Two methods for automatic chatter detection in outer diameter plunge feed grinding are proposed. The methods employ entropy and coarse-grained information rate (CIR) as indicators of chatter. Entropy is calculated from a power spectrum, while CIR is calculated directly from fluctuations of a recorded signal. The methods are verified using signals of the normal grinding force and RMS acoustic emission. The results show that entropy and CIR perform equally well as chatter indicators. Based on the normal grinding force, they detect chatter in its early stage, while only cases of strong chatter are detected based on RMS acoustic emission.
Fatigue-crack initiation was investigated by testing high-strength steels (AFNOR 35 NCD 16 and 35 CD 4) with 0.6-in. (15-mm) thick ASTM compact specimens having various notch-root radii between 0.003 in. (0.07 mm) and 0.04 in. (1 mm).
Measuring devices were used to detect flaws with a surface area of only a few square millimetres in their propagation planes.
In order to calculate the number of cycles required to initiate a crack, notch root behavior was investigated through several parameters. − ΔK/ √ρ, from linear-elastic fracture mechanics, which concentrate results when the initiation time is large; − KfEP, an experimental parameter derived from low-cycle fatigue data when Ni<105 cycles. In this case, the ratio between theoretical and experimental values of the initiation time is between one and two for a given nominal stress.
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