May 2013

NASA/TM–2013-217799

Ultrasonic Nondestructive Evaluation of 

PRSEUS Pressure Cube Article in Support of 

Load Test to Failure

Patrick H. Johnston

Langley Research Center, Hampton, Virginia
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May 2013

NASA/TM–2013-217799

Ultrasonic Nondestructive Evaluation of 

PRSEUS Pressure Cube Article in Support of 

Load Test to Failure

Patrick H. Johnston

Langley Research Center, Hampton, Virginia
Available from: 

NASA Center for AeroSpace Information 

7115 Standard Drive 

Hanover, MD 21076-1320 

443-757-5802 
1

 Begin your report below this instruction. Press F1 or Help for more. 

 

1.0 Introduction

The PRSEUS Pressure Cube Test [1] is a joint development effort between the Boeing 

Company and NASA Langley Research Center, sponsored in part by the Environmentally 

Responsible Aviation Project (ERA) and Boeing internal R&D. This Technical Memorandum

presents the results of ultrasonic inspections in support of the PRSEUS Pressure Cube Test, and is 

a companion document with the NASA test report [2] and a report on the acoustic emission 

measurements made during testing [3]. Portions of the content of these Technical Memoranda 

were reported at the 2012 Aircraft Airworthiness and Sustainment Conference [4].

2.0 Background

2.1 Pultruded Rod Stitched Efficient Unitized Structure (PRSEUS) Concept

The PRSEUS concept, depicted in Fig. 2.1, has been developed as a low-cost, lightweight 

composite structure for aircraft [5,6], which offers advantages over traditional metallic structure. 

The PRSEUS concept is comprised of a stitched carbon fiber-epoxy material system with the 

potential for reducing the weight and cost of transport aircraft structure by eliminating fasteners. 

By adding unidirectional carbon rods to the top of stiffeners, the panel becomes more structurally 

efficient. The combination of stitching with the pultruded rod-reinforced stiffener produces a 

more damage tolerant material system.

Some key features of the PRSEUS concept are: the improved stiffness provided by the 

pultruded rod; the crack-arresting nature of the stitches, which enables the use of failsafe design 

principles; reduced tooling size and weight enabled by the self-supporting nature of the stitched 

preform; and improved resin infusion through the use of Controlled Atmospheric Pressure Resin 

Infusion (CAPRI). A photograph of the stiffener side of a flat PRSEUS test panel is shown in Fig. 

2.2 [5].

Of note for this paper are the areas where the flanges are folded out from the vertical 

components (stiffeners, frames, end caps) to mate with the horizontal skin layers. These wedgeshaped volumes were loosely filled with linear bundles of fibers prior to laying down the skin 

layers, to provide some volume fraction of fibers. These linear areas are referred to as the 

“noodle” because of the resemblance of the placement of fiber material during manufacture to the 

laying down of floppy thin cooked noodles.

2.2 Pressure Box Test Article

The key test article for part of the ERA Program is a future full-scale multibay structure, 

representing the passenger compartment and luggage compartment of a notional aircraft 

fabricated using PRSEUS panels. The test article for the present study (Fig. 2.3) was a smaller

cube-like structure representing all the major features of the multibay structure, including crown, 

floor, rib panels and bulkhead panels. The main goal of this test was to verify the functionality of 

the joint design under pressure loading.

The detailed structure of various component parts of the cube is presented in Figures 2.4 

through 2.6. Each of the sides was a PRSEUS panel, having seven or eight stringers and two 

frames. Along the edges, end caps were provided as mating surfaces to fasten and seal to the 

adjoining face sheets.
2

2.3 Test Sequence

The test sequence was defined in a test specification document [1]. The test sequence is 

presented in Table 1. 

The Test Specification Document stated that NASA would be responsible for completing the 

items listed below. In general, NASA would perform test set-up, conduct the test and perform

post-test evaluation:

1. Inspect the assembly to ensure the pressure cube was not damaged and that fasteners are 

still torqued, or to find loose strain gages.

2. Set up testing.

3. Pre & post test photos and video.

4. Prepare the specimen OML surface for VIC-3D (Video Image Correlation in 3 

Dimensions) system.

5. Install LVDT’s.

6. Conduct the testing per test specification & procedure defined in Section 5. This includes 

leading the test and recording of all the data.

7. Perform pre-damage infliction NDI inspection

8. Impact panel with BVID

9. Perform post-impact NDI inspection

10. Perform post-test evaluation and post-test NDI inspection

The following sections will describe the highlighted NDI actions.

3.0 Ultrasonic Phased Array Inspection Methods

The flat surface of the PRSEUS panel provided a good interface to use a linear ultrasonic 

array with a solid plastic wedge, attached to a manually-operated X-Y encoder fitted with suction 

cups, as shown in Fig. 3.1. An area of approximately 20” X 20” could be inspected in 

approximately 20 minutes, including the time for positioning the scanner. A 10 MHz linear 

phased array (64 elements, each 10 mm X 0.5 mm) was used with an aperture of 16 elements. A 

zero-degree wedge was employed, and the beam was perpendicular to the inspection surface and

focused approximately 2 mm below the surface of the composite. Water was sprayed on the panel 

surface to provide adequate acoustic coupling.

Early success of this method was demonstrated during mechanical testing of flat PRSEUS 

panels in a load frame [7].

4.0 Ultrasonic NDE Results

4.1 Impact Site

As a part of the damage tolerance testing of the PRSEUS cube, a site was selectively inflicted 

with barely visible impact damage (BVID). Ultrasonic NDE was performed before and after the 

BVID to quantify the extent of damage produced by the impact.

Figure 4.1 presents C-scan views of the impact site before and after the impact. An orange 

oval illustrates the site of impact. The post-impact data show an area of indentation, and a 
3

surrounding brighter area, corresponding to delaminations, which were not observed in the preimpact data.

A close-up of the impact area is presented in Fig. 4.2. The lateral extent of the delamination 

is shown to be approximately 1.5 inches by 2.0 inches. A horizontally oriented B-scan (i.e.,

parallel to the outer edge of the rib panel) is presented in Fig. 4.3. Similarly, a vertically oriented

B-scan (i.e., perpendicular to the outer edge of the rib panel) is presented in Fig. 4.4. These 

figures both indicate the lateral extent of delamination, and also illustrate that the delaminations 

penetrate to approximately 0.2 inches from the indented surface of the composite.

4.2 Inspection of Areas of Interest Following 2P Loading

During the 2P pressure test case, some unexpected strain gage readings dictated that an 

inspection be performed of the crown panel end cap region centered between the frames. A Bscan from one of these inspections is presented in Fig 4.5. By comparison with the design 

drawing, in the lower panel, the strong back surface echoes can be identified as the number of 

fiber stacks is varied across the end cap flange. Also obvious is the ultrasonic “shadow” cast by 

the noodle material. To the inner side of the noodle appear several indications, apparently arising 

from delaminations in the stacks which form the curve of the inner corner of the end cap. Because 

of the shadow from the noodle, the only visible portions of the delaminations are those which 

extend beyond the arm of the noodle.

The occurrence of delaminations at this location was reasonable, given that pressurization of 

the cube would tend to open up the interior angle at the corner. This leads to stresses, which

operate to separate the laminae in the corner.

Inspections were done on the central areas of all four edges of the crown panel, indicated by 

the dashed boxes in Fig. 4.6. Corner delaminations were observed on the opposite sides, between 

the frames, as indicated by yellow boxes in the figure, and were measured over 13 inches on each 

of these sides. Because of the shadow cast by the noodle, however, it could not be determined 

how far into the corner the delaminations extended. Furthermore, the interior surface of the corner 

was inaccessible for direct inspection because of sealant.

4.3 Post-Failure

In the final phase of testing, the PRSEUS cube was taken to higher pressure to induce 

structural failure. At a pressure of above 48 psi, failure occurred, resulting that the front bulkhead 

panel separated from the cube and was destroyed. The remaining panels remained attached to 

each other. A number of areas on the remaining cube panels were selected for ultrasonic 

inspection.

4.3.1 Three Types of Damage Identified

In analyzing the ultrasonic measurements of the cube after the test to failure, there were three 

distinct types of flaws identified. These three types are schematically depicted in Fig. 4.7. These 

types are defined as follows:

Type A: Delaminations between essentially flat laminae, most typically between the skin 

stacks and the stacks making up the flanges of stiffeners or end caps. There were also some Type 

A delaminations observed between tear strap stacks and the adjacent flange laminae. Two 

examples of Type A delaminations are shown in Fig. 4.8. Here, the unsupported flange tips 
4

delaminated at the skin back surface. The delaminations terminated at the first row of stitches 

encountered under the stringer flange. In the end cap flange, the delamination extended past two 

stitch rows, before terminating at the third stitch row encountered. As will be discussed below, 

this particular end cap is the one to which the failed forward bulkhead had been attached.

Type B: Some delaminations were observed to occur in the laminae lying above the noodles 

of both stringers and frames. These occurred between the stitch rows on either side of the noodle.

Fig. 4.9 presents two examples of stringers containing Type B delaminations. Fig. 4.10 presents 

the occurrence of Type B delaminations at several different levels in the end of a crown frame. 

Depths of the delaminated areas from the surface are identified (in inches) in the figure. 

Type C: The corner delaminations, previously described as having been observed following 

the 2P test, are called Type C. These were observed in the interior fillet laminae of the end caps.

Examples of Type C flaws are depicted in Fig. 4.5 (after 2P test) and in Fig. 4.9 (after test to 

failure).

4.3.2 Crown Panel

The results of inspection of the crown panel are presented in Fig. 4.11. Different colored 

areas indicate the three types of damage: Type A in blue, Type B in orange and Type C in yellow.

Only a small amount of flange delamination (Type A) was observed. Two areas were found 

adjacent to the end cap and central stringer along the connection with the failed bulkhead panel. 

A third area was observed at the first stringer and frame intersection. This is near the location 

proposed as the initiation site of ultimate failure: the metallic splice plates connecting the crown 

and rib frames [2, 4].

Type B delaminations were observed on all the stringers, between the frames. Patches of 

Type B flaws were observed at several depths in all the frames, typical of those presented in Fig. 

4.10, near the corners where the frame intersects the end cap and stringer. 

Type C corner delaminations were observed over approximately 2/3 of the length of the end 

caps. Because these results only include those parts of the fillet delaminations which extend 

beyond the limb of the noodle cross-section, some unknown amount of Type C damage might 

have gone undetected during these inspections.

4.3.3 Right Rib Panel with Impact

Figure 4.12 presents a summary of results obtained for the right rib panel containing the 

impact site. The area inspected includes the forward end cap, the vertical structure on the right 

hand side containing the BVID impact and to which the failed bulkhead panel had been attached, 

and the vertically-oriented rib frame. The uppermost part of the scan includes the interface with 

the crown panel, and the seven stringers are horizontal.

There were no observable changes in the damage surrounding the BVID impact site.

Type A delaminations were found along the end cap flange at each bay. These were at the 

level of the face sheet stacks, and fell within the area of the unsupported flange ends, terminating 

at the first row of stitches. A much larger area of delamination was found in the upper right 

corner of the panel, near the intersection of the rib frame with the crown frame, the suspected 

initiation site for the ultimate failure.
5

Delaminations of Type A were observed in the flange of the rib frame, at each bay scanned. 

These fell at the level between the tear strap and the frame flange laminae.

Type B delaminations were found in each of the stringers scanned in the central area of the 

panel, between the frames.

Lengths of Type C delaminations were observed along the uppermost stringer, between the 

frames, and along the central span of end cap adjacent to the Aft Bulkhead.

4.3.4 Left Rib Panel

A summary of inspection results for the Left Rib Panel is given in Fig. 4.13. Type B 

delaminations were found in the stringers between the frames. Type C indications were observed 

in the central length of the bottom cap.

4.3.5 Aft Bulkhead Panel

The inspection of the Aft Bulkhead is summarized in Fig. 4.14. Type B delaminations were 

identified in the bottom cap and in stringers between the vertical frames. Small areas of Type A 

and Type B delaminations were found in the frames, with notable symmetry in the size, shape and 

locations of the flaws.

4.4 Inspection of Cutout Sections

After the post-failure ultrasonic inspections were completed, the remains of the cube test 

article were shipped from NASA LaRC back to Boeing for further analysis and dissection. 

Because the first indications of material damage appeared during the 2P test in the Crown Panel 

end caps near the midline between frames, a more detailed inspection of this material was 

requested, to involve immersion ultrasonic and x-ray computed tomography to be performed at 

NASA LaRC.

4.4.1 Description of cutout sections

Two sections of the crown end caps were dissected for analysis. Figure 4.15 indicates these 

areas by blue rectangles. The specimens were labeled Side A and Side B. Because the crown 

panel had been spray painted after the installation of strain gages and wiring, there was a clearly 

identifiable pattern on the two specimens where the gages, wiring and tape had been removed. 

These marks aided in identifying the precise locations of the two specimens on the crown panel. 

Photographs of specimen Side A and its location on the crown panel are compared in Fig. 4.16.

Examination of the end of the specimens is useful. In Fig. 4.17 an ultrasonic B-scan from this 

region, taken following the 2P load test (see Fig. 4.5), is overlaid onto a photograph of the end of 

specimen Side A. Some of the stitches are readily identifiable in the photograph; orange lines 

indicate others.

The broad, echo-free area in the B-scan is observed to correspond well to the crown edge of 

the “triangularly-shaped” noodle region, which was filled with a low density of bundled fibers 

during fabrication.

4.4.2 Ultrasonic inspection of cutout sections

Immersion ultrasonic data were acquired using a 10 MHz, 0.5-inch diameter, and 2.0-inch

focal length spherically focused immersion transducer. A C-scan acquired with the beam incident 
6

normal to the outer surface of specimen Side A is presented in Fig. 4.18 along with a photograph 

of the front surface for comparison. The C-scan data represents scattering from just beneath the 

surface of the part. At this level, the ultrasonic signal has clear disturbances corresponding to the 

stitching material at that surface. Colored dashed lines are used on the figure to indicate these 

stitch rows. The (nominally) vertically oriented stitch rows are in yellow, while the angled 

stitches are in red or orange, depending on the direction of the diagonal.

A B-scan through the specimens (like that in Fig. 4.17, but flipped horizontally) is shown in 

Fig. 4.19. Along the line of the echo arising from the front surface of the part, colored dots are 

used to indicate the positions of the stitch entry points on that surface, as shown on the C-scan in 

Fig. 4.18. Corresponding locations were identified for the exit points of the stitches on the back 

surface of the specimen by manipulating the grayscale representation of the data. These points are 

indicated by colored dots on the back surface echoes in Fig. 4.19. Connecting corresponding 

entry and exit dots with colored dashed lines indicates the approximate location of the stitch 

material in the volume of the composite.

A significant observation from this figure is that the ultrasonic echoes arising from Type C 

delaminations occur in the volume between the diagonal stitch adjacent to the noodle and the 

matching vertical stitch. On the noodle side of the diagonal stitch, ultrasonic echoes fade away 

into the echo-free zone.

Secondly, the extent of the very nearly echo-free area falls close to the diagonal stitch on 

either side of the noodle, which is not all in the geometrical shadow of the noodle material.

Figure 4.20 combines the B-scan from Fig. 4.19 (rotated 90° counterclockwise) with a C-scan 

of the specimen representing the peak echo amplitude from the interior of the specimen. The 

white dashed lines on the B-scan indicate the depth gate. The Type C delaminations are observed 

to extend the entire length of the specimen, and to be contained between the red stitch row and 

the adjacent yellow stitch row.

The end cap itself was also scanned. Figure 4.21 presents a C-scan and two B-scans of the 

cap. Again, on the C-scan, vertically oriented stitch rows are indicated by dashed yellow lines. A 

solid red line and a solid orange line indicate the locations of the B-scans presented in the figure. 

These fall in the area containing Type C delaminations adjacent to the internal fillet, and between 

two rows of stitches where no delamination indications are observed.

The Type C delaminations fall in the area between the first row of stitches at the fillet (out of 

the data region at the top of the scan) and the second row of stitches.

4.4.3 X-ray Computed Tomography (CT) of cut-out sections

A 1.5-inch long portion of the specimen Side A was imaged using high-resolution x-ray 

computed tomography (CT), with a voxel resolution of approximately 20 microns (0.0008 inch). 

A section of this data across the noodle and inner fillet region of the specimen, including one 

diagonal stitch, is presented in Fig. 4.22.

One general observation of the CT data is that the composite has few voids or resin-starved

areas, indicating a successful infusion of resin into the dry preform.

Also quite prominent is the relatively resin-rich noodle volume. Some degree of voids and 

cracking are observed in the noodle volume, predominantly within the resin.
7

The interior fillet laminae are observed to be highly delaminated. It appears that the boundary 

between each pair of stacks (7-ply layers, held together by polymer knitting threads, stacked up to 

build the composite) is delaminated, causing an effect resembling the layering of an onion. These 

multilayer delaminations were observed to extend over the entire 1.5-inch length of the CT. 

Almost all of the “onion-layer” delaminations in Fig. 4.22 end at the position of the diagonal 

stitch in the face sheet. Toward the end cap, the “onion-layer” delaminations end before or at the 

position of the first stitch row. At both ends of the curve, some small fraction of delaminations 

extends beyond the first stitches encountered. These are the portions of the delaminations found 

by ultrasonic inspection (Figs. 4.20 and 4.21), but all delaminations end before reaching the next 

row of stitching.

It is observed that some occasional small voids occur within or adjacent to the stitching 

threads. Some crack-like indications are observed along the boundary of the stitch threads and the 

surrounding composite, indicating thread separation from the composite during cure. These 

indications are not widespread, and their presence doesn not appear to affect the material 

behavior.

Figure 4.23 shows analysis results predicting high out-of-plane stresses in the inner fillet of 

the end cap, consistent with formation of the observed “onion-layer” delaminations. Interlaminar 

failures were predicted to occur at 12.4 psi, while the first indications of damage from strain 

gages occurred at approximately 16 psi during the 2P load test [4].

5.0 Discussion

Based on the results of ultrasonic and x-ray nondestructive testing, the PRSEUS system 

demonstrated damage contraint in this test. The damage from an intentional BVID site did not 

grow during applied load. The numerous delaminations that occurred within the structure at 

higher loads were almost completely contained by the first row of stitches. Where the 

delaminations did extend beyond the first stitch row, at all but two or three measured sites the 

delaminations ended before or at the second stitch row. Those few sites where two stitch rows 

were crossed were located adjacent to the failed bulkhead panel, and likely occurred during the 

last moments before catastrophic failure of the bulkhead [2].

One area of potential concern for nondestructive evaluation of PRSEUS is the behavior of the 

ultrasonic interrogation around the noodles. As illustrated by the B-scans in Figs. 4.5, 4.9, 4.17 

and 4.19, the material in the noodles was highly attenuative and/or poorly backscattering to the 

ultrasonic signal. The physical reasons for this behavior were made apparent by the highresolution of the CT cross-section of the noodle region.

The x-ray CT in Fig. 4.22 is reproduced in Fig. 5.1 to support this discussion. For all of the 

ultrasonic inspections from the outer surface of the cube, the ultrasonic beam was incident normal 

to the surface. The ultrasonic waves penetrating the face sheet are represented by the parallel 

vertical lines in the face sheet area in the figure. 

The noodle volume is seen to be a much different consistency than the material in the face 

sheet. Bundles of fibers (oriented roughly perpendicular to the image) are loosely distributed in 

the volume surrounded by resin matrix fill material. For reference, the approximate size of a 10 

MHz wavelength is displayed in white. Because the ultrasonic velocity in the resin is quite 

different than that in the fiber bundles, this noodle material exhibits ultrasonic velocity 

discontinuities which are on the order of several wavelengths in dimension, resulting in scattering 
8

and refractive phenomena which disperse the ultrasonic beam, with the result that little or no 

ultrasound is sent back in the direction of the transducer, causing an echo-free zone. The yellow 

arrows in Fig. 5.1 illustrate this behavior.

Further analysis of the structure suggests that another phenomenon, related to the curvature in 

the fillet laminae, is also acting in this case. The orange arrows in Fig. 5.1 illustrate the normalincidence ultrasonic waves propagating through the face sheet laminae into the parallel laminae 

of the end cap flange, beyond the first row of stitches from the end cap. Here, the ultrasonic 

waves encounter a delamination which has extended beyond the stitch row. This delamination is 

parallel to the interlaminar interface and perpendicular to the incident wave propagation, so the 

ultrasound is reflected from the delamination back to the transducer to be detected. These 

represent the delamination indications labeled Type C.

However, on the end cap side of the diagonal stitch row, the fillet laminae curve away from 

the flat face sheet laminae, and because of the thickness of the inner fillet, this curvature extends 

laterally away from the direct “shadow” of the “triangular” noodle volume. This enables a 

different refraction behavior to occur. 

Fiber-reinforced plastic composites exhibit anisotropic ultrasonic characteristics. The 

ultrasonic velocity is much faster for propagation in the direction of fibers than it is across the 

fibers. In a quasi-isotropic laminate, such as the stacks used in PRSEUS, the result is that the 

ultrasonic velocity is higher in the plane of the stack than normal to the plane. So, in the case 

presented in this region, the ultrasonic waves propagating normal to the laminae in the face sheet, 

then encounter laminae which are curving away from the plane. This causes the ultrasonic waves 

to deviate their path, due to refraction, toward the direction of faster ultrasonic velocity, i.e., 

toward the direction of the curving laminae. As illustrated by the red arrows in Fig. 5.1, these 

refracted waves divert away from a path which results in reflections back toward the transducer, 

leading to an effective widening of the echo-free zone, as best illustrated in Fig. 4.19.

6.0 Conclusions

It was observed that the damage incurred within the PRSEUS pressure cube during this series 

of mechanical tests was contained by the stitches.

It was also found that the construction of the noodles used in the PRSEUS Pressure Cube 

prevented a full ultrasonic inspection of the highly-stressed inner fillet of the integral caps.

7.0 References

1. Boeing Document ZA153690, Pressure Cube Test Specification, (2011).

2. Andrew E. Lovejoy, “PRSEUS Pressure Cube Test Data and Response,” NASA TM-2013-

217795.

3. Michael R. Horne, “Evaluation of Acoustic Emission SHM of PRSEUS Composite Pressure 

Cube Tests,” NASA TM-2013-217993.

4. Nicolette Yovanof, Andrew E. Lovejoy, Jaime Baraja and Kevin Gould, “Design, Analysis 

and Testing of a PRSEUS Pressure Cube to Investigate Assembly Joints,” 3rd Annual Aircraft 

Airworthiness and Sustainment Conference, Baltimore, MD, April, 2012.
9

5. A. Velicki, "Damage Arresting Composites for Shaped Vehicles," NASA-CR-2009-215932, 

(2009).

6. D. Jegley, “Experimental Behavior of Fatigued Single Stiffener PRSEUS Specimens,”

NASA-TM-2009-215955, (2009).

7. Patrick H. Johnston, “Pulse-Echo Phased Array Ultrasonic Inspection of Pultruded Rod 

Stitched Efficient Unitized Structure (PRSEUS),” Review of Progress in Quantitative 

Nondestructive Evaluation, vol 30, AIP Conf. Proc. 1335, pp. 1432-1439 (2011).
10

TABLE 1. Load Sequence

Load

Sequence

Load

Set

Instructions Comments

0 0.5P

(4.6 psi)

Instrumentation checkout.

Verify that all instrumentation

is working and being recorded

Instrumentation should be

completed prior to Boeing’s

arrival for test witnessing

1 1.33 P

(12.2 psi)

Build pressure to 0.5P, 1P &

1.15P stabilizing at each level.

Then build up to test pressure

of 1.33 psi. Hold pressure at

1.33 psi for 3 seconds, then

depressurize.

The panel is pressurized to

gather linear data. The data

will be used to calibrate with

analysis.

2 2P

(18.4 psi)

Build pressure to 1.33P and

stabilize. Then build up to test

pressure of 2P. Hold pressure

at 2P for 3 seconds, then

increase to 2P + 10% and

hold for 3 seconds, then

depressurize.

Check 1.33P panel

characteristics for linear

behaviors. The panel will

then be loaded up to 2P

under pristine condition.

The test will verify the

capacity of minimum gage

skin design with integral

caps as joints

3 Damage

Panel

The panel shall be impacted

with BVID as described in

Section 2.3 prior to testing to

failure. The panel shall be

inspected using NDI before

and after impacting at the

damage location with a radius

of 4 inches from the edge of

the damage.

In order to demonstrate the

capability of the joint under

BVID with 100 ft-lb impact

damage on the skin side of

the rib panel and the radius

of the integral cap, the

panel will be damaged prior

to failure.

4 To

Failure

Build pressure to 1.33 P and

stabilize. Build pressure to 2P

and stabilize, hold for 3

seconds. Then build pressure

to failure.

The impacted panel will be

pressurized until failure. The

test will verify the ultimate

capacities of the panel in

pristine condition.
11

Figure 2.1. The PRSEUS dry preform is built up from carbon fabric stacks for the frame, stringers 

and skin. The layers are stitched together with Vectran fibers, using a single-sided sewing 

method, then bagged and infused with resin [4].
12

Figure 2.2. An example of a PRSEUS panel. This particular flat panel comprises four frames and 

seven stringers [5].
13

Figure 2.3. Test specimen assembly, representing a portion of the large-scale multi-bay test 

article.

Figure 2.4. Crown panel, comprising two frames, seven stringers and end caps along all four 

edges
14

Figure 2.5. Rib panel, comprising two frames, seven stringers and end caps on vertical edges 

and bottom edge.
15

Figure 2.6. Bulkhead panel, comprising two frames, eight stringers and an end cap on the 

bottom edge.
16

Figure 3.1. A linear ultrasonic array attached to a manual X-Y encoder was used to interrogate the 

PRSEUS panel. Ultrasonic coupling was accomplished using a plastic wedge and soapy water.
17

PRE-IMPACT POST-IMPACT 

Figure 4.1. Ultrasonic C-scan results from the site of impact before (left) and after (right) the impact was 

performed.

Figure 4.2. Close-up C-scan of the impact site (upper left) with vertically oriented B-scan (right) and 

horizontally oriented B-scan (bottom).
18

Figure 4.3. Horizontally oriented B-scan through the impact site, highlighting the indentation of the surface 

and indicating the depth of impact-generated delamination damage.

Figure 4.4. Vertically oriented B-scan through the impact site, indicating the width and depth of impactgenerated delamination damage.
19

Figure 4.5. Ultrasonic scans were taken following anomalous strain gage readings during the 2P 

pressurization test. Notice the ultrasonic shadow cast by the highly-attenuative noodle material. It is likely 

that the delaminations extend further along the curve of the laminae, but are hidden from the inspection by 

the width of the noodle.
20

Figure 4.6. Summary of the crown panel damage observed following the 2P pressure test. Delaminations 

were observed adjacent to both end caps, at middle of crown panel, between the frames. The observable 

portion of the delaminations extended approximately 13 inches in length.
21

Figure 4.7. Definition of damage types found in cube following test to failure. Type A is a delamination 

between the skin laminae and the laminae comprising the flange of a stringer, frame or end cap. Type B is a

delamination in the laminae above the noodle of a stringer, frame or end cap. Type C delaminations occur 

in the curved laminae forming the inner corner of an end cap.
22

Figure 4.8. Example of a Type A delamination, which is an extension of the inner skin surface underneath 

the stringer flange laminae.
23

Figure 4.9. Example of a Type B and Type C delaminations Type B damage is seen above the noodle of 

two stringers. Type C damage is observed to the side of the noodle of the end cap.
24

Figure 4.10. An example of Type B delaminations above the noodle of a frame. 
25

Figure 4.11. Summary of the post-failure damage observed in the Crown panel.
26

Figure 4.12. Summary of the post-failure damage in the Right Rib panel containing the impact site.
27

Figure 4.13. Summary of the post-failure damage in the Left Rib panel.
28

Figure 4.14. Summary of the post-failure damage in the Aft Bulkhead panel.
29

Figure 4.15. Areas of Crown panel selected for cutout and further inspection
30

Figure 4.16. Photograph of the external surface of cutout labeled Side A. Below is a photograph of the 

intact crown under inspection, with the extent of Cut-out Side A identified by an orange dashed rectangle.
31

Figure 4.17. Photograph of the end of cut-out Side A, with ultrasonic B-scan data taken following the 2P 

test superimposed in approximate alignment.
32

Figure 4.18. Photograph of the external surface of cutout Side A, above an ultrasonic C-scan. The C-scan 

was from data gated just below the surface of the part, where echoes were observed corresponding to the 

surface stitch material. Colored dashed lines indicate the stitch rows. Yellow lines correspond to vertically 

oriented stitches. Red and orange correspond to the angles stitch rows. Arrows indicate the lateral direction 

of the angled stitches: red in the inboard direction and orange in the outboard direction. The diagonal 

stitches on either side of the noodle angle away from the centerline of the end cap, as indicated in Fig. 4.17.
33

Figure 4.19. Ultrasonic B-scan through the noodle region of cut-out Side A. Using ultrasonic indications of 

the entry points of stitches at the top surface and bottom surface, lines are drawn to indicate approximate 

locations of stiches through the thickness of the specimen. Two observations of note can be made. Firstly, 

the Type C delaminations observed fall within the area between the red diagonal stitch and the yellow 

vertical stitch. Secondly, the extent of the very nearly echo-free area falls close to the diagonal stitch on 

either side of the noodle.

Figure 4.20. The B-scan from Fig. 4.19 rotated 90° CCW, is reproduced on the left hand side of this figure. 

To the right is a C-scan of the panel, made from the reflected data from the interior of the composite. The 

dashed colored lines, as in Fig. 4.18, represent the stitch rows at the skin surface. The indications of Type C 

delaminations are observed to fall within the volume of composite between the yellow vertical stitch and 

the red diagonal stitch line.
34

Figure 4.21. Ultrasonic scan of end cap.
35

Figure 4.22. X-ray CT slice showing noodle and inner fillet region.

Figure 4.23. High out-out-plane stresses were predicted by analysis within inner fillet of end cap [4].
36

Figure 5.1. X-ray CT slice with superimposed ultrasonic ray tracings to schematically explain the 

interpretation of ultrasonic data.
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Technical Memorandum

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Ultrasonic Nondestructive Evaluation of PRSEUS Pressure Cube Article in 

Support of Load Test to Failure 

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Johnston, Patrick H.

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NASA Langley Research Center

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The PRSEUS Pressure Cube Test was a joint development effort between the Boeing Company and NASA Langley Research 

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Memorandum presents the results of ultrasonic inspections in support of the PRSEUS Pressure Cube Test, and is a companion 

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PRSEUS; composites; ultrasonic NDE

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