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Mechanical Characteristic and Strength Prediction of Filled Hole Composite Laminate Under Compressiv

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Tutor: YuYin ZhangXiaoJing
School: Shanghai Jiaotong University
Course: Aircraft design
Keywords: composite plate,filled-hole,bolt joint,compressive loading,strength prediction
CLC: V229.7
Type: Master's thesis
Year:  2012
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Abstract:
With mechanical joint widely used in composite structures, the bolt could introduce a complex stress distribute surround the bolt hole, and reduce the structure capability. The joint part could be a common position where failure happens. In the decades before 1995, the influence of compact damage and delaminate was verified on the compressive failure of composite laminate. But the majority of aviation structure was designed base on open-hole compressive allowable value. It is necessary to design based on the fill-hole compressive allowable value, because the local stress distribute of the fill-hole could represent the fastener hole with accuracy. It¡¯s conservative to treat the bolt hole as opening, filled-hole compression allowable value can improve the structure carrying capacity. In addition, the initial defect, such as the clearance delamination which is allow to existent at factory inspection of composite structures, should be considered in the design of composite structures. A large number of experimental studies showed that the tensile and compressive strength allowable value of typical layups could be determined by the composites with a hole of 6mm diameter(open-hole under tensile loading, filled-hole under compressive loading).Therefore, the prediction of filled-hole composite laminates compressive strength is of great significance.A predictive method was proposed to estimate the filled-hole compressive (FHC) strength of composite laminates based on the load distribution between composite plate and bolt filled in the plate. A calculation method was proposed to get the load distribute factor of composite laminate containing filled-hole under compressive load. The influence of stacking sequence and bolt stiffness was verified on the stress distribution of experiments concerning three different stacking sequences were taken to derive the open-hole and FHC strength. Test results showed that the FHC strength was 30% higher than the open-hole compressive strength. The predicted results complied with the experiment results with error less than 5%. Comparison was also applied between the results from the very method and the experiment results of T800/3900-2 shown in other works. The proposed method could well predict the FHC strength with accuracy, and has certain significance in engineering.Based on the works above, the influence of clearance, pre-torque of the bolt on the ultimate compressive stress of composite laminate was verified, the influence factor of clearance between laminate the bolt, pre-torque of the bolt was derived to predict the ultimate capability of the composite laminate.It assumed that the coupling between clearance and pre-torque could be ignored when these two factors acted on the laminate simultaneously, and the influence factor could be derived by the superposition of the factor of the own. as a result, the ultimate capability of composite laminate could be got. Comparison was also applied between the results from the very method and the experiment results of T800/3900-2 shown in other works. The proposed method could well predict the FHC strength of composite laminate with accuracy.
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