Papers by Keyword: Damage Model

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Authors: B. Michel, Thomas Helfer, I. Ramière, C. Esnoul
Abstract: This paper focuses on the numerical simulation of crack initiation and growth in ceramic materials. This work is devoted to nuclear fuel modelling under irradiation and more precisely to fuel pellet fragmentation assessment at macroscopic and microscopic scales. Simulation tools are developed in the framework of a cooperative program between the CEA, EDF and AREVA devoted to a unified fuel performance software environment called PLEIADES. A smeared crack model is proposed to have a continuous description of crack nucleation and growth at macroscopic scale. This unified description is based on crack extension process from the microscopic scale up to the macroscopic scale. In order to deal with unstable crack extension a specific algorithm is proposed to solve the quasi static nonlinear mechanical problem. A 3D application is presented to illustrate performances and robustness of the smeared crack approach to simulate crack extension in nuclear fuel ceramics. In this application with an internal pressure loading a new methodology is proposed in order to avoid convergence problem due to the indetermination of the quasi static formulation of a softening material equilibrium under Neumann boundary condition.
155
Authors: Fritz Klocke, Dieter Lung, Christoph Essig
Abstract: The aim of the presented work was to define a criterion for the prediction of chip breakage in turning C45E+N (AISI 1045). The chip formation, the chip flow and the expansion of the chip due to collision with the periphery were modelled three-dimensionally using the Finite Element Method (FEM). The mechanical loads in the chip breakage zone were determined by comparing the modelled chip with high speed filming records of the real chip breakage cycle. Based on the calculated loads in the chip breakage zone a novel damage criterion based on an approach of Johnson and Cook was developed. This criterion enables the FEM-model to simulate chip breakage three-dimensionally for different tool geometries and varying cutting parameters. The enhanced FE model correlated well with high speed filming records of the chip flow and breakage as well as with the empirical determined cutting forces and chip temperatures.
142
Authors: Kai Zhong Xie, Guang Qiang Chen, Li Lin Wei
Abstract: Collapse-mechanism analysis can simulate that bridges enter strong elasto-plastic and large displacement response and collapses phase, so that it is very important for the seismic design of bridges. In this paper, a damage model of reinforced concrete is introduced, and dynamic response and collapse of long span and high-pier continuous rigid frame bridge during strong earthquake is studied with damage model of reinforced concrete by the explicit dynamic analysis code (LS-DYNA). The simulation results indicate the development of the concrete elements from cracking to failure and the bridge from part collapse to the whole collapse of the bridge are studied. The damage and collapse mechanisms during strong earthquake are given of Long Span and High-pier Continuous Rigid Frame Bridges. References are provided for seismic analysis of this kind of bridges.
1431
Authors: Yong Ji, Hirohisa Narita, Lian Yi Chen, Hideo Fujimoto
Abstract: As environmental problems have become more serious, a sustainable society is necessary. To realize the inverse manufacturing system the prime problem is how to improve the rate of reusing the product modules. Therefore analyzing the life-time of the disassembled modules is very important before reassembling process. In this paper, a cumulative damage model is proposed to discuss the quality of the product that is assembled by reuse modules. It is supposed that modules suffer damages due to shocks and fails when the cumulative damage level exceeds the failure level. Then maintenance cost will be analyzed in order to minimize the expected maintenance cost-rate by optimal maintenance time T and optimal number of damages N in this cumulative damage model. The probable safe life-time of module reuse will be explored. Finally numerical examples are given to confirm the validity of the proposed model.
177
Authors: Dong Qing He, Bo Liu
Abstract: Based on the least squares theory and a damage variable , a damage model is formed for the freeze-thaw degradation of the layered hybrid fiber reinforced concrete (LHFRC). By the model the degradation equations for the LHFRC and the plain concrete(PC) are regressed with the experimental data, which are identical in the initial phase and different in the damage propagation phase and the is used to describe the damage process of concrete subjected to freeze-thaw cycles. The of LHFRC is smaller than that of PC in the damage propagation phase. Furthermore, the frost resistance of LHFRC is stronger than that of PC due to steel fibers and polypropylene fibers having retarded the degradation of concrete.
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Authors: Robert Jankowski
Abstract: The reports after earthquakes indicate that earthquake-induced pounding between insufficiently separated structures, or their parts, may cause substantial damage or even lead to structural collapse. One of the most spectacular example of pounding-involved destruction resulted from interactions between the Olive View Hospital main building and one of its independently standing stairway towers during the San Fernando earthquake of 1971. The aim of the present paper is to assess the range and intensity of damage caused by collisions between these reinforced concrete structures based on the results of a detailed 3D non-linear FEM analysis of poundinginvolved response. In the study, reinforced concrete has been modelled as layered material with rebar elements embedded into concrete. The non-linear material behaviour, including stiffness degradation of concrete due to damage under cyclic loading, has been incorporated in the numerical model. The results of the study show that pounding may lead to the significant increase of the range and intensity of damage at the base of the stairway tower, as a lighter structure, as well as may cause substantial damage at the points of contact. On the other hand, the intensity of damage induced in the heavier main building has been found to be nearly unaffected by structural interactions.
339
Authors: Maria Doig, Karl Roll
Abstract: Due to increasing demands to reduce C02-emission and to augment occupant’s safety new modern materials are developed ongoing. Because of relatively low production costs, high strength and simultaneously good formability the advanced high strength steels (AHSS) are applied among others for the lightweight design of body-in-white components in the automotive industry. Their already mentioned properties follow from the presence of mixed mild and hard ferrous phases. Due to this multiphase microstructure of the most AHSS steels, a complex material and damage behavior is observed during forming. The damage grows in a ductile manner during plastic flow and the cracks appear without necking. They are often characterized as the so called shear cracks. The damage predictions with standard methods like the forming limit curve (FLC) lack accuracy and reliability. These methods are based on the measurement of linear strain paths. On the other hand ductile damage models are generally used in the bulk forming and crash analysis. The goal is to prove if these models can be applied for the damage prediction in sheet metal forming and which troubles have to be overcome. This paper demonstrates the capability of the Gurson-Tvergaard-Needleman (GTN) model within commercial codes to treat industrial applications. The GTN damage model describes the existence of voids and they evolution (nucleation, growth and coalescence). After a short introduction of the model the finite element aspects of the simulative damage prediction have been investigated. Finally, the determination of the damage model parameters is discussed for a test part.
482
Authors: Zhen Wei Wang, Ping An Du, Ya Ting Yu
Abstract: Mechanical components are subjected heavy alternate load in industries, such as engine crankshaft, wheel axle, etc. The fatigue failure happens after a long work loading, which affects the production cost, safe and time. So the fatigue life predication is fundamental for the mechanical components design. Especially, it is very important for heavy, high-speed machinery. In this paper, both main fatigue life predication formulas are introduced briefly, including Manson-Coffinn formula and Damage strain model. Then, shortages of above life predication formulas are pointed out, and coefficients are explained in detail. Further calculation error analysis is conducted on the basis of experiments on 16 materials. Results show that above life predication formulas lack calculation accuracy. Finally, it is pointed out that coefficients of fatigue life predication formulas are dependent of material performance. So it is unreliable that coefficients are constants for Manson-Coffin and Damage strain model.
1599
Authors: Se Young Yang, Woon Seong Kwon, Soon Bok Lee, Kyoung Wook Paik
Abstract: The use of anisotropically conductive adhesives (ACA) for the direct interconnection of flipped silicon chips to printed circuits (flip chip packaging), offers numerous advantages such as reduced thickness, improved environmental compatibility, lowered assembly process temperature, increased metallization options, cut downed cost, and decreased equipment needs. Despite numerous benefits, ACA film type packages bare several reliability problems. The most critical issue among them is their electrical performance deterioration upon consecutive thermal cycles attributed to gradual delamination growth through chip and adhesive film interface induced by CTE mismatch driven shear and peel stresses. In this study, warpage of the chip is monitored by real time moiré interferometer during –50oC to +125oC temperature range. Moreover, reduction in chip warpage due to increase in delamination length is obtained as in function of thermal fatigue cycles. Finally, a new model to predict damage level of ACA package and remained life is proposed and developed.
887
Authors: Seyed Saleh Mostafavi, Liang Chi Zhang, Jason Lunn
Abstract: Edge chipping by an indenter has been used to investigate the fragmentation of brittle materials. This paper proposed a constitutive model for studying both the initiation and propagation of cracks during the chipping of concrete. The analysis was carried out by the finite element method using a commercially available code, LS-DYNA. The results showed that a zone with very high compressive stresses appears beneath the indenter and causes the material to break or crush. Most of the external work, about 78%, was dissipated in the crushing zone while only a small percentage (less than 17%) contributed to form chips/fragments. As the indentation proceeded, radian-median cracks initiated and propagated downward and parallel to the front surface of the material to form a half penny crack. The crack tips from both sides of the indenter on the surface would then deviate toward the free edge, leading to a chipping scallop at a critical load.
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