Ultrasonic-Testing Non distractive test technique

It's a ppt on ultrasonic testing

1. Ultrasonic Testing Ultrasonic Testing (UT) uses high frequency sound waves (typically 0.5-15 MHz) to conduct examinations and measurements. Beyond engineering applications like flaw detection and dimensional measurements, ultrasonics serve medical fields through sonography and therapeutic treatments.

2. How Ultrasonic Testing Works Pulse-Echo Method A pulser/receiver generates high voltage electrical pulses that drive the transducer to produce ultrasonic energy. Sound waves propagate through materials, and when encountering discontinuities like cracks, part of the energy reflects back. The transducer converts reflected waves into electrical signals displayed on screen. Knowing wave velocity, travel time directly relates to distance traveled. This provides information about reflector location, size, orientation, and other features.

3. Advantages & Disadvantages Key Advantages Detects surface and subsurface discontinuities Superior penetration depth Single-sided access with pulse-echo Highly accurate positioning Minimal part preparation Instantaneous results Nonhazardous operation Key Limitations Requires accessible surface Extensive training needed Coupling medium typically required Difficult for rough, irregular, or thin materials Coarse grain materials challenging Linear defects parallel to beam may be missed

4. Wave Propagation Modes Sound waves propagate through materials based on particle oscillation patterns. Understanding these modes is essential for effective ultrasonic testing. Longitudinal Waves Particles oscillate in the direction of wave propagation through compression and expansion. Also called pressure or density waves. Can propagate in gases, liquids, and solids. Fastest wave type. Shear Waves Particles oscillate perpendicular to propagation direction. Require solid material for effective propagation. Relatively weak compared to longitudinal waves. Travel approximately half the speed of longitudinal waves. Surface (Rayleigh) Waves Travel at surface with elliptical particle motion. Penetrate to one wavelength depth. Very sensitive to surface defects. Follow surface contours, useful for hard-to-reach areas. Plate (Lamb) Waves Complex vibrational waves in thin materials. Propagate parallel to surface throughout thickness. Two modes: symmetrical (extensional) and asymmetrical (flexural). Travel several meters in steel.

5. Wave Properties & Material Characteristics Fundamental Relationship Wavelength is directly proportional to velocity and inversely proportional to frequency. Velocity is fixed for each material, so increasing frequency decreases wavelength. Detection Rule of Thumb A discontinuity must be larger than one-half the wavelength for reasonable detection probability. Sound Velocity in Common Materials Material Longitudinal (m/s) Shear (m/s) Aluminum 6320 3130 Steel (1020) 5890 3240 Cast Iron 4800 2400 Copper 4660 2330 Titanium 6070 3310 Sensitivity vs. Resolution Sensitivity: Ability to locate small discontinuities. Increases with higher frequency. Resolution: Ability to distinguish closely spaced discontinuities. Also increases with frequency. Frequency Trade-offs Higher frequencies improve sensitivity and resolution but reduce penetration depth due to increased scattering from grain structure. Cast materials require lower frequencies; wrought products can use higher frequencies.

6. Acoustic Impedance & Reflection Acoustic impedance (Z = ρV) determines how sound energy transmits and reflects at material boundaries. The impedance mismatch between materials controls energy distribution . 88% Energy Reflected At water-steel interface 12% Energy Transmitted Into steel from water 1.3% Round-Trip Energy Returns to transducer after back surface reflection 99.996% Air-Steel Reflection Nearly complete reflection at air interface Acoustic Impedance Values Material Impedance (kg/m²s × 10⁶) Aluminum 17.1 Steel 46.1 Titanium 28.0 Water (20°C) 1.48 Air (20°C) 0.000413

7. Refraction, Mode Conversion & Critical Angles Snell's Law When ultrasonic waves pass through interfaces at oblique angles, refraction occurs due to velocity differences. Mode conversion generates both longitudinal and shear waves at interfaces. Critical Angles First Critical Angle: Incident angle where refracted longitudinal wave reaches 90°. Creates creep waves along interface. Second Critical Angle: Incident angle where refracted shear wave reaches 90°. Beyond this, Rayleigh surface waves generate. Angle beam transducers operate between first and second critical angles to introduce shear waves at desired angles. This eliminates longitudinal wave complications and optimizes flaw detection.

8. Transducer Technology & Types 01 Piezoelectric Effect Polarized materials convert electrical pulses to mechanical vibrations and vice versa. Lead zirconate titanate is most common ceramic. Element thickness is 1/2 desired wavelength. 02 Transducer Construction Includes impedance matching layer (1/4 wavelength thick), wear plate for protection, and backing material for damping control. Backing impedance affects bandwidth and sensitivity. 03 Contact Transducers Rugged design for direct surface contact. Require couplant (water, grease, oil) to eliminate air gap. Include normal beam, dual element, delay line, and angle beam types. 04 Immersion Transducers Operate in liquid environment with watertight connections. Feature matching layer for water interface. Available with planar, cylindrical, or spherical focusing for improved sensitivity.

9. Sound Field Characteristics Near Field & Far Field Sound originates from multiple points on transducer face, creating wave interference. The near field (Fresnel zone) exhibits extensive fluctuations and uneven intensity. The far field (Fraunhofer zone) provides uniform, intense wave field. Near Field Distance Where D is transducer diameter, f is frequency, and V is sound velocity. Optimal detection occurs just beyond near field at natural focus. Beam Spread Sound beam continuously spreads in far field due to particle vibration not perfectly aligned with propagation direction. Maximum pressure always on acoustic axis. Influencing Factors Beam divergence largely influenced by frequency and transducer diameter. Lower frequencies and smaller diameters increase beam spread. Strongest reflections from area directly in front of transducer.

10. Inspection Techniques & Calibration Normal Beam Measures distance using: d = Vt/2. Transducer perpendicular to surface. Backwall echo always present. Discontinuities appear between initial pulse and backwall. Angle Beam Introduces refracted shear waves. Calculates surface distance and depth using refraction angle. Essential for weld inspection. No backwall echo unless reflector in beam path. Data Presentation A-scan shows amplitude vs. time. B-scan displays cross-sectional profile. C-scan provides plan view of features. Each format serves different analysis needs. Calibration Standards Reference blocks (IIW, ASTM) validate equipment performance. DAC curves compensate for amplitude changes with distance. Essential for consistent, accurate measurements.