Ageing Degradation of Concrete Dams Based on Damage Mechanics Concepts

2009 ◽  
pp. 21-35 ◽  
Author(s):  
Somasundaram Valliappan ◽  
Calvin Chee
Keyword(s):  
Damage Mechanics ◽  
Concrete Dams ◽  
Mechanics Concepts

Application of Damage Mechanics and Polynomial Chaos Expansion for Lifetime Prediction of High-Temperature Components Under Creep-Fatigue Loading

2020 ◽  
Author(s):  
Felix Koelzow ◽  
Muhammad Mohsin Khan ◽  
Christian Kontermann ◽  
Matthias Oechsner
Keyword(s):  
High Temperature ◽  
Power Plants ◽  
Damage Mechanics ◽  
Fatigue Loading ◽  
Probabilistic Methods ◽  
Lifetime Prediction ◽  
Model Parameters ◽  
Creep Fatigue ◽  
High Temperature Components ◽  
Mechanics Concepts

Abstract Several (accumulative) lifetime models were developed to assess the lifetime consumption of high-temperature components of steam and gas turbine power plants during flexible operation modes. These accumulative methods have several drawbacks, e.g. that measured loading profiles cannot be used within accumulative lifetime methods without manual corrections, and cannot be combined directly to sophisticated probabilistic methods. Although these methods are widely accepted and used for years, the accumulative lifetime prediction procedures need improvement regarding the lifetime consumption of thermal power plants during flexible operation modes. Furthermore, previous investigations show that the main influencing factor from the materials perspective, the critical damage threshold, cannot be statistically estimated from typical creep-fatigue experiments due to massive experimental effort and a low amount of available data. This paper seeks to investigate simple damage mechanics concepts applied to high-temperature components under creep-fatigue loading to demonstrate that these methods can overcome some drawbacks and use improvement potentials of traditional accumulative lifetime methods. Furthermore, damage mechanics models do not provide any reliability information, and the assessment of the resultant lifetime prediction is nearly impossible. At this point, probabilistic methods are used to quantify the missing information concerning failure probabilities and sensitivities and thus, the combination of both provides rigorous information for engineering judgment. Nearly 50 low cycle fatigue experiments of a high chromium cast steel, including dwell times and service-type cycles, are used to investigate the model properties of a simple damage evolution equation using the strain equivalence hypothesis. Furthermore, different temperatures from 300 °C to 625 °C and different strain ranges from 0.35% to 2% were applied during the experiments. The determination of the specimen stiffness allows a quantification of the damage evolution during the experiment. The model parameters are determined by Nelder-Mead optimization procedure, and the dependencies of the model parameters concerning to different temperatures and strain ranges are investigated. In this paper, polynomial chaos expansion (PCE) is used for uncertainty propagation of the model uncertainties while using non-intrusive methods (regression techniques). In a further post-processing step, the computed PCE coefficients of the damage variable are used to determine the probability of failure as a function of cycles and evolution of the probability density function (pdf). Except for the selected damage mechanics model which is considered simple, the advantages of using damage mechanics concepts combined with sophisticated probabilistic methods are presented in this paper.

The Influence of Microstructure on the Tensile Damage of Lamellar Grey Cast Iron

1984 ◽  
Vol 34 ◽  
Author(s):  
A. Fontaine ◽  
G. Zambelli
Keyword(s):  
Cast Iron ◽  
Cross Sections ◽  
Damage Mechanics ◽  
Degradation Process ◽  
Grey Cast Iron ◽  
Heterogeneous Microstructure ◽  
The Matrix ◽  
Grey Cast ◽  
Mechanics Concepts ◽  
Two Parameters

ABSTRACTThe rupture behaviour of lamellar grey cast iron under tension depends on the overall damage suffered by the heterogeneous microstructure. In order to quantify the influence of microstructural components on the rupture behaviour of the material, it is therefore preferable to apply “Damage Mechanics” concepts rather than “Linear Fracture Mechanics”. In this preliminary study the damage process is assumed to be isotropic and two parameters are considered; firstly a damage limit σ0 and secondly, a damage rate B. Measurements made on a grey cast iron, cast in three different cross sections, show that these damage parameters may be used to separate the contributions of the graphite network and the matrix wich interact in the degradation process of the heterogeneous microstructure of lamellar grey cast iron.

scholarly journals To the modelling of the fatigue cracks propagation in a thin isotropic plates under biaxial asymmetric tension-compression

2019 ◽  
pp. 154-157
Author(s):  
Alla Plashchynska
Keyword(s):  
Circular Hole ◽  
Cyclic Load ◽  
Damage Mechanics ◽  
Fatigue Cracks ◽  
Equivalent Stress ◽  
Plane Stress State ◽  
Isotropic Plates ◽  
Cracks Propagation ◽  
Mechanics Concepts ◽  
Joint Consideration

The modelling of the fatigue fracture process of the thin isotropic infinite plates with cracks under external biaxial asymmetric cyclic loading is considered. The solution of the problem is based on the joint consideration of the fracture mechanics and continuous damage mechanics concepts and using two types of equivalent stress criteria’s. The first one reduces an asymmetrical cyclic load to the equivalent symmetric cyclic load in time of the rupture. The second one reduces a plane stress state in the vicinity of the top crack to a single-axial one. The obtained system of equations of the model a relatively equivalent stress intensity factor allows us to determine the duration of the incubation stage and the rate of fatigue crack propagation in plates with different stress concentrators. The calculated dependences of the crack length, which extends from the circular hole, from the number of load cycles in the infinite aluminum plate with a circular hole at the variation of the parameters of the asymmetrical cycle and the coefficient of the biaxiality loading are constructed.

Prediction of Ductile Material Failure by Using Innovative Damage Mechanics Concepts

2017 ◽  
Author(s):  
Simon Schaffrath ◽  
Markus Feldmann ◽  
Victoria Brinnel ◽  
Sebastian Münstermann ◽  
Denis Novokshanov
Keyword(s):  
Wall Thickness ◽  
Pressure Vessel ◽  
Damage Mechanics ◽  
Monotonic Loading ◽  
Ductile Material ◽  
Material Failure ◽  
Loading Conditions ◽  
Safety Factors ◽  
Mechanics Model ◽  
Mechanics Concepts

Material failure and plastic instability are currently in ASME and EN pressure vessel and piping standards prevented by applying experience-based safety factors. Due to the few existing experimental test results and the inaccuracy of the incorporated design equations, these safety factors are quite high. In particular, modern high strength steels are penalized because of the small yield-to-tensile ratio. Apart from monotonic loading conditions, an economical design of pressurized components to prevent material failure due to ultra-low-cycle fatigue (ULCF) is a big topic. Experimental tests are in general very expensive and not suitable for the common design. Therefore, a numerical based prediction of the actual burst pressure and the resistance against strong cyclic loading conditions would be favourable. During the last decades innovative damage mechanics concepts have been developed and successfully validated in the scope of structural and plant engineering. Depending on the size of the component and the applied loading condition, several different damage mechanics models are available. During the studies presented in this paper, a phenomenological damage mechanics model proposed by Bai and Wierzbicki has been utilized. It has been developed to describe the material failure in the upper shelf of the toughness temperature transition curve in case of monotonic loading conditions. Considering an extension based on the effective strain concept proposed by Ohata and Toyoda, the combined model is also able to predict failure in the range of ULCF. The presented work aims at validating the accurate numerical prediction of failure by using this damage mechanics model. Validation is performed by comparing numerical and experimental results of a burst test of a pressure vessel and cyclic deformation tests of almost constant pressurized bended pipes. The pressure vessel made of HSLA steel P690Q had a length of 3.0 m, a diameter of 1.2 m and a wall thickness of 50 mm. Tests on bended pipes can be separated in two series. A first series made of steel X60 with a diameter of 16 “ and a wall thickness of 9.5 mm as well as a second series made of steel X65 with a diameter of 8.625 “ and a wall thickness of 5.6 mm. The comparison of experimental and numerical results shows an acutely satisfying prediction of failure. Both, time point and location of failure coincide well. Mesh size dependency must be considered but the approach seems to be promising for further applications.

Damage–Rupture Process of Concrete Dams Under Strong Earthquakes

2014 ◽  
Vol 14 (07) ◽  
pp. 1450021 ◽  
Author(s):  
Hou-Qun Chen ◽  
De-Yu Li ◽  
Sheng-Shan Guo
Keyword(s):  
Damage Mechanics ◽  
Damage Model ◽  
Residual Deformation ◽  
Rupture Process ◽  
Arch Dam ◽  
Concrete Dams ◽  
Dam Foundation ◽  
Strong Earthquakes ◽  
Plastic Damage ◽  
Seismic Behaviors

A new concept for establishing the damage model for high concrete dams under earthquakes based on damage mechanics is presented in this paper. Unlike the conventional approach of considering the residual deformation by means of plastic-damage coupling, the proposed approach relates the degraded apparent elastic moduli of loading and unloading directly to the material experimental data. As such, the nonlinear analysis of the seismic response of dam-foundation systems is simplified and more reasonable, with no recourse to plastic-damage coupling. To verify the proposed approach of damage–rupture process for high concrete dams, the seismic behaviors of the Koyna gravity dam in India and the Shapai RCC arch dam in China both subjected to strong earthquakes were examined. It is demonstrated that the proposed approach can be reliably used to study the damage–rupture behavior of concrete dams under strong earthquakes.

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