Acoustic Emission as Toll for Identifying the Drill

Acoustic Emission as Toll for Identifying the Drill Position in Fiber Reinforced Plastic and Aluminum Stack Dr. Uri Ben-Hanan, ORT Braude College, Karmiel, Israel Dr. Andrea Stoll, Fraunhofer IWU, Chemnitz, Germany Mr. Steffen Ihlenfeldt, Fraunhofer IWU, Chemnitz, Germany Mr. Markus Wabner, Fraunhofer IWU, Chemnitz, Germany June 2013

Talk Outline • About Acoustic Emission (AE) • Motivation • AE signal vs. force and moment • Characteristic behaviors of the AE signal • Algorithm for finding the drill position in a stack • Regular drill • Step drill • Results • Summary • Future work June 2013

Acoustic Emission (AE) is a class of phenomenon whereby transient elastic wave are generated by rapid release of energy from localized sources within the material. The elastic (AE) waves propagate inside a material and are detected by an AE sensor. Except for contactless sensors, AE sensors are directly attached on the surface. June 2013

Typical AE sensor • In the most cases, a piezoelectric element in a protective housing is applied. The sensors are exclusively based on the piezoelectric effect out of lead zirconate titanate (PZT). • PZT sensors provide the best combination of low cost, high sensitivity, ease of handling and selective frequency responses. • Although PZT sensors are not normally suited for broad-band detection in basic studies of AE waveform analysis, they are practically useful for most AE experiments and applications. June 2013

Typical measurement system June 2013

Acoustic Emission Figure 1. The definitions for acoustic-emission events. June 2013 Figure 2. A typical AE system setup.

Motivation Improving the holes properties while drilling in CFRP skin and formers or ribs made of aluminum/titanium June 2013

The experimental system Regular drill Step drill d 1=6 mm Kistler platform Kistler AE sensor d 1=5 mm d 2=7. 93 mm l 3=1. 5 mm 16. 8 mm CFRP plate June 2013 10 mm aluminum plate

The filtered AE signal • A median filter was applied on the AE signal. The filter was applied on a series of 50 samples. The sampling frequency was 5 KHz, the filter did down sampling to 100 Hz. June 2013

The Acoustic Emission (AE) and force signals, drilling from CFRP to Al with regular drill Drilling the Al Entering CFRP Exiting CFRP June 2013

The AE signal, drilling with step drill June 2013

Drilling from Al to CFRP with a step drill June 2013

The algorithm June 2013

Drilling from Al to CFRP with regular drill June 2013

Drilling from CFRP to Al with regular drill June 2013

Result of drilling from Al to CFRP with a step drill 5 mm step in Al 7. 93 mm step in CFRP June 2013 7. 93 mm step in Al Drill tip exit CFRP Drill tip in CFRP

Drilling from CFRP to Al with step drill Zone Average Minimum Maximum First 50 holes Total number of difference failures 1 -0. 01 -0. 48 0. 18 0 0 2 0. 14 0. 04 0. 39 0 0 4 -0. 27 -0. 86 -0. 03 0 13 5 0. 04 0 0. 47 4 19 7 0 -0. 78 0. 3 15 43 June 2013

Some more results • Effect of the distance of the AE sensor form the hole Sensor L 1 Hole D 1 L 2 Hole C 8 • The relation between the AE signal and delamination/fraying June 2013 workpiece

Summary • It was shown that there is a method to recognize the change of material during the drilling process, in real time. • There is a well distinction when the drill is close to exit the CFRP material in both cases when the drilling starts at the CFRP layer and when it ends at the CFRP layer and with both types of drills. June 2013

Future work • Testing the algorithm with different materials properties like: thickness, FRP layers structure, drill types, drilling parameters. • Changing the drilling parameters according to the find drill depth algorithm • Applying the algorithm with hand drilling machine A GIF proposal is in preparation with partners from the Fraunhofer IWU. June 2013