investigation of sandwich composite panels under hydrodynamic slamming loads

What is it about?

Sandwich structures have been widely used in marine applications due to their properties such as high weight/strength ratio. In contrast, the failure mechanism of these structures has a significant effect on the local and global dynamic responses. In the present study, sandwich panels with polymeric skins and PVC foam cores subjected to slamming impact are investigated experimentally and numerically. A high speed shock machine is used to keep approximately a constant velocity during the impact event. The dynamic resistance was analysed in terms of hydrodynamic loads, dynamic deformation and failure mechanisms for different impact velocities. On the other hand, the slamming model was implemented in Abaqus/ Explicit software based on Coupled Eulerian Lagrangian model approach. In addition, different damage modes are incorporated in the numerical model, including the intralaminar, debonding in skin/core interface, and core shear to cover all possible damage modes throughout structures. Two failure criteria (Hashin criteria for the laminate composite and Christensen criteria for the core in sandwich structure) are defined and integrated into VUMAT sub-routine. In addition, the cohesive zone model is used to predict the debonding skin/core. A good agreement in both hydrodynamic loads and damage prediction were found between numerical and experimental results.

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Why is it important?

This study has yielded experimental and numerical results on the dynamic response of sandwich panel with glass-Fiber/ vinylester matrix for skins and PVC foam core under the water slamming impact. Firstly, the experiment tests were conducted for sandwich panel with different water entry velocities using a high speed shock machine with velocity control system. The structure response including the hydrodynamic force and the panel deformation has been analysed to identify the maximum structure resistance, according with increasing impact velocity. It was found that the peak force and significant dynamic noise increased as the velocity increased due to the structure flexibility. The maximum force and deformation which happen close to the chine has enough capacity to occur damages in the structure and leading to catastrophic failure. For this reason, more attention must be care in this location through the design phase by structure reinforcement (for example, transverse stiffeners, heavy core density and high bending skin). Secondly, three dimensional numerical model using Coupled Eulerian-Lagrangian Model (CEL) has been implemented in the finite element code (Abaqus/Explicit). The interlaminar damage (skin/core interface) was performed using the cohesive zone model (CZM) together with intralaminar skin and core shear damages using VUMAT subroutine. The numerical model has shown convincing results to judge experimental data but exhibited some differences in the time and the peak force. This is due to variations of the experimental velocity of the impact duration which is not constant as in the numerical model. It is possible to improve numerical results to better satisfy as in experimental data, this can be done by identifying the actual velocity profile in the numerical model but the computational time has increased significantly.

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