Damage accumulation near the cold-expanded hole due to high-cycle fatigue by crack compliance method

The novel destructive method is implemented for quantitative assessment of fatigue damage accumulation in the stress concentration zone accompanied by residual stress due to cold expansion of the through-thickness hole. Damage accumulation is reached by preliminary cyclic loading of plane specimens with cold-expanded holes. Narrow notches, emanating from the hole edge at different stages of high-cycle fatigue, serve to manifest a damage level. These notches are inserted without applying external load. Deformation response to local material removing, caused by pure residual stress influence, is measured by electronic speckle pattern interferometry (ESPI) in terms of in-plane displacement components. Normalized values of the notch mouth open displacement (NMOD), in-plane displacement component at the initial point of the notch acting in the notch direction (U0), in-plane displacement component at the final point of the notch acting in the notch direction (U1) and the stress intensity factor (SIF) are used as current damage indicators. Numerical integration of curves, describing an evolution of each fracture mechanics parameter over lifetime, produces the damage accumulation function in an explicit form. It is established that all four fracture mechanics parameters give very close results.

Higher-order Lamb waves with quasi-zero surface displacement components on a GaAs piezoelectric plate

Higher-order Lamb waves with quasi-zero surface displacement components are reported on (100)-cut GaAs propagating along the <110> direction where the total displacement at the surface of the plate is less than 10% of the maximum total displacement. The dispersion curves and the displacement component profiles show the reduction of total displacement at the surface of the plate starting when the phase velocities of the higher-order modes are crossing the shear bulk acoustic wave velocity to the value as low as 5%. Due to the concentration of acoustic energy inside the plate, the reported quasi-zero plate acoustic waves (QZ-PAW) further reduce the radiation of acoustic when the plate surface is in contact with liquid. The experimental results validate the occurrence of QZ-PAW with a reduction of viscous damping insertion loss compared to previously reported quasi-longitudinal Lamb waves (QL-LW). The results demonstrate the potential QZ-PAW mode for emerging applications such as dual-mode PAW sensors, PAW devices with integrated sensor and actuator, thin-film and ultra-high frequency (UHF) PAW sensors in highly viscous liquid media.

Multi-Monostatic Interferometric Radar with Radar Link for Bridge Monitoring

In recent years, interferometric radars have been extensively used as sensors for static and dynamic monitoring of bridges. Generally speaking, a radar can only detect the displacement component along its view direction. As the movement of a real bridge or a large structure can be rather complex, this limitation can be a significant drawback in engineering practice. In order toovercome this limitation, in this article, a multi-monostatic interferometric radar with radio link is proposed. This radar is able to detect a second component of displacement using a transponder. The transponder is connected to the radar through a radio link. The radio link allows the installation of the transponder far away from the radar, and even in the opposite direction. The equipment is based on a MIMO radar, two transceivers for the radio link, and a transponder. The transceivers and the transponder are essentially two antennas and an amplifier system. The equipment is experimentally tested in controlled scenarios and in the case study of Indiano Bridge, Florence, Italy.

Reconceptualization of Eating Addiction and Obesity as Displacement Behavior and a Possible Treatment

Purpose: Displacement behavior is a bio-behavioral mechanism that allows an animal to deal with situations that cannot readily be faced nor avoided, or that are thwarting. It may explain compulsive overeating (eating addiction). Resembling addiction, displacement behavior is irrepressible behavior that is contextually inappropriate, e.g., sleeping or feeding when threatened by a predator, or binge eating in response to a work altercation. It is thought to be due to rechanneling of overflow brain energy to another drive (e.g., feeding drive) when two drives, e.g., fight or flight, equally oppose each other. Moving the opposing drives out of equilibrium, by resolving the person’s underlying problem/stressful situations, theoretically should mitigate the displacement mechanism and addictive overeating. Methods: We developed a mobile phone intervention targeting addictive overeating, including a displacement mechanism component. A displacement use subgroup (N=37) ages 14-24 with obesity (mean BMI= 38.1) identified life situations they could neither face nor avoid, or that were thwarting them, and developed action plans to address each situation. Feasibility and acceptability were evaluated. Results: Participants found the displacement component to be understandable and user-friendly. The majority (26/37 – 70%) used the core “Dread List” feature to input 90 individual dreaded/problem situations fueling displacement-based overeating, coupled with action plans to address each problem. Conclusion: The displacement mechanism may be a useful basis for treatment of eating addiction and obesity, and may provide individuals with hope that they can curb their addiction without relying on willpower to not overeat. A randomized trial evaluating the displacement intervention is planned.

Residual stresses near cold-expanded hole at different stages of high-cycle fatigue by crack compliance data

Experimental method for a characterization of high-cycle fatigue evolution of residual stress near cold-expanded hole is developed and implemented. The technique is based on simultaneous measurements of deformation response to narrow notch, inserted in residual stress field, on opposite specimen’s faces by electronic speckle-pattern interferometry (ESPI). Two-side measurements of notch opening displacements are performed when a single notch, emanating from cold-expanded hole edge, is inserted. The transition from in-plane displacement component to residual stress intensity factor (SIF) values follows from the relationships of modified version of the crack compliance method. The approach provides a difference in residual stress values referred to mandrel entrance and exit surface. Notches are inserted at different stages of low-cycle fatigue without applying external load. The results obtained describe fine nuances of residual stress evolution, which cannot be considered as monotonic relaxation.

Measurement of Quasi-Static and Dynamic Displacements of Footbridges Using the Composite Instrument of a Smartstation and an Accelerometer: Case Studies

Monitoring the dynamic responses of bridge structures has received considerable attention. It is important to synchronously measure both the quasi-static and dynamic displacements of bridge structures. However, the traditional accelerometer method cannot capture the quasi-static displacement component, although it can detect the dynamic displacement component. To this end, a novel composite instrument of a smartstation was proposed to monitor vibration displacements of footbridges. Full-scale experiments were conducted on a footbridge to validate the feasibility of the composite instrument-based monitoring method. A Chebyshev filter and wavelet algorithms were developed to process the composite instrument measurements. It was concluded that the measurement noise of the composite instrument was mainly distributed in a frequency range of 0–0.1 Hz. In two case studies with displacement peaks of 5.7–10.0 mm and 1.3– 2.5 mm, the composite instrument accurately identified the quasi-static and dynamic displacements. The composite instrument will be a potential tool for monitoring structural dynamics because of its enhanced overall performance.

Measurement of Quasi-static and Dynamic Displacements of Footbridges Using the Composite Instrument of Smartstation and Accelerometer: Case Studies

Dynamic response monitoring of bridge structures has received considerable attention. It is important to synchronously measure both quasi-static and dynamic displacements of bridge structures. However, traditional accelerometer method cannot capture quasi-static displacement component although it can detect dynamic displacement component. To this end, a novel composite instrument of smartstation was proposed to monitor vibration displacements of footbridges. Full-scale experiments were conducted on a footbridge to validate the feasibility of the composite instrument-based monitoring method. Chebyshev filter and wavelet algorithms were developed to process the composite instrument measurements. Conclusions were drawn that the measurement noise of the composite instrument mainly distributed in a frequency range of 0 - 0.1 Hz. In two case studies with displacement peaks of 5.7 - 10.0 mm and 1.3 to 2.5 mm, the composite instrument accurately identified their quasi-static and dynamic displacements. The composite instrument will be a potential tool for structural dynamic monitoring with the enhancement of its overall performance.

Vector-acoustic full-waveform inversion: Taking advantage of wavefield separation and dealiasing

Vector-acoustic full-waveform inversion (VAFWI) directly inverts vector-acoustic (VA) data, which consist of pressure and particle displacement components, at the cost of conventional acoustic full-waveform inversion (FWI). VA data contain information about the direction of arrival of the recorded seismic waves. In VAFWI, this directional information is taken into account by introducing an appropriate data weighting. With this weighting, in the geometry of a marine seismic experiment, the VAFWI adjoint calculation approximates inverse wavefield extrapolation, resulting in the natural separation of up- and downgoing recorded waves. If the free-surface effects are modeled during the inversion, the wave separation leads to (1) suppression of surface-related artifacts, (2) constructive interference of receiver ghosts with their primaries leading to preservation of the low-frequency content in the adjoint fields, and (3) compensation for insufficient spatial wavefield sampling on the receiver side. The horizontal displacement component helps interpolate the missing data. Synthetic examples demonstrate that for undersampled data, VAFWI consistently recovers the subsurface properties with higher resolution and fewer artifacts than conventional FWI.

SAR and Optical Data Comparison for Detecting Co-Seismic Slip and Induced Phenomena during the 2018 Mw 7.5 Sulawesi Earthquake

We use both Synthetic Aperture Radar (SAR) and Optical data to constrain the co-seismic ground deformation produced by the 2018 Mw 7.5 Sulawesi earthquake. We exploit data processing techniques mainly based on pixel cross-correlation approach, applied to Synthetic Aperture Radar (SAR) and optical images to estimate the North–South (NS) displacement component. This component is the most significant because of the NNW–SSE geometry of the fault responsible for the seismic event, i.e., the Palu-Koro fault, characterized by a strike-slip faulting mechanism. Our results show a good agreement between the different data allowing to clearly identify the surface rupture due to the fault slip. Moreover, we use SAR and optical intensity images to investigate several secondary phenomena generated by the seismic event such as tsunami, landslides, and coastal retreat. Finally, we discuss differences between SAR and optical outcomes showing strengths and disadvantages of each one according to the investigated phenomenon.