Abstract
The mechanical response of a servo-hydraulic testing system is affected by the stiffness of test specimens. An adaptive controller helps in auto-tuning the system by setting the optimal proportional-integral-derivative values for the subsequent test as the stiffness changes. This paper presents the effect of auto-tuning of various channels on the flow response of several commercial Al and Mg alloys and a mild steel. Strain-controlled monotonic tensile tests were performed at a given strain rate of 1 × 10−4 s−1 after auto-tuning of position, load, and strain channels in different combinations. Serrated flow or Portevin–Le Chatelier effect was observed in the Al alloys after auto-tuning of either position channel only or position and load channels. However, the serrations of Al alloys were shielded after further auto-tuning of strain channel. The stress-strain curves of Mg alloys and mild steel were observed to be basically free of serrations under any combinations of auto-tuning, which confirms that the serrated flow is a property of specific materials rather than a machine system noise.
Highlights
Excessive oscillatory tendency in the hydraulic systems is the primary cause for instability of the system
Mg alloys and mild steel were observed to be basically free of serrations under any combinations of auto-tuning, which confirms that the serrated flow is a property of specific materials rather than a machine system noise
We reported for the first time, the effect of auto-tuning of various channels of a hydraulic fatigue testing system on the mechanical response of materials
Summary
Excessive oscillatory tendency in the hydraulic systems is the primary cause for instability of the system. The system was being stable during the tests, many researchers have reported the serrated flow in some materials under a certain strain rate and temperature range [7,8,9,10,11]. It was considered as the material property rather than the noise of machine. We reported for the first time, the effect of auto-tuning of various channels of a hydraulic fatigue testing system on the mechanical response of materials. The effect of auto-tuning of strain channel under strain control mode is of particular interest of the present study
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