The aim of this work was to use artificial neural networks (ANNs) to model the effect of mean tensile stresses on the fatigue resistance of an aluminum conductor steel reinforced. To train the ANN, ...fatigue data available for this type of conductor subjected to 2 different levels of mean stresses in the aluminium wires (49 and 74 MPa) were used. It is shown that the use of ANN enabled the construction of constant life diagrams (105, 106, 107, and 108 fatigue loading cycles) for the conductor. These results confirmed that the ANN is able to accurately estimate the effect of mean tensile stresses on conductor durability even considering just a limited number of data for its training.
The aim of this work was to conduct a test campaign to investigate the effect of temperature on the fretting fatigue life of aluminum alloy 6201-T81 wires taken from All Aluminum Alloy Conductors ...(AAAC) 900 MCM. To this end, fretting fatigue tests were conducted at room temperature (25 °C) and 75 °C. A three actuators fretting fatigue rig was upgraded with a heating system to allow the tests at elevated temperatures with an accuracy of ±2 °C. A methodology to ease the control of the temperature within the contact region was proposed and the details of the wire-against-wire fretting fatigue test were described. Two S–N curves were then obtained under the same load conditions, but each one at a different temperature. The results showed that at higher temperature the fretted wires could face up to 72 % reduction in fatigue life. Failure analysis of the fracture surfaces proved that the fatigue phenomenon in both conditions, i.e., at 25 °C and 75 °C, were very similar even though fatigue lives are quite different.
•The heating system developed in this study can carry out tests at a temperature of 75 °C with excellent stability and accuracy of ±2 °C.•In this study, it was possible to perform fretting fatigue tests on conductor cable wires at the operating temperature experienced by the actual conductor.•The device proved to be able to reproduce a fretting fatigue test between aluminum wires of overhead conductors, inducing elliptical fretting marks at wire surfaces (similar to those observed in internal layers in the conductors when tested under fatigue at full scale) and respecting the condition of partial slip regime, that is, the Amontons's principle, showing clearly defined stick and slip zones.
This study aimed to identify the potential use of the ceramic composite ZrO2(CeO2)-Al2O3 as a dental implant due to its intrinsic geometry and different masticatory loads based on finite element ...simulations. Ceramic samples were sintered at 1500 °C-2h, and characterized: The mechanical properties of the ceramic composite (hardness, fracture toughness, flexural strength, Young's Modulus, and Poisson ratio) were determined, in addition to the relative density and its structural characteristics. Commercial dental implant designs (incisal and third-molar) on CAD models were used in this study as an initial implant geometry applied in a typical simulated mandible anatomy. Finite element models were generated for implant geometries using CAD and CAE techniques. Loading cases were considered based on different intensities (100-500 N) and orientation angles to the implant axis (0° and 45°) to reproduce human masticatory conditions. For comparison purposes, the numerical predictions were compared with finite element simulations of gold-standard titanium implants. Ce-TZP/Al2O3 sintered ceramics showed flexural strength of 952.6 ± 88 MPa, hardness and fracture toughness of 1427 ± 46 HV and 11.3 ± 0.4 MPa m1/2, respectively, beside Young's modulus of 228.3 ± 65 GPa and Poisson ratio of 0.28. For both Ce-TZP/Al2O3 dental implant geometries, the implant prototypes showed adequate mechanical behavior regardless of the masticatory load value or the orientation angle applied in the simulations: All finite element predictions are lower than the values established by Mohr Coulomb's failure criterion, allowing the feasibility, preliminarily, of the proposed ceramics for dental implant applications without fracture risk.
– This article presents the design, production and testing of an experimental device that seeks to evaluate fretting fatigue of wires taken from conductors used in energy transmission lines. The ...fretting device has three independent actuators that allow tests to be carried out under controlled load (or displacement). Thus, the effect of relevant parameters to the fretting fatigue process (such as normal, tangential and bulk forces, wear level, and wear surface morphology) can be studied. To evaluate the device performance, tests were carried out on 6201 aluminum alloy wires, considering two different contact normal forces, P. Results showed that, for lives greater than 106 cycles, the increase of P from 250 to 500 N produced a substantial reduction on fatigue strength when compared to tests of smooth wire specimens. The SEM images and EDS analyses after the fretting fatigue test demonstrate that the wire-wire marks generated by the device show all the characteristics found in wires of internal layers of overhead conductors fractured by fatigue under fretting conditions.
•The device is able to reproduce a fretting fatigue test in wires of energy conductor cables.•The between device was designed to enable fretting tests at several possible angles formed by the wires.•Small variations in force in the tested wires perceived by the load cell are sent to controllers that readjust the loads.•The EDS images and analyses at the wire-wire marks generated by the device show fretting characteristics.•The device developed is able to precisely control and/or record the normal and bulk fatigue loads/displacements.
This work investigated the effect of adding ceria-stabilized tetragonal zirconia (Ce-TZP) on the fatigue behavior of alumina-based ceramic composites. Alumina powder (control group) and mixtures ...containing 5 wt.% (group A) and 20 wt.% (group B) of a commercial m-ZrO2/Al2O3/CeO2 powder mixture were milled/homogenized, compacted, sintered at 1600°C-2h, and submitted to hydrothermal degradation. The samples were characterized by relative density, microstructure, crystalline phases, and static mechanical properties. The cyclic fatigue strength was determined using the modified staircase method in 4-point bending tests. The results indicate that adding the m-ZrO2/Al2O3/CeO2 powder mixture to the Al2O3-matrix increases the tetragonal-ZrO2 grains (Ce-TZP) content, presenting 2.9 wt.% of Ce-TZP and 11.9 wt.% of Ce-TZP for group A and group B, respectively. Furthermore, the addition of Ce-TZP improves densification (98.5% → 99.1%) with a slight reduction in hardness and modulus of elasticity and a significant KIC increase of the composite (KIC = 6.7 MPa.m1/2, group B) when compared to monolithic alumina (KIC=2.4 MPa.m1/2). The fatigue strength limit of the control group was around 100 MPa, while the composites (groups A and B) presented the values of 279 MPa and 239 MPa, respectively. The results indicated that the incorporation of Ce-TZP significantly improves the fracture toughness of alumina-based ceramics. On the other hand, regarding the fatigue behavior, there was an increase in fatigue resistance in group A, resulting from the benefits of the t→m Ce-TZP grains transformation, which occurs during cyclic loading, producing a zone shielding that involves the tip of the crack, slowing its growth. The increase in the amount of Ce-TZP (group B) leads to an increase in the internal residual stresses between the phases due to anisotropy and difference in the thermal expansion coefficients, which accelerates the phase transformation and formation of microcracks at grain boundaries, reducing the fatigue strength of composites of group B.
In this work, controlled precipitation synthesis methods and polymeric precursors (Pechini) were used to obtain gadolinium-doped cerium oxide solid electrolytes (Ce0.8Gd0.2O1.9) and double-doped ...cerium oxide with gadolinium and samarium (Ce0.8Gd0.2−xSmxO1.9x=0.01; 0.03 and 0.05). The main results indicate that the synthesized powders by the Pechini method present better microstructural characteristics such as larger specific surface area and smaller particle size. Test specimens were compacted (187MPa) and sintered (1500°C/6h) and subsequently characterized. Through the impedance spectroscopy analysis, an increase in the percentage of the samaria caused an increase in the grain boundary and grain conductivity in all the samples under study. In the grain interior, samples without samaria showed heterogeneous regions, where the cation-vacancy pairs are tightly bound, precluding these vacancies from participating in ion conduction. In the samples with samaria, these defect groups are smaller, indicating structural homogeneity, resulting in greater ionic conductivity. Grain boundary specific conductivities show slight increase for samples codoped with samarium oxide. This effect suggests that Sm3+ additions change the charge equilibrium in space-charge layer favoring better dopant distribution.
En este trabajo se utilizaron los métodos de síntesis precipitación controlada y precursores poliméricos (Pechini) para obtener electrolitos sólidos de ceria dopada con gadolinio (Ce0.8Gd0.2O1.9) y óxido de ceria doblemente dopada con gadolinio y samario (Ce0.8Gd0.2−xSmxO1.9x=0.01; 0.03 and 0.05). Los principales resultados indicaron que los polvos sintetizados por el método Pechini presentaron mejores características microestructurales: mayor área de superficie específica y menor tamaño de partícula. Los polvos fueron compactados (187MPa), sinterizados (1500°C/6h) y, por fin, caracterizados. Con análisis de los espectros de impedancia se observó que el aumento del porcentaje de samario provocó aumento de la conductividad del grano y del contorno de grano en todas las muestras en estudio. En el interior del grano las muestras sin samaria mostraron regiones heterogéneas (grupos de defectos) donde pares catión-vacancia están estrechamente unidos, lo que impide su participación en la conducción iónica. En las muestras con samaria, estos grupos de defectos son más pequeños, indicando homogeneidad estructural, obteniendo una conductividad iónica mas alta. La conductividad específica del límite de grano muestra un ligero aumento para las muestras codopadas con óxido de samario. Este efecto sugiere que las adiciones de Sm3+ cambian el equilibrio de carga en la capa de carga espacial favoreciendo una mejor distribución del dopante.
•Cables A and B with the same chemical composition showed different fatigue strength.•Wires removed from cable A had fatigue life shorter than wires removed from cable B.•Cable A had lower amount of ...Mg2Si precipitates and higher number of iron impurities.•Inadequate aging step of heat treatment resulted in lower fatigue life of cable A.
Aeolian vibration can cause failure by fatigue in electric conductors and, in some cases, possible blackout. In this study, wires extracted from two cables (A and B) made of 6201 aluminum alloy were tested under fatigue. These tests were carried out aiming to evaluate causes of differences observed on fatigue resistance of the two cables, manufactured with the same chemical composition and, apparently, subjected to the same heat treatment (T81). Wires extracted from cable “A” exhibited lower fatigue life than wires of cable “B”. Scanning electron microscopy analyses of fractured wire surfaces demonstrated that failures were caused by fretting fatigue. Images and analyses using transmission electron microscopy and energy-dispersive spectroscopy demonstrated a lower concentration of Mg2Si hardening precipitates and appreciable concentration of plate-shaped β-Al5FeSi phases in cable “A” wires. The lower fatigue resistance of cable “A” wires compared to those of cable “B” are related to inefficient heat treatment applied to cable “A” and existing iron impurities possible originated from raw materials used during the manufacturing process of this conductor. The inadequate aging step of heat treatment gives rise to fewer hardening Mg2Si precipitates. This effect added to existing iron impurities shortened the mechanical properties of cable “A” and, thereby, its fatigue life, when compared to cable “B”.
When installing overhead conductors on transmission lines, a static stretching load is applied to maintain the line clearance according to the power line project and protect the conductor against ...harmful wind vibrations. The everyday stress (EDS) and parameter H/w, which control the stretching load, has been proposed as a means of safely designing power lines against fatigue due to wind excitation. As the stretching tension increases, the conductor becomes more vulnerable to Aeolian vibration, as its self-damping capacity is reduced and mean stress increases, can cause premature failure. However, there is a gap in the literature regarding the mean stress effect study on the fatigue life of conductors, as the modeling of the EDS (or H/w) effect on conductors. The diversity of conductor types (shape, materials, and arrangement) is one of the main reasons for this gap. Therefore, this work develops a master curve that allows predicting the fatigue life for any conductor about the effects of mean stress. To assess the mean stress effect on fatigue life, the SWT and Walker approaches with fatigue test results (carried out using different values of stretching load) were used to create the master curves and validate the application of such criteria to the fatigue life of different conductor families. This master curve provides a practical and simple tool that allows the prediction of fatigue life with an elevated level (three times the lifetime) at low cost, covering a variety of conductors. The power line transmission community could use a more conservative curve.
Accidental Injuries Caused by Automotive Frontal Collision Luján, Karen Viviana Pérez; Silva, Rita de Cassia; Oliveira, Alessandro Borges de Souza ...
Latin American Journal of Solids and Structures,
2021, Letnik:
18, Številka:
1
Journal Article
Recenzirano
Odprti dostop
This study aimed to use a simulated vehicle to asses quantitatively the head and neck injuries of the occupants, in a frontal car crash, when the driver has only one hand on the steering wheel, such ...as while using a cell phone when driving. First, we conducted a survey of NHTSA reports on real laboratory tests of frontal collisions involving sedans. The effects of these collisions on the neck of a Hybrid III 50th percentile male crash test dummy were measured in terms of average head acceleration and force along the X, Z, and Y-axes. These acceleration, force and torque values obtained from the NHTSA database were used to validate the simulated model. The results obtained were compared with case E, the standard dummy position used in frontal collision tests. The results obtained in the simulation of the four cases of driving with only one hand demonstrate a probability of more than 67% that the driver will sustain AIS+2 injuries during a frontal crash. In all the cases, the skull fracture percentage was the most representative, occurring between 89 and 94% of cases where the driver had only one hand on the steering wheel.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
Studies on fuel cell components have attracted interest due to the growing demand for sustainable energy sources. In the present study, synthesis of nanometric powders of the Ce0.8Sm0.2−xGdxO1.9 ...system (x = 0; 0.05; 0.1) system was carried out using the polymeric precursor method (Pechini), followed by calcination at 600°C for 1h and pressureless sintering. Characterizations were carried out with differential thermal analysis (DTA), thermogravimetric analysis (TG), infrared spectroscopy (FTIR), and X-ray diffraction (XRD). The grain and grain boundary contributions to the ionic conductivity of the ceramic disks obtained were assessed by complex impedance spectroscopy (CIS). Microstructural characterization was conducted by SEM. Electrical characterization showed greater grain conductivity for samples that were codoped with increasing levels of gadolinium, likely due to less deformation in the crystalline lattice with the addition of an element that contains an ionic radius closer to that of the host matrix of ceria (Ce < Gd < Sm). Grain boundary conductivity was lower than grain conductivity with a gradual rise in the same codoping element. This results from changes in microstructural characteristics due to increased codoping, including a reduction in relative density.
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