Papers by Keyword: Strain Field

Abstract: The strain field of η′ phase in an aged 7000 series aluminum alloy has been investigated using a combination of high resolution transmission electron microscopy (HRTEM) and geometric phase analysis (GPA) technique in this paper, and strain components ε_xx, ε_yy were mapped, respectively. The results showed that the strain is mainly generated near the matrix/η′ phase interface and gradually decreases with distance increasing away from the interface. There were convergence and divergence regions of the strain within the η′ phase, and maximum strain occurred in the position where about 0.25 nm far from the interface, value of the maximum strains was about 2.54%.

Abstract: The ZnO semiconductor multicrystalline film is utilized as the sensing material, and a sensors array is demonstrated in this paper. Based on the coupling effect of piezoelectric and semiconducting, an ultra-high sensitivity to the deformation is obtained that the gauge factor of the single units is derived up to 199, which is 100 times of that of the commercial foil gage (gauge factor = 2). After calibration on every sensing unit, the distribution of the uniform and non-uniform strain applied on the device is measured and mapped by the sensors array successfully. The results show a good application of the device on the deformation field sensing by contact test method.

Abstract: Full-field measurement methods have emerged in the last years and these methods are characterized by directly providing displacement and strain fields for all points over the specimen surface. Thus, the design of heterogeneous tests can be performed for material parameter identification purposes since the inhomogeneous strain fields can be measured. However, (i) no defined criterion yet exists for designing new heterogeneous tests, (ii) it is rather difficult to compare and rate different tests and (iii) a quantitative way to define the best test for material behavior characterization of sheet metals has yet to be proposed. Due to this, the goal of this work is the development of a global indicator able to assess mechanical tests. The proposed indicator quantifies the strain state range, the deformation heterogeneity and the strain level achieved in the test, based on a continuous evaluation of the strain field up to rupture. This global indicator was applied to rank some classical tests, such as uniaxial tensile, simple shear, plane strain and biaxial tensile tests. These tests were carried out numerically by reproducing the virtual behavior of DC04 mild steel. A constitutive model composed by the non-quadratic Yld2004-18p yield criterion combined with a mixed isotropic-kinematic hardening law and a macroscopic rupture criterion was used. The performance of the tests was compared with the indicator and a ranking was established. The results obtained show that biaxial tension is the test providing more information for the mechanical behavior characterization of the material. It was also verified that plane strain test presents a better performance than simple shear and uniaxial tensile tests.

Abstract: Dislocation core structures in Au and Cu crystals are investigated by means of quasicontinuum simulations combined with the embedded atom method potentials. A dislocation pair in a graphene sheet, which is observed by Warner et al. experimentally, is also analyzed in the present work. The strain fields around these dislocations in Au, Cu, and graphene crystals are calculated by analyzing the coordinates of discrete atoms, which is a strain tensor calculation method proposed by Zimmerman et al., and compared with theoretical predictions based on Foreman dislocation model. It is shown that the strain fields given by Zimmerman theory are completely suitable for describing the dislocation core structures of Au, Cu and graphene crystals. However, compared with the results of Au and Cu, the Zimmerman strain field in the vicinity of graphene dislocation core is a little less accurate, possibly due to the effect of lattice symmetry of graphene, which needs to be clarified in the future study.

Abstract: The contribution deals with the investigation of the influence of facet size and smoothing on the results obtained by low-speed digital image correlation (DIC) system by strain analysis performed on specimen with a small hole loaded by tension loading. In conclusion the obtained results are verified by a numerical solution using finite element method.

Abstract: Dynamic stress-strain states in Voronoi honeycombs are investigated by using cell-based finite element models. Two different loading scenarios are considered: the high-constant-velocity compression and the direct impact. The 2D local engineering strain fields are calculated. According to the feature of shock front propagation, the 1D distribution of local engineering strain in the loading direction is deduced from the 2D strain fields, which provide evidences of the existence of discontinuities at shock front in cellular materials and thus enhance the basis of the continuum-based shock models. A method to quantitatively clarify the local stress-strain states ahead of and behind the shock front is developed. The results show that the dynamic stress-strain states in the densification stage obtained from both loading scenarios are different from the quasi-static stress-strain relation. The stress ahead of the shock front obtained from the high-constant-velocity compression scenario is slightly smaller than the quasi-static yield stress, but that obtained from the direct impact scenario is larger than the quasi-static yield stress. The possible mechanisms of deformation and wave propagation are explored.

Abstract: In order to elucidate the different characters of elastic waves caused respectively by screw and edge dislocation movement, we calculated the stain field disturbance caused by migration of dislocation by elastic theory. Through the calculation, it was found that the strain field disturbance resulted from screw dislocation migration produces a transverse wave radiation while that resulted from edge dislocation migration produces transverse wave and longitudinal wave simultaneously. The result reveals the different energy radiation characters of screw dislocations and edge dislocations and explains the reason that edge dislocation moves faster than screw dislocation in general experiment. It also provides a theoretical basis for determining microcosmic mechanism of plastic deformation of metals by monitoring the changes of elastic waves.

Abstract: Combining the site relocation project of New Era Cement Co. Ltd, the early temperature and strain monitoring and numerical simulation are done on the cement vertical mills mass concrete equipment foundation sizing 15.6m×15.6m×5m, thus, the early trends and rules of mass concrete about temperature and strain are analyzed. Prevent temperature cracks due to temperature strain in mass concrete, therefore, ensure the construction quality of mass concrete.

Abstract: This work describes an experimental procedure to measure the progressive strain localization and crystal lattice rotation within metallurgical grains. A digital image correlation software was implemented and associated with mechanical tests carried out inside a scanning electron microscope on specimens exhibiting nanometric grainy patterns. Cross-correlation analyzes between electron backscattering diffraction maps were also developed to quantify the corresponding local crystal rotation relative to the original structure. The microscale strain and rotation fields on the surface of a tensile-loaded specimen made of austenitic stainless steel 316L are presented as an illustration. Their direct spatial correlation between strain heterogeneities and the progressive activation of slip systems is put into evidence and discussed.

Abstract: Based on the application of the CSI non-contact full field strains and 3D displacements gauge made in USA in the laboratory for wind engineering of Southwest Jiaotong University, the theory of DIC, a non-contact deformation measurement method, is studied in the paper. The reliability of the method is testified by contrast tests. The paper also offers some useful advice byanalysing the factors that affect the measurement accuracy.