Elastic-plastic fracture analysis of anisotropy effect on AA2050-T84 alloy at different temperatures: A Numerical Study

The third generation Al-Li alloy AA2050-T84 is widely used in aircraft applications due to its lightweight and significant mechanical properties. The anisotropic variations of tensile and compression properties of this alloy at various temperatures are substantial. In this work, the variations of the J-integral, CTOD, and Plastic Zone Size (PZS) due to anisotropy of a 4-inch thick AA2050-T84 plate at ambient and cryogenic temperatures were studied numerically by using Compact Tension (C(T)) specimen. The material anisotropy resulted in fracture and constraint parameter variation for Mode-I constant load. Numerical results indicated a decrease in crack driving forces and a constraint parameter with the decrease in temperature at the plate surface and central location. Plate surface locations appear to be isotropic for both temperatures under elastic-plastic fracture analyses as crack driving forces were almost identical. The temperature effect is more on constraint as the normalized PZS values at ambient temperature have been twice that of cryogenic temperature. The isotropic behavior of a plate under sub-zero temperature makes the plate suitable for cryogenic temperature applications.

Development of damage detection parameters over the lifetime of a rolling element bearing

This paper presents the trends of damage detection parameters over the lifetime of a rolling element bearing. In the experimental part, a series of bearing tests was performed using the twin-disc test device, until the monitored bearing was severely worn. This was followed by the analysis of measured acceleration and acoustic emission data in a constant-load condition, but also as loaded with impact-type loading. The results showed that traditionally used parameters, such as kurtosis and RMS, can indicate whether the bearing is damaged or not in a non-impact load condition. However, especially under impact-loading, the parameters based on acoustic emission data showed good performance and enabled monitoring of progress of the bearing damage.

Thermal Parametric Study of Butt Joints Using Friction Stir Welding

The purpose of this study is to look at the mechanical and microstructural properties of dissimilar 2024 and 7075 aluminum sheets that have been welded together using friction stir welding (FSW). The two sheets, which were aligned with perpendicular rolling directions, were successfully fused; the welded sheets were then tested under strain at room temperature to determine the mechanical response to the materials for the parents Since the fatigue behavior of light metals is known, the fatigue endurance (S–N) curves of welded joints have been achieved. A resonant electro-mechanical testing machine load is the best performance indicator for a significant part of industrial applications; welded sheets is the best performance indicator for a big part of industrial applications. At a load frequency of around 75 Hz, a constant load ratio R = 0.1 was employed. The microstructure that formed as a result of the FSW Optical and scanning electron microscopy have been used to investigate the process, both on ‘as welded’ specimens and on tested specimens following a rupture

Short-Term Creep-Rupture Behaviour of AISI 310S Austenitic Stainless Steel Sheets Manufactured in Salem Steel Plant, a Special Steels Unit of Steel Authority of India Limited, Ministry of Steel, Government of India

The creep behavior of AISI 310S stainless steel taken from SAIL’s Salem stainless steel plant has been investigated by constant load tensile creep test at the temperatures of 973, 1023, and 1073 K and loads of 66.6, 74.8, 86.6, and 94.8 MPa. It exhibits steadystate creep behavior in most test conditions. The double logarithm plot of rupture life and applied stress yielded straight lines at all the three test temperatures indicating that power-law creep due to dislocation climb is the operating mechanism of creep deformation. Linear relationship was obtained for plots of logarithm of rupture life against inverse temperature obeying Arrhenius type of temperature dependence with activation energy of 340 kJ/mol. The stress-rupture data yielded a master curve of Larson-Miller parameter. The plot of Monkman-Grant relationship is typical indicating that rupture is controlled by growth of grain boundary cavities. The metallographic examination of crept samples revealed formation of grain boundary voids and cracks leading to intergranular creep fracture. Deformation twins and carbide precipitates were also observed. Creep-rupture properties are compared with that of AISI 600 ironbased superalloy to analyze quantitatively its behavior

The Effects of Visual Feedback on Performance in Heart Rate- and Power-Based-Tasks during a Constant Load Cycling Test

Performance feedback can be essential for cyclists to help with pacing their efforts during competitions and also during standardized performance tests. However, the choice of feedback options on modern bike computers is limited. Moreover, little research on the effectiveness of the currently used feedback methods is available. In this study, two novel feedback variants using a bar or a tacho to visualize targets and deviation from targets were compared to a classic design using only numbers. Participants (6 female and 25 male trained to well-trained athletes) completed a protocol consisting of three heart rate-based tasks and one power-based task. The displays were compared with respect to their ability to guide athletes during their trials. Results showed lower root mean square error (RMSE) of the novel variants, but no significant effect of feedback variant on RMSE was found for both tasks (p > 0.05). However, when comparing the feedback variants on a person to person basis, significant differences were found for all investigated scenarios (p < 0.001). This leads to the conclusion that novel feedback variants can improve athletes’ ability to follow heart rate-based and power-based protocols, but even better results might be achieved by individualizing the feedback.

Nanoindentation creep testing: Advantages and limitations of the constant contact pressure method

Different loading protocols have been developed in the past to investigate the creep properties of materials using instrumented indentation testing technique. Recently, a new indentation creep method was presented, in which the contact pressure is kept constant during the creep test segment, similar to the constant stress applied in a uniaxial creep experiment. In this study, the results of constant contact pressure creep tests are compared to uniaxial and constant load hold indentation creep experiments on ultrafine grained Cu and CuAl5. The constant contact pressure method yields similar stress exponents as the uniaxial tests, down to indentation strain rates of 10–6 s−1, whereas the constant load hold method results mainly in a relaxation of the material at decreasing applied pressures. Furthermore, a pronounced change in the power law exponent at large stress reductions is found for both uniaxial and constant contact pressure tests, indicating a change in deformation mechanism of ultrafine grained metals. Graphical abstract

A novel direct torque and flux control of permanent magnet synchronous motor with analytically-tuned PI controllers

<span lang="EN-US">This work presents a novel direct torque and flux control (DTFC) of permanent magnet synchronous motor (PMSM) with analytically-tuned proportional integral (PI) controllers. The proportional (K_p) and integral (K_i) gains of the PI controllers were accurately determined, from first principle, using the model of the control system. The PI flux and torque controllers were then developed in rotor reference frame. The designed PI controllers, together with the torque and flux controllers, were tested on a permanent magnet synchronous motor (PMSM). The results obtained were compared with results from conventional DTFC system using manually-tuned PI controllers. The total harmonic distortion (THD) of motor phase currents is 18.80% and 4.81% for the conventional and proposed models respectively. This confirms a significant reduction in torque ripples. The control system was tested for step torque loading and found to offer excellent performance both during load changes, speed reversal, and constant load conditions.</span>

Tribological Behavior and Microstructural Analysis of Atmospheric Plasma Spray Deposited Thin Coatings on Cardan Cross Spindles

Cardan joints are used in transmissions between misaligned shafts, as in all-wheel-drive (AWD) cars and railway applications. Their functioning is accompanied by heavy cyclical loads, with the cardan cross spindles subjected to intensive abrasive wear and pitting. In this paper, a solution to the mentioned issue is proposed, thin anti-wear coatings of Metco 32 and Metco 72 metallic powders deposited by atmospheric plasma spray (APS) on cylindrical samples cut from spindles of two cardan crosses made of 40Cr10 and RUL2 steel. The morphological analysis of the coated surfaces was realized by scanning electron microscopy (SEM), and the elemental composition of the tested samples was elaborated by energy-dispersive X-ray spectroscopy (EDS). To investigate the wear resistance of the coated samples in dry and grease-lubricated conditions, tests at constant load and constant speed were carried out using an AMSLER tribometer. The results of greased tests proved that the expulsion of the lubricant from the tribological contact occurred no matter the combination of coated or uncoated samples. During grease-lubricated tests of ten minutes, the least coefficient of friction was measured for uncoated specimens with better surface finishing; but in dry friction tests, the lowest values of the mean friction coefficients were obtained for the Metco 72 coatings. The porous coatings may act as lubricant reservoirs in long-lasting tests, providing a solution to the expulsion phenomenon of the lubricant to the boundary outside the area of the larger-diameter roller.

Effect of Cryogenic Treatment on the Microstructure Modification of SKH51 Steel

This research aimed to investigate the microstructure modification mechanism used to improve the hardness and wear resistance of SKH51 steel. The cryogenic treatment (CT), including both shallow cryogenic treatment (SCT) and deep cryogenic treatment (DCT), was used to modify the microstructure of SKH51 steel in this research. The effect of short and long holding time (12 and 36 h) in CT was studied. The microstructures were evaluated by using a light optical microscopy (LOM) and a scanning electron microscopy (SEM). The phase identifications of the matrix, carbides, and a-parameter of the matrix were analyzed by using X-ray diffraction (XRD). The M6C and MC carbides size, aspect ratio, and distribution were analyzed using digimizer image analysis software on the SEM micrographs. Micro-Vickers were employed to evaluate the hardness of the targeted samples. Wear tests were performed by using a 6 mm diameter WC ball as the indenter and 5-N-constant load with a ball-on-disk wear tester. The results suggested that the increase of the secondary carbide was caused by the contraction and expansion phenomena of the matrix’s lattice, forcing the carbon atom out and acting as the carbide nucleation. The influence of holding time in the SCT and DCT regions was different. For the SCT, increasing the holding time increased the volume’s fraction of MC carbide. Conversely, the M6C carbide size grew with increasing holding time in the DCT region, while no significant increase in the number of MC carbide was observed. The cryogenic treatment was found to increase the volume fraction of the MC carbide by up to 10% compared to the conventional heat treatment (CHT) condition in the SCT region (both 12 and 36 h) and DCT with 12 h holding time. Due to the microstructure modification, it was found that the cryogenic treatment can improve material hardness and lead to an increase in the wear resistance of SKH51 by up to 70% compared to the CHT treated material. This was due to the increase in the compressive residual stress, precipitation of the MC, and growth of the M6C primary carbide.