Continuous Tensile Stress Research Articles

Microstructure and stress relief mechanism of C/C composite and GH3044 superalloy joints using (Cu)+Ti5Si3 foil filler

AbstractA Ti5Si3 reinforced (Cu) matrix foil composite filler was prepared and applied to join C/C composite and GH3044 superalloy, and a finite element model with random distribution particles was constructed to reveal the stress relief mechanism of composite brazing. Results showed the in‐situ synthesized Ti5Si3 reinforcements with a size of less than 5 µm were distributed uniformly in the (Cu) matrix, and their volume fraction reached 38%. The shear strength of the joint brazed with the composite filler reached 37.6 MPa, which is about 100% higher than that brazed with (Cu) filler. The Ti5Si3 reinforcements relieved the residual stress mainly by reducing residual stress values, introducing compressive stress into the joining layer, and transforming the continuous tensile stress into tensile stress/compressive stress.

The assessment of concrete subjected to preloading using non destructive testing methods

Different non-destructive tests are in use for the structural health monitoring. Test variables affecting non destructive behavior of concrete were discussed by some researchers, including the effect of instantaneous loading during testing for ultrasonic pulse velocity (UPV). This study aimed at determining rebound number (RN) using Schmidt hammer and UPV of concrete subjected to short term and continuous loadings. Tests were carried out on concrete cubes and cylinders to study the effect of short term loading, while to apply a continuous loading, reinforced concrete beams were loaded inside a rigid steel frame. Reduction of RN and UPV for concrete subjected to 80% compressive loading was found to be 8.1% and 10% respectively. There is some effect of loading cycle at high loading level especially for lower strength concrete. Also, RN was found to reduce with increasing tensile short term loading, in which for lower strength concrete reached 5%. There is a continuous reduction in UPV percentage with increasing tensile loading level, especially for lower strength concrete but the effect of tensile loading was found to be smaller than that of compressive loading. Analysis of data was made and equations were presented to calculate the changes take place due to short term loading effects. It is concluded that for concrete under continuous tensile stress, equations for UPV-compressive strength relationship should be modified with a reduction factor of 0.87 or calculated from an equation proposed in this study.

Waterproof Flexible InP@ZnSeS Quantum Dot Light‐Emitting Diode

AbstractThe development of flexible displays for wearable electronics applications has created demand for high‐performance quantum dot (QD) light‐emitting diodes (QLEDs) based on QD core@shell structures. Emerging indium phosphide (InP)‐based core@shell QDs show promise as lighting material in the field of optoelectronics because they are environmentally friendly material, can be produced in a cost‐effective manner, and are capable of tunable emission. While efforts have been made to enhance the performance of InP‐based QLED, the stabilities of InP@ZnSeS QDs film and InP@ZnSeS‐based QLED in water/air are not yet fully understood, limiting their practical applications. Herein, a highly durable, flexible InP@ZnSeS QLED encapsulated in an ultrathin film of CYTOP, a solution‐based amorphous fluoropolymer, is demonstrated. The CYTOP‐encapsulated green flexible QLED shows an external quantum efficiency (EQE) of 0.904% and a high luminescence of 1593 cd m−2 as well as outstanding waterproof performance. The flexible device emits strong luminescence after being immersed in water for ≈20 min. Even when subjected to continuous tensile stress with a 5 mm bending radius, the high luminescence is preserved. This waterproof architecture can be a promising strategy for wearable electronics applications.

Electrochemical polarization and impedance of reinforced concrete and hybrid fiber-reinforced concrete under cracked matrix conditions

In this paper, we investigate the influence of cementitious matrix cracking on the electrochemical polarization and impedance behaviors of corroding reinforced concrete and crack-resistant reinforced hybrid fiber-reinforced concrete (HyFRC). Samples were exposed to a chloride environment for 2.5 years while in either a continuous tensile stress state or in a nonloaded condition, and were periodically monitored for Tafel polarization responses. Electrochemical impedance spectroscopy (EIS) was additionally performed at the conclusion of the test program. Greater severity of corrosion-induced matrix splitting cracks along the length of embedded steel reinforcing bars and subsequent formation of anodic surfaces were found to affect several electrochemical parameters, including increase of the corrosion current and decrease of the ohmic resistance of concrete. Cathodic and anodic Tafel coefficients and Stern-Geary coefficients for passive and active samples are also reported, highlighted by a Stern-Geary coefficient of B = 28.1 mV for active corrosion.

Initial Load Stability of Different Trachea Suture Techniques: Tests on an Ex Vivo Model

Objective Tracheal anastomosis can be performed with different suture techniques. In this experimental work, the resilience of anastomotic techniques to pressure and tensile stress was studied. Study Design Ex vivo pig model. Setting Experimental. Subjects and Methods The trachea with the 2 main bronchi in freshly slaughtered pigs was isolated and intubated (CH 8.0). Both main bronchi were closed distally by a stapler. After resection of the trachea, an anastomosis (n = 15 per group) was created: group 1, single interrupted sutures; group 2, continuous running suture; group 3, mixed technique. A continuous tensile stress of 0, 500, 1000, or 1500 g was applied to the preparations. Mechanical ventilation with a maximum pressure of 70 mbar was initiated. The airtightness of the anastomosis was verified by submerging the entire preparation under water. Results At tensile loads of 0.5 and 1.0 kg, all anastomoses created in the single-stitch technique were airtight; at 1.5 kg, 93.3% were without leaks. In the continuous suture technique, the airtightness of anastomoses decreased with increasing tensile load: from 93.3% at 500 g to 73.3% at 1 kg and 66.6% at 1.5 kg ( P = .02 at 1.5 kg). Anastomoses in the mixed technique were airtight in 80% at 500 g, 66.6% at 1 kg, and 46.6% at 1.5 kg ( P = .01 in comparison with single stitches). Conclusion Anastomoses created with single interrupted sutures showed the highest resilience against combined pressure and tensile stress.

Ordered and Atomically Perfect Fragmentation of Layered Transition Metal Dichalcogenides via Mechanical Instabilities.

Thermoplastic polymers subjected to a continuous tensile stress experience a state of mechanical instabilities, resulting in neck formation and propagation. The necking process with strong localized strain enables the transformation of initially brittle polymeric materials into robust, flexible, and oriented forms. Here we harness the polymer-based mechanical instabilities to control the fragmentation of atomically thin transition metal dichalcogenides (TMDs). We develop a simple and versatile nanofabrication tool to precisely fragment atom-thin TMDs sandwiched between thermoplastic polymers into ordered and atomically perfect TMD nanoribbons in arbitrary directions regardless of the crystal structures, defect content, and original geometries. This method works for a very broad spectrum of semiconducting TMDs with thicknesses ranging from monolayers to bulk crystals. We also explore the electrical properties of the fabricated monolayer nanoribbon arrays, obtaining an on/off ratio of ∼106 for such MoS2 arrays based field-effect transistors. Furthermore, we demonstrate an improved hydrogen evolution reaction with the resulting monolayer MoS2 nanoribbons, thanks to the largely increased catalytic edge sites formed by this physical fragmentation method. This capability not only enriches the fundamental study of TMD extreme and fragmentation mechanics, but also impacts on future developments of TMD-based devices.

The Kinetics of Reorientation of Multi-Variants under the Continuous Tensile Stress: Phase-Field Simulation

The kinetics of martensitic variant reorientation as well as the evolutional pathway under the continuous tensile stress in NiMnGa alloys has been investigated by using Phase field method. The simulated results revealed that the final structures and the pathway of evolutioncan be determined by the different external stress and there existed a critical stress to obtain the single variant. The related kinetics and the mechanism of the structural conversion were proposed to explain the inner physical nature. The pseudo-elasticity related to the structural conversion was also investigated. The mechanism of the motion for interfacial step associated with the nucleation and growth of one variant in another variant at the twin boundary was discussed.

Effects of continuously applied stress on tin whisker growth

A simple four-point bending technique in conjunction with scanning electron microscopy (SEM) was employed to investigate the relationship between continuously applied mechanical stress and tin whisker growth on bright tin-plated copper specimens at room temperature. Measurements of whisker length and density were periodically taken for each specimen during a 7-month exposure to applied stress. Tin whiskers were found on the tin-plated specimens with or without the presence of mechanically applied stresses. A continuously applied compressive stress resulted in formation of longer and more dense tin whiskers, in comparison with the cases of no applied stress and applied tensile stress. However, an increase in the applied compressive stress level caused an increase in the whisker density but a decrease in the whisker length. On the other hand, a continuously applied tensile stress was found to reduce both the whisker density and length, compared to the case of no applied stress. Apparently, application of a continuous tensile stress could provide an effective means in retarding tin whisker growth.

Mechanical properties of human articular disk and its influence on TMJ loading studied with the finite element method

The present study was designed to investigate the elastic modulus of human temporomandibular joint (TMJ) disk under tension and its influences on TMJ loading. Seven human TMJ disks served as specimens. Continuous tensile stress was applied to each specimen, and the elastic moduli of human TMJ disks were calculated at 2% strain. Furthermore, using a three-dimensional finite element model of the mandible including the TMJ, changes in the TMJ stresses during clenching were evaluated in association of varying elastic moduli of the articular disk determined by the tensile tests. The elastic moduli at 2% strain varied from 27.1 to 65.2 MPa with a mean of 47.1 MPa. A significant correlation was found between the elastic moduli and age (P < 0.01). On the surface of condyle, compressive stress in the anterior area and tensile stress in the posterior area increased when the elastic moduli of the TMJ disk was varied from 25 to 65 MPa. In the TMJ disk, shear stresses in all the areas became larger with greater stiffness. In conclusion, it is shown that the elastic modulus of human TMJ disk is increased with age and that higher stiffness of the disk exerts substantial influences on mechanical loading for the TMJ structures.

Pathological changes of anastomotic false aneurysms.

Anastomotic parts of polyester vascular prostheses implanted in thoracic aortae of 270 dogs were examined. Anastomotic false aneurysms were seen with 3 cases (1.2%), in which disruption did not occur, however, the grafts which have no aneurysm showed the following features, i.e., suture migration, degenerative changes of the host arterial wall sustaining a suture and dissection between the host arterial wall and a prosthesis. From the results of an analysis of the arrangement pattern of smooth muscle cells in neointima, it was clarified that a suture had been subjected to continuous tensile stress. So that, the host arterial wall sustaining a suture is clinched and pulled toward prosthesis by the suture at every pulsation during implantation. These results indicate that the features mentioned above are phenomena of the developing into anastomotic false aneurysms.