## 5 Conclusions  
Conventional (single-element) ultrasonic testing and phased array ultrasonic testing (PAUT) methods are evaluated for inspection of composite materials. The capability comparison tests for waves traveling through the composite materials indicate that thickness of up to 25 mm could be tested in both SEUT and PAUT methods; however, the stability of the signal parameters is higher in PAUT and detectable signal can be observed at lower gain values. The calculated velocity from the capability experimental part was 3.1 mm/us, which is close to the estimated and expected velocities in composite plates and was used to identify the flaw's location. From the sensitivity comparison experimental results, it can be seen that a 0.8 mm diameter hole can be detected as the minimum size by both SEUT and PAUT, but PAUT generally has a better signal regarding SNR. However, PAUT does not increase the sensitivity by a big factor, but because of lower noise and jitter and better signal characteristics it may be possible to find smaller defect sizes such as 0.7 or 0.6 mm with PAUT as well.  
Figure 11: Typical PAUT guided wave signal of flaw detection for CFRP sample.  
Figure 12: Change of signal amplitude over distance for CFRP samples.  
Guided waves can also be generated using phased array ultrasonic probes and wedges with lower frequencies. Experimental results show that the different size of flaw (0.8, 1, and 1.2 mm diameter holes) can be detected by means of generated guided waves with the PAUT method. While the determination of the exact location of the flaw is affected by the dispersion characteristics of the guided waves, PAUT is a promising technique for detecting the size and location of defects in CFRP and GFRP composite materials.  
Conceptualization, H.T. and A.A.H.; Methodology, H.T.; Formal Analysis, H.T.; Investigation, H.T. and A.A.H.; Data Curation, H.T.; Writing--Original Draft Preparation, H.T.; Writing--Review and Editing, A.A.H.; Visualization, H.T. and A.A.H.; Supervision, A.A.H.  
Research sponsored by the U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy, Advanced Manufacturing Office, under contract DE-AC05-00 OR22725 with UT-Battelle, LLC.  
A debt of gratitude is owed to OLYMPUS NDT technical support and sales team for all their contributions to provide required equipment, support, and information.  
The authors declare no conflict of interests. Notice of Copyright: This manuscript has been authored by UT-Battelle, LLC under Contract No. DE-AC05-00 OR22725 with the U.S. Department of Energy. The United States Government retains and the publisher, by accepting the article for publication, acknowledges that the United States Government retains a non-exclusive, paid-up, irrevocable, world-wide license to publish or reproduce the published form of this manuscript, or allow others to do so, for United States Government purposes. The Department of Energy will provide public access to these results of federally sponsored research in accordance with the DOE Public Access Plan. ([[http://energy.gov/downloads/doe-public-access-plan](http://energy.gov/downloads/doe-public-access-plan)]([http://energy.gov/downloads/doe-public-access-plan](http://energy.gov/downloads/doe-public-access-plan))).