CHAPTER 3 MATERIALS AND EXPERIMENTAL PROCEDURE

Transcription

1 47 CHAPTER 3 MATERIALS AND EXPERIMENTAL PROCEDURE 3.1 INTRODUCTION Material selection is an important aspect of design and manufacturing. Often the success of the manufacturing is critically dependent on a material or materials performing as desired. The following may be considered for selection of materials. Material characterization data base Flight/Ship/Automobile history Cost, availability, lead time. The reinforcement material chosen is glass fiber. Fiber glass also called glass fiber reinforced plastic or GFRP is a fiber reinforced polymer made of a plastic matrix reinforced by fine fibers of glass. Fiberglass is a light weight, extremely strong and robust material. Although strength properties are somewhat lower than carbon fiber and it is less stiff, the material is typically far less brittle, and the raw materials are much less expensive. Its bulk strength and weight properties are also very favorable when compared to metals and it can be easily formed using molding processes. The materials used for preparation of laminates are procured and the different type of specimens is prepared as per ASTM standard. ASTM D3039 standard is used for tensile test of composite laminates. Single lap joint tensile

2 48 test specimen has been prepared according to ASTM D Double lap joint tensile test specimen has been prepared according to ASTM D Laminated specimens have been prepared according to ASTM D and laminated lap joint specimen according to ASTM D7136.The ASTM E is the definition for Acoustic Emission, ASTM E976 STANDARD (1994 (AE)) is used for Pencil Lead Break Test. 3.2 MATERIAL PROPERTIES The laminates were made from fiberglass roving (E-glass), LY 556/ Hardener HY 951 system for laminates with different orientation. The properties are Pot life : minutes at c Curing time : hours at 20 0 c

3 49 The hardener HY 951 is thoroughly mixed with resin. If a large quantity of a mixture is to be prepared and must be cooled, as otherwise strong exothermic heat is developed and the mixture will gel in a short time. 3.3 METHODS OF LAMINATE PREPARATION Hand Lay-Up Method The simplest manufacturing technique adopted is laying down unidirectional glass roving over a polished mould surface previously treated with a releasing agent: after this, a liquid thermosetting resin is worked into the reinforcement by hand with a brush or roller. The process is repeated a number of times equal to the number of layers required for the final composite. Epoxy resins are most commonly used with glass fibers because of their good strength properties. Resin and curing agents are pre-mixed and normally designed to cross-link and harden at room temperature. The major advantage of this manufacturing process is its great flexibility, since it suits most common mould sizes and complex shapes. Although tooling is normally expensive, it can be re-used for several runs and the actual cost of the raw materials make this process economically feasible Vacuum Bagging Method Also known as vacuum moulding, it requires a pump that will make use of atmospheric pressure to consolidate the material while curing by applying vacuum to the mould cavity. Usually the fibers are placed on a single mould surface and covered by a flexible membrane, sealed around the edges of the mould. The space between the mould and the membrane is then evacuated with a pump and the vacuum retained until the resin has cured. Figure 3.1 shows an example of vacuum bagging as given by Kornmann et al

4 50 (2005) where several layers of glass fabric were placed intercalated with epoxy resin. When the stack reaches the desired amount of layers, it is covered with a peel ply, a perforated film and a breather fabric and then introduced into a vacuum bag. An inlet and an outlet are placed on the breather fabric and then the bag is sealed with sealant tape. After that, vacuum is applied and for this particular case hydraulic pressure is also applied. Vacuum bagging processes normally deliver a better volume fraction ratio since any excess resin is drawn out of the composite. Also, the presence of voids is reduced due to the extra pressure applied. One disadvantage of this technique is the difficulty in maintaining a good vacuum over very large moulds from 10m. Also, particularly with epoxy resins, thick sections take time to fabricate due to the exothermic nature of the cross linking reaction. The reaction generates heat, which needs to be released for the resin to consolidate. Figure 3.1 Vacuum bagging technique

5 SPECIMEN PREPARATION FOR DEFECT CHARACTERIZATION STUDIES IN LAMINATES Preparation of Laminates from Unidirectional Glass Fibers GFRP composite laminates with different orientations such as 0 o, 90 o, cross ply (0 o /90 o ), angle ply (+45 o /-45 o ) of size 300 x 300 mm 2 are fabricated using vacuum bagging technique as shown in Figures 3.2 (a), (b) and (c). Ten layers of unidirectional glass roving along with LY556 epoxy matrix are used for the purpose of fabrication of the laminates. (a) (b) (c) Figure 3.2 (a) Zero degree orientation laminate (b) Angle ply laminate (c) Cross ply laminate Preparation of Tensile specimens from Unidirectional Glass Fibers ASTM D3039 Standard tensile specimens was cut using water jet cutting (Figure3.3) from the fabricated laminate of size 280x18x3mm 3 as shown in Figure 3.4 to avoid machining defects and to maintain good surface finish.

6 52 Figure3.3 Specimens preparation using water jet cutting machine Figure 3.4 ASTM D3039 standard tensile specimen For pure resin specimen, epoxy LY556 alone is used. Aluminum tabs of size 60 x 18 x 3 mm 3 are used to reduce the grip noise and prevent damaging the extremities of the laminate with possible unexpected failures external to the grip length as shown in Figure 3.5.

7 53 Figure 3.5 Specimens of epoxy matrix composite materials for tensile test as per ASTM D SPECIMEN PREPARATION FOR DEFECT CHARACTERIZATION STUDIES IN LAMINATED JOINTS WITH DIFFERENT ORIENTATION Cutting of Specimens from the Composite Laminates Specimens are cut from each GFRP laminate having dimensions 102x25.4x3mm 3 for laminated joints, as show in Figure 3.6. Figure 3.6 Specimens cut from water jet cutting machine

8 Surface Preparation and Curing Considering bonded joints the surface preparation takes an important role in perfect bonding, hand abrasion technique was used to introduce roughness in the surface. The entire mould with glass fabric lay-ups has been kept in 24 hours for curing. The curing has been done properly at a room temperature, to prevent the reduction in strength of the bond drastically. The major defects found in bonding of two materials are disbonding, porosity and voids are mostly due to improper curing. To prevent dislocation of specimen in bond region proper load is applied Preparation of Aluminum Tabs Aluminum Tabs of dimensions 25x25x3 mm 3 has been prepared to prevent the grip noise. Initially the surfaces of Aluminum tabs and specimen are prepared by using emery sheet for good bonding. The specimen is then allowed to cure for 24 hours under room temperature after bonding Specimen Specification for Joints Single lap joint Tensile test specimen has been prepared according to ASTM D from the fabricated laminate show in Figure 3.7. The dimension of tensile specimen according to ASTM D are as follows: Length mm Width - 25 mm Thickness - 3 mm Gauge length mm Bond length - 25mm

9 55 Figure 3.7 Tensile test specimen of ASTM D Double lap joint Tensile test specimen has been prepared according to ASTM D from the fabricated laminate shown in Figure 3.8. The dimensions of tensile specimen according to ASTM D are as follows: Figure 3.8 Tensile test specimen of ASTM D FABRICATION OF TEST SPECIMENS FOR ADHESIVE, BOLTED, HYBRID AND LAP JOINT WITH ATTACHMENTS Materials Used The laminates were made following correct procedure as shown earlier from fiberglass roving of E-glass (Figure3.9), LY 556/ Hardener HY

10 system. The density, thickness of the fiber glass roving is x 10-3 g/mm 3, 0.2 mm respectively. Figure 3.9 Fiber glass mat Laminate Preparation Process The required mould is placed on the table and a thin layer of resin is applied on the surface of the lower mould and the first layer of glass fabric is placed on the mould, rollers are used to squeeze the excess resin. The resin is applied over the first layer and the second layer is placed over the first one. The procedure is repeated with alternating layers of glass fiber and resin mixture until all required thickness. The vacuum bagging and cured at a pressure of 1 bar for 2 hours as shown in Figure 3.10.The GFRP laminate obtained from the vacuum bagging will be having dimensions of 600x600x3.5mm 3. Figure 3.10 GFRP laminate under vacuum bagging

11 Specimen Preparation for Joint Strength Analysis The specimens are prepared using single lap joint technique. These specimens are subjected to tensile testing with Acoustic Emission sensors positioned at -40mm to +40mm from the centre of the specimen. Four to six specimens are tested in each type. The failure strength, Load, Displacement, and Event Location Data of the four different specimens are compared and discussed. As per ASTM D standard tensile specimens of size 102x25x3.5mm 3 are cut from the fabricated laminates using water-jet cutting to avoid machining defects and to maintain good surface finish as shown in Figure Figure 3.11 Specimens cut from water jet cutting machine Aluminum tabs of size 25x 25 x 3.5 mm 3 are used to reduce the grip noise. The specimens are attached by bolt, adhesive and hybrid (bolt and adhesive). Specimens are prepared and attached using aluminium sheet for attachment with a thickness of 0.8mm, 1.2 mm And 2.0 mm with varying the angle of 30 0 and 45 0 as shown in Figure.3.12

12 58 (a) (b) Figure 3.12 Tensile test specimen prepared as per ASTM D for thickness of 0.8mm,1.2mm,2.0mm with varying angle for attachment at 30 0 and 45 0 (a) top view (b) side view 3.7 SPECIMEN PREPARATION FOR IMPACT TEST Preparation of Normal Specimen Impact test specimen has been prepared according to ASTM D from the fabricated laminate as shown in Figure3.13. The dimensions of impact specimen according to ASTM D are as follows; Length - 58mm Width - 58mm Thickness - 3.5mm Specification of the glass fiber lamina used: Weave style - plain Thickness mm Area weight - 320gsm Thermal stability - continuous use up to 500 o c Glass content %

13 59 Figure 3.13 Normal specimen Preparation of Adhesive Lap Joint Specimen Impact test specimen has been prepared according to ASTM D7136 from the fabricated laminate and attached with adhesive as shown in Figure The dimension of impact specimen according to ASTM D7136 is as follows; Length - 150mm Width - 100mm Lap length - 50mm Thickness - 3.5mm Specification of the glass fiber lamina used: Weave style - plain Thickness mm Area weight - 320gsm Thermal stability - continuous use up to 500 o c Glass content %

14 60 Figure 3.14 Single lap joint specimens for impact loading Impact Testing on Composite Laminates Laminates were subjected to drop impact test using a CEAST Fractovis Drop impact tower (Figure 3.15). The normal impact specimens with dimensions of 58mm x 58mm were clamped by using pneumatic fixtures shown in Figure.3.16 (a). Adhesively bonded specimens with dimension 150mm x 100mm x 3.5mm were tested by using a suitable fixture as shown in Figure 3.16 (b). Figure 3.15 Fractovis plus impact testing machine

15 61 Figure 3.16 (a) Normal specimen in fixture (b) Adhesively bonded specimen in fixture 3.8 SPECIMEN PREPARATION FOR RESIDUAL STRENGTH PREDICTION AND COMPARISION OF FAILURE MODES Damage by Drop-weight Impact Laminated specimens are prepared as per ASTM standard. The specimens fabricated are divided into four categories. One group of specimens are as-received, while the remaining specimens are subjected to drop impact at three different heights using a CEAST Fractovis Drop impact tower (Figure 3.17). The diameter of the hemispherical indenter is 12.7 mm with a clamping. Figure 3.17 Laminate with impact damage

16 Determination of Depth using Ultrasonic A-SCAN To determine the extent of damage due to impact Omni Scan MX type Ultrasonic scan facility is used as shown in Figure Figure 3.18 Ultrasonic omni scan Dressed Laminate The impacted region is grinded by decreasing length from the top surface (descending) as shown in Figure 3.19, maintaining the length of impact region more than 20 times its depth for good strength of the bonding patches. The thickness was maintained using vernier calipers correctly to avoid deviation in the failure load values. Figure 3.19 Dressed Laminate

17 Repair Mechanism The impacted or damaged specimens are repaired by scarf, single lap and double lap methods. The repair mechanism involves the process different technics. Glass fiber mat of different sizes (7mm x 18mm, 13mm x 18mm, 20mm x 18mm) are cut to apply patch in the grinded region. The prepared layers are patched on the damaged region of the specimen as the ascending order for scarf repair, using epoxy LY 556 & hardener HY 951. The patched surfaces are prepared for the overlap; according to overlap length the layers are prepared from glass fiber mat for the size 40mm, 50mm, 60mm and three layers of lap for each specimen. In single lap, the three layers are overlapped on one side of the patched region as per the length. In double lap, the three layers are overlapped on both sides. All the overlapped specimens are cured in room temperature for 24 hours and aluminum tabs of size 60mm x 3mm x 18mm are bonded on the surface of prepared specimens using epoxy-araldite Scarf repaired specimen Single lap of repair is done by layers of fiber cloth with resin mixture is applied over the damage removed region in a pattern that the length of each subsequent layers with increasing pattern of width, so that the inclined region reduce the peel stress while applying load (Figure 3.20). The above process is called as patching process. The wet layup technique is used here.

18 64 Figure 3.20 Scarf repaired model specimen Single lap repaired specimen Single lap repair is done by layers of fiber cloth with resin mixture is applied over the damage removed region in a pattern that the length of the each subsequent layers to reduce the peel stress while applying load (Figure 3.21). The wet layup technique is used here. After the patching technique, the overlapping the glass fiber layers as the number of 3 layers are placed on the patching specimen. Figure 3.21 Single lap repaired model specimen Double lap repaired specimen The same patching procedure is followed for the double lap repaired specimen. After finishing the patching, the same patching procedure will be followed. The overlapping is to be done on both sides of the specimen (Figure 3.22). The repair efficiency is determined by the changing overlapping length. The repair efficiency is evaluated by the manufacturing of five specimens on every overlap length. Compare the results by the tensile test and find the best repair technique.

19 65 Figure 3.22 Double lap repaired model specimen The cured specimens are tested by the tensile test with AE and the damage mechanism and the strength are compared to find the best repair technique. 3.9 TENSILE TESTING SET-UP IN UNIVERSAL TESTING MACHINE (UTM) Tensile Testing of Glass/epoxy Composite Determination with A.E. Sensors The specimens prepared from the laminates are tested using an INSTRON 3367 universal testing machine along with acoustic emission monitoring as shown in Figure Figure 3.23 Tensile testing of glass/epoxy composite has been determined with A.E. sensors

20 Tensile Strength under AE Monitoring The Specimens are subjected to uni-axial tension in 30kN INSTRON 3367 Universal Testing Machine (UTM) under acoustic emission monitoring using an 8-channel Acoustic Emission setup supplied by Physical Acoustics Corporation. The Specimens are mounted on the UTM machine and dimension of the specimens are entered in the software. The crosshead speed was maintained at a rate of 0.15mm/min AE signals are recorded for each specimen ACOUSTIC EMISSION MONITORING Equipment used in AE Monitoring The process of AE monitoring is made possible using an array of instruments. Each component has a unique role to play and is essential to ensure proper monitoring. A brief description of each component is detailed in this section Sensors They are the key instruments that detect the mechanical transient elastic waves generated from within a structure and convert them into electrical signals. Usually piezoelectric resonant sensors are used for AE testing. Figure 3.24 shows a plethora of various kinds of sensors available in today s market.

21 Couplants and holders Figure 3.24 Different types of Sensors Sensors are placed on the surface of the material to be tested using various couplants. These are mainly used to assist easy and complete conduction of acoustic waves generated from the source. Commonly used couplants are oil, glue, high vacuum grease, etc. Along with the use of couplants, most field tests require additional holders (e.g. mechanical or magnetic) to keep the sensors in place Pre-amplifiers The main purpose of the pre-amplifier shown in Figure 3.25 is to provide gain to boost and effectively and reject noise from areas outside the sensor operating range. Figure 3.25 Pre-amplifier

22 Data acquisition system Modern AE systems use computers and appropriate software providing a menu- driven parameter input and system control. All the signals received at the sensor end are acquired and stored in the acquisition system. The new generation systems also enable extensive post-processing possibilities. Acquisition systems have also been well adapted for continuous monitoring of structures using wireless technology and web-based remote monitoring. Figure 3.26 represents the schematic representation of acoustic emission testing set up. Figure 3.26 Acoustic emission monitoring Process A Generic AE System A schematic representation of an acoustic emission system and its detection procedure is represented in Figure The process chain basically consists of the following stages, which take place in a very short time, so that all stages can be perceived as simultaneous for testing purposes.

23 69 Figure 3.27 Schematic representation of acoustic emission (AE) Acoustic emission setup An 8 channel AE system supplied by Physical Acoustics Corporation (PAC) is used for the study. The sampling rate and preamplification are kept as 1 to 3 MSPS and 40 db respectively. Preamplifiers operating in the frequency band 10 khz-2 MHz are used. AE activities were sensed using wide band WD and NANO sensors, filtering out frequencies exceeding 900 khz and using a threshold of 45 db to eliminate the back ground noise. High vacuum silicon grease used as a couplant. The amplitude distribution covers the range 0-99 db (0 db corresponds to 1µv at the transducer output). After mounting two transducers on the sample at a mutual distance of 100 mm between them, so that they were both at the same distance from the centre of the specimen length, a pencil lead break procedure was used to generate repeatable AE signals for the calibration of each sensor. Velocity and attenuation studies are performed on the laminates. The Pre- Trigger values and the Hit length values are estimated as 26 µsec and 4K respectively.

24 Pencil lead break test Among the characteristics of the AE instrumentation system, sensitivity needs to be considered first. Of all the parameters and components contributing to the sensitivity, the piezoelectric sensor is the one most subject to variation. This variation can be a result of damage or aging, or there can be variations between nominally identical sensors (ASTM Standard E 1781). To detect such variations, it is desirable to have a method for measuring the response of a sensor to an acoustic wave. Specific reasons for checking sensors include: (1) checking the stability of its response with time; (2) checking the sensor for possible damage after accident or abuse. A recommended method to check the sensitivity of the sensor is the response of the system to pencil lead break test (ASTM E ). In this test, a repeatable acoustic wave can be generated by carefully breaking a pencil lead against the test panel. When the lead breaks, there is a sudden release of stress on the surface of the panel where the lead is touching. This stress release generates an acoustic wave. The Hsu pencil source uses a mechanical pencil and the Nielsen source can be used to aid in breaking the lead consistently. The pencil lead break test was performed to obtain the actual AE source for this research. The test scheme is shown in Figure 3.28 (ASTM E976 STANDARD (1994). Figure 3.28 Hsu-Nielsen source (NDT.net 2007)

25 Hsu Nielsen source Hsu-Nielson device (named after developer of the technique) is an aid to simulate an acoustic emission event using the fracture of a brittle graphite lead in a suitable fitting. This test consists in breaking a 0.5 mm diameter (2-H) pencil lead approximately 3 mm (+/- 0.5 mm) from its tip by pressing it against the surface of the piece. This generates an intense acoustic signal, quite similar to a natural AE source that the sensors detect as a strong burst. The purpose of this test is twofold. First, it ensures that the transducers are in good acoustic contact with the part being monitored. Generally, the lead breaks should register amplitudes of at least 80 db for a reference voltage of 1 mv and a total system gain of 80 db. Second, it checks the accuracy of the source location setup. This last purpose involves indirectly determining the actual value of the acoustic wave speed for the object being monitored INPUT PARAMETERS TO AE WIN SOFTWARE Wave Velocity The wave velocity is calculated by Hsu Nielsen pencil lead break procedure method as shown in Figure The pencil tip is broken at a known distance from the sensors and the corresponding time difference at which the signal is captured by the two sensors is noted down. Then the wave velocity is calculated from the following relation. WaveVelocity Distance between the sensors d Time interval at which signal is detected

26 72 Figure 3.29 Wave velocity calculations Wave Velocity Study The Acoustically emitted sound waves travel with different velocity in different types of materials. The wave velocity must be found to determine the other Acoustic Emission parameters. So the velocity is calculated using the following steps. Initially the sensors are fixed at two locations in the specimen (Figure 3.30). High vacuum grease is applied on the sensor and then fixed using tape. The distances between the two sensors are measured. Velocity study is done using Hsu-Nielson source (pencil lead break). The test is performed at various locations within the sensors. Then the velocity is calculated using the formula.

27 73 1 Sensor 2 47 A.E. Sensor Position Figure 3.30 A.E. Sensor position Hit Definition Time (HDT) The function of Hit Definition Time is to enable the system to determine the end of the hit, close out the measurement processes and store the measured attributes of the signal. Proper setting of HDT ensures that the AE signal from the structure is reported as one and only signal. The recommended range for the composites is µs (SAMOS AE user manual, Rev:2) Hit Lockout Time (HLT) The function of Hit Lockout Time is to inhibit the measurement of reflections and late arriving parts of the AE signal. With proper settings of the HLT, spurious measurements during the signal decay are avoided and data acquisition speed can be increased Peak Definition Time (PDT) The function of peak definition time is to enable determination of the time of true peak of the AE waveform. A proper setting of the PDT

28 74 ensures correct identification of the signal peak from rise time and peak amplitude measurements. The recommended range for the composites is 20-50µs (SAMOS AE user manual, Rev:2). PDT is calculated using the following relation. PDT Distance between the sensors Wave Velocity Data Acquisition Process Monitoring of AE signals generated from uni-axial Tensile Test is done by an acquisition system. The signals were detected using two Nano 30 piezoelectric transducers, which are attached to the specimen surface using high vacuum grease as a couplant and are fastened by tape. The signals from the transducer passed through PAC 2/4/6 G/A pre-amplifier before reaching the main unit. Wave velocity test is performed on the specimen and wave velocity is calculated. Next the sensors are connected to the 8-channel AE data acquisition system. UTM is switched ON and the tensile load is applied. Various AE parameters such as Amplitude, Counts, Energy, Rise, and Duration are recorded during the test. The data are processed.

29 Sample Rate This is the rate at which the data acquisition board samples the waveforms on a per second basis. A sample rate of 1 MSPS (Mega sample per second) means that one waveform sample is taken every µsec Pre-Trigger This value tells the software how long to record (in µsec) before the trigger point (the point at which the threshold is exceeded). The user may enter a value in the pre-trigger edit box. The minimum allowable pre-trigger value is zero. The maximum allowable pre-trigger value is calculated by dividing the hit length by the sample rate in MHz If, for example the hit length was 1k(1k = 1024) and the sample rate was 4 MHz, then the maximum allowable pre-trigger value would be 1024/4 = 256 µsec Hit Length This determines the size of a waveform message. The available hit length is in the range of 1k- 4k. At a 4 MSPS sampling rate, a hit length of 1k will allow up to 256 µsec of data, a hit length of 2k will allow 512 µsec of data (2*256) and so on. The timing parameters in the hardware settings are calculated for different materials and are listed in Table 3.1. The HDT is calculated from trial and error method. Proper setting of the HDT ensures that each signal from the structure is reported as one signal only.

30 76 Table 3.1 Timing parameters for glass fibre HDT (µs) PDT (µs) HLT (µs) Wave Velocity m/s Glass fiber/epoxy ( Unidirectional) Glass fiber/epoxy ( Bidirectional) The description of the sensors used in the experiments is listed in Table 3.2.The calibration certificates for both Nano30 and Wide Band sensors are shown in Figures 3.31(a) and 3.31(b) respectively. Table 3.2 Description of sensors Sensors Model Sensors Dimensions DIA X HT (mm) Operating Temperature ( 0 C ) Case Materials Operating Frequency Range (khz) Nano 30 PAC 8 X 8-65 to 177 Stainless steel WD (Wide Band) 18 X to 177 Stainless steel

31 SCANNING ELECTRON MICROSCOPE Scanning Electron Microscope Test on Specimens The S-3400N is a powerful, yet user-friendly SEM through newly developed electron optical and automated functions. The famous Hitachi image quality convinces at high and low beam energies, and optimized detector technology provides maximum information from your sample. Variable chamber pressure allows charge up-free observation of any sample without special preparation techniques such as coatings shown in Figure 3.31 (a). All samples must also be of an appropriate size to fit in the specimen chamber and are generally mounted rigidly on a specimen holder called a specimen stub as shown in Figure 3.31(b). (a) (b) Figure 3.31 (a) Scanning Electron Microscope (b) Specimens in SEM setup for testing 3.13 SUMMARY OF EXPERIMENTAL PROCEDURE In the present chapter, materials used and the different methods for manufacturing fiber reinforced composite plates were explained; the different fabrication techniques were described along with the production of laminates.

32 78 Preparation of the specimens as per ASTM standards for different loading conditions is also discussed in this chapter. The tensile test equipment was described; one 30 kn load cell Instron 3367 Universal testing machine was used for all the tests. Drop impact test was conducted using Fractovis drop impact tower. Scanning Electron Microscope S-3400N was used to identify the damages in the tested specimens. All the necessary equipment required to conduct AE investigation have been described along with the terminology of the standard data processing associated with AE. The sensors used in this research, their technical specifications are also presented. The recording apparatus was described thoroughly including the response from the system and how the signal is modified while travelling from the material to the processing software. A common way of calibrating an AE test in order to ensure some repeatability is described in detail. There are also several other parameters that need to be defined prior experimentation in order to make the best out of the recording system and obtain sensible data. The procedure involved in the selection of these AE hardware parameters for different materials are presented in this chapter. All the input parameters for the experimentation purpose are also presented in this chapter. More details about the geometries selected after damage observation are given in the following chapter.