三维编织复合材料压缩力学性能的实验研究

通过宏观压缩实验,研究了三维四向编织复合材料的抗压力学性能;同时,为了认识其压缩失效机理,对压缩试件的破坏断口进行了扫描电镜分析。实验结果表明:纵向压缩模量比横向压缩模量大得多;影响纵向压缩力学性能的主要参数是材料的编织角,随编织角的变化,复合材料的纵向压缩破坏机理发生了变化,编织角较小时,材料表现为脆性特征;当编织角大于某个角度,材料的应力-应变曲线趋于非线性,延性增加,更多地表现为塑性破坏特征。此外,横向压缩的破坏机理与纵向压缩明显不同。     

三维四向编织碳纤维/环氧树脂复合材料在热环境中的拉压力学性能实验

针对不同编织角度的三维四向编织碳纤维/环氧树脂复合材料,进行了热环境下的轴向拉伸和压缩力学性能实验研究,讨论了温度对三维四向编织复合材料的轴向拉伸和压缩力学性能的影响,并根据宏观断裂形貌和SEM图像分析了材料的破坏和断裂机制。结果表明,随着测试温度的升高,三维四向编织碳纤维/环氧树脂复合材料的纵向拉伸强度有小幅提高,而纵向压缩强度显著降低。在室温条件下,编织角对材料的纵向拉伸破坏特征没有影响,而对材料的纵向压缩破坏特征有较大影响。随着测试温度的升高,不同编织角度复合材料的纵向拉伸和压缩的损伤破坏形态均与室温条件下明显不同。      

三维五向炭纤维/酚醛编织复合材料的压缩性能及破坏机制

针对不同编织角、 不同纤维体积分数的三维五向炭纤维/酚醛编织复合材料在不同温度下进行了纵向(编织方向)压缩和横向压缩试验 , 获得了其主要压缩力学性能 , 分析了编织参数、 温度对材料压缩力学性能的影响。对试件断口进行了宏观及扫描电镜观察 , 从宏、 细观角度研究了材料的变形及其破坏机制。结果表明 , 三维五向炭纤维/酚醛编织复合材料的压缩应力2应变曲线呈现明显的非线性特征 , 且温度效应明显; 编织角和纤维体积分数是影响材料压缩性能的主要参数。三维五向炭纤维/酚醛编织复合材料的纵向压缩与横向压缩具有完全不同的破坏机制。      

三维五向编织复合材料纵向性能的实验研究

通过对具有不同编织结构参数的三维五向编织复合材料试件的纵向拉伸和压缩实验,分析了该类材料的纵向拉、压刚度和强度随编织工艺参数的变化规律以及材料的失效形式.三维五向编织复合材料在破坏前基本保持线弹性,纵向拉、压破坏具有脆性特征,拉伸模量和压缩模量比较接近,但拉伸强度远大于压缩强度.编织角和纤维体积含量对材料性能的影响显著,纱线粗细的影响不大.提高第五向纱线的比例,可提高材料的纵向性能.此外,研究中采用短标距薄板试件,以避免试件产生整体屈曲和端部纤维束开裂破坏.     

损伤形式对三维编织复合材料拉压性能的影响

通过对损伤前后三维编织复合材料试件进行纵向拉伸和压缩实验, 分析了材料的拉、压刚度和强度的变化规律和失效形式。主要讨论了4 种损伤加工方案, 包括沿宽度方向单边切割、沿宽度方向双边切割、沿厚度方向单边切割及沿宽度和厚度方向同时切割。实验结果表明, 宽度方向损伤对拉伸强度、模量和压缩强度影响不大, 压缩模量下降了20 %左右; 厚度方向损伤对纵向拉伸、压缩强度和模量影响较大。编织角20°时, 拉伸、压缩应力-应变曲线接近于线性, 试件的失效方式趋向于脆性破坏; 编织角35°时, 压缩应力-应变曲线表现出一定的非线性。      

三维编织C/SiC复合材料的拉压实验研究

针对三维编织C/SiC复合材料进行了拉伸试验和压缩试验,得到了材料拉伸、压缩的主要力学性能参数、损伤发展情况及破坏规律。从宏观角度比较了在两种载荷下材料弹性性能及强度的区别,得到了一些试验研究结论。结果表明:三维编织C/SiC在拉伸和压缩载荷下的应力-应变曲线有明显的非线性特性;拉伸模量低于压缩模量;拉伸强度高于压缩强度;声发射数据可以用来检测材料内部损伤的发展。      

基于面-内胞模型的三维四向编织复合材料渐进损伤数值模拟

为了准确预测三维四向编织复合材料的纵向拉伸力学性能,对编织复合材料的面胞和内胞细观实体模型进行参数化建模,面胞模型考虑了纱线空间轨迹的偏移和横截面的挤压变形。用体素网格离散模型并施加合适的边界条件,将各组分材料的损伤模型编入到有限元分析软件ABAQUS用户定义材料子程序UMAT中。分别对内编织角为30°和45°的三维四向碳纤维/环氧树脂编织复合材料的面-内胞模型进行数值分析,经体积加权平均获得不同厚度编织复合材料试件的纵向拉伸模量和强度,通过统计具有相同破坏模式的积分点数量研究复合材料的渐进损伤过程。结果表明:基于面-内胞模型预测三维四向编织复合材料的纵向拉伸力学性能与试验值吻合良好,损伤分析结果合理地反映了面胞和内胞的渐进损伤过程。      

三维六向编织复合材料渐进损伤模拟及强度预测

基于三维六向编织复合材料的细观结构,假设第六向纱线的截面形状为菱形,建立了三维六向编织复合材料的渐进损伤有限元模型。采用Linde等提出的失效准则,引入周期性位移边界条件,对三维六向编织复合材料的纵向拉伸应力-应变行为进行了渐进损伤数值模拟,讨论了单胞模型在纵向拉伸载荷作用下的细观损伤起始、扩展和最终失效的演化过程,并预测了材料的拉伸强度。在此基础上,进一步研究了编织角、纤维体积分数和编织纱水平取向角等参数对材料纵向拉伸力学性能的影响规律。研究结果表明,三维六向编织复合材料的轴向纱线拉伸断裂是导致其破坏的最主要因素。所得数值结果与现有试验值吻合较好,验证了该模型的有效性,为更深入研究此类材料的力学性能奠定了基础。     

三维四向编织复合材料动态压缩性能实验研究

利用分离式霍普金森压杆(SHPB)研究了三维四向编织碳纤维环氧树脂复合材料在动态压缩载荷作用下的力学性能。在横向对复合材料进行了动态压缩实验,得到了应变率从900/s―1500/s下的应力-应变曲线,并且与准静态压缩下的结果进行了对比。分析比较了应变率对三维编织复合材料横向压缩强度和模量的影响。实验中根据SHPB理论假设,采用波形整形技术,使得试件在加载过程中处于应力平衡和均匀变形状态。实验结果表明:压缩强度和模量具有一定的应变率强化效应;与准静态结果相比,在高应变率下的复合材料的强度和模量有明显的增大,并表现出明显的脆性。还分析了应变率对复合材料破坏模式的影响。     

三维四向大编织角复合材料的细观强度分析

编织角是影响三维编织复合材料力学性能的最重要因素.实验数据表明:大编织角复合材料在单向拉伸作用下的破坏形式较为复杂,其应力-应变曲线呈现非线性特性.本文建立了细观应力场的均匀化列式和有限元求解方法,运用该方法对三维大编织角复合材料的细观应力分布进行了数值模拟,结合相关的强度理论对材料进行失效分析,并进一步对材料的拉伸强度进行预测.强度计算结果与实验结果较为吻合.     

炭化过程中中空酚醛纤维结构性能的变化

以不同中空度和不同直径的中空酚醛纤维为原料,在N2保护下升温处理到不同温度,考察经不同温度处理后中空纤维的质量、直径、截面形貌和力学性能的变化;经过光学显微镜、扫描电子显微镜和纤维电子强力仪的观察测量,结果表明:随着热处理温度的提高,中空酚醛纤维分解缩聚反应加剧,质量和直径逐渐减小,截面形貌基本不变,力学性能也发生相应...     

动态拉伸载荷下应变率和温度对Kevlar 49芳纶纤维布增强环氧树脂复合材料力学性能的影响

为研究Kevlar 49芳纶纤维布增强环氧树脂复合材料在中等应变率和不同温度耦合作用下的力学响应和断裂行为,首先,利用MTS液压伺服高速机在不同初始应变率(25、50、100、200 s-1)和温度(-25、0、25、50、100℃)下对芳纶纤维增强复合材料(AFRP)进行单向动态拉伸测试;然后,采用Weibull分析模型量化了拉伸强度在不同应变率和温度下的离散程度。结果表明:在相同温度(25℃)下,随着应变率的增加,弹性模量和拉伸强度均先增大(初始应变率介于25~50 s-1范围内)后减小(初始应变率介于50~200 s-1范围内),极限应变则呈现出相反的变化趋势,而韧性随应变率的变化幅度不大;在相同初始应变率(25 s-1)下,与在25℃下的情况相比,温度的升高或降低均会造成弹性模量的降低,在温度为100℃时,极限应变显著增加,而拉伸强度和韧性均不会随温度的变化而发生明显改变。对AFRP断裂形态进行的对比分析表明不同试验条件下AFRP的断裂形态基本相同,均呈现出较为平整的断裂面。所得结论可为AFRP在极端载荷和环境作用下的理论研究和应用提供依据。      

混杂碳/碳复合材料超高温力学性能实验研究

利用快速通电加热测试技术,模拟混杂碳/碳复合材料的超高温工作环境,测试了材料不同温度下的拉伸、压缩力学性能,得到了材料的拉伸、压缩强度与模量随温度的变化规律,并给出了相应的拟合曲线。结果表明:材料的强度和模量在一定范围内随温度的升高而增加,在2000 K~2400 K之间达到最大值,当温度超过2700 K后迅速下降。材料轴向的拉伸、压缩性能随温度的变化较横向缓慢,强度的变化范围较模量的小。     

Modelling the effects of temperature and loading rate on fatigue properties of hot mixed asphalt

Fatigue cracking is one of the primary distresses of asphalt pavement. Critical strain energy density (CSED) has shown great potential to be a material parameter for fatigue cracking prediction. For the CSED to be used in future fatigue model and pavement design, a model is needed to predict the CSED as a function of the loading rate and the temperature, analogous to dynamic modulus. In this study, indirect tensile (IDT) tests were conducted to determine the properties of hot mixed asphalt at different loading rates and temperatures. It was found that time–temperature superposition principle is valid for IDT strength at both low and intermediate temperatures; and valid for failure strain and for the CSED at intermediate temperatures only. The shift factors for dynamic modulus were close to those of IDT strength and CSED, respectively. However, there was a discrepancy between shift factors of dynamic modulus and those of failure strain.     

Some factors for the high performances of mesophase pitch based carbon fibre

The tensile strength and Young's modulus of the carbon fibres prepared from naphthalene derived mesophase pitch were studied by varying the spinning temperature, heating rate and final temperature of the stabilization and graphitization temperatures to find the best properties obtainable from the particular pitch. The heating rate was very influential on the tensile strength of the fibre; a slow heating of 0.5° C min^–1, provided the highest strength, as high as 5 GPa at the optimum final temperature of stabilization. A higher or lower final temperature reduced the strength. Insufficient oxygen uptake or decomposition of oxygen groups at the surface of the fibre could induce defects, reducing the strength. In contrast, Young's modulus of the fibres was rather insensitive to preparation conditions. The carbonization and graphitization temperature influenced the mechanical properties as follows: the strength increased stepwise with the carbonization temperature, whereas the modulus increased sharply with the graphitization temperature. The structural factors most influential differed with these properties.     

Structure and properties of mesophase pitch carbon fibre with a skin-core structure carbonized under strain

Coal tar mesophase pitch fibres stabilized at 270° C to different extents were carbonized under strain by the constant load or constant length, using different heating rates, and further graphitized at 2500° C. Shallow and moderate stabilization provided a skin-core structure in the resultant fibres which exhibited higher orientation, tensile modulus, and better graphitizability after calcination at 1300° C and graphitization at 2500° C than deep stabilization. The tensile strength and modulus of the graphitized fibre was significantly improved through the strained carbonization when the stabilization was performed to a moderate extent. The strain tended to give an onion-like alignment in the fibre to improve the preferred orientation of carbon planes. Larger load and more rapid heating during carbonization modified the structure and properties of resultant fibres through a significant longitudinal elongation. The stabilization extent of pitch fibres governs the mobility or fusibility of mesogen molecules at the carbonization which allows their better alignment by the strain.     

纵向拉伸对尼龙帘线-橡胶复合材料横向拉伸力学性能影响的实验研究

采用十字形试件,在双轴拉伸条件下研究了尼龙帘线-橡胶复合材料单层板纵向定载荷对横向力学性能的影响和横向定载荷对纵向力学性能的影响。实验结果表明:纵向拉伸载荷对尼龙帘线-橡胶复合材料的横向拉伸力学性能有很大的影响。随着纵向拉伸载荷的增加,横向应力应变关系发生了很大的变化;横向拉伸强度先上升然后又下降;而其断裂变形和变形能却逐渐减小。横向拉伸载荷对尼龙帘线-橡胶复合材料的纵向拉伸力学性能影响却很小。这可能与材料纵向和横线拉伸性能差异太大有关。     

Transverse tensile behaviour of fibre reinforced titanium metal matrix composites

Four Ti MMCs have been tested in transverse tension, at ambient temperature and 600 °C. Generally, mechanical properties are reduced compared to monolithic Ti alloys. Transverse Young's modulus is, however, higher than in monolithic alloys, as a result of constraint of the matrix by the fibres.MMC proportional limits are associated with the onset of interfacial failure. Fibre coating cracking and longitudinal fibre splitting may also contribute to MMC yield and the associated acoustic emission peak. The fibre/matrix interface in IMI 834/SM1140+ appears to be weaker than in the other MMCs, resulting in a lower proportional limit and less acoustic emission. Final failure of the MMCs is generally via ductile shearing of matrix ligaments. The exception to this is IMI 834/SM1140+ in which the matrix fails in a brittle manner. This causes poor transverse tensile strength and failure strain in this MMC.A model to predict the MMC proportional limit, previously proposed by Jansson et al., has been modified to take account of the tensile strength of the fibre/matrix interface. The model previously used by Jansson et al. to predict the transverse tensile strength is acceptably accurate provided that the area fraction of matrix appearing on fracture surfaces is accurately determined.     

Kinetic studies on hot-stretching of polyacrylonitrile-based carbon fibres by using internal resistance heating Part II Changes in structure and mechanical properties

The effects of the stretching stress applied during high-temperature heat treatment of polyacrylonitrile-based carbon fibres on the development of the structure and the mechanical properties of the resulting carbon fibres, were investigated kinetically by using internal resistance heating. The tensile modulus of the carbon fibres increased with a faster rate under a larger stretching stress. The tensile strength decreased initially as the carbonization progressed, but increased appreciably under a larger stretching stress, a trend which was not observed under a smaller stretching stress. The temperature–time superposition was applicable with respect to the development of the crystallite and the microvoid structures and the changes in the resistivity, density and apparently the tensile strength, by using a common shift factor. The changes in the longitudinal strain, however, showed a different temperature dependence from that of the structural development.     

中高应变率和不同温度下离子型中间膜的拉伸力学性能及本构关系

为系统研究中高应变率和不同温度下离子型中间膜的拉伸力学性能,进行了1 s-1～800 s-1和-40℃～60℃下的系列动态拉伸试验.基于试验结果,确定了离子型中间膜的关键力学参数,并着重分析了温度和应变率的影响:随着应变率的升高和温度的降低,离子型中间膜的初始弹性模量、屈服强度和抗拉强度均普遍提高,但极限应变有所降低....