Public reporting burden for this collection of information is estimated to average 1 hour per response, including the time for reviewing instruction, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing the collection of information. Send comments regarding this burden estimate or any other aspect of this collection of information, including suggestions for reducing this burden, to FUNDING NUMBERS PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES)Naval Postgraduate School Monterey, CA 93943-5000 PERFORMING ORGANIZATION REPORT NUMBER SPONSORING /MONITORING AGENCY NAME(S) AND ADDRESS(ES)N 12b. DISTRIBUTION CODE ABSTRACT (maximum 200 words)Strengthening of composite joints is a topic of recent research. The benefits of using locally applied carbon nanotubes to reinforce a carbon fiber composite joint were studied. The effect of carbon nanotubes on enhancing the fracture toughness and joint interface strength was investigated by performing Mode I, Mode II, and Mixed Mode I/Mode II fracture with and without carbon nanotubes applied locally at the joint interface. Furthermore, the effects of seawater absorption on Mode II fracture were investigated. Finally, an optimization of carbon nanotube concentration was performed. During the study, the image correlation technique was used to examine the fracture mechanisms altered by the introduction of carbon nanotubes. The experimental study showed that carbon nanotubes can increase the fracture toughness of the composite interface significantly, especially for Mode II, including a physical change in the fracture mechanism. NUMBER OF PAGES 70 SUBJECT TERMS ABSTRACTStrengthening of composite joints is a topic of recent research. The benefits of using locally applied carbon nanotubes to reinforce a carbon fiber composite joint were studied. The effect of carbon nanotubes on enhancing the fracture toughness and joint interface strength was investigated by performing Mode I, Mode II, and Mixed Mode

Public reporting burden for this collection of information is estimated to average 1 hour per response, including the time for reviewing instruction, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing the collection of information. Send comments regarding this burden estimate or any other aspect of this collection of information, including suggestions for reducing this burden, to FUNDING NUMBERS PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES)Naval Postgraduate School Monterey, CA 93943-5000 PERFORMING ORGANIZATION REPORT NUMBER SPONSORING /MONITORING AGENCY NAME(S) AND ADDRESS(ES)N 12b. DISTRIBUTION CODE ABSTRACT (maximum 200 words)Strengthening of composite joints is a topic of recent research. The benefits of using locally applied carbon nanotubes to reinforce a carbon fiber composite joint were studied. The effect of carbon nanotubes on enhancing the fracture toughness and joint interface strength was investigated by performing Mode I, Mode II, and Mixed Mode I/Mode II fracture with and without carbon nanotubes applied locally at the joint interface. Furthermore, the effects of seawater absorption on Mode II fracture were investigated. Finally, an optimization of carbon nanotube concentration was performed. During the study, the image correlation technique was used to examine the fracture mechanisms altered by the introduction of carbon nanotubes. The experimental study showed that carbon nanotubes can increase the fracture toughness of the composite interface significantly, especially for Mode II, including a physical change in the fracture mechanism. NUMBER OF PAGES 70 SUBJECT TERMS ABSTRACTStrengthening of composite joints is a topic of recent research. The benefits of using locally applied carbon nanotubes to reinforce a carbon fiber composite joint were studied. The effect of carbon nanotubes on enhancing the fracture toughness and joint interface strength was investigated by performing Mode I, Mode II, and Mixed Mode

Fracture toughness tests were conducted for carbon composite scarf joints with and without carbon nanotube (CNT) reinforcement in order to study the effect of CNT on enhancing the fracture toughness of the scarf joint interface. Both mode I (i.e., opening mode) and mode II (i.e., shear mode) fracture tests were undertaken with and without CNT applied locally at the joint interface. During the study, the image correlation technique was used to examine the fracture mechanisms altered by the introduction of CNT. The experimental study showed that CNT increased the fracture toughness of the composite interface significantly, especially for the mode II fracture, with altering the fracture mechanism. On the other hand, there was no significant change on mode I fracture caused by CNT reinforcement. The enhancement of mode II fracture toughness was considered to result from the mechanical interlocking between polymers and CNT at the scarf joint interface.