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Cold dwell behaviour of Ti6Al alloy:Understanding load shedding using digital image correlation and dislocation based crystal plasticity simulations

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Journal of Materials Science & Technology 2022年第33期128卷 254-272页

作者： Yi Xiong NicolòGrilli Phani S.Karamched Bo-Shiuan Li Edmund Tarleton Angus J.Wilkinson Department of Materials University of OxfordParks RoadOxfordOX13PHUnited Kingdom Department of Mechanical Engineering University of BristolQueen’s BuildingUniversity WalkBristolUnited Kingdom Department of Engineering Science University of OxfordParks RoadOxfordOX13PJUnited Kingdom

digital image correlation(DIC)and dislocation based crystal plasticity simulation were utilised to study cold dwell behaviour in a coarse grain Ti-6Al alloy at 3 different temperatures up to 230℃.Strains extracted from large volume grains were measured during creep by DIC and were used to calibrate the crystal plasticity model.The values of critical resolved shear stresses(CRSS)of the two main slip systems(basal and prismatic)were determined as a function of temperature.Stress along paths across the boundaries of four grain pairs,three“rogue”grain pairs and one“non-rogue”grain pair,were determined at different temperatures.Large load shedding was observed in one of the“rogue”grain pairs,where a stress increment during the creep period was found in the“hard”grain.A minor load shedding mechanism was observed in two non-typical“rogue”grain pairs,in which the plastic deformation is nonuniform inside the grains and geometrically necessary dislocations accumulate in the centre of the grains.At elevated temperatures,120℃was found to be the worst case scenario as the stress difference at the grain boundaries of these four grain pairs was found to be the largest among the three temperatures analysed.The origin of this critical temperature is debated in the literature and it is investigated for the first time in the present work by analysing the simultaneous effects of the geometrically necessary dislocations(GND)and the strain rate sensitivity(SRS)of the slip systems.The analysis shows that the combined effects of the peak SRS of both prismatic and basal slip systems at 80℃and of the increase of the spread of the GND distribution around the grain boundary at higher temperatures are the origin of the observed worst case scenario.

关键词： Cold dwell fatigue digital image correlation Crystal plasticity Load shedding Titanium alloy

Microscopic damage evolution of anisotropic rocks under indirect tensile conditions: Insights from acoustic emission and digital image correlation techniques

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International Journal of Minerals,Metallurgy and Materials 2023年第9期30卷 1680-1691页

作者： Chaoqun Chu Shunchuan Wu Chaojun Zhang Yongle Zhang School of Civil and Resource Engineering University of Science and Technology BeijingBeijing 100083China Department of Civil&Mineral Engineering University of TorontoToronto ON M5S 1A4Canada Faculty of Land Resources Engineering Kunming University of Science and TechnologyKunmiing 650093China China Railway Sixth Group Limited Company Beijing 100036China

The anisotropy induced by rock bedding structures is usually manifested in the mechanical behaviors and failure modes of rocks.Brazilian tests are conducted for seven groups of shale specimens featuring different bedding angles. Acoustic emission (AE) and digital image correlation (DIC) technologies are used to monitor the in-situ failure of the specimens. Furthermore, the crack morphology of damaged samples is observed through scanning electron microscopy (SEM). Results reveal the structural dependence on the tensile mechanical behavior of shales. The shale disk exhibits compression in the early stage of the experiment with varying locations and durations. The location of the compression area moves downward and gradually disappears when the bedding angle increases. The macroscopic failure is well characterized by AE event location results, and the dominant frequency distribution is related to the bedding angle. The b-value is found to be stress-dependent.The crack turning angle between layers and the number of cracks crossing the bedding both increase with the bedding angle, indicating competition between crack propagations. SEM results revealed that the failure modes of the samples can be classified into three types:tensile failure along beddings with shear failure of the matrix, ladder shear failure along beddings with tensile failure of the matrix, and shear failure along multiple beddings with tensile failure of the matrix.

关键词： anisotropic rock failure mechanism acoustic emission digital image correlation Brazilian test

Assessment of fracture process in forta and polypropylene fiber-reinforced concrete using experimental analysis and digital image correlation

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Frontiers of Structural and Civil Engineering 2022年第12期16卷 1633-1652页

作者： Seyed Hamid KALALI Hamid ESKANDARI-NADDAF Seyed Ali EMAMIAN Department of Civil Engineering Hakim Sabzevari UniversitySabzevar ***Iran

This paper aims to characterize the evolution of the fracture process and the cracking behavior in fortaferro(FF)and polypropylene(PP)fiber-reinforced concrete under the uniaxial compressive loading using experimental analysis and digital image correlation(DIC)on the surface displacement.For this purpose,6 mix designs,including two FF volume fractions of 0.10%,and 0.20%and three PP volume fractions of 0.20%,0.30%,and 0.40%,in addition to a control mix were evaluated according to compressive strength,modulus of elasticity,toughness index,and stress–strain curves.The influence of fibers on the microstructural texture of specimens was analyzed by scanning electron microscope(SEM)imaging.Results show that FF fiber-reinforced concrete specimens demonstrated increased ductility and strength compared to PP fiber.DIC results revealed that the major crack and fracture appeared at the peak load of the control specimen due to brittleness and sudden gain of large lateral strain,while a gradual increase in micro-crack quantity at 75%of peak load was observed in the fiber specimens,which thenbegan to connect with each other up to the final fracture.The accuracy of the results supports DIC as a reliable alternative for the characterization of the fracture process in fiber-reinforced concrete.

关键词： fiber-reinforced concrete forta-ferro and polypropylene fiber fracture process cracking behavior digital image correlation

Revealing the role of local shear strain partition of transformable particles in a TRIP-reinforced bulk metallic glass composite via digital image correlation

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International Journal of Minerals,Metallurgy and Materials 2022年第4期29卷 807-813页

作者： Xiaoyuan Yuan Yuan Wu Xiongjun Liu Hui Wang Suihe Jiang Zhaoping Lü State Key Laboratory for Advanced Metals and Materials Beijing Advanced Innovation Center for Materials Genome EngineeringUniversity of Science and Technology BeijingBeijing 100083China

The coupling effects of the metastable austenitic phase and the amorphous matrix in a transformation-induced plasticity(TRIP)-reinforced bulk metallic glass(BMG)composite under compressive loading were investigated by employing the digital image correlation(DIC)technique.The evolution of local strain field in the crystalline phase and the amorphous matrix was directly monitored,and the contribution from the phase transformation of the metastable austenitic phase was revealed.Local shear strain was found to be effectively consumed by the displacive phase transformation of the metastable austenitic phase,which relaxed the local strain/stress concentration at the interface and thus greatly enhanced the plasticity of the TRIP-reinforced BMG composites.Our current study sheds light on in-depth understanding of the underlying deformation mechanism and the interplay between the amorphous matrix and the metastable crystalline phase during deformation,which is helpful for design of advanced BMG composites with further improved properties.

关键词： bulk metallic glass composite transformation-induced plasticity digital image correlation local shear strain

Full-field out-of-plane vibration displacement acquisition based on speckle-projection digital image correlation and its application in damage localization

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International Journal of Mechanical System Dynamics 2022年第4期2卷 363-373页

作者： Shancheng Cao Jinwei Yan Haibo Nian Chao Xu School of Astronautics Northwestern Polytechnical UniversityXi'anChina Yangtze River Delta Research Institute of Northwestern Polytechnical University TaicangJiangsuChina China Electronic Product Reliability and Environmental Testing Research Institute GuangzhouChina Guangdong Provincial Key Laboratory of Electronic Information Products Reliability Technology GuangzhouChina

Stereo-digital image correlation(Stereo-DIC)has been widely explored for modal analysis in plate-type structures due to its noncontact and full-field advantages.However,when the traditional stereo-DIC is adopted to capture the out-of-plane displacements,several challenging issues exist such as the development of surface speckles,asynchronous camera recording,and efficiency and accuracy degradation due to high computation costs.Moreover,with the captured out-of-plane displacements,effective and efficient evaluation of the high spatial resolution mode shapes and their application to damage localization are also critical problems.To tackle these issues,a speckle-projection DIC technique using a single high‐speed camera is proposed to obtain the out-of-plane vibration displacements.Moreover,an enhanced peak-picking modal analysis method is adopted to enhance the estimation accuracy and efficiency of mode shapes.In addition,the low‐rank property of mode shapes in an intact state and the spatial sparse property of damage locations are harnessed for the detection of damage positions without requiring reference data on the healthy state.Finally,the modal analysis and damage localization results based on the proposed speckle-projection DIC are compared with those of the traditional two-camera stereo-DIC technique to verify its feasibility and effectiveness.It is found that the differences in the identified resonant frequencies between these two methods are smaller than 1%for higher modes.Moreover,the proposed speckle-projection DIC has the same accuracy as the traditional two-camera stereo-DIC in terms of measurement accuracy,mode shape estimation,and damage localization.

关键词： damage localization digital image correlation low-rank property modal analysis out-of-plane displacement

In-situ strain measurement and error analysis of arc welding with 2D digital image correlation

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China Welding 2022年第3期31卷 17-23页

作者：黄宏浩胡明华徐爱杰宋育林陈华斌 School of Materials Science and Engineering Shanghai Jiao Tong UniversityShanghai200240China Shanghai Space Precision Machinery Research Institute Shanghai201600China

The deformation and residual stress generated by the welding process can seriously affect the use of components.As a result,it is very important to understand the evolution of stress and strain during the welding process.The strain measurement method based on digital image correlation(DIC)is an excellent method to detect welding strain and residual stress.The out-of-plane translation and out-of-plane rotation introduce errors to the two-dimensional DIC.In this paper,the causes of errors are analyzed theoretically,and the formulas of errors caused by the out-of-plane displacement and the out-of-plane rotation are derived.The out-of-plane translation experiment and the out-of-plane rotation experiment were carried out to verify the theory,and the experimental results are consistent with the theoretical analysis results.The error caused by the out-of-plane translation can be reduced by increasing the object distance;the error caused by the out-of-plane rotation is greatly affected by the rotation angle.

关键词： arc welding digital image correlation strain measurement error analysis

Characterization for elastic constants of fused deposition modelling-fabricated materials based on the virtual fields method and digital image correlation

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Acta Mechanica Sinica 2017年第6期33卷 1075-1083页

作者： Quankun Cao Huimin Xie AML Department of Engineering Mechanics Tsinghua University Beijing 100084 China

Fused deposition modelling(FDM), a widely used rapid prototyping process, is a promising technique in manufacturing engineering. In this work, a method for characterizing elastic constants of FDM-fabricated materials is proposed. First of all, according to the manufacturing process of FDM, orthotropic constitutive model is used to describe the mechanical behavior. Then the virtual fields method(VFM) is applied to characterize all the mechanical parameters(Q, Q, Q, Q) using the full-field strain,which is measured by digital image correlation(DIC). Since the principal axis of the FDM-fabricated structure is sometimes unknown due to the complexity of the manufacturing process, a disk in diametrical compression is used as the load configuration so that the loading angle can be changed conveniently. To verify the feasibility of the proposed method, finite element method(FEM) simulation is conducted to obtain the strain field of the disk. The simulation results show that higher accuracy can be achieved when the loading angle is close to 30?. Finally, a disk fabricated by FDM was used for the experiment. By rotating the disk, several tests with different loading angles were conducted. To determine the position of the principal axis in each test, two groups of parameters(Q, Q, Q, Q) are calculated by two different groups of virtual fields. Then the corresponding loading angle can be determined by minimizing the deviation between two groups of the parameters. After that, the four constants(Q, Q, Q, Q) were determined from the test with an angle of 27?.

关键词： Fused deposition modelling Virtual fields method digital image correlation Orthotropic constitutive model Disk compression

DAMAGE AND FRACTURE EVALUATION OF GRANULAR COMPOSITE MATERIALS BY digital image correlation METHOD

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Acta Mechanica Sinica 2004年第4期20卷 408-417页

作者：张珏熊春阳李宏举李明王建祥方竞 Department of Mechanics and Engineering Science Peking UniversityBeijing 100871China

This paper presents the applications of digital image correlation technique to the mesoscopic damage and fracture study of some granular based composite materials including steel- fiber reinforced concrete,sandstone and crystal-polymer composite.The deformation fields of the composite materials resulted from stress localization were obtained by the correlation computation of the surface images with loading steps and thus the related damage prediction and fracture parameters were evaluated.The correlation searching could be performed either directly based on the gray levels of the digital images or from the wavelet transform(WT)coefficients of the transform spectrum.The latter was developed by the authors and showed higher resolution and sensitivity to the singularity detection. Because the displacement components came from the rough surfaces of the composite materials without any coats of gratings or fringes of optical interferometry,both surface profiles and the deformation fields of the composites were visualized which was helpful to compare each other to analyze the damage of those heterogeneous materials.

关键词： digital image correlation deformation field evaluation granular based composites damage and fracture

Experimental study of shear properties of 3D woven composite using digital image correlation and acoustic emission

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Acta Mechanica Sinica 2020年第2期36卷 448-459页

作者： E.M.Strungar A.S.Yankin E.M.Zubova A.V.Babushkin A.N.Dushko Center of Experimental Mechanics Perm National Research Polytechnic University614990 PermRussian Federation Engineering Center PJSC“UEC-Saturn” 152903 RybinskRussian Federation

This work is dedicated to the experimental study of the shear properties of three-dimensional reinforced composites taking into account their structural features,in Iosipescu tests.Shear strains have been determined using Vic-3D non-contact three-dimensional digital optical system.The evolution of inhomogeneous strain fields on the surface of composite specimens of the structure under study has been analyzed.The variants of strain averaging in the specimen working area have been analyzed using Vic-3D tools.AMSY-6 acoustic emission system has been used to assess the structural integrity of composite materials under loading.

关键词： Carbon-fiber composite 3D reinforced composite digital image correlation Acoustic emission technique Iosipescu test