Acoustic Emission Monitoring of Fatigue in 7010 Aluminum Alloys

摘要

The acoustic emission (AE) was monitored in testpieces of 7010 aluminium alloy containing growing fatigue cracks. Both high purity and commercial casts were studied in underaged, peak and overaged conditions, using tension-tension fatigue with R=0.1 and 0.5, at crack growth rates in the range 0.1 to 3 microns/cycle. The reduction of grip noise and discrimination of AE events with sources distant from the plane of the crack were achieved by careful design of testpiece geometry and clamping, and by the use of two broadband point transducers with calibrated response. Analysis of the load distributon at which AE events occurred at the crack plane showed that most events occurred near peak loading. However, the frequency of detected AE events was sometimes greatly reduced by adding oil to the crack, implying that crack face rubbing was one source of emission. The frequency of events remaining after the removal of rubbing signals was shown to be consistent with the size of the plastic zone at the crack tip, the rate of cack growth and the inclusion size/density distribution. It is estimated that the fracture of inclusions of area greater than 40 sq microns could be detected by the testing system.