液体垫片对复合材料装配结构应力和应变的影响

复合材料较复杂的成型工艺导致其构件的制造精度偏低。装配时，偏差会使配合面间产生装配间隙，当间隙超过一定的大小时，需要采取补偿措施，即用垫片填补间隙。基于一种简化装配模型，通过实验和有限元分析方法，研究了液体垫片对复合材料装配结构应力和应变的影响。通过比较强迫装配和液体垫片补偿两种情况下施加螺栓预紧力时构件表面的应变，分析了复合材料构件的变形。进行应力分析时，通过提取单元积分点应力分量计算构件的安全裕度，研究液体垫片对复合材料装配结构应力的影响。得出如下结论：强迫装配时，处在装配间隙边缘的区域受间隙影响相对严重，该区域发生较大的弯曲变形，构件中间部分由于局部贴合反而使装配间隙的影响相对较小；液体垫片在改善间隙边缘危险区应变状态的同时，也使构件中间贴合部位的螺栓头挤压区和部分非挤压区的应变增大，但总体而言，液体垫片的引入使应变分布趋于均匀；当装配间隙大于0.7 mm后，液体垫片补偿对于构件安全裕度的提升作用明显下降。

Effect of liquid shim on stress and strain of composite assembly structure

The complex forming process of the composite material leads to low manufacturing precision. Assembly gap will be created between the mating surfaces due to the deviation of composite parts. Gap-filling needs to be taken when the thickness of gap exceeds a certain extent. Based on a simplified assembly model, the effect of liquid shim on strain and stress of composite assembly structure with bolt pre-tightening force was studied by means of experiment and finite element analysis. The surface strain under two conditions was compared to analyze the deformation of composite parts, including forced assembly situation and gap-filling situation with liquid shim. The strength ratio was calculated by extracting stress component of element integral points. And the effect of liquid shim on stress of composite assembly structure based on strength ratio was obtained. The primary conclusions are as follows:The area on composite near the edge of the assembly gap is affected by the assembly gap more greatly during forced assembly, while the impact of gap on middle section is relatively small because assembly gap disappears in this area under the clamping force. Liquid shim is helpful to improve the strain state of danger zone near the edge of the assembly gap, but the strain of the compression zone contacting with bolt head which located in middle section of composite is increased due to introduction of liquid shim. Overall, liquid shim makes the strain distribution more uniform. When the assembly gap thickness is more than 0.7 mm, the effect of liquid shim that enhances the strength ratio of the component shows obvious downward trend with the increase of assembly gap thickness.