Definition: Testing materials, components, or assemblies without destroying their serviceability.
Importance: Crucial in industries to identify defects without damage.
Comparison with Destructive Testing: Unlike tests like Ultimate Tensile Strength (UTS) that break samples, NDT preserves integrity.
NDT Methods Overview
Methods of NDT:
Magnetic Particle Testing
Liquid Penetrant Testing
Visual Testing
Radiography
Ultrasonic Testing (most commonly used).
Ultrasonic Testing
Advantages: Portable equipment, effective for detecting damages.
Challenges:
Uses bulk waves (high MHz frequency).
Requires coupling to the specimen.
"Dead Area" issue: Initial pulse can mask smaller cracks close to the surface.
Guided Wave Methods
Concept: Guided waves are excited at a point and reflected by boundaries. More effective for detecting superficial damage compared to conventional ultrasonic methods.
Types of Guided Waves:
Rayleigh Waves: Surface waves propagating on one surface.
Love Waves: Shear horizontal waves.
Lamb Waves: Propagate in thin plates with both boundary conditions.
Lamb Waves Characteristics
Modes: Symmetric and anti-symmetric modes.
Equations Governing Modes:
Involves Lamb's constants, wave number, velocities of longitudinal and transverse waves, etc.
Dispersion Curves: Show relationship between frequency-thickness product and wave velocities.
Damage Detection Techniques
Method Overview:
Damage detection relies on changes in wave characteristics when encountering defects.
Baseline methods require pristine data for comparison.
Baseline-Free Method: No initial data required.
Simulation Results: Demonstrates how damage affects wave propagation.
Experimental Setup for Guided Wave Testing
Components: Function generator, amplifier, and oscilloscope.
Signal Processing: Online or offline processing of received signals.