Impact identification on concrete panels using a surface-bonded smart piezoelectric module system

Timely identification of collision damage, especially in aging bridges, is critical for the safety of commuters. However, there is no efficient, cost-effective, in-situ technique to serve this purpose. Wave propagation-based structural health monitoring (SHM) using piezoelectric material is a promising alternative for remote sensing. To that end, this study aims to develop a wave propagation-based monitoring technique using surface-bonded smart piezoelectric modules (SPM) to determine the impact force, location, and projectile properties of low-velocity impacts on concrete panels. An impact source localization algorithm used in composite structures is adapted and simplified for concrete structures. This technique is validated using a combined experimental and numerical investigation, which shows good agreement with the actual impact source location. The impact force, projectile mass, and velocity is determined using a semi-theoretical-experimental technique based on Reed contact model. A special contact-SPM is fabricated and calibrated to determine the contact force at the impact location. The relationship between contact-SPM response and distributed-SPM response is determined using a drop-weight test with steel sphere. The peak contact force and contact duration are in good agreement with Reed contact model, although the latter overpredicts the given parameters. A simplified formula based on Reed contact model is used to inversely estimate the projectile velocity of a known mass and vice versa. Then, using pre-calibrated data, the impact force, projectile properties, and impact force-time distribution is determined using the response of distributed-SPM system. The technique is validated using an arbitrary steel sphere mass. As demonstrated in the combined experimental, theoretical, and numerical study, the proposed surface-bonded SPM system is capable of effectively identifying low-velocity impact incidents on concrete structures, which could potentially facilitate inexpensive, in-situ, real-time condition assessment.

QUALITY OF TROPICAL HARDWOOD FLOORS

ABSTRACT This study aimed to determine the basic density of the wood and to simulate the performance of flooring produced with wood from five tropical species: Dipteryx odorata (Cumaru), Handroanthus spp. (Ipê), Hymenaea Courbaril (Jatobá), Astronium Lecointei (Muiracatiara), and Bowdichia virgilioides (Sucupira-Preta). Falling steel sphere, static and dynamic friction, indentation caused by loads applied in small areas, rolling load, and abrasiveness impact tests were simulated. The results were subjected to analysis of variance and Tukey’s test at 5% significance, and Pearson’s correlation was performed between the basic density and the indexes of each flooring. The basic density of the wood flooring made from the evaluated species ranged from 0.735 to 0.958 g.cm-3. D. odorata, Handroanthus spp. and H. courbaril woods were classified as heavy, while those of A. Lecointei and B. Virgilioides as moderately heavy. It was possible to indicate D. odorata, Handroanthus spp., H. courbaril, and B. Virgilioides flooring for environments with intense traffic where there is dragging or falling objects such as industries and companies. The A. Lecointei flooring can be used in residential environments with light traffic, where the loads exerted are low. There was a correlation between the basic wood density and the flooring use simulation tests.

Fluid Leakage in Metallic Seals

Metallic seals are crucial machine elements in many important applications, e.g., in ultrahigh vacuum systems. Due to the high elastic modulus of metals, and the surface roughness which exists on all solid surfaces, if no plastic deformation would occur one expects in most cases large fluid flow channels between the contacting metallic bodies, and large fluid leakage. However, in most applications plastic deformation occurs, at least at the asperity level, which allows the surfaces to approach each other to such an extent that fluid leakage often can be neglected. In this study, we present an experimental set-up for studying the fluid leakage in metallic seals. We study the water leakage between a steel sphere and a steel body (seat) with a conical surface. The experimental results are found to be in good quantitative agreement with a (fitting-parameter-free) theoretical model. The theory predicts that the plastic deformations reduce the leak-rate by a factor $$\approx 8$$ ≈ 8 .

Experimental and numerical study of the behavior of a Glass Fiber Reinforced Plastic plate under oblique impact

Experimental and numerical studies on the effect of oblique impacts on the ballistic properties of GFRP were carried out. Ballistic tests of specimens using a steel sphere with a diameter of 6.35 mm were performed for inclination angles from the normal of 0, 15, 30, 45, and 60 degrees. Ballistic curves and ballistic limits for each case were obtained, and a function approximating these results was proposed. The size of the delamination area at different angles was also analyzed. The results showed that the most catastrophic failures cases of impact were impacts with angles of 0°–30°. Computational studies of impact loading during oblique impacts were carried out in LS-DYNA using the mesoscale yarn-level model (MSM). Finally, numerically obtained ballistic limits and damaged areas were compared with experimental ones.

Universal SMP gripper with massive and selective capabilities for multiscaled, arbitrarily shaped objects

Grippers are widely used for the gripping, manipulation, and assembly of objects with a wide range of scales, shapes, and quantities in research, industry, and our daily lives. A simple yet universal solution is very challenging. Here, we manage to address this challenge utilizing a simple shape memory polymer (SMP) block. The embedding of objects into the SMP enables the gripping while the shape recovery upon stimulation facilitates the releasing. Systematic studies show that friction, suction, and interlocking effects dominate the grip force individually or collectively. This universal SMP gripper design provides a versatile solution to grip and manipulate multiscaled (from centimeter scale down to 10-μm scale) 3D objects with arbitrary shapes, in individual, deterministic, or massive, selective ways. These extraordinary capabilities are demonstrated by the gripping and manipulation of macroscaled objects, mesoscaled steel sphere arrays and microparticles, and the selective and patterned transfer printing of micro light-emitting diodes.

Development and evaluation of physical properties of a low-cost handheld device for airway clearance therapy

ABSTRACT Several respiratory diseases are characterized by hypersecretion, requiring airway clearance therapy (ACT). Oral high-frequency oscillation (OHFO) devices are effective to enable daily ACT; however, they are still too expensive to become available for low-income patients. We sought to develop a low-cost device (OHFO-LC) and compare its physical properties with those OHFO commercially available (Shaker and Flutter). The OHFO-LC was developed from polyvinyl chloride material and one stainless steel sphere. Pressures and frequencies were measured at flows of 4, 6, 8, 10 and 15L/min. Pressures at the mouthpieces were measured by a transducer connected to a microcomputer. The oscillation frequencies were obtained from the graph of the pressure. The frequencies and pressures were compared among groups using one-way Anova and Tukey’s post hoc tests, p≤0.05. There were no differences among the frequencies of the three devices in all tested flows. The OHFO-LC device showed a higher positive expiratory pressure compared with the Shaker at all tested flows (4 L/min: 4.7±1.2 vs. 1.0±0.2 cmH2O; 6 L/min: 8.6±1.5 vs. 3.5±0.5 cmH2O; 8 L/min: 10.8±1.6 vs. 5.4±0.2 cmH2O; 10 L/min: 13.5±1.2 vs. 7.7±0.4 cmH2O; 15 L/min: 14.3±1.1 vs. 7.8±0.2 cmH2O; OHFO-LC vs. Shaker; p≤0.05) and at 10 and 15 L/min compared with Flutter (10 L/min: 13.5±1.2 vs. 7.5±1.2 cmH2O; 15 L/min: 14.3±1.1 vs. 8.2±1.2 cmH2O; OHFO-LC vs. Flutter, p≤0.05). The cost of the OHFO-LC device was much lower than both the Shaker and the Flutter. Our results showed that the OHFO-LC had physical properties with similar frequencies but higher pressures than other OHFO devices that are commercially available. Future studies are necessary to evaluate its clinical efficacy.

Post-Mortem Analysis of Inhomogeneous Induced Pressure on Commercial Lithium-Ion Pouch Cells and Their Effects

This work conducts a post-mortem analysis of a cycled commercial lithium-ion pouch cell under an induced inhomogeneous pressure by using a stainless-steel sphere as a force transmitter to induce an inhomogeneous pressure distribution on a cycled lithium-ion battery. After the cycling, a macroscopic and microscopic optical analysis of the active and passive materials was executed. Also, scanning electron microscopy was used to analyze active material particles. The sphere shape results in a heterogenic pressure distribution on the lithium-ion battery and induces a ring of locally high electrochemical activity, which leads to lithium plating. Furthermore, a surface layer found on the anode, which is a possible cause of electrolyte degradation at the particle–electrolyte interface. Significant deformation and destruction of particles by the local pressure was observed on the cathode. The analysis results validate previous simulations and theories regarding lithium plating on edge effects. These results show that pressure has a strong influence on electrolyte-soaked active materials.

Green turtle and fish identification based on acoustic target strength

Fisherman accidentally caught sea turtles in their fishnet. It could be dangerous for its population. This study measures the turtle target strength (TS) using modified echosounder. The result could be used to improve the efficiency of turtle repellent device. The experiment conducted in a hatchery fiber tank contained saline water. The Green were 1, 3, 12 and 18 years old. The study used three species of fish to ensure there are no overlapped value between fish and sea turtle. TS of the animals were calculated incorporating reference targets (sphere). The echo power of the turtle was compared with the solid steel sphere which is confirmed good agreements with the theoretical values. The echo power reference by applying Fast Fourier Transform (FFT) analysis has been used in calculating TS of the animal. From the echo evaluation in time domain at different angles, it is obviously shown that echo signal structure is different between the parts of turtle body. This study reveals that high echo strength is acquired from the carapace and the plastron parts. The finding also showed that there are significant differences between 3, 12, 18 years old turtles and fish in every angle measurement.