Dynamic Response And Failure Prediction Of Composite Hat Stiffeners
Mr. William Gregory, Anteon Corporation
Dr. Richard Cobb, Anteon Corporation
Dr. Jim Lua, Anteon Corporation

Mr. Joshua Gorfain, Anteon Corporation

Abstract:

A typical marine industry composite material design approach includes the use of glass-reinforced plastic (GRP) hat-stiffeners to reinforce a solid laminate GRP shell.  Understanding the dynamic response and failure modes of these hat-stiffened laminate structural configurations is a primary design consideration in the implementation of this approach.  To this end, and to help in the understanding of the dynamic response, medium weight shock machine (MWSM) tests of specimens representative of a hat-stiffened cross section were planned and conducted.  The results from these tests are examined and compared to analytical predictions using the LS-DYNA code.

Various load input methods and modeling approaches within LS-DYNA are investigated.  Both coarse and refined mesh finite element models have been developed with either a prescribed displacement or force boundary condition. The sensitivity of the frequency content in the hat stiffener when subjected to a hammer impact was examined under various loading functions and mesh densities and then compared with test data. In order to simulate the delamination failure and extract the interface fracture energy from the simulation model, a cohesive material model is developed and implemented within LSDYNA as a user-defined material model. A nonlinear cohesive force and relative displacement model is introduced to capture the dynamic fracture. Using the optimal dynamic response model, a dynamic failure analysis is performed by inserting a layer of cohesive zone elements between the hat and the base laminated plate. The dynamic failure model is validated by comparing the damage initiation!
propagation, and the final rupture with the experimental observations.  

This work was conducted under the auspices of the Shock Integrated Team (Shock IPT) of the NAVSEA 073R Composite Advanced Structures Program.  These studies support the current plan for shock qualification of the Virginia Class Advanced Sail (CAS).

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