Piezoelectric Active Damper for Surface Roughness Improvement in Hard Turning Processes

Surface roughness and profile accuracy on rolling or sliding surfaces are critical for the wear and fatigue of a component. A high roughness or poor profile accuracy results in higher friction and higher wear rate of the surface. One of the major factors affecting the surface roughness is chatter vibrations. This paper presents a novel design and development of an active damper for chatter suppression of hard turning processes using a piezoelectric actuator and strain signal for chatter detection. The active damper consists of a piezoelectric actuator with an embedded strain gauge for measuring the vibration displacement. In this work, the radial strain signal as a result of radial chatter vibrations from the strain gauge is used as a feedback signal to the actuator using a feedback controller. The experimental results showed a significant suppression in chatter vibrations and improvement of surface roughness using the proposed active damper. The details of the tool design, control design, hardware implementation and system validation are given hereinafter.

The duration-energy-size enigma for acoustic emission

Acoustic emission (AE) measurements of avalanches in different systems, such as domain movements in ferroics or the collapse of voids in porous materials, cannot be compared with model predictions without a detailed analysis of the AE process. In particular, most AE experiments scale the avalanche energy E, maximum amplitude Amax and duration D as E ~ Amaxx and Amax ~ Dχ with x = 2 and a poorly defined power law distribution for the duration. In contrast, simple mean field theory (MFT) predicts that x = 3 and χ = 2. The disagreement is due to details of the AE measurements: the initial acoustic strain signal of an avalanche is modified by the propagation of the acoustic wave, which is then measured by the detector. We demonstrate, by simple model simulations, that typical avalanches follow the observed AE results with x = 2 and ‘half-moon’ shapes for the cross-correlation. Furthermore, the size S of an avalanche does not always scale as the square of the maximum AE avalanche amplitude Amax as predicted by MFT but scales linearly S ~ Amax. We propose that the AE rise time reflects the atomistic avalanche time profile better than the duration of the AE signal.

Water-Jet Erosion of Grade-A Ship Steel: Experimental Research

A water-jet erosion test was carried out on grade-A ship steel to study the interaction and erosion mechanism of the water jet on the steel surface. When the water jet impacted, a STSS-1 stress-detection module was used to collect the dynamic strain signal on the rear of the ship’s plate, and a scanning electron microscope, transmission electron microscope, X-ray diffractometer, and other equipment were used to analyze the microstructure and phase of the grade-A ship steel before impact. The surface morphology of the material after impact was studied and analyzed. The impact stress of the water jet on the grade-A steel was an alternating stress, and the jet pressure decayed in the radial direction. The material surface was fatigued under the action of the jet alternating stress. After the water-jet erosion, the central area of the grade-A steel was dominated by an elongated cementite hard phase, and the peripheral area had a pearlite structure. A model for the jet erosion and peeling of grade-A ship steel was established to clarify the mechanism of erosion by the water jet.

Deciphering deformation along submarine fault branches below the eastern Sea of Marmara (Turkey): insights from seismicity, strainmeter, GPS and InSAR data

<p>More and more studies worldwide show that seismic and aseismic slip can occur jointly, impacting the seismic hazard in a region. It is thus important to be able to reconstruct the deformation partitioning and fault interactions. In this study, we focus on the eastern Sea of Marmara region south of the megalopolis of Istanbul (Turkey). In this region, the plate-bounding North Anatolian Fault (NAF) is splitting into several branches. The northern branch is locked and is considered to host the nucleation zone of a M~7 earthquake expected for the region. In 2016, a 3-days long foreshock sequence preceded a M<sub>W</sub> 4.2 event located at the junction of the two or more sub-branches. It has been argued that this sequence may have been driven by aseismic slip involved in the earthquake nucleation (Malin et al., 2018). Starting around the time of this earthquake, a large strain signal, lasting 50 days, was identified on a single strainmeter station located ~30km from the M4.2 epicenter (Martinez-Garzon et al., 2019). To better characterize this sequence, we revisit it adding new types of data: we analyze GPS and InSAR data together with reprocessed strainmeter recordings of all the availaible stations in the region during 18 months framing the observed strain signal. To enhance the tectonic features in the strainmeter data, we apply a variational Bayesian Independent Component Analysis (vbICA, Gualandi et al. 2015). Following the M4.2 earthquake, we highlight a 50 km westward migration of the seismicity starting from its epicentral area and lasting 6 months. Increases in the seismic activity correspond to variations in the tectonic components of the recordings at two nearby strainmeters. The first changes in seismicity and strainmeter data occur 2.5 months before the M<sub>W</sub>4.2 event, and are also concomitant with a variation in the trend of the GPS data. The GPS data, along with the strainmeter ones, exhibit a second clear change at the time of the mainshock, that is also lasting two months. Similarly, the InSAR data highlight a variation in the time series around the time of the earthquake, lasting several weeks. The combination of these different types of measurements covering various signal-frequency bands of deformation in the eastern Sea of Marmara highlights the presence of a measurable large-scale and long-lasting deformation transient that begins and ends several weeks before and after the occurrence of a Mw4.2 earthquake. These observations show that further reducing the observational gap both in terms of detection threshold and frequency band allows to decipher signals that usually remain undetected. This is non-trivial but relevant for seismic hazard and risk assessment especially in case of submarine faults collocated with population centers, as is the case of the study region.</p>

Verification of the Propagation Range of Respiratory Strain Using Signal Waveform Measured by FBG Sensors

The FBG (Fiber Bragg grating) sensor is an optical fiber type strain sensor. When a person breathes, strain occurs in the lungs and diaphragm. This was verified using an FBG sensor to which part of the living body this respiratory strain propagates. When measured in the abdomen, the signal waveforms were significantly different between breathing and apnea. The respiratory cycle measured by the temperature sensor attached to the mask and the strain cycle measured by the FBG sensor almost matched. Respiratory strain was measured in the abdomen, chest, and shoulder, and the signal amplitude decreased with distance from the abdomen. In addition, the respiratory rate could be calculated from the measured strain signal. On the other hand, respiratory strain did not propagate to the elbows and wrists, which were off the trunk, and the respiratory time, based on the signal period, could not be calculated at these parts. Therefore, it was shown that respiratory strain propagated in the trunk from the abdomen to the shoulder, but not in the peripheral parts of the elbow and wrist.