复合材料拉伸过程的声发射特性研究

为了研究16MnR／0Cr18Ni9Ti复合材料断裂过程的声发射特性,可以利用声发射技术对16MnR／OCr18Ni9Ti复合材料试件的拉伸过程进行全程监测。研究表明,材料拉伸断裂过程中,声发射信号丰富明显,可测性良好,并且不同破坏阶段的声发射信号具有不同的特征。通过对不同拉伸阶段声发射信号的参数分析,可以了解材料不同变形阶段的声发射特性,并据此来分析材料损伤的发生、发展及演变过程。与传统的力学试验方法相比,声发射技术在研究复合材料断裂过程方面具有明显的优势。     

防喷器壳体材料拉伸过程的声发射特性试验

采用声发射技术研究了防喷器主壳体材料ZG25GrNiMo的拉伸破坏过程。运用声发射参数分析方法分析了该材料在不同破坏阶段的声发射特性。分析结果表明,在材料屈服、塑性变形及断裂过程中的声发射特性具有明显的不同,且不同损伤模式的信号频谱存在明显的差异。     

HTPB推进剂温度冲击环境下损伤特性的声发射试验

为研究HTPB推进剂在温度冲击环境条件下的损伤情况,采用单轴定速拉伸声发射（AE）试验,对不同温度冲击周期试验后的HTPB推进剂的损伤特性进行了研究。结果表明：温度冲击后的HTPB推进剂单轴拉伸存在损伤成核、扩展和汇合断裂三个失效阶段;随温度冲击周期的增加,HTPB推进剂释放出的AE累积能量减少,说明在其内部会出现一定损伤,且损伤程度与温度冲击时间呈正相关性;温度冲击时间越长,损伤门槛值提前,越容易出现初始损伤。     

防喷器材料在拉伸过程中的声发射信号特性

用声发射技术研究防喷器材料ZG25CrNiMo裂纹试件的拉伸损伤与断裂行为。声发射仪器记录了ZG25CrNiMo裂纹试件在拉伸破坏过程中的声发射信号,运用声发射参数分析方法和波形分析方法对zG25crNiMo裂纹缺陷试件的声发射数据进行分析,得出材料在拉伸过程中的损伤类型以及各阶段所呈现的特性。试验结果表明,拉伸过程中破坏机制对声发射信号的特征具有显著影响,不同损伤阶段的信号频谱特征存在差异。     

Q345R疲劳损伤过程声发射信号特征分析

制冷系统压力容器应用非常广泛，对于该类在役压力容器还没有可靠的实时动态监测方法。提出采用声发射检测技术对制冷系统压力容器进行实时监测，通过对容器制造材料Q345R钢的疲劳载荷试验，采集材料损伤全过程的声发射信号进行特征参数分析、波形和频谱分析，发现材料从裂纹萌生到断裂失效过程的转折点，并对不同损伤阶段声发射信号波形和频谱的特性进行对比研究，找出各个阶段声发射信号的特征，为实现Q345R声发射动态监测和评价提供可靠依据。     

16MnR／0Cr18Ni9Ti复合钢板损伤与断裂过程的声发射特性试验

研究了16MnR／0Cr18Ni9复合钢板在承受拉伸载荷时的损伤与断裂行为。给出了损伤类型、阶段和恒载等关键声发射特性,发现了不同损伤类型表现出不同的声发射特性。损伤与断裂的不同阶段,可用声发射信号的几种关联图进行区分。     

声发射逆向分析及其在现代材料检测中的应用

人们一直在寻找无损评价现代材料诸如陶瓷和复合材料等的技术和方法.就陶瓷而言,最重要的课题之一是探测出<100μm的小裂纹;而对于复合材料,分辨各种微断裂则是当前的一个重要任务.为了提高现代材料的可靠性,人们同样希望将声发射源特性分析方法用于了解裂纹的尺寸、模式及取向等微断裂定量参数.本文首先介绍探测低幅度信号的低噪声换能器,概述了陶瓷的声发射信号特性;继而依据微断裂和结构评价的观点,提出了应用声发射技术评价纤维增强塑料的观点;随后讨论了声发射源特性对评价现代材料的作用.     

4种C/E复合材料NOL环试样拉伸试验过程的声发射特性

通过对4种C/E(碳纤维环氧树脂)复合材料NOL(美国海军军械实验室)环试样拉伸断裂过程的声发射特性研究发现,材料强度、模量以及缠绕工艺均会对材料损伤过程的声发射计数、信号幅度、持续时间等特征值产生显著影响。在材料的声发射特性试验中,准确得到材料损伤的特点和变化趋势是优化复合材料制造工艺、指导结构强度设计与检测的重要途径。     

用声发射技术研究水泥基复合材料脆性

观测了不同种类混凝土三点弯曲梁的声发射（AE）特性,发现掺加纤维对声发射特性有明显影响。掺加纤维的混凝土梁,声发射事件突发性明显减小,采用Weibull函数方法定量分析了材料特性对混凝土试件的声发射特性、断裂特性及脆性的影响。结果表明,参数m和θ具有明显的物理意义,m值表征由材料特性引起的脆性,而θ值表征由试件几何尺寸引起的试件脆性。     

16MnR钢板低温冲击过程的声信号特性

在20℃至-55℃下对16MnR材料进行Charpy冲击试验,用声发射技术监测各温度下冲击开裂的过程。采用小波分析结合傅里叶变换的方法,得到了16MnR试样开裂过程的波形频谱特性及电压幅值,并且采用金相和SEM对冲击断口进行了组织、形貌分析。结果表明:随着温度的下降,声发射计数率、声发射能量及声发射持续时间均呈降低趋势,声信号幅值变化不大。小波分解后的d2层能量包含冲击断裂的主要能量,与冲击功的变化趋势相似,具有较强的相关性。试验结果为声发射技术监测冲击载荷作用下的材料内部结构演化提供了一个思路。     

Möglichkeiten zur Früherkennung von Wasserstoffschädigungen in metallischen Werkstoffen durch Anwendung der Schallemissionsanalyse

Feasibility of early detection of hydrogen in metals by acoustic emission analysis Acoustic emission measurements are performed with the steels Ck 35 and 35 NCD 16. In function of the tensile strength tensile specimens are charged electrochemically with hydrogen. It is shown, that even in the charging phase acoustic emission signals can be registered. Especially during the repeated tensile test with hydrogen-charged specimens material damages can be detected with acoustic emission. In this case the well-known Kaiser effect in acoustic emission is omitted. The effect of the absorbed hydrogen is documented by changes of the mechanical properties of the material and by microfractographic investigations.     

铝合金疲劳裂纹扩展声发射监测

采用声发射(acoustic emission,AE)技术对7N01铝合金单边缺口三点弯曲试样不同应力比、不同峰值载荷下疲劳裂纹扩展过程中声发射信号进行了监测,建立了裂纹扩展速率、声发射计数(count)与应力强度因子之间的关系.结果表明,大部分的声发射信号主要产生于疲劳循环载荷的低应力阶段,这主要是低应力阶段的声发射活动主要与裂纹尖端的塑性变形和裂纹闭合现象有关,声发射计数与应力强度因子之间呈指数增长的关系.基于所建立的声发射计数率与裂纹扩展速率的关系,可以预测疲劳损伤结构的剩余寿命.     

高强铝合金沿晶断裂声发射研究

高强度铝合金沿晶界断裂过程中的声发射信号特征反映了材料沿轧制方向的宏观性能。在带有预制裂纹的双悬臂梁(DCB)试样中，裂纹失稳扩展前，先有一短距离的韧窝状穿晶撕裂的稳态裂纹扩展。稳态裂纹扩展起始于K1C并发射出许多幅值超过阈值35dB的信号。当稳态裂纹扩展至Kmax时，便出现失稳的沿晶开裂。对稳态及失稳的裂纹扩展两种情况，其累计声发射能量均与宏观断裂能呈线性关系。     

Application of a novel type Barkhausen noise sensor to continuous fatigue monitoring

A novel Barkhausen noise (BN) sensor with no need for external magnetization was tested and applied to continuous fatigue monitoring of mild steel and high strength steel specimens. This new type of sensor indicated an increase in the BN rms value under maximum tensile stress during one cycle in cyclic bending tests with increasing stress amplitude. The BN rms value under maximum compressive stress stayed, however, approximately constant. The reason for this behaviour was the stress-induced anisotropy of the BN. Bending fatigue experiments with constant stress amplitude and R=−1 were conducted at different stress levels. In addition to the BN also the acoustic emission of the specimen was measured. In the mild steel specimens the BN amplitude stayed constant after the initial saturation period, but just prior to the failure of the specimen the amplitude increased meaningfully. This increase occurred at the same time as the increase in the acoustic emission signal indicating the beginning of crack initiation and growth. In the high strength steel specimens the BN amplitude decreased after the initial saturation period. The increase of the BN signal started well before the failure of the specimen and even before the increase in the acoustic emission signal.     

Integrity evaluation of glass-fiber composites with varied fiber/matrix interfacial strength using acoustic emission

An advanced acoustic emission analysis method was used to study the dynamics and sequence of microfractures in uni-directional glass-fiber reinforced plastics (UD-GFRPs). UD-GFRPs (60 wt% fiber) with different interfacial qualities were prepared by adding a small amount (4 or 8 wt%) of paraffin wax into vinylester matrix without affecting much the mechanical properties of the matrix. The orientation dependence of both the P-wave velocity and attenuation were accurately measured by the laser ultrasonic method, and incorporated into the acoustic emission analysis of visco-elastic media. The analysis iteratively compares the acoustic emission signals (measured as out-of-plane displacements) with theoretical waveforms calculated assuming the time history and type of an acoustic emission source. The waveform simulation allows us to estimate the fracture dynamics and the sequence of the Mode-I fiber fracture (Type 1), Mode-I debonding (Type 2) and Mode-II disbonding (Type 3). The fiber fracture in UD-GFRPs without wax started at 0.1% strain. The initiation strain increased to 0.25 and 0.3% in the specimens with wax. The specimens with lower interfacial strength showed rapid succession of microfractures at higher stresses (above 100–200 MPa). Fracture dynamics showed distinct differences by wax addition. Using the present analysis method, we can determine quantitatively effects of interfacial quality on the microfracture processes and assess the integrity of UD-GFRPs.     

H62铜合金试件拉伸过程声发射监测与数据分析

铜材料由于具有较好的耐腐蚀性,近年来被广泛应用于化工等行业。应用声发射检测技术对铜制承压设备进行检测是较为有效的方法之一。制作了H62型号的铜拉伸试件,并对拉伸过程进行了声发射监测。研究结果表明,铜材料的弹性阶段较短;对于铜拉伸试件,由于其材料黏弹性较高,出现破坏时,高幅值信号较少;相同铜试件,有效声发射信号个数与加载速率有关,加载速率越快,有效声发射信号越多;铜材料声发射信号的波形峰值频率一般出现在210-340kHZ范围。相关结论可以为开展铜制承压设备的声发射监测提供参考。     

基于穷举法的三维声发射源定位算法

声发射源定位算法的选择直接影响数据利用率和定位精度。提出一种基于穷举法的三维声发射源定位算法,针对直接搜索穷举法的计算耗时问题,采用利用传感器激发顺序确定搜索区域的改进措施。执行了不同尺寸试件的断铅激发源定位试验和劈裂试验,给出了搜索节点间距选取的建议,并对某商业AE软件和两种穷举法定位计算的数据利用率、计算耗时和定位精度指标进行了比较和评价。结果表明,恰当选取搜索节点间距可使计算耗时和定位精度达到相对稳定的水平,改进后的穷举法计算耗时约为直接搜索穷举法的20%,穷举法的定位精度和数据利用率均比商业AE软件高。     

热模钢的脆性与热疲劳测定

本文阐述了热模钢的脆性与热疲劳测定方法,比较了常规热处理试样与渗猛处理试样的脆性行为和热疲劳特性。经金相观察、硬度测定、扫描电镜的电子探针和能谱分析、X射线衍射分析及声发射、热疲劳等试验,结果表明:渗锰试样的脆性低于常规处理试样,其耐热疲劳性则高于常规热处理试样。     

Acoustic emission monitoring of slow strain rate tensile tests of 304L stainless steel in supercritical water environment

An experimental set-up has been developed to perform slow strain rate tensile (SSRT) tests on tubular 304L stainless steel (SS) specimens in supercritical water (SCW) environment (550 °C, 250 bar). The supercritical water is circulated inside an internally pressurized tubular specimen mounted into a universal mechanical test rig and heated by a single loop resistance heating furnace. The set-up enables in situ monitoring of acoustic emission and electrochemical potential during the SSRT test. The SCW environment is found to significantly influence the mechanical performance of the material as a result of corrosion processes. A correlation between acoustic emission response and change of electrochemical potential is revealed. The findings are compared with preliminary results of tests performed on bulk SS specimens under the same condition in a commercial autoclave. The advantages and potentialities of both set-ups are discussed.