Residual Stress Measurement for Ion-implanted NiTi Alloy by Using Moiré Interferometry and Hole-drilling Combined Method

Residual stresses in ion-implanted NiTi alloy are measured by a combined method ofMoir6 interferometry and hole-drilling. Oxygen ions are implanted into the NiTi alloy under a voltage of 30 kV by a dose of 1.0×10^17ions/cm^2 for one hour. Subsequently, in order to avoid dimensional error, a hole is drilled exactly in the center of the sample. The distribution of residual stresses around the hole is measured. It is indicated that the method which combines the Moire interferometry with hole-drilling is able to be used to measure residual stresses produced by ion implantation.

Moiré superlattices arising from growth induced by screw dislocations in layered materials

Moiré superlattices(MSLs) are modulated structures produced from homogeneous or heterogeneous two-dimensional layers stacked with a twist angle and/or lattice mismatch. Enriching the methods for fabricating MSL and realizing the unique emergent properties are key challenges in its investigation. Here we recommend that the spiral dislocation driven growth is another optional method for the preparation of high quality MSL samples. The spiral structure stabilizes the constant out-of-plane lattice distance, causing the variations in electronic and optical properties. Taking SnS_(2) MSL as an example, we find prominent properties including large band gap reduction(~ 0.4 e V) and enhanced optical activity. Firstprinciples calculations reveal that these unusual properties can be ascribed to the locally enhanced interlayer interaction associated with the Moiré potential modulation. We believe that the spiral dislocation driven growth would be a powerful method to expand the MSL family and broaden their scope of application.

Nonlinear time-reversal interferometry with arbitrary quadratic collective-spin interaction

Atomic nonlinear interferometry has wide applications in quantum metrology and quantum information science.Here we propose a nonlinear time-reversal interferometry scheme with high robustness and metrological gain based on the spin squeezing generated by arbitrary quadratic collective-spin interaction,which could be described by the Lipkin–Meshkov–Glick(LMG)model.We optimize the squeezing process,encoding process,and anti-squeezing process,finding that the two particular cases of the LMG model,one-axis twisting and two-axis twisting outperform in robustness and precision,respectively.Moreover,we propose a Floquet driving method to realize equivalent time reverse in the atomic system,which leads to high performance in precision,robustness,and operability.Our study sets a benchmark for achieving high precision and high robustness in atomic nonlinear interferometry.

Peak structure in the interlayer conductance of Moirésuperlattices

We investigate the peak structure in the interlayer conductance of Moirésuperlattices using a tunneling theory wedeveloped previously.The theoretical results predict that,due to the resonance of two different partial waves,the doublepeakstructure can appear in the curve of the interlayer conductance versus twist angle.Furthermore,we study the influencesof the model parameters,i.e.,the chemical potential of electrodes,the thickness of Moirésuperlattice,and the strength ofinterface potential,on the peak structure of the interlayer conductance.In particular,the parameter dependence of the peakstructure is concluded via a phase diagram,and the physical meanings of the phase diagram is formulized.Finally,thepotential applications of the present work is discussed.

Theory and verification of moiréfringes for x-ray three-phase grating interferometer

Dual-phase and three-phase grating x-ray interference is a promising new technique for grating-based x-ray differential phase contrast imaging.Dual-phase grating interferometers have been relatively completely studied and discussed.In this paper,the corresponding imaging fringe formula of the three-phase grating interferometer is provided.At the same time,the similarities and differences between the three-phase grating interferometer and the dual-phase grating interferometer are investigated and verified,and that the three-phase grating interferometer can produce large-period moiréfringes without using the analyzing grating is demonstrated experimentally.Finally,a simple method of designing three-phase grating and multi-grating imaging systems from geometric optics based on the thin-lens theory of gratings is presented.These theoretical formulas and experimental results provide optimization tools for designing three-phase grating interferometer systems.

Study on the application of optical interferometry in the measurement of the coating thickness of color-coated plates

The principle and application of optical interferometry to measure the coating thickness of color-coated plates were introduced in this paper.Additionally,several factors affecting the test results,including coating refractive index,wavelength range,and film thickness range setting,were analyzed.Among these,the refractive index of the color coating,which cannot be measured directly,was identified as the key factor.A solution to this problem was proposed.Finally,the optical interference method and the current detection methods,including the micrometer method and the magnetic eddy current method,were analyzed and compared.The results show that optical interferometry has better repeatability and reproducibility than the current methods and show no significant difference from the current methods through statistical tests.Therefore,the method can be applied to the detection of the coating thickness of color-coated plates.

Study of the location of testing area in residual stress measurement by Moiré interferometry combined with hole-drilling method

This paper investigates the effect of the location of testing area in residual stress measurement by Moiréinterferometry combined with hole-drilling method.The selection of the location of the testing area is analyzed from theory and experiment.In the theoretical study,the factors which affect the surface released radial strainεr were analyzed on the basis of the formulae of the hole-drilling method,and the relations between those factors andεr were established.By combining Moiréinterferometry with the hole-drilling method,the residual stress of interference-fit specimen was measured to verify the theoretical analysis.According to the analysis results,the testing area for minimizing the error of strain measurement is determined.Moreover,if the orientation of the maximum principal stress is known,the value of strain will be measured with higher precision by the Moiréinterferometry method.

APPLICATION OF 2-D MOIRE INTERFEROMETRYOF STICKING FILM IN HUMAN TIBIA MEASUREMENT

This paper makes use of the method of testing and measuring the human body tibia by using2-D moire interferometry of sticking film. hased on the J'--y direction moire patterns recorded synchronously by 2-D optical path,the elastic constant,strain and displacement of the tibia are measured.Compared with the electric measuring method the error is samll and the sensitivity is high.

EXPERIMENTAL STUDIES ON J-DOMINANCE IN HETEROGENEOUS WELDED JOINTS BY MOIRE INTERFEROMETRY

Moire interferometry method is introduced to study the feasibilities of J integral as a plastic singularity parameter at the tip of the notch in the welded joints. The results show that J dominance in most studied cases is not validated in v and u displacement fields. Therefore, it can be concluded that J-integral as controlling parameter used to estimate the safety of welded structures is not always valid.

Hole-drilling method using grating rosette and Moire interferometry

The hole-drilling method is one of the most wellknown methods for measuring residual stresses. To identify unknown plane stresses in a specimen, a circular hole is first drilled in the infinite plate under plane stress, then the strains resulting from the hole drilling is measured. The strains may be acquired from interpreting the Moire signature around the hole. In crossed grating Moire interferometry, the horizontal and vertical displacement fields （u and v） can be obtained to determinate two strain fields and one shearing strain field. In this paper, by means of Moire interferometry and three directions grating （grating rosette） developed by the authors, three displacement fields （u, v and s） are obtained to acquire three strain fields. As a practical application, the hole-drilling method is adopted to measure the relief strains for aluminum and fiber reinforced composite. It is a step by step method; in each step a single laminate or equivalent depth is drilled to find some relationships between the drilling depth and the residual strains relieved in the fiber reinforced composite materials.

STUDY ON FRACTURE BEHAVIOR OF FERROELECTRIC CERAMICS UNDER COMBINED ELECTROMECHANICAL LOADING BY USING A MOIR(?) INTERFEROMETRY TECHNIQUE

This paper discusses an in situ observation of fracture behavior around a crack tip in ferroelectric ceramics under combined electromechanical loading by use of a moiré interferometry technique.The deformation field induced by the electric field and the stress concentration near the crack tip in three-points bending experiments was measured.By analysis of the moiré images it is found that under a constant mechanical load,the electric field almost has no effect on the crack extension in the case that the directions of the poling,electric field and crack extension are perpendicular to each other.When the poling direction is parallel to the crack extension direction and perpendicular to the electric field,the strain decreases faster than that calculated by FEM with and without electrical loading as one goes away from the crack tip.In addition,as the electric field intensity increases,the strain near the crack tip increases,and the strain concentration becomes more significant.

Carrier fringe method of moire interferometry for tiny strain measurements in micro-field

In this paper, we demonstrate a new optical method for tiny strain measurements based on the principle of carrier fringes of moire interferometry. A cross-line grating with frequency of 1200 lp/mm is replicated on the specimen surface, and the strain can be deduced from the changes in carrier fringes before and after the deformation of an object. Four coherent laser beams are used to obtain the carrier fringe patterns of field U and V. Both theoretical analysis and numerical simulation indicate that the ideal accuracy of strain can be controlled within a range of ±1με. Case study of a plane extension experiment shows that the measurement accuracy of strain can be controlled within the range of ±10με. The average strain values of every row of field U and every column of field V can be obtained by using this method, and approximated strain of every pixel in the whole-field can be further acquired, and thus it is possible to measure tiny strains occurred in a micro-field. The technology in this paper can provide comprehensive information for analyzing related mechanical content in the field of MEMS.

HIGH TEMPERATURE MOIRE INTERFEROMETRY TECHNOLOGY

In order to investigate the survivable specimen gratings, the crossed-line300 lines/mm gratings were chemically etched directly into the surface of the specimens.In order to obtain high diffraction efficiency and to minimize the shear lag, the etcheddepth of the gratings was one fourth the wave length of coherent light. The influence ofthe uneven window on the high temperature moire interferometry was preliminarily analyzed. The quartz and inconel 718 specimens were tested up to 1200℃ and 900℃. Thecrack tip deformation singular field as well as load-induced and thermal expansion displacement fields were measured by means of high temperature moire interferometry.

Separation of contact stress components by moire interferometry

A hybrid technique of combining moire measurement and analytical solution is developed to separate the normal and the tangential components of distributed contact stresses between two co-plane bodies. The moire interfe-rometry offers the displacement fields near the deformed contact zone, from which the tangential strains and boundary slopes of the deformed configurations can be evaluated. Those experimental results provide boundary conditions for the discrete integration of Flamant＇s solutions, to inversely compute the separated components of the contact stresses.

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.

MEASURING DISPLACEMENT FIELDS OF CURVED SURFACE BY MOIRE INTERFEROMETRY OF PARTIAL COHERENT LIGHT

This paper presents a method to measure the in-plane displacement fields of curved surface by moire interferometry of partial coherent light.The method has the following advantages:simple optical system,no requirement on vibration isolation,high sensitivity,large measuring range,high contrast of inter ference fringes and availability to in-situ structural testing.The present paper also gives theoretical analysis of the method and the formulas of light intensity and displacement field,and introduces a replication technique to form a high frequency reflectance grating on the curved surface.The experiments achieved the measurement of the surface displacement field of a cylindrical shell—the simultaneous circumferential,axial and 45° displacement fields.The torsional test data for surface displacement of a circular bar agree well with the theoretical result.

STUDY OF TRANSFORMATION PLASTICITY IN TETRAGONAL ZIRCONIA POLYCRYSTALS BY MOIRE INTERFEROMETRY

Transformation plasticity in ceria-stabilized tetragonal zirconia poly- crystals due to the stress-induced tetragonal-to-monoclinic martensitic transforma- tion under tension and bending is studied by moire interferometry. The whole fringe patterns including u fields and v fields are acquired. According to these patterns, the distributions of transformation plasticity in transformation zones are obtained, and the phenomenon of plastic flow localization for transformation is revealed. The above work provides a significant experimental foundation for establishing transformation constitutive relations

Achieving 1.2 fm/Hz^(1/2)Displacement Sensitivity with Laser Interferometry in Two-Dimensional Nanomechanical Resonators:Pathways towards Quantum-Noise-Limited Measurement at Room Temperature

Laser interferometry is an important technique for ultrasensitive detection of motion and displacement.We push the limit of laser interferometry through noise optimization and device engineering.The contribution of noises other than shot noise is reduced from 92.6%to 62.4%,demonstrating the possibility towards shotnoise-limited measurement.Using noise thermometry,we quantify the laser heating effect and determine the range of laser power values for room-temperature measurements.With detailed analysis and optimization of signal transduction,we achieve 1.2 fm/Hz^(1/2)displacement measurement sensitivity at room temperature in twodimensional(2D)Ca Nb_(2)O_(6)nanomechanical resonators,the best value reported to date among all resonators based on 2D materials.Our work demonstrates a possible pathway towards quantum-noise-limited measurement at room temperature.

Review of phonons in moiré superlattices

Moirépatterns in physics are interference fringes produced when a periodic template is stacked on another similar one with different displacement and twist angles.The phonon in two-dimensional(2D)material affected by moirépatterns in the lattice shows various novel physical phenomena,such as frequency shift,different linewidth,and mediation to the superconductivity.This review gives a brief overview of phonons in 2D moirésuperlattice.First,we introduce the theory of the moiréphonon modes based on a continuum approach using the elastic theory and discuss the effect of the moirépattern on phonons in 2D materials such as graphene and MoS_(2).Then,we discuss the electron-phonon coupling(EPC)modulated by moirépatterns,which can be detected by the spectroscopy methods.Furthermore,the phonon-mediated unconventional superconductivity in 2D moirésuperlattice is introduced.The theory of phonon-mediated superconductivity in moirésuperlattice sets up a general framework,which promises to predict the response of superconductivity to various perturbations,such as disorder,magnetic field,and electric displacement field.

MoiréDirac fermions in transition metal dichalcogenides heterobilayers

Monolayer group-VIB transition metal dichalcogenides(TMDs)feature low-energy massive Dirac fermions,which have valley contrasting Berry curvature.This nontrivial local band topology gives rise to valley Hall transport and optical selection rules for interband transitions that open up new possibilities for valleytronics.However,the large bandgap in TMDs results in relatively small Berry curvature,leading to weak valley contrasting physics in practical experiments.Here,we show that Dirac fermions with tunable large Berry curvature can be engineered in moirésuperlattice of TMD heterobilayers.These moiréDirac fermions are created in a magnified honeycomb lattice with its sublattice degree of freedom formed by two local moirépotential minima.We show that applying an on-site potential can tune the moiréflat bands into helical ones.In short-period moirésuperlattice,we find that the two moirévalleys become asymmetric,which results in a net spin Hall current.More interestingly,a circularly polarized light drives these moiréDirac fermions into quantum anomalous Hall phase with chiral edge states.Our results open a new possibility to design the moiré-scale spin and valley physics using TMD moiréstructures.