Session: 12-20-01: Composite Materials and Mechanics

Paper Number: 144152

144152 - Response of Polymeric Sandwich Composite Panels Subjected to Underwater Explosions 

INTRODUCTION

Polymeric composite sandwich structures are of immense interest to the marine industry due to their high specific strength and stiffness, as well as better corrosion resistance than their metal counterparts. Marine structures are prone to extreme impulsive loads due to underwater explosions. These underwater explosions could be encountered in various circumstances, such as constructing ports and navigation canals and rock excavation for pipelines or communication cables. Hence, it necessitates understanding the composite structures’ underwater shock response. This work examined the sandwich composite panels with different core densities and clamped boundary conditions for their underwater shock response. The near-field underwater explosion was carried out using a detonator explosive. Real-time panel deformations were captured using high-speed stereo DIC. An energy-based comparison of performance was done for the sandwich panels. Additionally, high-speed imaging was carried out for the explosion bubble and its interaction with the sandwich structure.

MATERIAL AND METHOD

Composite sandwich specimens used in this work contain 0.95 mm thick carbon fiber reinforced facesheets made of balanced, twill-woven carbon fiber prepregs (Supplier: GURIT) and a 6.35 mm thick core made of closed-cell PVC foam of two different density grades H45 and H130 (Supplier: DIAB group). The specimens were manufactured by co-curing the woven prepreg material and closed-cell PVC foam, using vacuum bagging at 85°C for 9 hours (1 bar vacuum pressure). The prepreg layup for the facesheet was such that the carbon fibers were aligned parallel to the sides of the sandwich panel. The sandwich specimen was restrained using a steel fixture mimicking the clamped boundary at all four edges.

The near-field underwater explosion was simulated in a 9.5 mm thick-walled steel tank with a 1.2 m square base and a water fill capacity of 1820 liters. The tank has polycarbonate viewports on all sides for imaging unit and light source placement. Through one of the viewports, a 305 x 305 mm cross-section tunnel with a 12.7 mm wall thickness extends 400 mm into the tank on which the specimen was mounted. The deformation on the back face of the sandwich panel was recorded with high-speed imaging cameras in stereo DIC configuration.

ANALYSIS AND RESULTS

1)    The specimens exposed to underwater explosions experienced primary shock loading followed by a secondary impulsive load because of the explosion bubble collapse.

2)    Cavitation occurred on the specimen surface due to the panel deformation.

3)    The increase in core density reduced the panel deformations.

4)    The cavitation bubble collapse event occurred earlier for the sandwich panel with a higher-density core.

5)    The following are the observations from the center point deflection history of the sandwich panel (obtained from DIC results):

v  The first deflection peak is due to the shock wave impinging on the specimen surface.

v  The second significant deflection is due to the collapse of the explosion gas bubble.

CONCLUSIONS

This study investigated the dynamic response of polymeric sandwich composite panels to underwater explosions. The results revealed that increasing the core density of the panels reduced their overall deformation in response to underwater shock loads. Additionally, the core density influenced the timing of the surface cavitation bubble collapse, which occurred earlier in panels with higher-density cores. These findings are significant for the marine industry, providing valuable insights into the design of composite structures for enhanced durability and performance in challenging underwater environments.

Presenting Author: Akash Pandey University of Rhode Island

Presenting Author Biography: Akash Pandey received his bachelor's degree in Mechanical Engineering in 2011 and worked in the Indian Space Research Organization from 2012 to 2021. During this period, he also pursued his master's degree in Applied Mechanics from Indian Institute of Technology Madras. Since January 2022, he has been pursuing his Ph.D. in Experimental Solid Mechanics under the supervision of Dr. Arun Shukla and Dr. Helio Matos at the University of Rhode Island. His research interest is in the dynamic behavior of materials under extreme loading.

Authors:

Akash Pandey University of Rhode Island
Piyush Wanchoo University of Rhode Island
Helio Matos University of Rhode Island
Arun Shukla University of Rhode Island