In-service bolt crack detection-3D TFM  imaging technique

No need to move the probe, enabling real-time 3D imaging of the entire bolt. And it can be rotated for observation, making the detection results more intuitive. The system provides defect analysis and storage functions, enabling accurate positioning and quantitative measurement of internal defects in the detected bolt.

 

Bolt is a type of fastener and a widely used mechanical basic component, mainly used for fastening and sealing connections. Due to complex stress, corrosion, temperature, and other factors, the connection parts of their threads are prone to fatigue cracks, which can cause bolt fracture or failure.

 

Although surface methods such as magnetic powder, penetration, and eddy current can be used to detect cracks and defects that occur during use after bolt disassembly, considering factors such as testing cycle and cost, it is usually necessary to detect whether cracks have occurred in the in-service state without disassembly. On the premise of not dismantling the bolts, phased array ultrasonic testing technology can be used to detect fatigue cracks generated in the threaded parts of the bolts.

 

I.Conventional phased array ultrasonic testing(PAUT)

The conventional PAUT technology uses the line scan or sector scan of the phased array to cover the threaded area of the bolt, and visualizes the detection results inside the bolt for crack detection. Compared with conventional ultrasonic testing technology, phased array ultrasonic testing technology has the following advantages:

1.Multiple views can display the detection results of defects, which can effectively distinguish between defect waves and structural waves, solving the problem of difficult identification of defect waves in bolt testing.

2.Can be applied to the detection of complex geometric structural components.

3.Phased array ultrasound technology has the function of multi angle adjustable focusing sound beam, which can cover the detection of defect areas, improve detection sensitivity and signal-to-noise ratio of images, and enhance defect recognition ability.

 

(Schematic diagram of PAUT longitudinal wave fan scan)

(PAUT spectrum of a certain bolt on site)

 

II.Total Focusing Method (TFM) Imaging Technique

The TFM is a core algorithm in ultrasonic phased array technology, which improves the imaging quality and upgrades the imaging method based on the phased array system. The algorithm processes the data transmitted and received by all probes to achieve comprehensive detection of all structures inside the detected object. The core idea is to focus the ultrasonic signal in two-dimensional or three-dimensional space in all directions, thus achieving the complete structure characterization and detection of the detected object.

 

Advantages of 3D TFM imaging technique:

1. Collect defect information inside the detected workpiece from various spatial angles in three-dimensional space, which enables more comprehensive information collection, a clear view of internal defects in the bolt, intuitive and reliable imaging, and avoids missed defects.

2. No need to move the probe, enabling real-time 3D imaging of the entire bolt. And it can be rotated for observation, making the detection results more intuitive. The system provides defect analysis and storage functions, enabling accurate positioning and quantitative measurement of internal defects in the detected bolt.

3.The detection time for one bolt is less than 2 seconds, which is highly efficient.

        (a)Artificial defects and 3D TFM imaging                (b)Crack defect and 3D TFM imaging