Hope College Department of Physics and Engineering Research Experiences for Undergraduates Summer 2002 Project Summary

Project Title: A Study of the Effects of Pre-Pressurization on Explosive Damage of Square Clamped Plates
Student Names: Jennifer Folkert, Amanda DeYoung
Student’s home institution: Hope College
Research Advisor(s): Dr. Roger Veldman
Source of Support (NSF-REU, or other): Federal Aviation Administration
 

This study investigates the effects of pre-pressurization on explosive damage in commercial aircraft. To do this, a square flat plate of aircraft fuselage aluminum skin (2024-T3) that measured 6 x 6 x 0.0064 inches was used.  A finite element analysis program, ANSYS, was employed to model the dynamic plate behavior and the predicted results were compared with those measured experimentally.

Experimental testing was conducted at Battelle Memorial Institute near Columbus, Ohio. Seven different explosive load cases, where either the charge size or the standoff distance from the plate varied, were utilized.  When a charge detonated, the incoming pressure wave, and the dynamic plate stains were recorded.  Figures 1 and 2 show the blast pressures and pressure wave arrival times for the seven load cases.  Figure 3 shows the explosion sequence as the charge detonated.
 
 

Figure 1 – The smallest charge sizes at the largest distance	Figure 2 – The largest charge sizes at the smallest distances

 
 

Figure 3 – The explosion sequence: before the explosion, at the detonation, the flame front, the propagation of the flame front, and after the explosion

Using the finite element program ANSYS, we modeled load cases EA and EB, two elastic cases in the study.  Good agreement between experimental data and predicted values were observed during the first two milliseconds of the unpressurized plate analysis (Figure 4).  When the plate was pre-pressurized to 9 psi, the predicted strains were significantly less than those experimentally measured (Figure 5).  It was observed that as we modeled larger pre-pressurizations there were larger variations between the experimental data and the predictive model (Figure 6).
 
 

Figure 4	Figure 5

From this study it was determined that pre-pressurization for elastic plate deflections has no effect on maximum dynamic strain (Figure 6).  Additionally, the finite element model was found to be less adequate for predicting plate response for increasing static pre-pressurization.
 

Figure 6 – A comparison between the experimental and predicted strains