Residual Variations Research Articles

Investigation into the distribution of residual stresses in pressed-braked thin-walled steel lipped channel sections using the 3D-FEM technique

Cold formed steel sections are normally produced by cold work manufacturing processes. The amount of cold work to form the sections may induce residual stresses in the section, especially in the area of bending. Studies by previous researchers of the effects of local buckling on the failure mechanics of thin-walled compression members have shown that ultimate failure will occur when the yielding has reached most of the middle surface in the corner region of the sections. Hence, these cold work processes may have significant effects on the section behaviour and load-bearing capacity. Most of the studies have investigated the effect of residual stresses raised from roll-forming operation and its influence on steel section behaviour. However, press-braking has not received much attention. Therefore, a 3D finite element simulation has been employed to simulate this forming process. This study investigated the magnitude and distribution of residual stresses along the length of the corner region and through thickness residual stress variations induced by the press-braking forming process. The study concluded that residual stresses are not linear longitudinally (along the corner region). Maximum residual stresses exist near the middle surface of the plate. The neutral surface contains a combination of compressive and tensile residual stresses. The neutral axis is shifted from mid-surface by 7.5% of the plate thickness due to bending. The comparison of the 3D-FE results with the existence of 2D-FE results illustrates that the 3D-FE results show a variation in the transverse and longitudinal residual stresses along the plate length.

Correcting symmetry imperfections in linear multipole traps.

Multipole radio-frequency (RF) traps are central to collisional experiments in cryogenic environments. They also offer possibilities to generate new type of ion crystals topologies and in particular the potential to create infinite 1D/2D structures: ion rings and ion tubes. However, multipole traps have also been shown to be very sensitive to geometrical misalignment of the trap rods, leading to additional local trapping minima. The present work proposes a method to correct non-ideal potentials, by modifying the applied RF amplitudes for each trap rod. This approach is discussed for the octupole trap, leading to the restitution of the ideal Mexican-Hat-like pseudo-potential, expected in multipole traps. The goodness of the compensation method is quantified in terms of the choice of the diagnosis area, the residual trapping potential variations, the required adaptation of the applied RF voltage amplitudes, and the impact on the trapped ion structures. Experimental implementation for macroscopic multipole traps is also discussed, in order to propose a diagnostic method with respect to the resolution and stability of the trap drive. Using the proposed compensation technique, we discuss the feasibility of generating a homogeneous ion ring crystal, which is a measure of quality for the obtained potential well.

Crack arrest in thin metallic film stacks due to material- and residual stress inhomogeneities

Miniaturized materials, in general, exhibit higher strength compared to their bulk counterparts. As a consequence, their resistance to fracture is often compromised. However, the effect of material inhomogeneities can be used to significantly improve the fracture toughness of thin film components. In this work, the material inhomogeneity effect on the crack driving force, caused by material property and residual stress variations in thin tungsten and copper stacks, is numerically investigated. To this purpose, a finite element analysis is performed using the concept of configurational forces. In this way, we are able to distinguish between the various inhomogeneity effects and draw conclusions about the effective crack driving force. It is demonstrated that the material inhomogeneity effect is not solely determined by the material property variations at the interfaces, since an important contribution emerges due to a smooth residual stress gradient within the layers. The possibility to separate the different effects represents an opportunity for cost efficient design of future reliable thin film microelectronic components.

Review of Residual Stress Measurement by Magnetic Barkhausen Noise Technique

Abstract Determination of residual stress state is important for quality, integrity, and service performance of the components and structures. Almost all manufacturing processes cause considerable amounts of residual stress; thus, any process or product design ignoring it involves a risk for distortion or early failure. Among the existing methods, the magnetic Barkhausen noise method has been gaining attention for measuring residual stresses nondestructively in ferromagnetic materials. It is sensitive to the interactions between the magnetic structure and microstructure or residual stress fields. So far, successful qualitative results have been obtained for monitoring the residual stress variations on the surfaces of the components manufactured by various processes. However, some challenging tasks exist, such as obtaining reliable quantitative results when residual stresses and microstructure change at the same time or extracting depth-specific information. This article reviews the studies for the measurement of residual stress by magnetic Barkhausen noise method, particularly focusing on the processes widely used in industry, namely shot peening and welding.

Modeling Binary Time Series Using Gaussian Processes with Application to Predicting Sleep States

Motivated by the problem of predicting sleep states, we develop a mixed effects model for binary time series with a stochastic component represented by a Gaussian process. The fixed component captures the effects of covariates on the binary-valued response. The Gaussian process captures the residual variations in the binary response that are not explained by covariates and past realizations. We develop a frequentist modeling framework that provides efficient inference and more accurate predictions. Results demonstrate the advantages of improved prediction rates over existing approaches such as logistic regression, generalized additive mixed model, models for ordinal data, gradient boosting, decision tree and random forest. Using our proposed model, we show that previous sleep state and heart rates are significant predictors for future sleep states. Simulation studies also show that our proposed method is promising and robust. To handle computational complexity, we utilize Laplace approximation, golden section search and successive parabolic interpolation. With this paper, we also submit an R-package (HIBITS) that implements the proposed procedure.

The Impact of Socio-Environmental Drivers and Japanese Encephalitis in Shaanxi, China, a Bayesian Spatial Analysis

Background: With the progress of global climate change and more extreme weather events, areas with lower mosquito borne disease incidence also meet with resurgence of disease. This study examined the association of meteorological and socio-demographical factors with Japanese encephalitis JE (2006-2014) in Shaanxi, China.Methods: JE data at the county level in Shaanxi were supplied by Shaanxi Center for Disease Control and Prevention. Population and socioeconomic data were provided by China Population Census in 2010 and statistical yearly book. Meteorological data were acquired from China Meteorological Administration. A Bayesian conditional autoregressive model was used to examine the association of meteorological and socioeconomic factors on JE.Results: A total of 1,197 JE cases were included in this study. The north of Shaanxi had lowest JE incidence while the south had the highest in most of the study years. Urbanization rate was inversely associated with JE incidence in the whole study period. Meteorological variables were more significantly associated with JE incidence between 2012 and 2014 than earlier years. The north had higher incidence from August to October, 2013 than the middle and south, which may be associated with the excessive precipitation in the north in July, 2013 with 1-3 months lag effect. The spatial residual variations indicated that the whole study area had more stable risk (0.80-1.19 across all the counties) between 2012 and 2014 than earlier years.Conclusion: Extreme weather outweighed other variables in association with spatial pattern of JE incidence. Public health interventions need to be implemented to reduce JE incidence, especially in rural areas and after extreme weather, e.g., rainfall.

Estimation formula for residual stress from the blind-hole drilling method

In this study, the accuracy of blind-hole method on weld residual stress estimation is investigated. A modified parameter group has also proposed to improve the accuracy. The thermal-elastic-plastic finite element model is employed to build up the residual stress distribution and the blind-hole process. The MSC Marc finite element software package is used to simulate the welding process and the welding residual stress and strain distributions around the weld of two inconel 690 alloy plates filled with I-52 GTAW filler. Then the process of the traditional blind hole is simulated by employing the inactive elements. The data of the residual strain variations of strain gages located around the blind hole is introduced into the blind-hole method to estimate the original residual stress components at the hole center. The effects of drilling depth, drilling size, gage radius, gage position, and the distance on the accuracy of estimated residual stress have also been studied and discussed. Based on the residual stress components simulated from the welding process, a modified stress parameter group has also been proposed to improve the accuracy of blind-hole method. Numerical results indicate that the accuracy of estimated residual stress can be improved significantly by employing the proposed blind-hole parameters.

Determining the Nature of Late Gunn–Peterson Troughs with Galaxy Surveys

Abstract Recent observations have discovered long (up to ∼110 Mpc/h), opaque Gunn–Peterson troughs in the z ∼ 5.5 Lyα forest, which are challenging to explain with conventional models of the post-reionization intergalactic medium. Here, we demonstrate that observations of the galaxy populations in the vicinity of the deepest troughs can distinguish two competing models for these features: deep voids where the ionizing background is weak due to fluctuations in the mean free path of ionizing photons would show a deficit of galaxies, while residual temperature variations from extended, inhomogeneous reionization would show an overdensity of galaxies. We use large (∼550 Mpc/h) semi-numerical simulations of these competing explanations to predict the galaxy populations in the largest of the known troughs at z ∼ 5.7. We quantify the strong correlation of Lyα effective optical depth and galaxy surface density in both models, and estimate the degree to which realistic surveys can measure such a correlation. While a spectroscopic galaxy survey is ideal, we also show that a relatively inexpensive narrowband survey of Lyα-emitting galaxies is ∼90% likely to distinguish between the competing models.

Online quality evaluation of tissue paper structure on new generation tissue machines

Abstract At present, the tissue paper manufacturing is mostly based on the dry crepe technology. During the last decade, the manufacturers have introduced new tissue machines concepts that increase the softness, bulk, and absorption capacity. Such machines produce a strong regular three-dimensional (3D) structure to the sheet before the Yankee cylinder. At present, the quality of the 3D structure is not evaluated, or it is evaluated only subjectively at the mill. This is mostly because of the difficulties to separate reliably the regular 3D pattern from other variations. This paper introduces a frequency analysis based method which separates the surface profile variances in tissue paper to the creping, to the regular 3D pattern and to the residual variation. The 3D surface profiles and their variances were determined online with the photometric stereo method. We show that the introduced analysis method evaluates the variance portions reliably and the results are consistent with the visual perception of the 3D surfaces. In one particular product, the regular 3D pattern explains 74 % of total surface variance; the creping explains 10 % and residual variations 16 %. Furthermore, the creping and residual variances are quite stable over time whereas the variance of the regular 3D pattern fluctuates significantly.

Real-time triple-frequency cycle slip detection and repair method under ionospheric disturbance validated with BDS data

In order to resolve the real-time cycle slip detection and repair problem with the data under ionospheric disturbance and low sample rate, a new method is proposed by using triple-frequency combinations. First, the geometry-free and ionospheric-free (GFIF) carrier phase combination and then the GFIF pseudorange minus phase linear combination are derived for cycle slip detection. The special slip groups which cannot be discovered by the two GFIF combinations are divided into two types, and each of them is designed to be detected by using three additional geometry-free (GF) linear combinations. In the estimation step, the two GFIF combinations and the pseudorange minus phase linear combination with B3 carrier phase observations are used together to determinate the cycle slip on the original three carriers. The strategy is first to search B3 for cycle slips and then find the B1 and B2 cycles using the two GFIF combinations by integer bootstrapping method. The ionospheric delay variations between two consecutive epochs are estimated using the carrier phase data of the previous epochs and used for compensating time-differenced linear combinations that contain residual ionospheric variations. Then, in the validation step, both the criterions of threshold judgment and minimum one norm are used to validate the cycle slip candidates and finally get the correct one. The real-data tests with simulated and real cycle slips reveal that the new method can repair all cycle slips with high reliability even under ionospheric disturbance. Several failed repairs may occur with the most insensitive slip combinations ± (1, 1, 1) under bad observation conditions, but these cycle slips can be detected.

The Light-time Effect in the Eclipsing Binaries with Early-type Components U CrB and RW Tau

A detailed study of the orbital-period variations of the Algol-type eclipsing binaries with earlyspectral- type primary components U CrB and RW Tau has been performed. The period variations in both systems can be described as a superposition of secular and cyclic variations of the period. A secular period increase at a rate of 2.58d × 10−7/year is observed for U CrB, which can be explained if there is a uniform flow of matter from the lower-mass to the higher-mass component, with the total angular momentum conserved. RW Tau features a secular period decrease at a rate of −8.6d × 10−7/year; this could be due to a loss of angular momentum by the binary due to magnetic braking. The cyclic orbital-period variations of U CrB and RWTau can be explained by the motion of the eclipsing binary systems along their long-period orbits. In U CrB, this implies that the eclipsing binary moves with a period of 91.3 years around a third body with mass M3 > 1.13M⊙; in RW Tau, the period of the motion around the third body is 66.6 years, and the mass of the third body is M3 > 1.24M⊙. It also cannot be ruled out that the variations are due to the magnetic cycles of the late-type secondaries. The residual period variations could be a superposition of variations due to non-stationary ejection of matter and effects due to magnetic cycles.

How Socio-Environmental Factors Are Associated with Japanese Encephalitis in Shaanxi, China-A Bayesian Spatial Analysis.

Evidence indicated that socio-environmental factors were associated with occurrence of Japanese encephalitis (JE). This study explored the association of climate and socioeconomic factors with JE (2006–2014) in Shaanxi, China. JE data at the county level in Shaanxi were supplied by Shaanxi Center for Disease Control and Prevention. Population and socioeconomic data were obtained from the China Population Census in 2010 and statistical yearbooks. Meteorological data were acquired from the China Meteorological Administration. A Bayesian conditional autoregressive model was used to examine the association of meteorological and socioeconomic factors with JE. A total of 1197 JE cases were included in this study. Urbanization rate was inversely associated with JE incidence during the whole study period. Meteorological variables were significantly associated with JE incidence between 2012 and 2014. The excessive precipitation at lag of 1–2 months in the north of Shaanxi in June 2013 had an impact on the increase of local JE incidence. The spatial residual variations indicated that the whole study area had more stable risk (0.80–1.19 across all the counties) between 2012 and 2014 than earlier years. Public health interventions need to be implemented to reduce JE incidence, especially in rural areas and after extreme weather.

Simulation and experimental comparison of the thermo-mechanical history and 3D microstructure evolution of 304L stainless steel tubes manufactured using LENS

Additive manufacturing enables the production of previously unachievable designs in conjunction with time and cost savings. However, spatially and temporally fluctuating thermal histories can lead to residual stress states and microstructural variations that challenge conventional assumptions used to predict part performance. Numerical simulations offer a viable way to explore the root causes of these characteristics, and can provide insight into methods of controlling them. Here, the thermal history of a 304L stainless steel cylinder produced using the Laser Engineered Net Shape process is simulated using finite element analysis (FEA). The resultant thermal history is coupled to both a solid mechanics FEA simulation to predict residual stress and a kinetic Monte Carlo model to predict the three-dimensional grain structure evolution. Experimental EBSD measurements of grain structure and in-process infrared thermal data are compared to the predictions.

Reconstruction of Obliterated Characters in Polycarbonate through Spectral Imaging.

In forensic sciences, there is an increasing demand for nondestructive and reliable methods to retrieve obliterated information in polymers. This study demonstrates a case study for the potential of Raman spectroscopy to reconstruct abraded serial numbers. Residual strain and local variations in the structural arrangement are nondestructively imaged through peak shifts and variations of the full width at half-maximum of specific Raman lines, respectively. We qualitatively validate our approach by successfully recovering an obliterated letter stamped with a pressure of ∼170 MPa in a polycarbonate sample, with a subsequent quantitative statistical analysis. The detection threshold is estimated from the propagation depth of plastic deformations to a value of ∼750-800 μm, substantially larger than typical obliteration depths, 200 μm in our case for an initial profile depth of 120 μm.

In-flight performance analysis of MEMS GPS receiver and its application to precise orbit determination of APOD-A satellite

An experimental satellite mission termed atmospheric density detection and precise orbit determination (APOD) was developed by China and launched on 20 September 2015. The micro-electro-mechanical system (MEMS) GPS receiver provides the basis for precise orbit determination (POD) within the range of a few decimetres. The in-flight performance of the MEMS GPS receiver was assessed. The average number of tracked GPS satellites is 10.7. However, only 5.1GPS satellites are available for dual-frequency navigation because of the loss of many L2 observations at low elevations. The variations in the multipath error for C1 and P2 were estimated, and the maximum multipath error could reach up to 0.8m. The average code noises are 0.28m (C1) and 0.69m (P2). Using the MEMS GPS receiver, the orbit of the APOD nanosatellite (APOD-A) was precisely determined. Two types of orbit solutions are proposed: a dual-frequency solution and a single-frequency solution. The antenna phase center variations (PCVs) and code residual variations (CRVs) were estimated, and the maximum value of the PCVs is 4.0cm. After correcting the antenna PCVs and CRVs, the final orbit precision for the dual-frequency and single-frequency solutions were 7.71cm and 12.91cm, respectively, validated using the satellite laser ranging (SLR) data, which were significantly improved by 3.35cm and 25.25cm. The average RMS of the 6-h overlap differences in the dual-frequency solution between two consecutive days in three dimensions (3D) is 4.59cm. The MEMS GPS receiver is the Chinese indigenous onboard receiver, which was successfully used in the POD of a nanosatellite. This study has important reference value for improving the MEMS GPS receiver and its application in other low Earth orbit (LEO) nanosatellites.

The VALUE perfect predictor experiment: Evaluation of temporal variability

Temporal variability is an important feature of climate, comprising systematic variations such as the annual cycle, as well as residual temporal variations such as short‐term variations, spells and variability from interannual to long‐term trends. The EU‐COST Action VALUE developed a comprehensive framework to evaluate downscaling methods. Here we present the evaluation of the perfect predictor experiment for temporal variability. Overall, the behaviour of the different approaches turned out to be as expected from their structure and implementation. The chosen regional climate model adds value to reanalysis data for most considered aspects, for all seasons and for both temperature and precipitation. Bias correction methods do not directly modify temporal variability apart from the annual cycle. However, wet day corrections substantially improve transition probabilities and spell length distributions, whereas interannual variability is in some cases deteriorated by quantile mapping. The performance of perfect prognosis (PP) statistical downscaling methods varies strongly from aspect to aspect and method to method, and depends strongly on the predictor choice. Unconditional weather generators tend to perform well for the aspects they have been calibrated for, but underrepresent long spells and interannual variability. Long‐term temperature trends of the driving model are essentially unchanged by bias correction methods. If precipitation trends are not well simulated by the driving model, bias correction further deteriorates these trends. The performance of PP methods to simulate trends depends strongly on the chosen predictors.

Effect of Thermal Annealing on Machining-Induced Residual Stresses in Inconel 718

Nickel-based alloys are widely employed in the manufacturing of aero-engines. These alloys are difficult to machine, and tensile residual stresses are generated during machining. These tensile residual stresses can negatively affect the performance of aero-engine components. Nevertheless, residual stresses can vary due to thermal or mechanical loading. These variations must be considered to evaluate the real influence of residual stresses on component behavior. This paper studies the effect of thermal loads on machining-induced residual stresses in the alloy Inconel 718. A ring-shaped Inconel 718 part was face-turned, and specimens were extracted from it. Specimens were exposed at 550 and 650 °C for 10 min, 1 and 10 h. Residual stresses were measured, and microstructure was observed before and after thermal exposure. Residual stress variations found after thermal exposure were the consequence of two factors: relaxation of strain bands during the early stage of exposure and diffusion-controlled creep. In addition, a modified Zener-Wert-Avrami model is proposed to predict residual stress relaxation caused by the diffusion-controlled creep. Once having fitted the modified Zener-Wert-Avrami model, the study was extended for a wider range of temperatures (400-650 °C). This analysis showed that surface residual stresses do not relax significantly at temperatures below 500 °C.

The probable quadruple systems FK Aql and FZ Del

Orbital-period variations of the eclipsing binaries FK Aql and FZ Del are analyzed. For each of the systems, a superposition of two cyclic variations of their orbital periods is found. FK Aql may be a quadruple system that contains two more bodies, besides the eclipsing binary, with masses M 3 ⩾ 1.75M ⊙ and M 4 ⩾ 1.47M ⊙, and the corresponding periods 15 and 82 yrs. This could also be a triple system with a third body of mass M 3 ⩾ 1.75M ⊙ and a period of the long-period orbit P 3 = 15 yrs, or with a third body of mass M 3 ⩾ 1.30M ⊙ and a period of the long-period orbit P 3 = 82 yrs. FZ Del may be a quadruple system with the additional componentmasses M 3 ⩾ 0.2M ⊙ and M 4 ⩾ 0.3M ⊙, with the periods 10.2 and 53.7 yrs. This could also be a triple system with a third-body mass M 3 ⩾ 0.2M ⊙ and a period of the long-period orbit P 3 = 10.2 yrs. In both systems, the residual period variations could be due to magnetic cycles of the secondary. The period variations of the eclipsing binary FZ Del could also be due to apsidal motion, together with the influence of a third body or the effects of magnetic activity.

Correlation of residual stress variations to electrical properties changes in ZNO thin films

Using Nd:YAG pulsed laser deposition, the modulation of the residual stress in thin films of ZnO and their effect on the electrical properties was studied. The variations of residual stress were correlated with the number of oxygen atoms grabbed in the plasma flux (PF) from the introduction of reactive oxygen partial pressure (P O ). A compressive to tensile residual stress generation in the films in function of P O is observed. We assume that this can be correlated to the driving force on the atoms deposited on the grain surface, normal at PF to induce flow at the grain boundary. These driving forces are attributable to the change of surface chemical potential generated by the flux of materials arriving on the substrate. This effect can induce that the surface chemical potential regulates the atoms at the grain boundary, creating a tensile residual stress as P O increases. The resistivity was an approximate linearly dependent on residual stress. The variation of the residual stress induces structural native defects, which favors the reduction of the electrical resistivity and consequently increases the concentration of charge carriers in the films.

Improved evaluation of field experiments by accounting for inherent soil variability

Abstract Well-controlled field experiments are used to test agronomic management practices and evaluate the performance of cultivars in highly managed plots at experimental stations, in breeding nurseries or on-farm. However, the performance of crops and therefore the interpretation of experiments is affected by the inherent soil variability. To avoid large residual errors, replicate measurements or optimized designs are usually helpful but seldom adequately consider the unknown soil variability. The use of spatial covariates, such as proximally sensed data, in the statistical modelling of the target variable may provide a better estimate of such experimental residual variations (errors). Therefore, the purpose of this study was to determine whether the apparent soil electrical conductivity, topographical parameters and location information (expressed as Gaus-Kruger coordinates) could be used for an enhanced spatial and temporal characterization of the long-term and annual wheat yields within a static, long-term nitrogen fertilizer experiment that included six different forms of nitrogen and three levels of nitrogen fertilizer. Furthermore, this investigation aimed to propose statistical strategies for analysing this background variation by testing ANOVA (Analysis of variance) and ANCOVA (Analysis of covariance). ANCOVA with soil ECa, location information and topographic parameters as covariates improved the accuracy of the yield estimates of the multi-annual means for all treatments. Without these independent variables in ANOVA, the coefficient of determination (R2) was smaller and the root mean square difference (RMSD) was larger than those of ANCOVA (fertilized plots ANOVA: R2 = 0.19, RMSD = 3.26 dt ha−1; ANCOVA: R2 = 0.87, RMSD = 1.29 dt ha−1). In addition to the factor level of fertilization and form of nitrogen fertilizer, ECa was the dominant covariate for the averaged long-term and annual yields. The ECa was measured with different sensors and configurations and represented a significant independent variable. Of the topographic relief parameters, the predictor plancurvature was the dominant independent variable. The inclusion of plot-wise, time-invariant soil and relief parameters significantly improved the discrimination of testing the treatment performance within the long-term field trial. A further application of this approach to other experimental sites and breeding nurseries would likely be highly rewarding.