MICROWAVE INSPECTION METHOD AND ITS APPLICATION TO FRP MTI AmeriTAC - - PowerPoint PPT Presentation

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MICROWAVE INSPECTION METHOD AND ITS APPLICATION TO FRP MTI AmeriTAC - - PowerPoint PPT Presentation

Aug 03, 2023 221 likes •646 views

MICROWAVE INSPECTION METHOD AND ITS APPLICATION TO FRP MTI AmeriTAC 2013 Robert J Stakenborghs General Manager Evisive, Inc. Baton Rouge, Louisiana, USA 1 OBJECTIVES Describe FRP and GRP Discuss failure modes Describe microwave

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MTI AmeriTAC 2013

MICROWAVE INSPECTION METHOD AND ITS APPLICATION TO FRP

Robert J Stakenborghs General Manager Evisive, Inc. Baton Rouge, Louisiana, USA

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OBJECTIVES

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  • Describe FRP and GRP
  • Discuss failure modes
  • Describe microwave inspection
  • Show inspection examples
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SLIDE 3

FRP AND ASSOCIATED PRODUCTS

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  • FRP is an acronym for Fiber Reinforced Plastic or Polymer
  • is a fiber reinforced polymer
  • plastic matrix
  • reinforced by fine fibers of many different materials
  • Glass is most common, called fiberglass
  • Aramid fibers, such as kevlar, are also becoming more popular

particularly in some specialty areas such as body armor

  • Carbon fiber is gaining in popularity because of its high strength
  • The plastic matrix may be
  • Epoxy, thermosetting plastic or thermoplastic
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SLIDE 4

FRP CHARACTERISTICS

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  • Fiber reinforced polymer composites are made of
  • Fiber reinforcements
  • Resin
  • Fillers and additives
  • The fibers provide increased stiffness and tensile capacity
  • The resin offers high compressive strength and binds the fibers into a

firm matrix

  • The fillers serve to reduce cost and shrinkage
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SLIDE 5

GRP OR GFRP

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  • Fiberglass
  • also called glass-reinforced plastic, GRP,
  • glass-fiber reinforced plastic, or GFRP
  • Most common FRP due to its low cost
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SLIDE 6

GLASS REINFORCEMENT

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Fine Ground Chopped Strand Mat

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ADVANTAGES

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  • Strong
  • Lightweight
  • Corrosion resistant
  • Less expensive than carbon fiber
  • Non conducting (dielectric)
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SLIDE 8

COMMON USES

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Tanks

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COMMON USES

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Pipe

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COMMON USES

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Boats (My favorite)

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FAILURE MODES GRP

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  • GRP Similar to concrete
  • Plastic matrix OK in compression, weak in tension
  • Glass fiber adds tensile strength
  • Some failure modes similar to metals
  • Overload
  • Too much load results in tearing of glass fiber
  • Usually a crushing or moment load
  • Often results in delamination
  • Environmental stress corrosion cracking
  • Chemical attack weakens glass fibers, resulting in failure at loads well below

what would be expected

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ESCC AND OVERLOAD EXAMPLES

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Overload where glass fibers pullout from plastic matrix ESCC where glass fibers lose strength and fail prematurely

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OTHER GRP FAILURE MODES

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  • Some failure modes unique to GRP
  • Hydrolysis
  • Water or other liquid seeps into matrix
  • Interaction with plastic matrix causes chemical reaction and formation of acidic

molecules

  • These molecules become mobile and occupy more volume than the original

molecules and pressure builds inside the laminate structure

  • This internal pressure results in blistering and delamination
  • Blister formation is typically on surface nearest the source of liquid
  • Boat hulls – external so visible
  • Piping – internal not visible
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SLIDE 14

HYDROLYSIS

Internal Pipe Blistering (Hard to see from

  • utside)

Hull Blistering (Easy to see from outside)

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OTHER GRP FAILURE MODES

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  • Erosion
  • Not unique to GRP
  • Attack is different because it affects the weaker plastic matrix
  • Leaves the glass fiber
  • Not necessarily in original orientation
  • Manufacturing issues
  • Resin poor regions
  • Weak area due to lack of binder, reacts differently to load
  • Resin rich area
  • Weak region due to low glass content
  • Poor layup practice
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SLIDE 16

MANUFACTURING PROBLEM

Fiberglass booms Voiding in corner near reinforcement

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OTHER GRP FAILURE MODES

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  • Assembly problems
  • Joint adhesive
  • Lack of adhesive
  • Incomplete adhesive
  • These are internal defects that are difficult to detect
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SLIDE 18

MICROWAVE INSPECTION

Background of Method

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Transmitter Receivers

Object being examined Defect

A B

If a dielectric system is bathed in microwave energy: What does the interaction of the microwave energy with the system look like? It was supposed that the interaction behaved IAW Snell’s law. That is, energy is reflected and transmitted based on the ratio of the indexes of refraction (a function of the dielectric constant of the various materials)

BASIC OPERATING CONCEPT

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EARLY TESTING

Early microwave transceiver Fabricated defect

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TIME DOMAIN SCAN

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CONCLUSIONS

Further testing clearly indicated the answer was YES Microwaves enter the system and reflect from areas of differing dielectric constant

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MICROWAVE NDE INSPECTION METHOD

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  • Current State of the art
  • Monochromatic, phase coherent electromagnetic radiation in

5-50 gigahertz frequency range

  • Sample material is bathed in low power (milliwatt) microwave

field

  • Microwave energy reflected and transmitted from regions of

differing dielectric constant

  • Detectors sense returning microwave energy
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SLIDE 24

MICROWAVE NDE INSPECTION APPARATUS

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  • Current Technology
  • Microwave probe
  • Transmitter (Microwave generator)
  • Two detectors
  • Position monitoring device
  • Analog/Digital signal converter
  • Computer for data collection and display
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SLIDE 25
  • 25
  • 20
  • 15
  • 10
  • 5

5 10 15 20 25 2 4 6 8 10 12 14 16 18

Sample Thickness

Ch C Ch A Ch B Back Wall

GENERATED MICROWAVE SIGNALS

Volts, DC

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BENEFITS OF A MICROWAVE SYSTEM

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  • Microwave energy has good penetrating power
  • Effective volumetric inspection at several inches of GRP
  • Easy to operate
  • Small portable system
  • No couplant required (i.e. – air coupled to part)
  • Unlike ultrasound there is no acoustic impedance mismatch at the air to material interface

so a large percentage of the microwave energy enters the material

  • Microwave energy is not attenuated to the extent of ultrasound in composite materials
  • Microwave energy likes air, that is, it is not adversely impacted by the presence of air in a

sample, such as air bubbles or foam cores

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EFFECTIVENESS OF SYSTEM

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Fiberglass plies POD Flaws 90% POD Size 3 98% ≤ 0.5” 6 88% 0.9” 9 80% 2.0”

Results of a Sandia Labs exercise for FAA aging aircraft program.

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CURRENT SYSTEM

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PIPING SYSTEM

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PIPE WITH MANUFACTURED DEFECTS

Pipe with erosion defects and insufficient glue Inspection image of pipe

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PIPE WITH MANUFACTURED DEFECTS

Gray scale image showing interference pattern at erosion hole 3D rendering of pipe

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MANUFACTURED DEFECTS IN FLANGE

Picture of flange with back drilled holes 3d rendering of inspection image

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Different depth of holes is apparent in 3D rendering

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MICROWAVE INSPECTION

Real world examples

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OVERLOADED SECTION OF FIBERGLASS BOOM

Boom section Inspection image

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Delamination

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INTERNAL EROSION OF PIPE

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Displaced structure caused by washout of resin matrix Localized Pit

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VOIDING AT MANUFACTURE

Boom with voiding Inspection image of boom

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Voiding identified in inspection image

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INTERNAL PIPE HYDROLYSIS

Picture of pipe ID Inspection image of pipe ID

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Internal blistering identified in image

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SLIDE 38

ENVIRONMENTAL DEGRADATION OF FURAN PIPE

Photo showing chemical attack Inspection image of chemical attack

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Degraded resin to right of line

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RESIN POOR AREAS OF PULTRUDED PANEL

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Tensile test results (Pounds load to failure)

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PANEL WITH VARIOUS TYPES OF FOD

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Image focus changes based

  • n relative

position of the end of the antenna with respect to the material surface

Metal, paper, cloth FOD

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QUESTIONS