May 2013

NASA/TM–2013-217988

Combining Through-Thickness Reinforcement 

and Self-Healing for Improved Damage

Tolerance and Durability of Composites

T. Kevin O’Brien, Michael W. Czabaj, and Jeffrey A. Hinkley 

Langley Research Center, Hampton, Virginia

Spiros Tsampas and Emile S. Greenhalgh

Imperial College, London, United Kingdom

Gregory McCombe, Ian P. Bond, and Richard Trask

University of Bristol, Bristol, United Kingdom
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May 2013

NASA/TM–2013-217988

Combining Through-Thickness Reinforcement 

and Self-Healing for Improved Damage 

Tolerance and Durability of Composites

T. Kevin O’Brien, Michael W. Czabaj, and Jeffrey A. Hinkley

Langley Research Center, Hampton, Virginia

Spiros Tsampas and Emile S. Greenhalgh

Imperial College, London, United Kingdom

Gregory McCombe, Ian P. Bond, and Richard Trask

University of Bristol, Bristol, United Kingdom
Available from:

NASA Center for AeroSpace Information

7115 Standard Drive

Hanover, MD 21076-1320

443-757-5802

The use of trademarks or names of manufacturers in this report is for accurate reporting and does not 

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1

Introduction

A well-established scheme for mitigating or suppressing delamination growth in a composite 

laminate is to insert carbon Z-pins in the through-thickness direction [1,2]. The apparent 

interlaminar fracture toughness of the composite is increased due to the tractions imposed by the 

Z-pins as they pull out during delamination growth, thereby providing improved damage 

tolerance [3,4]. Other attempts have been made to introduce self-healing resins to the crack plane 

as delaminations grow, to restore some of the initial fracture toughness. This may be 

accomplished via microencapsulation [5-7] or embedding the resin in hollow glass tubes in the 

planes of the fibers [8-10]. Introducing a self-healing resin has the added benefit of sealing the 

crack plane to prevent moisture ingression, and hence, improving durability. 

A study was undertaken to develop a prototype method for adding through-thickness hollow glass 

tubes infused with uncured resin and hardener to a carbon Z-pin through-thickness reinforcement 

field. The Z-pins are intended to provide delamination resistance as they pull out during a 

delamination event. Simultaneously, the glass tubes will fracture and release the enclosed resin 

and catalyst. The tractions provided by the Z-pin pull-out mechanism should allow time for the 

resin to cure, and minimize crack opening to reduce the volume that needs to be filled, resulting 

in a self-healed fracture plane. 

An “initial study” was first undertaken where half the carbon Z-pins were replaced by the hollow 

glass tubes in the foam preform prior to insertion in the uncured laminate. Because the survival 

rate of the glass tubes was not sufficient, a more detailed “main study” was then conducted where 

all of the carbon Z-pins in the preform were inserted into the uncured laminate, and then half 

were removed and replaced with hollow glass tubes. This technique resulted in a nearly 100% 

survival rate for the hollow glass tubes, allowing resin insertion, followed by testing, to evaluate 

the proposed concept.

Materials and Specimen Preparation

Z-pin pre-forms consisting of 0.5 mm diameter pultruded carbon fiber tows embedded in a low 

density foam were purchased from Albany Engineered Composites. The Z-pins are typically 

inserted in an uncured tape laminate using an ultrasonic hammer (fig.1), resulting in a 2% by 

weight areal density of through-thickness Z-pins. For this study, half of the Z-pins in the pre-form 

were replaced with 0.55 mm outer diameter, 0.4 mm inner diameter, hollow glass tubes. 

In the initial study, the tubes were placed in the foam (fig.2) replacing some Z-pins before 

insertion into three uncured 32-ply, 305 mm square, unidirectional IM7/8552 carbon epoxy 

prepreg panels. The panels contained a 13 micron thin Teflon film inserted along the middle of 

the panel at the laminate mid-plane, to create Double Cantilever Beam (DCB) interlaminar 

fracture toughness specimens. The panels were cured in a press, using the manufacturer’s 

recommended curing cycle, and then cut into 152 mm long by 20 mm wide coupons using a water 

cooled diamond saw. The panels were C-scanned to insure no manufacturing flaws were present. 

Each panel yielded five DCB specimens, for a total of 15 specimens. Loading blocks were then 

bonded to the specimens using a room temperature adhesive. 

In the main study, a second panel was manufactured using 24 plies of unidirectional IM7/8552 

carbon fiber epoxy prepreg tape material. As before, a 13 micron thin Teflon film was inserted 

along the middle of the panel at the laminate mid-plane to create DCB interlaminar fracture 

toughness specimens. The Z-pin field was inserted first in the uncured laminate, then every other 

row of Z-pins was removed. Hollow glass tubes were then manually inserted immediately 
2

following insertion of a sewing needle of similar diameter in the hole vacated by the Z-pins 

before relaxation of the resin that would tend to close these holes. Aluminum plates were used to 

support the unreinforced portion of the plate and prevent tube breakage during cure in the press 

(fig.3). The panel was cured in the press per the manufacturer’s specifications. Inspection of the 

panel after cure indicated nearly 100% survival of the glass tubes (fig.4). However, the thickness 

in the Z-pin field was larger than the remainder of the panel due to the lack of local compaction 

during cure. 

The self-healing resin chosen was Product #307 from Epoxy Systems, Inc. of Dunnellon, Florida.

This is a very low viscosity, two component, liquid epoxy resin system designed to be mixed at a

2-to-1 ratio of epoxy to hardener (fig.5). At room temperature, the resin-hardener mixture was 

observed to gel in less than 30 minutes. The manufacturer indicates that the mixture cures tackfree in five hours and is fully cured in seven days. The resin and hardener were colored with 1% 

by weight of commercially available soluble fluorescent dyes for enhanced visibility within the 

glass tubes and on the composite crack faces. Solvent orange 63 and solvent yellow 98 dyes were 

selected for the resin and hardener, respectively, because they mix well with epoxy components 

and fluoresce brightly under long-wave ultraviolet light [11]. When mixed, they yield a maroon 

color to the epoxy and an orange color to the hardener (fig.5).

Before cutting specimens from the 24-ply panel, the two-part epoxy was injected into the tubes in 

the region where the first six coupons were located, with part A (resin) filling two neighboring 

tubes and part B (hardener) filling the adjacent single tube. Prior to cutting these first six DCB 

specimens, the ends of the tubes were sealed using a liquid rubber cement to insure that the resin 

and hardener did not escape (fig.6). Coupons that were 152 mm long by 20 mm wide were cut 

from the panel using a diamond saw at a slow rate to prevent heat build up and to eliminate the 

need for a coolant and prevent moisture contamination (fig.7). The specimen width was chosen so 

that at least six tubes were present across the specimen width. Piano hinges were then bonded to 

the specimens using a Hysol 9460 epoxy. The adhesive was cured at room temperature for two 

days. X-ray tomography was performed on one specimen (3B) to illustrate the variability in pin 

and tube placement and the disturbance in the fiber straightness resulting from pin and tube 

insertion. Figure 8 shows the resin and hardener insertion pattern superposed on the X-ray image 

of the 24-ply DCB specimen. For each DCB specimen cut from the panel, each row of glass tubes 

had at least two sets of three tubes with the desired 2-to-1 ratio of resin and hardener. The 

remaining specimens were cut from the 24-ply panel before inserting the resin and hardener. 

Testing and Post-mortem Examination

Initial Study 

Specimens were cut from the three 32-ply panels and were tested without healing agents. A total 

of 15 specimens were tested. DCB tests (fig.9) were conducted according to ASTM D5528 [12]. 

Figure 10 shows a typical load–displacement plot with four distinct load drops corresponding to 

pull out of the four rows of carbon Z-pins. Optical and scanning electron microscopy were used 

for fractographic examination of the fracture plane in the vicinity of the hollow glass tubes. 

Fractography indicated that the tubes did fracture as the delamination grew in the DCB specimens 

while the Z-pins pulled out (fig.11a). However, it was evident that some of the tubes were either 

crushed during the insertion process (fig.11b), or broke and then filled with prepreg resin that 

bled during the cure cycle (fig.11c). Examination of all 15 specimens indicated that only 21-29% 

of the hollow glass tubes had survived the Z-pin insertion process and the panel curing cycle. 

Hence, no attempt was made to fill these specimens with healing agent. 
3

Main Study

DCB tests were conducted according to ASTM D5528 [12]. Tests were run in a 5-kip hydraulic 

load frame in displacement control at a rate of 0.04 in/min (1 mm/min). Load was monitored via a 

100 lbf (0.44 kN) capacity load cell mounted in series with the 5-kip (22.4 kN) load cell. During 

the test, delamination growth was observed on the specimen edges using a pair of traveling video 

cameras. Digital video images were saved periodically using a laptop computer that also captured 

the load and displacement associated with each saved video frame. The first three specimens 

tested (3A, 2A, and 3B) were from the initial group of six specimens that were filled with resin 

and hardener, in the 2-to-1 ratio prescribed, and sealed with rubber adhesive before being cut 

from the panel as described earlier.

The first DCB coupon cut from the 24-ply panel (specimen 3A) was loaded until delamination 

grew past all four rows of tubes (fig.12). Two digital cameras recorded the progression of 

delamination on the two specimen edges during the test (fig.13) and the load displacement trace 

was recorded and plotted (fig.14). The specimen was unloaded, then clamped shut for 24 hours. 

The specimen was reloaded to determine if the adhesive had released from the tubes and healed 

the crack plane. The first reloading load-displacement curve followed the original unloading 

curve up to the load where unloading began in the initial test, indicating no healing had occurred

(fig.14). Hence, either the resin did not flow out of the tubes once the delamination had passed, or 

the volume of the resin and hardener in the sealed tubes was not sufficient for adequate mixing 

and healing of the delamination fracture plane. The specimen was then reloaded a second time to 

grow the delamination to separate the crack planes for inspection. 

The second DCB coupon cut from the 24-ply panel (specimen 2A) was loaded until delamination 

grew past two rows of tubes. The specimen was unloaded, then clamped shut for 24 hours. The 

specimen was reloaded to determine if healing had occurred. The reloading load-displacement 

curve followed the original unloading curve up to the load where unloading began in the initial 

test, indicating no healing had occurred (fig.15). Hence, either the resin did not flow out of the 

tubes once the delamination had passed, or the volume of the resin and hardener in the sealed 

tubes was not sufficient for adequate mixing and healing of the delamination fracture plane. A 

wedge was inserted between the DCB arms before unloading. The sealing resin and hardener 

were mixed in the prescribed 2-to-1 ratio and injected directly into the crack plane with a 

hypodermic needle (fig.16). The DCB arms were clamped shut for 4 days. The specimen was 

then reloaded a second time to determine if the cured resin and hardener recovered the original 

toughness. The second reloading load-displacement plot followed the slope of the original test 

matching the original stiffness, and delamination began at approximately 80% of the original 

load, indicating that healing did occur (fig.15). Hence, the premixed healing resin bonded well 

with the 8552 base resin along the fracture plane once both the resin and hardener were mixed in 

the correct proportions and manually placed in the needed area.

The third DCB coupon cut from the 24-ply panel (specimen 3B) was loaded until delamination 

grew past all four rows of tubes, unloaded, then clamped shut for 24 hours. The unloading curve 

was not plotted because a wedge was inserted between the DCB arms before unloading to allow 

the healing resin and hardener opportunity to mix and fill the crack plane. The specimen was 

reloaded to determine if the healing resin and hardener had indeed released from the tubes and 

healed the crack plane. The first reloading load-displacement curve had a significantly lower 

slope than the initial loading curve, following what may have been the original unloading curve, 

up to the load where unloading began in the initial test, indicating no healing had occurred

(fig.17). Next, the sealing resin and hardener were mixed in the prescribed 2-to-1 ratio and 

injected directly into the crack plane with a hypodermic needle. The DCB arms were clamped 
4

shut for 24 hours. The specimen was then reloaded a second time to determine if the cured resin 

and hardener recovered the original toughness. The second reloading load-displacement plot 

followed the slope of the original test matching the original stiffness, and delamination began at 

approximately 125% of the original load, indicating that healing did occur (fig.17). Hence, the 

premixed healing resin chosen bonded well with 8552 base resin along the fracture plane once 

both the resin and hardener were mixed in the correct proportions and manually placed in the 

needed area. The increased crack initiation load compared to the original test may simply reflect 

the thicker bond line of the sealed delamination due to the inability to completely close the 

original crack grown through four rows of tubes and pins.

The remaining specimens tested were cut from the panel before any resin was injected into the 

tubes. The fourth DCB coupon cut from the 24-ply panel (specimen 11B) was initially tested 

without adhesive in the glass tubes. The specimen was loaded until delamination grew past the 

first two rows of tubes, then unloaded (fig.18). A wedge was inserted between the DCB arms, and 

the dye-enhanced healing resin and hardener were premixed in the prescribed 2-to-1 ratio and 

injected into the glass tubes with a hypodermic needle (fig.19). Ultraviolet light image of the 

specimen surface indicated that the healing resin was injected into a majority of the tubes, and in 

addition, covered the 8552 prepreg resin rich areas around the tubes and z-pins (fig.20). The DCB 

arms were clamped shut for 48 hours. The specimen was then reloaded to determine if the cured 

resin and hardener recovered the original toughness (fig.21). The reloading load-displacement 

plot followed the slope of the original test, matching the original stiffness. Delamination began at 

approximately 110% of the original load, indicating that healing did occur (fig.18). Hence, the 

self-healing resin chosen was clearly bonding to the fracture plane once both the resin and 

hardener were mixed in the correct proportions and manually place in the needed area via the 

glass tubes. The increased crack initiation load compared to the original test may simply reflect 

the thicker bond line of the sealed delamination due to the inability to completely close the 

original crack grown through two rows of tubes and pins. Loading was continued in an attempt to 

grow the delamination past the last two rows of tubes. Observations of the specimen edges during 

the test showed evidence of secondary branch delamination planes forming (fig.22). Nearly twice 

as much load, compared to the initial loading, was required to extend the delamination past the 

last two rows of carbon Z-pins. At this point the specimen failed completely. Post-mortem 

examination of the fracture surface indicated the healing resin had also adhered to the previously 

pulled out Z-pins (fig.23). This was most likely a result of the pre-mixed resin filling the cracked 

resin rich areas around the tubes and z-pins (fig.20). Hence, repeated loading had to overcome not 

only the sealed fracture plane, but the additional tractions necessary to pull out the Z-pins a 

second time as well. 

The fifth DCB coupon cut from the 24-ply panel (specimen 7B) was initially tested without 

adhesive in the glass tubes. The specimen was loaded until delamination grew past the first two 

rows of tubes, and was then unloaded (fig.24). A wedge was inserted between the DCB arms and 

the dye-enhanced healing resin and hardener were injected in-situ into the glass tubes separately 

using a hypodermic needle in an alternating pattern in each row, similar to that shown in figure 8. 

The DCB arms were clamped shut for 48 hours. The specimen was then reloaded to determine if 

the cured resin and hardener recovered the original toughness. The end of the specimen was 

clamped just beyond the fourth row of Z-pins to prevent complete separation of the DCB 

specimen, and the delamination was grown through all four rows of glass tubes. The reloading 

load-displacement plot followed the slope of the original unloading curve up to the end of the first 

two rows of tubes, indicating that no healing had occurred in the first two rows (fig.24). Hence, 

there was insufficient resin flow, mixing, and/or crack opening for healing to occur at this point. 

The specimen was held at the maximum load and the additional resin and hardener were injected 

in-situ using a hypodermic needle to mimic the additional resin supply available had a secondary 
5

reservoir of resin and hardener been attached to the tubes. Individual droplets of resin and 

hardener were observed inside the opened delamination plane at the specimen centerline (fig. 25). 

The specimen was unloaded and monitored via the traveling video cameras. Movement of the 

resin and hardener in the tubes was observed, filling the delamination plane as unloading 

occurred. Some resin was clearly visible on the edge once the specimen was completely unloaded 

and clamped (fig.26). The DCB arms were clamped shut for 48 hours. The specimen was then 

reloaded for a second time to determine if the in-situ injected healing resin and hardener cured 

and recovered the original toughness. The second reloading load-displacement plot followed the 

slope of the loading portion of the first reloading curve, indicating that healing may have 

occurred, at least in the vicinity of last two rows of tubes (fig. 27). Hence, in-situ injection of 

resin and hardener directly into glass tubes performed at maximum load after initial fracture

resulted in partial healing of the fracture plane. However, the maximum load never reached the 

level of the initial test, or first reloading test, before the specimen fractured into two pieces. 

Furthermore, during the test there was some evidence of uncured resin leaking from the tubes 

(fig.28). Ultraviolet images of the fracture surface indicated the presence of resin over much, but 

not all, of the delamination plane (fig.29).

For the sixth DCB coupon cut from the 24-ply panel (specimen 10B), the dye enhanced sealing 

resin and hardener were inserted separately in the glass tubes using a hypodermic needle in an 

alternating pattern in each row as done on the previous specimen. The specimen was loaded until 

delamination grew past all four rows of tubes, and was then unloaded (fig.30). The DCB arms 

were clamped shut for 48 hours. The specimen was then reloaded to determine if the cured resin 

and hardener recovered the original toughness. The reloading load-displacement plot followed the 

slope of the original unloading curve, indicating that no healing had occurred (fig.30). Hence, 

there was insufficient resin flow, mixing, and/or crack opening for healing to occur at this point. 

The specimen was held at the maximum load and the additional resin and hardener were inserted 

in-situ using a hypodermic needle to mimic the additional resin supply available had a secondary 

reservoir of resin and hardener been attached to the tubes. Some resin was visible on the edge 

once the specimen was completely unloaded and clamped (fig.31). The DCB arms were clamped 

shut for 48 hours. The specimen was then reloaded for a second time to determine if the in-situ 

injected resin and hardener reacted and recovered the original toughness. During the test there 

was some evidence of uncured resin leaking from the tubes (fig.32). The second reloading loaddisplacement plot had a slope in between the initial loading and the first reloading curve, 

indicating that some healing may have occurred (fig.33). Hence, in-situ injection of resin and 

hardener directly into glass tubes performed at maximum load after initial fracture resulted in 

partial healing of the fracture plane. In addition, the maximum load exceeded the level of the 

initial loading test, and nearly recovered the maximum load observed during the first reloading 

test. The specimen experienced significantly higher displacements before it eventually fractured 

into two pieces. Ultraviolet images of the fracture surface indicated the presence of resin over 

much, but not all, of the delamination plane (fig.34).

Results and Discussion

For the initial 32-ply panels, good bonding was achieved between the 8552 base resin and the 

glass tubes. During DCB tests, the carbon pins pulled out and glass pins fractured as the 

delamination progressed. However, microscopic examination indicated that the majority of glass 

tubes had cured resin inside from the manufacturing process. Examination of the fracture plane 

indicated glass tube survival rates of only 21-29% for the 15 specimens produced from the three 

panels via direct insertion of pins and tubes in the preform.
6

For all specimens tested from the 24-ply panel, manufactured via direct insertion of pins followed 

by pin removal and manual insertion of glass tubes, good bonding was also achieved between the 

8552 base resin and the glass tubes with nearly a 100% survival rate for the glass tubes. However, 

this tube insertion process was labor intensive and would require automation for practical 

application. During the DCB tests, the carbon pins pulled out and the glass pins fractured as the 

delamination progressed. No healing was observed for tests where the unmixed resin and 

hardener were initially placed in sealed tubes with limited material available to heal the crack 

plane. Healing did occur for tests where the resin and hardener were premixed in the 2 to 1 ratio 

prescribed and injected directly into the crack plane or injected in-situ through the glass tubes and 

allowed to drain into the crack plane. Hence, the self-healing resin system chosen bonded well 

with the 8552 base resin in the composite along the fracture plane. In one case, premixed resin 

may have filled the cracked resin-rich regions near tube insertion locations allowing healing agent 

to attach to pulled out Z-pins, indicating that additional healing may be possible via coating of 

pulled out Z-pins. In-situ injection of resin and hardener directly into glass tubes, in a staggered 

pattern to allow for 2 to 1 ratio mixing, resulted in partial healing of the fracture plane, but only if 

the injection was performed while the specimen was held at maximum load after initial fracture.

This preliminary study indicated that there is some potential for healing delamination via resin 

and hardener delivered through a through-thickness network of glass tubes, but only if the tubes 

are connected to a reservoir where additional material may be injected as needed. Furthermore, 

maximum effectiveness may only be achieved if the crack plane can be held open long enough 

for the healing material to flow and mix in the proportions needed prior to closing. A method for 

pumping resin from an attached reservoir may also be needed, in addition to capillary action, for 

efficient resin flow and mixing. Furthermore, additional recovery of strength may be possible if a 

technique was available for applying self-healing material directly to pulled out Z-pins.

References

[1] Childress, J.J., and Freitas, G., “Z-direction Pinning of Composite Laminates for Increased 

Survivability,” Proceedings of the AIAA Aerospace Design Conference, Irvine, California, USA, February 

1992, Paper 92-1099.

[2] Freitas, G., Magee, C., Dardsinski, P., and Fusco, T., “Fiber Insertion Process for Improved Damage 

Tolerance in Aircraft Laminates,” Journal of Advanced Materials, Vol. 24, July,1994, pp. 36-43.

[3] Ratcliffe, J.G., and O’Brien, T.K., “Discrete Spring Model for Predicting Delamination Growth in Z

Fiber Reinforced DCB Specimens,” NASA Technical Memorandum 2004-213019.

[4] Robinson, P., and Das, S., “Mode I DCB Testing of Z-Fiber Reinforced Laminates: A

Simple Model for the Investigation of Data Reduction Strategies,” Engineering Fracture

Mechanics, Vol. 71, 2004, pp. 345-364.

[5] White, S.R., Sottos, N.R., Geubelle, P.H., Moore, J.S., Kessler, M.R., Sriram, S.R., Brown, E.N., and

Viswanathan, S., “Autonomic Healing of Polymer Composites,” Nature 409, 2001, pp.794-797.

[6] O’Brien, T.K. and White S.R., “Assessment of Composite Delamination Self-healing via Microencapsulation,” Proceedings of 23rd Annual American Society for Composites Technical Conference, 

Memphis, TN, Sept. 2008, paper #181.

[7] O’Brien, T.K., “Assessment of Composite Delamination Self-healing Under Cyclic Loading,”

Proceedings of the 17th International Conference on Composite Materials (ICCM-17), Edinburgh, Scotland, 

July 2009, paper # 28:B5:3.

[8] Imperiale, V. and Bond, I.P., “A Novel Self-healing Agent (SHA) for Autonomous Healing in FRPs for 

Aerospace Applications,” Proceedings of the 49th AIAA/ASME/ASCE/AHS/ASC Structures, Structural 

Dynamics and Materials Conference, Schaumburg, IL, USA, 2008.

[9] Williams, G.J., Bond, I.P., and Trask, R.S., “Compression after impact assessment of self-healing 

CFRP,” Composites Part A, 40 (9), 2009, pp. 1399-1406. 

[10] Bond, I.P., Williams, G.J., and Trask, R.S., “Self-healing CFRP for Aerospace Applications,”

Proceedings of the 16th International Conference on Composite Materials (ICCM16), Kyoto, Japan, 2007.
7

[11] Crosby, B.J., Unsworth, J., and Rost, F.W.D., “Evaluation of fluorescent dyes for epoxy impregnation 

of porous ceramics,” Journal of Microscopy-Oxford, Vol. 181, 1996, pp. 61-67.

[12] ASTM Standard D5528-01, “Mode I Interlaminar Fracture Toughness of Unidirectional FiberReinforced Polymer Matrix Composites,” in: ASTM Annual Book of Standards, Vol. 15.03, ASTM, 2008.

Acknowledgements: 

The first author was supported by NASA Langley Research Center under the Thompson Fellowship 

program while conducting this research.

The fluorescent dyes were generously supplied by Buckeye Color and Chemical, LLC, of Dover, OH.
8

Figures

Fig. 1. Z-pin insertion via ultrasonic hammer

Fig. 2. Z-pin preform with hollow glass tubes
9

Fig. 3. Uncured 24-ply laminate set up in press with aluminum spacer plates 
10

Fig. 4. 24-ply composite panel with inserted Z-pins and hollow glass tubes
11

Fig. 5. Self-healing resin and hardener with fluorescent dyes. 

Fig. 6. Rubber cement seals tube ends
12

Fig. 7. Diamond saw cutting of 24-ply panel

Fig. 8. Illustration of resin and hardener injection pattern on X-ray image of a 24-ply DCB 

specimen containing inserted Z-pins and hollow glass tubes
13

Fig. 9. DCB test of 32-ply specimen

Fig. 10. Typical load-displacement plot for 32-ply laminate DCB test
14

(a) Broken hollow tube

(b) Crushed tube

(b) Crushed tube

(c) Broken tube filled with resin

Fig. 11. Scanning electron and optical microscopy images of fracture plane of 32-ply DCB 

specimens
15

Fig. 12. DCB test of 24-ply specimen 3A showing delamination growing past 4 rows of glass 

tubes

Fig. 13. Video images of delamination growth on edges of 24-ply DCB specimen
16

Fig. 14. Load-displacement plots for first 24-ply DCB test, specimen 3A
17

Fig. 15. Load-displacement plots for second 24-ply DCB test, specimen 2A

Fig. 16. Injection of premixed resin, hardener and dye into fracture plane
18

Fig. 17. Load-displacement plots for third 24-ply DCB test, specimen 3B
19

Fig. 18. Load-displacement plots for fourth 24-ply DCB test, specimen 11B

Fig. 19. Injection of premixed resin, hardener and dye into glass tubes
20

Fig. 20. Ultraviolet surface image of specimen 11B 

Fig. 21. DCB reloading test showing healing agent in glass tubes
21

Fig. 22. Formation of secondary branch delaminations

Fig. 23. Fracture surface of specimen 11B indicating the presence of self-healing resin 

on fracture plane and carbon Z-pins
22

Fig. 24. Initial and first reloading load-displacement plots for specimen 7B 

Fig. 25. In-situ injection of resin and hardener in specimen 7B showing droplets in 

delamination plane
23

Fig. 26. Sealing resin visible on edge of specimen 7B

Fig. 27. Load-displacement plots for specimen 7B
24

Fig. 28. Second reloading DCB test of Specimen 7B showing resin leakage

Fig. 29. Ultraviolet light image of fracture plane for specimen 7B
25

Fig. 30. Initial and first reloading load-displacement plots for specimen 10B 

Fig. 31. Sealing resin visible on edge of specimen 10B
26

Fig. 32. Second reloading DCB test of Specimen 10B

Fig. 33. Load-displacement plots for specimen 10B
27

Fig. 34. Ultraviolet light image of fracture plane for specimen 10B
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2. REPORT TYPE 

Technical Memorandum

 4. TITLE AND SUBTITLE

Combining Through-Thickness Reinforcement and Self-Healing for 

Improved Damage Tolerance and Durability of Composites 

5a. CONTRACT NUMBER

 6. AUTHOR(S)

O'Brien, T. Kevin; Czabaj, Michael W.; Hinkley, Jeffrey A.; Tsampas, 

Spiros; Greenhalgh, Emile S.; McCombe, Gregory; Bond, Ian P.; Trask, 

Richard

 7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES)

NASA Langley Research Center

Hampton, VA 23681-2199

 9. SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESS(ES)

National Aeronautics and Space Administration

Washington, DC 20546-0001

 8. PERFORMING ORGANIZATION

 REPORT NUMBER

L-20252

10. SPONSOR/MONITOR'S ACRONYM(S)

NASA

13. SUPPLEMENTARY NOTES

12. DISTRIBUTION/AVAILABILITY STATEMENT

Unclassified - Unlimited

Subject Category 24

Availability: NASA CASI (443) 757-5802

19a. NAME OF RESPONSIBLE PERSON

STI Help Desk (email: help@sti.nasa.gov)

14. ABSTRACT

A study was undertaken to develop a prototype method for adding through-thickness hollow glass tubes infused with uncured resin and 

hardener in a carbon Z-pin through-thickness reinforcement field embedded in a composite laminate. Two types of tube insertion techniques 

were attempted in an effort to ensure the glass tubes survived the panel manufacturing process. A self-healing resin was chosen with a very 

low viscosity, two component, liquid epoxy resin system designed to be mixed at a 2-to-1 ratio of epoxy to hardener. IM7/8552 carbon 

epoxy double cantilever beam (DCB) specimens were cut from the hybrid Z-pin and glass tube reinforced panels and tested. In-situ injection 

of resin and hardener directly into glass tubes, in a staggered pattern to allow for 2-to-1 ratio mixing, resulted in partial healing of the 

fracture plane, but only if the injection was performed while the specimen was held at maximum load after initial fracture. Hence, there is 

some potential for healing delamination via resin and hardener delivered through a network of through-thickness glass tubes, but only if the 

tubes are connected to a reservoir where additional material may be injected as needed. 

15. SUBJECT TERMS

Delamination; Self-Healing; Z-PIN

18. NUMBER

 OF 

 PAGES

32

19b. TELEPHONE NUMBER (Include area code)

(443) 757-5802

a. REPORT

U

c. THIS PAGE

U

b. ABSTRACT

U

17. LIMITATION OF 

 ABSTRACT

UU

Prescribed by ANSI Std. Z39.18

Standard Form 298 (Rev. 8-98)

3. DATES COVERED (From - To)

5b. GRANT NUMBER

5c. PROGRAM ELEMENT NUMBER

5d. PROJECT NUMBER

5e. TASK NUMBER

5f. WORK UNIT NUMBER

794072.02.07.03.03

11. SPONSOR/MONITOR'S REPORT

 NUMBER(S)

NASA/TM-2013-217988

16. SECURITY CLASSIFICATION OF:

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PLEASE DO NOT RETURN YOUR FORM TO THE ABOVE ADDRESS.

1. REPORT DATE (DD-MM-YYYY)

01- 05 - 2013