【作者】 苏军；

【导师】 武高辉；

【作者基本信息】 哈尔滨工业大学 ， 材料学， 2011， 博士

【摘要】 连续碳纤维增强铝基复合材料(Cf/Al)以其高比强度、高比刚度等优良的空间特性,已经成为优异的航天器件备选材料,其产品缺陷检测及质量评价已成为不可缺少的环节。实际构件中缺陷的存在是不可避免的,因此其可靠性、服役损伤容限设计变得至关重要。本文利用传统超声波检测方法对超声波信号进行参数化Chirplet(线调频小波)分解,从而对Cf/Al复合材料缺陷进行高清晰识别和表征;利用金相显微镜、扫描电子显微镜(SEM)等手段对Cf/Al复合材料缺陷特征进行分析并分类;采用电子拉伸机及扫描电镜原位观察技术等分析测试方法,系统研究了层状缺陷(铝聚集层、夹杂、分层)和圆孔缺陷对Cf/Al复合材料的拉伸、压缩力学性能及损伤失效机理的影响,进一步通过有限元分析方法和剩余强度预测模型对含层状缺陷和圆孔缺陷的Cf/Al复合材料的剩余强度进行了预测。在Cf/Al复合材料内部制备了铝聚集层、夹杂和分层三种层状缺陷,对三种层状缺陷的超声波信号进行Chirplet分解,提取出Chirplet参数变化量(中心频率和相位)作为表征缺陷的特征参数。深入分析了层状缺陷类型、埋藏深度(埋深)、厚度和缺陷边边缘的Chirplet参数变化量的特征,发现三种类型层状缺陷的特征参数明显不同;随着层状缺陷埋深的增加,Chirplet参数变化量基本不变;随铝聚集层厚度增加,Chirplet参数变化量单调变化,但是存在一个临界厚度(0.27mm);层状缺陷的边界对Chirplet参数变化量的影响敏感。通过对缺陷信号的Chirplet分解,编制了计算软件,实现了缺陷的Chirplet幅度、埋深、中心频率和相位四种C扫描成像。结果表明,幅度C扫描能提高图像的对比度;埋深C扫描能给出缺陷在试件中的埋深分布;而中心频率C扫描和相位C扫描使缺陷的边界特征明显;相位C扫描提高了对缺陷细节特征的分辨率,更加准确的表征分层扩展过程。在实现对Cf/Al复合材料缺陷的超声波检测的基础上,研究了铝聚集层、夹杂、分层和圆孔对Cf/Al复合材料拉伸和压缩强度的影响。在本试验条件下,人工制备的铝聚集层和夹杂使Cf/Al复合材料的拉伸强度分别下降了15.8%和35.2%,压缩强度下降了23.1%、50.5%,分层使压缩强度下降了47.9%。Cf/Al复合材料的拉伸和压缩强度与圆孔直径呈指数关系下降。通过有限元分析对含层状缺陷Cf/Al复合材料的分析表明:在拉伸载荷下,夹杂边缘过渡区的轴向和剪切应力集中比铝聚集层更为严重;应力分布不随层状缺陷的横向尺寸的增加而变化,采用最大应力准则对含层状缺陷Cf/Al复合材料剩余拉伸强度进行估算,与试验结果相吻合。在压缩载荷下,夹杂边缘过渡区横向应力集中最严重,分层次之,铝聚集层最小;采用最大应力准则估算的剩余压缩强度结果与试验值基本吻合。采用点强度准则(PSC)、平均强度准则(AVC)、损伤区准则(DZC)和有效裂纹扩展模型(ECGM)对含圆孔Cf/Al复合材料试样的剩余拉伸强度进行预测,结果表明,圆孔直径与试样宽度之比(D/W)在0.05~0.5的整个测试范围内,ECGM和DZC预测结果与试验值一致;当D/W>0.2时,PSC和AVC的预测结果误差较大。对剩余压缩强度的预测结果表明,PSC和AVC在D/W>0.2时,预测结果也存在较大误差。采用扫描电镜原位观察了在拉应力下,含缺口、铝聚集层和夹杂单一缺陷Cf/Al复合材料的失效破坏过程。结果表明,铝聚集层具有较好的韧性和强度,能够缓解复合材料内部主裂纹前端的应力集中,从而阻碍裂纹的扩展,延缓了Cf/Al复合材料的失效破坏。夹杂因较低的强度使裂纹垂直传播,并穿过夹杂和复合材料的界面,造成复合材料的瞬间失效破坏。同时也原位观察了在压应力下,含铝聚集层、夹杂和分层三种单一缺陷Cf/Al复合材料的压缩失效过程。结果表明,Cf/Al复合材料的压缩失效机理主要包括纤维的微屈曲和界面分层。含夹杂和分层复合材料的压缩失效主要是屈曲分层。而含铝聚集层复合材料的压缩失效是纤维微屈曲破坏和屈曲分层两种失效机制的共同作用。超声波Chirplet参数C扫描实现了对含铝聚集层、夹杂和分层Cf/Al复合材料压缩载荷下损伤扩展过程的表征,相位C扫描对损伤扩展过程的表征更加清晰。更多还原

【Abstract】 Continuous carbon fiber reinforced aluminum matrix composite (Cf/Al) becomes outstanding alternative material for space devices due to its good space characteristics,such as high specific strength and high stiffness. Thus, it is necessary to detect the anomaly and evaluate the quality of composite products. However, anomalies exist in component are inevitable, so the design of reliability and service damage tolerance becomes highly important. In this paper, by using parametric Chirplet decomposition to Ultrasonic signal based on ultrasonic detection method, anomalies of composite were identificated and characterized legibly. The effect of anomalies (e.g. Al-rich, inclusion, delamination and holes) on the tensile and compressive mechanical properties, damage failure mechanisms of Cf/Al composite was systematically studied through by electronic tensile machine and SEM in situ observation technique. Furthermore, residual strength of Cf/Al composite with layer anomalies and hole anomalies was obtained by finite element method and residual strength prediction model.The artificial anomalies were introduced into Cf/Al composite, which were able to simulate the layer anomalies of Al-rich, inclusion and delamination. The Chirplet parameters (center frequency and phase) variance was obtained through the Chirplet decomposition for ultrasonic signal of the above anomalies, which could be used as the characteristic parameters for the anomaly characterization. Furthermore, the effect of anomaly type, depth, thickness and anomaly boundaries on Chirplet parameters was deeply studied, the results show that the ultrasonic signal characteristic parameters of three types of anomalies were obviously different; the Chirplet parameters of the layer anomaly were essentially invariable with the anomaly depth, but they increased with increasing thickness of aluminum accumulation layer in less than the critical thickness (0.27mm); the Chirplet parameters could significantly improve the identification of anomaly boundary.The C scan imaging of Chirplet range, depth, center frequency and phase of anomalies was gained through the Chirplet decomposition of the anomaly signals. The results show that the C scan imaging of range could improve the contrast of C scan images; the C scan imaging of depth could show the depth distribution of anomalies in the samples; the center frequency and phase imaging made the anomaly border clear and distinct, which could improve the measurement accuracy of the anomaly size; the C scan imaging of phase could improve the resolution of the details and characteristics of the anomalies, so it made the characterization of delamination growth process more accuratly.The effect of Al-rich, inclusion, delamination and holes on the tensile and compressive strength of Cf/Al composite material was studied on the basis of the ultrasonic testing. The follwing results were obtained: the tensile and compressive strength respectively decreased by 15.8% and 23.1% for the composite containing Al-rich; the tensile and compressive strength respectively decreased by 35.2% and 50.5% for the composite containing inclusion anomaly; the compressive strength decreased by 47.9% for the the composite containing delamination; the tensile and compressive strength both decreased exponentially with the pore diameter.The finite element analysis results of the Cf/Al composite with the local layer anomalies show that the axial and shear stress concentration in the edge transition zone of the inclusions is more serious than that of composite with the Al-rich anomalies under the same tensile load conditions. Stress distribution of the composite with layered anomalies is changeless with the increase of transverse dimensions, the residual strength of the Cf/Al composite with the local layer anomalies were calculated under the axial maximum stress criterion, the obtained results have a good agree with the experimental results. Under the compressive load, the transverse stress concentration of inclusions in the edge transition area is the most serious, the delamination takes the second place, and Al-rich affects the minimum. The compression residual strength of Cf/Al composites with Al-rich, delamination or inclusions was estimated under transverse and axial maximum stress criteria, the estimated results of compression residual strength was slightly less than experimental results.The tensile residual strength of the Cf/Al composite with holes was predicted by using point strength criterion (PSC), average strength criterion (AVC), damaged zone criterion (DZC) and effective crack growth model (ECGM). Results show that in the whole test range of 0.05~0.5 (D/W), high predicted precision can be obtain from the ECGM and the DZC; when D/W > 0.2, the predicted result from the PSC and the AVC can’t predict accurately the tensile residual strength because of the greater error. DZC and ECGM are not suitable for residual strength prediction of the Cf/Al composite with holes because of the different failure mechanisms between the tensile load and the compressive load.The failure process of notch contained Cf/Al composite with Al-rich layer and inclusion was observed by the SEM in suit observation technique. The results show that the Al-rich with good toughness and strength can release stress concentration in the front of the internal main crack of Cf/Al composite and make the crack spread around, which prevents the crack propagation and delays the damage failure of Cf/Al composite. However, the inclusion, which has lower strength, can make the cracks spread vertically, which results in the instantaneous destruction of composite materials and accelerats the crack propagation and failure of composite. Compression failure process of Cf/Al composite with layer anomalies (including Al-rich, inclusions and local delamination) was observed with the method of in-situ observation composite by scanning electron microscopy (SEM).The results show that the compression failure mechanism of Cf/Al composite mainly includes fiber micro-buckling and the interface delamination. And the compression failure mode of the composites containing inclusions or local delamination is mainly buckling delamination. The compression failure mode for the composite with the Al-rich is the combination of fiber micro- buckling failure and buckling delamination.The characterization of the damage extension of Cf/Al composite with anomalies (e.g. Al-rich, inclusions and local delamination) under the compressive load was realized by Ultrasonic Chirplet Parameter C Scan. It is more significant for Phase C Scans to obtain the characterization comparing with Ultrasonic Chirplet Parameter C Scan.更多还原