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Comparison of Non-Destructive Testing Methods

Resonant Inspection Compared to Other Non-Destructive Testing Techniques

Below you will find a general outline of the capabilities of common nondestructive testing (NDT) methods. This is intended as brief summary of each discipline's capabilities.

Traditional NDT Technique Comparison

Excellent ExcellentFair FairPoor Poor
 RAM
Resonant
Acoustic		ET
Eddy
Current		MT/PT
Magnetic/
Penetrant		UT
Ultrasonic		RT
Radiography
Defect/Issue
Cracks/Chips/VoidsExcellentExcellentExcellentExcellentFair
Material PropertiesExcellentPoorPoorPoorFair
Missed OperationsExcellentPoorPoorPoorPoor
Structural IntegrityExcellentExcellentExcellentExcellentExcellent
Product Lot VariationFairFairExcellentExcellentExcellent
Defect Location
Surface (External)ExcellentExcellentExcellentExcellentPoor
InternalExcellentPoorPoorExcellentExcellent
Brazing/Bonding/WeldingExcellentPoorPoorFairFair
Speed/Training/Cost
ThroughputExcellentFairFairExcellentPoor
Training/Certification ExcellentPoorPoorPoorPoor
Total Inspection CostsExcellentFairFairPoorPoor
Automation Capacity
Quantitative ResultsExcellentPoorPoorFairPoor
Ease of AutomationExcellentFairFairPoorPoor
Cost of AutomationExcellent  FairFairPoorPoorPoor
 

Quick Links

Resonant Inspection
(RI)		Ultrasonic Testing
(UT)		Radiography
(RT)		Eddy Current
(ET)
Liquid Penetrant
(LPI / PT)		Magnetic Particle
(MT / MPI)		Infrared Thermography
 		Visual Inspection
(VT)

 

RESONANT INSPECTION (RI)

Resonant Inspection is a whole-body test method which detects resonant frequency shifts resulting from changes in mass, stiffness or damping of a part. Resonance can detect defects such as cracks, voids, chips, brazing problems, nodularity, variations in hardness, missed manufacturing processes, delamination, and more.

Applications include, but are not limited to, powder metal parts, castings, ductile iron parts, brazed assemblies, forgings, stampings and ceramic parts.

Non-Destructive Testing Resonant Acoustic Method (NDT-RAM) is a form of resonant inspection offered by The Modal Shop. NDT-RAM is available in automated, semi-automated, manual, and small-part drop-test systems. Learn more about  which system is right for you. 

AdvantagesDisadvantages
  • Whole body test for internal and external flaws
  • Fast testing time: 1 to 3 seconds per part (typical)
  • No part preparation or cleaning required
  • Objective pass/fail result
  • No consumables expenses
  • Easily automated
  • Easily integrated into manufacturing process
  • Permanent record capability
  • Easily finds first n number of natural frequencies for NVH applications
  • Best for high volume quality inspection
  • Designed to be on the plant floor
  • PCRT (Process Compensated Resonance Testing) techniques account for normal process variation
  • Not diagnostic - does not indicate where flaw is, just that there is one
  • Materials that resonate only - metal, composites and ceramic parts
  • Large parts (> 100 lbs.) difficult to test
  • Significant manufacturing process variations can mask defect detection

 

ULTRASONIC TESTING (UT)

Measures thickness, velocity or detects internal defects and variations, such as cracks, lack of fusion, delaminations and lack of bond.

Applications include wrought metals, welds, brazed joints, adhesive or bonded joints, non-metallic materials, in-service parts.

AdvantagesDisadvantages
  • Most sensitive to cracks
  • Immediate results
  • Automation possible
  • Permanent record capability
  • Portable
  • High penetration capability
  • Couplant required
  • Complex, or small parts may be difficult to check
  • Defect may be missed if not in the path of the ultrasonic signal
  • Reference standards required
  • Trained operators for manual inspections
  • Special probes
  • Surface condition

 

RADIOGRAPHY (RT)

Measures or detects, internal defects and variations, porosity, inclusions, cracks, lack of fusion, corrosion, geometry variation, density changes, misassembled and misaligned parts. 

AdvantagesDisadvantages
  • Permanent records
  • Portable
  • Geometry variation does not affect direction of radiation beam
  • Radiation hazard
  • Expensive
  • Trained operators needed
  • Linear defect may be missed
  • Depth of defect not indicated
  • Access to at least two sides of the part required

 

EDDY CURRENT (ET)

Measures or detects surface and subsurface cracks and seams, alloy content, heat treatment variations, wall and coating thickness, crack depth, conductivity and permeability.

AdvantagesDisadvantages
  • High speed
  • Low cost
  • Permanent record capability
  • No couplant required
  • No probe contact required
  • Conductive material only
  • Shallow depth of penetration
  • Surface roughness may affect test quality

 

LIQUID PENETRANT (LPI / PT)

Measures or detects defects open to the surface of parts such as cracks, porosity, seams, laps and through wall leaks.

AdvantagesDisadvantages
  • Low cost
  • Portable
  • Indications may be further examined
  • Defect must be open to the surface
  • Parts must be cleaned before and after testing
  • Surface films, such as coatings, scale, and smeared metal may visually mask defects

 

MAGNETIC PARTICLE INSPECTION (MT/ MPI)

Measures or detects surface and qualified subsurface defects, cracks, seams, porosity, inclusions, and very sensitive for locating small tight cracks.

AdvantagesDisadvantages
  • Low cost
  • Portable
  • Subsurface defects
  • Ferromagnetic materials only
  • Alignment of magnetic field is critical
  • Demagnetization required after the test
  • Surface coatings can mask defects
  • Pre and post cleaning necessary
  • Messy
  • Subjective: dependent on operator interpretation
  • Difficult to automate

 

INFRARED THERMOGRAPHY

Measures or detects hot spots, heat transfer, temperature ranges, temperature monitoring and electrical assemblies.

AdvantagesDisadvantages
  • Permanent record or thermal picture
  • Remote sensing
  • Portable
  • Expensive
  • Reference standards required
  • Poor resolution on thick sections

 

 

VISUAL TESTING (VT)

Measures or detects surface flaws, blemishes, missing features, and dimensional flaws.

AdvantagesDisadvantages
  • Generally fast test time
  • Can be automated
  • Good at finding dimensional flaws or surface blemishes
  • Portable
  • Reference standards required
  • May require multiple cameras and viewing angles for automated systems
  • Subject to operator interpretation if not automated