of the most significant recent advances in NDT has been the development
and use of computer modeling that allows inspection variables to
be scientifically and mathematically evaluated. In a few cases,
these models have been combined with a graphical user interface
to produce inspection simulation programs that allow engineers
and technicians to evaluate the inspectability of a component
in a virtual computer environment. One such program, XRSIM, was
designed and developed at Iowa State University's Center for Nondestructive
Evaluation. The program simulates radiographic inspections using
a computer aided design (CAD) model of a part to produce physically
accurate simulated radiographic images. XRSIM allows the operator
to select a part, input the material properties, input the size,
location, and properties of a defect. The operator then selects
the size and type of film and adjusts the part location and orientation
in relationship to the x-ray source. The x-ray generator settings
are then specified to generate a desired radiographic film exposure.
Exposure variables are quickly and easily revised allowing the
operator to make and see results of defect size, material, and
part or defect orientation.
The almost instantaneous results produced by simulation programs
make them especially valuable in education and training settings.
Successful radiography depends on numerous variables that affect
the outcome and quality of an image. Many of these variables have
a substantial effect on image quality and others have little effect.
Using inspection simulation programs, inspections can be modified and
the resulting images viewed and evaluated to assess the impact
these variables have on the image. Many inspection scenarios can
be rapidly modeled since the shot setup and exposure can be quickly
accomplished and the film-developing step is eliminated. Not only
can a greater number and variety of problems be explored, but
also the effects of variables can be learned and self-discovered
through experimentation, which is one of the most effective modes
of learning. Results are not complicated by unnecessary variables
such as film processing variables and artifacts. Distractions
unrelated to the primary learning exercise are eliminated. Through
the use of simulation programs a more effective understanding
of the scientific concepts associated with radiography will be
important aspect of the program is that it does not require a
real part for the inspections. Inspections can be simulated that
would otherwise be impossible or too costly to perform outside
the computer environment. Flaws of various shapes, sizes, and
materials can be easily introduced into the CAD model to produce
a sample set for probability of detection exercises.
It should be noted that densities produced in the simulated images may not
match exactly the images produced in the laboratory using similar
equipment settings. The difference between the actual and simulated
radiographs are due to variations in the X-ray spectrum of various
tubes and approximations made in the scattering model used to keep the computation times reasonable. As scattering
effects become more dominant, the predicted density will agree
less with the actual density on the radiograph.
For example, when a one-inch steel sample
is radiographed at 250 keV, over half of the total flux reaching
the detector is due to scattering.
For more information on how the XRSIM program operates, the
users manual is available here for downloading. The educational
version of the program is available commercially.
the XRSIM Users Manual
Ten X-ray inspection exercises have been developed by the Collaboration
for NDT Education that make use of XRSIM program. Educators can
download these lessons from this site. More
information on the XRSIM lessons.