Jikai Du

Phased Array Ultrasonic Technique Parametric Evaluation for Composite Materials

A series of ultrasonic elements arranged in a phased array transducer can provide the capability to activate each element separately but in a programmed sequence. This will help the acoustic signal to be generated at desired focusing distances and anticipated angles for specific materials and structures. In case of composite material inspection, this characteristic of the phased array method can improve the undesirable effects of the high attenuation and anisotropic structure of composite materials on response signals. In this study different phased array probes and wedges which are commercially available were evaluated for their response signals’ characteristics. First, the capability and resolution of bulk wave generation were studied for each set of probe and wedge, and the response signals were compared to that of the conventional single element ultrasonic transducers for different thicknesses composite plates. Then the resolution of the response signals and their sensitivity to defect size were evaluated and compared to the single element transducers as well. Next, each phased array probe and wedge set was used to generate plate waves in aluminum plates based on plate wave propagation theory, probe and wedge physical properties and the definition of delay law. Results show a general improvement in response signals’ strength and resolution for phased array method in comparison to the single element transducers. Also some plate wave modes could be generated with optimized signal generation parameters in phased array system.Copyright

Ultrasonic phased array techniques for composite material evaluation

The increasing rate of composite materials usage in the industries and researches implies finding the suitable method for testing and evaluation of composite materials. The composites are susceptible to flaws during production and the inspection costs suggest the use of NDT methods. Non-destructive testing is an appropriate method to detect the flaws and anomalies in the materials, however, due to an-isotropic structure of the composite materials, it is required to modify the techniques to find the most appropriate and accurate process for detecting flaws and anomalies in composite materials. The objective of this paper is to evaluate the feasibility and accuracy of nondestructive testing methods with emphasis on ultrasonic phased array technique for the integrity and structural evaluation of composite materials. In this approach three different composite samples were used for testing including one carbon fiber and two glass fiber samples. ultrasound phased array technique evaluated to perform the testing...

Interface Integrity Evaluation of Explosively Welded Metallic Structures

Explosively bonded tubes have been applied in high pressure and high temperature environments, such structures are usually consisting of dissimilar metals which are very difficult to be welded together by other conventional welding methods. In this study, various experimental techniques were used for the evaluation of interface integrity between steel major tube and tantalum donor tube. First, X-ray diffraction technique was used to profile the residual stress levels in the tantalum donor tube before bonding and steel major tube after bonding, especially the hoop stress level which is critical to quality control. Also, other experimental techniques including digital microscopy for interface geometrical features, X-ray fluorescence spectroscopy for interface compositions, and nano-hardness testing for materials strength at micro/nano scale were further applied to explain bonding mechanisms and to quantify bonding interface conditions. Then nondestructive ultrasound C-scan technique was used to create acoustic images of the bonding interfaces and the results showed that the technique has the potential to find weak interface and to further quantify good and poor bonds. Finally, destructive testing techniques were used to measure the interface shear and tensile strength and to study the interface failure mechanisms, and the results agree well with other experimental techniques.Copyright

Ultrasound Characterization of IM7/PEEK Composite Materials

IM7/PEEK composite materials may experience large mechanical and thermal stresses during service, and their failure mechanisms can be complex and have various modes. In this study, IM7/PEEK specimens for interlaminar shear strength testing were evaluated by both nondestructive ultrasound method and standard destructive test. First, IM7/PEEK specimens were fabricated under various processing parameters including roller speed, torch temperature, roller temperature, compaction level, N2 flow rate, and material tension level. Then ultrasound longitudinal wave velocity that is normal to fiber direction was evaluated and the influence of measuring locations and ultrasound frequencies from 0.5 MHz to 10.0 MHz were studied. Experimental results showed that 5.0 MHz is the most sensitive frequency to fabrication conditions and that ultrasound velocity can be related to some processing parameters such as materials tension, N2 flow rate and temperature. Finally, interlaminar shear strength experiments were carried out by standard short beam bending destructive tests. The relationship between ultrasound velocity and standard destructive tests were analyzed and the potential of ultrasound velocity for interlaminar shear strength evaluation was discussed.Copyright

Acoustic Emission and Ultrasound Phased Array Technique for Composite Material Evaluation

The successful application of various acoustic evaluation techniques to composite materials and structures depends on the understanding of the acoustic wave propagation mechanisms. However, due to the anisotropic nature of composite materials, where the acoustic signal velocity and attenuation depend on its traveling direction, the correlation of the different material failure modes to the recorded acoustic signals, such as during of an acoustic emission (AE) inspection, is difficult to be defined. This issue becomes even more challenging for ultrasound phased array technique, where unlike a conventional ultrasound single element transducer, an ultrasound phased array of sensors will generate and receive acoustic energy at various desired directions and locations. Such heightened flexibility and sensitivity is essential for the complex shape of modern composite structures. In this paper, the influence of fiber orientation on AE signal was first studied. AE parameters such as counts, duration, energy, rise time and amplitude for aluminum and composite plate were analyzed in MS-Excel and results were compared to AE software. Acoustic velocities along various fiber directions were also theoretically studied and experimentally measured. Then ultrasound phased array technique and related parameters such as ultrasound beam angle and focusing, frequency and material attenuation factors were quantitatively analyzed, and the optimization and limitation of ultrasound phased array inspection procedure were summarized.Copyright