Learning material law from displacement fields by artificial neural network

The recently developed data-driven approach can establish the material law for nonlinear elastic composite materials(especially newly developed materials)by the generated stress-strain data under different loading paths(Computational Mechanics,2019).Generally,the displacement(or strain)fields can be obtained relatively easier using digital image correlation(DIC)technique experimentally,but the stress field is hard to be measured.This situation limits the applicability of the proposed data-driven approach.In this paper,a method based on artificial neural network(ANN)to identify stress fields and further obtain the material law of nonlinear elastic materials is presented,which can make the proposed data-driven approach more practical.A numerical example is given to prove the validity of the method.The limitations of the proposed approach are also discussed.

MEASUREMENT OF WELDING DYNAMIC DISPLACEMENT FIELDS BY ELECTRONIC SPECKLE PATTERN INTERFERENCE

In order to effectively control the stress and distortion which produced in welding process, the dynamic change laws of displacement field is the most important factor. The characteristics of the welding dynamic displacement field is high temperature, high strain velocity, thus ordinary methods such as resistance strain gauge or Moiré method can not be used for the measurement of the zone of high temperature. Speckle interference method has the merits of non-contact, resistance to the disturbance of impure lights, high accuracy of measurement (half of wavelength).The paper represents the measurement of dynamic displacement field of argon-arcspot welding, by which it shows that the method of speckle interference is feasible for the measurement of welding dynamic displacement.

Data compression of displacement fields in digital image correlation by non-integer quantization

To solve the real-time transmission problem of displacement fields in digital image correlation,two compression coding algorithms based on a discrete cosine transform(DCT)and discrete wavelet transform(DWT)are proposed.Based on the Joint Photographic Experts Group(JPEG)and JPEG 2000 standards,new non-integer and integer quantizations are proposed in the quantization procedure of compression algorithms.Displacement fields from real experiments were used to evaluate the compression ratio and computational time of the algorithm.The results show that the compression ratios of the DCT-based algorithm are mostly below 10%,which are much less than that of the DWT-based algorithm,and the computational speed is also significantly higher than that of the latter.These findings prove the algorithm s effectiveness in real-time displacement field wireless transmission.

Effect of dynamic loading orientation on fracture properties of surrounding rocks in twin tunnels

For expedited transportation,vehicular tunnels are often designed as two adjacent tunnels,which frequently experience dynamic stress waves from various orientations during blasting excavation.To analyze the impact of dynamic loading orientation on the stability of the twin-tunnel,a split Hopkinson pressure bar(SHPB)apparatus was used to conduct a dynamic test on the twin-tunnel specimens.The two tunnels were rotated around the specimen’s center to consider the effect of dynamic loading orientation.LS-DYNA software was used for numerical simulation to reveal the failure properties and stress wave propagation law of the twin-tunnel specimens.The findings indicate that,for a twin-tunnel exposed to a dynamic load from different orientations,the crack initiation position appears most often at the tunnel corner,tunnel spandrel,and tunnel floor.As the impact direction is created by a certain angle(30°,45°,60°,120°,135°,and 150°),the fractures are produced in the middle of the line between the left tunnel corner and the right tunnel spandrel.As the impact loading angle(a)is 90°,the tunnel sustains minimal damage,and only tensile fractures form in the surrounding rocks.The orientation of the impact load could change the stress distribution in the twin-tunnel,and major fractures are more likely to form in areas where the tensile stress is concentrated.

On Scalar Planck Waves

The sound of space-time at the large scale is observed in the form of gravitational waves, which are disturbances in space-time produced by wavelike distortions (or kinks) in the gravitational field of an accelerating parcel or distribution of energy. In this study, we investigate a hypothetical wave mode of quantum space-time, which suggests the existence of scalar Planck waves. According to this hypothesis, the sound of quantum space-time corresponds to kinks propagating in the gravitational displacement field of an oscillating energy density. In evaluating the emission of scalar Planck waves and their effect on the geometry of space-time, one finds that they not only transport a vanishingly small amount of energy but can also be used to simulate gravity.

Determination of the full-field stress and displacement using photoelasticity and sampling moirémethod in a 3D-printed model

The quantitative characterization of the full-field stress and displacement is significant for analyzing the failure and instability of engineering materials.Various optical measurement techniques such as photoelasticity,moiréand digital image correlation methods have been developed to achieve this goal.However,these methods are difficult to incorporate to determine the stress and displacement fields simultaneously because the tested models must contain particles and grating for displacement measurement;however,these elements will disturb the light passing through the tested models using photoelasticity.In this study,by combining photoelasticity and the sampling moirémethod,we developed a method to determine the stress and displacement fields simultaneously in a three-dimensional(3D)-printed photoelastic model with orthogonal grating.Then,the full-field stress was determined by analyzing 10 photoelastic patterns,and the displacement fields were calculated using the sampling moirémethod.The results indicate that the developed method can simultaneously determine the stress and displacement fields.

Analysis of the Wenchuan Ms8.0 Earthquake's Co-seismic Stress and Displacement Change by Using the Finite Element Method

The variation of in situ stress before and after earthquakes is an issue studied by geologists. In this paper, on the basis of the fault slip dislocation model of Wenchuan Ms8.0 earthquake, the changes of co-seismic displacement and the distribution functions of stress tensor around the Longmen Shan fault zone are calculated. The results show that the co-seismic maximum surface displacement is 4.9 m in the horizontal direction and 6.5 m in the vertical direction, which is almost consistent with the on-site survey and GPS observations. The co-seismic maximum horizontal stress in the hanging wall and footwall decreased sharply as the distance from the Longmen Shan fault zone increased. However, the vertical stress and minimum horizontal stress increased in the footwall and in some areas of the hanging wall. The study of the co-seismic displacement and stress was mainly focused on the long and narrow region along the Longmen Shan fault zone, which coincides with the distribution of the earthquake aftershocks. Therefore, the co-seismic stress only affects the aftershocks, and does not affect distant faults and seismic activities. The results are almost consistent with in situ stress measurements at the two sites before and after Wenchuan Ms8.0 earthquake. Along the fault plane, the co-seismic shear stress in the dip direction is larger than that in the strike direction, which indicates that the faulting mechanism of the Longmen Shan fault zone is a dominant thrust with minor strike-slipping. The results can be used as a reference value for future studies of earthquake mechanisms.

3-D rheologic model of earthquake preparation (I)—Displacement field

Based on the three-dimensional ela stic inclusion model proposed by Dobrovolskii, we developed a three-dimensional rheologic inclusion model and theory to study the earthquake preparation process. By using correspondence principle in the theory of rheologic mechanics, we derived the analytic expression of the viscoelas-tic displacement at an arbitrary point (x, y, z) in three directions of x, y and z-axes (i. e., U(r, t), V*(r, t) and W(r, t)) produced by a three-dimension inclusion in the semi-infinite rheologic medium defined by the standard linear rheologic model.

Analyis on the indirect tension displacement and strain field of asphalt mixture based on ABAQUS and DICM

In order to study the damage mechanism of asphalt mixture,it is important to obtain the distribution of displacement and strain of its sample in the indirect tension mode.As a result,the digital image correlation method (DICM) was used to evaluate the displacement field and strain field of asphalt mixture.The results showed that the displacement fields under DICM and ABAQUS are similarly;the strain fields are different due to the different modulus of mastic and aggregate;and DICM is an practical method to study the indirect tension displacement and stain.

Lateral displacement of silty clay under cement-fly ash-gravel pile-supported embankments: Analytical consideration and field evidence

Based on back analysis of lateral displacements measured in situ by using the analytical solution, a useful method for estimating stress concentration ratio of geosynthetic-reinforced and pile-supported(GRPS) embankments was proposed. In order to validate the proposed method, a full-scale high-speed railway embankment(HSRE) with four instrumented subsections over medium compressibility silty clay was constructed in three stages. The soil profile, construction procedure and monitoring of settlements and lateral displacements of the four test sections were described. The field deformation analysis results show that 1) the combined reinforcement of CFG piles and geosynthetic layer perform well in terms of reducing lateral displacements; 2) the development of lateral displacements lags behind the increase of fill load, which can be attributed to the vertical load transfer mechanism of the pile foundation; and 3) pile length has a dominant effect on the stress distribution proportion between piles and surrounding soils. The comparison between predicted and experimental results suggests that the proposed analytical solution and the back analysis-based method are capable of reasonably estimating the lateral deformation and the stress concentration ratio, respectively, if the appropriate soil elastic modulus is chosen.

Study on displacement field generated by aftershocks in Landers earthquake fault zone and its adjacent areas

The displacement field generated by aftershocks in Landers earthquake fault zone and its adjacent areas is calculated in this study. The result is compared with the displacement field of the main shock calculated by co-seismic slip model of Wald and Heaton (1994). The result shows that the direction of displacement generated by aftershocks in Landers seismic fault plane and its adjacent areas is consistent with that generated by main shock. The rupture of aftershock is generally inherited from main shock. The displacement generated by aftershocks is up to an order of centimeter and can be measured by GPS sites nearby. So when we use geodetic data measured after earthquake to study the geophysical problems such as crustal viscosity structure, afterslip distribution, etc., only the displacement field generated by aftershocks considered, can uncertainty be reduced to minimum and realistic result be obtained.

Simulation of surface displacement and strain field of the 2011 Japan Mw9. 0 earthquake

Based on dislocation theory of 0kada, we adopted a finite-element fault model inverted by Gavin Hayes from seismic data for the 2011 Japan Mw9.0 earthquake, and obtained the corresponding surface displacement and strain fields. The calculated displacement field is consistent with the observed GPS results in the trend of changes. Also the surface displacement and strain fields both show large variations in space.

Investigation on displacement field characteristics of tunnel's surrounding rock and coal seam at FMTC face

The change rules of displacement field characteristics of coal seam and tunners surrounding rock were obtained by means of numerical simulation-FLAC^3D and site observation, and according to engineering geology and exploitation technology of 1151 （3） fully mechanized top coal caving （FMTC） face in Xieqiao colliery. The research＇s results show that the top coal displacement on the top of FMTC face is apparently larger than those of the middle and the bottom, the top coal begins to move in the front of the face＇s wall, and the sub-level top coal-rock moves ahead of the low-level top coal-rock, the vertical displacement of top coal-rock increases gradually as the decreasing of distance to face Top coal and overlying strata in vertical direction are always in compressed state in the front of face, then the top coal begins to separate from the overlying strata at the upside of face. The support loading at face is mainly the deformation pressure due to top coal and main roof＇s movement, and it is not suitable for the FMTC face with traditional support design. Surrounding rock movement of the face is of near-field effect, the surrounding rock deformation is acute greatly near to the face, the ideas of supporting design for the tailentry and headentry should be changed from loading control to deformation control.

THE APPLICATION OF MOIRE INTERFEROMETRY IN THE MEASUREMENT OF DISPLACEMENT FIELD AND STRAIN FIELD AT NOTCH-TIP AND CRACK-TIP

This paper presents the application of Moire interferometry in measuring the displacement and strain field at notch-tip and crack-tip before and after crack propagation.The experiment is carried out using a three point bending beam with a notch.The N_x and N_y fringe patterns representing displacement field,and the ΔN_x/Δx and ΔN_y/Δy fringe patterns representing the strain field are obtained.The sensitivity of the meas- ured displacement is 0.417μm per fringe order.The displacement and strain distribution along the section x=0 have been worked out according to N_x and N_y fringe patterns.

Processes of the displacement field change of the 2009 April 6 M_W6.3 L'Aquila earthquake using persistent scatterer and small baseline methods

Using a time series method that combines both the persistent scatterer and small baseline approaches, we analyzed 9 scenes Envisat ASAR data over the L＇Aquila earthquake, and obtained a Shocke＇s displacement field and its evolution processes. The results show that： （1） Envisat ASAR clearly detected the whole processes of displacement field of the L＇Aquila earthquake, and distinct variations at different stages of the displacement field. （2） Preseismic creep displacement → displacement mutation when faulting → constantly slowed down after the earthquake. （3） The area of the strongest deformation and ground rupture was a low-lying oval depression region to the southeast. Surface faulting within a zone of about 22 km× 14 km, with an orientation of 135°, occurred along the NW-striking and SW-dipping Paganica-S. Demetrio normal fault. （4） In analyzing an area of about 54 km x 59 km, bounded by north-south axis to the epicenter, the displacement field has significant characteristics of a watershed： westward of the epicenter shows uplift with maximum of 130 mm in line-of-sight （LOS）, and east of the epicenter was a region with 220 mm of maximum subsidence in the LOS, concentrating on the rupture zone, the majority of which formed in the course of faulting and subsequence.

Unloading damage patterns of rock slopes in open pit mines and analyses of their mechanisms

The stability of slopes is essential for ensuring safe production in open-pit mines.Analyzing and managing the deformation and failure of the slope rock mass becomes more challenging as the slope height increases.To investigate the damage patterns of slopes with varying heights,three slope models were developed based on a rock slope in Dagushan,China.The deformation failure processes of slopes under the influence of excavation and unloading were analyzed using the base friction test method in combination with digital image technology contrasting.The results supported the following findings:(1)Unloading tensile stress caused lateral partitioning in the slope.Both the foot and top of the slope underwent initial tensile cracks.(2)The destabilization mechanism of unloading deformation in slopes of different heights involved a combination of traction at the foot of the slope or pushing at the top of the slope,followed by accelerated deformation,deceleration creep,and overall destabilization.(3)The unloading damage patterns of slopes at different heights were summarized as follows:compression tension cracking,traction,and slip damage for medium and low slopes;compression tension cracking,traction,and slip failure for the upper part of high slopes;and relaxation tension cracking,pushing,traction,and slip failure for the lower part.Moreover,the upper part of ultra-high slopes exhibited compression tension cracking,traction,and slip failure,while the middle and lower parts displayed relaxation tension cracking,pushing,traction,and slip patterns.Finally,numerical simulations were conducted to verify the results of the test analyses,which demonstrated good consistency.These research results were of great engineering value for proposing effective safety management measures for high slopes.

Determination of wax pattern die profile for investment casting of turbine blades

In order to conform to dimensional tolerances, an efficient numerical method, displacement iterative compensation method, based on finite element methodology （FEM） was presented for the wax pattern die profile design of turbine blades. Casting shrinkages at different positions of the blade which was considered nonlinear thermo-mechanical casting deformations were calculated. Based on the displacement iterative compensation method proposed, the optimized wax pattern die profile can be established. For a A356 alloy blade, substantial reduction in dimensional and shape tolerances was achieved with the developed die shape optimization system. Numerical simulation result obtained by the proposed method shows a good agreement with the result measured experimentally. After four times iterations, compared with the CAD model of turbine blade, the total form error decreases to 0.001 978 mm from the orevious 0.515 815 mm.

Apparently Negative Electric Polarization in Shaped Graded Dielectric Materials

By using a first-principles approach, we investigate the pathway of electric displacement fields in shaped graded dielectric materials existing in the form of cloaks with various shapes. We reveal a type of apparently negative electric polarization （ANEP）, which is due to a symmetric oscillation of the paired electric permittivities, satisfying a sum rule. The ANEP does not occur for a spherical cloak, but appears up to maximum as a/b （the ratio between the long and short principal axis of the spheroidal cloak） is about 5/2, and eventually disappears as a/b becomes large enough corresponding to a rod-like shape. Further, the cloaking efficiency is calculated for different geometrical shapes and demonstrated to closely relate to the ANEP. The possibility of experiments is discussed. This work has relevance to dielectric shielding based on shaped graded dielectric materials.

Geometrical Moir Methodand Its Application

A geometrical moir method for displaying directly isochromatics and isoclinics of a diametrically pressed circular disk is presented. It is demonstrated that by using two identical or different Wulff nets (or grids) not only the stress fields of a circular disk can be displayed, but the u -and v -displacement fields can also be produced.

Numerical simulation of Dabie orogenicbelt's tectonic evolution

The influence of hot mantle intrusive body on tectonic stress field and displacement field of Dabie orogenic belthave been analyzed by means of finite element method. Numerical simulations show that the intrusion of hot mantle material leads to an extensional stress state in the upper crust of central Da bie mountains, while compressivestress state appears on both sides of orogenic belt under the action of horizontal compression from Yang tze craton.This is in accordance with the actual faulting tectonics in this area. Possible evolution trend in transition area isdiscussed, too.