Sress and strain concentration factors for plate with small notch subjected to biaxial loading – Three dimensional finite element analysis

AbstractThe through-thickness variations of stress and strain concentration factors for plate with small central notch, circular notch or double U-notch, subjected to uniaxial and biaxial loading have been systematically analyzed by using three dimensional finite element method (3D FEM). It is found that the maximum stress and strain concentration factors occur on the mid plane of plate only in the case of thin plate. However, in the case of thick plates, the sites of these maximum values are found near the plate surface. Furthermore, this site is more close to the plate surface in the case of small notch radius and/or large plate thickness. The stress and strain concentration factors increase with decreasing the biaxial ratio at the plate interior, while, the opposite trend is found at the plate surface

Finite element analysis of the behavior of bonded composite patches repair in aircraft structures

This paper aims to analyze the multi-effects of the glass fiber reinforced polymer (GFRP) composite patch to repair the inclined cracked 2420-T3 aluminum plate. Three-dimensional finite element method (FEM) was used to study the effect of GFRP composite patch with different stacking composite laminate sequence, [0°]4, [90o]4, [45o]4, [0o/45o]2s and [0°/90°]4s on the crack driving force, J-integral, of inclined cracked 2420-T3 aluminum plate. Furthermore, the effects of patch geometry, number of layers, single or double side patch and crack incline angle are described. The present results show that the patch has a high effect in case of a crack in pure mode I. Furthermore, the effectiveness of the composite patch is increasing with the crack length increases. Moreover, the efficiency of the composite patch has a high effect by changing the fiber orientation, the number of layers, and the single or double side patch

Effect of location and dimensions of welded cover plate on stress intensity factors of cracked plates

Three dimensional finite element model was utilized to determine mode I stress intensity factor through the front of a single edge crack in main plate with welded cover plate. The numerical results showed that the ratio of the crack length to the position of the welded cover plate end is a crucial parameter for describing the efficiency of the cover plate location. When the crack tip just reached the cover plate end, the cover plate efficiency is only dependent on the cover plate dimensions regardless the location of the cover plate or the crack length. In the case of crack front not reached the cover plate end, the location of cover plate near the edge of the main plate, i.e., near the crack mouth, is less efficient than that faraway. However, the opposite trend was found for cracks pass beneath the cover plate

Effect of clamping force and coefficient of friction on the elastic-plastic behavior of cracked bolted joint

The effect of clamping force, Fc, and coefficient of friction, μ, on the elastic-plastic behavior of cracked bolted joint has been studied numerically using 3-D elastic-plastic extended finite element method. Two different failure modes of a single steel plate which contain a fastener hole are considered, i.e. net tension and bearing mode of failures.It was found that, Fc and μ have a significant effect on the development of the monotonic plastic zone around the tip of the crack emanating from fastener hole. The effect of Fc and μ on mode I stress intensity factor, KI, of such a crack is more pronounced when the crack tip still beneath the washer. In this region, KI is almost constant regardless the length of the crack. When the crack grows outside the washer, second region, KI increased with increasing the crack length. In both regions, KI decreased with increasing Fc and μ. Keywords: Bolted metallic joint, Crack tip plastic zone, Failure modes, Stress intensity factors, J-integra

Power frequency AC voltage measurement based on double wound Rogowski coil

This study presents a technique for power frequency AC voltage measurement. The proposed technique utilises a capacitor having a low capacitance in addition to a double wound Rogowski coil. This technique depends on capacitor current measurement using the double wound Rogowski coil. The voltage across the capacitor that connected in parallel with the system at which AC voltage is intended to be measured is reconstructed. The proposed technique is experimentally evaluated by designing the measurement system and using a digital signal processing board for the reconstruction processes. Moreover, the experimental results based on Rogowski coil measurements are compared with those obtained from reference techniques. Finally, the obtained results validate the efficacy of the proposed technique in power frequency AC voltage measurement

A Single-Layer Vialess Wideband Reflective Polarization Rotator Utilizing Perforated Holes

A wideband reflective polarization rotator featuring a single layer and vialess design is proposed in this letter. The curved bowtie resonator is employed to accomplish wideband performance. Two notch resonators are etched at both terminals of the bowtie resonator to widen the operating bandwidth. Perforated air holes are utilized to improve the polarization conversion ratio at the high-frequency band. The proposed design exhibits four resonant frequencies at 17.3, 26.4, 44.4, and 56.2 GHz with polarization conversion ratio above 89% from 16.2 to 57 GHz, which represents 111.5% operational bandwidth. The structure thickness is 0.085 lambda(max), where lambda(max) is the free-space wavelength at the lowest operating frequency. The development process of the unit cell is illustrated originating from the simplest resonator shape, strip resonator. To verify the simulated results, a prototype is fabricated and measured. The fabricated prototype consists of 40 x 40 unit cells. A comparison with related recent designs is performed to investigate the notability of the proposed design regarding the wideband performance and required topology.11Nsciescopu

Cardioprotective effect of propofol in cardioplegia compared to systemic propofol in heart valves surgery; a randomized controlled trial

Abstract Background Myocardial protection is still a focus of ongoing research. Propofol is used widely during the induction of anaesthesia in cardiac surgery. So, this triggers us to investigate the cardioprotective effect of the propofol when added to the cardioplegia compared to systemic propofol by measuring the troponin T level. Methods This clinical randomized controlled trial was carried out on 150 patients operated for elective valvular heart surgery. Patients were assigned into three equal groups: Group 1: received propofol in the cardioplegia, Group 2: received propofol injection in the aortic line before and after the aortic cross-clamp, and Group 3 (control group): patients without propofol in the cardioplegia or aortic line. All patients were subjected to full medical histories, physical examinations, routine tests, and echocardiography. Cardiac troponin T was measured before surgery and 4 times postoperatively. Results In group 1, there was a significant improvement in troponin T level at the last reading compared with the control group (mean ± SD. of group 1 was 246.4 ± 131.4, mean ± SD. of group 3 was 317.0 ± 117.9, p = 0.031), denoting propofol's cardioprotective effect when added as a cardioplegia additive. In group 2, there was a significant improvement of troponin T level at the last reading compared with the group 1 and control group (mean ± SD. of group 2 was 202.54 ± 156.03, mean ± SD. of group 3 was 317.0 ± 117.9, p < 0.001), denoting propofol's more cardioprotective effect when used systemically during cardiopulmonary bypass than when added as a cardioplegia additive. Conclusions In valvular cardiac surgery, propofol has an additional cardioprotective effect and a superior cardiac outcome when administered systematically during cardiopulmonary bypass rather than added to cardioplegia. Trial registration Pan African Clinical Trials Register PACTR201907764652028. Registered on 01 July 2019, retrospectively registered, https://pactr.samrc.ac.za/ TrialDisplay.aspx?TrialID = 5726

Numerical study and experimental validation of the size effect of smooth and mode I cracked semi-circular bend specimens

Abstract The edge-cracked semi-circular bend (SCB) specimen subjected to three-point bending loading is used in many applications to measure the fracture behavior of quasi-brittle materials. The main objective of the present work was to study the effect of the crack length to SCB specimen radius ratio (a/R), span to specimen diameter ratio (S/D), and specimen size on its flexural and mode I crack growth behavior. The contour integral method was implemented using the 3-D finite element method to determine the mode I stress intensity factor. In addition, high-strength concrete specimens were experimentally studied to validate the numerical results. The results show that the maximum compression stress is not sensitive to the S/D value, while the tensile stress is very sensitive. The value of S/D is the main parameter controlling the crack driving force (i.e., the crack mouth opening displacement (CMOD) and the normalized stress intensity factor, Y I ). For the same S/D, the SCB specimen diameter value change has a marginal effect on CMOD and Y I. The specimen with S/D = 0.8 showed that it is the most compatible specimen with three-point bending test conditions, regardless of the SCB specimen size. A good agreement between the numerical and experimental results was achieved

An Assessment of ASTM E1922 for Measuring the Translaminar Fracture Toughness of Laminated Polymer Matrix Composite Materials

The main objective of this work is to predict the exact value of the fracture toughness (KQ) of fiber-reinforced polymer (FRP). The drawback of the American Society for Testing Materials (ASTM) E1922 specimen is the lack of intact fibers behind the crack-tip as in the real case, i.e., through-thickness cracked (TTC) specimen. The novelty of this research is to overcome this deficiency by suggesting unprecedented cracked specimens, i.e., matrix cracked (MC) specimens. This MC exists in the matrix (epoxy) without cutting the glass fibers behind the crack-tip in the unidirectional laminated composite. Two different cracked specimen geometries according to ASTM E1922 and ASTM D3039 were tested. 3-D FEA was adopted to predict the damage failure and geometry correction factor of cracked specimens. The results of the TTC ASTM E1922 specimen showed that the crack initiated perpendicular to the fiber direction up to 1 mm. Failure then occurred due to crack propagation parallel to the fiber direction, i.e., notch insensitivity. As expected, the KQ of the MC ASTM D3039 specimen is higher than that of the TTC ASTM D3039 specimen. The KQ of the MC specimen with two layers is about 1.3 times that of the MC specimen with one layer