Showing papers on "Deformation (meteorology) published in 2016"

Stress and Deformation Evaluations of Scanning Strategy Effect in Selective Laser Melting

Abstract: Selective laser melting (SLM) has emerged as one of the primary metal additive manufacturing technologies used for many applications in various industries such as medical and aerospace sectors. However, defects such as part distortion and delamination resulted from process-induced residual stresses are still one of the key challenges that hinder widespread adoptions of SLM. For process parameters, the laser beam scanning path will affect the thermomechanical behaviors of the build part, and thus, altering the scanning pattern may be a possible strategy to reduce residual stresses and deformations through influencing the heat intensity input distributions. In this study, a 3D sequentially coupled finite element (FE) model was developed to investigate the thermomechanical responses in the SLM process. The model was applied to test different scanning strategies and evaluate their effects on part temperature, stress and deformation. The major results are summarized as follows. (1) Among all cases tested, the out-in scanning pattern has the maximum stresses along the X and Y directions; while the 45° inclined line scanning may reduce residual stresses in both directions. (2) Large directional stress differences can be generated by the horizontal line scanning strategy. (3) X and Y directional stress concentrations are shown around the edge of the deposited layers and the interface between the deposited layers and the substrate for all cases. (4) The 45° inclined line scanning case also has a smaller build direction deformation than other cases.

Deformation Mechanisms in Austenitic TRIP/TWIP Steel as a Function of Temperature

Abstract: A high-alloy austenitic CrMnNi steel was deformed at temperatures between 213 K and 473 K (−60 °C and 200 °C) and the resulting microstructures were investigated. At low temperatures, the deformation was mainly accompanied by the direct martensitic transformation of γ-austenite to α′-martensite (fcc → bcc), whereas at ambient temperatures, the transformation via e-martensite (fcc → hcp → bcc) was observed in deformation bands. Deformation twinning of the austenite became the dominant deformation mechanism at 373 K (100 °C), whereas the conventional dislocation glide represented the prevailing deformation mode at 473 K (200 °C). The change of the deformation mechanisms was attributed to the temperature dependence of both the driving force of the martensitic γ → α′ transformation and the stacking fault energy of the austenite. The continuous transition between the e-martensite formation and the twinning could be explained by different stacking fault arrangements on every second and on each successive {111} austenite lattice plane, respectively, when the stacking fault energy increased. A continuous transition between the transformation-induced plasticity effect and the twinning-induced plasticity effect was observed with increasing deformation temperature. Whereas the formation of α′-martensite was mainly responsible for increased work hardening, the stacking fault configurations forming e-martensite and twins induced additional elongation during tensile testing.

Full length articleStress and deformation evaluations of scanning strategy effect in selective laser melting

Abstract: Selective laser melting (SLM) has emerged as one of the primary metal additive manufacturing technologies used for many applications in various industries such as medical and aerospace sectors. However, defects such as part distortion and delamination resulted from process-induced residual stresses are still one of the key challenges that hinder widespread adoptions of SLM. For process parameters, the laser beam scanning path will affect the thermomechanical behaviors of the build part, and thus, altering the scanning pattern may be a possible strategy to reduce residual stresses and deformations through influencing the heat intensity input distributions. In this study, a 3D sequentially coupled finite element (FE) model was developed to investigate the thermomechanical responses in the SLM process. The model was applied to test different scanning strategies and evaluate their effects on part temperature, stress and deformation. The major results are summarized as follows. (1) Among all cases tested, the out-in scanning pattern has the maximum stresses along the X and Y directions; while the 45° inclined line scanning may reduce residual stresses in both directions. (2) Large directional stress differences can be generated by the horizontal line scanning strategy. (3) X and Y directional stress concentrations are shown around the edge of the deposited layers and the interface between the deposited layers and the substrate for all cases. (4) The 45° inclined line scanning case also has a smaller build direction deformation than other cases.

Low temperature deformation behavior of an electromagnetically bulged 5052 aluminum alloy.

Abstract: The fundamental understanding of the deformation behavior of electromagnetically formed metallic components under extreme conditions is important. Here, the effect of low temperature on the deformation behavior of an electromagnetically-bulged 5052 aluminum alloy was investigated through uniaxial tension. We found that the Portevin-Le Chatelier Effect, designated by the serrated characteristic in stress-strain curves, continuously decays until completely disappears with decreasing temperature. The physical origin of the phenomenon is rationalized on the basis of the theoretical analysis and the Monte Carlo simulation, which reveal an increasing resistance to dislocation motion imposed by lowering temperature. The dislocations are captured completely by solute atoms at −50 °C, which results in the extinction of Portevin-Le Chatelier. The detailed mechanism responsible for this process is further examined through Monte Carlo simulation.

A review of the use of terrestrial laser scanning application for change detection and deformation monitoring of structures

Abstract: Change detection and deformation monitoring is an active area of research within the field of engineering surveying and other overlapping areas such as structural and civil engineering. This paper reviews the application of terrestrial laser scanning in the monitoring of structures and discusses registration and georeferencing of scan data. Past terrestrial laser scanning research work has shown trends in addressing issues such as accurate registration and georeferencing of scans, error modelling, point cloud processing techniques for deformation analysis, scanner calibration and detection of millimetre deformations. However, several issues are still open to investigation such as robust methods of point cloud processing for detecting change and deformation, incorporation of measurement geometry in deformation measurements, design of data acquisition and quality assessment for precise measurements and modelling the environmental effects on the performance of laser scanning. A three-stage process model for ...

Phase transformation strengthening of high-temperature superalloys

Abstract: Decades of research has been focused on improving the high-temperature properties of nickel-based superalloys, an essential class of materials used in the hot section of jet turbine engines, allowing increased engine efficiency and reduced CO2 emissions. Here we introduce a new ‘phase-transformation strengthening’ mechanism that resists high-temperature creep deformation in nickel-based superalloys, where specific alloying elements inhibit the deleterious deformation mode of nanotwinning at temperatures above 700 °C. Ultra-high-resolution structure and composition analysis via scanning transmission electron microscopy, combined with density functional theory calculations, reveals that a superalloy with higher concentrations of the elements titanium, tantalum and niobium encourage a shear-induced solid-state transformation from the γ′ to η phase along stacking faults in γ′ precipitates, which would normally be the precursors of deformation twins. This nanoscale η phase creates a low-energy structure that inhibits thickening of stacking faults into twins, leading to significant improvement in creep properties. Nanoscale processes may directly impact macroscopic mechanical behaviour. Here authors describe a ‘phase-transformation strengthening’ mechanism in nickel-based high temperature alloys, allowing suppression of deleterious deformation processes at elevated temperatures by specific alloying elements.

Deformation and Degradation Mechanisms of Railway Ballast under High Frequency Cyclic Loading

Abstract: The increased demand for higher speeds and increased freight capacity in railroad transportation exacerbates the rate of ballast degradation that leads to unacceptable track deformation and frequent maintenance. In response, a series of large-scale cyclic triaxial tests was performed to investigate the combined effect of train speed (frequency), axle load, and confinement on the deformation and degradation of ballast. In these tests, the load frequency f was varied from 5 to 60 Hz to simulate train speeds of 40–400 km/h. Two sets of deviator stress magnitude qmax,cyc (230 and 370 kPa) were applied to resemble axle loads of 25 and 40 t, respectively, and the effect of three levels of confining pressure σ3′ (10, 30, and 60 kPa) was examined. The results indicate that three distinct categories of permanent deformation mechanisms exist at various levels of f, qmax,cyc, and σ3′. Ballast degradation was more pronounced at higher f, and it had a more profound effect on cyclic densification. The resilien...

Multiscale Graphene Topographies Programmed by Sequential Mechanical Deformation.

Abstract: Multigenerational graphene oxide architectures can be programmed by specific sequences of mechanical deformations. Each new deformation results in a progressively larger set of features decorated by smaller preexisting patterns, indicating a structural "memory." It is shown that these multiscale architectures are superhydrophobic and display excellent functionality as electrochemical electrodes.

Macrodeformation Twins in Single-Crystal Aluminum

Abstract: Deformation twinning in pure aluminum has been considered to be a unique property of nanostructured aluminum. A lingering mystery is whether deformation twinning occurs in coarse-grained or single-crystal aluminum at scales beyond nanotwins. Here, we present the first experimental demonstration of macrodeformation twins in single-crystal aluminum formed under an ultrahigh strain rate (∼10^{6} s^{-1}) and large shear strain (200%) via dynamic equal channel angular pressing. Large-scale molecular dynamics simulations suggest that the frustration of subsonic dislocation motion leads to transonic deformation twinning. Deformation twinning is rooted in the rate dependences of dislocation motion and twinning, which are coupled, complementary processes during severe plastic deformation under ultrahigh strain rates.

Inflation-predictable behavior and co-eruption deformation at Axial Seamount

Abstract: Deformation of the ground surface at active volcanoes provides information about magma movements at depth. Improved seafloor deformation measurements between 2011 and 2015 documented a fourfold increase in magma supply and confirmed that Axial Seamount’s eruptive behavior is inflation-predictable, probably triggered by a critical level of magmatic pressure. A 2015 eruption was successfully forecast on the basis of this deformation pattern and marked the first time that deflation and tilt were captured in real time by a new seafloor cabled observatory, revealing the timing, location, and volume of eruption-related magma movements. Improved modeling of the deformation suggests a steeply dipping prolate-spheroid pressure source beneath the eastern caldera that is consistent with the location of the zone of highest melt within the subcaldera magma reservoir determined from multichannel seismic results.

Learning Semantic Deformation Flows with 3D Convolutional Networks

Abstract: Shape deformation requires expert user manipulation even when the object under consideration is in a high fidelity format such as a 3D mesh. It becomes even more complicated if the data is represented as a point set or a depth scan with significant self occlusions. We introduce an end-to-end solution to this tedious process using a volumetric Convolutional Neural Network (CNN) that learns deformation flows in 3D. Our network architectures take the voxelized representation of the shape and a semantic deformation intention (e.g., make more sporty) as input and generate a deformation flow at the output. We show that such deformation flows can be trivially applied to the input shape, resulting in a novel deformed version of the input without losing detail information. Our experiments show that the CNN approach achieves comparable results with state of the art methods when applied to CAD models. When applied to single frame depth scans, and partial/noisy CAD models we achieve \({\sim }60\,\%\) less error compared to the state-of-the-art.

Extending the geometric deformation: New black hole solutions

Abstract: By using the extension of the Minimal Geometric Deformation approach, recently developed to investigate the exterior spacetime of a self-gravitating system in the Braneworld, we identified a master solution for the deformation undergone by the radial metric component when time deformations are produced by bulk gravitons. A specific form for the temporal deformation is used to generate a new exterior solution with a tidal charge Q. The main feature of this solution is the presence of higher-order terms in the tidal charge, thus generalizing the well known tidally charged solution. The horizon of the black hole lies inside the Schwarzschild radius, h < rs = 2ℳ, indicating that extra-dimensional effects weaken the gravitational field.

Precipitation behavior during high-temperature isothermal compressive deformation of Inconel 718 alloy

Abstract: The precipitation behaviors of γ″ and δ phases during high-temperature isothermal compressive deformation of Inconel 718 alloy are investigated under the strain rate of 2.2·10−4 s−1. It is found that the precipitation behaviors are tailored by deformation temperatures, and lead to the disparately abnormal deformation characteristics. Under the deformation temperature of 800 °C, the microstructure is composed of incoherent needle-shaped γ″ precipitates at grain boundaries and ultrafine spherical γ″ particles within grains, resulting in the exceptional decrease of flow stress with absence of DRX. When deformed at 900 °C, it becomes needle-shaped δ precipitates at grain boundaries and intragranular disc-shaped γ″ precipitates, and the DRX softening degree is lowered consequently.

Crustal structure and deformation beneath the NE margin of the Tibetan plateau constrained by teleseismic receiver function data

Abstract: Qiong Wang,1,2,3 Fenglin Niu,3,4 Yuan Gao2 and Yuntai Chen1 1Institute of Geophysics, China Earthquake Administration, Beijing, China 2Institute of Earthquake Science, China Earthquake Administration, Beijing, China, E-mail: gaoyuan@seis.ac.cn 3Department of Earth Science, Rice University, Houston, TX, USA 4State Key Laboratory of Petroleum Resource and Prospecting, and Unconventional Natural Gas Institute, China University of Petroleum at Beijing, Beijing, China

Laboratory Assessment of the Role of Particle Size Distribution on the Deformation and Degradation of Ballast under Cyclic Loading

Abstract: The deformation and degradation of ballast is influenced by the size of the aggregates. In this study, a series of cyclic drained triaxial tests was conducted on ballast with different sizes using the large-scale cylindrical triaxial apparatus designed and built at the University of Wollongong, and two different frequencies of cyclic loading were used to simulate low-speed and high-speed trains. From the laboratory results, coarse particles experience less vertical and lateral strains, whereas the volumetric strains decrease and then increase as the coefficient of uniformity increases, regardless of the loading frequency. Resistance to deformation and degradation is found to be improved by increasing ballast density. Different trends between the extent of breakage and particle size are observed for different breakage indices, and accordingly the extent of breakage is characterized into two distinct zones, depending on the coefficient of uniformity (Cu), where the significantly reduced breakage cor...

An Analytical Foundation for Optimal Compensation of Three-Dimensional Shape Deformation in Additive Manufacturing

Abstract: Additive Manufacturing (AM) or three-dimensional (3D) printing is a promising technology that enables the direct fabrication of products with complex shapes without extra tooling and fixturing. However, control of 3D shape deformation in AM built products has been a challenging issue. One viable approach for accuracy control is through compensation of the product design to offset the geometric shape deformation. This work establishes an analytical foundation of optimal compensation of 3D shape deformation for high-precision AM.