| Composite sandwich structure is widely used in various area due to its low density,high ratio strength and ratio stiffness,but it is vulnerable to low-velocity impact during using.The strength of the damaged composite sandwich structure will be greatly reduced,which affects its safety significantly.Therefore,it is necessary to study the anti-fatigue properties of the sandwich structure after low-velocity impact.In this paper,low-velocity impact tests were implemented on composite sandwich structures with three different layups.Firstly,determined the impact energy which could make a 1mm indentation,and then used this energy to impact the remaining specimen to ensure that all specimen with the equivalent damage.Then,static compression tests were implemented on the damaged composite sandwich structure to measure its static compression strength value.According to this static value,different percentage fatigue loads were set for the remaining uncompressed specimen,and then fatigue compression tests were performed to study its fatigue resistance,then drew the S-N curve according to the experiment data.Based on the results of the impact tests,a low-velocity impact finite element model of the composite sandwich structure was established,which comprehensively considered the matrix failure,fiber failure,and delamination,and simulated the whole impact response.The simulation results and the experimental results corresponded well which verified the reasonableness and accuracy of the numerical model.Based on the results of compression tests,a finite element model for compression after impact of damaged sandwich structures was established.According to the simulated stress states and the S-N curve of the composite laminate,S-N curve of the sandwich structure was predicted.Comparing the predicted S-N curve with the experimental S-N curve,there was high consistence between two curves.Therefore,a method for effectively predicting the fatigue life of composite sandwich structure was proposed. |
