| Plain woven composite(PWC)is widely used in aviation,aerospace and other fields for their excellent in-plane performance.The cross-wound fiber bundle distribution makes their in-plane performance significantly better than that of traditional unidirectional fiber composites.When subjected to low-speed impact,plain weave laminates can cause unseen damage and pose a threat to safety in use,which is caused by their laminate structure.Similarly,the PWC repaired structure is also highly susceptible to impact damage during service.In this study,the impact resistance of PWC patch repaired structures was investigated by numerical analysis based multiscale approach,and the damage evolution of the repaired structure during impact was analyzed by using the continuous damage mechanics(CDM)model and cohesive zone model(CZM),and the accuracy of the model was verified by low-velocity impact experiment.Based on this,the patch parameters were optimized by combining response surface methodology(RSM)and multi-island genetic algorithm(MIGA)to determine the repair solution with the best impact resistance.Firstly,a numerical analysis model combining microscopic,fine and macroscopic scales was established based on the characteristics of the periodic symmetry of the PWC repaired structure.The representative volume elements(RVE)of fiber bundles at microscale and mesoscale were developed to predict the mesoscale material properties.And then the mesoscale RVE model was transformed into equivalent cross-ply laminate(ECPL),and the ECPL equivalent properties were obtained using the volume homogenization method,and the array was extended to obtain the macroscale equivalent model of the PWC repaired structure.The accuracy of the multi-scale numerical model was verified by the drop-weight impact experiment.Next,the differences between the impact response of plain woven and unidirectional laminated composite repair structures were investigated.Based on the model of plain woven repaired structure,the finite element model of unidirectional fiber patch repaired structure was established,and the macroscale mechanical properties of unidirectional fiber composite were calculated by the simplified Chaims mechanics equation.The impact resistance of the two material repaired structures were compared,and the results show that the PWC patch repaired structure has better impact resistance.Then,by extracting the damage form,impact force,absorbed energy and delamination area of the repaired structure,the damage evolution of the PWC at different impact energies and the effect of single patch parameters on the impact resistance of the repaired structure were investigated.The results show that when the impact energy is less than 4 J,the damage of the repair structure was concentrated in the patch,and when the impact energy is between 4 J and 12 J,the damage of the patch is aggravated and the mother laminate starts to show slight damage,and when the impact energy is greater than 12 J,the damage of the patch is serious and the mother laminate shows obvious damage;for a single patch parameter,the repaired structure exhibit better impact resistance when the following patch parameters are used,with a circular shape,thickness of 0.75 mm,radius of 20 mm,and off-axis angle of 22.5°.Finally,an agent model was established by combining DOE and RSM.Based on the agent model,an objective function with the improvement rate of structural impact resistance as the optimization variable was established.And then the patch thickness,patch size and patch off-axis angle were optimized by MIGA.The results show that the repaired structure has the best impact-resistance when the thickness of patch is 0.87 mm,the diameter of patch is 66 mm and the off-axis angle of patch is 44.2 °. |
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