声光调Q Nd:YAG脉冲激光修锐树脂结合剂CBN砂轮

采用声光调Q Nd:YAG脉冲激光径向辐照，对树脂结合剂CBN砂轮进行修锐试验研究。研究了单脉冲激光辐照下，平均功率，脉冲频率和离焦量等参数对烧蚀凹坑深度的影响，由此可方便获得合适的激光修锐参数；分析了声光调Q YAG脉冲激光修锐树脂CBN砂轮的选择性去除机理，观察并比较了声光调Q脉冲激光，连续激光和机械法修锐后砂轮表面的地形地貌，试验表明声光调Q Nd:YAG脉冲激光径向辐照修锐树脂CBN砂轮，可获得更为良好的修锐效果。     

声发射技术在氧化膜破裂监测中的应用

在高温腐蚀领域,声发射技术是一种最有效且具有极高灵敏度的监测氧化膜破裂的技术.通过分析声发射计数,可以判断氧化膜首次发生破裂的时间及最后破裂的程度.如对声发射频谱进行分析,则可以判别氧化膜内发生塑性变形、开裂及剥落的过程.利用声发射技术还可以测量氧化膜/合金界面处预存物理缺陷大小及分布.此外,将声发射技术与其它技术结合,可建立全新的分析测试系统.综述了声发射技术用于监测氧化膜破裂的原理和方法,以及多种性能测试方面的应用与新发展.     

Preparation of flee-standing diamond films for high frequency SAW devices

Free-standing diamond films were prepared by hot filament chemical vapor deposition （HFCVD） method under different conditions. Inter-digital transducers （IDTs） were formed on the nucleation sides of free-standing diamond films by photolithography technique. Then piezoelectric ZnO films were deposited by radio-frequency（RF） reactive magnetron sputtering to obtain the ZnO/diamond film structures. Surface morphologies of the nucleation sides and the IDTs were characterized by means of scanning electron microscopy （SEM）, atomic force microscope （AFM） and optical microscopy. The results indicate that the surfaces of nucleation sides are very smooth and the IDTs are of high quality without discontinuity and short circuit phenomenon. Raman spectra show the sharp diamond feature peak at about 1 334 cmI and the small amount of non-diamond carbon in the nucleation side. X-ray diffraction （XRD） patterns of the structure of ZnO/diamond films show a strong diffraction peak of ZnO （002）, which indicates that as-sputtered ZnO films are highly c-axis oriented.     

EFFECT OF TOOL WEAR ON MICROSTRUCTURE, MECHANICAL PROPERTIES AND ACOUSTIC EMISSION OF FRICTION STIR WELDED 6061 Al ALLOY

Tool condition is one of the main concerns in friction stir welding （FSW）, because the geometrical condition of the tool pin including size and shape is strongly connected to the microstrueture and mechanical performance of the weld. Tool wear occurs during FSW, especially for welding metal matrix composites with large amounts of abrasive particles, and high melting point materials, which significantly expedite tool wear and deteriorate the mechanical performance of welds. Tools with different pin-wear levels are used to weld 6061 Al alloy, while acoustic emission （AE） sensing, metallographic sectioning, and tensile testing are employed to evaluate the weld quality in various tool wear conditions. Structural characterization shows that the tool wear interferes with the weld quality and accounts for the formation of voids in the nugget zone. Tensile test analysis of samples verifies that both the ultimate tensile strength and the yield strength are adversely affected by the formation of voids in the nugget due to the tool wear. The failure location during tensile test clearly depends on the state of the tool wear, which led to the analysis of the relationships between the structure of the nugget and tool wear. AE signatures recorded during welding reveal that the AE hits concentrate on the higher amplitudes with increasing tool wear. The results show that the AE sensing provides a potentially effective method for the on-line manitoring of tool wear.     

Fracture dynamics of sprayed and laser-glazed titania by an inverse processing of elastic waves

A new elastic wave (EW) or acoustic emission (AE) monitoring and signal processing system has been developed and used to elucidate the fracture behavior of sprayed and laser-glazed ceramic coatings. The system measures the minute surface displacements excited by the propagation of elastic waves. It enables elucidation of the fracture dynamics (fracture mode and kinetics) of stressed coatings. The surface displacement at the sensor position was computed by the convolution integral of an assumed source wave with the dynamic Green’s function until signals resembled the measured wave. This new signal processing method was used to determine the fracture strength and dynamics of microcracks in sprayed and laser-glazed titania subjected to four-point bending. It was found that mode II shear cracking along the interface between the coating and substrate occurred prior to mode I cleavage cracking. The fracture strength of laser-glazed titania was higher than that of as-sprayed titania in most cases; however, this depended on the coating structure. This article introduces the principle of source inversion processing of elastic waves, the monitoring system, laser glazing of sprayed titania, and experimental work on the fracture behavior of titania coatings.     

功率超声对Pb-Sn合金凝固行为的影响

研究了功率超声对铅锡合金凝固过程的影响,分析了其影响机制.结果表明,在功率超声作用下,声空化效应和声流效应使含铅5%的铅锡合金的凝固组织明显细化,并且经过功率600W的超声处理后,先析出相的析出温度升高3℃,凝固温度升高了5℃.随着超声功率的增加,合金组织的细化程度提高,但功率提高到一定程度时,细化作用减弱.     

电磁超声传感器检测不同材质钢管的试验研究

通过试验确定了不同材质钢管的磁致伸缩曲线，得到了不同材质钢管缺陷检测的电磁超声传感器（EMAT）直流电磁铁的励磁电流与超声波幅值的关系，确定了最佳励磁电流，并得出其变化规律与磁致伸缩曲线变化趋势一致的结论。为电磁超声传感器设计和开发提供了依据。     

声发射方法测定SiCw／Al复合材料的界面强度

对ＳｉＣｗ／Ａｌ复合材料形变断裂过程中的声发射（ＡＥ）特征的研究表明，用ＡＥ技术能准确测定ＳｉＣ纤维的断裂次数，并能测定其断枝长度，从而测定了纤维和基体间的界面强度和ＳｉＣ纤维的断裂强度。     

基于Aqua-Sim的水声传感器网络MAC层协议分析

分析了水声传感器网络中MAC层协议的特点和分类.利用基于NS2的Aqua-Sim水声网络仿真模拟软件仿真了Broadcast MAC协议和R-MAC协议在五个节点的集中式拓扑结构的水声传感器网络中的传输过程,分析比较了两种协议在平均数据包延时、平均能量消耗以及平均吞吐量上的异同.得出在集中式拓扑结构的水声传感器子网中,Broadcast MAC协议更适合于要求较高吞吐量的应用环境,而R-MAC协议更适合于在能量消耗方面有严格要求的应用环境.     

LDPC码在基于FH-FSK的AUV水声通信系统中的应用

水声信道严重的多途干扰和频率选择性衰落,将增加水声FH-FSK系统的平均误码率.此外,由于自主式水下交通工具(AUV)平台的运动特性,接收信号易产生时间选择性衰落,在接收端产生成串的突发错误甚至导致通信的中断.以上两方面因素将降低移动FH-FSK系统的可靠性,针对此问题,将多元低密度奇偶校验(LDPC)码与FH-FSK系统相结合,提出了一种基于多元LDPC码的水声FH-FSK系统.对比了基于二元LDPC码的FH-FSK系统与基于卷积码的FH-FSK系统的抗干扰性能,实验结果表明:前者具有更强的抗干扰能力.对比了基于多元LDPC码的FH-FSK系统与基于二元LDPC码的FH-FSK系统,仿真与实验结果表明:基于多元LDPC码的FH-FSK系统具有更强的抗干扰能力,可以进一步提高FH-FSK系统的可靠性.