
Modeling in Ultrasonic Nondestructive Evaluation
Prior Work 
2D Boundary Element Method (BEM)
Simulation of the Ultrasonic Inspection of Aircraft Holes with Fatigue Cracks

Background
The focus
of the modeling work concerns the ultrasonic scattering of waves from weep
holes in C141 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 AFRLMLLP)
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
C141 rib clip hole) were also investigated.
For more information, see
Chapter 1: Introduction
.

Empty Weep Hole Model
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
inplane 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
.

Fluidfilled Hole Model
A transient elastodynamic simulation was also developed
using BEM for the scattering from fluidfilled 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
inplane 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
inplane 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 fluidfilled weep hole case, see
Chapter 5: Model and Methodology for Crack Detection on a FluidFilled
Cylindrical Hole
.

Model for Hole Containing Elastic Insert and Stiffness
Interface
(To be added.)
Figure
4. Contour plots of the total displacement field generated by an incident
inplane 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
.

Ultrasonic Inspection Simulator for Aircraft Holes
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.


