应用扰动广义微分求积法的复合材料层合板剪切屈曲分析与优化

广义微分求积(GDQ)法求解复合材料层合板剪切屈曲时存在计算精度差、计算振荡不收敛问题,研究发现该现象源于载荷矩阵存在奇异,为此,提出扰动GDQ法,通过扰动主对角线权重系数以改善载荷矩阵的奇异性来消除计算振荡。数值算例验证了扰动策略的有效性,实现复合材料层合板剪切屈曲问题的高效稳定求解。在此基础上,结合直接搜索模拟退火算法,开展了含剪切载荷的复合材料层合板铺层顺序优化。结果表明：剪切工况时对称复合材料层合板的优化铺层不受铺层数和铺设形式影响,优化铺层角随长宽比增大而趋于60°;而剪切与轴压组合工况下较小的剪切力能改善层合板屈曲性能,随着剪切力的增大,优化屈曲性能逐渐降低,优化铺层趋同于剪切工况。研究结果为复合材料层合板的剪切屈曲性能设计提供了参考。     

层合板弹性性能的实验研究

采用散斑干涉法,对两种铺层方式的环氧基玻璃纤维层合板的弹性模量、泊松比和应力－应变曲线进行了实验研究。实验揭示了两种铺层方式层合板的弹性性能,为复合材料的铺层设计和建立相应的理论与计算方法提供了依据。     

不同铺层方式的复合材料层合板弯曲性能的研究

以碳纤维缠绕电动节能车车架为研究对象,采用有限元分析和力学试验对比的方式研究碳纤维铺层角及铺层层数对碳纤维复合材料层合板弯曲性能的影响。以层合板铺层角度、铺层层数为变量设置试验对比组,在ANSYS Composite Prep/Post复合材料分析模块中创建层合板的有限元模型研究层合板在承受弯曲载荷时的抗弯表现。结合弯曲试验结果,分析不同铺层方式对碳纤维复合材料层合板弯曲性能的影响。结果表明:在铺设一定数量的±45°铺层的基础上,增加0°/90°正交铺层可提高层合板的静承载强度;增加铺层层数,可提高层合板的弯曲强度。     

不同铺层转角T700/E44 复合材料拉伸强度有限元分析

碳纤维复合材料的失效行为与复合材料内部的应力状态有关,不同铺层转角的单向碳纤维复合材料层合板的性能具有明显差异。文中利用HyperWorks 商用有限元软件建立了T700/E44 复合材料层合板拉伸模型,基于Chang-Chang 复合材料失效模型对不同铺层转角复合材料层合板的 X 向及 Y 向拉伸性能进行了数值模拟分析。研究结果表明,复合材料层合板以45° 铺层转角对称结构层合时,复合材料有着最佳的综合拉伸性能。这对高性能雷达中复合材料部件的铺层结构设计具有重要的指导意义。     

孔口缝合补强对层间应力影响的数值模拟

使用空间杆单元模拟缝合线,对含孔复合材料层合板开口缝合补强结构进行有限元模拟计算。研究含孔复合材料层合板在轴向拉伸载荷作用下,圆孔附近各个铺层交界面处层间正应力和剪应力的分布情况,将缝合后的层间应力值与缝合前的相关数值进行比较,并研究不同缝合参数(针距、行距、边距、单缝合和双缝合)对孔边层间应力的影响。结果表明,缝合补强后孔边的层间应力明显减小。孔边附近层间应力的分布与相邻铺层的铺层角有很大关系,不同铺层之间的层间应力有显著差别。不同铺层之间的层间应力沿孔边区域存在应力转换点(即层间应力由正值变为负值)。     

复合材料层合板冲击损伤影响因素分析

应用三维逐渐累积损伤理论和有限元分析技术对复合材料层合板的低能冲击过程进行了详细分析,研究了不同材料的冲头、不同复合材料体系和不同铺层方式对复合材料层合板冲击损伤的影响规律。研究结果可为更有效地进行复合材料抗冲击结构设计提供一定的指导。     

单向拼接复合材料层合板的抗拉强度研究

碳纤维增强树脂基复合材料层合板具有较高的抗拉强度,复合材料结构设计中会遇到含铺层拼接的层合板的问题,需要考虑拼接对层合板力学性能的影响。因此建立交错拼接单向层合板的力学模型,对其层间应力和承载能力进行分析,得到单向层合板拼接位置的层间应力分布和抗拉强度的解析解,并提出有效拼接长度的概念,可用于交错拼接层合板的设计。并建立不同拼接长度的交错拼接单向层合板模型,计算得到层间应力分布,并采用渐进损伤方法预测抗拉强度,解析解和有限元方法的强度预测结果均与试验结果具有较好的一致性。含交错拼接单向层合板拼接位置的层间切应力和抗拉强度决定于材料刚度、单层厚度、界面厚度和拼接长度。     

冲击后复合材料板剩余抗拉强度影响因素分析

应用提出的全程分析方法和三维逐渐累积损伤理论,对层合板的冲击过程以及冲击后含损伤层合板在拉伸载荷下的破坏过程进行详细分析.研究不同冲击能量、不同材料的冲头、不同复合材料体系和不同铺层方式等因素对层合板冲击损伤及剩余抗拉强度的影响规律,为更有效地进行复合材料抗冲击结构设计提供一定的指导作用.     

泡沫夹层复合材料与复合材料层合板低速冲击性能的比较

采用[0°]8,[0°,90°]2s方式铺成的碳纤维增强环氧树脂预浸料作为泡沫夹层复合材料的面板,PMI(聚甲基丙烯酰亚胺)泡沫作为芯材,制得泡沫夹层复合材料(12mm厚);采用相同预浸料和[0°]16,[0°,90°]4s的铺层方式制备了复合材料层合板(2mm厚),对比研究了两种复合材料的低速冲击性能。结果表明:无论是泡沫夹层复合材料还是复合材料层合板,正交铺层结构比单向铺层结构的冲击载荷峰值高,冲击损伤程度小,抗冲击能力好;在两种铺层方式下,泡沫夹层复合材料的抗冲击能力明显优于复合材料层合板的。     

带圆孔层合板孔边层间应力分析、失效研究及软件开发

依据边界层理论分析的带圆孔对称复合材料层合板的应力解析解,开发相应的软件,计算铺层交界处的层间应力.进一步增加Hashin失效判据,得到层合板各个铺层不同失效形式下的区域分布.该软件是基于Matlab开发的,非常适用于带圆孔复合材料层合板结构打样阶段的分析.     

Interlaminar stress analysis of general composite laminates

In this study, based on the reduced from of elasticity displacement field for a long laminate, an analytical method is established to exactly obtain the interlaminar stresses near the free edges of generally laminated composite plates under the extension and bending. The constant parameters, which describe the global deformation of a laminate, are properly computed by means of the improved first-order shear deformation theory. Reddy's layerwise theory is subsequently utilized for analytical and numerical examinations of the boundary layer stresses within arbitrary laminated composite plates. A variety of numerical results are obtained for the interlaminar normal and shear stresses along the interfaces and through the thickness of laminates near the free edges. Finally the effects of end conditions of laminates on the boundary-layer stress are examined.     

Free-edge stresses in general composite laminates

In the present study, by starting from the reduced form of elasticity displacement field for a long flat laminate, an analytical method is developed in order to accurately calculate the interlaminar stresses near the free edges of generally laminated composite plates under extension. The constant parameter appearing in the reduced displacement field, which describes the global rotational deformation of a laminate, is appropriately obtained by employing an improved first-order shear deformation theory. The accuracy and effectiveness of the proposed first-order theory are verified by means of comparison with the results of Reddy's layerwise theory as a three-dimensional benchmark. Reddy's layerwise theory is then utilized for analytical and numerical investigations of the boundary-layer stresses within arbitrarily laminated composite plates. Various numerical examples are presented for the interlaminar normal and shear stresses along the interfaces and through the thickness of laminates in the vicinity of the free edges. The effects of end conditions of laminates, fibers orientation angles as well as the stacking sequences of the layers within laminates, and geometric parameters on the boundary-layer stresses are presented and discussed.     

Effect of E-Glass fibre and ply orientation on the mechanical behaviour of FRP composites used for pressure pipe

The main goals of this experimental investigation were to compare the mechanical behaviour of resins reinforced with different woven fabrics (bidirectional and quadriaxial rovings), manufactured with the classical hand lay-up process, and to find the more appropriate industrial pressure pipe. In order to realize such applications, several mechanical properties need to be evaluated. So, a focus was essentially done on the evaluation of the effect of resin and E-Glass fibre ply orientation on the mechanical properties such as tensile strength and flexural strength of the studied composite laminates. An experimental failure analysis was carried out to observe the crack paths and failure mechanisms in the investigated laminate composites. From the main results, it was found that the composites based on R500 fabrics show the best behaviour in tensile while the laminates based on RM fabrics present the best flexural properties. The quadriaxial composite laminates (QA/VE and QA/UP) with stacking sequences of [0°, +45°, 90°, ?45°] present a very ductile tensile behaviour and the highest interlaminar fracture resistance. Consequently, they can be more appropriate for the industrial pressure pipe.     

利用超声成像分析不同复合材料层压结构冲击损伤行为

复合材料各向异性和吸能的特点,在受到外来冲击作用时容易产生损伤,呈现表里迥然不同的损伤行为和分布规律。为研究不同复合材料层压结构的冲击损伤行为,设计制备树脂传递模型工艺(Resin transfer molding, RTM)缝合和预浸料复合材料层压结构两种不同成型工艺的试样,通过冲击试验模拟复合材料在外力作用下产生的冲击损伤,采用超声反射法,通过点聚焦换能器对试样进行超声B扫描成像,揭示两种复合材料层压结构试样内部断面损伤行为及其扩展规律。试验结果表明,冲击引起的试样内部损伤比表面损伤要大得多;随着冲击能量在试样内部传递,会在不同深度铺层产生新的损伤,而且损伤分布并不仅沿层间界面扩展;冲击点附近和远离冲击点附近的内部损伤具有明显不同的分布规律;RTM缝编与预浸料复合材料结构呈现明显不同的损伤行为,其中RTM缝合复合材料结构中的纵向缝线,对冲击损伤在试样内部沿层间的扩展有显然的阻止作用。研究结果对更好地理解复合材料的损伤行为、寻找新的改进复合材料层压结构损伤行为的机制有非常重要的指导意义和帮助。     

真空导入树脂模塑工艺对EKB1100/430LV复合材料纤维含量及力学性能的影响

通过真空导入树脂模塑工艺制备了EKB1100/430LV复合材料,研究了不同工艺参数对复合材料中玻璃纤维含量及力学性能的影响。结果表明:纤维含量随真空度的增大而增加,靠近树脂注入口区域的纤维含量较低,而真空抽口附近的纤维含量最高;复合材料的拉伸强度和压缩强度也随真空度的增大而增大;充模前对预成型体实施压缩可提高纤维含量;充模过程中溢流一定的树脂可提高弯曲强度和层间剪切强度。     

A simple method to calculate mode components of strain energy release rate of free-edge delaminations in composite laminates

A simple method, which calculates the mode components of the strain energy release rate of free-edge delaminations in the laminates, is proposed. The interlaminar stresses are evaluated as an interface moment and interface shear forces that are obtained from the equilibrium equations at the interface between the adjacent layers. Deformation of an edge-delaminated laminate is calculated by using a generalized quasi-three dimensional classical lamination theory developed by the author. The analysis provides closed-form expressions for the three components of the strain energy release rale. The analyses are performed on [+30/−30/90]s laminates subjected to uniaxial extension, with free-edge delaminations located symmetrically and asymmetrically with respect to the laminate midplane. Comparison of the results with a finite element solution using the virtual crack closure technique shows good agreement. The simple nature of this method makes it suitable for primary design analysis for the delaminations of composite laminates.     

Pitch-catch ultrasonic study on unidirectional CFRP composite laminates using Rayleigh wave transducers

The importance of carbon fiber reinforced plastics (CFRP) has been generally recognized, and CFRP composite laminates have become widely used. Thus, a nondestructive technique would be very useful for evaluating CF/epoxy composite laminates. A pitch-catch UT signal is more sensitive than is a normal incidence backwall echo of a longitudinal wave in composites. The depth of the sampling volume where the pitch-catch UT signal came from is relatively shallow, but the depth can be increased by increasing the separation distance of the transmitting and receiving probes. Moreover, a method is utilized to determine the porosity content of a composite lay-up by processing micrograph images of the laminate. The porosity content of a composite structure is critical to the overall strength and performance of the structure. The image processing method developed utilizes software to process micrograph images of the test sample. The results from the image processing method are compared with existing data. Beam profile is characterized in unidirectional CFRP using pitch-catch Rayleigh probes. The one-sided and two-sided pitch-catch techniques are utilized to produce C-scan images with the aid of an automatic scanner. The pitch-catch ultrasonic signal corresponds with the simulated results of unidirectional CFRP composites.     

受面内载荷的层压复合材料的层间应力分析

研究任意多向铺层层压复合材料层间应力的有限元分析方法。分别考虑两种建模方法，一种是采用8结点等参实体单元逐层进行离散化，每个子层都视为正交异性材料；另一种方法是在子层面内采崩4结点板元进行离散化，而在层间采用刚性元和弹簧元进行离散化，称为准三维模型。计算实例为两种不同铺层的T300／QY8911碳纤维／双马树脂层压板条，其中一个板条连续，另一个含圆孔，均受到面内拉伸载衍作用。采用的计算软件为MSc．Nastran。计算结果表明，在受拉板条的自由边和孔口附近存在不能忽视的层间应力。两种建模方法有各自的特点，计算结果可以互相印证，而后一种方法更加灵活和有更广泛的适应性。     

Some observations on the interlaminar strength of composite laminates

Definition of the influence of interlaminar stresses on the failure characteristics of composite laminates may require the development of novel experimental characterization procedures. The so-called free edge problem in laminate elasticity offers a cnovenient mechanism to accomplish this purpose because of the high interlaminar stresses in the neighbourhood of a free boundary. The detailed design of a laminate specimen which can exhibit catastrophic delamination induced by interlaminar tension is presented, along with a preliminary failure hypothesis to characterize this mode of rupture and the associated experimental demonstration of the phenomena.