Experimental and numerical analysis of the mechanical behavior of composite-to-titanium bolted joints with liquid shim
Experimental and numerical analysis of the mechanical behavior of composite-to-titanium bolted joints with liquid shim
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DOI：
10.1016/j.ast.2015.11.029
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发表时间：
2016-02
影响因子：
5.6
通讯作者：
Longquan Liu;Jun-Yu Zhang;Kun-kun Chen;Hongyang Wang;Mengxing Liu
中科院分区：
文献类型：
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作者：
Longquan Liu;Jun-Yu Zhang;Kun-kun Chen;Hongyang Wang;Mengxing Liu
现代飞机是一种高级产品，由于部件[1]、[2]的功能，其部件和组件通常制造成比其他行业高得多的精度(相对公差小至3×10−4)。在将不同的大型结构装配在一起时，通常会在翼面产生缝隙，例如，商用民用飞机的中箱和外翼往往是用不同的工具制造的，需要最终连接在一起。对于复合材料结构来说，这个问题可能会加剧，因为控制复合材料零件的几何特征比控制金属零件的几何特征要困难得多。这些间隙和装配力会引入预应力，导致复合材料中分层裂纹的发展，并危及结构的性能[3]、[4]、[5]。为了避免这些问题，经常使用液体垫片来填补缝隙，以消除由装配力[6]可能引入的预应力。一些规范[7]、[8]、[9]、[10]、[11]和专利[12]、[13]、[14]、[15]被公布以指导垫片的应用。然而，关于液体垫片用于复合材料结构完整性的知识仍然有限，这会导致上一代客机(B787和A380)的复合材料蒙皮出现裂缝[16]。为了研究液体垫片对接头性能的影响，Comer等人[17]通过实验研究了热载荷和机械疲劳载荷对带有液体垫片的复合材料-铝混杂接头寿命的影响，但没有观察到液体垫片在机械刚度损失方面的显著劣化。Huhne等人[18]进行了准静态试验，研究了液体垫片厚度对碳纤维叠层单螺栓接头强度和结构性能的影响，他们发现，当液体垫片厚度为1.5 mm时，节点的刚度随着垫片厚度的增加而降低，但最终连接载荷不受影响。然而，Mil-Handbook[19]持有不同的观点：它指出，即使垫片很薄，使用垫片也会导致螺栓组合接头的承载强度降低，并且随着垫片厚度的增加，降低的幅度将更大。
Modern aircraft is a high level product which makes its components and assemblies typically built to much higher precision (tolerances as small as 3× 10− 4 on a relative basis) than other industries because of the functions of the components [1],[2]. Gaps usually occur at the faying surfaces during assemble different large-scale structures together, for example, the centre box and the outer wing of the commercial civil aircraft are often manufactured using different tools and need to join together finally. This problem can be exacerbated for the composite structures as it is comparably more difficult to control the geometric features of the composite parts than those of metallic ones. Pre-stress would be introduced by these gaps and the assembly forces, which would result in the development of cracks of delamination in composite material and would compromise the performance of the structure [3],[4],[5]. To avoid these problems, liquid shim was often used to fill the gaps to eliminate the possible pre-stress introduced by the assembly force [6].Some specifications [7],[8],[9],[10],[11] and patents [12],[13],[14],[15] were published to guide the application of shims. However, the knowledge about the usage of liquid shim on the structural integrity of composite structures is still limited, which causes cracks in composite skin on the last generation of airliners (B787 and A380)[16]. To investigate the influences of liquid shims on the joint performance, Comer et al.[17] experimentally studied the influences of thermal and mechanical-fatigue loading on the life of composite–aluminum hybrid joint with liquid–shim, but no significant degradation of the liquid–shim in terms of a loss of mechanical stiffness was observed. Huhne et al.[18] carried out quasi-static tests to investigate the influence of liquid–shim thickness on the strength and structural behavior of carbon fiber laminate single-bolt joints, and they found the joint stiffness reduced with shim thickness but ultimate joint load was unaffected up to a liquid–shim thickness of 1.5 mm. However, Mil-Handbook [19] hold different point of view: it states the usage of shims will cause reduction of bearing strength in bolted composite joints even if the shim is very thin, and as the thickness of the shim increases, the reduction will be greater.