Sensitivity is determined because the bolt holes are covered by flat washers, and in-situ detection is only possible if the cracks are beyond the washer. Macroscopically detectable cracks are not allowed in the use of helicopter moving parts. If the initial crack length of the tail blade joint is set to a0=5.18mm (equal to a0=1.0mm from the edge of the gasket), it is equivalent to allowing the tail blade to be fixed. The length crack flight, in order to ensure safety, the damage rate is set to R = 10-7.

According to the formula of the material and the damage tolerance spectrum of the tail blade, the crack propagation life Lt at different failure rates can be determined, which is the relationship between the crack propagation life and the failure rate. The two curves in the figure are calculated from the edge of the hole, and the initial crack length a0 = 1.25 mm and a0 = 5.18 mm (a0 = 5.18 mm from the edge of the hole, which corresponds to a0 = 1.0 mm from the edge of the gasket).

Crack propagation life Lt/t crack propagation life and failure rate curve If considering the crack formation life, the crack propagation life from the initial crack propagation to the complete structural failure is also considered. The failure rate of the initial crack formation life of the component is Rs, and the failure rate of the component from the initial crack to the complete fracture is R. As two independent events, if both occur simultaneously, the component is considered to be broken or failed. The damage rate R is: R = RsR For the helicopter moving parts, it is required to control the damage rate within R = 10-6. It is safe to set the tail blade failure rate of the initial crack of 5.18 mm to R=10-7.

According to the analysis, a crack of 1.0 mm beyond the gasket is allowed. Therefore, the area of ​​the web around the gasket can be detected to determine if the bolt hole is a dangerous defect. If the crack exceeds the gasket and the eddy current detecting probe is close, the eddy current generated in the crack region and the eddy current generated in the intact region are different, and the change in the voltage and impedance of the probe coil is also different. In the flaw detection process, as long as we put this When the difference is detected, it is possible to judge the presence or absence of the defect.

The eddy current flaw detector not only ensures the reliability of the test but also considers the practicability. The WT-5 type eddy current flaw detector is used. Probe Selection When using an unshielded probe to detect the area of ​​the web around the gasket, the gasket must interfere with the probe. To avoid interference, a shielded pen probe is used.

The test block is made so that the test block state is consistent with the web bolt hole, a bolt is removed from the scrapped tail blade, and a radial crack is processed in the bolt hole by wire cutting. The crack exceeds the gasket by 1.0 mm, and the outer surface The paint and internal surface treatment conditions remain unchanged.

The test probe is placed on the test block for adjustment. Place the probe in the intact area around the washer of the test block and adjust the “Zero” knob so that the meter pointer points to the “0” position. Then place the probe on the natural crack on the test block and adjust the “sensitivity” knob so that the indication value is about 50% of the full scale. At this time, the instrument is calibrated.

Conclusion It is feasible to use the eddy current testing method to detect the tail blade of this model. This method can be extended to the inspection of other helicopter tail blade joint webs and rotor joint webs.

PCR Tubes

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More info about PCR Tubes:

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PCR tubes are small tubes made of high-quality virgin polypropylene with a conical bottom. They have uniform thin walls to facilitate efficient heat transfer to the sample. These tubes are autoclavable and work well with most thermal cyclers.

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The most common application of PCR tubes includes various molecular biology biochemistry experiments requiring real-time PCR (Polymerase Chain Reaction). As these tubes have ultra-thin walls, they are perfect for accurate and steady thermal transfer in an array of thermocyclers. Our thin-wall PCR tubes meet the protocols required for PCR, qPCR, reverse transcriptions, and a variety of other applications.

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