复合材料Ⅱ型分层损伤演化声发射监测

通过风电叶片复合材料Ⅱ型分层扩展力学性能实验,并借助声发射技术手段,研究复合材料[0/0]、[0/45]和[+45/-45]层间界面损伤演化特性。复合材料试件弯曲加载时,采用声发射实时监测整个分层损伤过程。结果表明,[0/0]复合材料分层试件裂纹扩展快、分层面积大、前沿平齐,不稳定扩展对应较多高幅值、长持续时间的声发射信号;受±45°方向纤维作用,[0/45]和[+45/-45]复合材料试件不稳定分层扩展前声发射撞击累积数较高,裂纹扩展相对缓慢,分层面积小,前沿不齐。复合材料分层损伤演化可分为预分层裂纹尖端区域微损伤累积和分层不稳定扩展两个基本的过程。     

复合材料单搭接胶接头破坏声发射监测

摘要：采用声发射技术对单向拉伸载荷作用下复合材料单搭接胶接头的剪切破坏试验进行实时监测的方法,研究搭接长度对单搭接胶接头损伤破坏的影响规律及其相应的声发射响应特征。结果表明,随搭接长度的增加,引起单搭接胶接头的受力不均匀性增加,损伤易发生在胶层边缘应力集中区域,胶接头承载能力不断上升的同时,平均剪切应力逐渐降低;胶层边缘应力集中更明显,从而出现较多的声发射信号,且幅度在60～80 dB的声发射信号明显增多,声发射撞击累积数有上升趋势。声发射相对能量、幅度分布等声发射信号与胶层的损伤破坏过程相对应。     

风电叶片复合材料压缩损伤破坏声发射监测

研究了风电叶片单向复合材料的压缩力学特性及其声发射响应特征.结果表明,复合材料的横向和纵向压缩力学性能及其声发射响应特性明显不同,纵向压缩强度、模量高,失效应变小,对应的声发射相对能量、幅度高,但撞击累积总数少.复合材料具有脆性破坏的特点,横向压缩以45°剪切失效为主,纵向压缩以层间劈裂为主.风电叶片复合材料压缩损伤破...     

碳纤维复合材料弯曲损伤的声发射试验研究

采用声发射技术研究了碳纤维复合材料的弯曲损伤与破坏行为。实验结果表明,碳纤维铺层在损伤与断裂不同阶段所释放的声发射信号特征不同,声学检测能有效的监测其剪切分层,混合分层,张力分层过程,声发射检测能有效判断碳纤维复合材料内部活动过程,判定损伤类型,在碳纤维复合材料结构与完整性评价中有良好的应用价值。     

环氧／玻纤复合材料弯曲损伤过程的声发射研究

采用声发射技术研究环氧树脂／玻璃纤维复合材料的弯曲损伤过程，并讨论了声发射特性及其与玻璃纤维含量的关系。     

循环加载下复合材料胶接面变形与破坏实验研究

复合材料胶接结构损伤变形和演化行为的实时表征对其服役的安全性和可靠性评估具有重要的意义。结合数字图像相关(Digital Image Correlation,简称"DIC")和声发射(Acoustic Emission,简称"AE")技术,研究循环拉伸加载条件下复合材料单搭接界面的损伤变形与破坏行为。依据单向拉伸失效载荷均值,取准静态破坏载荷的70%和80%分别进行循环拉伸加载实验。通过不同阶段复合材料胶接界面的损伤变形场、应变场信息及演化过程中获取的AE信号,分析循环加载下复合材料单搭接界面损伤破坏的力学机制与实时变形和AE特征信号的对应关系。结果表明,复合材料单搭接试件损伤破坏的实时微位移场特征和AE相对能量、撞击累积数及幅度谱等反映了胶接界面微裂纹的萌生及扩展行为。随应力水平的升高,复合材料单搭接试件破坏前的循环次数呈递减趋势。     

复合材料胶接修补界面损伤演化声发射监测

利用声发射技术实时监测四点弯曲载荷作用下含纤维断裂玻璃纤维增强复合材料胶接修补后试件的损伤演化过程,结合声发射信号统计分析方法,研究贴补片尺寸对修复效果的影响。结果表明,弯曲载荷作用下,两类贴补修补试件破坏模式均以贴补界面开裂为主,随着胶接修补贴补面积的增加,试件失效载荷呈增大趋势。贴补修补片长度为90mm时,其破坏载荷约为未修补试件破坏载荷的2倍。修补试件损伤破坏过程与对应声发射特征表现出良好的相关性,声发射信号统计性描述方法能够有效用于评估胶接修补复合材料试件的微损伤演化行为。     

风电叶片复合材料层间剪切破坏声发射监测

采用声发射技术对含分层缺陷风电叶片多轴向复合材料的层间剪切破坏实验进行实时监测,研究分层缺陷对复合材料层间力学性能的影响规律及其损伤破坏过程的声发射响应特征.结果表明,具有不同分层面积的两类复合材料试样破坏载荷相近,当分层缺陷位于剪切面中间位置时,分层缺陷大小对界面承载能力影响不大,损伤演化主要集中在剪切面上偏离中心两侧的区域;随着分层缺陷面积的增加,声发射撞击累积数有上升趋势,声发射相对能量、幅度分布、撞击源定位信号与剪切面上偏离中心两侧高应力区域的损伤破坏过程相对应.     

复合材料波纹褶皱区域损伤变形测量及声发射监测

对含波纹褶皱缺陷的玻璃纤维单向复合材料进行压缩试验,结合声发射(Acoustic Emission,简称"AE")和数字图像相关(Digital Image Correlation,简称"DIC")互补技术,研究复合材料波纹褶皱区域的损伤变形与演化规律。在复合材料试件压缩加载的过程中,采集波纹褶皱区域损伤变形场、应变场信息和实时声发射监测信号,分析复合材料压缩力学响应行为与缺陷区域变形场、应变场以及声发射信号特征之间的对应关系。结果表明:波纹褶皱会严重影响复合材料的力学性能,通过分析声发射信号,发现随着波纹褶皱宽高比减小,复合材料的力学性能呈现降低的趋势;当波纹褶皱宽高比一定时,随着波纹褶皱高度不断增加,复合材料的力学性能呈现降低的趋势。通过DIC测得的应变场与位移场信息,发现对于相同的载荷增量,最大应变呈增加趋势,且波纹褶皱宽高比越大应变增幅越大;越趋近于褶皱中部,水平位移越大,加载方向位移与试件失稳破坏位置有关,接近破坏区域的加载方向位移大。损伤区域位移场和应变场清晰地反映了玻璃纤维复合材料的损伤变形特征。     

UHMWPE/LDPE复合材料拉伸破坏的声发射特性研究(Ⅱ)

本文续“UHMWPE/LDPE复合材料拉伸破坏的声发射特性研究(Ⅰ)”,进一步研究了UHMWPE/LDPE复合材料拉伸破坏的声发射特性,具体研究了[0°]、[90°]在拉伸破坏过程中声发射参数特征,并对拉伸破坏机理进行了初步的研究。     

Adherence evaluation of paint coatings using a three‐point flexure test and acoustic emission

The adherence of paint coatings on aluminum substrates was tested using a three‐point flexure test (TPFT) combined with acoustic emission (AE) evaluation. The mechanical test was defined according to the French Standard. During bending of the paint‐coated specimen, acoustic emission signals were recorded and analyzed. Substrate pretreatments were chosen to show a set of visual interfacial ruptures and a set of visual cohesive ruptures in the paint. The formulation of the paint was fixed by industrial regulations. The varying nature of systems showed different AE patterns, particularly for two types of specimens: those that corresponded to solvent degreasings and the others to aqueous chemical pretreatments. The behavior of the paint coating differed, with significant AE, damage, and crack propagation in the first case and instantaneous phenomena in the other case. It is then possible to establish a relationship between the analysis of the recorded AE signal and the type of joint rupture. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 1848–1857, 2001     

Measurement of 2-ethyl-1-hexanol emitted from flooring materials and adhesives

It has been reported that 2-ethyl-1-hexanol (2E1H) was emitted through hydrolysis between di-2-ethylhexyl phthalate used as plasticizer in flooring material and moisture generated from a strongly alkaline material such as concrete slab. The purpose of this study was to clarify the relationship between diffusion of 2E1H in flooring material and 2E1H emission rate from floor surface. In this study, we measured 2E1H emitted from floor paper, poly(vinyl chloride) (PVC) tile, cushion floor and carpet for 200,?days and effective diffusion coefficients for 2E1H in various flooring materials were measured. Effective diffusion coefficients of 2E1H for cushion floor and PVC tile were 115?×?10^?9 and 7.8?×?10^?9 m²/s, respectively. Emission rate of 2E1H emitted from flooring material significantly depends on the kind and shape of flooring materials and was influenced by the effective diffusion coefficient for 2E1H of flooring material. Emission rates of 2E1H from floor surface varied with the amount of 2E1H and resin present in the adhesive. When carpet was attached to the flooring material with high water content using adhesive, emission of 2E1H significantly increased. The results show that primary and secondary emissions of 2E1H from the adhesive influence the emission rate of 2E1H for flooring material.     

Theoretical and Experimental Analysis of the Scarf Joint Bonded Structure: Influence of the Adhesive Thickness on the Micro-mechanical Behavior

In this work, we have studied the influence of the adhesive thickness on the micro-mechanical behavior of a scarf joint bonded structure loaded in uniaxial tension. Adherends are made of mild steel containing 0.18% Carbon (French Standard XC18), the adhesive is a two-component epoxy resin with a 5800 MPa elastic modulus. The experimental method is based on strain gauge measurements and acoustic emission. It makes it possible to determine the following zones:

—the areas of the joint where the start of microcracks occurs (threshold Fd);

—the areas where crack propagation occurs (threshold Fg) up to the failure (threshold Fr). The experimental results confirm the good correlation between the different thresholds. They also show that there is an optimal adhesive thickness close to 0.1 mm, which confers to the scarf joint the greatest resistance to microcrack initiation and crack extension. We have compared our experimental measurements with the main theories in this domain to determine their limits and their fields of application, particularly in the angular singularities regions near the ends of the lap.     

Theoretical and Experimental Analysis of the Scarf Joint Bonded Structure: Influence of the Adhesive Thickness on the Micro-mechanical Behavior

In this work, we have studied the influence of the adhesive thickness on the micro-mechanical behavior of a scarf joint bonded structure loaded in uniaxial tension. Adherends are made of mild steel containing 0.18% Carbon (French Standard XC18), the adhesive is a two-component epoxy resin with a 5800 MPa elastic modulus. The experimental method is based on strain gauge measurements and acoustic emission. It makes it possible to determine the following zones:

—the areas of the joint where the start of microcracks occurs (threshold Fd);

—the areas where crack propagation occurs (threshold Fg) up to the failure (threshold Fr). The experimental results confirm the good correlation between the different thresholds. They also show that there is an optimal adhesive thickness close to 0.1 mm, which confers to the scarf joint the greatest resistance to microcrack initiation and crack extension. We have compared our experimental measurements with the main theories in this domain to determine their limits and their fields of application, particularly in the angular singularities regions near the ends of the lap.     

声发射技术在复合材料中的应用及研究进展

本文介绍了声发射的发展史和当前国内外声发射技术在复合材料方面的应用及发展现状，最后介绍了声发射技术应用于检测复合材料飞轮的损伤与断裂的研究情况。     

Mode I and mode II delamination of a chopped strand mat E-glass reinforced vinyl ester composite

The objective of the present work is to investigate mode I and mode II delamination behaviour of chopped strand mat (CSM) E-glass reinforced vinyl ester (VE) composite. Double cantilever beam and end notched flexure tests were carried out to evaluate the mode I and mode II delamination, respectively. The fracture toughnesses were calculated using the experimental calibration method. Results showed that the average mode I and mode II fracture toughnesses were 185 and 2386?N?m^?1, respectively. Furthermore, the mode II–mode I ratio for this material was 12.9. This value was the highest when compared with other composite materials from the literature. Finally, through scanning electron micrographs, the dominant failure mechanisms were found to be matrix cracking, fibre debonding and fibre breakage. In addition, shear cusps were observed in mode II specimen, which signified the shearing between the layers.     

Interlaminar fracture toughness of a plain weave flax/epoxy composite

ABSTRACT

In recent decades, flax fibre has become a popular natural resource as reinforcement in polymeric composites. However, the pure mode characterisation of flax fibre composites is rather limited. Furthermore, the mixed-mode delamination is not yet available. Nevertheless, delamination behaviour is important to be characterised as it is a major problem in composite laminates. This study examined the delamination behaviour of a woven flax/epoxy composite. Specimens were tested using mode I double cantilever beam, mode II end-notched flexure and mixed-mode I+II single leg bending tests. Results showed that the mode I, mode II and mixed-mode I+II fracture toughness were 363.23, 962.17 and 649.06?N?m^?1, respectively. When the fracture toughness values were fitted using Benzeggagh–Kenane criterion, it was found that the best-fit material parameter η was attained at 0.88. This information is useful to estimate the variation of fracture toughness with the mode ratio. Finally, through scanning electron micrographs, it was noticed that fibre/matrix debonding was the major fracture mechanism in all loading modes. In conclusion, the findings from this study suggested that the composite was suitable to be used for structural applications under mixed-mode loading.