Utilization of Secondary Jet in Cavitation Peening and Cavitation Abrasive Jet Polishing

The cavitation peening (CP) and cavitation abrasive jet polishing (CAJP) processes employ a cavitating jet to harden the surface or remove surface irregularities. However, a zero incidence angle between the jet and the surface limits the efficiency of these two processes. This limitation can be improved by introducing a secondary jet. The secondary jet interacts with the main jet, carrying bubbles to the proximity of the workpiece surface and aligning the disordered bubble collapse events. Through characterizing the treated surface of AL6061 in terms of the hardness distribution and surface roughness, it was found out that the secondary jet can increase the hardening intensity by 10%, whereas the material removal rate within a localized region increased by 66%. In addition, employing multiple secondary jets can create a patched pattern of hardness distribution. Another finding is that the hardening effect of the cavitation increases with the processing time at first and is then saturated.

Investigating the Etiology and Diagnosis of Sacroiliac Joint Pain

The sacroiliac (SI) joint is often characterized as a large, auricular-shaped, and diarthrodial synovial joint. The SI ligamentous structure is more extensive in the dorsal part due to the absence of the posterior capsule, which functions as a connecting band between the sacrum and ilium. In addition, a network of muscles supports the SI joint that helps deliver regional muscular forces to the pelvic bones. The third and fourth decades of life promote senescent changes manifested by surface irregularities, crevice formation, fibrillation, and clumping of chondrocytes.

SURFACE IRREGULARITIES OF OAK WOOD AFTER TRANSVERSAL CUTTING WITH A CIRCULAR SAW

This paper deals with the effect of saw blade type (24, 40 and 60 teeth) and sawn distance on the primary profile (Pz) of tranvesre surface of European oak (Quercus robur L.) after transversal cutting. Transversal cutting was provided at constant cutting speed vc = 62 m.s-1and with manual feeding using circular saw blade. An additional parameter was to determine the maximum sawn distance for each type of saw blade up to the point where the saw blade overheated, as well as the beginning of the blackening of the wood surface. The highest values of the primary profile (Pz) were achieved with a saw blade with 24 teeth, lower values were measured on wood cut with a 40 tooth blade and the lowest values after cutting with a 60 tooth blade. As the saw distance increased, there was no rapid and steep increase in the primary profile values, but these values gradually increased slightly, probably due to the gradual blunting of the tool.

Small-scale topographic irregularities on Phobos: image and numerical analyses for MMX mission

The mothership of the Martian Moons eXploration (MMX) will perform the first landing and sampling on the surface of Phobos. For the safe landing, the 2.1-m-wide mothership of the MMX should find a smooth surface with at most 40 cm topographic irregularity, however, whose abundance or even existence is not guaranteed based on current knowledge. We studied the highest resolution (a few meters per pixel) images of Phobos for possible topographic irregularities in terms of boulder (positive relief feature) and crater distributions. We find that the spatial number densities of positive relief features and craters can vary significantly, indicating that the surface irregularities vary significantly over the entire surface. We extrapolate the size-frequency distributions of positive relief features to evaluate the surface roughness below the image resolution limit. We find that the probabilities that topographic irregularities are < 40 cm for the areas of 4 × 4 m and 20 × 20 m are > 33% and < 1% for boulder-rich areas and > 88% and > 13% for boulder-poor areas, respectively, even for the worst-case estimates. The estimated probabilities largely increase when we reduce the assumed number of positive relief features, which are more realistic cases. These indicate high probabilities of finding a smooth enough place to land on Phobos’ surface safely. Graphical Abstract

Foil tape—a simple, versatile tool for turtle shell repair

The repair of shell fractures in turtles is often delayed due to the time, labor and resources involved in many current shell repair methods, resulting in increased stress, handling and recovery time for the patient. This article introduces a new repair technique using aluminium foil tape combined with cyanoacrylate glue, which allows quick, simple and long-lasting closure of fresh shell injuries. Strips of malleable but inelastic foil tape are cut to size and positioned across the fracture at critical junctures, then glued in place on either side of the wound and burnished down to conform to surface irregularities and insure consistent adhesion. This technique is non-invasive, requires no curing time and can be customized for a wide range of turtle sizes and injuries, either as a stand-alone method or a preliminary stabilization tool. In the author’s experience, it has proven to be consistently effective at reducing fractures and staying in place until removal, when it is easily peeled off with no residual damage. The speed, ease and endurance of the foil tape method may encourage more widespread repair of fresh shell fractures and, in so doing, optimize recovery time and results for chelonian patients.

Tribological Performance of Random Sinter Pores vs. Deterministic Laser Surface Textures: An Experimental and Machine Learning Approach

This work critically scrutinizes and compares the tribological performance of randomly distributed surface pores in sintered materials and precisely tailored laser textures produced by different laser surface texturing techniques. The pore distributions and dimensions were modified by changing the sintering parameters, while the topological features of the laser textures were varied by changing the laser sources and structuring parameters. Ball-on-disc tribological experiments were carried out under lubricated combined sliding-rolling conditions. Film thickness was measured in-situ through a specific interferometry technique developed for the study of rough surfaces. Furthermore, a machine learning approach based on the radial basis function method was proposed to predict the frictional behavior of contact interfaces with surface irregularities. The main results show that both sintered and laser textured materials can reduce friction compared to the untextured material under certain operating conditions. Moreover, the machine learning model was shown to predict results with satisfactory accuracy. It was also found that the performance of sintered materials could lead to similar improvements as achieved by textured surfaces, even if surface pores are randomly distributed and not precisely controlled.

Simulation of a vehicle movement on a roadway with stochastic irregularities prescribed by the power spectral density

A vehicle represents a mechanical system, which consists of bodies interconnected by joints, force elements, constraints and other coupling elements. When a vehicle moves on a roadway, it is excited due to roadway surface irregularities. It results to vibration of the vehicle mainly in the vertical direction. These vertical movements are known as a vertical dynamics of vehicles. The level of vibrations characterized by their frequency and amplitudes considerably effects two main phenomena, i.e. driving safety and ride comfort for passengers. Therefore, it is necessary to investigate and analyse response of vehicles to the vertical excitations. This article is aimed at evaluation and research of driving properties of a vehicle by means of simulation computations. In case of analysing vehicle’s mechanical system using a virtual model, it is necessary to define in a proper way not only parameters of an investigated vehicle, but also parameters of the excitations due to a roadway surface irregularities. In the reality, roadway surface irregularities have a stochastic behaviour. These fact is processed using statistical methods and it results to the power spectral density of the roadway surface irregularities. A presented research is focused on evaluation of selected output quantities of a vehicle, which moves on the road at various speeds and on various road qualities. An evaluated vehicle uses independent front wheels suspension, which design comes from the utility model. The rear axle is a rigid axle. Dynamic analyses and assessment of the resulting parameters were performed in the Simpack multibody software package. Based on reached results it is obvious, that vertical dynamics of the vehicle is affected by road quality and driving speed. Moreover, the performed analyses have proven, that the used independent front wheels suspension improves driving properties of the vehicle, contributes to better ride comfort and ensures required driving safety.

Surface profile of different heat-treated nickel-titanium files before and after root canal preparation

The aim of this study was to evaluate surface wear, presence of microcracks and surface irregularities of WaveOne (WO) and WaveOne Gold (WOG) instruments before and after multiple uses. Eight Primary instruments of the WO and WOG systems were evaluated, each one was used to prepare six mesial canals of extracted human mandibular molars. The surface of the instruments was evaluated before use (T0), after instrumentation of three (T1) and six (T2) root canals. Surface wear was analyzed using a three-dimensional optical profiler and the presence of microcracks and surface irregularities were evaluated using a tabletop scanning electron microscopy. The Friedman test was used to assess surface wear and Kruskal-Wallis test to evaluate the presence of microcracks and surface irregularities, with a 5% significance level. There was a significant increase in wear in both groups at T2, compared to T0 (p=0.0003). The surface wear after instrumentation of six canals (T2-T0) was statistically greater in the WOG group, than in the WO group (p=0.02), where the presence of microcracks was significantly greater and increased after multiple uses (p<0.05). The presence of surface irregularities in the cutting blade before and after use was statistically greater in the WOG group than WO group (p<0.05). Wear of the cutting blade, microcracks and surface irregularities were observed on the surface topography of all the instruments after multiple uses. These surface changes may affect the cutting efficiency of WOG files and increase the risk of fracture of WO files.

DEVELOPMENT OF ALGORITHM FOR AUTOMATED ASSESSMENT OF THE TIGHTNESS OF CONTACT SEALING CONNECTIONS OF ISOLATION VALVES

The paper analyzes the prospects for using applied mathematical and algorithmic support for the study of the sealing ability of contact sealing connections of isolation valves. To ensure the operability of the equipment, it is necessary to determine the required level of sealing forces (contact pressures) that affect the weight and size characteristics of the product. The relevance of the study is related to the task of reducing the amount of time and material resources at the stage of design and experimental testing of pipeline fittings. The purpose of this work is to develop methods for automated assessment of the tightness of contact sealing connections to develop proposals for reducing the required level of contact pressures and weight and size characteristics of isolation valves. The paper presents an overview and analytical study of methods for determining the tightness of contact sealing connections, as well as a mathematical apparatus for modeling surface irregularities and defining sealing characteristics of isolation valve connections. An algorithm for evaluating these parameters has been developed, which modules can be further implemented as software for automating the assessment of the tightness of contact sealing connections at various stages of designing isolation valves. The developed algorithm makes it possible to filter out irrelevant sets of design parameters at the early stages of design without the need for their experimental verification, which will reduce the total amount of time and material resources in the development of isolation valves of pipelines.