Strain Measurement Method Research Articles

Analysis of Circular PDMS Microballoons With Ultralarge Deflection for MEMS Design

This paper presents the simplified analytical and numerical analyses of the ultralarge deflection of circular polydimethylsiloxane (PDMS) microballoons (MBs) under pressure for microelectromechanical systems design. The analytical model assuming spherical symmetry on the deformed shape of MB yields a simplified solution on the pressure-normalized maximum deflection and two in-plane principal strains of the ultralargely deflected MB. The accuracy of the theoretical model is evaluated by comparing against the experimental results. Furthermore, by using a computational analysis that incorporates a Mooney-Rivlin model for a PDMS micromembrane, the properties of the PDMS fabricated at a mixing ratio of 10:1 base to catalyst, a curing temperature of 20°C, and a curing time of 48 h are determined for noncircular PDMS micromembrane analysis. In the experimental study, eight types of PDMS MBs, each of which has a membrane radius of 143, 202, 452, or 904 μm and a membrane thickness of 10 or 20 μm, are characterized in air and in cell culture media. A new strain-measuring method using fluorescent polymer microspheres for the PDMS MB is also introduced. The characterization of the PDMS MBs in air validates our theoretical model and shows an increase in elastic modulus as the membrane thickness decreases. The effect of cell culture media on the membrane rigidity of PDMS is also examined for biological applications of PDMS.

Strain Measurement Method for Tilted Planar Object by Phase-shifting Digital Holography Combined with Grating Projection Method

Strain Measurement Method for Tilted Planar Object by Phase-shifting Digital Holography Combined with Grating Projection Method

An Approach to Analyse Errors Introduced in the Random Grid Strain Measurement Method

Abstract: The present work refers to the errors imposed by the recently introduced random‐grid mesh‐free full field strain measurement method. Excluding systematic errors of the digital camera, the method itself is not an error‐free procedure. A possible cause of errors could be the misplacement of the spot‐centre (centroid) with regard of the spot boundaries. Another cause of errors is the limited order of approximation in the field function. A third one, emerges from the so‐called ‘sub‐pixel effect’. This kind of error is difficult to trace, so direct comparison between the results of the method and exact solutions is required. In the present work, proper analytical or numerical derivations of those errors are presented and reasonable upper limits are estimated. Finally, numerical and experimental examples are presented to demonstrate the accuracy of the method.

Phase-shifting laser scanning confocal microscopy moiré method and its applications

The laser scanning confocal microscopy (LSCM) moiré method is an effective method for full-field displacement and strain measurement in the micrometer scale. In this study, the phase-shifting LSCM moiré method is proposed for automatic processing of the moiré fringe. A combined phase-shifting and loading system for LSCM was developed, which could offer a tensile load on the plate type sample with a maximum load range of up to 500 N. Using the PZT (piezoelectric ceramic) phase shifter in the loading system, the moiré fringe phase was shifted and measured. Full field deformation was calculated according to the phase data. With the combination of LSCM and the self-developed loading system, tensile deformation of the aluminum sample was measured by the phase-shifting LSCM moiré technique. Full-field deformations under the different loads and elastic modulus of the sample were obtained. Experimental results demonstrated the feasibility of this technique, and the accuracy for deformation measurement is clearly improved.

INVESTIGATION OF STRAIN MEASUREMENT METHOD WITH BALANCING CURRENTS

It is shown that construction state identification systems are integral part of public and local warning and security systems. Structure of construction of state identification system is proposed and analysed. It is established that in order to ensure wide usage of such systems it is necessary to solve some scientific problems. A new method for measurement of construction strain is presented. It is based on evaluation of small changes of resistance with balancing currents. Measurements methods of these days are listed and their main advantages are discussed. Structure of strain gauge and formulas for calculating code of resistance changes is presented. Computerized and experimental models are made.

Surface plastic deformation distribution and microstructural evolution in the compound rolling of Ti–50Al billet

Compound rolling, which uses two different roller profiles to create plastic strain variation in the surface of a material, is described in this study. Based on the local load theory, equipment for the plastic deformation on the surface of the rectangular billet has been produced. The compound rolling behavior of Ti–50Al billet has been studied using this equipment. In order to study the deformation distribution of compound rolling, the flow net method for strain measurement has been employed. The deformation differences between compound rolling and flat rolling have been investigated with the commercial finite element method (FEM) code DEFORM-3D. The microstructure and the hardness from the surface to the center of the Ti–50Al billet developed through compound rolling has been characterized. These results indicate that the compound rolling technique results in severe plastic deformation near the surface with limited strain towards the center of the billet. This can result in compound microstructures, with fine recrystallized grains in the near surface region and the original directionally solidified microstructures in the center, and improve the hardness on the surface of the billet significantly.

短いロッドにおけるひずみ計測

Strain measurements are conducted on drill rods to investigate the rock drillability for percussion drilling. When the length of drill rod with a uniform cross section is short, the method of two-point strain measurement must be employed to separate an incident wave and a reflective wave.Strain measurements on two types of short drill rod (rod 1 and rod 2) using the two-point method are described. Results from experimental measurements using rod 1 include the following: (1) An accurate analysis of strain at the evaluation point could not be obtained when the 4-gage method was applied. On the other hand, accurate strain measurements were obtained using the 2-gage method (opposite side) . (2) Measurements using strain gages of length 5 mm were more suitable for the analysis of strain at the evaluation point than measurements using 2-mm strain gages. Results from tests to measure strain in two parts of rod 2 (part S and part F) include the following: (3) A complete measurement of a strain wave could not be obtained at part S, even using the 2-gage method. However, approximately two-thirds of the wave could be analyzed correctly. (4) For part F, an almost complete measurement of the strain wave was obtained using the 2-gage method. In addition, the similarity of the strain waves of part S and part F was confirmed.Finally, based on the results for rod 2, the complete percussion energy per hammer blow for part S was estimated.

Diffraction measurement of plastic strain in A533B ferritic steel – a feasibility study

It is known that the physical properties of many engineering materials may be strongly affected by previous loading, in particular prior plastic deformation. Most obviously, work hardening will alter subsequent yielding behaviour. Plastic deformation may also preferentially align the material grain structure, resulting in anisotropy of subsequent behaviour and a change in material fracture resistance. When physical characterisation is undertaken by experimental testing it is, therefore, important to have some knowledge of the current state of the material. As a result, it is desirable to have methods of quantitatively evaluating the level of plastic deformation which specimen material may have experienced prior to testing. This paper presents the results of a feasibility study, using a ferritic reactor pressure vessel steel, into the use of diffractive methods for plastic strain evaluation. Using neutron diffraction, changes in diffraction peak width and anisotropy of peak response were correlated with plastic deformation in a tensile test. The relationships produced were then used to evaluate permanent deformation levels in large samples, representative of standard fracture toughness test specimens. 2 Experimental measurements In order to investigate the effectiveness of two methods of plastic strain measurement (anisotropy strain and diffraction peak broadening [1]) it was necessary to manufacture suitable test specimens containing well defined plastic strain fields. Tensile test specimens were chosen as calibration specimens for the two techniques. In addition, a number of pre-strained ‘blanks’ for compact tension (C(T)) type fracture specimens were fabricated in order to compare with the data obtained from the tensile test samples. All samples were manufactured from A533B ferritic steel. This material was chosen as it is part of an ongoing study into the effects of plastic strain on fracture and it is typical of the type of steel commonly used in the power generation industry. A number of tensile tests were undertaken, according to the ASTM E8 standard, and consistent stress-strain behaviour was recorded in all tests. The tensile test specimens were cylindrical, with diameter 8mm and gauge length 80mm. To pre-strain the C(T) blanks, such that a uniform strain field was created with minimal residual stress, a number of large tensile-type specimens were manufactured. These were preloaded to the desired level of uni-axial plastic strain (1%, 3% and 5%), determined according to clip gauges fixed to the centre of the specimens, before being cut into sections. The specimens used were designed to provide the simplest possible, uni-axial plastic strain field in order to minimise the number of complicating factors when comparing the effectiveness of the two techniques. Neutron diffraction measurements were made using the ENGIN-X instrument on the ISIS neutron source at Rutherford Appleton laboratories, U.K.

401 マルチスケールひずみ計測法とその応用(材料・加工・構造物の信頼性を支える評価・モニタリング技術(1),ものづくりにおける基礎研究と先端技術の融合)

401 マルチスケールひずみ計測法とその応用(材料・加工・構造物の信頼性を支える評価・モニタリング技術(1),ものづくりにおける基礎研究と先端技術の融合)

Combined full field stress and strain measurement methods for granular materials

The current paper re-introduces the photoelastic measurement method in experimental geomechanics. A full-field phase stepping polariscope suitable for geomechanical model tests has been developed. Additional constraints on the measurement and mechanical setup arising from geomechanical test conditions are outlined as well as the opportunity to measure the displacement fields in the sample with digital image correlation. The capability of the current setup in retrieving the stress and strain field in a granular material is demonstrated.

Development of a Dynamic Strain Measurement Method using the Piezo Cable by Applying a Constant Cyclic Load

Development of a Dynamic Strain Measurement Method using the Piezo Cable by Applying a Constant Cyclic Load

Strain, curvature, and twist measurements in digital holographic interferometry using pseudo-Wigner–Ville distribution based method

Measurement of strain, curvature, and twist of a deformed object play an important role in deformation analysis. Strain depends on the first order displacement derivative, whereas curvature and twist are determined by second order displacement derivatives. This paper proposes a pseudo-Wigner-Ville distribution based method for measurement of strain, curvature, and twist in digital holographic interferometry where the object deformation or displacement is encoded as interference phase. In the proposed method, the phase derivative is estimated by peak detection of pseudo-Wigner-Ville distribution evaluated along each row/column of the reconstructed interference field. A complex exponential signal with unit amplitude and the phase derivative estimate as the argument is then generated and the pseudo-Wigner-Ville distribution along each row/column of this signal is evaluated. The curvature is estimated by using peak tracking strategy for the new distribution. For estimation of twist, the pseudo-Wigner-Ville distribution is evaluated along each column/row (i.e., in alternate direction with respect to the previous one) for the generated complex exponential signal and the corresponding peak detection gives the twist estimate.

An Investigation of Factors Impacting Nitinol Wire Fatigue Life

Abstract The purpose of this study is to identify factors that affect superelastic Nitinol fatigue resistance using a commercially available wire specimen. The study reveals the fatigue resistance of Nitinol wire as functions of surface finish, inclusions, processing, and applied stress applied. Nitinol wires were fatigue tested using the rotating beam fatigue method. The sample strains were verified using a direct strain-measurement method. Wires with outer diameters ranging from 0.127 to 0.343 mm processed with a mechanical and/or electropolished surface finish were compared to one another.

Investigation of the grid method for accurate in-plane strain measurement

This paper deals with the accurate measurement of the in-plane strain components on a deformed specimen using the grid method. A crossed grid transferred on the specimen surface is used for this purpose. Images of this grid are captured with a CCD camera before and after deformation. The complete strain state is deduced by processing these images with a suitable procedure described in the paper. The originality of this procedure is twofold. The first one is to determine the phase derivatives directly from the images. The second one is to compensate local variations of the grid pitch as well as local rotations of the grid, because these two phenomena may corrupt the final strain maps if they are not taken into account. The metrological performance of this procedure is assessed and discussed in terms of accuracy, measurement noise and spatial resolution. Two types of tests are used for this purpose: a translation and a rotation. These tests simulate the effect of rigid-body motion in a strain field that is rigorously equal to zero. One example finally illustrates the procedure: a tensile test performed on an open-hole specimen.

Full-field evaluation of the onset of microplasticity in a steel specimen

This work deals with the study of the local onset of microplasticity in a steel specimen under tensile test through the use of a full-field strain measurement method at the micrometric scale. The kinematic measurements were performed by the so called grid method. In order to produce the gratings, direct interferential photolithography was used. The gratings were digitized through the use of a white-light interferometric microscope. An adapted image stitching algorithm, applied to the phase maps, has been developed and implemented in order to extend the size of the region of interest. With this method, and by paying a particular attention to the conduct of the mechanical tests, the strain resolution obtained ranges from 1 to 2 × 10 −3 for a spatial resolution of about 20 μ m. In this paper, the method was applied to the study of the onset of local elasto-plastic strains in a ferritic steel coupon. The results show that the method is well suited to study small localized strains, for which few alternatives exist. To the best knowledge of the authors, it is the first time that white-light interferometric microscopy is used to measure full-field strains. The technique is reasonably easy to set up although a number of limitations exist. The paper is concluded by some considerations about further work required to extend the range of applicability of the method.

Influence of specimen dimensions and strain measurement methods on tensile stress–strain curves

Miniature tensile specimens, having various sizes and geometries, are often used to measure the mechanical properties of bulk nanostructured materials. However, these samples are generally too small for use with conventional extensometers so that the strains are usually calculated from the crosshead displacements. This study uses experimental results and finite element modeling (FEM) to critically evaluate the influence of the specimen dimensions and strain measurement methods on the tensile curves obtained from miniature specimens. Using coarse-grained Cu as a model material, the results demonstrate that the values of strain obtained from the crosshead displacement are critically influenced by the specimen dimensions such that the uniform elongation and the post-necking elongation both increase with decreasing gauge length and increasing specimen thickness. The results provide guidance on the optimum procedures for the tensile testing of miniature specimens of both coarse-grained and nanostructured materials.

Characterization of Ductile Core Materials

This article describes an experimental investigation of characterization methods for ductile core materials. Full-field optical strain measurement methods are used to determine the strain distributions in standard testing methods such as block shear and four-point beam testing, particularly for highly ductile cores subjected to large deformations. The results show that the stress and strain fields in both block shear and sandwich beam tests are very different to those assumed by the testing standards. The test methods result in complex post yield states of stress in the core materials, meaning the core shear strength and ultimate shear strain should not be calculated by classical methods in the post yield region.

Whole Bone Strain Quantification by Image Registration: A Validation Study

Quantification of bone strain can be used to better understand fracture risk, bone healing, and bone turnover. The objective of this work was to develop and validate an intensity matching image registration method to accurately measure and spatially resolve strain in vertebrae using microCT imaging. A strain quantification method was developed that used two sequential microCT scans, taken in loaded and unloaded configurations. The image correlation algorithm implemented was a multiresolution intensity matching deformable registration that found a series of affine mapping between the unloaded and loaded scans. Once the registration was completed, the displacement field and strain field were calculated from the mappings obtained. Validation was done in two distinct ways: the first was to look at how well the method could quantify zero strain; the second was to look at how the method was able to reproduce a known applied strain field. Analytically defined strain fields that linearly varied in space and strain fields resulting from finite element analysis were used to test the strain measurement algorithm. The deformable registration method showed very good agreement with all cases imposed, establishing a detection limit of 0.0004 strain and displaying agreement with the imposed strain cases (average R2=0.96). The deformable registration routine developed was able to accurately measure both strain and displacement fields in whole rat vertebrae. A rigorous validation of any strain measurement method is needed that reports on the ability of the routine to measure strain in a variety of strain fields with differing spatial extents, within the structure of interest.

SURFACE PLASTIC DEFORMATION REGULARITY AND MICROSTRUCTURAL EVOLUTION IN THE COMPOUND ROLLING OF Q235 BILLET

In order to meet the double demands on the high temperature creep and the fatigue property, compound rolling is put forward in this study. This technique obtains dual microstructures of billet, fine microstructure on the surface and original state microstructure in the center, through localizing the plastic deformation on the surface layer and leaving little plastic deformation in the center. Based on the local load theory, a set of equipment for the compound rolling has been produced. In order to study the deformation regularity of the compound rolling, Q235 billets have been used and the flow net method for strain measurement has been employed. The deformation regularity difference between the compound rolling and the flat rolling has been investigated. In addition, the microstructural evolution after the compound rolling on the surface and in the center of the Q235 billet has been observed. The results indicate that the compound rolling technique will localize the plastic deformation on the surface of the billet but leave little plastic deformation in the center.

Discrimination of strain and temperature based on a polarization-maintaining photonic crystal fiber incorporating an erbium-doped fiber

A simple sensing method for simultaneous measurement of temperature and strain is investigated by using a Sagnac fiber loop mirror composed of a polarization-maintaining photonic crystal fiber (PM-PCF) incorporating an erbium-doped fiber (EDF). Amplified spontaneous emission created by a pumped EDF is transmitted to a Sagnac fiber loop mirror. The interference between two counter-propagating signals in a Sagnac fiber loop mirror generates a periodic transmission spectrum with respect to wavelength. When external temperature is increased, the transmission peak power reduces because the amplified spontaneous emission of the EDF is decreased by the applied temperature change (0.04dB/°C). The peak wavelength is shifted into the shorter wavelength because of the negative temperature dependence of the birefringence of the PM-PCF (0.3pm/°C). As the applied strain increases, the peak wavelength of the transmission spectrum of the Sagnac loop mirror incorporating the EDF shifts into a longer wavelength (1.3pm/με) because the phase change of the proposed sensing probe is directly proportional to the applied strain. The transmission peak power, however, is not changed by the applied strain. Since the source and the sensing probe are integrated, the overall system configuration is significantly simplified without requiring any additional broadband light source. Therefore, it is possible to simultaneously measure temperature and strain by monitoring the variation of transmission peak power and peak wavelength, respectively.