激光超声技术在先进复合材料无损检测中的应用研究

为实现航空航天先进复合材料的非接触、高精度检测,研究激光超声技术在复合材料无损检测中的应用。制备预埋人工缺陷的碳纤维树脂基复合材料和陶瓷基复合材料试样,利用自主研制的激光激励、激光探测的全光学激光超声无损检测系统进行试验研究,实现碳纤维复合材料层压结构模拟分层缺陷检测,层压复合材料紧固孔边沿分层检测,以及陶瓷基复合材料分层检测。研究结果表明:激光超声检测技术可以有效检出碳纤维树脂基复合材料内部直径2 mm以上分层型缺陷,可检出碳纤维复合材料紧固孔边沿的小尺寸分层,可表征C/SiC复合材料内部直径5 mm以上分层,在航空航天工程领域应用前景广阔。     

短纤维／晶须增强金属基复合材料的弹塑性本构关系

研究了短纤维／晶须增强金属基复合材料在弹塑性变形中的应变分布，得到了增强体与基体应变的统计规律、提出了短纤维／晶须增强金属基复合材料的材料模型、导出了相应的弹塑性本构关系，预测了硼酸铝晶须增强Al基([AlBO]w／Al)复合材料单轴拉伸应力应变关系．结果与实验吻合良好。     

基于纤维增强复合材料的超声振动辅助加工技术综述

纤维增强复合材料是一类使用范围不断扩大的具有优良机械性能的工程复合材料,但由于其具有各向异性及增强体纤维稳定的理化性能,使得传统金属加工方法很难对纤维增强复合材料进行高质量的加工,特别是对于以芳纶纤维等断裂伸长率较高的纤维为增强体的复合材料,存在较为严重的撕裂、毛刺和分层等加工缺陷。超声振动辅助加工是一种将超声振动附加在机械加工过程中的加工方式。超声振动的加入可使刀具与工件周期性接触,减小切削阻力,降低切削温度,可在一定程度上提高纤维增强复合材料加工的表面质量,减少加工缺陷。在介绍超声振动辅助技术的分类、系统组成和加工机理,及纤维复合材料表面质量、材料去除、加工机理和加工缺陷的基础上,从套料制孔、螺旋铣孔和轮廓铣削三类常见加工工艺方面,论述了针对纤维复合材料的超声振动辅助切削技术的国内外研究进展。基于纤维复合材料超声振动辅助切削技术的发展状况,从基础理论研究、材料表面改性和新加工工艺探索、超声振动加工系统的开发完善等方面,总结了现有研究和应用中的成果及普遍存在的问题,同时对未来研究的发展趋势做出了展望。     

碳纤维复合材料构件超声自动检测系统

针对航空领域专用的碳纤维复合材料板材，以超声波脉冲反射法的检测方法为基础，研制了用于碳纤维复合材料内部缺陷检测的超声波自动检测系统。介绍了脉冲反射法检测原理，机械系统、硬件系统结构和软件系统的设计开发思想，最后用实验得到构件的超声C扫描图像。实验结果表明，该系统具有较高的精度和效率，对碳纤维复合材料缺陷的检测很适用。     

SiC纤维增强高温合金复合材料可行性分析

SiC纤维增强金属基复合材料因耐高温、低密度等特点,在航空航天领域逐渐推广。为进一步提高SiC纤维增强金属基复合材料的使用温度,国内外开始尝试将SiC纤维与高温合金进行复合,以期发挥两者的优点,获得性能更加优良的高温结构材料。但SiC纤维增强高温合金复合材料发展缓慢,诸多尝试均未取得突破性的成功,界面问题是制约该类材料发展的"瓶颈"。虽然在克服界面反应方面也采取了诸多尝试,但该问题并未获得实质性的解决,因此有必要从根源入手对SiC纤维增强高温合金复合材料这一研究方向的可行性进行探讨。本文采用资料研究和实验研究相结合的方式,从SiC纤维增强高温合金复合材料的发展历史、界面反应问题的解决方案、SiC与高温合金界面反应的本质等几个方面逐层展开、一一论述,对SiC纤维增强高温合金复合材料的可行性进行阐述和分析。     

Subcritical crack growth in CVI SiCf/SiC composites at elevated temperatures: effect of fiber creep rate

Subcritical crack-growth studies in SiC_f/SiC composites were conducted with composites reinforced with Hi-Nicalon fibers over a broad temperature range for comparison to earlier studies on materials reinforced with Nicalon-CG fibers. Composites with a 0/90 plain weave architecture and carbon interphase were tested in argon from 1173 to 1473 K. Crack growth data obtained in inert environments are consistent with a proposed fiber-creep-controlled crack-growth mechanism. Measured crack-growth activation energies and time–temperature exponents in argon agree with fiber creep-activation energies and nonlinear creep equations for both fiber types. Estimates of local strains during crack growth are in reasonable agreement with estimated fiber creep strains for the given times and temperatures. The increased creep resistance of Hi-Nicalon fibers is reflected in reduced crack-growth rates for composites containing those fibers.     

An experimental bone defect healing with hydroxyapatite coating plasma sprayed on carbon/carbon composite implants

Hydroxyapatite coatings with proper thickness were coated on fusion-cage-like carbon fiber reinforced carbon composite implants for bone tissue reconstruction by the plasma spraying technique. Autogenously bone filled fusion-cage-like implants were grafted in hybrid goats' tibia for 328 days. By means of X-ray photography, histological observation and scanning electron microscopy, the biological behaviors of the coating were compared with the pure carbon fiber reinforced carbon composites and the bone defect healing effect of the implants was evaluated. The results indicated that hydroxyapatite coating has more obvious osteoconductive effect than the pure carbon fiber reinforced carbon composites with surface bioinert. The calcium and phosphorus ions leached from HA provide a suitable biological mineralization environment that accelerates the metabolism of bone, the osteoblast differentiation and collagen synthesis. The coating can significantly speed up the bone defect healing process and improve the surface bioactivity of carbon fiber reinforced carbon composites.     

超声辅助磨削SiCf/SiC陶瓷基复合材料

针对碳化硅纤维增强陶瓷基复合材料(SiC_f/SiC)存在加工质量差、刀具磨损严重等问题,开展金刚石砂轮端面超声辅助磨削SiC_f/SiC复合材料试验,对比研究超声辅助磨削和普通磨削SiC_f/SiC过程中的磨削力、表面形貌及表面粗糙度,并分析其材料去除机理。结果表明:超声辅助磨削可有效降低磨削力;超声作用能促使SiC纤维断裂,形成较短纤维而被去除,减少了纤维的折断和剥落,提高了其表面加工质量;在纵向振动端面磨削条件下,超声振幅在一定范围内有助于改善其表面加工质量,振幅过大则会导致表面冲击作用过强而使其表面质量降低。      

SiC纤维增强钛基复合材料界面强度研究进展

综述SiC纤维增强钛基复合材料界面强度的影响因素、微观实验测试技术以及数值模拟技术。在此基础上着重分析了微观实验测试技术与数值模拟技术存在的问题，指出了界面强度定量研究的发展方向。     

陶瓷纤维增强铝合金的制造工艺和性能研究

用国产氧化铝和硅酸铝陶瓷纤维为增强材料制造铝基复合材料，前者性能稳定，受制造工艺变的影响小；后者的性能与制造工艺和纤维性质有关，其中，纤维制造方法，纤维打断时间，预制体用粘接剂和挤压铸造的压力对合金性能的影响明显。     

高能超声对原位合成Al_3Ti/6070复合材料凝固组织的影响及机制

以Al-K_2TiF_6为反应体系,采用熔体反应法,在高能超声场下原位合成Al_3Ti/6070复合材料.采用XRD、SEM、EDS等手段研究不同超声参数如超声时间和超声强度对Al_3Ti/6070复合材料增强体形貌及尺寸的影响.建立了超声作用下熔体中颗粒行为模型,并对其机制进行了探讨.结果表明:在一定的超声强度下(0.66 kW/cm~2),颗粒尺寸随超声作用时间的延长(1～7 min)先减小后增大,当作用时间为3 min时,颗粒最细小,尺寸为1～2 μm,形貌主要为小块状或短棒状;当超声作用时间大于3 min时,颗粒数量随时间增加而急剧减少;在相同的超声作用时间(3 min)下,颗粒尺寸随超声强度的增加而减小,当超声强度为0.82 kW/cm~2时,颗粒尺寸为0.5～1 μm,颗粒形貌主要为小块状或粒状,当超声功率大于0.82 kW/cm~2时,颗粒数量随超声功率增加而急剧减少.高能超声作用下Al_3Ti/6070复合材料的最佳制备工艺为:超声强度0.66～0.82 kW/cm~2,超声作用时间3 min.     

碳化硅颗粒增强Al基复合材料的新型制备工艺

综述了碳化硅增强铝基复合材料的几种主要制备工艺,重点阐述了高能超声半固态复合法制备SiCp／Al复合材料。首先用渗流法制备SiC体积分数高的SiCp／Al预制块,进行SiC预分散,然后将预制块加入处于半固态温度条件下的铝合金熔体中,最后导入超声波进行搅拌。此法很好地改善了增强颗粒与基体之间的润湿性,使SiC在基体中均匀分布。     

Processing technique and fiber orientation angle affecting the mechanical properties of E-glass fiber reinforced wood/PVC composites

In this work, E-glass fibers (GF) with different fiber forms, loadings and orientation angles were introduced into wood/poly(vinyl chloride) (WPVC) composites. The GF reinforced WPVC composites were manufactured either by compression molding or by twin-screw extrusion process, and the mechanical properties of the composites from these two processes were then compared. The experimental results suggested that the compression process was more effective for the production of GF reinforced WPVC composites than the twin-screw extrusion process. The specific density of the GF/WPVC composite by the compression technique was greater. The orientation angle of glass fiber was found to have a more pronounced effect on the impact properties of the GF/WPVC composites. The maximum mechanical properties of the GF/WPVC composites could be obtained by using the compression molding technique to manufacture the composite products with fiber orientation angle of 0°.     

超声辅助螺旋磨削SiCf/SiC陶瓷基复合材料

针对SiC纤维增强SiC陶瓷基复合材料(SiC_f/SiC)存在加工质量差、材料去除困难等问题,开展金刚石砂轮超声辅助螺旋磨削SiC_f/SiC陶瓷基复合材料试验,研究其出口质量、孔壁形貌及孔壁表面粗糙度。结果表明:与传统制孔相比,超声辅助螺旋磨削制孔出口处材料无大面积崩边;砂轮磨削速度方向与纤维方向的夹角θ的周期性变化导致孔壁表面形貌呈现规律性变化。当θ在0°/180°时,纤维与基体多发生脱黏现象;当θ在45°时,纤维多发生剪切断裂;当θ在90°时,纤维多发生挤压断裂;当θ在135°时,纤维既发生剪切断裂又发生挤压断裂;孔壁表面粗糙度S_a在θ为90°时最低,在θ为135°时最高。在一定范围内,表面粗糙度S_a随着超声振幅的增大而降低,最大降幅为38.7%;随着进给速度的增大而升高,最大增幅为39.3%。      

3D simulations and experiments of guided wave propagation in adhesively bonded multi-layered structures

Understanding guided wave propagation in multi-layered plates and interaction with discontinuities can be difficult, as well as the interpretation of the ultrasonic signals. Propagation of guided waves can be studied analytically solving the equations of motion with the proper boundary conditions; nevertheless analytical models can be difficult to solve for complex multi-layered structures or having inner discontinuities. The problem can be efficiently studied using numerical techniques. Simulation of guided wave propagation in multi-layered structures, for ultrasonic waves in the MHz range, is solved here with the finite element analysis based on an explicit integration rule to solve the equations of motion in a dynamic analysis. Simulation allows a better understanding of propagation and interference phenomena by creating a window of observation in the multi-layered plate. Numerical results determined for a three-layer Al plate, without or with discontinuities, matched very well with experiments, providing an efficient tool to visualize and extract significant information in the transmitted waves and to optimize wave mode and configuration for a rigorous ultrasonic inspection.     

英国先进的复合材料无损检测技术

在20世纪90年代初,大面积复合材料的在役检测被证明十分必要。全面介绍了英国复合材料无损检测的发展历史以及目前正在研究的各种复合材料无损检测技术,如超声检测技术、碳纤维增强塑料的超声C扫描检测标准的发展、自动分析和评定技术、低频振动技术、微波、激光错位散斑、热像技术和声像技术。同时介绍了英国的无损评价研究中心机构、用于查询和互助的复合材料检测的交互式知识库以及复合材料无损检测的年度短训班。     

Numerical simulation of solidification kinetics in A356/SiCp composites for assessment of as-cast particle distribution

The present work is aimed at studying the effect of solidification rate on reinforcement clustering in particle reinforced metal matrix composites (PMMCs) through numerical simulations and experimental studies. A macrotransport-solidification kinetics (MTSK) model was used to simulate the solidification kinetics of the PMMCs. The experimental validation of the numerical model was achieved through the Newtonian and Fourier thermal analysis methods. Results reveal that the MTSK model can be successfully used to predict the local microstructural scales and to evaluate the risk of cluster formation in cast particle reinforced composites.     

载荷下碳纤维复合材料电阻变化研究进展

碳纤维复合材料中具有良好导电性能的碳纤维相互接触形成了导电网络,在外部载荷作用下会发生分层损伤、纤维断裂等损伤或破坏,从而引起导电网络发生变化,改变导电性能,导致电阻发生变化。阐述了国内外在碳纤维复合材料常见导电理论和计算模型相关方面的研究结果,及载荷下碳纤维复合材料电阻变化的研究情况等,指出碳纤维复合材料电阻变化研究存在的不足,并提出了碳纤维复合材料电阻变化研究的趋势。     

Application of the ultrasonic pulse-echo technique for quality control of the multi-layered plastic materials

The main aim of the ultrasonic pulse-echo technique application for quality control is to characterize the internal structure of the object under investigation. The advantage of such technique is a possibility to perform non-contact and one-side access measurements, and to investigate the internal structure of multi-layered materials as well. The presented novel application of the ultrasonic pulse-echo technique for characterization of the multi-layered plastic materials covers the complete attenuation measurement in the frequency domain and is based on ill-posed Tikhonov regularization task for each layer separately. The law of the frequency-dependent attenuation has been estimated from the inverse transfer function approximation in the frequency domain. Phase velocity dispersion curves have been estimated in two ways: from the experimental signal phase spectra and from the causal Kramers–Kronig relations. The developed method enables to predict waveforms of the reflected signals from the interfaces of the individual layers in on-line mode.According to this approach, the step-by-step iterative analysis has been performed for each layer using the information about the previous layers. During each step, the acoustic properties of an individual layer, such as density, absorption, ultrasound velocity and phase velocity dispersion, have been recovered using numerical optimization. Optimization has been performed comparing the real ultrasonic signal, reflected by multi-layered object, with the simulated response of the model. The comparison of the predicted waveforms with the experimental ones has shown a good correspondence.     

芳纶/聚合物基复合材料层间剪切性能研究

按照国内外现行试验方法进行芳纶复合材料层间剪切性能测试,发现试样仅出现大弯曲变形,没有出现层间分层失效模式,推断现有方法无法正确表征和测试芳纶纤维增强聚合物基复合材料的层间剪切强度。通过基于界面元原理的复合材料层合板试验数值仿真,优化了试样的厚度和试验跨厚比。按照优化参数试验,试样出现了层间分层的正确失效模式,获得了真实的层间剪切强度,并与仿真结果吻合较好。由此,建议修订现有试验方法或建立专门的芳纶复合材料层合板层间剪切强度标准试验方法。