• Background
• 2D BEM Models for Aircraft Hole Inspection
• Empty Weep Hole Model
• Fluid-filled Hole Model
• Model for Hole Containing Elastic Insert and Stiffness Interface
• Ultrasonic Inspection Simulator for Aircraft Holes

     The focus of the modeling work concerns the ultrasonic scattering of waves from weep holes in C-141 aircraft.  Prior modeling work explored the benefit of generating 'leaky' Rayleigh waves about the hole surface in conjunction with a dual transducer measurement apporach to detect radial fatigue cracks.  This work was led by Prof. Peter B. Nagy of the University of Cincinnati in conjunction with Mark Blodgett (of AFRL-MLLP) and Matt Golis (of Advanced Quality Concepts).

     The primary area of our research concerns the simulation of the measurement signals resulting from the scattering of ultrasonic waves from cavities with surface breaking cracks.  The boundary element method (BEM) was used to model the scattering response for transducer signals.  Special cases such as fluid filled cavities, cavities with elastic layers and cavities containing elastic inserts (such as the C-141 rib clip hole) were also investigated.

For more information, see Chapter 1:  Introduction .

     A transient elastodynamic simulation was developed using BEM for the scattering from empty cylindrical holes in an elastic media for both no and with cracks (notch) cases.

Figure 1.  Contour plots of the total displacement field response to an incident in-plane shear pulse on a 1/4" weep hole for (a) no crack and (b) with a 1.8 mm (0.070”) crack cases for four time steps, t = 0,2,4,6.

     For more information concerning BEM modeling of the empty weep hole case, see Section 2.2:  BEM Model Formulation for Transient Elastodynamic Problems .
 

     A transient elastodynamic simulation was also developed using BEM for the scattering from fluid-filled cylindrical holes in an elastic media for both no and with cracks (notch) cases.

Figure 2.  Contour plots of the total displacement field response to an incident in-plane shear pulse on a 1/4" fluid filled weep hole with no crack for nine time steps,t = 0,1,2,3,4,5,6,7,8.
 
 

Figure 3.  Contour plots of the total displacement field response to an incident in-plane shear pulse on a 1/4" fluid filled weep hole with no crack for nine time steps,t = 0,1,2,3,4,5,6,7,8.

     For more information concerning BEM modeling of the fluid-filled weep hole case, see Chapter 5:  Model and Methodology for Crack Detection on a Fluid-Filled Cylindrical Hole .
 

Figure 4.  Contour plots of the total displacement field generated by an incident in-plane shear pulse on a 3/16" diameter rib clip hole with no crack and containing an aluminum insert – elastic contact between insert and hole for nine time steps,t = 0,1,2,3,4,5,6,7,8.

     For more information concerning BEM modeling of aircraft holes case, see Chapter 7:  Models and Inspection Procedure for a Cylindrical Hole with an Elastic Insert .
 

     To ease the process of simulating a variety of aircraft hole inspection conditions, an ultrasonic insepction simulation user interface was developed (interface written in VB, solution subroutine in DVF.)
 
 

Figure 5:  Sample view of simulation user interface.