Developing of the optimal shape and reinforcement structure of the specimen for adequate determination of the tensile strength in unidirectional composites

Unidirectional composites exhibit the highest strength when stretched along the fibers. However, the proper determination of the strength faces great methodological difficulties. The main problems of tensile testing of polymer composites consisted in developing of the specimen shape and the method of specimen fixation which ensure the minimum impact of the stress concentration near the grips on the strength measurements. A conventional shape of the specimen with fillets is unsuitable for unidirectional polymers due to the splitting occurred in the fillet zones upon loading. Therefore, the specimens are usually standardized in the form of rectangular strips fixed using pads or special grips which provide constant transverse forces. However, with such a specimen shape, a significant stress concentration inevitably occurs at the edge of grips and the lower the ratio of the interlayer shear modulus to the longitudinal Young’s modulus, the greater the stress concentration impact. For the purpose of the most correct determination of the strength we propose to use specimens with smoothly varying dimensions at the same cross-sectional area which ensures keeping the total number of unbroken fibers in each section. The specimen thickness decreases when moving from the working part of the specimen to the gripping part, whereas the width (while maintaining the section area) grows to prevent the specimen collapsing resulting from transverse forces in standard self-tightening grips. Analytical and FEM modeling is performed to select a rational contour shape. Technological equipment has been developed and a procedure of manufacturing testing specimens has been worked out. The tensile test of specially manufactured curvilinear reinforced specimens showed higher strength values compared to standard rectangular strips or specimens with semicircular fillets.

A closed modified V-shaped uniplanar triple band ACS fed antenna for wireless applications

In the proposed paper, a uniplanar asymmetric coplanar strip (ACS) fed antenna with closed V-shaped radiating patch of size printed on FR4 substrate with loss tangent ( =0.02, height (h)=1.6mm, and dielectric constant of 4.4 covering WiMAX, X-band and WLAN applications is presented. The proposed closed V-shaped radiating patch is formed by joning two rectangular stubs. The resultant shape of the radiating patch is obtained by adding rectangular strips to feed line until desired multiband results are achieved. The advantage of this structure is that it forms simple configuration as well as helps the overall antenna in attaining three distinict useful frequency band with good impedance matching for S11-10 dB criteria. The proposed ACS fed antenna operates at 3.1 (WiMAX), 5.0 (WLAN) and 9.9 (X-band) GHz with impedance bandwidth ranging from 2.7-3.9 GHz, 4.4-5.5 GHz and 9.5-10.3 GHz in simulation. Under measurement the proposed antenna shows multiband phenomenon at 3.2, 5.3 and 9.7 GHz with impedance bandwidth ranging from 2.8-3.7 GHz, 4.6-5.4 GHz and 9.4-10 GHz, respectively. The antenna exhibits simulated gain of 2.51, 1.18 and 1.96 dB at the corresponding frequency bands of 3.1, 5.0 and 9.9 GHz. The key parameters of the antenna like length and width of the multi-branched strips are optimized to get the multiband operation. The deisign simulation is carried out in Ansys HFSS (High frequency Simulation Software) where different characteristics of the proposed antenna are investigated. The evolution and optimization process is dealt in detail with the help of S11, VSWR, current distributions, radiation patterns and gain.

A quad band planar slotted microstrip patch antenna for wireless applications

This research paper presents two different types of multiband patch antenna. The first design is a dual-band antenna and the second design is a quad-band antenna. Both the antennas have a compact size of , and is designed on FR4 substrate with loss tangent (=0.02, height (h)=1.6 mm, with dielectric constant of 4.4. The dual-band antenna operates at frequencies 3.9 and 5.71 GHz. These dual band operations are accomplished by utilizing L-shaped slot in the ground part and T-shaped slot in the radiating part of the patch antenna. The gain corresponding to the two frequency bands are 1.27 and 1.35 dB, respectively. The quad band antenna operates at frequencies 3.6, 4.9, 7.4 and 8 GHz. The gain corresponding to these frequencies are 0.18, 1.69, 2.25 and 3.99 dB. For achieving quad band operation from the dual band antenna the back plane L-shaped slot is modified by cutting a rectangular strip in the middle, hence dividing it into two different slots. The front plane is also modified by introducing two rectangular strips to the T-shaped patch. The proposed antenna shows multiband and has the advantage of simple structure compact size and good impedance matching. All the simulations of the proposed design are carried out in HFSS v.13.0.

ATR-FTIR Analysis and One-Week Stress Relaxation of Four Orthodontic Aligner Materials

The aim of this study was to estimate possible differences in the chemical composition and relaxation of orthodontic aligner materials. Four commercially available thermoplastic materials CAM (Scheu-Dental, Iserlohn, Germany), COP (Essix, Dentsply Raintree Essix Sarasota, FL, USA), DUR (Great Lakes Dental Technologies, Tonawanda, NY) and ERK (Erkodent Erich Kopp, Pfalzgrafenweiler Germany) were included in this study. Rectangular strips from each material were prepared according to the manufacturer’s instructions and subjected to attenuated total reflection-Fourier transform infrared (ATR-FTIR) spectroscopy and stress relaxation characterization. The reduction in applied stress (RAS) after one week was estimated and statistically analyzed by one-way ANOVA at the 0.05 level of significance. All specimens were subjected to optical microscopy before and after stress relaxation testing under transmittance polarized illumination. ATR-FTIR microscopy revealed that all materials are made of polyethylene terephthalate glycol (PETG) while no significant differences were identified in RAS values among materials tested, which ranged from 6%–10% (p ≥ 0.05). All samples illustrated the developments of shear bands during relaxation testing according to optical microscopy findings. The tested materials illustrated similar chemical composition and relaxation behavior and thus no differences in their clinical efficacy are anticipated.

The Transient Flow behind an Instantaneously Started Circular Cylinder with Two Symmetrical Strips

The finite volume method, based on the dynamic mesh method, is used to investigate the transient viscous incompressible flow around an impulsively and translationally started cylinder with strips. The strips of different shapes are installed at different locations on the surface of the cylinder. The main purpose of this paper is to investigate the influence of the locations and shapes of strips on the flow caused by boundary motion. The present solutions agree well with the experimental results reported in literature. Six placement angles of strips were selected: 0°, 20°, 60°, 90°, 120° and 150°. The development of wake shows some new phenomena with different strip locations, and the significant difference appears at α = 90°. The vortex intensity is much larger than that of other locations. On the other hand, four shapes of strips were selected: arc, triangle, rectangle and trapezoid. The rectangular strips had the greatest influence on the drag coefficient and the maximum of the drag coefficient increased from 0.4 to 2.8, compared with the smooth cylinder. The maximum of negative velocity had the most significant change when the shape of strip is arc, increasing by 34% compared with the smooth cylinder, at T = 3.

New approach for the prediction of compression pressure using the cut strip method

The main objective of the current research is the development of a new mathematical model for the prediction of compression pressure based on the incorporation of some new parameters. These new parameters include deformed width (wf), true stress ([Formula: see text]), true/logarithm strain ([Formula: see text]), true modulus of elasticity ([Formula: see text]), along with measurement of engineering stress ([Formula: see text]), engineering strain ([Formula: see text]) and engineering modulus of elasticity ([Formula: see text]) at ankle position. Various brands of compression socks comprising similar fibrous combinations, as well as knit type, were purchased. Initially they were hand washed, put on the leg for marking, marked in a square, sliced, and cut into rectangular strips. The rectangular cut strips were evaluated for force–elongation characterization at different strain values considering the requisite practical elongation values (circumferential difference between leg and sock at ankle portion). For pressure measurement, a Salzmann MST MK IV pressure measuring device using a standard-sized wooden leg (circumference = 240 mm) was used. For tensile evaluation, a Testometric tensile tester was used. In this research we developed the two mathematical models based on true Young’s modulus and engineering Young’s modulus were compared with Hooke’s law and Laplace’s law. The developed models were also compared with previously existing models statistically.

Variation of Axial Residual Strains Along the Course and Circumference of Human Aorta Considering Age and Gender

Our understanding of aortic biomechanics is customarily limited by lack of information on the axial residual stretches of the vessel in both humans and experimental animals that would facilitate the identification of its actual zero-stress state. The aim of this study was thus to acquire hitherto unreported quantitative knowledge of axial opening angle and residual stretches in different segments and quadrants of the human aorta according to age and gender. Twenty-three aortas were harvested during autopsy from the aortic root to the iliac bifurcation and were divided into ≥12 segments and 4 quadrants. Morphometric measurements were taken in the excised/curled configuration of rectangular strips considered to be under zero-stress using image-analysis software to study the axial/circumferential variation of axial opening angle, internal/external residual stretch, and thickness of the aortic wall. The measured data demonstrated: (1) an axial opening angle peak at the arch branches, decreasing toward the ascending and to a near-constant value in the descending thoracic aorta, and increasing in the abdominal aorta; (2) the variation of residual stretches resembled that of opening angle, but axial differences in external residual stretch were more prominent; (3) wall thickness showed a progressive diminution along the vessel; (4) the highest opening angle/residual stretches were found in the inner quadrant and the lowest in the outer quadrant; (5) the anterior was the thinnest quadrant throughout the aorta; (6) age caused thickening but greatly reduced axial opening angle/residual stretches, without differences between males and females.