Research On Low-velocity Impact Damage Of Stiffened Laminate And Parametric Modeling

Composite laminates and stiffened laminates have been widely used in aircraft design. Althoughvarious merits they possess, the low interface strength between plies have limited their applications inmain load bearing parts in aircraft. Delamination vulnerably takes place for them under thelow-velocity impact and which are usually hard to be discovered by eye. Delamination will causelaminated structure greatly reduce on the strength, especially the compressive strength. Therefore, thelow-velocity impact damage in laminated composites is one of the key problems in their safetyassessment. For the complexity of this problem, it is still be an open problem. The main contents inthis master thesis are summarized as follows:(1) Based upon ABAQUS software platform, a system combining parametric modeling of lowvelocity impact simulation of (stiffened) composite laminate and visualization of impact process andvarious damage models was developed via the scripting language of Python. The system is open forthe user to put in other damage models in convenient. Further, user can define the subdivision of thefinite element mesh to improve the computational efficiency without the cost of accuracy.(2) A modified element model that one element containing multi-ply was proposed forimproving computational efficiency. In this model, damage effects can be considered on individualply via discounting equivalent elastic constants. It has been realized based on the user materialfunction in ABAQUS/Explicit of Vumat.(3) The widely employed delamination criteria for laminated composites, named Choi-Changlaw and Cohesive law, were modified in this thesis. For the former, the effect of stress along thethickness direction was put in the original law, and for the later the effect of transverse stress in theunder ply was considered. They have also realized as the users material in ABAQUS via Vumat.(4) Low velocity impacts of composite laminates and stiffened laminates under various impactconditions were simulated by the theories and the parametric modeling system developed in this thesis.The results agree well with the data from the literature, so the feasibilities of the theories and softwarehave been verified.