Ultrasonic inspection refers to some sort of nondestructive screening technique which inspects any work piece and resources by ultrasonic and the help of an ultrasonic designed detector. When these kinds of ultrasonic waves which are inside the materials to be inspected meet the defects, a part of the waves will mirror, then this receptor analyzes all the reflection waves thus finding out the present defects. All the present defects are detected precisely.
This method can also screen the placement and dimensions of defects within, or be used to find out the thickness of supplies. The benefits of this method are apparent. The penetrating capability of the technique is fantastic. And also, the flaw inspection sensitivity is large, especially for plane kind defects including, cracks, sandwich and different others.
Automated systems can either be squirter systems or submerged reflector plate systems. Squirter systems, the most frequently used in production, are usually large gantry systems with as much as a 7 axis scanning bridge. They are computer controlled to track the contour of the part and keep the transducers normal to the surface. They also index at the end of each scan pass.
The ultrasonic energy is converted to digital data and stored in a file. Imaging software allows scan displays in either shades of gray or color. Modern units are capable of scan speeds of up to 40 inch s-1 and some units can record through transmission and pulse echo data simultaneously, eliminating the need to scan the part twice.
As the ultrasonic beam passes through the composite, it is attenuated due to scattering, absorption and beam spreading. This loss or attenuation is usually expressed in decibels. Thicker laminates will attenuate more sound than thinner laminates. Though transmission ultrasonics is one of the two most common methods used to inspect fabricated composite laminates and assemblies.
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.
Laser heating at the surface causes a temperature increase and a resultant local expansion of the material. If the laser pulses are short (10-100 ns), the expansion will create a wave in the 1-10 MHz range. The receiving laser detects light scattered off the surface that is analyzed by a Fabry-Perot interferometer to extract the its signal. In this process, it is important to generate as much ultrasound as possible without causing heat damage to the composite surface.
Surface temperatures are normally restricted to a given temperature. An additional benefit of laser ultrasonic inspection is that the ultrasound propagates perpendicular to the surface somewhat independent of the laser angle of incidence. The transmitters and receivers can be off axis to normal at a specified angle without loss of performance. However, since the part must have a thin layer of resin on the surface for effective sound generation, resin starved or machined surfaces may limit the success of the technique.
This method can also screen the placement and dimensions of defects within, or be used to find out the thickness of supplies. The benefits of this method are apparent. The penetrating capability of the technique is fantastic. And also, the flaw inspection sensitivity is large, especially for plane kind defects including, cracks, sandwich and different others.
Automated systems can either be squirter systems or submerged reflector plate systems. Squirter systems, the most frequently used in production, are usually large gantry systems with as much as a 7 axis scanning bridge. They are computer controlled to track the contour of the part and keep the transducers normal to the surface. They also index at the end of each scan pass.
The ultrasonic energy is converted to digital data and stored in a file. Imaging software allows scan displays in either shades of gray or color. Modern units are capable of scan speeds of up to 40 inch s-1 and some units can record through transmission and pulse echo data simultaneously, eliminating the need to scan the part twice.
As the ultrasonic beam passes through the composite, it is attenuated due to scattering, absorption and beam spreading. This loss or attenuation is usually expressed in decibels. Thicker laminates will attenuate more sound than thinner laminates. Though transmission ultrasonics is one of the two most common methods used to inspect fabricated composite laminates and assemblies.
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.
Laser heating at the surface causes a temperature increase and a resultant local expansion of the material. If the laser pulses are short (10-100 ns), the expansion will create a wave in the 1-10 MHz range. The receiving laser detects light scattered off the surface that is analyzed by a Fabry-Perot interferometer to extract the its signal. In this process, it is important to generate as much ultrasound as possible without causing heat damage to the composite surface.
Surface temperatures are normally restricted to a given temperature. An additional benefit of laser ultrasonic inspection is that the ultrasound propagates perpendicular to the surface somewhat independent of the laser angle of incidence. The transmitters and receivers can be off axis to normal at a specified angle without loss of performance. However, since the part must have a thin layer of resin on the surface for effective sound generation, resin starved or machined surfaces may limit the success of the technique.
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