On the propagation and pulsation of Portevin-Le Chatelier deformation bands: An experimental study with digital speckle pattern metrology

Three dimensional(3D) displacements, which can be translated further into 3D strain, are key parameters for design, manufacturing and quality control. Using different optical setups, phase-shift methods, and algorithms, several different 3D electronic speckle pattern interferometry(ESPI) systems for displacement and strain measurements have been achieved and commercialized. This paper provides a review of the recent developments in ESPI systems for 3D displacement and strain measurement. After an overview of the fundamentals of ESPI theory, temporal phase-shift, and spatial phase-shift techniques, 3D deformation measurements by the temporal phase-shift ESPI system, which is suited well for static measurement, and by the spatial phase-shift ESPI system, which is particularly useful for dynamic measurement, are discussed. For each method, the basic theory, a brief derivation and different optical layouts are presented. The state of art application, potential and limitation of the ESPI systems are shown and demonstrated.

Review of electronic speckle pattern interferometry (ESPI) for three dimensional displacement measurement

Synergetic principles of physical mesomechanics

In-plane Electronic Speckle Pattern Interferometry has been successfully used during tensile testing of semi-hard copper sheets in order tomeasure the strain rate. On one hand, heterogeneity in strain rate ﬁeld has been found before the maximum of the tensile force ( e t 19.4 and25.4%, respectively). Thus, a localization phenomenon occurs before the classic Consid`ere’s criterion (d F =0) for the diffuse neck initiation. Onthe other hand, strain rate measurement before fracture shows the moment where one of the two slip band systems becomes predominant, thenstrain concentrates in a small area, the shear band. Uncertainty evaluation has been carried out, which shows a very good accuracy of the totalstrain and the strain rate measurements.© 2005 Elsevier B.V. All rights reserved. Keywords: Tensile test; ESPI; Strain rate measurement; Strain localization; Necking; Uncertainty determination 1. Introduction Thetensiletestisprobablythemostcommonlyusedmechan-ical test. It allows determining many mechanical properties ofmaterials, such as Young’s modulus, yield stress, tensile stress,strain hardening coefﬁcient and ductility. Many metals exhibittensile stress–strain curves whose initial linear portion (elasticregion) passes gradually to the elasto-plastic region. In a ﬁrststage of the latter, strains are homogeneous along the speci-men. This stage ends when a diffuse neck appears. Classically,it is considered [1] that the diffuse neck occurs when the forcereaches its maximum. Then, strains begin to be heterogenous upto the localized neck, which is a shear band for a sheet in uniax-ial tensile test, whose width is of the same order of magnitudeas the specimen thickness.Several theoretical models have been developed since the1950s [2–12]. Swift [2] has proposed a criterion for the deter-mination of the maximum principal stress generating the plastic

Strain rate measurement by Electronic Speckle Pattern Interferometry: A new look at the strain localization onset

A method for smoothing measured displacements and computing strains utilizing a finite element method is proposed. Nodal displacement values of a finite element model are determined by fitting the interpolation functions of finite elements to measured displacement values using the method of least-squares. Then, the smoothed displacement distributions are obtained. The displacements in the region where the measurement values are not obtained or unreliable are determined by solving finite element equations. The validity is demonstrated by applying the proposed method to displacements of a plate with a hole obtained by finite element method. Results show that the displacements and the strains can be determined accurately by the proposed method. Furthermore, the strains near free boundaries can be determined easily. As strains can be evaluated easily and accurately, it is expected that the proposed method can be applied to various problems in solid mechanics.

Smoothing Measured Displacements and Computing Strains Utilizing Finite Element Method

An experimental scheme of digital speckle pattern interferometry using two electromagnetic shutters and a three-frame color image board is presented to measure two in-plane components of incremental displacement field of diffuse objects. The deformation of the entire process from initial elastic deformation to fracture can be observed by using a Magneto Optical (MO) disk that has enough memory to record the image data of the entire process. By this system, some tensile experiments are achieved to investigate the mechanism of plastic deformation. The experimental results show that plastic deformation of tensile deformation is nonuniform. The material deforms in the distribution of domains. In the domains, the main deformation is uniform shear and rotation. At the boundary of the domains, the deformation is very large normal strain. With load, both the range and mode of domains are changing. At the end of plastic deformation, only two domains become dominant, and fracture happens at the boundary of the two domains.

X. L. Gong

Papers

Investigation on mechanism of plastic deformation by digital speckle pattern interferometry

A Systematic Review on The Strategies Of Reducing Asphalt Pavement Temperature