A deformation measurement method based on surface texture information of rocks and its application

Users of the digital image correlation method are faced with the problem of poor operability,low repeatability,and lack of standardized specifications for spraying speckles.To solve the problem,the research proposed a rock deformation measurement method that obviates the need to spray speckles.A local binary model was established by using the local binary pattern(LBP)operator based on deep texture features on rock surfaces.The resulting LBP digital speckle pattern can substitute artificial speckle patterns and demonstrates high quality and strong applicability.Based on the LBP digital speckle pattern,the target tracking algorithm was employed to achieve non-contact measurement of the dynamic displacements of rocks.The feasibility and effectiveness of the algorithm in practical application were verified by conducting shear tests on granite and siltstone.Test results show that the deformation characteristics in the displacement nephograms are in line with the measured data pertaining to rock fracturing and conform to the basic characteristics of the shear failure of rocks.The deformation measurement method based on surface texture information can realize non-contact displacement measurement of rocks under conditions without speckles:this obviates the influence of the quality of sprayed speckles on the accuracy of the measurement of deformation.

Videometric research on deformation measurement of large-scale wind turbine blades

Utilization of wind energy is a promising way to generate power,and wind turbine blades play a key role in collecting the wind energy effectively.This paper attempts to measure the deformation parameter of wind turbine blades in mechanics experiments using a videometric method. In view that the blades experience small buckling deformation and large integral deformation simultaneously, we proposed a parallel network measurement(PNM) method including the key techniques such as camera network construction,camera calibration,distortion correction,the semi-automatic high-precision extraction of targets,coordinate systems unification,and bundle adjustment,etc. The relatively convenient construction method of the measuring system can provide an abundant measuring content,a wide measuring range and post processing.The experimental results show that the accuracy of the integral deformation measurement is higher than 0.5 mm and that of the buckling deformation measurement higher than 0.1mm.

Bam earthquake: Surface deformation measurement using radar interferometry

On the 26th December 2003 an earthquake with MW=6.5 shook a large area of the Kerman Province in Iran. The epicenter of the devastating earthquake was located near the city of Bam. This paper described the application of differential synthetic aperture radar interferometry (D-INSAR) and ENVISAT ASAR data to map the coseismic surface deformation caused by the Bam earthquake including the interferometric data processing and results in detail. Based on the difference in the coherence images before and after the event and edge search of the deforma- tion field, a new fault ruptured on the surface was detected and used as a data source for parameter extraction of a theoretical seismic modeling. The simulated deformation field from the model perfectly coincides with the result derived from the SAR interferometric measurement.

Application of 3D Projection Profilometry in the High Speed Impaction Surface Deformation Measurement Research

In order to study the strength of the composite material plate problems, need to adopt a nondestructive testing method to obtain the specimen surface under the effect of high-speed impact regularity of shape. The projection profilometry was used to measure the surface profile or the full field deformation. Furtherly, by using the Fourier transform algorithm, there is only one frame of captured image which is needed in the measurement, so that it can be introduced into the high speed impaction procedure measurement. An experimental system, which was contained with an impact setup and the projection profilometry measurement part, was constructed for the impaction action characteristic research. The metallic impact object can be launched by a gas gun or a spin fan, respectively. The detected object is manufactured by composite materials. In order to increase the surface deformation measurement accuracy, the calibration method and the error was discussed with different calibration specimen. And then, the proposed profilometry measurement method is proved by the gas gun and spin fan projectile test. The surface deformation of the manufactured composite plates and fan case are measured in the impaction procedure. So that the impact action details can be described much more clearly than the traditional video monitoring method.

Macro-Analysis on Across-Fault Crustal Deformation Measurement Data Along the Northern Edge of the Qinghai-Xizang Block

Based on the arrangement of the across-fault measurement data along the northern edge of the Qinghai-Xizang block,we divide the deformation into different types and probe the nature of various fault movements based on these types.The recent situation of tectonic movement of main structural belts and seismicity in this area are expounded.From the above,it is concluded that across-fault measurement can reflect not only the conditions of fault movement nearby but also the change of regional stress fields; not only is this a method to obtain regional seismogenic information and to conduct short-term prediction but it is also involved with large scale space-time prediction of moderate and strong earthquakes on the basis of the macro characteristics of fractures.

New speckle pattern interferometry for precise in situ deformation measurements

A new electronic speckle pattern interferometry method is proposed to realize in situ deformation measurements.The feature of the method is the combination of a high-speed camera and multiple laser Doppler vibrometers(LDVs)for synchronous measurements.The high-speed camera is used to record and select effective interferograms,while the LDVs are used to measure the rigid body displacement caused by vibrations.A series of effective interferograms with known shifted phase values are obtained to calculate the deformation phase.The experimental results show that the method performs well in measuring static and dynamic deformations with high accuracy in vibrating environments.

Mirror-assisted multi-view high-speed digital image correlation for dual-surface dynamic deformation measurement

Based on the recently proposed mirror-assisted multi-view digital image correlation(MV-DIC),we establish a cost-effective and easy-to-implement mirror-assisted multi-view high-speed digital image correlation(MVHS-DIC)method and explore its applications for dual-surface full-field dynamic deformation measurement.In contrast to the general requirement of four expensive high-speed cameras for dual-surface dynamic deformation field measurement,the established mirror-assisted MVHS-DIC halves the cost by involving only two synchronized high-speed cameras and two planar mirrors.The two synchronized high-speed cameras can dynamically measure the front and rear surfaces of a sheet sample simultaneously through the reflection of the two mirrors.The results on the two surfaces are then transformed into the same coordinate system,leading to the required dual-surface 3D dynamical deformation fields.The effectiveness and accuracy of the established system are validated through modal tests of a cantilever aluminum sheet.The vibration measurement of a drum and dual-surface transient deformation measurement of a smartphone in the drop-collision process further prove its practicability.Benefiting from the attractive advantages of multi-view dynamic deformation measurement in a cost-efficient way,the established mirror-assisted MVHS-DIC is expected to encourage more comprehensive dynamic mechanical behavior characterization of regular-sized materials and structures in vibration and impact engineering fields.

A multi-sensor-based distributed real-time measurement system for glacier deformation

Glacier disasters occur frequently in alpine regions around the world,but the current conventional geological disaster measurement technology cannot be directly used for glacier disaster measurement.Hence,in this study,a distributed multi-sensor measurement system for glacier deformation was established by integrating piezoelectric sensing,coded sensing,attitude sensing technology and wireless communication technology.The traditional Modbus protocol was optimized to solve the problem of data identification confusion of different acquisition nodes.Through indoor wireless transmission,adaptive performance analysis,error measurement experiment and landslide simulation experiment,the performance of the measurement system was analyzed and evaluated.Using unmanned aerial vehicle technology,the reliability and effectiveness of the measurement system were verified on the site of Galongla glacier in southeastern Tibet,China.The results show that the mean absolute percentage errors were only 1.13%and 2.09%for the displacement and temperature,respectively.The distributed glacier deformation real-time measurement system provides a new means for the assessment of the development process of glacier disasters and disaster prevention and mitigation.

High-accuracy 3-D deformation measurement method with an improved structured-light principle

In this paper,a high-accuracy 3-D deformation measurement(HADM)method with structured light is proposed and applied to wing deformation measurement in wind tunnel experiments.The present method employs an arbitrarily arranged fringe projector and a perpendicularly placed camera.The exact phase-height mapping using the phase differences of the projected sinusoidal fringe patterns,as well as the spatial distribution of the fringe,is accurately derived.It not only presents high feasibility but also reduces systemic uncertainties arising from deviations between the ideal model and the real-world conditions.Meanwhile,a dynamic boundary process algorithm is proposed to reduce the measurement uncertainty caused by fringe fracture near the object boundary.It is calibrated that a high accuracy with the average measurement uncertainty of 0.0237 mm is achieved,which is less than 0.01%of the side length of 25 cm of the field of view.In the wind tunnel experiments,the 3-D deformations of the elastic wing,particularly the key geometric parameters such as wing tip position,angle of attack,and dihedral angle,are well reconstructed to provide an in-depth explanation for the aerodynamic characteristics.

Automatic Monitoring System for 3-D Deformation of Crustal Fault Based on Laser and Machine Vision

An automatic monitoring method of the 3-D deformation is presented for crustal fault based on laser and machine vision. The laser source and screen are independently set up in the headwall and footwall, the collimated laser beam creates a circular spot on the screen, meanwhile, the industrial camera captures the tiny deformation of the crustal fault by monitoring the change of the spot position. This method significantly reduces the cost of equipment and labor, provides daily sampling to ensure high continuity of data. A prototype of the automatic monitoring system is developed, and a repeatability test indicates that the error of spot jitter can be minimized by consecutive samples. Meanwhile, the environmental correction model is determined to ensure that environmental changes do not disturb the system. Furthermore, the automatic monitoring system has been applied at the deformation monitoring station(KJX02) of China Beishan underground research laboratory, where continuous deformation monitoring is underway.

Deformation Measurement of Glass Structure Using FBG Sensor

Glass has been widely used as an important component in structures such as reflection glass curtainwalls,high speed trains,and landscape glass bridges with advantages of transparent and easy to clean,which are exposed to extreme weather conditions and external loads.Over time,these factors can lead to a damage of glass.So the health status of glass structure is critical,which should be routinely monitored to improve safety and provide reliable maintenance strategy.In this paper,fiber Bragg grating(FBG)sensors are used to monitor glass damage based on the fact that the main components of both the optical fiber and the glass are silica,which hints that both optical fiber and glass have the similar mechanical properties.Furthermore,the diameter of FBG installed on the glass structure is small,which has little effect on the beauty of glass.In order to validate the feasibility of the damage monitoring method,one common glass panel model with two-side fixations is loaded impact and static loads respectively,on the upper and lower surfaces of which four FBG sensors and two resistance strain gages are installed.A comparison study among the measured strains from the FBG sensors,those from the resistance strain gages,and those calculated from finite element model(FEM)analysis is conducted and the result obtained with experiments agrees with the element result.Test results show that the FBG sensors can effectively measure the glass deformation or damage under the impact and static load.

Bridge Continuous Deformation Measurement Technology Based on Fiber Optic Gyro

Bridge is an important part of modem transportation systems and deformation is a key index for bridge＇s safety evaluation. To achieve the long span bridge curve measurement rapidly and timely and accurately locate the bridge maximum deformation, the continuous deformation measurement system （CDMS） based on inertial platform is presented and validated in this paper. Firstly, based on various bridge deformation measurement methods, the method of deformation measurement based on the fiber optic gyro （FOG） is introduced. Secondly, the basic measurement principle based on FOG is presented and the continuous curve trajectory is derived by the formula. Then the measurement accuracy is analyzed in theory and the relevant factors are presented to ensure the measurement accuracy. Finally, the deformation measurement experiments are conducted on a bridge across the Yangtze River. Experimental results show that the presented deformation measurement method is feasible, practical, and reliable; the system can accurately and quickly locate the maximum deformation and has extensive and broad application prospects.

Simultaneous 2D in-plane deformation measurement using electronic speckle pattern interferometry with double phase modulations

Electronic speckle pattern interferometry（ESPI） and digital speckle pattern interferometry are wellestablished non-contact measurement methods. They have been widely used to carry out precise deformation mapping. However, the simultaneous two-dimensional（2D） or three-dimensional（3D） deformation measurements using ESPI with phase shifting usually involve complicated and slow equipment. In this Letter, we solve these issues by proposing a modified ESPI system based on double phase modulations with only one laser and one camera. In-plane normal and shear strains are obtained with good quality. This system can also be developed to measure 3D deformation, and it has the potential to carry out faster measurements with a highspeed camera.

Experimental Study on Full-Surface Buckling of Variable Curvature Cylindrical Shell Using Multi-camera 3D-DIC System

To achieve full-surface strain measurement of variable curvature objects,a 360°3D digital image correlation(DIC)system is proposed.The measurement system consists of four double-camera systems,which capture the object’s entire surface from multiple angles,enabling comprehensive full-surface measurement.To increase the stitching quality,a hierarchical coordinate matching method is proposed.Initially,a 3D rigid body calibration auxiliary block is employed to track motion trajectory,which enables preliminary matching of four 3D-DIC sub-systems.Subsequently,secondary precise matching is performed based on feature points on the test specimen’s surface.Through the hierarchical coordinate matching method,the local 3D coordinate systems of each double-camera system are unified into a global coordinate system,achieving 3D surface reconstruction of the variable curvature cylindrical shell,and error analysis is conducted on the results.Furthermore,axial compression buckling experiment is conducted to measure the displacement and strain fields on the cylindrical shell’s surface.The experimental results are compared with the finite element analysis,validating the accuracy and effectiveness of the proposed multi-camera 3D-DIC measuring system.

Recent Developments of Image Based Measurement Methods for Application to Transonic Flows in Industrial Wind Tunnels

The experimental investigation of unsteady complex flow fields in wind tunnels requires advanced measurement techniques. The most important of such image based measurement techniques are those for the measurement of planar flow velocity fields, planar pressure distribution, model location and deformation, model temperature and quantitative high speed flow visualization. The applications as carried out by DLR range from low speed flows to transonic flows, from high lift configurations to propellers and rotors, from wake vortex investigations in catapult facilities and water towing tanks to investigations of vortex break down phenomena on delta wings. The capability to use image based measurement techniques in transonic flows requires dedicated technical developments and experienced scientists due to the special environment of a transonic wind tunnel. In this paper an overview of the state-of-the art of the application of image based measurement techniques in transonic flows as performed by DLR＇s Institute of Aerodynamics and Flow Technology will be given.

Measuring 3D face deformations from RGB images of expression rehabilitation exercises

Background The accurate(quantitative)analysis of 3D face deformation is a problem of increasing interest in many applications.In particular,defining a 3D model of the face deformation into a 2D target image to capture local and asymmetric deformations remains a challenge in existing literature.A measure of such local deformations may be a relevant index for monitoring the rehabilitation exercises of patients suffering from Par-kinson’s or Alzheimer’s disease or those recovering from a stroke.Methods In this paper,a complete framework that allows the construction of a 3D morphable shape model(3DMM)of the face is presented for fitting to a target RGB image.The model has the specific characteristic of being based on localized components of deformation.The fitting transformation is performed from 3D to 2D and guided by the correspondence between landmarks detected in the target image and those manually annotated on the average 3DMM.The fitting also has the distinction of being performed in two steps to disentangle face deformations related to the identity of the target subject from those induced by facial actions.Results The method was experimentally validated using the MICC-3D dataset,which includes 11 subjects.Each subject was imaged in one neutral pose and while performing 18 facial actions that deform the face in localized and asymmetric ways.For each acquisition,3DMM was fit to an RGB frame whereby,from the apex facial action and the neutral frame,the extent of the deformation was computed.The results indicate that the proposed approach can accurately capture face deformation,even localized and asymmetric deformations.Conclusion The proposed framework demonstrated that it is possible to measure deformations of a reconstructed 3D face model to monitor facial actions performed in response to a set of targets.Interestingly,these results were obtained using only RGB targets,without the need for 3D scans captured with costly devices.This paves the way for the use of the proposed tool in remote medical rehabilitation monitoring.

DIGITAL SPECKLE CORRELATION METHOD IMPROVED BY GENETIC ALGORITHM

The digital speckle correlation method is an important optical metrology for sur- face displacement and strain measurement.With this technique,the whole field deformation in- formation can be obtained by tracking the geometric points on the speckle images based on a correlation-matching search technique.However,general search techniques suffer from great com- putational complexity in the processing of speckle images with large deformation and the large random errors in the processing of images of bad quality.In this paper,an advanced approach based on genetic algorithms (GA) for correlation-matching search is developed.Benefiting from the abilities of global optimum and parallelism searching of GA,this new approach can complete the correlation-matching search with less computational consumption and at high accuracy.Two experimental results from the simulated speckle images have proved the efficiency of the new approach.

Variability on Raman Shift to Stress Coefficient of Porous Silicon

Porous silicon film is a capillary-like medium, which is able to reveal different meso-elastic modulus with porosity. During the preparation of porous silicon samples, the capillary force is a non-classic force related to the liquid evaporation which directly influences the evolution of residual stress. In this study, a non-linear relation of Raman shift to stress coefficient and the porosity is obtained from the elastic modulus measured with nano-indentation by Bellet et al. [J. Appl. Phys. 60 （1996） 3772] Dynamic capillarity during the drying process of porous silicon is investigated using micro-Raman spectroscopy, and the results reveal that the residual stress resulted from the capillarity increased rapidly. Indeed, the dynamic capillarity has a close relationship with a great deal of micro-pore structures of the porous silicon.

Optimization of the forearm angle for arm wrestling using multi-camera stereo digital image correlation: A preliminary study

This study analyzes the function of different muscles during arm wrestling and proposes a method to analyze the optimal forearm angle for professional arm wrestlers.We built a professional arm-wrestling platform to measure the shape and deformation of the skin at the biceps brachii of a volunteer in vivo during arm wrestling.We observed the banding phenomenon of arm skin strain during muscle contraction and developed a model to evaluate the moment provided by the biceps brachii.According to this model,the strain field of the area of interest on the skin was measured,and the forearm angles most favorable and unfavorable to the work of the biceps brachii were analyzed.This study demonstrates the considerable potential of applying DIC and its extension method to the in vivo measurement of human skin and facilitates the use of the in vivo measurement of skin deformation in various sports in the future.

Electron Moirémethod

It is very important to measure local deformations for an in-depth understanding of mechanical properties and fracture mechanism of structural and functional materials. In this paper, different types of model grid fabrication methods and many types of electron Moire methods using an electron beam drawing system, a scanning electron microscope or a focus ion beam are reported, together with their applications in the measurement of deformations occurring in various engineerings and materials science research.