Anja Weidner, Horst Biermann

Institute of Materials Engineering

Colloquium Oulu – 2019, February 14th

Very high cycle fatigue at Freiberg

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Very high cycle fatigue at Freiberg

Ultrasonic fatigue testing

• 3 Ultrasonic fatigue testing machines

• (BOKU Wien, 2011 und 2013, Industrial partner 2017)

• high testing frequency (20 kHz)

• (N > 109 within few days)

• Different load ratios (R = -1, R > 0)

• Continuous testing or puls-pause mode

• inclusive compressed air cooling (spot-cooler)

• In situ measurement of resonance frequency (controlling

parameter, non-linearity parameter)

• Coroborrated by infrared thermography

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Very high cycle fatigue at Freiberg

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Very high cycle fatigue at Freiberg

strain

amplitude

vibration

amplitude

Ultrasonic

converter

Spot cooling

Amplification

horn

specimen

Very high cycle fatigue at Freiberg

Principle of ultrasonic fatigue testing

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Very high cycle fatigue at FreibergVery high cycle fatigue at Freiberg

Resonance frequency and non-linearity parameter

• Resonance frequency fres

feedback signal of ultrasonic fatigue testing

strongly influenced by temperature

• Non-linearity parameter brel

change of sinusoidal ultrasonic wave during cyclic loading

use of higher harmonics

different processes: hardening, softening, crack initiation …

Am

plit

ude

Frequency

Fundamental

(1st order)

2nd order

3d order

20 kHz

40 kHz

60 kHz

non-deformeddeformed

Kumar et al. J. Appl. Phys. 106 (2009)

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Very high cycle fatigue at Freiberg

Infrared thermography

• VarioCamhr head (Infratec, Dresden)

• Temperature resolution: 30 mK

• Frame rate: 50-60 Hz

• Infraredt pixel resolution: 640 × 320 pxl

• Lateral resolution (microscopic objective: 25 µm

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Very high cycle fatigue at Freiberg

Infrared thermography – full surface view

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Very high cycle fatigue at Freiberg

Infrared thermography – full surface view

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NHD = 0.225 mmσa = 625 MPa

Nf = 2,182,000

Very high cycle fatigue at Freiberg

Infrared thermography – correlated fractography

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Direct

thermogram

Reflected

thermograms

Very high cycle fatigue at Freiberg

Infrared thermography – full surface view

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Very high cycle fatigue at Freiberg

Resonance frequency, non-linearity parameter and

temperature

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Compressed air cooling

Radial fan

Induction coil

Pyrometer

Photonic sensor

Specimen

Pressure sensor

Temperature sensor

Vibration sensor

Very high cycle fatigue at Freiberg

VHCF at high temperatures

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(5) HF-Generator

Specimen

(1) Pyrometer

Vibration sensor (2) IR-Temperature measurement

(6) Ultraschall-Prüfmaschine

Controll-Parameter:1) Temperature (Pyrometer)

2) Temperature (IR-Sensor)

3) Pressure

4) Elongation (Photonic sensor)

5) Condition HF-Generator

6) Condition USFT

(3) Pressure sensor

(4) Photonic

sensor

Controlling software

Compressed air

Very high cycle fatigue at Freiberg

VHCF at high temperatures

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Very high cycle fatigue at Freiberg

VHCF at high temperatures