聚酰亚胺树脂基MT300/KH420复合材料高温力学性能(Ⅱ)——弯曲性能

从宏、微观的角度研究了碳纤维增强聚酰亚胺树脂基MT300/KH420复合材料的高温力学性能,重点揭示了MT300/KH420复合材料[0°]14和[±45°/0°/90°/+45°/0°2]s层合板在常温~500℃的弯曲性能变化规律。研究表明:MT300/KH420复合材料高温力学性能优异,[0°]14层合板在420℃的弯曲强度保持在51%以上,弯曲模量在500℃以内变化很小。[0°]14层合板在常温下断口粗糙,且贯穿厚度,表现为脆性破坏;随温度升高,树脂流动性增强,呈现出黏弹效应,破坏逐渐集中在加载点处,在500℃,部分树脂热解,纤维束脱离基体并氧化。[±45°/0°/90°/+45°/0°2]s层合板高温弯曲性能较为稳定,主要破坏为上、下表面沿45°方向开裂,并伴有层间分离,在500℃出现严重分层破坏;相比于受基体控制的层合板弯曲性能,温度对受纤维控制的层合板弯曲性能影响较小。     

温度老化对GFRP/BFRP筋残余弯曲性能的影响

对玻璃/玄武岩纤维增强复合材料(GFRP/BFRP)筋材在温度老化作用后的弯曲性能进行了试验研究,重点探讨了不同作用温度及恒温时间对不同直径的两类FRP筋材的弯曲性能影响特性,同时采用扫描电子显微镜(SEM)对温度老化作用后部分GFRP/BFRP筋的微观结构变化及损伤机理进行了分析.试验与分析结果表明:(1)温度老化作用后GFRP/BFRP筋材弯曲强度与最大应变随作用温度升高均呈阶段性下降的趋势,而弯曲弹性模量无明显退化,其保留率均在90％以上;(2)温度老化作用后直径较大的GFRP筋材的弯曲性能退化更为明显;且G12筋的弯曲性能保留率退化曲线均高于B12筋,说明BFRP筋的弯曲性能对温度作用更为敏感;(3)在270℃高温环境下,GFRP/BFRP筋弯曲性能随着恒温时间的延长均呈现线性下降趋势;(4)结合试验结果和SEM微观结构分析,可认为造成温度老化作用后两类FRP筋弯曲强度退化的主要原因是纤维与树脂基体间协同工作效果和纤维-树脂基体界面性能的显著降低.最后,结合本试验结果,给出了500℃以内温度老化作用后GFRP/BFRP筋材弯曲强度退化的计算模型以及线性插值预测方法,便于实际工程应用.     

火灾高温后混凝土内GFRP筋剪切性能退化试验与理论

为研究火灾高温后混凝土内玻璃纤维增强树脂复合材料(GFRP)筋材的剪切性能，选取了100℃、150℃、200℃、300℃、350℃、400℃、500℃、650℃及800℃共9个温度工况，对混凝土内GFRP筋进行了高温作用及水平剪切试验；结合本试验及已有相关试验结果，对高温后混凝土内GFRP筋水平剪切强度预测方法进行了探讨。试验及分析结果表明：300℃高温以内，混凝土内GFRP筋表面温度存在滞后现象，其高温劣化程度明显低于裸筋，剪切强度退化也较缓慢；随着温度超过300℃及混凝土表面裂缝不断发展，内部GFRP筋受高温侵蚀逐步加大，剪切强度出现急剧下降，并出现与裸筋相似的退化规律；在300℃(接近树脂热分解温度)高温下，GFRP筋剪切强度随恒温时间的增加而线性下降，恒温1～3 h时其剪切强度保留率从76.4%降为46.5%。结合双曲正切函数模型，建立了高温后混凝土内GFRP筋水平剪切强度预测模型，其预测值与试验值吻合较好。最后，以剪切强度保留系数0.7为基准，给出了不同保护层厚度下GFRP筋的耐火时间预测值，供工程应用参考。     

基于宏微观分析的碳纤维增强高分子复合材料强度性能表征

微观力学强度理论(MMF)是一种新型的基于物理失效模式的复合材料强度理论。通过对碳纤维/树脂(UTS50/E51)复合材料单向层合板进行纵向、横向静载拉伸、压缩和弯曲试验, 得到层合板的基本力学性能和宏观强度指标。建立了碳纤维增强树脂基复合材料微观力学模型, 获取树脂基体和纤维不同位置的机械载荷应力放大系数和热载荷应力放大系数。结合获取的应力放大系数及试验测得的单向层合板宏观强度, 计算出层合板组分的MMF强度特征值。绘制了基于MMF强度理论的层合板破坏包络线, 并与Tsai-Wu失效准则预测结果进行对比。实现了对UTS50/E51层合板MMF强度特征值的表征。     

自动铺放成型热塑性复合材料的非等温结晶动力学研究

利用差示扫描量热仪结合Avrami方程研究玻璃纤维增强聚丙烯复合材料自动铺放成型过程非等温结晶动力学,推导非等温结晶动力学模型,并通过构建冷压辊下方铺层的冷却模型,将结晶动力学模型和传热模型相结合,设定自动铺放成型过程中的冷却条件,探讨冷却速率及冷却时间对基体材料结晶行为的影响,求解出不同冷却速率下的最大铺放速率。研究结果表明:铺层树脂基体的结晶度随冷却速率的增大而依次减小;随着冷却速率的提高,树脂结晶起始温度和结晶完成温度均向低温方向移动,且树脂相对结晶度随温度变化规律接近反S形曲线;自动铺放成型实验件的压缩强度及层间剪切强度随着铺层结晶度的增大基本呈增大趋势,而冲击强度与铺层结晶度的变化趋势完全相反,随着结晶度的增大,材料韧性越差。     

二氧化双环戊二烯改性树脂基复合材料的制备与性能

采用双酚A型环氧树脂(E-51)改性二氧化双环戊二烯树脂(CDR-0122),以改善其力学性能。首先根据复合材料力学性能选择较好的稀释剂,然后比较树脂基体在改性前后的玻璃纤维(Gf)和炭纤维(Cf)复合材料的基本力学性能和耐热性能。结果表明,环己二醇二缩水甘油醚(CDX-1180)是优于丙酮的一种稀释处理剂。同时用CDX-1180做稀释剂处理时,树脂基体经改性后,所制得的Gf层合板拉伸强度和拉伸模量分别提高了19.1%和16.8%,弯曲强度和弯曲模量分别提高了20.5%和12.6%;所制得的Cf层合板拉伸强度和拉伸模量分别提高了9.7%和8.7%,弯曲强度和弯曲模量分别提高了26.2%和7.0%;E-51改性CDR-0122树脂复合材料相比纯的CDR-0122树脂复合材料的玻璃化转变温度和热稳定性都略有提高。     

单向碳纤维增强树脂基复合材料的超低温力学性能

采用真空袋-热压罐工艺制备单向碳纤维增强树脂基复合材料(CFs/EP)层合板,并将高低温试验箱与万能试验机相结合,通过合理使用低温胶和低温引伸计,并在降温过程中实施应力-应变实时调零等关键技术,在室温和液氧超低温度(-183℃)下对单向CFs/EP层合板进行拉伸和弯曲试验,研究了其超低温力学性能,并根据室温和超低温试验后试样的微观和宏观特征,揭示了超低温环境下复合材料力学性能变化机制。结果表明,与室温力学性能相比,单向CFs/EP层合板超低温拉伸强度下降约为9.5%,而拉伸模量上升约为6.2%,主要是由于超低温环境下,树脂的收缩使绝大部分碳纤维与树脂间形成了强界面,拉伸后试样呈"劈裂式"破坏形式,无法使每根纤维都充分发挥其强度,拉伸强度下降,同时超低温也限制了树脂大分子链的运动,所以导致单向CFs/EP层合板拉伸模量上升;单向CFs/EP层合板超低温弯曲强度和弯曲模量分别提高约54.75%和11.64%,这是由于单向CFs/EP层合板的常温和超低温的弯曲破坏形式均为分层剪切破坏,超低温下复合材料的界面增强,提高了单向CFs/EP层合板抵抗剪切分层的能力,进而使CFs/EP的弯曲性能得到提高。     

高温作用后GFRP筋与海水珊瑚混凝土粘结性能试验研究

为了研究高温后玻璃纤维增强树脂复合材料(GFRP)筋与海水珊瑚混凝土的残余粘结性能,对54个GFRP筋珊瑚混凝土试件及钢筋珊瑚混凝土对比试件进行了高温作用后的中心拔出试验,最高温度为350℃,混凝土强度等级考虑C20～C30。观察了高温后试件的表观变化及粘结破坏形态,获取了各试件的粘结-滑移曲线、粘结强度、粘结刚度和峰值滑移量,分析了不同温度、GFRP筋直径、海水珊瑚混凝土强度等因素对高温后GFRP筋与海水珊瑚混凝土粘结性能的影响。基于烧失率和XRD分析,剖析了GFRP筋海水珊瑚混凝土的高温劣化机制。最后,提出高温后GFRP筋与珊瑚混凝土的剩余粘结强度计算式和粘结-滑移本构模型。研究结果表明：高温作用后,尽管GFRP筋与珊瑚混凝土的粘结破坏形态与常温相似,GFRP筋的碳化和珊瑚混凝土的分解使得二者界面发生显著劣化;随着温度的提高,GFRP筋与珊瑚混凝土的粘结强度逐渐降低,峰值滑移量增大;GFRP筋直径越小,高温后的剩余粘结强度和剩余粘结刚度越小;珊瑚混凝土强度等级越高,剩余粘结刚度越大,峰值滑移量越小。所提出的高温后GFRP筋与珊瑚混凝土剩余粘结强度和粘结-滑移本构关系计算结果与试验结...     

国产CCF300/双马树脂层合板高温拉伸与压缩性能试验研究

对碳纤维(CCF300)/双马树脂(GW-300)复合材料层合板进行了200 ℃和300 ℃高温环境下的拉伸和压缩性能试验, 研究其在不同温度环境下基本力学性能的变化。研究结果表明, 由基体控制试件在高温下的拉伸强度和模量比由纤维控制试件降低的比例大; 随着温度的升高, 厚试件的压缩强度比薄试件的压缩强度提高幅度明显; 高温下, 拉伸性能保持率较高, 而压缩性能保持率较低; 300 ℃下基体控制试件和纤维控制试件的拉伸强度保持率分别达70%以上和90%以上, 而厚试件和薄试件的压缩强度保持率都只略高于30%。      

多轴向玻璃纤维增强树脂基复合材料的破坏特性和损伤机制

通过对玻纤增强环氧乙烯基酯树脂(GF/EVE)和玻璃纤维增强不饱和聚酯树脂(GF/UP)复合材料的多轴向铺层设计试件进行低速冲击、弯曲和剪切破坏性力学试验,分析了不同铺层方式的GF/EVE和GF/UP复合材料冲击、弯曲和剪切载荷作用下产生的损伤及失效模式。结果表明:在铺层设计与工艺相同的情况下,CF/EVE的弯曲强度、冲击韧性均优于CF/UP;[0,90]6试件冲击能量吸收性能优于其他五种铺层方式;铺设角设计、树脂基体类型、铺层厚度对层合板剪切力学性能的影响较小。并基于SEM与超声C扫描成像检测(C-SAM)对复合材料的微观界面脱粘机制及损伤演化行为进行阐释。     

The effect of time and temperature on flexural creep and fatigue strength of a silica particle filled epoxy resin

Composite materials that use an epoxy resin as a matrix resins have superior mechanical properties over standard structural materials, but these materials exhibit time and temperature behavior when used for long periods and under high temperatures. This time and temperature behavior has not been fully explained. The purpose of this paper is to further describe this time and temperature behavior, increasing the reliability of this class of composite materials. The time and temperature dependence of flexural strength was examined by creep and fatigue testing. Flexural creep tests were carried out at various temperatures below the glass transition temperature. Flexural fatigue tests were carried out at various stress ratios, temperatures below the glass transition temperature and 2 frequencies. The time-temperature superposition principle held for the flexural creep strength of this material. A method to predict flexural creep strength based on the static strength master curve and the cumulative damage law is proposed. When the fatigue frequency was decreased while temperature and stress ratio are held constant the flexural fatigue strength decreases. The time-temperature superposition principle was also found to hold for the flexural fatigue strength with respect to frequency.     

考虑时间和温度影响的复合材料开孔层板压缩失效分析

鉴于复合材料性能的时间-温度相关性,对固化后的树脂基体(5228A)进行了动力学分析(Dynamic Mechanical Analysis,DMA),得到了试验窗口中不同温度下的储能模量曲线片段,利用封闭平移(Closed Form Shifting,CFS)方法对其进行扩展,建立了主曲线并得到了曲线片段对应的平移因子。根据加速试验方法(Accelerated Testing Methodology,ATM),分别以两种铺层的准各向同性开孔层板(CCF300/5228A)为研究对象,建立了匀应变率(Constant Strain Rate,CSR)压缩强度主曲线。借助微距拍摄和超声波C扫描,对其渐进损伤过程和不同温度下的破坏形貌进行了观测。结果表明:即使温度低于玻璃态转变温度,树脂基体动态力学性能也会随时间的增加而降低;单层较厚的开孔层板压缩强度对时间和温度更加敏感,而单层较薄的开孔层板则具有更好的损伤容限性能;温度升高、加载速率降低时,开孔层板压缩最终破坏主导因素从分层损伤趋于纤维屈曲。     

Cryogenic through-thickness tensile characterization of plain woven glass/epoxy composite laminates using cross specimens: Experimental test and finite element analysis

This paper investigates the through-thickness tensile behavior of woven glass fiber reinforced polymer (GFRP) composite laminates at cryogenic temperatures. Tensile tests were carried out with cross specimens at room temperature and liquid nitrogen temperature (77 K), and the through-thickness elastic and strength properties of the woven GFRP laminates were evaluated. The failure characteristics of the woven GFRP laminates were also studied by optical and laser scanning microscopy observations. A three-dimensional finite element analysis was performed to calculate the stress distributions in the cross specimens, and the failure conditions of the specimens were examined. It is found that the cross specimen is suitable for the cryogenic through-thickness tensile characterization of laminated composite materials. In addition, the through-thickness Young's modulus of the woven GFRP composite laminates is dominated by the properties of the matrix polymer in the given temperature, while the tensile strength is characterized by both, the fiber to matrix interface energy and the cohesion energy of the matrix polymer.     

Accelerated testing for long-term durability of GFRP laminates for marine use

Our proposed accelerated testing methodology for the long term durability of polymer composites is based on the time–temperature superposition principle to be held for the viscoelasticity of polymer matrix. The long term flexural fatigue life of plain woven glass fiber/vinyl-ester (GFRP) laminates for conventional marine use was predicted based on the proposed methodology. As results, the flexural fatigue strengths of GFRP laminates decreases strongly with increasing time and temperature as well as the number of cycles to failure. The long term fatigue strength at any time, temperature and number of cycles to failure can be predicted using the master curves of fatigue strength obtained based on our proposed accelerated testing methodology.     

Effect of damage on the interlaminar shear properties of hybrid composite laminates at cryogenic temperatures

This paper presents the experimental and numerical characterization of the interlaminar shear failure of hybrid composite laminates at cryogenic temperatures. Cryogenic short beam shear tests were performed on hybrid laminates consisting of woven glass fiber reinforced polymer (GFRP) composites and polyimide films to evaluate their interlaminar shear strength. Microscopic observations of damage accumulation and failure mechanisms were also made on failed specimens. In addition, a progressive damage analysis was conducted to predict the initiation and growth of damage in the specimens, and the interlaminar shear strength was determined from the maximum shear stress in the failure region. The damage effect on the interlaminar shear properties of hybrid laminates at cryogenic temperatures was examined based on the experimental and numerical results.     

玻璃纤维复合材料中不同破坏类型的声发射特征

本文就七种不同类型玻璃纤维复合材料试样在拉伸过程中的声发射幅度分布特征作了分析比较,对几种基本破坏模式的声发射幅度分布进行了探讨.它们具有各自的特点,从而有可能对一些铺层类型的复合材料的损伤扩展过程进一步认识.      

Layered silicates nanocomposite matrix for improved fiber reinforced composites properties

Three-phase glass fiber reinforced composites (GFRP) consisting of traditional woven glass fiber and polyamide-6 (PA6) matrix dispersed with organically modified layered silicates were prepared and investigated in this study. The fabrication of GFRP with different weight percentages of layered silicates was successful when the matrix contains less than 5 wt% of the layered silicates. The improvement due to the high aspect ratio and high stiffness of the layered silicates is illustrated through the matrix-controlled properties of the GFRP. The results showed that the GFRP with 5 wt% layered silicates offer the largest improvement of approximately 30% increase in both flexural strength and compressive strength at elevated temperatures. On the other hand, the in-plane shear properties measured from [±45]_s laminates revealed that the layered silicates help improved both the in-plane shear strength and modulus appropriately. By utilizing a nanocomposite matrix, improvement of stiffness and strength, as well as thermal and barrier properties is obtained without any change in processing temperature of the fiber composites.     

Residual strength distribution of impacted glass/epoxy laminates with embedded shape memory alloy at low temperature

This paper evaluated the strength reduction and probabilistic behaviors of the residual flexural strength for impacted glass/epoxy laminates with embedded shape memory alloy (SMA) wires at various temperatures. A series of impact tests were performed on base (glass/epoxy laminates without SMA wires) and SMA laminates (glass/epoxy laminates with embedded SMA wires) at temperatures of 293 K, 263 K and 233 K. Three point flexural tests were then carried out so as to investigate the post-impact strength at the aforementioned temperatures. Strength reduction behavior of impacted laminates could be described by Caprino’s residual strength prediction model. A probabilistic model was developed in order to estimate the variation in residual strength of the impacted laminates with temperature. As the temperature decreased, the variation in residual strength increased due to the embrittlement of the constituent materials of the laminates at lower temperatures. When compared to the base laminates, the SMA laminates exhibited a higher variation in residual strength, especially at lower temperatures.     

Effects of hydrothermal aging on glass–fiber/polyetherimide (PEI) composites

The moisture absorption behavior and the influence of moisture on thermal and mechanical properties of glass–fiber/polyetherimide (PEI) laminates have been investigated. The laminates were exposed to hydrothermal aging at two different temperatures and high moisture rates. The properties of as-received and hydrothermally aged samples were compared. The hydrothermally aged laminates contained a large amount of moisture which caused decrease in the glass transition temperature and deterioration in mechanical properties (interlaminar shear strength, flexural modulus, bearing strength, etc.). Fractographic analysis revealed interfacial debonding as the dominant failure mechanism, indicating a strong influence of water degradation on fracture toughness results. Alterations in visco-elastic properties of glass/PEI composite which was exposed to hydrothermal aging were analyzed with the dynamic mechanical thermal analysis (DMTA) method. DMTA tests give evidence of plasticization of the PEI matrix.