acoustic-emission

name	acoustic-emission
description	Acoustic emission (AE) testing — Kaiser effect, source location, AE parameters (count, energy, amplitude), wave modes, transducer selection, pressure vessel monitoring, ASME Section V Article 12, ASTM E1316.
metadata	{"priority":7,"promptSignals":{"phrases":["acoustic emission","AE testing","Kaiser effect","acoustic emission monitoring","AE source location","acoustic emission NDT"],"minScore":3}}

Acoustic Emission Testing — Complete Skill

Physical Basis

Acoustic emission (AE): transient elastic waves generated by rapid stress relaxation within a material Sources: crack initiation/growth, plastic deformation, corrosion, phase transformation, fiber breakage (composites), delamination, leaks (fluid AE)

Wave propagation: body waves (P and S) + guided waves (Lamb) in plate structures Frequency range: 20 kHz – 1 MHz (most structural AE: 50–400 kHz) Velocity: V_P = √[E(1-ν) / (ρ(1+ν)(1-2ν))] [m/s; longitudinal wave] V_S = √[G/ρ] = V_P × √[(1-2ν)/(2(1-ν))] [m/s; shear wave] Steel: V_P ≈ 5960 m/s; V_S ≈ 3230 m/s

Key AE Parameters

Hit: single AE event exceeding threshold at one sensor

AE signal parameters:

• Amplitude A: peak voltage of waveform [dBae; 0 dBae = 1 μV at transducer] A [dBae] = 20 log₁₀(V_peak [μV])
• Ring-down count: number of threshold crossings in one hit; indicative of signal duration
• Duration: time from first to last threshold crossing [μs]
• Rise time: time from first crossing to peak [μs]
• Energy E: integral of squared voltage over duration [aJ or arbitrary units] E = (1/R_load) ∫ V²(t) dt
• Frequency: peak frequency or centroid frequency [kHz]

Threshold setting: Fixed threshold: 40–50 dBae typical (above noise floor by 6 dB) Floating threshold: adapts to background noise (EMI environments) Peak definition threshold (PDT): 20–50 μs after first crossing

Kaiser and Felicity Effects

Kaiser effect: no AE below previously applied maximum load Material is "quiet" when re-loaded below prior maximum stress → indicates material has not experienced additional damage

Felicity effect (reverse of Kaiser): AE occurs below prior maximum load Felicity Ratio: FR = P_AE_onset / P_previous_max [< 1 indicates damage] ASTM E569 accepts FR ≥ 0.95 for composite vessels; FR < 0.85 → significant damage

Significance: FR ≥ 1.0 → no new damage since last test (Kaiser effect holds) FR < 1.0 → progressive damage; source re-activates at lower load

Source Location

Linear Location (1D)

Two sensors A and B at distance d apart Δt = t_B - t_A [time difference of arrival] Source location x from midpoint: x = Δt × V / 2

Planar Location (2D)

Three or more sensors; solve: (x_source - x_i)² + (y_source - y_i)² = (V × t_i - d_ref)² Overdetermined system → least squares solution Accuracy: ±5–20 mm for well-calibrated systems

Time Difference of Arrival (TDOA)

TDOA_ij = t_i - t_j = (d_i - d_j) / V Hyperbolae intersection → source

Velocity calibration: Use pencil lead break (Hsu-Nielsen source) at known locations PLB: 2H mechanical pencil; 0.3 or 0.5 mm; standardized AE source

Transducer Types

Resonant transducers: high sensitivity at resonant frequency (most common)

• Frequency range: 50–400 kHz (narrow band)
• Typical resonance: 150 kHz or 300 kHz
• Sensitivity: −65 to −55 dBV/μbar (resonant); referenced to manufacturer calibration

Wideband transducers: 50–1000 kHz flat response; for signal analysis and source characterization Less sensitive than resonant; used in research applications

Sensor coupling: thin layer of grease (Dow Corning 111); magnetic hold-down or band clamp Coupling check: pencil lead break test; amplitude > threshold + adequate waveform

Preamplifier: gain 40 or 60 dB; located at sensor; filters noise before long cable run System gain: 0 + 40 dB preamplifier + software gain

Test Configuration — Pressure Vessel

Sensor spacing: V_P × t_rise → maximum source-to-sensor distance for detection For steel vessel: V_P = 5960 m/s; t_rise ≈ 1 ms (detectability); max distance ≈ 6 m Practical: sensors every 3–5 m on large vessels

Pressurization protocol (ASME V Art. 12): Load in steps (25%, 50%, 75%, 90%, 100% design pressure) Hold at each step; monitor AE activity; proceed only if AE stable Rate: 5–10% of design pressure per minute

Accept/reject criteria (ASME PCC-3): Grade A: low activity, no location, no Felicity effect → acceptable Grade B: moderate activity, located sources → monitor, evaluate Grade C: high activity, Felicity effect FR < 0.85 → reject; inspect source by other NDE Grade D: continuous AE; test aborted → failed

Composite Pressure Vessels

CFRP vessel monitoring: AE sources: matrix cracking (50–150 kHz), delamination (100–250 kHz), fiber fracture (300–500 kHz) Burst precursor: amplitude increase + frequency shift toward higher frequency ASTM E1888 / EN 14585: AE test procedure for composite overwrapped pressure vessels

Discrimination: Matrix cracking: low amplitude (45–60 dBae), high count/energy ratio Fiber fracture: high amplitude (70–90 dBae), low count/energy Delamination: intermediate amplitude, long duration

Leak Detection with AE

Fluid leak through crack or orifice: Turbulent flow generates broad-band AE (10–500 kHz) P_AE ∝ Q_leak × ΔP [proportional to flow rate × pressure difference]

Leak location: time-of-arrival difference between two sensors Minimum detectable leak: 0.1–1.0 cc/min depending on vessel, pressure, sensor

Standards

Standard	Scope
ASME Section V Article 12	AE examination of metallic pressure vessels
ASTM E1316	AE terminology
ASTM E976	Mounting and coupling transducers
ASTM E569	AE monitoring during hydrostatic testing
ASTM E1888	AE testing of composite pressure vessels
EN 1330-9	AE terms and definitions

Output

Provide: sensor type and frequency [kHz], sensor spacing [m], threshold [dBae], preamplifier gain [dB], AE parameters to record (amplitude, energy, count, duration, frequency), source location method and expected accuracy [mm], pressurization protocol (steps [%], rate [%/min]), Kaiser/Felicity ratio check procedure, accept/reject criteria (Grade A–D per ASME PCC-3), and applicable standard (ASME Section V Article 12, ASTM E569).