Papers by Keyword: Strain Localization

Abstract: We address the differences in yield stresses between hot and cold rolled medium manganese steel showing continuous yielding. Continuous yielding in both, the hot and cold rolled samples were resulting from reverted austenite islands plastically deforming first and less strain in the tempered martensite matrix. At higher global strains, strain was taken up not only by the reverted austenite, but also by tempered martensite and fresh martensite formed from the austenite through martensitic phase transformation during deformation. Strain localization was also observed in the hot rolled samples. This localization is caused by cumulative deformation of colonies of lamellar reverted austenite islands. It is interpreted in terms of the spatial alignment of austenite colonies to the loading direction in addition to the crystallographic orientation.

Abstract: This work presents some novel results obtained by using the strain injection techniques for modeling crack propagation in challenging 3D benchmark tests. The techniques were already tested and validated by static and dynamic simulations in 2D ADDIN EN.CITE ADDIN EN.CITE.DATA [ HYPERLINK \l "_ENREF_1" \o "Dias, 2012 #1526" 1-4], so the main goal of this paper is to verify if the most important advantages of the method, low computational cost and independence of the results on the finite element mesh, are kept in 3D. The methodology, implemented in the finite element framework, consists essentially in injecting those elements that are going to capture the cracks with some enhanced strain modes for improving the performance of the elements for modeling propagating material failure.

Abstract: The present contribution aims to investigate the ability of drawing predictive conclusions from homogenization in case of damage. Therefor, two topics will be addressed. On the one hand, material properties for the constituents on the microscale have to be derived, to render a predictive homogenization possible. The investigation at hand is concerned with glass fiber reinforced epoxy resin. In this example the properties of the fiber and the matrix have to be studied individually by experiments. Furthermore, the interface between both materials needs to be examined. To this end experiments on several models of single fiber composites have been developed in the literature. For the present material combination single fiber fragmentation tests and pullout tests have been conducted and evaluated. On the other hand, boundary conditions are necessary, that allow for the strain localization in a volume element without leading to spurious localization zones.

Abstract: Digital image correlation (DIC) became indispensable when monitoring and analyzing adevelopment of displacement or strain fields. The method is capable of capturing strain localization, itis not limited to a relative measurement of discrete points as conventional methods and appears to bemore accurate than measurements by means of extensometers or strain-gauges that often suffer fromimperfect attachment to the measured surface. As open source DIC tools appear, the method becomesfeasible and the development is supported by the growing computational power of modern computers.The presented paper introduces open source 2D DIC tools and simple rules to follow when employingthe method. The presented case study on behavior of fiber reinforced high-performance concretedemonstrates a computational feasibility, accuracy and sensitivity of the method for a relatively lowfinancial cost.

Abstract: This paper summarizes the implementation of an elasto-plastic constitutive model for a micro-polar continuum in the constitutive models framework of the software INSANE (INteractive Structural ANalysis Environment). Such an implementation is based on the tensorial format of a unified constitutive models formulation, that allows to implement different constitutive models independently on the peculiar numerical method adopted for the solution of the problem. The basic characteristics of the micro-polar continuum model and of the unified formulation of constitutive models are briefly recalled. A generalization of the micro-polar model is then introduced in order to include this model in the existent tensor-based formulation. Finally, an enhanced version of the general closest-point algorithm, ables to manage the generalized micro-polar formulation, is derived. A strain localization problem modeling illustrates the implementation.

Abstract: This paper investigates the impact of strain sensitivity on the linear model mock-up bearing (LMMB) using digital image correlation (DIC) technique. This work addresses the lack of norms, standards, reference of elastic/plastic deformation of bearings elements. Towards that, experimental set-up was designed and fabricated with a set of LMMB (AISI4140) with commercially purchased steel balls (AISI52100) to study the raceway relative approach and localized strain rate on steel ball, wherein raceway relative approach is measured using LVDT & screw gauge and results are compared with DIC results. These data are very much useful in design and development of large diameter slewing bearing for fast breeder reactor and also these results can be used to optimize the number of ball, load, and tolerance on bearing.

Abstract: Damp Newton algorithm based on FEPG system is developed for calculating strain softening problem. The algorithm can solve displacement and yield surface equation simultaneously. Soften modulus is introduced into D-P yield function. The example result shows that, the algorithm with damp factor can be used to solve softening problems. The plastic theory described by finite element weak form has no requirement of continuity, so appropriate outcome can be obtained by first-order element. Descent segment of stress-strain curve and cloud picture of finite shear band are presented.

Abstract: Bendability is an important material property for ultra-high strength steel. The bendability of a certain material is expressed as the minimum bending radius R_min of the inner surface of the bend and expressed in multiples of the sheet thickness. Bendability is limited by either cracking on the surface or the edges of the bend or by surface waviness that usually precedes cracking on the outer surface. Surface waviness is a form of strain localization in bending and the intensity of the phenomenon is dependent on e.g. the punch radius, the lower tool width and the sheet thickness. In this study the bendability of a 960MPa grade steel was investigated using optical strain measurements of three-point bending tests to determine the strain level and the bending angle when localization starts with different punch radii. The unbent samples were marked with a grid using laser marking and the deformation was measured with the GOM ARGUS strain analysis system after bending. The quality of the bend was also evaluated visually. In addition, tensile tests were performed and evaluated with the GOM ARAMIS deformation analysis system to investigate the local mechanical properties of the studied steel. The results of strain measurements and visual evaluation were then compared. It was found that beyond a certain angle the maximum strain across the bend did not significantly change with further increases in the bending angle when the punch radius was at least three times the sheet thickness. But with smaller punch radii the maximum strain increased almost linearly with increasing bending angle until fracture appeared. With the smaller punch radii deformation localizes and surface waviness begins to form in smaller bending angles because the deformation is concentrated in a narrow zone.

Abstract: Plastic strain localization patterns in compression-strained alkali halide (NaCl, KCl, and LiF) crystals have been studied using a double-exposure speckle photography technique. The main parameters of strain localization autowaves at the linear stages of deformation hardening in alkali halide crystals have been determined. A quantitative relationship between the macroscopic parameters of plastic flow localization and microscopic parameters of strained alkali halide crystals has been established.

Abstract: In the present study, the features of plastic strain localization and structure of polycrystalline low carbon steel Fe-0.07%C were investigated after hot rolling and electrolytic hydrogen saturation. The method of double-exposure speckle photographyhave been used for identification of main types and parameters of plastic flow localization at different stages of strain hardening.Shown the effect of hydrogen on changing of defect substructure and cementite morphology by using optical and electron microscopy.