Simulation of Low-Velocity Impact Damage on Composite Laminates

Low-velocity impact events occur with some frequency on composite applications such as airplane components. From ground operations to unavoidable birds, there is a range of situations where an aircraft outer component may be subjected to unexpected impact loads. In most cases, such as tool dropping, the impactor has a relatively high mass but low-velocity. The damage produced in such cases is mostly in the form of delaminations which are not easily noticeable through routine naked eye inspections. However, the spread of these delaminations over wide areas of the structure may severely compromise the residual compressive strength of the structure, possible even below the limit load for which it was initially designed. Therefore, the ability to predict the impact damage resultant from impact events likely to happen is of utmost importance in the aeronautical industry. Traditionally, impact damage models rely on either analytical calculations or extensive experimental data. By one side, analytical predictions of the impact damage resistance and tolerance of composite laminates are overly simplified and unreliable. On the other side, testing each promising design is time consuming and costly. Low-cost virtual testing by means of nonlinear finite element analyses can replace most of the actual impact testing of laminates. Once the dynamics of the impact phenomena and the damage mechanisms are correctly simulated, progressive failure analyses can be a valuable tool in the accurate prediction of impact damage resistance of composites. In this research, a reliable virtual tool for the numerical simulation of the impact damage on composite laminates is proposed. A continuum material model for the simulation of intraply damage phenomena is implemented in a numerical scheme as a user subroutine of the commercially available Abaqus finite element package. Delaminations are simulated by making use of cohesive elements. I.