Papers by Keyword: Softening

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Authors: Ladislas P. Kubin, Benoit Devincre, G.R. Canova, Yves Bréchet
Authors: Kyriakos I. Kourousis
Abstract: Advanced light metals have recently attracted the interest of the aerospace and automotive industry. The need for accurate description of their cyclic inelastic response under various loading histories becomes increasingly important. Cyclic mean stress relaxation and ratcheting are two of the phenomena under investigation. A combined kinematic isotropic hardening model is implemented for the simulation of the behavior of Aluminum and Titanium alloys in uniaxial mean stress relaxation and ratcheting. The obtained results indicate that the model can perform well in these cases. This preliminary analysis provides useful insight for the evaluation of the models capabilities.
Authors: Giovanni Minafò, Marinella Fossetti, Maurizio Papia, Giuseppe Patti
Abstract: Reinforced concrete (RC) jacketing is becoming increasingly common among the different retrofit techniques for poor RC members, due to its economical and practical advantages. Experimental investigations in the literature have shown that the actual axial capacity of RC jacketed members can be substantially lower than that analytically evaluated by adapting the most common theoretical models for confined concrete. This fact can be explained by taking into account the presence of tensile stresses developing in the concrete, due to a mutual interaction between the inner core and the external jacket. This phenomenon is relevant especially in members where the concrete properties of the jacket are different with respect to those of the core, causing the premature failure of the external layer. This paper presents a simplified approach able to evaluate these effects. Circular RC jacketed sections are studied and a model is presented to predict the concrete softening effect. The section is modeled by joining circular hollow layers and circumferential and radial stresses are firstly calculated under the assumption of linear elastic behaviour and plane strain state. The model is extended in the non-linear range by adopting a secant constitutive law. Finally, comparisons are made with experimental data available in the literature, showing good agreement.
Authors: Li Sun, W.M. Huang
Abstract: Abrupt softening phenomenon was observed in a shape memory CuAlNi single crystal upon uniaxial compression. Sudden martensite variant(s) reorientation was found to be the reason behind this anomalous behavior. The significance of this finding is twofold. On one hand, it clearly demonstrates that the stress induced transformation can follow a sequence of the phase transformation (martensitic transformation, austenite to martensite) and then reorientation (from one martensite variant to another). On the other hand, the anomalous softening provides a good evidence for explaining the propagation of the phase transformation front.
Authors: Ju Hua Xiong, Xiao Yong Kou, Fang Liu, Ming Jing Jiang
Abstract: Methane hydrate is ice-like clathrate compound that attracts global attention due to its huge potential as a future energy source. The constitutive law of methane hydrate-bearing sediments remains unknown and becomes a barrier in sustainable exploitation of methane hydrate from marine sediments. The Duncan-Change model is a nonlinear elastic model which was widely accepted by the geotechnical community in approximating the constitutive response of geo-materials. This model and its evolved versions were employed in this study to model the stress-strain response observed in triaxial tests on methane hydrate-bearing sands. Duncan-Chang type models capture well the strain hardening behaviors. However, they fall short of incorporating the dependency of temperature and saturation degree of methane hydrate, which have to be taken into account in future constitutive models of methane hydrate-bearing deposits.
Authors: František Šebek, Petr Kubík, Jindřich Petruška
Abstract: The paper presents a complex material model which covers the elastic-plastic behavior, material deterioration and ductile fracture. The calibration of such model was conducted for Aluminum Alloy (AA) 2024-T351 using specimens with various geometries and loading which covers various stress states. The model was then applied to the simulations of tensile test of plates. The computations were carried out in Abaqus/Explicit using the user subroutine Vectorized User MATerial (VUMAT), where the crack initiation and subsequent propagation was realized using the element deletion technique. The results were compared to the experimental observation in the end.
Authors: Erik Schlangen
Abstract: This paper describes a method to measure the 3D-microstructure of a material which can be used to perform fracture simulations. A model concrete is made and the 3D structure is obtained with a CTscanner. Uni-axial tensile tests are performed on cylindrical specimens of the model concrete a regular concrete and of a mortar. The model concrete shows more micro-cracking, a more tortuous crack path, a lower tensile load and a less brittle behaviour compared to the mortar and the regular concrete. Furthermore it is found that the opening of the crack is more uniform when the material is more heterogeneous, which results in a more stable fracture.
Authors: Erik Schlangen
Abstract: In a companion paper in this conference [1] an experimental study is presented that deals with measuring fracture properties and obtaining 3D images of the particle structure in heterogeneous materials as mortars and concrete. The fracture mechanisms observed in the tests are modelled with a 3D lattice model. The heterogeneity of the model is directly implemented from the 3D images obtained in a CT-scanner. With this method realistic crack patterns can be obtained.
Authors: Zong De Liu, Kun Yang, Xue Ping Mao, Shu Lin Bai, J.Y. An
Authors: Lilia R. Saitova, Heinz Werner Höppel, Matthias Göken, A.R. Kilmametov, Irina P. Semenova, Ruslan Valiev
Abstract: Ti-6Al-4V ELI (extra low interstitials) was processed by equal channel angular pressing in order to obtain an ultrafine-grained (UFG) microstructure which is known to enhance the fatigue behavior of metallic materials. Fatigue properties of UFG Ti-6Al-4V ELI were studied by strain and stress controlled fatigue tests. UFG Ti-6Al-4V ELI shows an improvement of the fatigue behavior compared to conventional grain (CG) size counterpart. Microstructural investigations prior to and after fatigue testing confirm a high structural stability of the UFG material. Hence, the UFG alloy has a high potential for prospective use in biomedical and engineering applications.
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