Acoustic Emission Monitoring Systems

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Acoustic Emission Monitoring SystemsThe Next Generation of Vibration Monitoring

Nikolaas Van Riet - Test & Measurement Solutions

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Let’s start with the basics

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Acoustic Emission Monitoring Systems

Acoustic Emission (AE) is a method used to detect and locate faults and cracks in mechanically loaded structures

AE is a mature technology with a proven track record




When metal cracks in response to any type of loading, the relief of mechanical stress creates a broadband elastic wave or acoustic emission

The deformation tends to relief and smooth out the local stress

Acoustic Emission (AE) monitoring is a great way to detect and locate faults and cracks in mechanically loaded structures

AE occurs at locations where the local stress is high enough to cause new deformations.

The use of AE sensors at different locations allows you to triangulate the exact location of the event (crack formation)




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Data logging and processing is now becoming advanced enough to fully exploit the possibilities of Acoustic Emission monitoring

As the event is a very short (im)puls, the resulting wave carries energy at all frequencies

High frequency (100-500kHz) contact transducers have shown the best results, but downside is the requirement for very fast sampling and resulting in enormous amounts of data

Because electronics was not fast enough, traditional AE measuring was limited to parameters like threshold, rise time and event counting




AE waves can be visualized by thinking of the ripples produced by stone dropped into a pond

The ripples spread out and eventually reach the banks where they reflect, creating a complex wave pattern

A cork floating near the banks will bob up and down in result of the complex ripples. An AE sensor will do the same on acoustic ripples created by a cracking event




All these non metallic components are less ductile than the metallic matrices in which they are embedded, therefore they break more easily

Beside the formation and growth of cracks also breaking of non-metallic inclusions can be detected

These non-metallic inclusions can be:• Microscopic specks of sulfide, oxide or carbide

• Manganese sulfide “stringers” formed during the rolling of steel• slag inclusions introduced during welding

• Non metallic corrosion products connected to the surface


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Sensing & Measurement

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Essential in the signal shaping is the sensing element

For AE wave typically piezoelectric transducers are used which are sensitive to motion in any direction

The sensitivity of AE sensors change with frequency, because of the resonating nature of piezocrystals, but sensitivity also changes on direction of motion




AE measuring systems

Best signal to noise is in typically in the 100kHz to 500kHz range, electronics is fast enough for even GHz sampling.

FPGA’s enable faster I/O response times and open the way to organize even faster sampling and recognition procedures

MHz sampling rate gives too much data to be stored: it occupies too much memory and data transfer is time consuming

Solution is limiting logging with event detection through an embedded system. For example: FPGA bases systems have onboard logical gates for event detection


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Advantages and limitation

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ADVANTAGES

AE can be used in:• Proof testing• Online condition & structural health monitoring• Leak detection and localization• In process weld quality monitoring • Mechanical property testing & validation• Diagnosis of the integrity of large structures• Tool monitoring• Quality inspection of bonding in composites and laminated structures




ADVANTAGES

Can also detect:• lack of lubrication and friction

• Can detect problems with very slowly rotating machinery• Very early developed damage

Real-time evaluationNon intrusive

Less geometry sensitive




LIMITATIONS

Repeatability: Acoustic emission stress relief is unique for each event

High frequency noise can limit the possibilities

High speed logging and processing is necessary


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Asset monitoring, Vibration Analysis, Lubricant analysis, Acoustic emission, Infrared thermography, Ultrasound testing (Material Thickness/Flaw Testing), Signature analysis, Failure oriented maintenance, Preventive maintenance, Condition based maintenance, Predictive maintenance, Condition monitoring systems can lead to:higher productivity high availability-lower risks-longer life cyclesplanned standstillsinvestment protection


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You want to know more…

Please do not hesitate to get in contact with me.

About Test & Measurement Solutions Group: T&M Solutions develops multidisciplinary solutions to test, measure, inspect, assemble and validate products in nearly all segments of the production industry. The company helps its customers produce zero-defect products, thereby optimizing production and operational costs. Certified specialists develop tailor-made solutions and systems for quality control and quality guarantee, helping to guard the reputation of its customers and their products. Test & Measurement Solutions supports customers across the globe from its offices in Belgium, the Netherlands and Poland. www.tm-solutions.eu . Click on the picture on left for a case study on condition monitoring

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Acoustic Emission Monitoring Systems

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