Papers by Keyword: Damage Model

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Authors: Dario Gastaldi, Valentina Sassi, Lorenza Petrini, Maurizio Vedani, Stefano P. Trasatti, Francesco Migliavacca
Abstract: The main drawback of conventional stenting procedure is the high risk of restenosis. The idea of a stent that "disappears" after having fulfilled its mission is very intriguing and fascinating. The stent mass should diminishing in time to allow the gradual transmission of the mechanical load to the surrounding tissues. Magnesium and its alloys seem to be among the most appealing materials to design biodegradable stents. The objective of this work is to develop, in a finite element (FE) framework, a model of magnesium degradation able to predict the corrosion rate and thus providing a valuable tool to design biodegradable stents. Continuum damage approach is suitable for modelling different damage mechanisms, including several types of corrosion. Corrosion is modelled by a scalar damage field which accounts for the material strength loss due to geometrical discontinuities. As damage progresses, the material stiffness decreases. Corrosion damage results as the superposition of stress corrosion process and uniform corrosion. The former describes the stress-mediated localization of the corrosion attack through a stress-dependent evolution law similar to the one used in analytical models, while the latter affects the free surface of the material exposed to an aggressive environment. The effects of both phenomena described are modelled through a linear composition of the two specific damage evolution laws. The model, developed in a FE framework, manages the mesh dependency, typical of strain-softening behaviour, including the FE characteristic length in the damage evolution law definition. The developed model is able to reproduce the behaviour of different magnesium alloys subjected to static and slow-strain-rate corrosion tests. Moreover, 3D stenting procedures accounting for the interaction with the arterial vessel are simulated.
Authors: Hamdi Aguir, Hedi Bel Hadj Salah
Abstract: The simulation of the metal forming processes requires accurate constitutive models describing the material behaviour at finite strain, and taking into account several conditions. The choice of a rheological model and the determination of its parameters should be made from a test that generates such conditions. The major difficulty encountered is that there is no experimental test satisfying all these criteria. The use of more than one test seems well adapted, and is utilized to characterize the rheological behaviour at operating conditions corresponding to metal forming applications. Inverse analysis is then considered. Therefore, the difficulty lies with the long computing time that was taken when an optimization procedure is coupled with a finite element computation (FEC) to identify the material parameters. In order to solve the computing time problem, this paper proposes a hybrid identification method based on an artificial neural network and a genetic algorithm (ANN-GA). The proposed strategy is applied to identify the damage material parameters of the AISI 304 steel and using the bulge test.
Authors: Hui Mei Zhang, Geng She Yang
Abstract: Considering the heterogeneous characteristics of rock at mesoscopic level, the damage propagation constitutive relation and evolution equation of freeze-thaw and loaded rock were established by using the theory of macro phenomenological damage mechanics and the generalized theory of strain equality. The evolutionary mechanisms of micro-structural damage and materials mechanical properties for the loaded rock were discussed under freeze-thaw condition, verified by experimental results of the freeze-thaw cycle and compression test of rock. It is shown that the freeze-thaw and loaded damage model can represent the complicated relations among the freeze-thaw, load and the damage inside the rock, reveal the coupling failure mechanism of macroscopic rock under the freeze-thaw and load from the micro-damage evolution. The combined effect of freeze-thaw and load exacerbates the total damage of rock with obvious nonlinear properties, but the coupling effect weakens the total damage. The lithology and initial damage state of the freeze-thaw and loaded rock in engineering structures in cold regions determine the weights of influence factors to mechanical properties, including environmental factor, loading factor and the coupling effects, so the rock performances different damage mechanical characteristic.
Authors: Wei Wei Yu, Xuan Guo
Abstract: This paper builds the formulations of damage model for dissipative materials with generalized non-linear strength theory. The proposed model reflects the internal structural configuration and damage behavioure. The structural evolution parameters are introduced to account for the progressive loss of the internal structure. The proposed damage model is proposed by generalized non-linear strength theory, the capability of the models in predicting behavior of clay has been examined.
Authors: Christian Carloni, Susanna Casacci, Stefano de Miranda, Angelo Di Tommaso, Cristina Gentilini, Francesco Ubertini
Abstract: Experimental and numerical results show that the predominant failure mode of FRP strengthened masonry structures is the interfacial debonding, which occurs prior to reaching the compressive strength of the substrate and/or the tensile strength of the FRP composite. In this paper, a three-dimensional numerical model is developed to simulate the experimental response of direct shear test of FRP-masonry joints and. A damage model is adopted for both mortar and bricks characterized by a different behavior in tension and compression.
Authors: Massimiliano Lucchesi, Barbara Pintucchi, Nicola Zani
Abstract: A FE beam model to perform static and dynamic analysis of fiber-reinforced masonry arches is presented. Based on a constitutive equation formulated for no-tension masonry beams, the model accounts for a limit to the material deformability and provides for irreversible damage occurring under compression. In order to capture any possible FRP debonding, a procedure is also formulated to reduce the performance of the fiber when the tangential and normal stresses at the masonry-composite interface reach a critical value. Some dynamic analyses are performed on a case study with the aim of evaluating the effectiveness of FRP-retrofitting in improving seismic performances.
Authors: Rong Guo, Shuang Guo, Rong Xia Wang
Abstract: Abstract. In order to establish damage model of concrete-filled rectangular tubular (CFRT) column, the paper utilized the cumulative dissipated hysteretic energy through 7 CFRT columns’pseudo static test. Moreover, the earthquake damage model based on CFRT columns has been set up by regression analysis. The damage model offers references for reinforcing the damaged structures caused by earthquakes and evaluating the ability of aseismatic of structures.
Authors: Zhi Ying Chen, Xiang Huai Dong
Abstract: Uniaxial tension tests for galvanized steel sheets are performed. Fractured surfaces of the specimens are observed by means of the scanning electron microscope (SEM). It is confirmed that the specimens experience ductile fracture. Based on the Gurson meso-damage theory, Hill’48-GTN anisotropic damage model is presented, and used to analyze the uniaxial tension test. The true stress-strain curves are fitted by three kinds of main flow stress models. After comparing the fitting precisions, the Voce model is selected as the flow stress model for the simulation analysis. The simulation results show that the Hill’48-GTN model can be used to accurately predict the whole process of damage occurrence, evolution and fracture in tension, and void volume fraction can be taken as a forming limit parameter of sheet metal forming.
Authors: Wooram Noh, Dong Hoon Yoo, Young Woo Koh, Kwan Soo Chung, Xin Yang
Abstract: Resistance spot welding (RSW) is commonly employed in the automotive industry to join sheet metal parts, which often involves several thousands of welds for one vehicle. Therefore, the proper evaluation of their formability/failure behavior is so vital to accurately predict overall crash performance of vehicles. In this work, the failure performance of spot welds has been experimentally and numerically analyzed for welds in which the base material is the TRIP (Transformation induced plasticity steel) 980 sheet. The mechanical properties of the base and welds have been characterized utilizing the inverse method based on the standard and miniature simple tension tests along with the lap-shear tests.
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