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TECHNICAL PAPERS

As-Built Modeling of Objects for Performance Assessment

[+] Author and Article Information
Edwin J. Kokko, Harry E. Martz, Diane J. Chinn, Henry R. Childs, Jessie A. Jackson, David H. Chambers, Daniel J. Schneberk, Grace A. Clark

 Lawrence Livermore National Laboratory, 7000 East Avenue, Livermore, CA, 94550

The term “analysis model” is used in a general context and can be loosely defined as any computational model constructed and used as input to a numerical analysis code (finite element, finite volume, multi-body dynamics, etc.) requiring some geometric (2-D or 3-D) and material detail in order to capture a certain class of physics (mechanical, thermal, electrical, electromagnetic, etc.).

J. Comput. Inf. Sci. Eng 6(4), 405-417 (Jun 29, 2006) (13 pages) doi:10.1115/1.2353856 History: Received September 22, 2005; Revised June 29, 2006

The goal of “as-built” computational modeling is to incorporate the most representative geometry and material information for an (fabricated or legacy) object into simulations. While most engineering finite element simulations are based on an object’s idealized “as-designed” configuration with information obtained from technical drawings or computer-aided design models, as-built modeling uses nondestructive characterization and metrology techniques to provide the feature information. By incorporating more representative geometry and material features as initial conditions, the uncertainty in the simulation results can be reduced, providing a more realistic understanding of the event and object being modeled. In this paper, key steps and technology areas in the as-built modeling framework are: (1) inspection using nondestructive characterization and metrology techniques; (2) data reduction (signal and image processing including artifact removal, data sensor fusion, and geometric feature extraction); and (3) engineering and physics analysis using finite element codes. We illustrate the process with a cylindrical phantom and include a discussion of the key concepts and areas that need improvement. Our results show that reasonable as-built initial conditions based on a volume overlap criteria can be achieved and that notable differences between simulations of the as-built and as-designed configurations can be observed for a given load case. Specifically, a volume averaged difference of accumulated plastic strain of 3% and local spatially varying differences up to 10%. The example presented provides motivation and justification to engineering teams for the additional effort required in the as-built modeling of high value parts. Further validation of the approach has been proposed as future work.

Copyright © 2006 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Example of as-built modeling process applied to a spherical reference standard

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Figure 2

Schematic of the as-built modeling analysis process applied to a concentric cylindrical phantom

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Figure 3

CAD models of the three cylindrical phantoms. This represents the as-designed configuration for each of the objects. As shown, the designs include different geometric features.

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Figure 4

Photograph of the three phantoms fabricated. As-built process is discussed for the concentric-cylindrical phantom (on the right).

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Figure 5

Design details for the concentric-cylindrical phantom (left). Artist’s rendering of the designed phantom (top right). Photograph of the as-built phantom (bottom right).

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Figure 6

Photograph of the PCAT digital radiography and computed tomography system (left). Photograph of the inside of the PCAT detector box (right).

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Figure 7

Representative digital radiographic projection I, (left) and CT slice μ, (right) of the concentric cylindrical phantom. The projection reveals the epoxy, aluminum rod, and air but not the cellulose. The CT slice is at a location that reveals the epoxy and aluminum materials.

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Figure 8

Concentric-cylindrical phantom on ultrasound test bed

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Figure 9

A typical UT waveform or A-scan (top) shows amplitude versus time of the acoustic signal. A B-scan (bottom) plots multiple A-scans taken by scanning 360° around the object. Amplitude is mapped to color in the B-scan.

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Figure 10

As-designed sketch of section and elevation views (left), CT slice at A-A′ (middle-top) and ultrasound slice at A-A′ (right-top). Note that section A-A′ is located where there is epoxy, cellulose, and air. An elevation view from the x-ray CT data is shown at middle-bottom. The CT results clearly reveal the epoxy, aluminum, and air, but not the cellulose. This is because the x-ray attenuation for cellulose and epoxy are about the same value. The ultrasound slice reveals the epoxy-cellulose interface as indicated.

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Figure 11

The geometric feature integration procedure (registration) consists of alignment and scaling in each of the axes to obtain consistent spatial coordinates

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Figure 12

UT/CT Slice 20 x-ray CT polar plot (top left) and lineout (bottom left); ultrasound B-scan (top right) and A-scan (bottom right)

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Figure 13

UT/CT Slice 40 x-ray CT polar plot (top left) and lineout (bottom left); ultrasound B-scan (top right) and A-scan (bottom right)

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Figure 14

Summary of the CT and UT characterization results

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Figure 15

Segmented isovolumes for the as-built geometry. The light-gray represents epoxy, the blue region represents the aluminum, the green region the air pocket, and the orange region a manufacturing feature (glue). These materials were directly determined from the x-ray CT data. Note that the area shaded in dark gray representing the cellulose region was determined from the UT data and manually included for visualization. The cellulose region was not processed directly within VisIt.

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Figure 16

Geometric feature extraction operations for aluminum, air, and glue regions (a)–(c) as labeled. Note that with each operation slight deviations (gray) from the original data accumulate, as shown in (d) and (e).

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Figure 17

Cubit tetrahedral mesh for describing the as-built geometry from the VisIt STL concentric-cylindrical phantom data set

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Figure 18

As-designed versus as-built phantom. The as-built material regions are specified in the key on the right. The baseline as-designed object is represented as a semi-transparent yellow color superimposed over the as-built material regions. Note the model slice numbers shown have no correlation to the NDC slice numbers in previous figures.

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Figure 19

The as-designed geometry (in red) and the as-built geometry (in yellow) are superimposed over the as-built CT results. The location of the slice numbers are shown in Fig. 1. Slices 05 through 20 reveal the aluminum while 25 and 27 reveal the air (with the cellulose absent from the data).

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Figure 20

Elevation cross sections of the as-designed and as-built models. The rightmost figure is an overlay of the as-built on the as-designed.

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Figure 21

Pressure time-sequence plots for the as-designed and as-built simulations. Note the subtle differences on the as-built section (bottom right) beginning at the two-o’clock position and extending to the four-o’clock position. The elevation cross-sections are shown overlaid onto the pressure time plots for visualizing the phantom material boundaries.

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Figure 22

Effective plastic-strain (a useful cumulative state variable) at the final time-state. Again, note the subtle differences (right).

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Figure 23

As-designed configuration differenced with as-built configuration. Plot of effective plastic-strain (a useful cumulative state variable) at the final time-state for two orthogonal axial slice planes. Red to yellow regions indicate locations where the as-built configuration accumulated more plastic strain (represented as a percentage ranging from 0.0% to 50.0%) relative to the as-designed configuration. Blue to cyan regions indicate locations where the as-designed configuration accumulated more plastic strain (0.0% to 50.0%) relative to the as-built configuration.

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Figure 24

Volume-averaged effective plastic strain (a useful cumulative state variable) time-history plot for the as-designed and as-built configurations

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