Central Notch Research Articles

Characterization of dual band and double polarized notched metallic ring FSS and their equivalent parallel metallic strip structures

ABSTRACTIn this work three rejecting band filters for multi band and dual polarization applications are proposed. The first proposed structure is an open quasi square FSS with a centered notch. The variation of the notch position to the left leads to the tenability of frequencies in both directions of polarization. The addition of a second notch has resulted in a third frequency in the y direction maintaining two resonant frequencies in the x direction. The structures are simulated by the Wave concept Iterative Method and the Comsol Multiphysics software 4.3b. In the second part of this paper a new approach is proposed to obtain an equivalent FSS structures based on non-coupled parallel metallic strips. The new equivalent FSS structures allow the frequency adjustment by the variation of the corresponding strip lengths. The results obtained by the WCIP method and measurements are compared and a good agreement is obtained.

Single Band Notched Characteristics UWB Antenna using a Cylindrical Dielectric Resonator and U-shaped Slot

In this manuscript, a novel hybrid dielectric resonator antenna for ultrawideband applications is designed, and single notched bands performance is proposed . The circle radiating patch is printed on FR4 substrate 1.64 mm thickness and loss tangent tan� =0.02, and is fed by coplanar waveguide. The size of the UWB antenna is minimized to 50-40 mm 2 . The operation bandwidth of the designed antenna is from 3.1 GHz to over 12 GHz. WIMAX Band notches characteristics of antenna to reject, is realized by etching U Shaped slot in the radiating patch. The center notch frequency can be adjusted from 3.4 to 4.5 GHz, by changing the position of cylindrical Dielectric Resonator. The band notched characteristics, VSWR, and radiation patterns are studied using CST and HFSS high frequency simulators

Analysis of the Tensile Strength of Copy Paper with a Center Notch Based on Four Strength Theories

Analysis of the Tensile Strength of Copy Paper with a Center Notch Based on Four Strength Theories

Numerical Analysis of the Failure Behavior of a C50/60 Brazilian Disc Test Specimen with a Central Notch

The Brazilian disc test with central notch is widely used to evaluate the fracture resistance of rocks and concrete by analytical formulas. However, studies of the post peak behavior are limited. In this contribution the post peak behavior of a C 50/60 concrete was studied using the finite element software Abaqus. The numerical results were compared to experimental data provided by BUT.

Characterization of Adhesion Properties by Delamination of Ceramic-Metal Interfaces in Four Point Bending

The adhesive strength of ceramic - copper interfaces was measured in four point bending using a central notch for crack initiation. According to our method, plastic deformation may occur during the delamination process. FEM simulations were employed in order to separate elastic and plastic contributions to the energy consumption of the experiment. In conclusion, a novel delamination criterion based on the stress intensity at the crack tip was established. Here, the stress invariant J3 is used as indicator for delamination of the interface. Agreement between experiments and theoretical interpretation is demonstrated for copper layers directly bonded to aluminum oxide.

Insights on rock fracture from digital imaging and numerical modeling

Rock fracture and the induced displacement field are investigated through physical and numerical experiments. A Berea sandstone specimen with a central notch was tested in three-point bending. Digital image correlation (DIC) was used to obtain the displacement patterns as the fracture initiated and propagated. The DIC results clearly show the development of a damage zone and displacement discontinuity along the center line of the beam at peak load. It is suggested that a traction-free or cohesionless crack may exist before the unstable growth, a condition normally ruled out in the literature based on numerical modeling within the frame work of a cohesive zone finite element analysis. In this note, the displacement profiles determined from DIC are compared with those from numerical simulations using (i) nonlinear finite element and (ii) bonded particle models. It is shown that the bonded particle model is capable of reproducing the physical displacement field with better accuracy compared to that from the finite element model with softening. Furthermore, as supported by experiments and bonded particle simulations, it appears that a cohesionless crack can develop at peak load, an observation that is not confirmed by the nonlinear finite element analysis.

Fracture response of alkali-activated slag mortars reinforced by carbon fibres

The paper reports a study of the effect of carbon fibres on the mechanical fracture parameters of alkali-activated slag mortars. The carbon fibres were added in the amount of 1, 2 and 3%, respectively with respect to the mass of the slag. The mechanical fracture parameters were determined using evaluation of fracture tests carried out on 40 × 40 × 160 mm beam specimens with an initial central edge notch. The monitored parameters were compressive strength, modulus of elasticity, effective fracture toughness and specific fracture energy. The specimen response during fracture tests was also monitored by means of acoustic emission. It was shown that as the addition of carbon fibres increased the value of compressive strength and modulus of elasticity of alkali-activated slag dropped to 50% in case of the highest amount of fibres. The effective fracture toughness is not significantly influenced by addition of carbon fibres. On the other hand, the fracture energy value gradually increases with addition of carbon fibres, up to more than twofold increase in case of the highest amount of fibres.

Fracture parameters of fine-grained composites based on the alkali-activated slag

The paper deals with the experimental determination of fracture parameters of the composites based on the alkali-activated slag (AAS) at different ages. The main aim of the experimental investigation was to verify the effect of the addition of shrinkage reducing admixture (SRA) on the overall progress of length changes and fracture properties during AAS composites ageing. Two AAS composites, which differed only in the presence of SRA, were prepared for the purpose of experiments. The mechanical fracture parameters were determined using evaluation of fracture tests carried out on 40 × 40 × 160 mm beam specimens with an initial central edge notch. The monitored parameters were modulus of elasticity, effective fracture toughness and specific fracture energy. These parameters were determined at the age of 3, 28 and 90 days. The obtained results are supplemented by the results of relative length changes measurements performed on both studied composites.

The influences of mode II loading on fracture process in rock using acoustic emission energy

The influences of mode II loading on fracture process in Berea sandstone were investigated by comparing mode I and mixed-mode fractures that were created by center and eccentric notch beams under three-point bending. Fracture process was characterized by Acoustic Emission (AE) and related energy. Experimental results show mode II loading does not affect the length of fully-developed fracture process zone and maximum value of AE energy. However, it affects the zone from reaching fully-developed stage, i.e., mixed-mode fracture before or at peak load, and mode I after the peak. It also breaks the similarity and symmetry of AE events pattern.

Sagittal otolith morphology and the relationship between its mass and the age of Liza haematocheila in the Yangtze Estuary, China

To examine the relationship of morphological characters of sagittal otolith and the age of Liza haematocheila in the Yangtze Estuary, we analyzed the morphological parameters of 324 pairs of otoliths extracted from 358 L. haematocheila specimens from the Yangtze Estuary in February to June of 2017. The results showed that sagittal otolith had rostrum, antirostrum and obvious central notch. The size and shape of sagittal otolith significantly changed with their growth, from regular melon seeds shape outline to long narrow leaf shape and increasing irregular wavy outline. The average density of sagittal otolith was 1.52 mg·mm-2. The average rectangularity was 0.68. The length of sagittal otolith was 0.021%-0.047% of entire body length (BL), the width was 0.009%-0.021% of entire BL, and the mass was 0.045‰-0.731‰ of the entire body mass (BM). Otolith length (OL), otolith width (OW) and otolith mass (OM) were all significantly related to the BL, with the determination coefficient for OW and OM model being the highest (R2=0.928). The relationship between OM and BL was described best by exponential regression: OM=0.0009BL1.8737(R2=0.967). The relationships between OM and age (A), BL and A were well fitted by multinomial regressions, respectively: OM=2.9262A2+4.8437A+2.1894 (R2=0.847), BL=-3.2248A2+102.54A+38.373 (R2=0.858). In addition, OM was linearly correlated with A. The estimated otolith's ages from the model did not significantly variate from the real ages counting from annulus counts. Therefore, OM could be an effective parameter for the age estimation of L. haematocheila.

Liquid crystal based tunable spurline filters with notch frequencies at 50 and 85 GHz

AbstractElectrically tunable double‐spurline notch filters with a nematic liquid crystal (LC) material as a dielectric medium were modeled, manufactured, and characterized. The spurlines, which were embedded into an inverted microstrip, consisted of quarter‐wavelength resonant elements. A Finite Difference Time Domain solver was used to model the filters. Photolithography and thin film deposition were employed to create the filters, followed by standard LC cell assembly. The filters, with central notch frequencies at 50 and 85 GHz, were characterized on‐wafer with a vector network analyzer. The stopband frequencies were tunable by 3% when a 14 volt peak‐to‐peak AC bias was applied across the 38 μm thick LC layer (electric field of 0.19 V/μm). The minimum stopband insertion loss of both filters achieved lower than −50 dB, while the stopband return loss varied from −4 to −12 dB. The −3 dB passband widths of the stopband filters were 12.2 and 28.3 GHz for the 50 and 85 GHz filters, respectively, giving a Q‐factor of 3–4.

Stable crack growth in Al-Cu-Mg alloy under various stiffness of loading system in bodies with concentrators

In the present work, the influence of the stiffness of the loading system on regularities of inelastic behavior and on processes of the equilibrium crack growth during uniaxial tension in bodies with stress concentrators was studied. Flat specimens (Al-Cu-Mg alloy) with a center notch and initial fatigue crack were extended with a biaxial servo-hydraulic testing system Instron 8850 at room temperature. The mechanical tests were complemented by a digital image correlation (DIC) and an infrared thermography. By using the 3D DIC-measurement system Vic-3D and the software module ‘virtual extensometer’, it was possible to evaluate the crack opening value, to analyze the evolution of heterogeneous strain fields during the initiation and propagation of cracks. It was revealed that with increasing stiffness of the loading system (by decreasing the gauge length of specimens), the realization of the stable postcritical deformation stage is increasing as well as the inhomogeneity of plastic flow and temperature in the crack tip.

Crack initiation of selected geopolymer mortars with hemp fibers

The aim of this paper is to quantify particularly fracture properties of selected types of mortars prepared with an alkali activated binder and hemp fibers. The main attention is focused on evaluation of three-point bending fracture tests of prismatic specimens with an initial central edge notch made of alkali activated fly ash mortars. The load versus crack mouth opening displacement (F–CMOD) diagrams were recorded during the fracture tests and subsequently evaluated using the Double-K fracture model. This model allows the quantification of two different levels of crack propagation: initiation, which corresponds to the beginning of stable crack growth, and the level of unstable crack propagation. The course of fracture tests was also monitored by acoustic emission method.

Multi-axial fatigue numerical crack propagation in cruciform specimens

Two cracks, initiated from the opposite tips of a 45° inclined central notch, were considered in cruciform specimens made of Ti6246. A static load was applied along an arm of the cruciform specimen together with an alternating load (R=-1) applied along the other arm. Experimental results were available from literature allowing a validation of the numerical procedure adopted to calculate the crack propagation paths and crack growth rates monitored during such tests. In particular, numerical evaluations by means of the Dual Boundary Element Method (DBEM) were performed, using the Minimum Strain Energy Density (MSED) criterion for the crack path assessment and J-integral approach for SIFs evaluations. Allowance for non-linear contact with friction was provided for those load cases in which contact between the crack faces occurred. Crack growth rates were predicted by using the Walker law, previously calibrated using the set of data coming from the first tested specimen. A good agreement between experimental and numerical crack paths was obtained. It was found that the cracks propagate without appreciable kinking, on the initial notch plane, for static loads lower than 10-15% of dynamic load amplitude, whereas the cracks develop perpendicular to the static load direction when the latter exceeds 25% of the dynamic load amplitude.Both propagation paths and crack growth rates were provided as a function of the static to dynamic load ratio.

Total fatigue life analysis of a nodular cast iron plate specimen with a center notch

The crack initiation and propagation phases of the fatigue life of a plate specimen with a center hole are analyzed. The local transient stress–strain relationship is investigated by means of finit...

Fracture Mechanical Properties of Rocklike Materials Under Half Symmetric Loading

AbstractThe authors studied the fracture mechanical properties under half-symmetric loading in this paper. The stress distribution around the crack tip and the stress intensity factor of three kinds of notched specimens under half symmetric loading were compared. The maximum tensile stress σmax of double notch specimens was much greater than that of single notch specimens and the maximum shear stress τmax was almost equal, which means that the single notch specimens were more prone to Mode II fractures. The intensity factors KII of central notch specimens were very small compared with other specimens and they induced Mode I fractures. For both double notch and single notch specimens, KII was kept at a constant level and did not change with the change of a/h, and KII was much larger than KI. KII has the potential to reach its fracture toughness KIIC before KI and Mode II fractures occurred. Rock-like materials were introduced to produce single notch specimens. Test results show that the crack had been initiated at the crack tip and propagated along the original notch face, and a Mode II fracture occurred. There was no relationship between the peak load and the original notch length. The average value of KIIC was about 0.602 MPa×m1/2, and KIIC was about 3.8 times KIC. The half symmetric loading test of single notch specimens was one of the most effective methods to obtain a true Mode II fracture and determine Mode fracture toughness.

Experimental Studies on Strength Behaviour of Notched Glass/Epoxy Laminated Composites under Uni-axial and Bi-axial Loading

The use of FRP composite materials in aerospace, aviation, marine, automotive and civil engineering industry has increased rapidly in recent years due to their high specific strength and stiffness properties. The structural members contrived from such composite materials are generally subjected to complex loading conditions and leads to multi-axial stress conditions at critical surface localities. Presence of notches, much required for joining process of composites, makes it further significant. The current practice of using uni-axial test data alone to validate proposed material models is inadequate leading to evaluation and consideration of bi-axial test data. In order to correlate the bi-axial strengths with the uni-axial strengths of GFRP composite laminates in the presence of a circular notch, bi-axial tests using four servo-hydraulic actuators with four load cells were carried out. To determine the in-plane strength parameters, bi-axial cruciform test specimen model was considered. Three different fibre orientations, namely, 0°, 45°, and 90° are considered with a central circular notch of 10 mm diameter in the present investigation. From the results obtained, it is observed that there is a reduction in strength of 5.36, 2.41 and 13.92% in 0°, 45°, and 90° fibre orientation, respectively, under bi-axial loading condition as compared to that of uni-axial loading in laminated composite.

Evaluation of mixed mode I/II fracture toughness of C 50/60 from Brazilian disc test

Durability and sustainability of structures made from concrete like materials is getting more into an interest of civil engineers. Structures are subjected not only to uniaxial load, this means if there is a crack inside the load could be divided into mode I and shear mode II, but also to a mixed mode I/II. Therefore, it is necessary to perform test, which covers mixed mode loads and could be used for specimen made from concrete core-drill. Recommended test specimens used for evaluation of fracture mechanical parameters has usually a prismatic or rectangular shape. The cost of reshaping cylinder into rectangular is expensive and not very efficient, therefore it is very effective to use Brazilian disc test specimen with central notch to obtain mixed mode fracture parameters. The contribution deals with numerical support for Brazilian disc test to obtain calibration curves for mode I and mode II, evaluation of experimental results and compare them with data adapted from literature.

A Numerical Model for the Simulation of Fatigue Induced Damage Onset and Evolution

In this work, a numerical model for the simulation of the onset and propagation of fatigue induced damages through a GFRP panel loaded in tension is presented. The model has been validated by numerical/experimental comparisons in terms of stiffness reduction over the number of loading cycles, considering three different applied loads. Finally, the model has been adopted to study the damage behaviour of a panel with a central notch damage.

Reconfigurable Bandpass Filter With Resonators in Cul-De-Sacs for Producing Notches

We present a new design method for bandpass filters capable of adjusting center frequencies, bandwidths, and notches. For designing such filters, filter topologies employing frequency-tunable resonators in cul-de-sacs are developed. The cul-de-sac resonators are mainly responsible for constructing notches, while the resonators in main paths form passbands. For verifying the presented design method, we have designed two bandpass filters. Each filter consists of two different resonator types: microstrip-line resonators for forming passbands and substrate-integrated waveguide resonators for producing notches. The measured results of the two designed filters show that frequency-tunable notches can be placed next to the passbands without producing unwanted resonant peaks that are usually observed in bandpass-bandstop filter cascades. This indicates that the filters designed using the presented topologies can replace bandpass-bandstop filter cascades.