Z-pin增强复合材料T型加筋结构增强机理研究

发布时间：2018-09-09 09:22

【摘要】：复合材料加筋壁板结构是航空航天复合材料结构中应用非常广泛的一种典型结构,其中筋条和蒙皮的脱粘是主要的损伤形式。Z-pin增强技术作为一种适用于预浸料成形复合材料的层间增强技术,可用于加筋壁板结构连接界面的增强。本文在Z-pin增强T型加筋结构制备工艺试验的基础上,针对复合材料T型加筋结构的界面连接性能,开展试验研究和数值分析,研究参数对结构承载力的影响规律及Z-pin增强机理,为Z-pin在复合材料加筋结构增强中的实际应用提供指导及参考。(1)研究Z-pin增强T型加筋结构试样的成型工艺,并对工艺进行改进。设计制作专用成型模具,进行热压罐固化成型。结果表明,利用增加模具突缘厚度、增大筋条拐角半径、增加拐角区的填充量等方法,可以解决Z-pin不能完全穿透预浸料坯料、填充区不密实等问题,有效改善试件的成型质量。(2)通过面外拉伸试验和剪切试验表征T型加筋结构筋条-蒙皮间的连接性能,并研究Z-pin对加筋结构的增强机理。研究表明,Z-pin对T型加筋结构的初始载荷没有影响,但能提高极限载荷及残余载荷;随着加载过程,Z-pin受力状况由纯I型方向层间应力逐渐转变为I/II型方向混合应力,导致Z-pin发生侧向挤压,这一过程对Z-pin的增强效果有强化作用。剪切试验发现,试样筋条和蒙皮发生瞬间分离破坏,Z-pin明显提高初始载荷,但对试样掉载后残余承载能力的作用不明显。(3)研究Z-pin体积含量对T型加筋结构拉伸承载力的影响规律,在此基础上研究Z-pin对含损伤T型加筋结构的增强作用,并进一步研究突缘长度对Z-pin增强效果的影响。Z-pin含量对比试验结果表明,T型加筋结构拉伸承载力随Z-pin含量增加而先上升后下降,Z-pin可使极限载荷的提高高达70.4%。预制缺陷试验结果表明,对于T型接头中占粘结面10%~30%尺度的层间缺陷,Z-pin桥联作用能实现对结构承载能力较大程度的保持,将相同尺度缺陷空白T型接头的极限载荷提高90%以上。突缘试验结果表明,试样的失效形式随突缘长度增加发生转变;Z-pin植入后,T型接头的最优突缘长度由60mm降低为40mm,对结构减重有重要意义。(4)借助估算法确定界面刚度和强度的取值,并利用能量差值平均化方法对现有的Z-pin增强等效方法进行改进,采用分区内聚力模型建立Z-pin增强T型加筋结构的二维数值模型。以此为基础,利用该模型对不同约束跨距、蒙皮厚度的T型加筋结构拉伸承载力进行分析。结果表明,在试验范围内,随着跨距增大或蒙皮厚度减小,筋条-蒙皮连接界面拉剪应力比值减小,Z-pin由拔脱失效转变为拔脱/断裂混合失效,Z-pin增强T型接头的拉伸承载力下降。
[Abstract]:Composite stiffened panel structure is a typical structure widely used in aerospace composite structure. The debonding of tendons and skin is the main damage form. Z-pin reinforcement is a kind of interlaminar strengthening technology suitable for prepreg forming composite materials. It can be used to strengthen the interface of stiffened panels. In this paper, based on the experimental results of Z-pin reinforced T-reinforced structures, the experimental study and numerical analysis are carried out to study the influence of parameters on the bearing capacity of T-reinforced composite structures and the mechanism of Z-pin reinforcement, aiming at the interfacial bonding properties of T-reinforced composite structures. It provides guidance and reference for the practical application of Z-pin in reinforced composite structure. (1) the forming process of Z-pin reinforced T-reinforced structure specimen is studied and the process is improved. Design and manufacture special moulds to solidify the hot-pressed tank. The results show that by increasing the thickness of the die edge, increasing the corner radius of the bar and increasing the filling amount of the corner area, the problems of Z-pin can not penetrate the blank of prepreg completely and the filling area is not dense, etc. (2) the tensile test and shear test were used to characterize the bonding properties of T-type reinforced structure between the stiffened strip and the skin, and the reinforcement mechanism of the reinforced structure by Z-pin was studied. The results show that Z-pin has no effect on the initial load of T-type reinforced structure, but it can increase the limit load and residual load, and with the process of loading, the interlaminar stress in the direction of pure I-type is gradually changed to the mixed stress in the direction of I/II. The lateral extrusion of Z-pin results in the enhancement of Z-pin by this process. The results of shear test show that the breaking of the strip and the skin increases the initial load obviously, but the effect on the residual bearing capacity of the specimen is not obvious. (3) the effect of the volume content of Z-pin on the tensile capacity of T-reinforced structure is studied. On this basis, the enhancement effect of Z-pin on T-stiffened structures with damage was studied. Furthermore, the effect of edge length on the strength of Z-pin was studied. The results showed that the tensile capacity of T-type reinforced structure increased first and then decreased with the increase of Z-pin content, and the ultimate load increased as high as 70.4%. The experimental results of prefabricated defects show that for T-joints with 10% or 30% of bonding surface, Z-pin bridging can maintain the bearing capacity of the structure to a large extent, and increase the limit load of blank T-joints with the same size defects by more than 90%. The results of edge test show that the failure form of the specimen changes with the length of the edge. The optimum edge length of T-joint is reduced from 60mm to 40mm after Z-pin implantation. (4) the value of interface stiffness and strength is determined by means of estimating method. The energy difference averaging method is used to improve the existing Z-pin enhancement equivalent method, and the two-dimensional numerical model of Z-pin reinforced T-stiffened structure is established by using the zone cohesion model. Based on this model, the tensile capacity of T-type reinforced structures with different restrained span and skin thickness is analyzed. The results show that in the range of test, with the increase of span or the decrease of skin thickness, the ratio of tensile shear stress at the interface of stiffened strip and skin decreases from pull-out failure to mixed pull-out / fracture failure. The tensile strength of T-joint reinforced by Z-pin decreases.
【学位授予单位】：南京航空航天大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TB33

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