带不同深度缺陷Q235B板材拉伸过程声发射特征

通过对带有不同深度缺陷的Q235B板材的拉伸试验,利用声发射监测材料拉伸过程,获得材料拉伸过程中声发射信号,结合载荷时间曲线对声发射能量、撞击数、幅值等参数进行分析,研究各阶段声发射信号变化,以及不同深度缺陷声发射信号变化趋势。结果表明:声发射信号能够较好地反映损伤过程,屈服阶段声发射信号主要集中在下屈服点附近,随着缺陷的深度增加,下屈服点附近撞击数峰值有所下降;超过70 d B的幅值信号随缺陷深度增加而增多,其数量占总幅值数量的比例也随之增加;持续时间超过500μs的幅值信号分为A、B两类。试验结果对起重机械声发射监测的损伤判定提供依据。     

2.25Cr-1Mo钢后续热处理中的磷偏聚行为

根据溶质晶界偏聚理论和原子扩散原理研究了2.25Cr-1Mo钢服役12年后磷晶界偏聚行为及脱脆处理工艺。采用俄歇电子能谱实验对溶质原子的晶界偏聚程度进行了测试分析。结果表明:对于已脆化的2.25Cr-1Mo钢,存在临界脆化温度,且脆化程度越高,临界脆化温度越低;高于临界脆化温度数小时的保温即可消除脆化现象,即2.25Cr-1Mo钢的脱脆速率远大于脆化速率。     

Q235B钢板拉伸损伤试验的声发射特性

制作完整和焊接两种Q235B板材试样,利用声发射技术对其拉伸过程的损伤特性进行监测,根据获得的拉伸过程载荷时间历程曲线和材料损伤声发射信号,结合金属材料力学行为特性,对材料损伤声发射信号的幅度、振铃计数以及能量等参数进行分析,获得了材料塑性屈服、强化变形以及断裂等损伤阶段所表现出的声发射特性,通过对声发射信号撞击幅度和能量的统计分析,初步得到了不同损伤阶段所对应的声发射参数分布范围。对比分析完整和焊接两种试样损伤所表现出的不同声发射特性,结果表明声发射特性参数能够很好地描述焊接对材料力学特性的影响,并能以声发射参数"双峰"分布的形式从微观上反映焊接对试样屈服所造成的影响。实验结果为声发射技术应用于起重机结构状态监测提供了参考数据。     

Q235焊接钢板受剪声发射时频特性分析

Q235钢板在工程中应用广泛,为了研究焊接对于Q235钢板性能的影响,开展了焊接试样和完整试样的受剪实验,利用数字声发射系统对实验过程的声发射信号进行实时采集。根据声发射计数率划分不同阶段,采用魏格纳-维尔分布,平滑伪魏格纳-维尔分布,对信号进行时频分析。实验结果表明:受剪实验中,焊接试样与完整试样的声发射特性明显不同,主要表现在受剪过程的各阶段中声发射信号能量集中的频带不同,弹性变形阶段信号时频带主要集中在80~100 k Hz附近;钢板塑性变形阶段时频带集中在100~140 k Hz范围内;焊缝塑性变形阶段,时频能量主要集中的频带范围在300~350 k Hz之间,部分能量较弱的信号分布在100 k Hz附近频段。     

SPCC钢滑动摩擦与拉伸声发射信号比较分析

为了将声发射技术应用在金属塑性加工中的摩擦监测中,以SPCC钢在拉伸过程与相对运动速度为100mm/min、正压力为7.5kg的摩擦过程产生的声发射信号特征为研究对象,分别用数据统计、平均值等方法对比分析了两种声发射信号的能量、振铃计数、幅度等参数。实验结果表明:SPCC钢拉伸的声发射能量值要远小于摩擦声发射能量值;拉伸的声发射振铃计数分布范围要略大于摩擦声发射振铃计数分布范围;拉伸的声发射幅度要小于摩擦声发射的幅度。最后对出现该现象的原因进行了探讨。     

氢致304L奥氏体不锈钢脆断机理的研究

本文先对304L不锈钢进行■■充氧然后对充氢试样进行室温下拉伸,并用扫描电镜对拉伸断口进行形貌观察,同时对经不同拉伸变形后的充氧气样表面上的滑移线进行金相观察,此外还用X射线衍射法定量测定了钢中氢致马氏体的数量及γ基相的点阵常数变化情况。试验结果表明,阴极充氢可使304L不锈钢产生脆性断裂,其原因主要与钢中发生了不可逆的氢致马氏体相变有关。     

几种结构钢在人造海水中自腐蚀电位和析氢电位的研究

本文介绍了16Mn钢和2 1/4Cr-1Mo钢[注1]在人造海水中的自腐蚀电位和析氢电位的测量原理和方法。在实验中用怛电位仪测量不同试样的自腐蚀电位和析氢电位;研究了温度对试样自腐蚀电位的影响;不同热处理方法对试样自腐蚀电位和析氢电位的影响。     

新型Cr-Mo抗氢钢——2．25Cr-1Mo-0．25V

2．25Cr-1Mo-0．25V钢是一种新型的Cr—Mo抗氢钢,其抗氢腐蚀性能和抗氢脆性能比普通的Cr-Mo钢明显提高。但2．25Cr-1Mo-0．25V钢在焊接时易产生裂纹,因此,其焊接过程需要严格控制。     

30CrMnSiNi2A钢的氢致断裂研究

本文研究了30CrMnSiNi2A 钢在三种不同充氢条件下的裂纹扩展速率 dα/dt,声发射计数率 dn/dt 与应力强度因子 K_1之间的关系。实验结果表明,dα/dt 和 dn/dt 取决于 K_1的大小和试样中的原始含氢量,在双对数坐标中,dα/dt 和 dn/dt 都随 K_1的增加成直线关系增加,且随充氢时间的增加而增加,裂纹扩展的声发射讯号是断续突发性的。用缺陷增强氢的扩散过程的模型进行了理论计算,对实验结果进行了解释。     

含裂纹钢试样在拉伸过程中的声发射特性

对于带有I型裂纹的SM490A钢和SUS304钢试样,通过测量其在拉伸断裂过程中的声发射特征参数及裂纹尖端特定点的温度,分析了裂纹尖端和塑性变形区域的力学特征.结果表明:声发射能量计数、振铃累积计数在裂纹扩展的各个阶段都有着明显的曲线特征,且曲线特征和屈服、强化阶段的应力-应变曲线基本吻合,因此可以用声发射能量计数、振...     

Acoustic emission characterization of steel in H2S solution subjected to tensile load

Abstract

This paper investigates the characteristics of acoustic emission (AE) signals generated from hydrogen induced cracking (HIC) and sulfide stress corrosion cracking (SSCC) for a medium strength steel in hydrogen sulfide (H₂S) solution. The experiments performed in this study include the constant load test (CLT) and the constant extension rate test (CERT).

From the results of the CLT, the AE count rate caused by SSCC was found to be much higher than that resulted from the HIC; and the increase of the AE count rate was observed to be approximately proportional to the increase of the applied loading. In addition, the AE frequency distribution diagrams obtained from these tests were found to contain potential information for distinguishing the mechanisms of HIC and SSCC. From the results of CERT, the AE signals detected from the specimens tested in the H₂S solution were compared with those obtained from the specimens tested in the air. In addition, the AE count rate detected from the tensile specimens was studied according to the different deformation stages of the specimens. From this study, the variation of the AE count rate in each deformation stage was described.     

Characterization of Hydrogen Embrittlement in 2.25cr-1mo-0.25v Steel by Eddy Current Method

Eddy current method has been recently developed to characterize mechanical properties of materials and assess internal hydrogen content of high strength low alloy steels. The application of eddy current testing in evaluating hydrogen embrittlement state of 2.25Cr-1Mo-0.25V ferritic steel has been investigated using tensile test and electrochemical hydrogen charging test. The relationship between the embrittlement index and eddy current signal is well established. It found that there is a good linear relation between the hydrogen-induced plasticity loss and the eddy current signal. This shows eddy current testing is an effective method for evaluating hydrogen embrittlement state of 2.25Cr-1Mo-0.25V steel.     

Acoustic emission during the tensile deformation of Incoloy 901 superalloy

Observations have been made on the acoustic emission (AE) response related to the deformation-damage mechanisms during tensile tests of a common engine material, Incoloy 901 superalloy. Results show that dislocation motion, twinning and inclusion fracture cooperated to generate acoustic emission during tensile deformation of Incoloy 901. Based on AE recorded results and microstructural examination, a dislocation-saturation model was developed to describe AE activity during elastic and plastic deformation, and to distinguish between the AE response in the yield region and in the work-hardening region. Furthermore, the effects of strain rate and loading methods on AE outputs were examined. The dependence of acoustic emission on dislocation motion and saturation, deformation twinning, and decohesion and fracture of inclusions and secondary particles are discussed.Formerly a postdoctoral student, Faculty of Mechanical Engineering, Technion, Israel.     

Acoustic emission as a technique to study breakaway oxidation and spalling behaviour of 2.25Cr-1 Mo steel

The onset of breakaway oxidation and cracking of the oxide scale formed on 2.25Cr-1Mo steel in air at 1173 K have been studied by the acoustic emission (AE) technique. AE parameters, i.e. events, ring-down counts, rise time, event duration and root mean square voltage show negligible increase during isothermal heating at this temperature, until a point where a sudden increase in AE activity is found. This point corresponds to the onset of breakaway oxidation. An enormous increase in AE activity after the start of cooling from the oxidation temperature has been attributed to separation of the oxide scale from the matrix. The peak amplitude distribution is measured and a derived b parameter is calculated. This has helped in distinguishing the phenomena of isothermal oxidation at 1173 K and internal cracking of oxide scale during cooling from 1173 K.     

SUS304不锈钢拉伸过程中的声-热像特征

测量了含有Ⅰ型裂纹的SUS304不锈钢试样的单轴拉伸过程中的塑性变形和断裂。分析了裂纹尖端区域的塑性变形和断裂过程。结果表明:SUS304的各向异性在断裂阶段对声发射信号影响较大;红外热图像中的温度分布与塑性应变率有关;通过声发射参数和红外热图像可以从微观和宏观两方面分析裂纹尖端区域的塑性变形和断裂。     

Effects of hydrogen on the mechanical response of X80 pipeline steel subject to high strain rate tensile tests

Hydrogen‐induced degradation of X80 pipeline steel was investigated through a high strain rate tensile test (2 × 10^?4/s) with interposed unloading, reloading, aging at 30°C, or annealing at 200°C with or without hydrogen charging. The results indicated that plasticity degradation does not occur in the hydrogen‐precharged specimens; however, hydrogen embrittlement occurs in the reloading stage when the specimens are charged with hydrogen in the unloading stage after applying a prestrain. Interposed aging at 30°C or annealing at 200°C can also increase the degradation. It indicates that the hydrogen traps caused by the strain along with hydrogen charging are the major source of dislocations. The formation of a hydrogen atmosphere around mobile dislocations, which is related to the rates of hydrogen diffusion and dislocation movement, plays an important role in the degradation process. Both pinning and depinning of dislocations affect plasticity degradation.     

聚乙烯自增强复合材料损伤过程的声发射特征

复合材料在承受外载时, 声发射可产生于基体破裂、纤维-基体界面脱粘和纤维断裂等。测定了U HMWPE/ HDPE 复合材料在拉伸载荷作用下的声发射(AE) 振幅信号。对特殊试样, 即预测到断裂有明确方式, 如纤维-基体界面脱粘、基体破裂、纤维断裂和分层等的试样, 实施加载直至破坏。用扫描电子显微镜(SEM) 观测试样的断裂表面, 对产生于若干特殊损伤类型的AE 信号进行了鉴别。在相同加载条件下, 完成了不同种类的U HMWPE/ HDPE 准各向同性层合板声发射检测。结果在特殊试样损伤类型与声发射信号事件振幅之间建立了对应关系, 揭示了上述各种准各向同性层合板损伤扩展过程的AE 特征与损伤破坏机制。各种准各向同性层合板试样的声发射事件累计数对拉伸应力关系曲线相异, 其相同损伤类型发生时所对应的拉伸载荷水平不等, 表明它们的铺设角度和铺设顺序对损伤演变过程有显著的影响。结果证实了它们的最终破坏由严重层间分层造成。      

Effect of gaseous hydrogen charging on the tensile properties of standard and medium Mn X70 pipeline steels

The tensile properties of two X70 steels with high (1.14 wt-%) and medium (0.5 wt-%) Mn contents have been investigated by testing at 25°C of tubular specimens charged with an internal gas pressure of 10?MPa of hydrogen or argon. The hydrogen-charged samples were additionally tested at 50 and 100°C. Tensile testing showed that the equiaxed ferrite–pearlite microstructure of higher Mn steel was most sensitive to hydrogen embrittlement and that the banded ferrite–pearlite microstructure of the higher Mn strip was more susceptible to hydrogen embrittlement than the medium Mn strip. The more highly banded ferrite–pearlite microstructure in the higher Mn steel provided numerous sites for concentration of hydrogen to levels that promoted crack initiation and growth. Test temperatures up to 100°C reduced the yield and tensile strengths, increased the total elongation and decreased the extent of hydrogen embrittlement because of enhanced dislocation mobility and less effective hydrogen trapping.     

基于声发射检测技术的PE/PE自增强复合材料破损机理分析

用声发射(AE)技术研究了聚乙烯自增强复合材料的拉伸损伤与断裂行为.宽带传感器记录了不同角度纤维铺层的复合材料试样在拉伸破坏过程中的声发射信号,用扫描电子显微镜(SEM)观察了试样的几种典型的损伤破坏断面,对比分析了不同类型的损伤机制.实验分析表明,拉伸过程中破坏机制对声发射信号的特征具有显著影响,不同损伤模式的信号频谱特征存在明显的差异.声发射检测能有效提取热塑性复合材料损伤破坏信息,在材料的结构损伤主动监测中有良好的应用潜力.