June 2013 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

Talk Outline June 2013 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

Acoustic Emission June 2013 Acoustic Emission (AE) is a class of phenomenon whereby transient elastic wave are generated by rapid release of energy 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.

Typical AE sensor June 2013 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.

Typical measurement system June 2013

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

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

June 2013 The experimental system d 1 =6 mm d 1 =5 mm d 2 =7.93 mm l 3 =1.5 mm Regular drill Step drill Kistler AE sensor Kistler platform 16.8 mm CFRP plate 10 mm aluminum plate

June 2013 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 Entering CFRP Exiting CFRP Drilling the Al

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

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 Al Drill tip in CFRP 7.93 mm step in CFRPDrill tip exit CFRP

Drilling from CFRP to Al with step drill June 2013 ZoneAverage difference MinimumMaximumFirst 50 holes failures Total number of failures

June 2013 Some more results Effect of the distance of the AE sensor form the hole The relation between the AE signal and delamination/fraying workpiece Sensor Hole D1 Hole C8 L1 L2

Summary June 2013 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.

Future work June 2013 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.