用动态规划算法研究了微裂纹的分布和取向对材料断裂韧性的影响。根据不同取向微裂纹的统计分布规律,给出了材料断裂韧性和微裂纹标量密度之间的解析式。     

Toughness of aluminium alloy foams

The fracture behaviour of closed cell aluminium-based foams (trade-name “Alulight”) is characterized for the compositions Al–Mg1–Si0.6 and Al–Mg1–Si10 (wt%), and for a relative density in the range 0.1–0.4. The toughness testing procedures are critically analysed, and the origins of the observed R-curve behaviour for metal foams are explored. A major contribution to the observed increasing crack growth resistance with crack advance is in the development of a crack bridging zone behind the crack tip. The crack bridging response is quantified in terms of a crack traction vs extra displacement curve by performing independent tests on deep notch specimens. The area under the bridging traction vs extra displacement curve from the deep notch tests is approximately equal to the measured initiation toughness J_IC, in support of the crack bridging concept. A line spring model is then used to interpret the fracture response. The effect of material composition and relative density upon the initiation toughness is measured, and the accuracy of an existing micromechanical model for the fracture toughness of a brittle foam is assessed. Finally, the reduction in tensile and compressive strengths due to the presence of an open hole is determined; it is found that the Alulight foams are notch-insensitive, with the net section strength equal to the unnotched strength.     

Influence of the notch root radius on the fracture toughness of brittle metals: Nanostructure tungsten alloy,a case study

Tungsten and tungsten-based alloys are considered to be candidate materials for next-generation nuclear fusion reactors. Unfortunately, their use in structural applications is compromised due to their inherent brittleness. To improve this crucial feature, it is necessary to accurately measure their fracture toughness as a real property independent of geometrical parameters and the method used to introduce the induced crack. This goal is the objective of this work; where the notch tip radius influence on the fracture toughness of a brittle nanostructured tungsten alloy is analyzed in depth.Three-point bending tests at room temperature were performed on four types of notch geometries in which the notch root radius was gradually reduced. The notches were introduced using four different methods: with a classical diamond disc, a diamond wire, a razor blade and an ultra-short pulsed laser. The results showed that single edge notched beam specimens overestimate the fracture toughness values and introduce some deformation into the notch root grains. However, the razor blade yields very good results with a low dispersion, but is only suitable for coarse grain materials since the size effect appears as the grain size decreases. Therefore, for nanostructured materials such as in this case, the notch root radius is still too large (several times the grain size), requiring the implementation of a new method. Very sharp single edge laser-notched beam specimens with a 5–20 nm root radius were accordingly produced by using ultra-short pulsed laser ablation. This method has been previously used on ceramics but no evidence of its use was found on metals.     

焊接接头高应变率下的动态断裂韧度分析

对采用Hopkinson气炮加载－Charpy V形冲击试样试验方法对焊接接头高应变率下的动态断裂韧度数据进行了分析研究，通过对试样断口形貌、冲击吸收功、断裂韧度及其影响因素进行分析，表明在高应变率加载条件下，焊接接头冲击试样断口形貌有特殊的表现，延伸带或钝化区的尺寸大小反映了裂纹萌生前的塑性变形大小，也反映了裂纹萌生功的变化趋势。同时说明焊接接头在高速动态冲击载荷作用下，其断裂韧度参量受组配强度、冲击速度及环境温度等因素影响显著，焊接热影响区的断裂韧度值关系到焊接接头断裂韧度的好坏。     

晶粒尺寸对纳晶双峰材料断裂韧性的影响

为了描述由纳晶基体和粗晶颗粒组成的纳晶双峰材料的断裂韧性,通过建立一个粘聚力模型来研究纳晶双峰材料的临界应力强度因子K_(IC)(表征材料断裂韧性)。考虑到纳晶双峰材料的一个典型情况:裂纹位于2个纳晶颗粒的交界面处,裂纹尖端与粗晶粒的晶界相交,假设粘聚区的尺寸等于纳晶颗粒的尺寸d。裂纹的钝化和扩展过程受位错和粘聚力的共同影响,刃型位错是从粘聚力裂纹的尖端发射,该过程对裂纹产生屏蔽效应。模型计算结果显示:当粗晶颗粒尺寸D确定时,K_(IC)随着纳晶材料晶粒尺寸d的增大而增大;当纳晶材料晶粒尺寸d确定时,K_(IC)随着粗晶材料晶粒尺寸D的增大而增大;相对于纳晶颗粒的尺寸,断裂韧性对粗晶晶粒的尺寸更加敏感。     

Effect of notch-root radius on the fracture toughness of composite Si3N4 ceramics

In-situ silicon nitride and a whisker-reinforced silicon nitride-silicon nitride composite, densified via gas pressure sintering and hot pressing, respectively, were evaluated using the single-edge V-notched beam (SEVNB) fracture toughness technique. The mean value ofK _IC for each material was 5.7 and 7.9 MPa·m^1/2, respectively, and the toughness was influenced by the presence of the elongated Si₃N₄ grains in the microstructure. The notch radius was observed to have the same effect as a sharp crack when notch-root radius was smaller than 10 μm, which was considered to be a realK _IC for these materials.     

硬质相晶粒尺寸对MO2FeB2基金属陶瓷断裂韧性的影响

以Mo、Fe、FeB等为原材料,采用最高烧结温度（保温时间）分别为1170℃（0min）、1250℃（0min）以及1250oC（40min）的真空烧结工艺制备了硬质相晶粒尺寸不同的M02FeB：基金属陶瓷,所得烧结体的硬质相晶粒尺寸分别为1．12、1．31和1｜73wm。利用压痕法测定了M02FeB：基金属陶瓷的断裂韧性。结果表明：M02FeB：基金属陶瓷的断裂韧性随着硬质相晶粒尺寸的增加而增大,当晶粒尺寸从1．12μm增加到1．73μm时,Mo2FeB2基金属陶瓷的断裂韧性从11．4MPa·m^1/2增加到14．2MPa·m^1/2。随着硬质相晶粒尺寸增加,裂纹偏转增强,并出现裂纹桥联和晶粒拔出现象,导致裂纹扩展路径和能量消耗增大,从而提高了Mo2FeB2基金属陶瓷的断裂韧性。     

采用顶出方法研究纤维增强钛基复合材料的界面断裂韧性

为了估计单向SiC纤维增强钛基复合材料的界面断裂韧性G_IIc,本文提出了一个关于单根纤维顶出试验的新模型,在本模型中,界面脱粘开始于试样的底端面。本文以断裂力学为基础推导出了G_IIc 的理论公式,并且讨论了几个关键因素对G_IIc的影响,如裂纹扩展所需的外加应力,裂纹长度以及界面的摩擦剪切应力。并且运用此模型预测了复合材料 Sigma1240/Ti-6-4, SCS/Ti-6-4, SCS/Timetal 834 and SCS/Timetal 21s 的界面断裂韧性,并与以前的有限元结果进行了比较。结果显示,对于脱粘起始于试样的底端面的顶出试验,本模型能较可靠地预测钛基复合材料的界面断裂韧性。     

Sources of Variability and Lower Values in Toughness Measurements of Weld Metals

In this paper, the sources of variability and lower values in toughness measurements of a high-strength low alloy weld metal are investigated by detailed observations of fracture surfaces and the microstructures at crack initiation. The results reveal that the variability of the notch Charpy toughness is related to the location of the cleavage initiation origins. The three factors jointly contribute to give rise to variability and lower value of toughness. That is, (1) the location that the notch is sampled at deposited weld metal or reheated weld metal, (2) the location that a large grain region is appeared on the path ahead of the notch root, (3) the distributed location of the defect or the brittle second-phase particle. When three factors were simultaneously satisfied, the lower value of the Charpy toughness is appeared. The notch is sampled at the largest grain region at deposited weld metal, and the defect or the brittle second-phase particle is close to the notch root and sampled by its high stress field, the lowest Charpy toughness is obtained.     

定向凝固Nb-Ti-Si基超高温合金的组织与室温条件断裂韧性

采用真空自耗电弧熔炼法制备了Nb-Ti-Si基超高温合金的母合金锭,在2050℃的熔体温度下实现了合金的有坩埚整体定向凝固.测定了电弧熔炼态与定向凝固试样的室温条件断裂韧性,采用SEM,EDS等方法分析了凝固速率V分别为10,20和50 μm/s的整体定向凝固组织、单边切口梁弯曲试样的断口形貌及裂纹扩展路径,并讨论了其断裂机理.结果表明:合金的整体定向凝固组织主要由沿着试棒轴向挺直排列的横截面为多边形的初生(Nb,X)5Si3 (X代表Ti,Hf和Cr元素)棒与耦合生长的层片状Nbss/(Nb,X)5Si3共晶团(Nbss表示铌基固溶体)组成.整体定向凝固显著提高合金的室温条件断裂韧性KQ,且V=50μm/s时的最高,达16.1 MPa·m1/2,较电弧熔炼态试样的KQ提高了50.5％.定向凝固试样中Nbss与(Nb,X)5Si3沿垂直于受力方向的定向排列以及粗糙的Nbss产生的裂纹桥接和偏转,增大了裂纹扩展阻力,从而提高了合金的室温条件断裂韧性.     

Effect of Trace Element on Microstructure and Fracture Toughness of Weld Metal

The microstructure and fracture toughness of weld metal under Ti-free and Ti-containing different fluxes were investigated in this study.It was found that the trace element Ti of flux in submerged arc welding produced significant influence on the fracture toughness.The addition of 60 ppm Ti induced the sharp increase in J_(0.2) value from 232.78 to 364.08 kJ/m~2.Microstructure characterization revealed that a large number of oxide inclusions prompted the nucleation of acicular ferrites and refined grains,which improved the fracture toughness of Ti-containing weld metal greatly.Moreover,the crack propagation path was more tortuous and bifurcated due to the small amount of carbide precipitations along grain boundaries and blocky martensite-austenite islands for Ti-containing weld metal.Meanwhile,the large-angle grain boundaries caused crack deflection and increased the resistance of crack propagation compared to Ti-free weld metal.