РОЗРИВАЛЬНІ ХАРАКТЕРИСТИКИ КОМПЛЕКСНОЇ ПОЛІЕТИЛЕНОВОЇ НИТКИ

Purpose. To investigate the influence of the number of threads resisting to break, the griping length, and the change in the position of the interlacing point when threading with a loop the breaking characteristics of complex polyethylene threads in the form of a loop.Methodology. In the course of the research, experimental research methods were used to determine the breaking characteristics of high molecular weight polyethylene threads on a WDW-5ES tensile machine in accordance with DSTU ISO 2062: 2004, the main provisions of textile materials science and knitting theory, methods of analysis and synthesis of the results obtained. Results. Based on the results of the studies, the influence of different factors on the breaking characteristics of complex multifilament threads was determined, namely: the influence of the number of threads resting on the break, the griping length and the change in the position of the weave point when threading with a loop. In the course of research, the griping length was changed in the range from 25mm to 300mm, and with a stable griping length (100 mm), the location of the thread weave point relative to the lower grip (25mm, 50mm, 75mm) was changed. It has been found that the breaking characteristics of a complex polyethylene yarn are influenced by both the griping length and the location of the weave point in the case of a loop-shaped break. The magnitude of the specific breaking force in the study of loop-shaped rupture is greater than in the study of straight segments of the thread. This is due to parallelization and compaction of the filaments due to the presence of the weave point on the thread that resists tearing. Scientific novelty. Regularities of the effect of griping length, linear density, and location of the point of weave of the complex high molecular threads in relation to the downer and upper grip are established provided that the griping length (100 mm) remains unchanged on the value of breaking load and elongation.Practical significance. Determination of the factors affecting the breaking characteristics of a complex polyethylene yarn will allow in the future, at the stage of designing the structure of knitwear in computer 3D modeling systems, to provide for the magnitude of the breaking force.

Operating Speed Prediction Models for Tangent Segments: A Brief Review

This paper provides a review of studies aimed at developing operating speed prediction models for road tangent sections. The review included many studies, conducted in different geographical areas of the world, in terms of road classification, types of vehicles, techniques and devices used in data collection, number of study sites, the principle adopted in extracting the free-flow speed, as well as the topography that the road path passes through and grads of the studied sections. Moreover, this review mentioned the analysis methods adopted in the modeling, and included the model formulas that the researchers have reached in their studies, as it showed all the geometric elements and traffic characteristics that appeared in the models as independent variables. The author has avoided critiquing or evaluating the methodologies of the reviewed research and accordingly this paper has been prepared for documentation only. The author aims primarily to save the effort and time of graduate students and researchers interested in modeling the operating speed on straight segments, as all data and information are arranged in tables and coordinated for this purpose. Doi: 10.28991/cej-2021-03091784 Full Text: PDF

Adaptive Finite Element Model for Simulating Crack Growth in the Presence of Holes

This study presents a developed finite element code written by Visual Fortran to computationally model fatigue crack growth (FCG) in arbitrary 2D structures with constant amplitude loading, using the linear elastic fracture mechanics (LEFM) concept. Accordingly, optimizing an FCG analysis, it is necessary to describe all the characteristics of the 2D model of the cracked component, including loads, support conditions, and material characteristics. The advancing front method has been used to generate the finite element mesh. The equivalent stress intensity factor was used as the onset criteria of crack propagation, since it is the main significant parameter that must be precisely predicted. As such, a criterion premised on direction (maximum circumferential stress theory) was implemented. After pre-processing, the analysis continues with incremental analysis of the crack growth, which is discretized into short straight segments. The adaptive mesh finite element method was used to perform the stress analysis for each increment. The displacement extrapolation technique was employed at each crack extension increment to compute the SIFs, which are then assessed by the maximum circumferential stress theory to determine the direction of the crack growth and predict the fatigue life as a function of crack length using a modified form of Paris’ law. The application examples demonstrate the developed program’s capability and performance.

Stovner Tower Accessible Pedestrian Walkway to the Fiord Viewpoint

<p>The Stovner Tower forms part of an activity park in the Stovner district of Oslo. The tower, providing a serpentine walkway through the treetops with a maximum height of 15m, is designed to be universally accessible. The route is based on a series of straight lengths connected with abrupt changes of direction. The 2m wide walkway has an overall length of 270m with a constant 1:15 slope. There are four intermediate horizontal platforms intended as relaxation and viewing areas, each one with different sizes. The principal deck structure is steel, formed from a central tube with a diameter of 762mm. The tube is made up of a series of 2m long straight segments which form the walkway change of direction. Steel cantilever ribs are located at 1.5m centres to support both the solid timber decking and the 1.3m high guardrail. The central steel tube is supported at multiple locations by tripod columns formed from GL32c glulam timber sections varying from 200x200mm to 350x350mm. The timber columns are anchored to the bedrock located close to the surface in this area. Steel walkway sections were shop welded in transportable lengths with bolted on- site connections. Timber to steel connections were also bolted. Steel is painted for corrosion protection. All timber, both solid C24 for decking and glulam columns, is treated for external use. A 3D SAP2000 FE model was used for verifications including a buckling analysis for the slender timber columns and a modal analysis to check for frequencies that would make the structure susceptible to pedestrian-induced vibrations.</p>

Isogonal piecewise linear embeddings of 1-periodic weaves and some related structures

Crystallographic descriptions of isogonal piecewise linear embeddings of 1-periodic weaves and links (chains) are presented. These are composed of straight segments (sticks) that meet at corners (2-valent vertices). Descriptions are also given of some plaits – woven periodic bands, three simple periodic knots and isogonal interwoven rods.

Longitudinal shear stress response in human endothelial cells to atheroprone and atheroprotective conditions

The two main blood flow patterns, namely, pulsatile shear (PS) prevalent in straight segments of arteries and oscillatory shear (OS) observed at branch points, are associated with atheroprotective (healthy) and atheroprone (unhealthy) vascular phenotypes, respectively. The effects of blood flow-induced shear stress on endothelial cells (ECs) and vascular health have generally been studied using human umbilical vein endothelial cells (HUVECs). While there are a few studies comparing the differential roles of PS and OS across different types of ECs at a single time point, there is a paucity of studies comparing the temporal responses between different EC types. In the current study, we measured OS and PS transcriptomic responses in human aortic endothelial cells (HAECs) over 24 h and compared these temporal responses of HAECs with our previous findings on HUVECs. The measurements were made at 1, 4, and 24 h in order to capture the responses at early, mid, and late time points after shearing. The results indicate that the responses of HAECs and HUVECs are qualitatively similar for endothelial function-relevant genes and several important pathways with a few exceptions, thus demonstrating that HUVECs can be used as a model to investigate the effects of shear on arterial ECs, with consideration of the differences. Our findings show that HAECs exhibit an earlier response or faster kinetics as compared to HUVECs. The comparative analysis of HAECs and HUVECs presented here offers insights into the mechanisms of common and disparate shear stress responses across these two major endothelial cell types.

Driver Response to a Dynamic Speed Feedback Sign on Freeway Exit Ramps based on Sign Location, Interchange Type, and Time of Day

Roadway segments that include horizontal curves experience a disproportionate number of crashes compared to straight segments. Many of these crashes are lane departure-related, and excessive speed is often a contributing factor. One particularly vulnerable area for such crashes is freeway interchange ramps, which require a substantial reduction in speed to be safely negotiated. While dynamic speed feedback signs (DSFS) have been found to be an effective speed and crash reduction countermeasure at horizontal curves, the use of such signs on freeway interchange ramps has been limited nationwide. Consequently, the effectiveness of DSFS as a speed reduction countermeasure in such settings has remained largely untested. A before-and-after field evaluation was performed at three freeway exit ramps to assess the impacts of a DSFS on driver speed selection and braking characteristics while approaching and entering the ramp curves. The effectiveness of the feedback sign was tested across various conditions, including sign location, interchange type, time of day, light condition, and vehicle type. In general, the greatest benefits to driver behavior were achieved with the DSFS positioned at the point of curvature, during which curve entry speeds were reduced by approximately 2 mph compared to the pre-DSFS condition. These findings were consistent between the system- and service-interchanges and across all vehicle types. The DSFS was also found to be most effective during daytime off-peak periods compared to peak periods and at night. Based on the study findings, the continued use of DSFS as a speed reduction treatment at freeway exit ramps is recommended.

Natural Frequencies and Band Gaps of Periodically Corrugated Beams

Structures with geometric periodicity can present interesting dynamic properties like stop and pass frequency bands. In this case, the geometric periodicity has the effect of filtering the propagating waves in the structure, in a similar way to that of phononic crystals and metamaterials (non-homogeneous materials). Hence, by adopting such structures, we can design systems that present dynamic characteristics of interest, e.g., with minimum dynamic response in a given frequency range with large bandwidth. In the present work, we show that corrugated beams also present the dynamic properties of periodic structures due to their periodic geometry only (no need of changing mass or material properties along the beam). Two types of corrugated beams are studied analytically: beams with curved bumps of constant radii and beams with bumps composed of straight segments. The results show that, as we change the proportions of the bump, the natural frequencies change and tend to form large band gaps in the frequency spectrum of the beam. Such shifting of the natural frequencies is related to the coupling between longitudinal and transverse waves in the curved beam. The results also show that it is possible to predict the position and the limits of the first band gap (at least) as a function of the fundamental frequency of the straight beam (without bumps), irrespective of the total length of the corrugated beam.