IMPACT ECHO TEST on destructive Test .pptx

It is the type of NDT test

1. IMPACT – ECHO A Non – Destructive Testing Technique

2. CONTENTS: Introduction Instrumentation Purpose Operation Interpretation Strengths/Weaknesses

3. INTRODUCTION A Non – Destructive Test Looks for flaws/imperfections in the material Can estimate thickness to within 3% Primarily used for concrete and masonry Approx. 25 years old – Developed from ultrasonic pulse echo (1940’s) Similar idea to chain dragging

4. A mechanical impact creates stress waves through a material. These (reflected) waves can be measured to gage depth of a discontinuity. Certain waves will dominate based on location of the discontinuity. Wave velocities must be known to determine depth of flaw. Theory – Stress Waves (Sound or Pressure)

5. INSTRUMENTATION Steel ball (4-15mm) impacts (2-10m/s) the concrete, creating stress waves. (<80kHz & λ = 5cm-6cm) Transmitter → Pulse echo Can be spring loaded Start from large impactor → small Transducer measures surface displacements Placed adjacent to impactor Measures primarily P-waves Piezoelectric Conical displacement transducer in housing to permit testing vertical surfaces Spring-loaded mechanical impactor

6. PURPOSE Plain, Reinforced and Post – Tensioned Concrete Can be used to sense: Cracks Delamination Voids Honeycombing Debonding

7. OPERATION Impact produces stress waves in the material; reflected waves from voids are detected by the transducer. These reflected waves set up a resonance condition having a distinctive frequency. Waveform is transformed into spectra (FFT). Should have an idea of what to look for – Size of flaw Operate parallel to regular occurring grooves.

8. (a) For a test over a solid portion of a 0.5m thick concrete slab. (b) For a test over a disk-shaped void embedded in another portion of the same slab. Examples of amplitude spectra:

9. INTERPRETATION Peaks are associated with a certain “characteristic frequency”, specifying a distance to the discontinuity. d = where, d – depth from which stress waves are reflected. C – wave speed. f – frequency of signal.  

10. STRENGTHS Only need access to one surface Internal flaws can be detected Can determine depth of the internal flaws Easily repeatable Can construct a map of discontinuities

11. WEAKNESSES Data can be difficult to interpret; especially on thick plates or on layered materials (overlays, soil). Small voids can be missed – limited by size of wavelength. Complicated geometries poses difficulties. Flaws beneath sensed flaw must be evaluated from the opposite side. Flaw detection length constraints: L min = d/4, L > d/3 Requires adequate frequency resolution, Δ t max ≈ 1/10f

12. EQUIPMENTS:

13. TRANSDUCERS: Cylindrical Transducer Pistol Grip Transducer Dual-Head Transducer

14. Use of Each Transducers: Cylindrical Transducer – for testing in narrow and confined spaces. Pistol Grip Transducer – is easier to use and well suited to flat surfaces. Dual-Head Transducer – used for independent measurements of wave speed which can be used to determine depth and thickness.

15. ASTM C 1383 Procedures Procedure A is used to determine the P-wave speed. Procedure B is used to determine the thickness frequency. Two step procedure for measuring plate thickness:

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