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Editorial:Advances in Optical Techniques for Mechanical Measurements

Recently,optical techniques have attracted great attention due to their excellent non-destructive,non-contact,high-resolution, and full-field characteristics.Applications can be found in diverse fields such as precision mechanics and manufacturing,aerospace and automotive testing and inspection,materials science,and biomedical engineering.Advances in Optical Techniques for MechanicalMeasurementspresentsthelatestresearchprogressesin several widely used optical techniques with applications in precision mechanical engineering.

This special issue consists of six research papers written by innovative experts in optical engineering describing twodimensional and three-dimensional digital image correlation（DIC）,photoelasticity,phase-shifting or phase-stepping,and moiré methods.There are five theme articles published in this special issue as well as an article in the preceding issue（issue 3, pp.126-130）.Applications range from the deformation measurement to the residual stress measurement of transparent and opaque materials.This special issue expatiates the principles and the usages of these optical techniques,the fabrication processes of basic deformation carriers,and the detailed measurement results of displacements,strains,and residual stresses.

The papers in this issue can be divided into three categories—method development,application specific,and testing methodology.In the first category,there are articles on a global look-up table strategy with cubic B-spline interpolation for DIC,an instantaneous phase-step method using a pixelated micro-polarizer array for single shot quantitative phase determination,and the fabrication methods of micron-scale gratings using a femtosecond laser and nano-scale speckles using ion beam milling for high resolution moiré and DIC applications.With regard to applications,articles related to residual stress distributions of injection molded components,the dynamic phase distributions of transparent polymethyl methacrylate（PMMA）,facialskinmetrologyusingstereovisionand the displacement compensation due to mechanical movement in a scanning electron microscope are showcased.From the angle of testingenvironment,thisspecialissuefocusesonmeasurementsin extreme environments including three-dimensional,dynamic and micron/nano-scale measurements.

These research papers enable readers and audiences to gain deeper understandings and insights into the optical techniques for mechanical measurements.We would like to thank all the authors forcontributingtheirinterestingresearchworksandalltheeditors for their generous assistance and help.

Anand Asundi is currently Professor and Director of the Centre for Optical and Laser Engineering in the School of Mechanical and Aerospace Engineering at the Nanyang Technological University in Singapore.His teaching area is in Optical Engineering and Engineering Mechanics with research interests in Computational Optical Metrology, Photomechanics,and Fiber Optics Sensors.He has numerous patents,has published extensively and presented invited seminars/talks at various institutions and at international conferences.He is Editor of Optics and Lasers in Engineering and Fellow of SPIE,the International Society of Optical Engineers and the Institution of Engineers,Singapore.He is founding chair of the Optics and Photonics Society of Singapore,Asian Committee on Experimental MechanicsandtheAsiaPacificCommitteeonSmartMaterialsandNanotechnology. He has organized numerous conferences and served on the Membership,Scholarship/Awards and Presidential Asian Advisory committees of SPIE and its Board of Directors.He is also the founder and director of d’Optron Pte Ltd.

Qinghua Wang received her Ph.D.degree from Tsinghua University in 2011,and worked as a JSPS（Japan Society for thePromotionofScience）PostdoctoralFellowforoverseas researchers in National Institute for Materials Science in Japantill2013.Atpresent,sheisatenure-trackResearcher in Research Institute for Measurement and Analytical Instrumentation in National Institute of Advanced Industrial Science and Technology in Japan.Her research interests include micro/nano-scale optical techniques for deformation measurement feature recognition techniques of periodic structures,mechanical properties,and buckling behaviors of films and composites.Her recent awards include the Encouragement Award for Promising Researchers from the Japanese Society for Experimental Mechanicsin2016andtheOutstandingAchievementAwardofScientificResearch（Science and Technology）in Colleges and Universities—Second Prize of Natural Science issued by Ministry of Education of China in 2014 as a co-winner.

Anand Asundi

School of Mechanical&Aerospace Engineering，

Nanyang Technological University（NTU），Singapore 639798，

Singapore

Qinghua Wang

Research Institute for Measurement and Analytical Instrumentation，

National Institute of Advanced Industrial Science and Technology

（AIST），Tsukuba，Ibaraki 305-8568，

Japan

Available online 4 August 2016

http://dx.doi.org/10.1016/j.taml.2016.08.001

2095-0349/

?2016 Published by Elsevier Ltd on behalf of The Chinese Society of Theoretical and Applied Mechanics.This is an open access article under the CC BY-NC-ND license（http://creativecommons.org/licenses/by-nc-nd/4.0/）.