Application Note: Barkhausen Noise vs. Nital Etch on Fillet Radius

In this application grinding temper on a crankshaft fillet radius was measured with Bakhausen noise method as an alternative to nital etch.

The problem: Grind temper on a crankshaft fillet radius

A manufacturer experienced a quality leak due to grind temper on a crankshaft fillet radius which led to premature failure in service. Nital etch was initially used to sort the suspect parts but the results did not correlate with fatigue life data. Barkhausen noise was then investigated as an alternative to nital etch.

Close up view of the radius with severe grind temper.
Figure 1: Close up view of the radius with severe grind temper.

The testing method: Non-destructive Barkhausen noise method

Barkhausen noise was used via hand testing at strategic locations on the circumference of the shaft at the fillet radius.

Barkhausen noise sensor measuring, top view.
Figure 2: Testing – top view.
Barkhausen noise sensor measuring, side view.
Figure 3: Testing – side view.

The results

Barkhausen noise proved to be a superior method over Nital etch for predicting failures.  Note that all of the parts with etch rating of 5 or greater failed Nital etch inspection and were scrapped. Barkhausen noise inspection reduced the occurrence of “false rejects” and correlated closely to the fatigue life results.  This ultimately saved the customer a significant amount of money in unnecessary scrap and allowed them to perform inspections on 100% of the parts in lieu of a statistical survey with nital etch.

Barkhausen Noise vs. Ginder Burn Rating (via Nital Etch) vs. Fatigue Life (P/F).
Figure 4: Barkhausen Noise vs. Ginder Burn Rating (via Nital Etch) vs. Fatigue Life (P/F).

Instrument used for this application:

Rollscan 350

Barkhausen noise signal analyzer Rollscan 350 is designed for surface quality control and testing of near-surface defects such as grinding burns, heat treatment defects, as well as changes in stress and microstructure in a wide variety of ferritic steel and other ferromagnetic materials.

Rollscan 350 analyzer and general purpose sensor measuring a bearing

Related articles

Barkhausen Noise as an Alternative to Nital Etch for the Detection of Grind Temper on Gears

Application Note: XRD on Cranks for Grinding Stress

Article Type: Application note
Part Under Inspection: Crankshaft
Product Line: Rollscan