Showing papers on "Deformation (meteorology) published in 2011"

High-temperature digital image correlation method for full-field deformation measurement at 1200 ◦ C

Abstract: A simple, easy-to-implement yet effective high-temperature digital image correlation (DIC) method is established for non-contact full-field deformation measurement at elevated temperatures. The technique employs a bandpass optical filter to eliminate the influence of black-body radiation of high-temperature objects on the intensity of captured images. With the bandpass filter, high-quality digital images of an object at high temperatures up to 1200 °C can be easily acquired and directly compared with the reference image recorded at room temperature using the DIC technique to extract full-field deformation information with high fidelity. To verify the performance of the proposed technique, a chromium-nickel austenite stainless steel sample was heated from room temperature to 1200 °C using an infrared heating device, and the surface images at various temperatures were captured using the bandpass filter imaging system. Afterwards, full-field thermal deformation and coefficient of thermal expansion of the sample were determined using the DIC technique. Experimental results indicate that the proposed high-temperature DIC method is easy to implement and can be applied to practical full-field high-temperature deformation measurement with high accuracy.

Bounded biharmonic weights for real-time deformation

Abstract: Object deformation with linear blending dominates practical use as the fastest approach for transforming raster images, vector graphics, geometric models and animated characters. Unfortunately, lin...

In situ characterization of the deformation and failure behavior of non-stochastic porous structures processed by selective laser melting

Abstract: Cellular materials are promising candidates for load adapted light-weight structures Direct manufacturing (DM) tools are effective methods to produce non-stochastic structures Many DM studies currently focus on optimization of the geometric nature of the structures obtained The literature available so far reports on the mechanical properties but local deformation mechanisms are not taken into account In order to fill this gap, the current study addresses the deformation behavior of a lattice structure produced by selective laser melting (SLM) on the local scale by means of a comprehensive experimental in situ approach, including electron backscatter diffraction, scanning electron microscopy and digital image correlation SLM-processed as well as heat treated lattice structures made from TiAl6V4 alloy were employed for mechanical testing It is demonstrated that the current approach provides means to understand the microstructure-mechanical property–local deformation relationship to allow for optimization of load adapted lattice structures

The role of crustal quartz in controlling Cordilleran deformation

Abstract: Large-scale deformation of continents remains poorly understood more than 40 years after the plate tectonic revolution. Rock flow strength and mass density variations both contribute to stress, so both are certain to be important, but these depend (somewhat nebulously) on rock type, temperature and whether or not unbound water is present. Hence, it is unclear precisely how Earth material properties translate to continental deformation zones ranging from tens to thousands of kilometres in width, why deforming zones are sometimes interspersed with non-deforming blocks and why large earthquakes occasionally rupture in otherwise stable continental interiors. An important clue comes from observations that mountain belts and rift zones cyclically form at the same locations despite separation across vast gulfs of time (dubbed the Wilson tectonic cycle), accompanied by inversion of extensional basins and reactivation of faults and other structures formed in previous deformation events. Here we show that the abundance of crustal quartz, the weakest mineral in continental rocks, may strongly condition continental temperature and deformation. We use EarthScope seismic receiver functions, gravity and surface heat flow measurements to estimate thickness and seismic velocity ratio, v(P)/v(S), of continental crust in the western United States. The ratio v(P)/v(S) is relatively insensitive to temperature but very sensitive to quartz abundance. Our results demonstrate a surprising correlation of low crustal v(P)/v(S) with both higher lithospheric temperature and deformation of the Cordillera, the mountainous region of the western United States. The most plausible explanation for the relationship to temperature is a robust dynamical feedback, in which ductile strain first localizes in relatively weak, quartz-rich crust, and then initiates processes that promote advective warming, hydration and further weakening. The feedback mechanism proposed here would not only explain stationarity and spatial distributions of deformation, but also lend insight into the timing and distribution of thermal uplift and observations of deep-derived fluids in springs.

Mapping Three-Dimensional Surface Deformation by Combining Multiple-Aperture Interferometry and Conventional Interferometry: Application to the June 2007 Eruption of Kilauea Volcano, Hawaii

Abstract: Surface deformation caused by an intrusion and small eruption during June 17-19, 2007, along the East Rift Zone of Kilauea Volcano, Hawaii, was three-dimensionally reconstructed from radar interferograms acquired by the Advanced Land Observing Satellite (ALOS) phased-array type L-band synthetic aperture radar (SAR) (PALSAR) instrument. To retrieve the 3-D surface deformation, a method that combines multiple-aperture interferometry (MAI) and conventional interferometric SAR (InSAR) techniques was applied to one ascending and one descending ALOS PALSAR interferometric pair. The maximum displacements as a result of the intrusion and eruption are about 0.8, 2, and 0.7 m in the east, north, and up components, respectively. The radar-measured 3-D surface deformation agrees with GPS data from 24 sites on the volcano, and the root-mean-square errors in the east, north, and up components of the displacement are 1.6, 3.6, and 2.1 cm, respectively. Since a horizontal deformation of more than 1 m was dominantly in the north-northwest-south-southeast direction, a significant improvement of the north-south component measurement was achieved by the inclusion of MAI measurements that can reach a standard deviation of 3.6 cm. A 3-D deformation reconstruction through the combination of conventional InSAR and MAI will allow for better modeling, and hence, a more comprehensive understanding, of the source geometry associated with volcanic, seismic, and other processes that are manifested by surface deformation.

Tectonic geomorphology along the eastern margin of Tibet: insights into the pattern and processes of active deformation adjacent to the Sichuan Basin

Abstract: Abstract We present a review and synthesis of the tectonic geomorphology along the eastern margin of the Tibetan Plateau adjacent to and north of the Sichuan Basin. Re-evaluation of spatial variations in the form of fluvial longitudinal profiles provides a refined image of the distribution of anomalously steep channels. Three new analyses demonstrate that these variations in channel steepness reflect variations in the locus and rate of differential rock uplift. First, measurements of channel width along trunk streams reveal systematic co-variations in channel hydraulic geometry and slope that suggests channels are dynamically adjusted to spatial variations in erosion rate. Second, recent determinations of the functional relationship between channel steepness indices and erosion rate allow a quantitative estimation of erosion rate from channel profile form. Third, comparison of rock uplift patterns to variations in the distribution of slip associated with the 2008 Wenchuan earthquake confirms that channel gradients reflect differential rock uplift. Our analysis suggests that reactivated fault systems adjacent to the Sichuan Basin are primarily responsible for accommodating differential rock uplift, but that rock uplift northward along the margin is not associated with active faults and is likely sustained by flow and thickening in the deep crust.

High-temperature deformation behavior of Ti60 titanium alloy

Abstract: Isothermal compressions of near-alpha Ti60 alloy were carried out on a Gleeble-3800 simulator in the temperature range of 960-1110 degrees C and strain rate range of 0.001-10.0 s(-1). The high-temperature deformation behavior was characterized based on an analysis of the stress-strain behavior, kinetics and processing map. The flow stress behavior revealed greater flow softening in the two-phase field compared with that of single-phase field. In two-phase field, flow softening was caused by break-up and globularization of lamellar a as well as deformation heating during deformation. While in the single-phase field, flow softening was caused by dynamic recovery and recrystallization. Using hyperbolic-sine relationships for the flow stress data, the apparent activation energy was determined to be 653 kJ/mol and 183 kJ/mol for two-phase field and single-phase field, respectively. The processing map exhibited two instability fields: 960-980 degrees C at 0.3-10 s(-1) and 990-1110 degrees C at 0.58-10 s(-1). These fields should be avoided due to the flow localization during the deformation of Ti60 alloy. (C) 2011 Elsevier B.V. All rights reserved.

Nonlinear Deformation of a Ferrofluid Droplet in a Uniform Magnetic Field

Abstract: This paper reports experimental and numerical results of the deformation of a ferrofluid droplet on a superhydrophobic surface under the effect of a uniform magnetic field. A water-based ferrofluid droplet surrounded by immiscible mineral oil was stretched by a magnetic field parallel to the substrate surface. The results show that an increasing flux density increases the droplet width and decreases the droplet height. A numerical model was established to study the equilibrium shape of the ferrofluid droplet. The governing equations for physical fields, including the magnetic field, are solved by the finite volume method. The interface between the two immiscible liquids was tracked by the level-set method. Nonlinear magnetization was implemented in the model. Comparison between experimental and numerical results shows that the numerical model can predict well the nonlinear deformation of a ferrofluid droplet in a uniform magnetic field.

Ultra High Speed DIC and Virtual Fields Method Analysis of a Three Point Bending Impact Test on an Aluminium Bar

Abstract: This paper deals with the analysis of an aluminium beam impacted in a three point bending configuration using a Hopkinson bar device. Full-field deformation measurements were performed using Digital Image Correlation on images captured with an ultra high speed camera (16 frames at a time resolution of 10 μs). The performance of the deformation and strain measurements were evaluated and the data were then used quantitatively to analyse the very complex dynamic behaviour of the beam. It was shown that the deformation of the beam was controlled by the interaction between the striker and the flexural bending wave triggered by the initial impact. The principle of virtual work was used to reconstruct the impact force from the shear strains and to analyze how this impact force relates to the acceleration of the specimen (inertia forces) and the development of the bending stresses. The results are in good agreement with expectations. This opens up new perspectives in the quantitative use of full-field measurements to extract elasto-plastic constitutive parameters from such impact tests.

Effect of autogenous deformation on the cracking risk of slag cement concretes

Abstract: Autogenous deformation under restrained conditions often leads to cracking and durability problems in concrete structures. It is therefore important to monitor accurately the early age development of autogenous deformation. However, its expression depends strongly on the measuring methods and on the choice of the time-zero. In order to determine the effect of slag on the evolution of autogenous deformation, a test rig was designed to monitor this deformation for three concretes with different slag content. The choice of different time-zero was also discussed based on different methods: setting evolution, time of peak expansion and evolution of deformation rate. Moreover, their restrained shrinkage was studied by means of a Temperature Stress Testing Machine (TSTM). Following these experiments, the slag cement concretes crack later than the Portland cement concrete despite the fact that they are characterized by a larger autogenous shrinkage. This behavior is mainly due to the expansion of their cement matrix at early age and their largest capacity to relax internal stresses.

Improvement of Geometric Accuracy in Incremental Forming by Using a Squeezing Toolpath Strategy With Two Forming Tools

Abstract: Single point incremental forming (SPIF) is plagued by an unavoidable and unintended bending in the region of the sheet between the current tool position and the fixture. The effect is a deformation of the region of the sheet in between the formed area and the fixture as well as deformation of the already formed portion of the wall, leading to significant geometric inaccuracy in SPIF. Double sided incremental forming (DSIF) uses two tools, one on each side of the sheet to form the sheet into the desired shape. This work explores the capabilities of DSIF in terms of improving the geometric accuracy as compared to SPIF by using a novel toolpath strategy in which the sheet is locally squeezed between the two tools. Experiments and simulations are performed to show that this strategy can improve the geometric accuracy of the component significantly by causing the deformation to be stabilized into a local region around the contact point of the forming tool. At the same time an examination of the forming forces indicates that after a certain amount of deformation by using this strategy a loss of contact occurs between the bottom tool and the sheet. The effects of this loss of contact of the bottom tool on the geometric accuracy and potential strategies, in order to avoid this loss of contact, are also discussed.

Hot deformation behavior of delta-processed superalloy 718

Abstract: Flow stress behavior and microstructures during hot compression of delta-processed superalloy 718 at temperatures from 950 to 1100 °C with strain rates of 10−3 to 1 s−1 were investigated by optical microscopy (OM), electron backscatter diffraction (EBSD) technique and transmission electron microscopy (TEM). The relationship between the peak stress and the deformation conditions can be expressed by a hyperbolic-sine type equation. The activation energy for the delta-processed superalloy 718 is determined to be 467 kJ/mol. The change of the dominant deformation mechanisms leads to the decrease of stress exponent and the increase of activation energy with increasing temperature. The dynamically recrystallized grain size is inversely proportional to the Zener–Hollomon (Z) parameter. It is found that the dissolution rate of δ phases under hot deformation conditions is much faster than that under static conditions. Dislocation, vacancy and curvature play important roles in the dissolution of δ phases. The main nucleation mechanisms of dynamic recrystallization (DRX) for the delta-processed superalloy 718 include the bulging of original grain boundaries and the δ phase stimulated DRX nucleation, which is closely related to the dissolution behavior of δ phases under certain deformation conditions.

The dynamic response of sandwich beams with open-cell metal foam cores

Abstract: The deformation and failure modes of dynamically loaded sandwich beams made of aluminum skins with open-cell aluminum foam cores were investigated experimentally. The dynamic compressive stress–strain curves of core materials, open-cell aluminum foam, were obtained using Split Hopkinson Pressure Bar. And then the dynamic impact tests were conducted for sandwich beams with open-cell aluminum foam cores. The photographs showing the deflected profiles of the dynamically loaded sandwich beams are exhibited. Several impact deformation modes of sandwich beams can be observed according to contrastive photographs, i.e. large inelastic deformation, face wrinkle and core shear with interfacial failure. A comparison of the measurements is made with analytical predictions, which indicates that the experimentally measured deflections agree well with predictions employing both the inscribing and circumscribing yield loci. For comparison, the quasi-static punching deformation and failure modes of sandwich beams is presented.

Fluid Effects in Polymers and Polymeric Composites

Abstract: 1. Introduction.- 2. Background to Polymers and Composites.- 3. Fluid Ingress Processes, Basic and Preliminaries.- 4. Fluid Sorption and Polymeric Material Data.-5. Diffusion Models.- 6. Hygrothermal Viscoelastic Response.- 7. Effects of Fluids on Strength, Deformation and Fatigue of Polymeric Composites.- 8. Sea Water Effects on Foam Cored Sandwich Structures.- 9. Special Issues.- 10.Summary and Conclusions.

Experimental determination of temperature threshold for melt surface deformation during laser interaction on iron at atmospheric pressure

Abstract: Recoil pressure is the principal driving force of molten metal in laser processing in the intensity range 10−1–102 MW cm−2. It is thus essential to estimate the recoil pressure in order to describe physical processes or to carry out numerical simulations. However, there exists no quantitative estimation of the recoil pressure near the boiling temperature (Tv), which is particularly important in the welding process. In this study we experimentally investigated the recoil pressure of pure iron around Tv. The main interest was to determine the threshold surface temperature to start deformation of melt surface. Using camera-based temperature measurement with accurate evaluation of emissivity from experiment, it was shown that the surface temperature has to reach Tv to initiate the melt surface deformation. This result provides the first experimental evidence for the frequently used assumption that a deep keyhole welding requires surface temperature over Tv. It is indicated also that, in normal gas-assisted laser cutting process, the recoil pressure hardly contributes to material ejection when the surface temperature is lower than Tv, as opposed to the commonly believed presumption.

On deformation twinning in a 17.5% Mn–TWIP steel: A physically based phenomenological model

Abstract: TWinning Induced Plasticity (TWIP) steel is a typical representative of the 2nd generation advanced high strength steels (AHSS) which exhibits a combination of high strength and excellent ductility due to the deformation twinning mechanisms. This paper discusses the principal features of deformation twinning in faced-centered cubic austenitic steels and shows how a physically based macroscopic model can be derived from microscopic-level considerations. In fact, a dislocation-based phenomenological model, with internal state variables including dislocation density and micro-twins volume fraction describing the microstructure evolution during deformation process, is proposed to model the deformation behavior of TWIP steels. The originality of this work lies in the incorporation of a physically based model on twin nucleation and volume fraction evolution in a conventional dislocation-based approach. Microstructural level experimental observations with scanning electron microscope (SEM) and transmission electron microscope (TEM) techniques together with the macroscopic quasi-static tensile test, for the TWIP steel Fe–17.5 wt.% Mn–1.4 wt.% Al–0.56 wt.% C, are used to validate and verify the modeling assumptions. The model could be regarded as a semi-phenomenological approach with sufficient links between microstructure and the overall mechanical properties, and therefore offers good predictive capabilities. Its simplicity also allows a modular implementation in finite element-based metal forming simulations.

Materials Science and Engineering A

Abstract: a b s t r a c t Instrumented sharp indentation experiments using both conical and Vickers diamond pyramidal indenters were carried out to study deformation characteristics of Zr55Cu30Al10Ni5 bulk metallic glass. Finite element simulations of instrumented indentation were also performed to formulate an overall constitutive response. Comparing the experimentally obtained results with the finite element predictions, it can be stated that mechanical deformation of the bulk metallic glass can be described well by both Mohr–Coulomb and Drucker–Prager constitutive criteria. Using these criteria, the extent of material pile-up observed around the indenter was also estimated very well.