Posts
Ultrasonic inspection by ultrasonic test equipment is the most valuable technique for aerospace composite material inspection. The two most prevalent fabrication defects in solid laminates are porosity and foreign objects. Porosity is detectable because it contains solid-air interfaces that transmit very little and reflect large amounts of sound. Inclusions, or foreign objects, are detectable if the acoustic impedance of the foreign object is sufficiently different than that of the composite material.
The technique operates on the principle of transmitted and reflected sound waves. An ultrasonic wave traveling through a composite laminate that encounters a defect will reflect some of the energy at the interface while the remainder of the energy passes through the porosity. The more severe the porosity, the greater the amount of reflected energy and the lesser it is transmitted through the defect.
The measurement and depth of the defects can also be determined. In addition, its screening pipe, the sole dependable program applied in the industry, is light in weights and thus transportable, and protected to function. This makes it easy to carry out the process in an automatic manner.
Flaws are detectable since they alter the amount of sound returned to the receiver. The test equipment conducts inspection in the frequency range of 1 to 30 MHz, although most composite material inspection is usually tested at 1 to 5 megahertz. High frequencies are more sensitive to small defects, while low frequencies or longer wavelengths can penetrate to greater depths.
There are also special units for cylindrical parts that contain turntables that rotate during the scanning operation. The output from these automated units is displayed as a C-scan, which is a planar map of the part, where light (white) areas indicate less sound attenuation and are of higher quality than darker areas (gray to black) that indicate more sound attenuation and are of lower quality. The darker the area, the more severe sound attenuation is and the poorer the quality of the part.
The transducers are placed close to the part surface (within an inch) and frequencies of 50 kHz to 5 MHz are employed. A relatively new inspection technology is laser ultrasonics. It provides essentially the same information as conventional inspection except that it is faster than conventional methods, especially for highly contoured parts. Two lasers are used. The first laser, generally a carbon dioxide laser, generates ultrasound in the part by causing thermoelastic expansion, while the second laser, normally a neodymium: yttrium-aluminum garnet laser, detects the sound signal as it returns to the top surface.
Through transmission is excellent at detecting porosity, unbonds, delaminations and some types of inclusions. However, this method cannot detect all types of foreign objects and it cannot detect the depth of any defects. Mylar film and nylon tapes are particularly difficult to detect with through transmission. Through transmission is usually conducted in water tank immersion systems or by using water squitter systems.
As other techniques cannot be relied on of detecting all types of foreign objects and the depth of defects, pulse echo ultrasonic inspection is frequently used in conjunction with through transmission ultrasonics to inspect parts. In the pulse echo method, the sound is transmitted and received by the same transducer. Thus, it is an excellent method when there is access to only one side of the part. The amplitude of a echo received from the back surface is reduced by the presence of defects in the structure.
The technique operates on the principle of transmitted and reflected sound waves. An ultrasonic wave traveling through a composite laminate that encounters a defect will reflect some of the energy at the interface while the remainder of the energy passes through the porosity. The more severe the porosity, the greater the amount of reflected energy and the lesser it is transmitted through the defect.
The measurement and depth of the defects can also be determined. In addition, its screening pipe, the sole dependable program applied in the industry, is light in weights and thus transportable, and protected to function. This makes it easy to carry out the process in an automatic manner.
Flaws are detectable since they alter the amount of sound returned to the receiver. The test equipment conducts inspection in the frequency range of 1 to 30 MHz, although most composite material inspection is usually tested at 1 to 5 megahertz. High frequencies are more sensitive to small defects, while low frequencies or longer wavelengths can penetrate to greater depths.
There are also special units for cylindrical parts that contain turntables that rotate during the scanning operation. The output from these automated units is displayed as a C-scan, which is a planar map of the part, where light (white) areas indicate less sound attenuation and are of higher quality than darker areas (gray to black) that indicate more sound attenuation and are of lower quality. The darker the area, the more severe sound attenuation is and the poorer the quality of the part.
The transducers are placed close to the part surface (within an inch) and frequencies of 50 kHz to 5 MHz are employed. A relatively new inspection technology is laser ultrasonics. It provides essentially the same information as conventional inspection except that it is faster than conventional methods, especially for highly contoured parts. Two lasers are used. The first laser, generally a carbon dioxide laser, generates ultrasound in the part by causing thermoelastic expansion, while the second laser, normally a neodymium: yttrium-aluminum garnet laser, detects the sound signal as it returns to the top surface.
Through transmission is excellent at detecting porosity, unbonds, delaminations and some types of inclusions. However, this method cannot detect all types of foreign objects and it cannot detect the depth of any defects. Mylar film and nylon tapes are particularly difficult to detect with through transmission. Through transmission is usually conducted in water tank immersion systems or by using water squitter systems.
As other techniques cannot be relied on of detecting all types of foreign objects and the depth of defects, pulse echo ultrasonic inspection is frequently used in conjunction with through transmission ultrasonics to inspect parts. In the pulse echo method, the sound is transmitted and received by the same transducer. Thus, it is an excellent method when there is access to only one side of the part. The amplitude of a echo received from the back surface is reduced by the presence of defects in the structure.
About the Author:
If you need top quality ultrasonic inspection services click this link to Nordstrom Testing Service. For info on NDE testing and GPR services, visit us at http://nordstromtesting.com today.
No comments:
Post a Comment