Multi-Scale Modeling of Residual Stresses Evolution in Laser Powder Bed Fusion of Inconel 625

Laser powder bed fusion exhibits many advantages for manufacturing complex geometries from hard to machine alloys such as IN625. However, a major drawback is the formation of high tensile residual stresses, and the complex relationship between the process parameters and the residual stresses has not been fully investigated. The current study presents multi-scale models to examine the variation of process parameters on melt pool dimensions, cyclic temperature evolutions, cooling rate, and cyclic stress generation and how they affect the stress end state. In addition, the effect of the same energy density, which is often overlooked, on the generated residual stresses is investigated. Multi-level validation is performed based on melt pool dimensions, temperature measurements with a two-color pyrometer, and finally, in-depth residual stress measurement. The results show that scan speed has the strongest effect on residual stresses, followed by laser power and hatch spacing. The results are explained in light of the non-linear temperature evolution, temperature gradient, and cooling rate during laser exposure, cooling time, and the rate during recoating time.

Mathematical analysis of two-phase blood flow through a stenosed curved artery with hematocrit and temperature dependent viscosity

A two-phase blood flow model is considered to analyze the fluid flow and heat transfer in a curved tube with time-variant stenosis. In both core and plasma regions, the variable viscosity model ( Hematocrit and non linear temperature-dependent, respectively) is considered. A toroidal coordinate system is considered to describe the governing equations. The perturbation technique in terms of perturbation parameter ε is used to obtain the temperature profile of blood flow. In order to find the velocity, wall shear stress and impedance profiles, a second-order finite difference method is employed with the accuracy of 10−6 in the each iteration. Under the conditions of fully-developed flow and mild stenosis, the significance of various physical parameters on the blood velocity, temperature, wall shear stress (WSS) and impedance are investigated with the help of graphs. A validation of our results has been presented and comparison has been made with the previously published work and present study, and it revels the good agreement with published work. The present mathematical study suggested that arterial curvature increase the fear of deposition of plaque (atherosclerosis), while, the use of thermal radiation in heat therapies lowers this risk. The positive add in the value of λ1 causes to increase in plasma viscosity; as a result, blood flow velocity in the stenosed artery decreases due to the assumption of temperature-dependent viscosity of the plasma region. Clinical researchers and biologists can adopt the present mathematical study to lower the risk of lipid deposition, predict cardiovascular disease risk and current state of disease by understanding the symptomatic spectrum, and then diagnose patients based on the risk.

Biaxial FBAR Magnetic Sensor Based on Fe80Ga20 Anisotropic ΔE Effect

With the increasing application of personal navigation system in consumer electronics, the demand for multi-axis magnetic sensors based on MEMS is growing. We report a biaxial MEMS DC magnetic sensor consisting of an Mo/AlN/Fe80Ga20 film bulk acoustic resonator (FBAR), with anisotropy ΔE effect-based sensing principle. Different from the previously reported one-dimensional magnetic sensor based on the ΔE effect, the anisotropic ΔE effect was used to realize in-plane and out-of-plane two-dimensional magnetic field responses on a discrete sensor, and the sensor had two readout methods: resonant frequency f and return loss S11. The magnetic sensor realized the resonant frequency f shifted by 1.03 MHz and 0.2 MHz in the 567 Oe in-plane magnetic field and 720 Oe out-of-plane magnetic field, respectively, and the S11 changes by -30.2 dB and -0.92 dB. As the applied magnetic field increases, the -3 dB bandwidth quality factor Q3dB of the S11 curve gradually increases, and its maximum values in the in-plane and out-of-plane magnetic fields are 77143 and 1828, respectively, which reduces the detection limit of the magnetic sensor. The resonant magnetic sensor has stable high linear temperature and frequency drift characteristics, and its temperature frequency coefficient is -48.7 ppm/℃.

Time Period of the Vibration of the Circular Plate with Circular Variation Both in Thickness and Density

An analysis was carried out to investigate the time period of the thermally induced vibration of clamped and simply supported circular plates with circular variation both in thickness and density. Prior to this study, the variations considered were either linear, quadratic, parabolic, or exponential in nature. To study thermal effect, one-dimensional linear temperature variation on the plates is taken into consideration. Rayleigh–Ritz method is applied to compute the time period of the first three modes of vibration for both plates by varying tapering parameter, thermal gradient, and density. Convergence study of frequency modes for both plates conducted suggests that the convergence rate in case of circular variation is faster than the other studies done. A comparison of time period with the available published results is done. The comparison done concludes that time period obtained in the present study by varying thermal gradient and tapering parameter is found to be less than the other studies done for the same set of parameters. This study helped to establish the fact that, by using circular variation in plate parameters, we can get less time period of frequency modes in comparison to other variations considered till date.

Buckling Analysis of Functionally Graded Sandwich Plates under Both Mechanical and Thermal Loads

This paper presents an analytical solution for the thermomechanical buckling of functionally graded material (FGM) sandwich plates. The solution is obtained using a four-variable equivalent-single-layer (ESL) plate theory. Two types of sandwich plates are included: one with FGM facesheets and homogeneous core, and vice versa for the other. The governing equations are derived based on the principle of minimum total potential energy. For simply supported boundary conditions, these equations are solved via the Navier method. The results on critical buckling load and temperature increment of simply supported FGM sandwich plates are compared with the available solutions in the literature. Several results are presented considering various material and geometrical parameters as well as their effect on the thermomechanical buckling response of FGM sandwich plates. The relationship between the mechanical load and the temperature increment for uniform/linear temperature rise of FGM sandwich plates under combined mechanical and thermal loads is studied.

Entropy Measurements of Li-Ion Battery Cells with Li- and Mn-Rich Layered Transition Metal Oxides via Linear Temperature Variation

Changes in the partial molar entropy of lithium- and manganese-rich layered transition metal oxides (LMR-NCM) are investigated using a recently established electrochemical measuring protocol, in which the open-circuit voltage (OCV) of a cell is recorded during linear variation of the cell temperature. With this method, the entropy changes of LMR-NCM in half-cells were precisely determined, revealing a path dependence of the entropy during charge and discharge as a function of state of charge, which vanished as a function of OCV. This observation is in line with other hysteresis phenomena observed for LMR-NCM, of which the OCV hysteresis is the most striking one. For a systematic investigation of the entropy changes in LMR-NCM, measurements were conducted during the first activation cycle and in a subsequent cycle. In addition, two LMR-NCM materials with different degrees of overlithiation were contrasted. Contributions from configurational and vibrational entropy are discussed. Our results suggest that the entropy profile during activation exhibits features from the configurational entropy, while during subsequent cycling the vibrational entropy dominates the entropy curve.

Regime Shifts in Glacier and Ice Sheet Response to Climate Change: Examples From the Northern Hemisphere

Glaciers and ice sheets are experiencing dramatic changes in response to recent climate change. This is true in both mountain and polar regions, where the extreme sensitivity of the cryosphere to warming temperatures may be exacerbated by amplification of global climate change. For glaciers and ice sheets, this sensitivity is due to a number of non-linear and threshold processes within glacier mass balance and glacier dynamics. Some of this is simply tied to the freezing point of water; snow and ice are no longer viable above 0°C, so a gradual warming that crosses this threshold triggers the onset of melting or gives rise to an abrupt regime shift between snowfall and rainfall. Other non-linear, temperature-dependent processes are more subtle, such as the evolution from polythermal to temperate ice, which supports faster ice flow, a shift from meltwater retention to runoff in temperate or ice-rich (i.e., heavily melt-affected) firn, and transitions from sublimation to melting under warmer and more humid atmospheric conditions. As melt seasons lengthen, there is also a longer snow-free season and an expansion of glacier ablation area, with the increased exposure of low-albedo ice non-linearly increasing melt rates and meltwater runoff. This can be accentuated by increased concentration of particulate matter associated with algal activity, dust loading from adjacent deglaciated terrain, and deposition of impurities from industrial and wildfire activity. The loss of ice and darkening of glaciers represent an effective transition from white to grey in the world's mountain regions. This article discusses these transitions and regime shifts in the context of challenges to model and project glacier and ice sheet response to climate change.

Predicting Winter Wheat Heading Date: A Simple Model and its Validation in Kansas

Accurate prediction of winter wheat [Triticum aestivum L.] heading date is important for determining the potential incidence of diseases and abiotic stresses such as freeze or heat events. Wheat phenological modeling requires cultivar- and crop zone-specific vernalization and photoperiod knowledge. Previous models applied in Kansas showed that the uncertainties of predicting heading date were large and could be improved. In this study, a modification to the Scientific Impact assessment and Modeling Platform for Advanced Crop and Ecosystem Management (SIMPLACE) model was developed and implemented to improve the accuracy of winter wheat heading date estimation. The cultivar- and crop zone-specific model parameters were calculated using a Markov chain Monte Carlo simulation. The modified models were calibrated by using the longest observation site to cover all cultivars planted in each crop zone. Model performance was then evaluated for seven winter wheat cultivars at eight experiment sites distributed across four crop zones in Kansas. Our modified model (MS) had a root mean square error (RMSE) between predicted and observed heading date of 4 days, which reflects an improved accuracy by 5 to 8 days on average compared to the Agricultural Production Systems sIMulator (APSIM) or the original SIMPLACE models. There was a clear correlation between the uncertainty of the modeled heading date and the sowing date in previous models. Our modified model demonstrates that integrating non-linear temperature response functions, temperature stress factors, and sowing date information improved prediction of the heading date in winter wheat across Kansas.

Free vibration of piezoelectric FGM sandwich beam with porous core embedded in thermal environment and elastic foundation

This paper aims to present thermo-electrical free vibration characteristics of functionally graded material (FGM) sandwich beam placed on the two-parameter elastic foundation. The beam is constructed of a foam core, two middle FGM layers, and two outer piezoelectric layers. It is assumed that the beam is subjected to a constant voltage and a uniform/linear temperature distribution. Physical properties of the core and two middle layers vary smoothly through the thickness according to the cosine and power-law forms, respectively. Lagrange equations in conjunction with the Reddy third-order beam theory is employed to derive the governing equations of motion. A simple polynomial trial function-based Ritz method is adopted for the approximation of the displacement field to obtain the vibration response. The correctness of the study is verified by comparisons with other authors’ published results. Influences of geometry parameters, material property distribution, applied voltage, elastic foundation, temperature distribution, temperature change, porosity coefficient, span-to-height ratio, and boundary conditions are investigated through parametric studies.