SiC nanoparticles reinforced magnesium matrix composites fabricated by ultrasonic method

SiC nanoparticles reinforced magnesium matrix composites were fabricated by ultrasonic method.The AZ91 alloy and SiC nanoparticles with the average diameter of 50 nm were used as the matrix alloy and the reinforcement,respectively.The addition of nanoparticles was 0.1%,0.3%,and 0.5%(mass fraction) of the composites.The results of microstructural evaluation and mechanical properties indicate that the nanoparticles can be dispersed into magnesium alloys efficiently and uniformly with the aid of ultrasonic vibration.As compared with the matrix alloys,the grains of composites were refined and the mechanical properties of composites were improved significantly.The SEM and DSC analyses show that the SiC nanoparticles can act as the heterogeneous nucleation of α-Mg.Also,the strengthening mechanism responsible for the composites reinforced with SiC nanoparticles was discussed.

Nano-SiC_P particles distribution and mechanical properties of Al-matrix composites prepared by stir casting and ultrasonic treatment

Nano-ceramic particles are generally difficult to add into molten metal because of poor wettability. Nano-SiC_Particles reinforced A356 aluminum alloy composites were prepared by a new complex process, i.e., a molten-metal process combined with high energy ball milling and ultrasonic vibration methods. The nano particles were β-SiC_P with an average diameter of 40 nm, and pre-oxidized at about 850 °C to form an oxide layer with a thickness of approximately 3 nm. The mm-sized composite granules containing nano-SiC_P were fi rstly produced by milling the mixture of oxidized nano-SiC_P and pure Al powders, and then were remelted in the matrix-metal melt with mechanical stirring and treated by ultrasonic vibration to prepare the composite. SEM analysis results show that the nano-SiC_P articles are distributed uniformly in the matrix and no serious agglomeration is observed. The tensile strength and elongation of the composite with 2 wt.% nano-SiC_P in as-cast state are 226 MPa and 5.5%, improved by 20% and 44%, respectively, compared with the A356 alloy.

Simplified Matrix Focusing Imaging Algorithm for Ultrasonic Nondestructive Testing

Full matrix focusing method of ultrasonic phased array has been proved with advantages of good signal-to-noise ratio and imaging resolution in the field of Ultrasonic NDT.However,it is still suffering from the time-consuming data acquisition and processing.In order to solve the problem,two simplified matrix focusing methods are provided in the paper.One provided method is a triangular matrix focusing algorithm based on the principle of reciprocity for the multi-channel ultrasonic system.The other provided method is a trapezoidal matrix focusing algorithm based on the energy weight of the different channel to the focusing area.Time of data acquisition and computational is decreased with the provided simplified matrix focusing methods.In order to prove the validity of two provided algorithms,both side-drilled holes and oblique cracks are used for imaging experiments.The experimental results show that the imaging quality of the triangular matrix focusing algorithm is basically consistent to that of the full matrix focusing method.And imaging quality of the trapezoidal matrix focusing algorithm is slightly reduced with the amount of multi-channel data decreasing.Both data acquisition and computational efficiency using the triangular matrix focusing algorithm and the trapezoidal matrix focusing algorithm have been improved significantly compared with original full matrix focusing method.

Detecting Impact Damage in Carbon Fabric/epoxy-matrix Composites by Ultrasonic F-scan and Electrical Resistance Measurement

The status and the variation of electrical resistance of impacted carbon fiber/epoxy-matrix composites were studied by ultrasonic F-scan and electrical resistance measurement The experimental results shows that impact damage energy threshold value of carbon fabric/epoxy-matrix composites can determine by using ultrasonic F-scan. When the impact energy exceeds the threshold value, damage is generated in composites. Electrical resistance of impacted composites is changed owing to the contact of each carbon fiber unit in composites, which cause a change of the series-parallel in conductors. The veracity of detecting impact damage in composites can be improved in this case.

Damage analysis for particle reinforced metal matrix composite by ultrasonic method

The damage characteristic of particle reinforced metal matrix composite (PMMC) was studied by ultrasonic non-destructive evaluation method. After the sample was damaged induced by tensile load, the ultrasonic wave that propagated in the sample were collected. The damage parameter was defined by ultrasonic parameter and the wave signals were analyzed by correlation method. The results show that with the increase of tensile load, the damage parameter increases and the correlation coefficient decreases. The fracture section morphologies of PMMC under tensile load were observed by SEM. It is found that there are many concaves in the metal matrix. Therefore the damage evolution can be concluded. The initial damage is induced by void nucleation, growth and subsequent coalescence in the matrix or interface separation.

The Experimental and Theoretical Research of "Local Resonance" in Ultrasonic Honing System

In 1982, Professor Fang Guoliang found the "Non full resonance" phenomenon in a tool system while he use the thin-long tool ultrasonically machining deep-small hole. He called it as "local resonance". Also this "Non full resonance" phenomenon was discovered in the ultrasonic drilling and the ultrasonic honing system later. To its mechanism, professor Fang thought that the coupling of long-thin tool bar and driving system is weak, so the tool bar can vibrate independently, but the quantitative relation between the coupling factor and diameter ratio is not made certain. Then several theories come forth to interpret it but still haven’t a common conclusion. Through the systematic experimental and theoretical research, this paper reveals that the "local resonance" phenomenon of ultrasonic honing system has the same essence with the "local resonance" phenomenon in deep hole machining system: when the section area ratio of tool bar and driving system is small enough, some resonance frequencies of combined system are close to the resonance frequencies of "fixed-free" state tool bar, the combined system is still resonant. According to the given depth of hole and structure size, we can use the transfer matrix deduced in this paper to design flexible bar and oilstone seat not only satisfying mechanical structure size but also achieving enough magnitude. It greatly simplified the design. This new method can be named as "local resonance" design method for ultrasonic honing system. The experiment, deduction and design method have a certain common meaning to the study and design of other ultrasonic system.

Ultrasonic dissolution of brazing of 55% SiC_p/A356 composites

The brazing of 55% SiCp/A356 (volume fraction) composites in air using Zn-Al alloy as a filler metal was investigated.During the brazing process,ultrasonic vibrations were applied to samples for bonding and a significant dissolution of the filler metal into the matrix alloy in the base materials occurred.As brazing temperatures were increased,the thickness of the partial melting layers in the base material increased.SiC particles in the partial melting layer of the base material were transferred into the liquid filler under ultrasonic action and a bond with homogeneously distributed reinforcements was obtained after solidification.The volume fraction of SiC particles in the bonds could be varied by changing the brazing temperature.The maximum SiC particle volume fraction of the bond material reached 37% at a brazing temperature of 500 ℃.The shear strength of the brazed bonds was improved at pressures up to 244 MPa (at 20 ℃) and increased by 133.8% (at 200 ℃) compared with the filler of the Zn-based alloy.

Diagnosis of Temperature Field by Ultrasonic CT-In case of limited projection angle

超声波CT作为一种热测量方法 ,具有不接触、对温度场不干扰的优点。本文发展一种新的超声波CT再现方法 ,用于解决受限透视角度所产生的信息量不足的问题。新的超声波CT再现算法建立在逆矩阵变换的基础上 ,它不同于通常的采用SL过滤器的所谓FBPCT再现方式。论文中描述了三种CT迭代再现算法 ,用计算机模拟结果和三维温度场测量实验数据验证了再现算法的可靠性。同时根据计算和实验结果 ,建议在受限的透视角度情况下 。

管道超声相控阵全聚焦成像仿真及算法优化

针对厚壁管道内部缺陷识别困难、可视化差等问题,提出基于超声相控阵理论和全聚焦算法对厚壁管道内部缺陷进行图像重构。并针对全聚焦成像效率低的缺点,采用有限元法对外径为550 mm,壁厚为65 mm的厚壁管道超声相控阵全聚焦成像进行仿真,模拟缺陷检测过程和成像结果,并使用稀疏矩阵对算法进行优化。结果表明:在基本满足成像质量要求的情况下,采用激发中心频率为5 MHz,阵元宽度为0.5 mm,阵元间距为1 mm,阵元数量为32时,稀疏激发矩阵比全矩阵全聚焦成像效率提高了74.81%,有效提高了成像速度,满足全聚焦快速成像的需求。

Cf/C-SiC烧蚀行为及激光复合超声磨削可行性研究

目的揭示激光与Cf/C-SiC陶瓷基复合材料相互作用机理,分析激光能量密度对材料形性演变的影响规律。提出Cf/C-SiC陶瓷基复合材料激光复合超声磨削加工方案,探究硬脆材料多能场复合加工的可行性。方法使用不同能量密度的激光束扫描Cf/C-SiC陶瓷基复合材料表面,以明确材料烧蚀行为。在材料表面预制不同间距的平行纹理沟槽,进而对比传统磨削、超声辅助磨削和激光复合超声磨削的加工效果,同时研究不同扫描间距的预制沟槽对磨削效果的影响规律。结果陶瓷基复合材料(CMC)在激光作用下可呈现2种截然不同的状态,改性状态时材料以氧化等热化学变化为主,样件内出现热影响区和裂纹区。烧蚀状态时材料以热物理和热机械变化为主,样件内出现烧蚀凹坑、重铸层、热影响区和裂纹区。纤维束中界面经整体脱黏后,裂纹向下延伸并发生偏转。基体中的裂纹多起源于纤维界面处,并在扩展过程中发生偏转、分叉。激光烧蚀作用可改变材料的可加工性,有利于后续超声磨削加工。激光复合超声磨削的两方向磨削力相较传统磨削分别减小了51.4%和56.5%,同时表面粗糙度Sa可降低至4.228μm。结论激光复合超声磨削可有效降低磨削力和加工表面粗糙度,从而提高加工质量,该方法在实现硬脆材料高质量低成本加工方面具有较大的潜能。

旋转超声加工对TiBw网状钛基复合材料表面残余应力的影响

为研究不同切削条件下旋转超声加工对材料表面残余应力的影响,选取硼化钛晶须(TiB whiskers,TiBw)网状钛基复合材料为实验对象,使用镍基电铸金刚石砂轮进行旋转超声加工,并分析了加工后材料的表面残余应力。结果表明:由于钛基复合材料具有网状结构和优异的高温性能,使切削热和微观相变产生的残余应力较小,磨粒机械作用产生的残余应力更大。随着超声振动的引入,磨粒高频冲击工件表面,使旋转超声加工工件表面残余应力均大于普通磨削。在主轴转速n=9000 r/min,进给速度v f=8 mm/min,加工深度a p=25μm的加工参数下,旋转超声加工工件表面存在-540 MPa的残余压应力,随着主轴转速增大,残余应力显著减小,并且残余应力的影响层深度逐渐减小。超声振动的引入增大工件表面残余压应力,提高材料抗疲劳性能。

双探头梯形矩阵聚焦成像方法

R角是曲面变壁厚结构,传统超声检测方法难以对其轮廓和缺陷进行完整成像显示。针对此问题,首先,提出双探头全聚焦成像方法,实现R角区域的完整成像显示;其次,为了改善双探头全聚焦成像效率较低的问题,采用梯形矩阵聚焦成像算法,实现高效实时成像;最后,对典型变壁厚R角试件开展聚焦成像实验,验证了双探头梯形矩阵聚焦成像方法的有效性。结果表明,与传统单探头全聚焦成像方法相比,双探头梯形矩阵聚焦成像方法能够显示R角结构的完整内轮廓,并清楚显示和定位内部缺陷。

改进FFT算法在频域全聚焦超声成像中研究

针对钢块中孔洞缺陷的超声成像检测,目前普遍采用时域超声成像算法。该方法中的延时叠加过程需要进行重复、繁琐的迭代运算,无法满足高质量实时成像的需求,频域超声成像算法具有更高的成像分辨率和更快的成像速度。提出了一种针对任意非0值输入的基2-FFT输入分级截断算法,将该算法应用在频域FMC-PSM算法成像中,得到改进的FMC-PSM算法,用于钢块中孔洞缺陷检测超声成像。实验结果证明,相较于标准FMC-PSM算法,改进的频域FMC-PSM算法能够在呈现更高质量图像的同时将成像速度提高了15%,有望解决超声成像中成像质量和成像效率难以兼顾的问题。

超声振动优化铝基复合材料中亚微米TiB_(2)颗粒分布及其对力学性能的影响

利用熔盐-金属反应法成功制备了9 mass%TiB_(2)颗粒原位增强Al-4.5Cu铝基复合材料,研究超声振动处理对团聚状亚微米TiB_(2)颗粒分布的改善作用。结果表明:利用超声振动产生的空化效应和声流效应,有效消除了熔体中颗粒团聚的现象。经超声处理4 min后,TiB_(2)颗粒均匀地分散在整个熔体中,由小于100 nm的TiB_(2)颗粒形成的微小团聚也被打散。复合材料凝固后,有一些小于400 nm的TiB_(2)颗粒分散在晶界附近的基体中。超声振动处理4 min后,复合材料的屈服强度比基体合金和未超声振动处理的复合材料分别提高119%和64.3%,这主要是由于超声振动处理使得TiB_(2)颗粒细小并弥散分布在复合材料的基体中,导致Orowan强化和热膨胀错配强化效果增强,从而使其强度增加。

纳米TiB_(2)/7075铝基复合材料超声滚压数值仿真研究

超声滚压数值仿真研究亟待丰富和深入开展。采用温度-应变率相关Johnson-Cook本构模型描述纳米TiB_(2)/7075铝基复合材料塑性变形行为,通过Gleeble热压缩模拟实验结合最小二乘拟合标定相关本构参数。利用有限元软件ABAQUS构建3D全六面体渐变网格模型,通过6个步骤对复合材料超声滚压强化过程进行了数值仿真研究。结果表明,残余应力分布的仿真结果与实测结果存在明显差异,但网格失效形式较好地反映了表层材料的开裂和分层,从模拟角度验证了往复超声滚压过程中过度塑性变形导致材料表面损伤的现象。该结果对金属基复合材料超声滚压工艺的探索和相关数值仿真研究的深入开展具有重要指导意义。

相控阵超声相位相干成像(PCI)检测原理及应用

为了了解相控阵超声相位相干成像(PCI)检测技术在工业无损检测应用中的效果及特点,详细介绍了相控阵超声全聚焦成像与相位相干成像(PCI)检测技术的基本原理,从原理上分析了PCI检测技术与全聚焦成像检测技术的差异性。通过试验测试了PCI检测技术对点状缺陷、面状缺陷与体积状缺陷的检测特点及效果,根据得到的检测效果,展示了PCI检测技术对于不同类型缺陷的检测优势与不足,以推动该技术在工业无损检测中的正确应用。

定位夹具对CNTs/6061Al复合材料超声波焊接接头质量影响研究

采用超声波焊接制备CNTs增强铝基复合材料,针对超声波焊接定位不准,接头搭接面不贴合等问题,基于定位夹具以保证焊接过程质量,在工艺参数组合焊接能量500J,焊接压力0.45MPa,焊接振幅35μm下进行焊接试验。利用扫描电镜(SEM)、能谱仪(EDS)等对接头界面组织和成分进行了研究,并对焊接接头进行了剪切力和硬度测试。结果表明:在定位夹具下焊接的接头界面发生明显塑性且CNTs在铝基体扩散较好,接头强度显著提升,剪切力平均值达到786.55N、硬度为72HV,本研究对现有的有色金属超声波焊接制造工艺提出一种新的解决思路和方案,具有一定的工程应用价值和经济效益。

On the liquid-phase technology of carbon fiber/aluminum matrix composites

The main problems with the liquid-phase technology of carbon fiber/aluminum matrix composites include poor wetting of the fiber with liquid aluminum and formation of aluminum carbide on the fibers’surface.This paper aims to solve these problems.The theoretical and experimental dependence of porosity on the applied pressure were determined.The possibility of obtaining a carbon fiber/aluminum matrix composite wire with a strength value of about 1500 MPa was shown.The correlation among the strength of the carbon fiber reinforced aluminum matrix composite,the fracture surface,and the degradation of the carbon fiber surface was discussed.

PCD刀具超声振动辅助切削TiC_(p)/TC4材料表面缺陷

研究微观角度下PCD刀具超声振动辅助切削TiC_(p)/TC4时,超声振动对材料表面缺陷的影响。基于ABAQUS/Explicit有限元软件,建立PTMCs二维切削微观非均质模型,开展不同体积分数下的多颗粒切削仿真;并采用仿真和实验相结合的方法,分析切削速度对切削温度变化的影响规律,阐述TiC_(p)/TC4在切削过程中的颗粒受力破碎过程,讨论同体积分数的TiC_(p)/TC4切削表面缺陷的表现形式。结果表明:超声振动切削时,切削温度始终较低,TiC_(p)/TC4表面缺陷表现形式多为颗粒切断和颗粒突起;且超声振动能有效阻断颗粒与基体间的应力持续传递,使应力优先在颗粒间传递,减小了基体变形,促使颗粒破碎,提升材料表面加工质量,同时验证实验结果与仿真结果相符。

基于传输矩阵法的任意变厚度环型压电超声换能器

变厚度环型径向振动压电超声换能器可以实现阻抗变换、能量集中,具有辐射面积大、全指向性等优点,在功率超声、水声等领域被广泛应用.由于求解复杂变厚度金属圆环径向振动的波动方程比较困难,本文使用传输矩阵法将变厚度金属圆环的径向振动转化为N个等厚度金属圆环径向振动的叠加,得到了任意变厚度金属薄圆环径向振动的等效电路图、共振频率方程和位移放大系数表达式,分析了锥型、幂函数型、指数型、悬链线型金属圆环的位移放大系数与几何尺寸的关系.在此基础上,推导了由任意变厚度金属圆环和等厚度压电圆环复合而成的压电超声换能器径向振动的等效电路和共振频率方程.为了验证理论结果的正确性,使用有限元软件进行仿真,所得一阶、二阶的共振频率和位移放大系数的数值解与理论解符合较好.本研究给出了任意变厚度金属圆环径向振动的普适解,为设计和优化径向压电超声换能器提供了理论指导.