Ultrasonic Technique Development Using Imagine 3DWalter Weber
UTEX Scientific Instruments Inc., Doug Mair, Focal Point NDE Technologies
Mississauga, Ontario, Canada
Corresponding Author Contact:
|TABLE OF CONTENTS|
This paper reports our progress on the development of a three-dimensional raytracing program called Imagine3D. This commercially successful computer program uses three-dimensional graphics that can be rotated to any viewing angle to fully simulate ultrasonic inspections.
Imagine3D can handle any number of longitudinal and shear mode conversions and can accurately identify where unexplained echoes are originating. A simple yet powerful A-scan display will show, in color, the various signals arriving back at the transducer and which signals belong to which sound path. Simulated B-scans can display how stray sound modes and part geometry might accidentally shadow flaws.
Another advantage of the program is that it improves the communication of inspection procedures. If fixturing is required, Imagine3D can provide a text printout that lists the probe angles, spacing and water-path distances. Simulated B-scan data can be saved as a Winspect image file so that theoretical results can be compared with real inspection data side by side using Winspect.
Inspection targets (parts) can be constructed from a list of primitive shapes such as blocks, rods, tubes, cones and spheres. They can also be imported from 3D DXF CAD drawings or can be extruded or revolved as solids from 2D DXF CAD drawings. NURBS surfaces are also now supported.
The transducer modeling features can simulate both contact and immersion transducers of any frequency and bandwidth. Imagine3D supports spherical, cylindrical and elliptical focusing with transducer elements that are circular, elliptical or rectangular in shape. Both pulse echo and pitch catch ultrasonic inspections are supported. The transducers can automatically follow the part surface at a fixed distance and inspection angle.
Imagine3D was developed to solve a range of everyday problems in ultrasonic testing from simple weld inspections to the most difficult composite airframe inspections. Imagine3D allows you to develop an inspection technique with the benefit of understanding how potential problems such as shadowing and internal multiples might limit your real-world results.
The idea here is to experiment and try things out before committing to fixturing. Imagine3D takes you through the same steps as you would experience in the real world with the added benefit of being able to see where the sound is actually going inside the part. Simulated B-Scans can show you how flaws might be accidentally shadowed by part geometry or other sound modes. Simulated B-Scans can also quickly show you all of the modes that are generated as the probe moves across the surface of the part.
Technique development is usually an iterative process. The use of workspaces makes it possible to work through a number of scenarios and share the results with others so that they might contribute to the development of the technique as well.
The object to be inspected can be constructed out of primitive solid shapes such as spheres, cylinders or tubes. The objects are represented internally as various types of constrained surfaces, such as planes or quadric surfaces.
Parts of even greater complexity can be imported from CAD drawings using the DXF file format. These imported drawings can then be combined with other drawings and primitive shapes to produce almost any structure.
Shapes are combined using a set of logical operations as shown in the table below. For example, the embed function can insert a weld nugget of any shape into the surface of a plate or pipe. The simulated weld can then be fully inspected from any angle. Flaws can then be inserted that simulate lack of fusion or foreign material.
In the above example, two rods have been removed from a sphere. The removal of the first rod created a hole down the center of the sphere. The removal of the second rod changed the surface of the sphere.
Any number of primitive shapes or CAD drawings can be combined using the logical operators shown above.
Raytracing is achieved by finding the intersection points of the rays and the primitive objects in the inspection target. Intersection points are kept or discarded according to the logical relationship between the combined objects.
For instance, if a ray enters into a hollowed-out void, the object that was "removed" to create the void is treated as if it did not exist. The removed object just disappears and blends into the background material.
A-scans are calculated by recording the arrival times when rays hit the receiver. The hits can be rejected if their angle of incidence on the receiver is greater than a user-defined limit. This simulates the beam spread of the receiver. To produce the A-scan, hit times are convolved with a modeled pulse calculated from the transmitter and receiver frequency responses. Frequency, bandwidth and focal length are adjustable.
A-scan generation is currently based on raytracing. However, since Imagine3D offers an open interface, sophisticated users may add their own modeling methods. Utex is actively working with other theoretical model developers so that their advanced model offerings receive exposure in the marketplace using the Imagine3D interface.
Ultrasonic sound fields are calculated using a summation of Gaussian solutions to the parabolic wave equation. Behavior upon reflection and transmission is estimated by transforming the coefficients for each component of the beam. An interesting characteristic of the beam model is that it can regenerate a new wave at each new interface.
Unlike the three-dimensional raytracing model, simulated sound fields are projected onto a 2D surface plane. The user can control the orientation of this plane to match the inspection viewing angle.
Each time the center ray encounters an interface, a line of text is added to the listing in the Center Ray Statistics section. The text describes the current material, mode of propagation, transit time, distance traveled, angle, ray starting point and ray direction.
Whenever a ray finally hits the surface of the receiver two lines of text are added to the listing in the A-Scan Arrivals section.
Text descriptions of all of the user-requested modes from the Mode document are presented in the Modes section.
Any UT calibration standard can be imported into Imagine3D to confirm that the technique you developed for your part will work in practice.
Signals measured with a real flaw detector and a real calibration block can be compared with the simulated results. If simulation and calibration compare well, it is very likely that the inspection technique developed for your part will also be of high quality.
The above IIW block was imported from an AutoCAD drawing. It started as a simple 2D drawing using closed polylines and was then extruded by Imagine3D to its final 1" depth after being imported.
The Main Window is where all of the other documents are displayed as well as toolbars and information status bars.
Ray Documents are the primary document used for any given project and it is the one document that holds all other types of documents.
Target Documents define the parts to be inspected including the flaws and the materials of which they are constructed.
Probe Documents define the transmitter and receiver characteristics. Probe frequency, bandwidth, shape and dimensions are entered in this document.
Modes Documents define the sound modes that are to be displayed including transmitted or reflected longitudinal or shear waves.
Material Properties is a table that contains velocities, densities and attenuation values for any solid, liquid or gas.
Workspace Documents save everything so that you can continue your work later. Window screen positions and contents are restored when workspaces are recalled.
B-Scan Documents are a plot showing all arriving echoes as the probe moves over the inspection part.
Cross-section Documents are a 2D profile that can be extruded into a 3D solid. They can be constructed inside Imagine3D using the built-in editor or they can be imported from DXF drawings.
An ActiveX interface surrounds the core functionality of Imagine3D. Users may write programs that under external program control will move transducers, interrogate rays and substitute simulation models.
NURBS Surfaces now allow arbitrarily shaped objects that allow surface discontinuities to be represented with a limited number of control points. Surfaces can be more easily trimmed for the modeling of sections.
Imagine3D has become a commercially successful ultrasonic simulation and raytracing tool. One important use for the program is in ultrasonic technique development. Users now have a standard platform for seeking help from associates and consultants. All work can be performed and displayed on inexpensive personal computers.
The market demand for more advanced simulation models has been increased through the wide distribution of Imagine3D's affordable and easy-to-use interface. This new demand is in part due to the increased comfort level of average NDT users who are trying simulation tools for the first time. Once users start relying on the tools, they naturally evolve and need to solve problems of ever-increasing complexity. As the user base advances, so will the models used in Imagine3D.