Discovering Crustal Deformation Bands by Processing Regional Gravity Field

Objectives： This article presents a new computational procedure to discover scratches buried in the earth＇s crust. We also validate this new interdisciplinary analysis method with regional gravity data located in a well-known Dabie orogenic zone for test. Methods： Based on the scratch analysis method evolved with mathematical morphology of surfaces, we present a procedure that extracts information of the crustal scratches from regional gravity data. Because the crustal scratches are positively and highly correlated to crustal deformation bands, it can be used for delineation of the crustal deformation belts. The scratches can be quantitatively characterized by calculation of the ridge coefficient function, whose high value traces delineate the deformation bands hidden in the regional gravity field. In addition, because the degree of crustal deformation is an important indicator of tectonic unit divisions, so the crust can be further divided according to the degree of crustal deformation into some tectonic units by using the ridge coefficient data, providing an objective base map for earth scientists to build tectonic models with quantitative evidence. Results： After the ridge coefficients are calculated, we can further enhance the boundary of high ridge-coefficient blocks, resulting in the so-called ridge-edge coefficient function. The high-value ridge-edge coefficients are well correlated with the edge faults of tectonic units underlay, providing accurate positioning of the base map for compilation of regional tectonic maps. In order to validate this new interdisciplinary analysis method, we select the Dabie orogenic zone as a pilot area for test, where rock outcrops are well exposed on the surface and detailed geological and geophysical surveys have been carried out. Tests show that the deformation bands and the tectonic units, which are conformed by tectonic scientists based on surface observations, are clearly displayed on the ridge and ridge-edge coefficient images obtained in this article. Moreover, these computer-generated images provide more accurate locations and geometric details. Conclusions： This work demonstrates that application of modern mathematical tools can promote the quantitative degree in research of modern geosciences, helping to open a door to develop a new branch of mathematical tectonics.

Deformation banding in β working of two-phase TA15 titanium alloy

To study deformation banding inβworking of TA15titanium alloy,hot simulation compression experiments were carried out on a Gleeble3500thermal simulator,and the microstructure was investigated by optical microscopy(OM)and electron backscattered diffraction(EBSD).It is found that inβworking of TA15titanium alloy,deformation banding is still an important grain refinement mechanism up to temperature as high as0.7Tm(Tm is the melting temperature).Boundaries of deformation bands(DBBs)may be sharp or diffusive.Sharp DBBs retard discontinuous dynamic recrystallization(DDRX)by prohibiting nucleation,while the diffusive ones are sources of continuous dynamic recrystallization(CDRX).Deformation banding is more significant at high strain rate and large initial grain size.The average width of grain subdivisions is sensitive to strain rate but less affected by temperature and initial grain size.Multi-directional forging which produces crossing DDBs is potential to refine microstructure of small-size forgings.

TEM OBSERVATION OF LOCAL DEFORMATION BAND AT CRACK TIP

The thin foil specimen of a ferrite-austenite duplex stainless steel was tensiled under transmis- sion electron microscope(TEM).It was found that both in ferrite and austenite the local deformation band at crack tip was formed near to the crack propagating direction.Its forma- tion was related with the crack tip Schmid factor,dislocation shielding,latent hardening and hardening coefficient.When the crack tip emitted dislocations to a slip system by the action of pure mode Ⅱ stress resolute,and the decreasing rate of hardening coefficient was suitable,lo- cal deformation band was easy to form.

DEFORMATION LOCALIZATION AND SHEAR BAND FRACTURE IN STRONG ANISOTROPY SHEET TENSION

The tensile deformation localization and the shear band fracture behaviors of sheet metals with strong anisotropy are numerically simulated by using Updating Lagrange finite element method, Quasi-how plastic constitutive theory([1]) and B-L planar anisotropy yield criterion([2]). Simulated results are compared with experimental ones. Very good consistence is obtained between numerical and experimental results. The relationship between the anisotropy coefficient R and the shear band angle theta is found.

Kink-band formation in directionally solidified Mg/Mg_(2)Yb and Mg/Mg_(2)Ca eutectic alloys with Mg/Laves-phase lamellar microstructure

For the development of high-strength Mg alloys,active use of Laves phases such as C14-type Mg_(2)Yb and Mg_(2)Ca is strongly expected.However,the brittleness of the Laves phases is the biggest obstacle to it.We first found that kink-band formation can be induced in directionally solidified Mg/Mg_(2)Yb and Mg/Mg_(2)Ca eutectic lamellar alloys when a stress is applied parallel to the lamellar interface,leading to a high yield stress accompanied with ductility.That is,microstructural control can induce a new deformation mode that is not activated in the constituent phases,thereby inducing ductility.It was clarified that the geometric relationship between the operative slip plane in the constituent phases and the lamellar interface,and the microstructural features that provide kink-band nucleation sites are important factors for controlling kink-band formation.The obtained results show a possibility to open the new door for the development of novel high-strength structural material using the kink bands.

The MT inversion for conductivity anisotropy and EDA precursor，stress field and deformationbandintheEarthsdeepcrust

The conductivity anisotropy behaviour is described for certain environment in the Earths crust and the MT inversion method for a layered symmetrically anisotropic model is presented. The inversion interpretations of the anisotropic model from the observational data are helpful to identify the earthquake precusors as indicated by the deep conductivity anisotropic variations, and also provide some useful information to investigate the stress states and deformation bands in the deep crust of the Earth.

Sand Textural Control on Shear-Enhanced Compaction Band Development in Poorly-Lithified Sandstone

Sand textural control on SECB （shear-enhanced compaction band） formation is analyzed combining field observations, detailed material characterization and mechanical testing for poorly lithified sandstone units in Provence （France）. Field observations show that SECBs are densely distributed in a coarse-grained unit with moderate porosity （27%）, whereas few SECBs are developed within the overlying fine-grained, high-porosity （39%） unit. Results from textural characterization show that the main difference between the two sand units is grain size and sorting, whereas they are similar with respect to composition and grain angularity. Packing density is introduced as an important parameter for comparing the compaction properties independent of the textural variations between the two units. Compaction experiments show a slightly faster compaction of the coarse-grained sand as compared to the fine-grained sand, and more pronounced grain crushing is observed in the coarse-grained unit. The results indicate that the preferential localization of SECBs to the coarse-grained unit is controlled by a slightly denser packing of the coarse-grained material at the time of band formation together with higher stress concentrations on grain contacts. Hence, this study emphasizes that porosity alone is an insufficient parameter for predicting deformation band evolution in sand （stone）.

Influence of external constraint and rolling geometry on deformation banding of copper single crystals with {123}<634> orientation

In order to further understand the similarity and difference betweendeformation mechanisms of single crystals and poly-crystalline materials, the influence of externalconstraint and rolling geometry on the deformation behaviour of copper single crystals with{123}<634> orientation was investigated by embedding them into metal frames of different strengths.The metal frames were made of aluminum and mild steel, respectively. The results show that thedeformation banding degree of the crystal increases with the strength of metal frame and shearstrain. For the crystals rolled under lower (gamma)g ((gamma)g is the ratio of the geometricalredundant shear strain to the normal rolling strain), the deformation is homogeneous. For thecrystals rolled under higher (gamma)g, the deformation is extremely inhomogeneous. The deformationis more homogeneous in the crystals rolled in steel frames than that rolled in aluminum frames. TheS-orientation is more stable in the crystals rolled under lower (gamma)g than that rolled underhigher (gamma)g.

Enhanced creep resistance in Mg-Y-Nd alloy via regulating prior thermo-mechanical treatment

In this study,the tensile creep behavior of a hot-rolled Mg-4Y-3.5Nd alloy subjected to different prior thermo-mechanical treatments was investigated at 220℃.Five groups of samples were prepared using different combinations of the solid solution(S),aging treatment at 220℃ for 30 h(A),and hot compression at 490℃ to a true strain of 0.25(C).The abbreviations for the samples are S,SA,SC,SAC,and SCA.Upon examining the yield strength and creep resistance,it was found that creep resistance could not be directly predicted by the yield strength.The stability of the deformation bands(DBs)induced by prior thermo-mechanical treatment plays an important role in determining the creep resistance.The dislocation of the DBs and demonstrated the best creep resistance in the SAC sample,which were prepared using a solid solution,aging treatment,and subsequent hot compression.However,despite the highest yield strength,frequent dislocation motions destroyed the stability of the DBs and deteriorated the creep resistance of the SCA sample,which were prepared using a solid solution,hot compression,and subsequent aging treatment.Among the thermo-mechanical treatments used in this study,the application of aging treatment was important to obtain the resultant creep resistance.When the aging treatment was performed prior to hot compression,the creep resistance could be further enhanced based only on hot compression.Accordingly,the sequence from the strongest to the weakest creep resistance was SAC>SC>S>SCA>SA.

Microstructure of asymmetric twin-roll cast AZ31 magnesium alloy

The microstructural distribution along thickness of asymmetric twin-roll cast AZ31 magnesium alloy slab was investigated. It was found that the microstructure along the thickness of the slab was significantly inhomogeneous. There were many deformed bands with flow form near the upper surface of twin-roll cast plate. Very few deformed bands could be seen in the central part of the plate where the dendrites were thick. Fine dendritic structures dominated near the lower surface of the twin-roll cast strip. It is concluded that the shear strain caused by linear velocity difference between surfaces of upper and lower rolls results in the deformed bands of the twin-roll cast slab. Aluminum, zinc and manganese segregate to the boundary of dendrites, while silicon distributes inside the α-Mg solid solution.

Microstructure evolution of Al-Cu-Mg alloy during rapid cold punching and recrystallization annealing

The microstructure evolution of spray formed and rapidly solidified Al-Cu-Mg alloy with fine grains during rapid cold punching and recrystallization annealing was investigated by transmission electron microscopy(TEM). The results show that the precipitates of fine-grained Al-Cu-Mg alloy during rapid cold punching and recrystallization annealing mainly consist of S phase and a small amount of coarse Al6Mn phase. With the increase of deformation passes, the density of precipitates increases, the size of precipitates decreases significantly, and the deformation and transition bands disappear gradually. In addition, the grains are refined and tend to be uniform. Defects introduced by rapid cold punching contribute to the precipitation and recrystallization, and promote nucleation and growth of S phase and recrystallization. Deformation and transition bands in the coarse grains transform into deformation-induced grain boundary during the deformation and recrystallization, which refine grains, obtain uniform nanocrystalline structure and promote homogeneous distribution of S phase.

High temperature tribological behaviors of aluminum matrix composites reinforced with solid lubricant particles

The AA6061-10 wt.%B4 C mono composite, AA6061-10 wt.%B4 C-Gr(Gr: graphite) hybrid composites containing 2.5, 5, and 7.5 wt.% Gr particles, and AA6061-10 wt.%B4 C-Mo S2 hybrid composites containing 2.5, 5, and 7.5 wt.% Mo S2 particles were fabricated through stir casting. The dry sliding tribological behaviors of the mono composite and hybrid composites were studied as a function of temperature on high temperature pin-on-disc tribotester against EN 31 counterface. The wear rate and friction coefficient of the Gr-reinforced and Mo S2-reinforced hybrid composites decreased in the temperature range of 30-100 ℃ due to the combined lubrication offered by the wear protective layer and its solid lubricant phase. Scanning electron microscopy(SEM) observation of the worn pin surface revealed severe adhesion, delamination, and abrasion wear mechanisms at temperatures of 150, 200, and 250 ℃, respectively. At 150 ℃, transmission electron microscopy(TEM) observation of the hybrid composites revealed the formation of deformation bands due to severe plastic deformation and fine crystalline structure due to dynamic recrystallization.

Numerical Simulation of the Elastic Shrinkage Induced by Portevin-Le Chatelier Effect

A new one-dimensional phenomenological model based on the dynamic strain aging mechanism is developed. In order to account for the elastic shrinkage induced by the Portevin-Le Chatelier effect, elastic deformation is considered under the boundary conditions of the present model. The simulated results are found to be in good agreement with the experimental observations.

Constitutive equations and finite element implementation of strain localization in sand deformation

A recently proposed model coupling with the solid-fluid of the saturated sand was utilized to study the deformation band. Based on the critical state plasticity model by Borja and Andrade, the hydraulic conductivity tensor was naturally treated as a function of the spatial discretization matrix about the displacement and the stress field, allowing a more realistic representation of the physical phenomenon. The fully Lagrangian form of the Darcy law was resolved by Piola algorithm, and then the flow law was gained, leading to the implementation of a modified model of the saturated sand. Then the criterion for the onset of localization was derived and utilized to detect instability. The constitutive model was implemented in a finite element program coded by FORTRAN, which was used to predict the formation and development of shear bands in plane strain compression of saturated sand. At last, the formation mechanism of the shear band was discussed. It is shown that the model works well, and the simulation sample bifurcates at 1.18% axial strain, which is in a good qualitative agreement with the experiment. The pore pressure greatly affects the onset and development of the deformation band, and it obviously increases around the localization-prone regions with the direction toward the outer side of the normal of the shear band, while the pore stress flows nearly horizontally and is distributed equally far away the shear band region.

Some Observations of Flow Localization and Shear Cracking in Pearlite during Deformation

Flow localization, which is an importantmode of deformation in engineering materi-als, has been the interesting subject ofa number of experimental observationsand theoretical investigations in recentyears. However, the basic mechanism ofthe phenomena is not well understood atpresent. In a tensile test, the initiationand growth of a shear band are often simul-taneous. Therefore, it is rather difficult

Deformation bands in fully pearlitic steel during wire drawing

The deformation of fully pearlitic steels during wire drawing has been investigated for botb longitudinal section and transverse section by back-scattered electron imaging （BSEI）, electron back-scattered diffraction （EBSD）, and transmission electron mi- croscope （TEM）. The results show that a large number of deformation bands （DBs） composed of a mixture of kink-like bands and shear-like bands were observed both in the longitudinal section and the traverse section of the drawn wires. The formation of such bands involves two aspects： heterogeneous deformation in the scale of pearlite colonies and instability of fer- rite-cementite interfaces due to stress concentration during wire drawing. The development of suck bands in fully pearlitic steels dominates the formation of metallograpbic texture, reduces the pearlite interlamellar spacing and promotes the development of 〈 110〉 fiber crystalline texture of ferrite matrix during wire drawing.

Chiral geometry in multiple chiral doublet bands

The chiral geometry of multiple chiral doublet bands with identical configuration is discussed for different triaxial deformation parameters γ in the particle rotor model with πh11/2×γh11/2^-1.The energy spectra,electromagnetic transition probabilities B（M1） and B（E2）,angular momenta,and K-distributions are studied.It is demonstrated that the chirality still remains not only in the yrast and yrare bands,but also in the two higher excited bands whenγ deviates from 30°.The chiral geometry relies significantly on γ,and the chiral geometry of the two higher excited partner bands is not as good as that of the yrast and yrare doublet bands.

Multiple ballistic impacts on 2024-T4 aluminum alloy by spheres:Experiments and modelling

Multiple ballistic impacts are carried out on a 2024-T4 aluminum alloy by spherical steel projectiles(5-mm diameter)at~400 m s^(-1),to investigate its dynamic deformation and damage.The ballistic impact process is captured with high-speed photography.Postmortem samples are characterized with optical imaging,three-dimensional laser scanning,microhardness testing and electron backscatter diffraction.With increasing number of impacts,crater diameter increases slightly,but crater depth and crater volume increase significantly,and strain accumulation leads to microhardness increase overall.Crater parameters all follow power-law relations with the number of impacts.Twin-like deformation bands and macroscopic deformation twins are produced by impact as a result of spontaneous dislocation self-pinning under high strain rate,large shear deformation.Under multiple impacts,shear strain accumulation in the arc-shaped region of the crater induces deformation twinning when it exceeds a critical value(~1.1-1.6).It is highly possible that the deformation twins are related to deformation bands,since they both share one set of the{111}pole with the initial matrix grain.A finite element method model is optimized to reproduce experimental observations and interpret deformation mechanisms.

In-situ Tension of Dendrite-Reinforced Zr-based Metallic-GlassMatrix Composites

The evolution of shear bands in the glassy matrix composites was observed and analyzed during in-situ tension.Based on the simple calculation,the temperature rise within the shear bands is sufficient to cause the formation of viscous shearing layer,resulting in the early failure.Zr-based metallic-glass-matrix composites（labeled as DH1 and DH2） exhibit improved tensile ductility rather than brittle failure,since the existence of secondary ductile dendrites promotes the impedance of prompt propagation of shear bands,evidenced by the multiplication of shear bands.