Intelligent-based Structural Damage Detection Model
Lee, Eric Wai Ming; Yu, K.F.
2010-05-21
This paper presents the application of a novel Artificial Neural Network (ANN) model for the diagnosis of structural damage. The ANN model, denoted as the GRNNFA, is a hybrid model combining the General Regression Neural Network Model (GRNN) and the Fuzzy ART (FA) model. It not only retains the important features of the GRNN and FA models (i.e. fast and stable network training and incremental growth of network structure) but also facilitates the removal of the noise embedded in the training samples. Structural damage alters the stiffness distribution of the structure and so as to change the natural frequencies and mode shapes of the system. The measured modal parameter changes due to a particular damage are treated as patterns for that damage. The proposed GRNNFA model was trained to learn those patterns in order to detect the possible damage location of the structure. Simulated data is employed to verify and illustrate the procedures of the proposed ANN-based damage diagnosis methodology. The results of this study have demonstrated the feasibility of applying the GRNNFA model to structural damage diagnosis even when the training samples were noise contaminated.
Ductile damage modeling based on void coalescence and percolation theories
Tonks, D.L.; Zurek, A.K.; Thissell, W.R.
1995-09-01
A general model for ductile damage in metals is presented. It includes damage induced by shear stress as well as damage caused by volumetric tension. Spallation is included as a special case. Strain induced damage is also treated. Void nucleation and growth are included, and give rise to strain rate effects. Strain rate effects also arise in the model through elastic release wave propagation between damage centers. The underlying physics of the model is the nucleation, growth, and coalescence of voids in a plastically flowing solid. The model is intended for hydrocode based computer simulation. An experimental program is underway to validate the model.
NASA Astrophysics Data System (ADS)
Grelot, Frédéric; Agenais, Anne-Laurence; Brémond, Pauline
2014-05-01
In France, since 2011, it is mandatory for local communities to conduct cost-benefit analysis (CBA) of their flood management projects, to make them eligible for financial support from the State. Meanwhile, as a support, the French Ministry in charge of Environment proposed a methodology to fulfill CBA. Like for many other countries, this methodology is based on the estimation of flood damage. Howerver, existing models to estimate flood damage were judged not convenient for a national-wide use. As a consequence, the French Ministry in charge of Environment launched studies to develop damage models for different sectors, such as: residential sector, public infrastructures, agricultural sector, and commercial and industrial sector. In this presentation, we aim at presenting and discussing methodological choices of those damage models. They all share the same principle: no sufficient data from past events were available to build damage models on a statistical analysis, so modeling was based on expert knowledge. We will focus on the model built for agricultural activities and more precisely for agricultural lands. This model was based on feedback from 30 agricultural experts who experienced floods in their geographical areas. They were selected to have a representative experience of crops and flood conditions in France. The model is composed of: (i) damaging functions, which reveal physiological vulnerability of crops, (ii) action functions, which correspond to farmers' decision rules for carrying on crops after a flood, and (iii) economic agricultural data, which correspond to featured characteristics of crops in the geographical area where the flood management project studied takes place. The two first components are generic and the third one is specific to the area studied. It is, thus, possible to produce flood damage functions adapted to different agronomic and geographical contexts. In the end, the model was applied to obtain a pool of damage functions giving
NASA Astrophysics Data System (ADS)
Grelot, Frédéric; Agenais, Anne-Laurence; Brémond, Pauline
2015-04-01
In France, since 2011, it is mandatory for local communities to conduct cost-benefit analysis (CBA) of their flood management projects, to make them eligible for financial support from the State. Meanwhile, as a support, the French Ministry in charge of Environment proposed a methodology to fulfill CBA. Like for many other countries, this methodology is based on the estimation of flood damage. However, existing models to estimate flood damage were judged not convenient for a national-wide use. As a consequence, the French Ministry in charge of Environment launched studies to develop damage models for different sectors, such as: residential sector, public infrastructures, agricultural sector, and commercial and industrial sector. In this presentation, we aim at presenting and discussing methodological choices of those damage models. They all share the same principle: no sufficient data from past events were available to build damage models on a statistical analysis, so modeling was based on expert knowledge. We will focus on the model built for agricultural activities and more precisely for agricultural lands. This model was based on feedback from 30 agricultural experts who experienced floods in their geographical areas. They were selected to have a representative experience of crops and flood conditions in France. The model is composed of: (i) damaging functions, which reveal physiological vulnerability of crops, (ii) action functions, which correspond to farmers' decision rules for carrying on crops after a flood, and (iii) economic agricultural data, which correspond to featured characteristics of crops in the geographical area where the flood management project studied takes place. The two first components are generic and the third one is specific to the area studied. It is, thus, possible to produce flood damage functions adapted to different agronomic and geographical contexts. In the end, the model was applied to obtain a pool of damage functions giving
Distributed Damage Estimation for Prognostics based on Structural Model Decomposition
NASA Technical Reports Server (NTRS)
Daigle, Matthew; Bregon, Anibal; Roychoudhury, Indranil
2011-01-01
Model-based prognostics approaches capture system knowledge in the form of physics-based models of components, and how they fail. These methods consist of a damage estimation phase, in which the health state of a component is estimated, and a prediction phase, in which the health state is projected forward in time to determine end of life. However, the damage estimation problem is often multi-dimensional and computationally intensive. We propose a model decomposition approach adapted from the diagnosis community, called possible conflicts, in order to both improve the computational efficiency of damage estimation, and formulate a damage estimation approach that is inherently distributed. Local state estimates are combined into a global state estimate from which prediction is performed. Using a centrifugal pump as a case study, we perform a number of simulation-based experiments to demonstrate the approach.
Dynamic brittle material response based on a continuum damage model
Chen, E.P.
1994-12-31
The response of brittle materials to dynamic loads was studied in this investigation based on a continuum damage model. Damage mechanism was selected to be interaction and growth of subscale cracks. Briefly, the cracks are activated by bulk tension and the density of activated cracks are described by a Weibull statistical distribution. The moduli of a cracked solid derived by Budiansky and O`Connell are then used to represent the global material degradation due to subscale cracking. This continuum damage model was originally developed to study rock fragmentation and was modified in the present study to improve on the post-limit structural response. The model was implemented into a transient dynamic explicit finite element code PRONTO 2D and then used for a numerical study involving the sudden stretching of a plate with a centrally located hole. Numerical results characterizing the dynamic responses of the material were presented. The effect of damage on dynamic material behavior was discussed.
NASA Astrophysics Data System (ADS)
Roy, Koushik; Bhattacharya, Bishakh; Ray-Chaudhuri, Samit
2015-08-01
The study proposes a set of four ARX model (autoregressive model with exogenous input) based damage sensitive features (DSFs) for structural damage detection and localization using the dynamic responses of structures, where the information regarding the input excitation may not be available. In the proposed framework, one of the output responses of a multi-degree-of-freedom system is assumed as the input and the rest are considered as the output. The features are based on ARX model coefficients, Kolmogorov-Smirnov (KS) test statistical distance, and the model residual error. At first, a mathematical formulation is provided to establish the relation between the change in ARX model coefficients and the normalized stiffness of a structure. KS test parameters are then described to show the sensitivity of statistical distance of ARX model residual error with the damage location. The efficiency of the proposed set of DSFs is evaluated by conducting numerical studies involving a shear building and a steel moment-resisting frame. To simulate the damage scenarios in these structures, stiffness degradation of different elements is considered. It is observed from this study that the proposed set of DSFs is good indicator for damage location even in the presence of damping, multiple damages, noise, and parametric uncertainties. The performance of these DSFs is compared with mode shape curvature-based approach for damage localization. An experimental study has also been conducted on a three-dimensional six-storey steel moment frame to understand the performance of these DSFs under real measurement conditions. It has been observed that the proposed set of DSFs can satisfactorily localize damage in the structure.
Model-based damage evaluation of layered CFRP structures
NASA Astrophysics Data System (ADS)
Munoz, Rafael; Bochud, Nicolas; Rus, Guillermo; Peralta, Laura; Melchor, Juan; Chiachío, Juan; Chiachío, Manuel; Bond, Leonard J.
2015-03-01
An ultrasonic evaluation technique for damage identification of layered CFRP structures is presented. This approach relies on a model-based estimation procedure that combines experimental data and simulation of ultrasonic damage-propagation interactions. The CFPR structure, a [0/90]4s lay-up, has been tested in an immersion through transmission experiment, where a scan has been performed on a damaged specimen. Most ultrasonic techniques in industrial practice consider only a few features of the received signals, namely, time of flight, amplitude, attenuation, frequency contents, and so forth. In this case, once signals are captured, an algorithm is used to reconstruct the complete signal waveform and extract the unknown damage parameters by means of modeling procedures. A linear version of the data processing has been performed, where only Young modulus has been monitored and, in a second nonlinear version, the first order nonlinear coefficient β was incorporated to test the possibility of detection of early damage. The aforementioned physical simulation models are solved by the Transfer Matrix formalism, which has been extended from linear to nonlinear harmonic generation technique. The damage parameter search strategy is based on minimizing the mismatch between the captured and simulated signals in the time domain in an automated way using Genetic Algorithms. Processing all scanned locations, a C-scan of the parameter of each layer can be reconstructed, obtaining the information describing the state of each layer and each interface. Damage can be located and quantified in terms of changes in the selected parameter with a measurable extension. In the case of the nonlinear coefficient of first order, evidence of higher sensitivity to damage than imaging the linearly estimated Young Modulus is provided.
Multiple Damage Progression Paths in Model-Based Prognostics
NASA Technical Reports Server (NTRS)
Daigle, Matthew; Goebel, Kai Frank
2011-01-01
Model-based prognostics approaches employ domain knowledge about a system, its components, and how they fail through the use of physics-based models. Component wear is driven by several different degradation phenomena, each resulting in their own damage progression path, overlapping to contribute to the overall degradation of the component. We develop a model-based prognostics methodology using particle filters, in which the problem of characterizing multiple damage progression paths is cast as a joint state-parameter estimation problem. The estimate is represented as a probability distribution, allowing the prediction of end of life and remaining useful life within a probabilistic framework that supports uncertainty management. We also develop a novel variance control mechanism that maintains an uncertainty bound around the hidden parameters to limit the amount of estimation uncertainty and, consequently, reduce prediction uncertainty. We construct a detailed physics-based model of a centrifugal pump, to which we apply our model-based prognostics algorithms. We illustrate the operation of the prognostic solution with a number of simulation-based experiments and demonstrate the performance of the chosen approach when multiple damage mechanisms are active
Search-based model identification of smart-structure damage
NASA Technical Reports Server (NTRS)
Glass, B. J.; Macalou, A.
1991-01-01
This paper describes the use of a combined model and parameter identification approach, based on modal analysis and artificial intelligence (AI) techniques, for identifying damage or flaws in a rotating truss structure incorporating embedded piezoceramic sensors. This smart structure example is representative of a class of structures commonly found in aerospace systems and next generation space structures. Artificial intelligence techniques of classification, heuristic search, and an object-oriented knowledge base are used in an AI-based model identification approach. A finite model space is classified into a search tree, over which a variant of best-first search is used to identify the model whose stored response most closely matches that of the input. Newly-encountered models can be incorporated into the model space. This adaptativeness demonstrates the potential for learning control. Following this output-error model identification, numerical parameter identification is used to further refine the identified model. Given the rotating truss example in this paper, noisy data corresponding to various damage configurations are input to both this approach and a conventional parameter identification method. The combination of the AI-based model identification with parameter identification is shown to lead to smaller parameter corrections than required by the use of parameter identification alone.
Life prediction modeling based on cyclic damage accumulation
NASA Technical Reports Server (NTRS)
Nelson, Richard S.
1988-01-01
A high temperature, low cycle fatigue life prediction method was developed. This method, Cyclic Damage Accumulation (CDA), was developed for use in predicting the crack initiation lifetime of gas turbine engine materials, where initiation was defined as a 0.030 inch surface length crack. A principal engineering feature of the CDA method is the minimum data base required for implementation. Model constants can be evaluated through a few simple specimen tests such as monotonic loading and rapic cycle fatigue. The method was expanded to account for the effects on creep-fatigue life of complex loadings such as thermomechanical fatigue, hold periods, waveshapes, mean stresses, multiaxiality, cumulative damage, coatings, and environmental attack. A significant data base was generated on the behavior of the cast nickel-base superalloy B1900+Hf, including hundreds of specimen tests under such loading conditions. This information is being used to refine and extend the CDA life prediction model, which is now nearing completion. The model is also being verified using additional specimen tests on wrought INCO 718, and the final version of the model is expected to be adaptable to most any high-temperature alloy. The model is currently available in the form of equations and related constants. A proposed contract addition will make the model available in the near future in the form of a computer code to potential users.
A damage model based on failure threshold weakening
NASA Astrophysics Data System (ADS)
Gran, Joseph D.; Rundle, John B.; Turcotte, Donald L.; Holliday, James R.; Klein, William
2011-04-01
A variety of studies have modeled the physics of material deformation and damage as examples of generalized phase transitions, involving either critical phenomena or spinodal nucleation. Here we study a model for frictional sliding with long-range interactions and recurrent damage that is parameterized by a process of damage and partial healing during sliding. We introduce a failure threshold weakening parameter into the cellular automaton slider-block model which allows blocks to fail at a reduced failure threshold for all subsequent failures during an event. We show that a critical point is reached beyond which the probability of a system-wide event scales with this weakening parameter. We provide a mapping to the percolation transition, and show that the values of the scaling exponents approach the values for mean-field percolation (spinodal nucleation) as lattice size L is increased for fixed R. We also examine the effect of the weakening parameter on the frequency-magnitude scaling relationship and the ergodic behavior of the model.
Structural damage measure index based on non-probabilistic reliability model
NASA Astrophysics Data System (ADS)
Wang, Xiaojun; Xia, Yong; Zhou, Xiaoqing; Yang, Chen
2014-02-01
Uncertainties in the structural model and measurement data affect structural condition assessment in practice. As the probabilistic information of these uncertainties lacks, the non-probabilistic interval analysis framework is developed to quantify the interval of the structural element stiffness parameters. According to the interval intersection of the element stiffness parameters in the undamaged and damaged states, the possibility of damage existence is defined based on the reliability theory. A damage measure index is then proposed as the product of the nominal stiffness reduction and the defined possibility of damage existence. This new index simultaneously reflects the damage severity and possibility of damage at each structural component. Numerical and experimental examples are presented to illustrate the validity and applicability of the method. The results show that the proposed method can improve the accuracy of damage diagnosis compared with the deterministic damage identification method.
NASA Astrophysics Data System (ADS)
Williams, Kevin Vaughan
Rapid growth in use of composite materials in structural applications drives the need for a more detailed understanding of damage tolerant and damage resistant design. Current analytical techniques provide sufficient understanding and predictive capabilities for application in preliminary design, but current numerical models applicable to composites are few and far between and their development into well tested, rigorous material models is currently one of the most challenging fields in composite materials. The present work focuses on the development, implementation, and verification of a plane-stress continuum damage mechanics based model for composite materials. A physical treatment of damage growth based on the extensive body of experimental literature on the subject is combined with the mathematical rigour of a continuum damage mechanics description to form the foundation of the model. The model has been implemented in the LS-DYNA3D commercial finite element hydrocode and the results of the application of the model are shown to be physically meaningful and accurate. Furthermore it is demonstrated that the material characterization parameters can be extracted from the results of standard test methodologies for which a large body of published data already exists for many materials. Two case studies are undertaken to verify the model by comparison with measured experimental data. The first series of analyses demonstrate the ability of the model to predict the extent and growth of damage in T800/3900-2 carbon fibre reinforced polymer (CFRP) plates subjected to normal impacts over a range of impact energy levels. The predicted force-time and force-displacement response of the panels compare well with experimental measurements. The damage growth and stiffness reduction properties of the T800/3900-2 CFRP are derived using published data from a variety of sources without the need for parametric studies. To further demonstrate the physical nature of the model, a IM6
Model-Based Fatigue Prognosis of Fiber-Reinforced Laminates Exhibiting Concurrent Damage Mechanisms
NASA Technical Reports Server (NTRS)
Corbetta, M.; Sbarufatti, C.; Saxena, A.; Giglio, M.; Goebel, K.
2016-01-01
Prognostics of large composite structures is a topic of increasing interest in the field of structural health monitoring for aerospace, civil, and mechanical systems. Along with recent advancements in real-time structural health data acquisition and processing for damage detection and characterization, model-based stochastic methods for life prediction are showing promising results in the literature. Among various model-based approaches, particle-filtering algorithms are particularly capable in coping with uncertainties associated with the process. These include uncertainties about information on the damage extent and the inherent uncertainties of the damage propagation process. Some efforts have shown successful applications of particle filtering-based frameworks for predicting the matrix crack evolution and structural stiffness degradation caused by repetitive fatigue loads. Effects of other damage modes such as delamination, however, are not incorporated in these works. It is well established that delamination and matrix cracks not only co-exist in most laminate structures during the fatigue degradation process but also affect each other's progression. Furthermore, delamination significantly alters the stress-state in the laminates and accelerates the material degradation leading to catastrophic failure. Therefore, the work presented herein proposes a particle filtering-based framework for predicting a structure's remaining useful life with consideration of multiple co-existing damage-mechanisms. The framework uses an energy-based model from the composite modeling literature. The multiple damage-mode model has been shown to suitably estimate the energy release rate of cross-ply laminates as affected by matrix cracks and delamination modes. The model is also able to estimate the reduction in stiffness of the damaged laminate. This information is then used in the algorithms for life prediction capabilities. First, a brief summary of the energy-based damage model
Flood risk modelling based on tangible and intangible urban flood damage quantification.
ten Veldhuis, J A E; Clemens, F H L R
2010-01-01
The usual way to quantify flood damage is by application stage-damage functions. Urban flood incidents in flat areas mostly result in intangible damages like traffic disturbance and inconvenience for pedestrians caused by pools at building entrances, on sidewalks and parking spaces. Stage-damage functions are not well suited to quantify damage for these floods. This paper presents an alternative method to quantify flood damage that uses data from a municipal call centre. The data cover a period of 10 years and contain detailed information on consequences of urban flood incidents. Call data are linked to individual flood incidents and then assigned to specific damage classes. The results are used to draw risk curves for a range of flood incidents of increasing damage severity. Risk curves for aggregated groups of damage classes show that total flood risk related to traffic disturbance is larger than risk of damage to private properties, which in turn is larger than flood risk related to human health. Risk curves for detailed damage classes show how distinctions can be made between flood risks related to many types of occupational use in urban areas. This information can be used to support prioritisation of actions for flood risk reduction. Since call data directly convey how citizens are affected by urban flood incidents, they provide valuable information that complements flood risk analysis based on hydraulic models. PMID:20595770
A continuous damage model based on stepwise-stress creep rupture tests
NASA Technical Reports Server (NTRS)
Robinson, D. N.
1985-01-01
A creep damage accumulation model is presented that makes use of the Kachanov damage rate concept with a provision accounting for damage that results from a variable stress history. This is accomplished through the introduction of an additional term in the Kachanov rate equation that is linear in the stress rate. Specification of the material functions and parameters in the model requires two types of constituting a data base: (1) standard constant-stress creep rupture tests, and (2) a sequence of two-step creep rupture tests.
Evaluation of a threshold-based model of fatigue in gamma titanium aluminide following impact damage
NASA Astrophysics Data System (ADS)
Harding, Trevor Scott
2000-10-01
Recent interest in gamma titanium aluminide (gamma-TiAl) for use in gas turbine engine applications has centered on the low density and good elevated temperature strength retention of gamma-TiAl compared to current materials. However, the relatively low ductility and fracture toughness of gamma-TiAl leads to serious concerns regarding its ability to resist impact damage. Furthermore, the limited fatigue crack growth resistance of gamma-TiAl means that the potential for fatigue failures resulting from impact damage is real if a damage tolerant design approach is used. A threshold-based design approach may be required if fatigue crack growth from potential impact sites is to be avoided. The objective of the present research is to examine the feasibility of a threshold-based approach for the design of a gamma-TiAl low-pressure turbine blade subjected to both assembly-related impact damage and foreign object damage. Specimens of three different gamma-TiAl alloys were damaged in such a way as to simulate anticipated impact damage for a turbine blade. Step-loading fatigue tests were conducted at both room temperature and 600°C. In terms of the assembly-related impact damage, the results indicate that there is reasonably good agreement between the threshold-based predictions of the fatigue strength of damaged specimens and the measured data. However, some discrepancies do exist. In the case of very lightly damaged specimens, prediction of the resulting fatigue strength requires that a very conservative small-crack fatigue threshold be used. Consequently, the allowable design conditions are significantly reduced. For severely damaged specimens, an analytical approach found that the potential effects of residual stresses may be related to the discrepancies observed between the threshold-based model and measured fatigue strength data. In the case of foreign object damage, a good correlation was observed between impacts resulting in large cracks and a long-crack threshold-based
Damage evaluation by a guided wave-hidden Markov model based method
NASA Astrophysics Data System (ADS)
Mei, Hanfei; Yuan, Shenfang; Qiu, Lei; Zhang, Jinjin
2016-02-01
Guided wave based structural health monitoring has shown great potential in aerospace applications. However, one of the key challenges of practical engineering applications is the accurate interpretation of the guided wave signals under time-varying environmental and operational conditions. This paper presents a guided wave-hidden Markov model based method to improve the damage evaluation reliability of real aircraft structures under time-varying conditions. In the proposed approach, an HMM based unweighted moving average trend estimation method, which can capture the trend of damage propagation from the posterior probability obtained by HMM modeling is used to achieve a probabilistic evaluation of the structural damage. To validate the developed method, experiments are performed on a hole-edge crack specimen under fatigue loading condition and a real aircraft wing spar under changing structural boundary conditions. Experimental results show the advantage of the proposed method.
Oxidative DNA damage background estimated by a system model of base excision repair
Sokhansanj, B A; Wilson, III, D M
2004-05-13
Human DNA can be damaged by natural metabolism through free radical production. It has been suggested that the equilibrium between innate damage and cellular DNA repair results in an oxidative DNA damage background that potentially contributes to disease and aging. Efforts to quantitatively characterize the human oxidative DNA damage background level based on measuring 8-oxoguanine lesions as a biomarker have led to estimates varying over 3-4 orders of magnitude, depending on the method of measurement. We applied a previously developed and validated quantitative pathway model of human DNA base excision repair, integrating experimentally determined endogenous damage rates and model parameters from multiple sources. Our estimates of at most 100 8-oxoguanine lesions per cell are consistent with the low end of data from biochemical and cell biology experiments, a result robust to model limitations and parameter variation. Our results show the power of quantitative system modeling to interpret composite experimental data and make biologically and physiologically relevant predictions for complex human DNA repair pathway mechanisms and capacity.
Evaluation of Creep-Fatigue Damage Based on Simplified Model Test Approach
Wang, Yanli; Li, Tianlei; Sham, Sam; Jetter, Robert I
2013-01-01
Current methods used in the ASME Code, Subsection NH for the evaluation of creep-fatigue damage are based on the separation of elevated temperature cyclic damage into two parts, creep damage and fatigue damage. This presents difficulties in both evaluation of test data and determination of cyclic damage in design. To avoid these difficulties, an alternative approach was identified, called the Simplified Model Test or SMT approach based on the use of creep-fatigue hold time test data from test specimens with elastic follow-up conservatively designed to bound the response of general structural components of interest. A key feature of the methodology is the use of the results of elastic analysis directly in design evaluation similar to current methods in the ASME Code, Subsection NB. Although originally developed for current material included in Subsection NH, recent interest in the application of Alloy 617 for components operating at very high temperatures has caused renewed interest in the SMT approach because it provides an alternative to the proposed restriction on the use of current Subsection NH simplified methods at very high temperatures. A comprehensive review and assessment of five representative simplified methods for creep-fatigue damage evaluation is presented in Asayama [1]. In this review the SMT methodology was identified as the best long term approach but the need for test data precluded its near term implementation. Asayama and Jetter [2] is a summary of the more comprehensive report by Asayama [1] with a summary of the SMT approach presented by Jetter [3].
Probability-based damage detection using model updating with efficient uncertainty propagation
NASA Astrophysics Data System (ADS)
Xu, Yalan; Qian, Yu; Chen, Jianjun; Song, Gangbing
2015-08-01
Model updating method has received increasing attention in damage detection of structures based on measured modal parameters. In this article, a probability-based damage detection procedure is presented, in which the random factor method for non-homogeneous random field is developed and used as the forward propagation to analytically evaluate covariance matrices in each iteration step of stochastic model updating. An improved optimization algorithm is introduced to guarantee the convergence and reduce the computational effort, in which the design variables are restricted in search region by region truncation of each iteration step. The developed algorithm is illustrated by a simulated 25-bar planar truss structure and the results have been compared and verified with those obtained from Monte Carlo simulation. In order to assess the influences of uncertainty sources on the results of model updating and damage detection of structures, a comparative study is also given under different cases of uncertainties, that is, structural uncertainty only, measurement uncertainty only and combination of the two. The simulation results show the proposed method can perform well in stochastic model updating and probability-based damage detection of structures with less computational effort.
NASA Astrophysics Data System (ADS)
Paul, Pijush Kanti
In the fault damage zone modeling study for a field in the Timor Sea, I present a methodology to incorporate geomechanically-based fault damage zones into reservoir simulation. In the studied field, production history suggests that the mismatch between actual production and model prediction is due to preferential fluid flow through the damage zones associated with the reservoir scale faults, which is not included in the baseline petrophysical model. I analyzed well data to estimate stress heterogeneity and fracture distributions in the reservoir. Image logs show that stress orientations are homogenous at the field scale with a strike-slip/normal faulting stress regime and maximum horizontal stress oriented in NE-SW direction. Observed fracture zones in wells are mostly associated with well scale fault and bed boundaries. These zones do not show any anomalies in production logs or well test data, because most of the fractures are not optimally oriented to the present day stress state, and matrix permeability is high enough to mask any small anomalies from the fracture zones. However, I found that fracture density increases towards the reservoir scale faults, indicating high fracture density zones or damage zones close to these faults, which is consistent with the preferred flow direction indicated by interference and tracer test done between the wells. It is well known from geologic studies that there is a concentration of secondary fractures and faults in a damage zone adjacent to larger faults. Because there is usually inadequate data to incorporate damage zone fractures and faults into reservoir simulation models, in this study I utilized the principles of dynamic rupture propagation from earthquake seismology to predict the nature of fractured/damage zones associated with reservoir scale faults. The implemented workflow can be used to more routinely incorporate damage zones into reservoir simulation models. Applying this methodology to a real reservoir utilizing
Damage-based long-term modelling of a large alpine rock slope
NASA Astrophysics Data System (ADS)
Riva, Federico; Agliardi, Federico; Amitrano, David; Crosta, Giovanni B.
2016-04-01
The morphology and stability of large alpine rock slopes result from the long-term interplay of different factors, following a complex history spanning several glacial cycles over thousands of years in changing morpho-climatic settings. Large rock slopes often experience slow long-term, creep-like movements interpreted as the macroscopic evidence of progressive failure in subcritically stressed rock masses. Slope damage and rock mass weakening associated to deglaciation are considered major triggers of these processes in alpine environments. Depending on rock mass properties, slope topography and removed ice thickness, valley flanks can progressively evolve over time into rockslides showing seasonal displacement trends, interpreted as evidence of hydro-mechanically coupled responses to hydrologic perturbations. The processes linking the long-term evolution of deglaciated rock slopes and their changing sensitivity to hydrologic triggers until rockslide failure, with significant implications in risk management and Early Warning, are not fully understood. We suggest that modelling long-term rock mass damage under changing conditions may provide such a link. We simulated the evolution of the Spriana rock slope (Italian Central Alps). This is affected by a 50 Mm3 rockslide, significantly active since the late 19th century and characterized by massive geological and geotechnical investigations and monitoring during the last decades. Using an improved version of the 2D Finite-Element, damage-based brittle creep model proposed by Amitrano and Helmstetter (2006) and Lacroix and Amitrano (2013), we combined damage and time-to-failure laws to reproduce diffused damage, strain localization and the long-term creep deformation of the slope. The model was implemented for application to real slopes, by accounting for: 1) fractured rock mass properties upscaling based on site characterization data; 2) fluid pressures in a progressive failure context, relating fluid occurrence to
NASA Technical Reports Server (NTRS)
Wang, John T.; Pineda, Evan J.; Ranatunga, Vipul; Smeltzer, Stanley S.
2015-01-01
A simple continuum damage mechanics (CDM) based 3D progressive damage analysis (PDA) tool for laminated composites was developed and implemented as a user defined material subroutine to link with a commercially available explicit finite element code. This PDA tool uses linear lamina properties from standard tests, predicts damage initiation with an easy-to-implement Hashin-Rotem failure criteria, and in the damage evolution phase, evaluates the degradation of material properties based on the crack band theory and traction-separation cohesive laws. It follows Matzenmiller et al.'s formulation to incorporate the degrading material properties into the damaged stiffness matrix. Since nonlinear shear and matrix stress-strain relations are not implemented, correction factors are used for slowing the reduction of the damaged shear stiffness terms to reflect the effect of these nonlinearities on the laminate strength predictions. This CDM based PDA tool is implemented as a user defined material (VUMAT) to link with the Abaqus/Explicit code. Strength predictions obtained, using this VUMAT, are correlated with test data for a set of notched specimens under tension and compression loads.
NASA Astrophysics Data System (ADS)
Misra, Anil; Singh, Viraj
2015-09-01
Thermomechanics and granular micromechanics approaches are combined to derive constitutive equations for modeling rate-dependent granular materials with damage and plasticity. The derivation is motivated by the recognition that the effect of micro-scale mechanisms upon the macro-scale behavior is known to be significant for granular materials. A general thermomechanical framework applicable to rate-dependent granular materials with damage and plasticity is developed. Based upon this framework, an expression for macro-scale Cauchy stress tensor is obtained in terms of the micro-scale grain interaction forces and the relationship between micro- and macro-scale kinematics. In addition, a Clausius-Duhem type inequality applicable to inter-granular interaction is derived, which is used to establish micro-scale constitutive relations for particular type of inter-granular interactions. The expression for Cauchy stress tensor and the micro-scale constitutive relations is then combined under a mean field kinematic assumption to obtain evolution-type macro-scale constitutive equations. The advantage of the granular micromechanics approach is that the damage and plasticity are defined using simple 1d functions at micro-scale, and complicated plastic potentials, damage functions and rules for their evolution are not required. The resultant model is applied to investigate primary, secondary and tertiary creep, creep-recovery as well as rate-dependent response under uniaxial compressive loading. Model applicability is also demonstrated for asymmetric tensile-compressive response under creep-recovery loading. The model is used to evaluate the evolution of elastic energy, and viscous, plastic and damage dissipation at the macro- and micro-scale with respect to creep time and loading level. The results show the development of loading-induced anisotropy due to damage and plasticity in these materials.
A Micromechanics-Based Damage Model for [+/- Theta/90n]s Composite Laminates
NASA Technical Reports Server (NTRS)
Mayugo, Joan-Andreu; Camanho, Pedro P.; Maimi, Pere; Davila, Carlos G.
2006-01-01
A new damage model based on a micromechanical analysis of cracked [+/- Theta/90n]s laminates subjected to multiaxial loads is proposed. The model predicts the onset and accumulation of transverse matrix cracks in uniformly stressed laminates, the effect of matrix cracks on the stiffness of the laminate, as well as the ultimate failure of the laminate. The model also accounts for the effect of the ply thickness on the ply strength. Predictions relating the elastic properties of several laminates and multiaxial loads are presented.
A Micromechanics-Based Damage Model For The Strength Prediction of Composite Laminates
NASA Technical Reports Server (NTRS)
Camanho, Pedro P.; Mayugo, Joan A.; Maimi, Pere; Davila, Carlos G.
2006-01-01
A new damage model based on a micromechanical analysis of cracked [+/-0deg/90deg(sub n)]s laminates subjected to multiaxial loads is proposed. The model predicts the onset and accumulation of transverse matrix cracks in uniformly stressed laminates, the effect of matrix cracks on the stiffness of the laminate, as well as the ultimate failure of the laminate. The model also accounts for the effect of the ply thickness on the ply strength. Predictions relating the elastic properties of several laminates and multiaxial loads are presented.
Damage evaluation of reinforced concrete frame based on a combined fiber beam model
NASA Astrophysics Data System (ADS)
Shang, Bing; Liu, ZhanLi; Zhuang, Zhuo
2014-04-01
In order to analyze and simulate the impact collapse or seismic response of the reinforced concrete (RC) structures, a combined fiber beam model is proposed by dividing the cross section of RC beam into concrete fiber and steel fiber. The stress-strain relationship of concrete fiber is based on a model proposed by concrete codes for concrete structures. The stress-strain behavior of steel fiber is based on a model suggested by others. These constitutive models are implemented into a general finite element program ABAQUS through the user defined subroutines to provide effective computational tools for the inelastic analysis of RC frame structures. The fiber model proposed in this paper is validated by comparing with experiment data of the RC column under cyclical lateral loading. The damage evolution of a three-dimension frame subjected to impact loading is also investigated.
NASA Astrophysics Data System (ADS)
Sakaris, Christos S.; Sakellariou, John S.; Fassois, Spilios D.
2015-07-01
A Generalized Functional Model Based Method for vibration-based damage precise localization on structures consisting of 1D, 2D, or 3D elements is introduced. The method generalizes previous versions applicable to structures consisting of 1D elements, thus allowing for 2D and 3D elements as well. It is based on scalar (single sensor) or vector (multiple sensor) Functional Models which - in the inspection phase - incorporate the mathematical form of the specific structural topology. Precise localization is then based on coordinate estimation within this model structure, and confidence bounds are also obtained. The effectiveness of the method is demonstrated through experiments on a 3D truss structure where damage corresponds to single bolt loosening. Both the scalar and vector versions of the method are shown to be effective even within a very limited, low frequency, bandwidth of 3-59 Hz. The improvement achieved through the use of multiple sensors is also demonstrated.
Cumulative fatigue damage models
NASA Technical Reports Server (NTRS)
Mcgaw, Michael A.
1988-01-01
The problem of calculating expected component life under fatigue loading conditions is complicated by the fact that component loading histories contain, in many cases, cyclic loads of widely varying amplitudes. In such a case a cumulative damage model is required, in addition to a fatigue damage criterion, or life relationship, in order to compute the expected fatigue life. The traditional cumulative damage model used in design is the linear damage rule. This model, while being simple to use, can yield grossly unconservative results under certain loading conditions. Research at the NASA Lewis Research Center has led to the development of a nonlinear cumulative damage model, named the double damage curve approach (DDCA), that has greatly improved predictive capability. This model, which considers the life (or loading) level dependence of damage evolution, was applied successfully to two polycrystalline materials, 316 stainless steel and Haynes 188. The cumulative fatigue behavior of the PWA 1480 single-crystal material is currently being measured to determine the applicability of the DDCA for this material.
Movahed, Pooya; Kreider, Wayne; Maxwell, Adam D; Hutchens, Shelby B; Freund, Jonathan B
2016-08-01
A generalized Rayleigh-Plesset-type bubble dynamics model with a damage mechanism is developed for cavitation and damage of soft materials by focused ultrasound bursts. This study is linked to recent experimental observations in tissue-mimicking polyacrylamide and agar gel phantoms subjected to bursts of a kind being considered specifically for lithotripsy. These show bubble activation at multiple sites during the initial pulses. More cavities appear continuously through the course of the observations, similar to what is deduced in pig kidney tissues in shock-wave lithotripsy. Two different material models are used to represent the distinct properties of the two gel materials. The polyacrylamide gel is represented with a neo-Hookean elastic model and damaged based upon a maximum-strain criterion; the agar gel is represented with a strain-hardening Fung model and damaged according to the strain-energy-based Griffith's fracture criterion. Estimates based upon independently determined elasticity and viscosity of the two gel materials suggest that bubble confinement should be sufficient to prevent damage in the gels, and presumably injury in some tissues. Damage accumulation is therefore proposed to occur via a material fatigue, which is shown to be consistent with observed delays in widespread cavitation activity. PMID:27586763
NASA Astrophysics Data System (ADS)
Trinh, B. T.; Hackl, K.
2014-07-01
A model for high temperature creep of single crystal superalloys is developed, which includes constitutive laws for nonlocal damage and viscoplasticity. It is based on a variational formulation, employing potentials for free energy, and dissipation originating from plasticity and damage. Evolution equations for plastic strain and damage variables are derived from the well-established minimum principle for the dissipation potential. The model is capable of describing the different stages of creep in a unified way. Plastic deformation in superalloys incorporates the evolution of dislocation densities of the different phases present. It results in a time dependence of the creep rate in primary and secondary creep. Tertiary creep is taken into account by introducing local and nonlocal damage. Herein, the nonlocal one is included in order to model strain localization as well as to remove mesh dependence of finite element calculations. Numerical results and comparisons with experimental data of the single crystal superalloy LEK94 are shown.
NASA Astrophysics Data System (ADS)
Sakaris, C. S.; Sakellariou, J. S.; Fassois, S. D.
2016-06-01
This study focuses on the problem of vibration-based damage precise localization via data-based, time series type, methods for structures consisting of 1D, 2D, or 3D elements. A Generalized Functional Model Based method is postulated based on an expanded Vector-dependent Functionally Pooled ARX (VFP-ARX) model form, capable of accounting for an arbitrary structural topology. The FP model's operating parameter vector elements are properly constrained to reflect any given topology. Damage localization is based on operating parameter vector estimation within the specified topology, so that the location estimate and its uncertainty bounds are statistically optimal. The method's effectiveness is experimentally demonstrated through damage precise localization on a laboratory spatial truss structure using various damage scenarios and a single pair of random excitation - vibration response signals in a low and limited frequency bandwidth.
NASA Technical Reports Server (NTRS)
Coats, Timothy William
1994-01-01
Progressive failure is a crucial concern when using laminated composites in structural design. Therefore the ability to model damage and predict the life of laminated composites is vital. The purpose of this research was to experimentally verify the application of the continuum damage model, a progressive failure theory utilizing continuum damage mechanics, to a toughened material system. Damage due to tension-tension fatigue was documented for the IM7/5260 composite laminates. Crack density and delamination surface area were used to calculate matrix cracking and delamination internal state variables, respectively, to predict stiffness loss. A damage dependent finite element code qualitatively predicted trends in transverse matrix cracking, axial splits and local stress-strain distributions for notched quasi-isotropic laminates. The predictions were similar to the experimental data and it was concluded that the continuum damage model provided a good prediction of stiffness loss while qualitatively predicting damage growth in notched laminates.
NASA Astrophysics Data System (ADS)
Heyden, S.; Li, B.; Weinberg, K.; Conti, S.; Ortiz, M.
2015-01-01
We formulate a simple one-parameter macroscopic model of distributed damage and fracture of polymers that is amenable to a straightforward and efficient numerical implementation. We show that the macroscopic model can be rigorously derived, in the sense of optimal scaling, from a micromechanical model of chain elasticity and failure regularized by means of fractional strain-gradient elasticity. In particular, we derive optimal scaling laws that supply a link between the single parameter of the macroscopic model, namely, the critical energy-release rate of the material, and micromechanical parameters pertaining to the elasticity and strength of the polymer chains and to the strain-gradient elasticity regularization. We show how the critical energy-release rate of specific materials can be determined from test data. Finally, we demonstrate the scope and fidelity of the model by means of an example of application, namely, Taylor-impact experiments of polyurea 1000 rods.
NASA Astrophysics Data System (ADS)
Avendaño-Valencia, L. D.; Fassois, S. D.
2015-07-01
The problem of damage detection in an operating wind turbine under normal operating conditions is addressed. This is characterized by difficulties associated with the lack of measurable excitation(s), the vibration response non-stationary nature, and its dependence on various types of uncertainties. To overcome these difficulties a stochastic approach based on Random Coefficient (RC) Linear Parameter Varying (LPV) AutoRegressive (AR) models is postulated. These models may effectively represent the non-stationary random vibration response under healthy conditions and subsequently used for damage detection through hypothesis testing. The performance of the method for damage and fault detection in an operating wind turbine is subsequently assessed via Monte Carlo simulations using the FAST simulation package.
Incorporating Micro-Mechanics Based Damage Models into Earthquake Rupture Simulations
NASA Astrophysics Data System (ADS)
Bhat, H.; Rosakis, A.; Sammis, C. G.
2012-12-01
The micromechanical damage mechanics formulated by Ashby and Sammis, 1990 and generalized by Deshpande and Evans 2008 has been extended to allow for a more generalized stress state and to incorporate an experimentally motivated new crack growth (damage evolution) law that is valid over a wide range of loading rates. This law is sensitive to both the crack tip stress field and its time derivative. Incorporating this feature produces additional strain-rate sensitivity in the constitutive response. The model is also experimentally verified by predicting the failure strength of Dionysus-Pentelicon marble over a wide range of strain rates. Model parameters determined from quasi-static experiments were used to predict the failure strength at higher loading rates. Agreement with experimental results was excellent. After this verification step the constitutive law was incorporated into a Finite Element Code focused on simulating dynamic earthquake ruptures with specific focus on the ends of the fault (fault tip process zone) and the resulting strong ground motion radiation was studied.
Stora, E.; Bary, B.; Deville, E.; Montarnal, P.
2010-08-15
The assessment of the durability of cement-based materials, which could be employed in underground structures for nuclear waste disposal, requires accounting for deterioration factors, such as chemical attacks and damage, and for the interactions between these phenomena. The objective of the present paper consists in investigating the long-term behaviour of cementitious materials by simulating their response to chemical and mechanical solicitations. In a companion paper (Stora et al., submitted to Cem. Concr. Res. 2008), the implementation of a multi-scale homogenization model into an integration platform has allowed for evaluating the evolution of the mineral composition, diffusive and elastic properties inside a concrete material subjected to leaching. To complete this previous work, an orthotropic micromechanical damage model is presently developed and incorporated in this numerical platform to estimate the mechanical and diffusive properties of damaged cement-based materials. Simulations of the chemo-mechanical behaviour of leached cementitious materials are performed with the tool thus obtained and compared with available experiments. The numerical results are insightful about the interactions between damage and chemical deteriorations.
Multivariate pluvial flood damage models
Van Ootegem, Luc; Verhofstadt, Elsy; Van Herck, Kristine; Creten, Tom
2015-09-15
Depth–damage-functions, relating the monetary flood damage to the depth of the inundation, are commonly used in the case of fluvial floods (floods caused by a river overflowing). We construct four multivariate damage models for pluvial floods (caused by extreme rainfall) by differentiating on the one hand between ground floor floods and basement floods and on the other hand between damage to residential buildings and damage to housing contents. We do not only take into account the effect of flood-depth on damage, but also incorporate the effects of non-hazard indicators (building characteristics, behavioural indicators and socio-economic variables). By using a Tobit-estimation technique on identified victims of pluvial floods in Flanders (Belgium), we take into account the effect of cases of reported zero damage. Our results show that the flood depth is an important predictor of damage, but with a diverging impact between ground floor floods and basement floods. Also non-hazard indicators are important. For example being aware of the risk just before the water enters the building reduces content damage considerably, underlining the importance of warning systems and policy in this case of pluvial floods. - Highlights: • Prediction of damage of pluvial floods using also non-hazard information • We include ‘no damage cases’ using a Tobit model. • The damage of flood depth is stronger for ground floor than for basement floods. • Non-hazard indicators are especially important for content damage. • Potential gain of policies that increase awareness of flood risks.
How useful are complex flood damage models?
NASA Astrophysics Data System (ADS)
Schröter, Kai; Kreibich, Heidi; Vogel, Kristin; Riggelsen, Carsten; Scherbaum, Frank; Merz, Bruno
2014-04-01
We investigate the usefulness of complex flood damage models for predicting relative damage to residential buildings in a spatial and temporal transfer context. We apply eight different flood damage models to predict relative building damage for five historic flood events in two different regions of Germany. Model complexity is measured in terms of the number of explanatory variables which varies from 1 variable up to 10 variables which are singled out from 28 candidate variables. Model validation is based on empirical damage data, whereas observation uncertainty is taken into consideration. The comparison of model predictive performance shows that additional explanatory variables besides the water depth improve the predictive capability in a spatial and temporal transfer context, i.e., when the models are transferred to different regions and different flood events. Concerning the trade-off between predictive capability and reliability the model structure seem more important than the number of explanatory variables. Among the models considered, the reliability of Bayesian network-based predictions in space-time transfer is larger than for the remaining models, and the uncertainties associated with damage predictions are reflected more completely.
A Robust Damage Assessment Model for Corrupted Database Systems
NASA Astrophysics Data System (ADS)
Fu, Ge; Zhu, Hong; Li, Yingjiu
An intrusion tolerant database uses damage assessment techniques to detect damage propagation scales in a corrupted database system. Traditional damage assessment approaches in a intrusion tolerant database system can only locate damages which are caused by reading corrupted data. In fact, there are many other damage spreading patterns that have not been considered in traditional damage assessment model. In this paper, we systematically analyze inter-transaction dependency relationships that have been neglected in the previous research and propose four different dependency relationships between transactions which may cause damage propagation. We extend existing damage assessment model based on the four novel dependency relationships. The essential properties of our model is also discussed.
Improving Flood Damage Assessment Models in Italy
NASA Astrophysics Data System (ADS)
Amadio, M.; Mysiak, J.; Carrera, L.; Koks, E.
2015-12-01
The use of Stage-Damage Curve (SDC) models is prevalent in ex-ante assessments of flood risk. To assess the potential damage of a flood event, SDCs describe a relation between water depth and the associated potential economic damage over land use. This relation is normally developed and calibrated through site-specific analysis based on ex-post damage observations. In some cases (e.g. Italy) SDCs are transferred from other countries, undermining the accuracy and reliability of simulation results. Against this background, we developed a refined SDC model for Northern Italy, underpinned by damage compensation records from a recent flood event. Our analysis considers both damage to physical assets and production losses from business interruptions. While the first is calculated based on land use information, production losses are measured through the spatial distribution of Gross Value Added (GVA). An additional component of the model assesses crop-specific agricultural losses as a function of flood seasonality. Our results show an overestimation of asset damage from non-calibrated SDC values up to a factor of 4.5 for tested land use categories. Furthermore, we estimate that production losses amount to around 6 per cent of the annual GVA. Also, maximum yield losses are less than a half of the amount predicted by the standard SDC methods.
Application of damage models in metal forming
Zhu, Y.Y.; Zacharia, T.
1995-06-01
The development of damage models in the analysis of metal forming processes, to characterize the formability limits, is an important area of ongoing research. In this paper, two energy-based damage models for the simulation of crack initiation in metal forming processes are presented. The first one is an isotropic damage model with two damage variables. The second one is an anisotropic model with a damage characteristic tensor. The damage models are developed within the general framework of continuum thermodynamics for irreversible processes by identifying a proper set of internal variables together with their associated generalized forces. An approach is proposed to account for microcrack opening and closing. A viscoplastic regularization algorithm is used to take into account the strain rate effect and to improve numerical stability. Both models have been incorporated into the finite element code, LAGAMINE. The models were applied to simulations of upsetting of collar cylinders and nonisothermal hemispherical punch stretching. The results of the analyses were validated by comparing the finite element simulations with experimentally obtained data.
NASA Astrophysics Data System (ADS)
Abdullah, A. B. M.; Rice, Jennifer A.; Hamilton, H. R.
2014-03-01
Post-tensioned segmental bridges are common throughout the US; however, in recent years, the incidence of tendon failure in bonded post-tensioned bridges has raised questions regarding their design, construction, and maintenance. These failures have led to the investigation of the applicability of using replaceable unbonded tendons in segmental construction and new methods for monitoring their condition. This paper presents a damage detection algorithm to identify strand breakage in unbonded tendons based on the relative variation of strains in the anchorage. In unbonded construction, the anchorage assembly usually undergoes a severe stress-state condition as the entire prestressing force only passes through the deviator and end anchorage locations. The strain distribution in the anchorage mechanism, therefore, goes through significant changes in response to the breakage of an individual wire or an entire strand in a multi-strand arrangement. In this way, breakage of a post-tensioning strand can be identified by observing a non-uniform variation of the strain field over the anchorage region in contrast to a uniform variation of strains due to environmental or traffic loading. A reduced scale laboratory experiment is performed followed by an extensive finite element simulation to conduct a parametric study with wire/strand breakages at different locations on multi-strand anchorages commonly used in industry. Based on the observed strain variations from simulation, a damage detection model is proposed that enables the adoption of an automated monitoring strategy to characterize the breakage programmatically.
Modeling laser damage to the retina
NASA Astrophysics Data System (ADS)
Clark, Clifton D.
This dissertation presents recent progress in several areas related to modeling laser damage to the retina. In Chapter 3, we consider the consequences of using the Arrhenius damage model to predict the damage thresholds of multiple pulse, or repetitive pulse, exposures. We have identified a few fundamental trends associated with the multiple pulse damage predictions made by the Arrhenius model. These trends differ from what would be expected by non-thermal mechanisms, and could prove useful in differentiating thermal and non-thermal damage. Chapter 4 presents a new rate equation damage model hypothesized to describe photochemical damage. The model adds a temperature dependent term to the simple rate equation implied by the principle of reciprocity that is characteristic of photochemical damage thresholds. A recent damage threshold study, conducted in-vitro, has revealed a very sharp transition between thermal and photochemical damage threshold trends. For the wavelength used in the experiment (413 nm), thermal damage thresholds were observed at exposure levels that were twice the expected photochemical damage threshold, based on the traditional understanding of photochemical damage. Our model accounts for this observed trend by introducing a temperature dependent quenching, or repair, rate to the photochemical damage rate. For long exposures that give a very small temperature rise, the model reduces to the principle of reciprocity. Near the transition region between thermal and photochemical damage, the model allows the damage threshold to be set by thermal mechanisms, even at exposure above the reciprocity exposure. In Chapter 5, we describe a retina damage model that includes thermal lensing in the eye by coupling beam propagation and heat transfer models together. Thermal lensing has recently been suggested as a contributing factor to the large increase in measured retinal damage thresholds in the near infrared. The transmission of the vitreous decreases
A continuum damage model of fatigue-induced damage in laminated composites
NASA Technical Reports Server (NTRS)
Harris, Charles E.; Allen, David H.
1988-01-01
A model is presented which predicts the stress-strain behavior of continuous fiber reinforced laminated composites in the presence of microstructural damage. The model is based on the concept of continuum damage mechanics and uses internal state variables to characterize the various damage modes. The associated internal state variable growth laws are mathematical models of the loading history induced development of microstructural damage. The model is demonstrated by using it to predict the response of damaged AS-4/3502 graphite/epoxy laminate panels.
NASA Astrophysics Data System (ADS)
Song, Di; Kang, Guozheng; Kan, Qianhua; Yu, Chao; Zhang, Chuanzeng
2015-08-01
Based on the experimental observations for the uniaxial low-cycle stress fatigue failure of super-elastic NiTi shape memory alloy microtubes (Song et al 2015 Smart Mater. Struct. 24 075004) and a new definition of damage variable corresponding to the variation of accumulated dissipation energy, a phenomenological damage model is proposed to describe the damage evolution of the NiTi microtubes during cyclic loading. Then, with a failure criterion of Dc = 1, the fatigue lives of the NiTi microtubes are predicted by the damage-based model, the predicted lives are in good agreement with the experimental ones, and all of the points are located within an error band of 1.5 times.
NASA Astrophysics Data System (ADS)
Zhao, Jie; DeSmidt, Hans; Yao, Wei
2015-04-01
A novel vibration-based damage identification methodology for the truss system with mass and stiffness uncertainties is proposed and demonstrated. This approach utilizes the damaged-induced changes of frequency response functions (FRF) to assess the severity and location of the structural damage in the system. The damage identification algorithm is developed basing on the least square and Newton-Raphson methods. The dynamical model of system is built using finite element method and Lagrange principle while the crack model is based on fracture mechanics. The method is synthesized via numerical examples for a truss system to demonstrate the effectiveness in detecting both stiffness and mass uncertainty existed in the system.
NASA Astrophysics Data System (ADS)
Yu, Chih-Peng; Cheng, Chia-Chi; Lai, Jiunnren; Chiang, Chih-Hung
2012-04-01
In this study, a linear model with frequency dependent structural property was used to generate the corresponding frequency response function and dynamic stiffness for selected dynamic problems where certain nonlinearity can be resulted from time/space varying characteristics of the bridge vibrations. Derivation of the proposed formula is based on the vibration theory of the elementary member with frequency dependent elastic properties, in which Modulus of Elasticity can be interpreted as serial and parallel connections of springs and dashpots. This paper first describes the use of the proposed formulation to reasonably depict the nonlinear cable vibration associated with the varying tension forces over time. The proposed formulation can also be used to simulate flexural vibration of damage beams in which the elastic property involves certain space varying or time varying characteristics. Simple numerical/experimental data were next used to demonstrate and confirm the potential application of such simulation idea. Consequently, it is concluded that such assessment model with frequency dependent parameters can be practically feasible and serve as a useful tool in the spectral analysis regarding dynamic problems of slender bridge members.
A Thermodynamically Consistent Damage Model for Advanced Composites
NASA Technical Reports Server (NTRS)
Maimi, Pere; Camanho, Pedro P.; Mayugo, Joan-Andreu; Davila, Carlos G.
2006-01-01
A continuum damage model for the prediction of damage onset and structural collapse of structures manufactured in fiber-reinforced plastic laminates is proposed. The principal damage mechanisms occurring in the longitudinal and transverse directions of a ply are represented by a damage tensor that is fixed in space. Crack closure under load reversal effects are taken into account using damage variables established as a function of the sign of the components of the stress tensor. Damage activation functions based on the LaRC04 failure criteria are used to predict the different damage mechanisms occurring at the ply level. The constitutive damage model is implemented in a finite element code. The objectivity of the numerical model is assured by regularizing the dissipated energy at a material point using Bazant's Crack Band Model. To verify the accuracy of the approach, analyses of coupon specimens were performed, and the numerical predictions were compared with experimental data.
Brittle damage models in DYNA2D
Faux, D.R.
1997-09-01
DYNA2D is an explicit Lagrangian finite element code used to model dynamic events where stress wave interactions influence the overall response of the system. DYNA2D is often used to model penetration problems involving ductile-to-ductile impacts; however, with the advent of the use of ceramics in the armor-anti-armor community and the need to model damage to laser optics components, good brittle damage models are now needed in DYNA2D. This report will detail the implementation of four brittle damage models in DYNA2D, three scalar damage models and one tensor damage model. These new brittle damage models are then used to predict experimental results from three distinctly different glass damage problems.
Continuum Fatigue Damage Modeling for Use in Life Extending Control
NASA Technical Reports Server (NTRS)
Lorenzo, Carl F.
1994-01-01
This paper develops a simplified continuum (continuous wrp to time, stress, etc.) fatigue damage model for use in Life Extending Controls (LEC) studies. The work is based on zero mean stress local strain cyclic damage modeling. New nonlinear explicit equation forms of cyclic damage in terms of stress amplitude are derived to facilitate the continuum modeling. Stress based continuum models are derived. Extension to plastic strain-strain rate models are also presented. Application of these models to LEC applications is considered. Progress toward a nonzero mean stress based continuum model is presented. Also, new nonlinear explicit equation forms in terms of stress amplitude are also derived for this case.
NASA Astrophysics Data System (ADS)
Molladavoodi, H.
2013-09-01
Analysis of stresses and displacements around underground openings is necessary in a wide variety of civil, petroleum and mining engineering problems. In addition, an excavation damaged zone (EDZ) is generally formed around underground openings as a result of high stress magnitudes even in the absence of blasting effects. The rock materials surrounding the underground excavations typically demonstrate nonlinear and irreversible mechanical response in particular under high in situ stress states. The dominant cause of irreversible deformations in brittle rocks is damage process. One of the most widely used methods in tunnel design is the convergence-confinement method (CCM) for its practical application. The elastic-plastic models are usually used in the convergence-confinement method as a constitutive model for rock behavior. The plastic models used to simulate the rock behavior, do not consider the important issues such as stiffness degradation and softening. Therefore, the use of damage constitutive models in the convergence-confinement method is essential in the design process of rock structures. In this paper, the basic concepts of continuum damage mechanics are outlined. Then a numerical stepwise procedure for a circular tunnel under hydrostatic stress field, with consideration of a damage model for rock mass has been implemented. The ground response curve and radius of excavation damage zone were calculated based on an isotropic damage model. The convergence-confinement method based on damage model can consider the effects of post-peak rock behavior on the ground response curve and excavation damage zone. The analysis of results show the important effect of brittleness parameter on the tunnel wall convergence, ground response curve and excavation damage radius. Analiza naprężeń i przemieszczeń powstałych wokół otworu podziemnego wymagana jest przy szerokiej gamie projektów z zakresu budownictwa lądowego, inżynierii górniczej oraz naftowej. Ponadto
Survey of four damage models for concrete.
Leelavanichkul, Seubpong; Brannon, Rebecca Moss
2009-08-01
properties. The RHT model appears to similarly support optional uncertainty and automated settings for scale-dependent material parameters. The K&C, RHT, and CSCM models support rate dependence by allowing the strength to be a function of strain rate, whereas the BF1 model uses Duvaut-Lion viscoplasticity theory to give a smoother prediction of transient effects. During softening, all four models require a certain amount of strain to develop before allowing significant damage accumulation. For the K&C, RHT, and CSCM models, the strain-to-failure is tied to fracture energy release, whereas a similar effect is achieved indirectly in the BF1 model by a time-based criterion that is tied to crack propagation speed.
Ductile damage model with void coalescence
Tonks, D.L.
1995-03-01
A general model for ductile damage in metals is presented. It includes damage induced by shear stress as well as damage caused by volumetric tension. Spallation is included as a special case. Strain induced damage is also treated. Void nucleation and growth are included and give rise to strain rate effects. Strain rate effects also arise in the model through elastic release wave propagation between damage centers. Underlying physics of the model is the nucleation, growth, and coalescence of voids in a plastically flowing solid. Implementation of the model in hydrocodes is discussed.
Interacting damage models mapped onto ising and percolation models
Toussaint, Renaud; Pride, Steven R.
2004-03-23
The authors introduce a class of damage models on regular lattices with isotropic interactions between the broken cells of the lattice. Quasistatic fiber bundles are an example. The interactions are assumed to be weak, in the sense that the stress perturbation from a broken cell is much smaller than the mean stress in the system. The system starts intact with a surface-energy threshold required to break any cell sampled from an uncorrelated quenched-disorder distribution. The evolution of this heterogeneous system is ruled by Griffith's principle which states that a cell breaks when the release in potential (elastic) energy in the system exceeds the surface-energy barrier necessary to break the cell. By direct integration over all possible realizations of the quenched disorder, they obtain the probability distribution of each damage configuration at any level of the imposed external deformation. They demonstrate an isomorphism between the distributions so obtained and standard generalized Ising models, in which the coupling constants and effective temperature in the Ising model are functions of the nature of the quenched-disorder distribution and the extent of accumulated damage. In particular, they show that damage models with global load sharing are isomorphic to standard percolation theory, that damage models with local load sharing rule are isomorphic to the standard ising model, and draw consequences thereof for the universality class and behavior of the autocorrelation length of the breakdown transitions corresponding to these models. they also treat damage models having more general power-law interactions, and classify the breakdown process as a function of the power-law interaction exponent. Last, they also show that the probability distribution over configurations is a maximum of Shannon's entropy under some specific constraints related to the energetic balance of the fracture process, which firmly relates this type of quenched-disorder based damage model
Interacting damage models mapped onto Ising and percolation models.
Toussaint, Renaud; Pride, Steven R
2005-04-01
We introduce a class of damage models on regular lattices with isotropic interactions between the broken cells of the lattice. Quasi-static fiber bundles are an example. The interactions are assumed to be weak, in the sense that the stress perturbation from a broken cell is much smaller than the mean stress in the system. The system starts intact with a surface-energy threshold required to break any cell sampled from an uncorrelated quenched-disorder distribution. The evolution of this heterogeneous system is ruled by Griffith's principle which states that a cell breaks when the release in potential (elastic) energy in the system exceeds the surface-energy barrier necessary to break the cell. By direct integration over all possible realizations of the quenched disorder, we obtain the probability distribution of each damage configuration at any level of the imposed external deformation. We demonstrate an isomorphism between the distributions so obtained and standard generalized Ising models, in which the coupling constants and effective temperature in the Ising model are functions of the nature of the quenched-disorder distribution and the extent of accumulated damage. In particular, we show that damage models with global load sharing are isomorphic to standard percolation theory and that damage models with a local load sharing rule are isomorphic to the standard Ising model, and draw consequences thereof for the universality class and behavior of the autocorrelation length of the breakdown transitions corresponding to these models. We also treat damage models having more general power-law interactions, and classify the breakdown process as a function of the power-law interaction exponent. Last, we also show that the probability distribution over configurations is a maximum of Shannon's entropy under some specific constraints related to the energetic balance of the fracture process, which firmly relates this type of quenched-disorder based damage model to standard
Vibration-based damage detection algorithm for WTT structures
NASA Astrophysics Data System (ADS)
Nguyen, Tuan-Cuong; Kim, Tae-Hwan; Choi, Sang-Hoon; Ryu, Joo-Young; Kim, Jeong-Tae
2016-04-01
In this paper, the integrity of a wind turbine tower (WTT) structure is nondestructively estimated using its vibration responses. Firstly, a damage detection algorithm using changes in modal characteristics to predict damage locations and severities in structures is outlined. Secondly, a finite element (FE) model based on a real WTT structure is established by using a commercial software, Midas FEA. Thirdly, forced vibration tests are performed on the FE model of the WTT structure under various damage scenarios. The changes in modal parameters such as natural frequencies and mode shapes are examined for damage monitoring in the structure. Finally, the feasibility of the vibration-based damage detection method is numerically verified by predicting locations and severities of the damage in the FE model of the WTT structure.
Micromechanical Modeling of Impact Damage Mechanisms in Unidirectional Composite Laminates
NASA Astrophysics Data System (ADS)
Meng, Qinghua; Wang, Zhenqing
2016-05-01
Composite laminates are susceptible to the transverse impact loads resulting in significant damage such as matrix cracking, fiber breakage and delamination. In this paper, a micromechanical model is developed to predict the impact damage of composite laminates based on microstructure and various failure models of laminates. The fiber and matrix are represented by the isotropic and elastic-plastic solid, and their impact failure behaviors are modeled based on shear damage model. The delaminaton failure is modeling by the interface element controlled by cohesive damage model. Impact damage mechanisms of laminate are analyzed by using the micromechanical model proposed. In addition, the effects of impact energy and laminated type on impact damage behavior of laminates are investigated. Due to the damage of the surrounding matrix near the impact point caused by the fiber deformation, the surface damage area of laminate is larger than the area of impact projectile. The shape of the damage area is roughly rectangle or elliptical with the major axis extending parallel to the fiber direction in the surface layer of laminate. The alternating laminated type with two fiber directions is more propitious to improve the impact resistance of laminates.
NASA Astrophysics Data System (ADS)
Sanders, B. F.; Gallegos, H. A.; Schubert, J. E.
2011-12-01
The Baldwin Hills dam-break flood and associated structural damage is investigated in this study. The flood caused high velocity flows exceeding 5 m/s which destroyed 41 wood-framed residential structures, 16 of which were completed washed out. Damage is predicted by coupling a calibrated hydrodynamic flood model based on the shallow-water equations to structural damage models. The hydrodynamic and damage models are two-way coupled so building failure is predicted upon exceedance of a hydraulic intensity parameter, which in turn triggers a localized reduction in flow resistance which affects flood intensity predictions. Several established damage models and damage correlations reported in the literature are tested to evaluate the predictive skill for two damage states defined by destruction (Level 2) and washout (Level 3). Results show that high-velocity structural damage can be predicted with a remarkable level of skill using established damage models, but only with two-way coupling of the hydrodynamic and damage models. In contrast, when structural failure predictions have no influence on flow predictions, there is a significant reduction in predictive skill. Force-based damage models compare well with a subset of the damage models which were devised for similar types of structures. Implications for emergency planning and preparedness as well as monetary damage estimation are discussed.
Modeling of glass fracture damage using continuum damage mechanics - Static spherical indentation
Sun, Xin; Khaleel, Mohammad A.
2004-07-01
Continuum damage mechanics based constitutive model is used to study the stone-impact resistance of automotive windshields. An axisymmetric finite element model is created to simulate the transient dynamic response and impact induced damge tensors for laminated glass layers subject to stone-impact loading. The windshield glass consists of two glass outer layers laminated by a thin poly-vinyl butyral (PVB) layer. The constitutive behavior of the glass layers is simulated suing continuum damage mechanics model with linear damage evolution. The PVB layer is modeled with linear viscoelastic solid. The model is used to predict and examine damage patterns on different glass surfaces for different windshield designs including variations in ply thickness and curvatures.
Nonlinear creep damage constitutive model for soft rocks
NASA Astrophysics Data System (ADS)
Liu, H. Z.; Xie, H. Q.; He, J. D.; Xiao, M. L.; Zhuo, L.
2016-06-01
In some existing nonlinear creep damage models, it may be less rigorous to directly introduce a damage variable into the creep equation when the damage variable of the viscous component is a function of time or strain. In this paper, we adopt the Kachanov creep damage rate and introduce a damage variable into a rheological differential constitutive equation to derive an analytical integral solution for the creep damage equation of the Bingham model. We also propose a new nonlinear viscous component which reflects nonlinear properties related to the axial stress of soft rock in the steady-state creep stage. Furthermore, we build an improved Nishihara model by using this new component in series with the correctional Nishihara damage model that describes the accelerating creep, and deduce the rheological constitutive relation of the improved model. Based on superposition principle, we obtain the damage creep equation for conditions of both uniaxial and triaxial compression stress, and study the method for determining the model parameters. Finally, this paper presents the laboratory test results performed on mica-quartz schist in parallel with, or vertical to the schistosity direction, and applies the improved Nishihara model to the parameter identification of mica-quartz schist. Using a comparative analysis with test data, results show that the improved model has a superior ability to reflect the creep properties of soft rock in the decelerating creep stage, the steady-state creep stage, and particularly within the accelerating creep stage, in comparison with the traditional Nishihara model.
NASA Technical Reports Server (NTRS)
Pineda, Evan J.; Waas, Anthony M.
2011-01-01
A thermodynamically-based work potential theory for modeling progressive damage and failure in fiber-reinforced laminates is presented. The current, multiple-internal state variable (ISV) formulation, enhanced Schapery theory (EST), utilizes separate ISVs for modeling the effects of damage and failure. Damage is considered to be the effect of any structural changes in a material that manifest as pre-peak non-linearity in the stress versus strain response. Conversely, failure is taken to be the effect of the evolution of any mechanisms that results in post-peak strain softening. It is assumed that matrix microdamage is the dominant damage mechanism in continuous fiber-reinforced polymer matrix laminates, and its evolution is controlled with a single ISV. Three additional ISVs are introduced to account for failure due to mode I transverse cracking, mode II transverse cracking, and mode I axial failure. Typically, failure evolution (i.e., post-peak strain softening) results in pathologically mesh dependent solutions within a finite element method (FEM) setting. Therefore, consistent character element lengths are introduced into the formulation of the evolution of the three failure ISVs. Using the stationarity of the total work potential with respect to each ISV, a set of thermodynamically consistent evolution equations for the ISVs is derived. The theory is implemented into commercial FEM software. Objectivity of total energy dissipated during the failure process, with regards to refinements in the FEM mesh, is demonstrated. The model is also verified against experimental results from two laminated, T800/3900-2 panels containing a central notch and different fiber-orientation stacking sequences. Global load versus displacement, global load versus local strain gage data, and macroscopic failure paths obtained from the models are compared to the experiments.
Probabilistic flood damage modelling at the meso-scale
NASA Astrophysics Data System (ADS)
Kreibich, Heidi; Botto, Anna; Schröter, Kai; Merz, Bruno
2014-05-01
Decisions on flood risk management and adaptation are usually based on risk analyses. Such analyses are associated with significant uncertainty, even more if changes in risk due to global change are expected. Although uncertainty analysis and probabilistic approaches have received increased attention during the last years, they are still not standard practice for flood risk assessments. Most damage models have in common that complex damaging processes are described by simple, deterministic approaches like stage-damage functions. Novel probabilistic, multi-variate flood damage models have been developed and validated on the micro-scale using a data-mining approach, namely bagging decision trees (Merz et al. 2013). In this presentation we show how the model BT-FLEMO (Bagging decision Tree based Flood Loss Estimation MOdel) can be applied on the meso-scale, namely on the basis of ATKIS land-use units. The model is applied in 19 municipalities which were affected during the 2002 flood by the River Mulde in Saxony, Germany. The application of BT-FLEMO provides a probability distribution of estimated damage to residential buildings per municipality. Validation is undertaken on the one hand via a comparison with eight other damage models including stage-damage functions as well as multi-variate models. On the other hand the results are compared with official damage data provided by the Saxon Relief Bank (SAB). The results show, that uncertainties of damage estimation remain high. Thus, the significant advantage of this probabilistic flood loss estimation model BT-FLEMO is that it inherently provides quantitative information about the uncertainty of the prediction. Reference: Merz, B.; Kreibich, H.; Lall, U. (2013): Multi-variate flood damage assessment: a tree-based data-mining approach. NHESS, 13(1), 53-64.
Applicability of mode-based damage assessment methods to severely damaged steel building
NASA Astrophysics Data System (ADS)
HoThu, Hien; Mita, Akira
2012-04-01
After a large earthquake, the evaluation of damage of structures is an important task for structural health assessment. Therefore, the structural health monitoring (SHM) has become major researches which focus in the area of structural dynamics. As we known, the presence of damage or deterioration in a structure can be detected by the changes in the natural frequencies of the structure. Furthermore mode shape changes can be categorized as damage localization1. Besides, many damage detection algorithms based on the modal properties of structure such as modal frequencies, mode shapes, curvature mode shapes and modal flexibilities have been studied for several decades. However, in most algorithms, identifying the precise location and magnitude of the damage is difficult. If not completely impossible, the accuracy and reliability is not sufficient2. Using only modal frequencies and their mode shapes changes to qualify damage seems very difficult to get the real damage in many previous studies. This research desires to test the applicability of mode-based damage assessment method to the real-size building, in order to give correlation between simulation models and real building with the changes in frequencies and mode shapes. The data of the simulations and E-defense Tests on the full-scale four-story steel building will be used to test this exiting method.
Damage modeling and damage detection for structures using a perturbation method
NASA Astrophysics Data System (ADS)
Dixit, Akash
This thesis is about using structural-dynamics based methods to address the existing challenges in the field of Structural Health Monitoring (SHM). Particularly, new structural-dynamics based methods are presented, to model areas of damage, to do damage diagnosis and to estimate and predict the sensitivity of structural vibration properties like natural frequencies to the presence of damage. Towards these objectives, a general analytical procedure, which yields nth-order expressions governing mode shapes and natural frequencies and for damaged elastic structures such as rods, beams, plates and shells of any shape is presented. Features of the procedure include the following: 1. Rather than modeling the damage as a fictitious elastic element or localized or global change in constitutive properties, it is modeled in a mathematically rigorous manner as a geometric discontinuity. 2. The inertia effect (kinetic energy), which, unlike the stiffness effect (strain energy), of the damage has been neglected by researchers, is included in it. 3. The framework is generic and is applicable to wide variety of engineering structures of different shapes with arbitrary boundary conditions which constitute self adjoint systems and also to a wide variety of damage profiles and even multiple areas of damage. To illustrate the ability of the procedure to effectively model the damage, it is applied to beams using Euler-Bernoulli and Timoshenko theories and to plates using Kirchhoff's theory, supported on different types of boundary conditions. Analytical results are compared with experiments using piezoelectric actuators and non-contact Laser-Doppler Vibrometer sensors. To illustrate the ability of the procedure to effectively model the damage, it is applied to beams using Euler-Bernoulli and Timoshenko theories and to plates using Kirchhoff's theory, supported on different types of boundary conditions. Analytical results are compared with experiments using piezoelectric actuators and
Doblaré, M; García, J M
2001-09-01
In this work, a new model for internal anisotropic bone remodelling is applied to the study of the remodelling behaviour of the proximal femur before and after total hip replacement (THR). This model considers bone remodelling under the scope of a general damage-repair theory following the principles of continuum damage mechanics. A "damage-repair" tensor is defined in terms of the apparent density and Cowin's "fabric tensor", respectively, associated with porosity and directionality of the trabeculae. The different elements of a thermodynamically consistent damage theory are established, including resorption and apposition criteria, evolution law and rate of remodelling. All of these elements were introduced and discussed in detail in a previous paper (García, J. M., Martinez, M. A., Doblaré, M., 2001. An anisotrophic internal-external bone adaptation model based on a combination of CAO and continuum damage mechanics technologies. Computer Methods in Biomechanics and Biomedical Engineering 4(4), 355-378.), including the definition of the proposed mechanical stimulus and the qualitative properties of the model. In this paper, the fundamentals of the proposed model are briefly reviewed and the computational aspects of its implementation are discussed. This model is then applied to the analysis of the remodelling behaviour of the intact femur obtaining densities and mass principal values and directions very close to the experimental data. The second application involved the proximal femoral extremity after THR and the inclusion of an Exeter prosthesis. As a result of the simulation process, some well-known features previously detected in medical clinics were recovered, such as the stress yielding effect in the proximal part of the implant or the enlargement of the cortical layer at the distal part of the implant. With respect to the anisotropic properties, bone microstructure and local stiffness are known to tend to align with the stress principal directions. This
Development of a viscoelastic continuum damage model for cyclic loading
NASA Astrophysics Data System (ADS)
Sullivan, R. W.
2008-12-01
A previously developed spectrum model for linear viscoelastic behavior of solids is used to describe the rate-dependent damage growth of a time dependent material under cyclic loading. Through the use of the iterative solution of a special Volterra integral equation, the cyclic strain history is described. The spectrum-based model is generalized for any strain rate and any uniaxial load history to formulate the damage function. Damage evolution in the body is described through the use of a rate-type evolution law which uses a pseudo strain to express the viscoelastic constitutive equation with damage. The resulting damage function is used to formulate a residual strength model. The methodology presented is demonstrated by comparing the peak values of the computed cyclic strain history as well as the residual strength model predictions to the experimental data of a polymer matrix composite.
Schaller, Martin; Bein, Matthias; Korting, Hans C.; Baur, Stefan; Hamm, Gerald; Monod, Michel; Beinhauer, Sabine; Hube, Bernhard
2003-01-01
Secreted aspartyl proteinases (Saps) contribute to the ability of Candida albicans to cause mucosal and disseminated infections. A model of vaginal candidiasis based on reconstituted human vaginal epithelium (RHVE) was used to study the expression and role of these C. albicans proteinases during infection and tissue damage of vaginal epithelium. Colonization of the RHVE by C. albicans SC5314 did not cause any visible epithelial damage 6 h after inoculation, although expression of SAP2, SAP9, and SAP10 was detected by reverse transcriptase PCR. However, significant epithelial damage was observed after 12 h, concomitant with the additional expression of SAP1, SAP4, and SAP5. Additional transcripts of SAP6 and SAP7 were detected at a later stage of the artificial infection (24 h). Similar SAP expression profiles were observed in three samples isolated from human patients with vaginal candidiasis. In experimental infection, secretion of antigens Sap1 to Sap6 by C. albicans was confirmed at the ultrastructural level by using polyclonal antisera raised against Sap1 to Sap6. Addition of the aspartyl proteinase inhibitors pepstatin A and the human immunodeficiency virus proteinase inhibitors ritonavir and amprenavir strongly reduced the tissue damage of the vaginal epithelia by C. albicans cells. Furthermore, SAP null mutants lacking either SAP1 or SAP2 had a drastically reduced potential to cause tissue damage even though SAP3, SAP4, and SAP7 were up-regulated in these mutants. In contrast the vaginopathic potential of mutants lacking SAP3 or SAP4 to SAP6 was not reduced compared to wild-type cells. These data provide further evidence for a crucial role of Sap1 and Sap2 in C. albicans vaginal infections. PMID:12761103
NASA Technical Reports Server (NTRS)
Dateo, Christopher E.; Fletcher, Graham D.
2004-01-01
As part of the database for building up a biochemical model of DNA radiation damage, electron impact ionization cross sections of sugar-phosphate backbone and DNA bases have been calculated using the improved binary-encounter dipole (iBED) model. It is found that the total ionization cross sections of C3'- and C5'-deoxyribose-phospate, two conformers of the sugar-phosphate backbone, are close to each other. Furthermore, the sum of the ionization cross sections of the separate deoxyribose and phosphate fragments is in close agreement with the C3'- and C5'-deoxyribose-phospate cross sections, differing by less than 10%. Of the four DNA bases, the ionization cross section of guanine is the largest, then in decreasing order, adenine, thymine, and cytosine. The order is in accordance with the known propensity of oxidation of the bases by ionizing radiation. Dissociative ionization (DI), a process that both ionizes and dissociates a molecule, is investigated for cytosine. The DI cross section for the formation of H and (cytosine-Hl)(+), with the cytosine ion losing H at the 1 position, is also reported. The threshold of this process is calculated to be 17.1 eV. Detailed analysis of ionization products such as in DI is important to trace the sequential steps in the biochemical process of DNA damage.
NASA Technical Reports Server (NTRS)
Koharchik, Michael; Murphy, Lindsay; Parker, Paul
2012-01-01
An impact model was developed to predict how three specific foam types would damage the Space Shuttle Orbiter insulating tiles. The inputs needed for the model are the foam type, the foam mass, the foam impact velocity, the foam impact incident angle, the type being impacted, and whether the tile is new or aged (has flown at least one mission). The model will determine if the foam impact will cause damage to the tile. If it can cause damage, the model will output the damage cavity dimensions (length, depth, entry angle, exit angle, and sidewall angles). It makes the calculations as soon as the inputs are entered (less than 1 second). The model allows for the rapid calculation of numerous scenarios in a short time. The model was developed from engineering principles coupled with significant impact testing (over 800 foam impact tests). This model is applicable to masses ranging from 0.0002 up to 0.4 pound (0.09 up to 181 g). A prior tool performed a similar function, but was limited to the assessment of a small range of masses and did not have the large test database for verification. In addition, the prior model did not provide outputs of the cavity damage length, entry angle, exit angle, or sidewall angles.
Nucleation in models of damage mechanics
NASA Astrophysics Data System (ADS)
Gran, J. D.; Rundle, J. B.; Klein, W.; Turcotte, D. L.
2010-12-01
A variety of studies have modeled the physics of material deformation and damage as examples of generalized phase transitions, involving either critical phenomena or spinodal nucleation. Here we study two cellular automaton models of damage mechanics which. The first model is a modified slider-block model with failure threshold weakening. A block is considered partially damaged after its first slip, and any subsequent failure of that block will occur at reduced failure threshold. Damage here is defined as the fraction of blocks that have a reduced failure threshold. The threshold weakening parameter is viewed as a scaling field similar to the occupation probability in site percolation. The second model is time-dependent fiber-bundle model, where the time to failure for each element is specified from a Poissonian distribution and the hazard rate is assumed to have a power-law dependence on stress. Damage here is defined to be the fraction of blocks or fibers that have failed. Because there is no healing, catastrophic failure occurs. The transient behavior prior to rupture propagation is studied and scaling laws are obtained. We compare both models to mean-field percolation which has been shown to be representative of spinodal nucleation and to laboratory experiments that display power-law behavior.
NASA Astrophysics Data System (ADS)
Romo, David Ricardo
Foreign Object Debris/Damage (FOD) has been an issue for military and commercial aircraft manufacturers since the early ages of aviation and aerospace. Currently, aerospace is growing rapidly and the chances of FOD presence are growing as well. One of the principal causes in manufacturing is the human error. The cost associated with human error in commercial and military aircrafts is approximately accountable for 4 billion dollars per year. This problem is currently addressed with prevention programs, elimination techniques, and designation of FOD areas, controlled access, restrictions of personal items entering designated areas, tool accountability, and the use of technology such as Radio Frequency Identification (RFID) tags, etc. All of the efforts mentioned before, have not show a significant occurrence reduction in terms of manufacturing processes. On the contrary, a repetitive path of occurrence is present, and the cost associated has not declined in a significant manner. In order to address the problem, this thesis proposes a new approach using statistical analysis. The effort of this thesis is to create a predictive model using historical categorical data from an aircraft manufacturer only focusing in human error causes. The use of contingency tables, natural logarithm of the odds and probability transformation is used in order to provide the predicted probabilities of each aircraft. A case of study is shown in this thesis in order to show the applied methodology. As a result, this approach is able to predict the possible outcomes of FOD by the workstation/area needed, and monthly predictions per workstation. This thesis is intended to be the starting point of statistical data analysis regarding FOD in human factors. The purpose of this thesis is to identify the areas where human error is the primary cause of FOD occurrence in order to design and implement accurate solutions. The advantages of the proposed methodology can go from the reduction of cost
NASA Astrophysics Data System (ADS)
Ochiai, S.; Okuda, H.; Fujimoto, M.; Shin, J.-K.; Sugano, M.; Hojo, M.; Osamura, K.; Oh, S. S.; Ha, D. W.
2012-05-01
The change in n-value and critical current with bending strain and the relation of n-value to critical current of bending-damaged Bi2223 composite tape were studied experimentally and analytically. The n-value of the bending-damaged Bi2223 filamentary composite tape decreased very slightly with increasing bending strain and with decreasing critical current, in comparison with that of tension-damaged tape. To describe the experimental result for bending-damaged tape, a damage evolution model was applied in which the steep tensile-strain variation in the thickness direction, the shape of the core into which the superconducting filaments are bundled and the damage strain parameters obtained from the analysis of the tensile stress-strain curve were incorporated. The measured change in n-value and critical current with bending strain and the relation of n-value to critical current under applied bending strain were described satisfactorily by the present approach.
NASA Astrophysics Data System (ADS)
Gao, Dongyue; Wu, Zhanjun; Yang, Lei; Zheng, Yuebin
2016-04-01
Multi-damage identification is an important and challenging task in the research of guide waves-based structural health monitoring. In this paper, a multi-damage identification method is presented using a guide waves-based local probability-based diagnostic imaging (PDI) method. The method includes a path damage judgment stage, a multi-damage judgment stage and a multi-damage imaging stage. First, damage imaging was performed by partition. The damage imaging regions are divided into beside damage signal paths. The difference in guide waves propagation characteristics between cross and beside damage paths is proposed by theoretical analysis of the guide wave signal feature. The time-of-flight difference of paths is used as a factor to distinguish between cross and beside damage paths. Then, a global PDI method (damage identification using all paths in the sensor network) is performed using the beside damage path network. If the global PDI damage zone crosses the beside damage path, it means that the discrete multi-damage model (such as a group of holes or cracks) has been misjudged as a continuum single-damage model (such as a single hole or crack) by the global PDI method. Subsequently, damage imaging regions are separated by beside damage path and local PDI (damage identification using paths in the damage imaging regions) is performed in each damage imaging region. Finally, multi-damage identification results are obtained by superimposing the local damage imaging results and the marked cross damage paths. The method is employed to inspect the multi-damage in an aluminum plate with a surface-mounted piezoelectric ceramic sensors network. The results show that the guide waves-based multi-damage identification method is capable of visualizing the presence, quantity and location of structural damage.
NASA Astrophysics Data System (ADS)
Iseri, Y.; Iwasaki, A.; Miyazaki, C.; Kanae, S.
2014-12-01
Tropical cyclones (TCs) sometimes cause serious damages to human society and thus possible changes of TC properties in the future have been concerned. In fact, the Fifth Assessment Report (AR5) by IPCC (Intergovernmental Panel on Climate Change) mentions likely increasing in intensity and rain rate of TCs. In addition, future change of socioeconomic condition (e.g. population growth) might worsen TC impacts in the future. Thereby, in this study, we developed regression models to estimate economic damages by TCs (hereafter TC damage model), and employed those models to project TC economic damages under several future climate and socioeconomic scenarios. We developed the TC damage models for each of 4 regions; western North Pacific, North American, North Indian, and Southern Hemisphere. The inputs for TC damage model are tropical cyclone central pressure, populations in the area exposed by tropical cyclone wind, and GDP (Gross Domestic Product) per capita. The TC damage models we firstly developed tended to overestimate very low damages and also underestimate very high damages. Thereby we modified structure of TC damage models to improve model performance, and then executed extensive validation of the model. The modified model presented better performance in estimating very low and high TC damages. After the modification and validation of the model, we determined the structure of TC damage models and projected TC economic damages. The result indicated increase in TC economic damage in global scale, while TC economic damage against world GDP would decrease in the future, which result is consistent with previous study.
Vibration Based Sun Gear Damage Detection
NASA Technical Reports Server (NTRS)
Hood, Adrian; LaBerge, Kelsen; Lewicki, David; Pines, Darryll
2013-01-01
Seeded fault experiments were conducted on the planetary stage of an OH-58C helicopter transmission. Two vibration based methods are discussed that isolate the dynamics of the sun gear from that of the planet gears, bearings, input spiral bevel stage, and other components in and around the gearbox. Three damaged sun gears: two spalled and one cracked, serve as the focus of this current work. A non-sequential vibration separation algorithm was developed and the resulting signals analyzed. The second method uses only the time synchronously averaged data but takes advantage of the signal/source mapping required for vibration separation. Both algorithms were successful in identifying the spall damage. Sun gear damage was confirmed by the presence of sun mesh groups. The sun tooth crack condition was inconclusive.
Sequential damage detection based on the continuous wavelet transform
NASA Astrophysics Data System (ADS)
Liao, Yizheng; Balafas, Konstantinos; Rajagopal, Ram; Kiremidjian, Anne S.
2015-03-01
This paper presents a sequential structural damage detection algorithm that is based on a statistical model for the wavelet transform of the structural responses. The detector uses the coefficients of the wavelet model and does not require prior knowledge of the structural properties. Principal Component Analysis is applied to select and extract the most sensitive features from the wavelet coefficients as the damage sensitive features. The damage detection algorithm is validated using the simulation data collected from a four-story steel moment frame. Various features have been explored and the detection algorithm was able to identify damage. Additionally, we show that for a desired probability of false alarm, the proposed detector is asymptotically optimal on the expected delay.
Mathematical modeling of damage in unidirectional composites
NASA Technical Reports Server (NTRS)
Goree, J. G.; Dharani, L. R.; Jones, W. F.
1981-01-01
A review of some approximate analytical models for damaged, fiber reinforced composite materials is presented. Using the classical shear lag stress displacement assumption, solutions are presented for a unidirectional laminate containing a notch, a rectangular cut-out, and a circular hole. The models account for longitudinal matrix yielding and splitting as well as transverse matrix yielding and fiber breakage. The constraining influence of a cover sheet on the unidirectional laminate is also modeled.
Unwin, Stephen D.; Lowry, Peter P.; Layton, Robert F.; Toloczko, Mychailo B.; Johnson, Kenneth I.; Sanborn, Scott E.
2011-07-01
This is a working report drafted under the Risk-Informed Safety Margin Characterization pathway of the Light Water Reactor Sustainability Program, describing statistical models of passives component reliabilities.
Density Functional Theory Models for Radiation Damage
NASA Astrophysics Data System (ADS)
Dudarev, S. L.
2013-07-01
Density functional theory models developed over the past decade provide unique information about the structure of nanoscale defects produced by irradiation and about the nature of short-range interaction between radiation defects, clustering of defects, and their migration pathways. These ab initio models, involving no experimental input parameters, appear to be as quantitatively accurate and informative as the most advanced experimental techniques developed for the observation of radiation damage phenomena. Density functional theory models have effectively created a new paradigm for the scientific investigation and assessment of radiation damage effects, offering new insight into the origin of temperature- and dose-dependent response of materials to irradiation, a problem of pivotal significance for applications.
Irreversible entropy model for damage diagnosis in resistors
Cuadras, Angel Crisóstomo, Javier; Ovejas, Victoria J.; Quilez, Marcos
2015-10-28
We propose a method to characterize electrical resistor damage based on entropy measurements. Irreversible entropy and the rate at which it is generated are more convenient parameters than resistance for describing damage because they are essentially positive in virtue of the second law of thermodynamics, whereas resistance may increase or decrease depending on the degradation mechanism. Commercial resistors were tested in order to characterize the damage induced by power surges. Resistors were biased with constant and pulsed voltage signals, leading to power dissipation in the range of 4–8 W, which is well above the 0.25 W nominal power to initiate failure. Entropy was inferred from the added power and temperature evolution. A model is proposed to understand the relationship among resistance, entropy, and damage. The power surge dissipates into heat (Joule effect) and damages the resistor. The results show a correlation between entropy generation rate and resistor failure. We conclude that damage can be conveniently assessed from irreversible entropy generation. Our results for resistors can be easily extrapolated to other systems or machines that can be modeled based on their resistance.
Adaptive Finite Element Methods for Continuum Damage Modeling
NASA Technical Reports Server (NTRS)
Min, J. B.; Tworzydlo, W. W.; Xiques, K. E.
1995-01-01
The paper presents an application of adaptive finite element methods to the modeling of low-cycle continuum damage and life prediction of high-temperature components. The major objective is to provide automated and accurate modeling of damaged zones through adaptive mesh refinement and adaptive time-stepping methods. The damage modeling methodology is implemented in an usual way by embedding damage evolution in the transient nonlinear solution of elasto-viscoplastic deformation problems. This nonlinear boundary-value problem is discretized by adaptive finite element methods. The automated h-adaptive mesh refinements are driven by error indicators, based on selected principal variables in the problem (stresses, non-elastic strains, damage, etc.). In the time domain, adaptive time-stepping is used, combined with a predictor-corrector time marching algorithm. The time selection is controlled by required time accuracy. In order to take into account strong temperature dependency of material parameters, the nonlinear structural solution a coupled with thermal analyses (one-way coupling). Several test examples illustrate the importance and benefits of adaptive mesh refinements in accurate prediction of damage levels and failure time.
Herr, Lisa; Friedrich, Thomas; Durante, Marco; Scholz, Michael
2014-01-01
We present a new approach to model dose rate effects on cell killing after photon radiation based on the spatio-temporal clustering of DNA double strand breaks (DSBs) within higher order chromatin structures of approximately 1-2 Mbp size, so called giant loops. The main concept of this approach consists of a distinction of two classes of lesions, isolated and clustered DSBs, characterized by the number of double strand breaks induced in a giant loop. We assume a low lethality and fast component of repair for isolated DSBs and a high lethality and slow component of repair for clustered DSBs. With appropriate rates, the temporal transition between the different lesion classes is expressed in terms of five differential equations. These allow formulating the dynamics involved in the competition of damage induction and repair for arbitrary dose rates and fractionation schemes. Final cell survival probabilities are computable with a cell line specific set of three parameters: The lethality for isolated DSBs, the lethality for clustered DSBs and the half-life time of isolated DSBs. By comparison with larger sets of published experimental data it is demonstrated that the model describes the cell line dependent response to treatments using either continuous irradiation at a constant dose rate or to split dose irradiation well. Furthermore, an analytic investigation of the formulation concerning single fraction treatments with constant dose rates in the limiting cases of extremely high or low dose rates is presented. The approach is consistent with the Linear-Quadratic model extended by the Lea-Catcheside factor up to the second moment in dose. Finally, it is shown that the model correctly predicts empirical findings about the dose rate dependence of incidence probabilities for deterministic radiation effects like pneumonitis and the bone marrow syndrome. These findings further support the general concepts on which the approach is based. PMID:24392100
Electromagnetomechanical elastodynamic model for Lamb wave damage quantification in composites
NASA Astrophysics Data System (ADS)
Borkowski, Luke; Chattopadhyay, Aditi
2014-03-01
Physics-based wave propagation computational models play a key role in structural health monitoring (SHM) and the development of improved damage quantification methodologies. Guided waves (GWs), such as Lamb waves, provide the capability to monitor large plate-like aerospace structures with limited actuators and sensors and are sensitive to small scale damage; however due to the complex nature of GWs, accurate and efficient computation tools are necessary to investigate the mechanisms responsible for dispersion, coupling, and interaction with damage. In this paper, the local interaction simulation approach (LISA) coupled with the sharp interface model (SIM) solution methodology is used to solve the fully coupled electro-magneto-mechanical elastodynamic equations for the piezoelectric and piezomagnetic actuation and sensing of GWs in fiber reinforced composite material systems. The final framework provides the full three-dimensional displacement as well as electrical and magnetic potential fields for arbitrary plate and transducer geometries and excitation waveform and frequency. The model is validated experimentally and proven computationally efficient for a laminated composite plate. Studies are performed with surface bonded piezoelectric and embedded piezomagnetic sensors to gain insight into the physics of experimental techniques used for SHM. The symmetric collocation of piezoelectric actuators is modeled to demonstrate mode suppression in laminated composites for the purpose of damage detection. The effect of delamination and damage (i.e., matrix cracking) on the GW propagation is demonstrated and quantified. The developed model provides a valuable tool for the improvement of SHM techniques due to its proven accuracy and computational efficiency.
A damage mechanics based general purpose interface/contact element
NASA Astrophysics Data System (ADS)
Yan, Chengyong
Most of the microelectronics packaging structures consist of layered substrates connected with bonding materials, such as solder or epoxy. Predicting the thermomechanical behavior of these multilayered structures is a challenging task in electronic packaging engineering. In a layered structure the most complex part is always the interfaces between the strates. Simulating the thermo-mechanical behavior of such interfaces, is the main theme of this dissertation. The most commonly used solder material, Pb-Sn alloy, has a very low melting temperature 180sp°C, so that the material demonstrates a highly viscous behavior. And, creep usually dominates the failure mechanism. Hence, the theory of viscoplasticity is adapted to describe the constitutive behavior. In a multilayered assembly each layer has a different coefficient of thermal expansion. Under thermal cycling, due to heat dissipated from circuits, interfaces and interconnects experience low cycle fatigue. Presently, the state-of-the art damage mechanics model used for fatigue life predictions is based on Kachanov (1986) continuum damage model. This model uses plastic strain as a damage criterion. Since plastic strain is a stress path dependent value, the criterion does not yield unique damage values for the same state of stress. In this dissertation a new damage evolution equation based on the second law of thermodynamic is proposed. The new criterion is based on the entropy of the system and it yields unique damage values for all stress paths to the final state of stress. In the electronics industry, there is a strong desire to develop fatigue free interconnections. The proposed interface/contact element can also simulate the behavior of the fatigue free Z-direction thin film interconnections as well as traditional layered interconnects. The proposed interface element can simulate behavior of a bonded interface or unbonded sliding interface, also called contact element. The proposed element was verified against
Modeling Coal Seam Damage in Cast Blasting
Chung, S.H.; Preece, D.S.
1998-11-23
A discrete element computer program named DMC_BLAST (Distinct Motion Code) has been under development since 1987 for modeling rock blasting (Preece & Taylor, 1989). This program employs explicit time integration and uses spherical or cylindrical elements that are represented as circles in two dimensions. DMC_BLAST calculations compare favorably with data from actual bench blasts (Preece et al, 1993). Coal seam chilling refers to the shattering of a significant portion of the coal leaving unusable fines. It is also refereed to as coal damage. Chilling is caused during a blast by a combination of explosive shock energy and movement of the adjacent rock. Chilling can be minimized by leaving a buffer zone between the bottom of the blastholes and the coal seam or by changing the blast design to decrease the powder factor or by a combination of both. Blast design in coal mine cast blasting is usually a compromise between coal damage and rock fragmentation and movement (heave). In this paper the damage to coal seams from rock movement is examined using the discrete element computer code DMC_BLAST. A rock material strength option has been incorporated into DMC_BLAST by placing bonds/links between the spherical particles used to model the rock. These bonds tie the particles together but can be broken when the tensile, compressive or shear stress in the bond exceeds the defined strength. This capability has been applied to predict coal seam damage, particularly at the toe of a cast blast where drag forces exerted by movement of the overlying rock can adversely effect the top of the coal at the bench face. A simulation of coal mine cast blasting has been performed with special attention being paid to the strength of the coal and its behavior at t he bench face during movement of the overlying material.
An overview of modal-based damage identification methods
Farrar, C.R.; Doebling, S.W.
1997-09-01
This paper provides an overview of methods that examine changes in measured vibration response to detect, locate, and characterize damage in structural and mechanical systems. The basic idea behind this technology is that modal parameters (notably frequencies, mode shapes, and modal damping) are functions of the physical properties of the structure (mass, damping, and stiffness). Therefore, changes in the physical properties will cause detectable changes in the modal properties. The motivation for the development of this technology is first provided. The methods are then categorized according to various criteria such as the level of damage detection provided, model-based vs. non-model-based methods and linear vs. nonlinear methods. This overview is limited to methods that can be adapted to a wide range of structures (i.e., are not dependent on a particular assumed model form for the system such as beam-bending behavior and methods and that are not based on updating finite element models). Next, the methods are described in general terms including difficulties associated with their implementation and their fidelity. Past, current and future-planned applications of this technology to actual engineering systems are summarized. The paper concludes with a discussion of critical issues for future research in the area of modal-based damage identification.
Modeling neural activity with cumulative damage distributions.
Leiva, Víctor; Tejo, Mauricio; Guiraud, Pierre; Schmachtenberg, Oliver; Orio, Patricio; Marmolejo-Ramos, Fernando
2015-10-01
Neurons transmit information as action potentials or spikes. Due to the inherent randomness of the inter-spike intervals (ISIs), probabilistic models are often used for their description. Cumulative damage (CD) distributions are a family of probabilistic models that has been widely considered for describing time-related cumulative processes. This family allows us to consider certain deterministic principles for modeling ISIs from a probabilistic viewpoint and to link its parameters to values with biological interpretation. The CD family includes the Birnbaum-Saunders and inverse Gaussian distributions, which possess distinctive properties and theoretical arguments useful for ISI description. We expand the use of CD distributions to the modeling of neural spiking behavior, mainly by testing the suitability of the Birnbaum-Saunders distribution, which has not been studied in the setting of neural activity. We validate this expansion with original experimental and simulated electrophysiological data. PMID:25998210
Shell-NASA Vibration-Based Damage Characterization
NASA Technical Reports Server (NTRS)
Rollins, John M.
2014-01-01
This article describes collaborative research between Shell International Exploration and Production (IE&P) scientists and ISAG personnel to investigate the feasibility of ultrasonic-based characterization of spacecraft tile damage for in-space inspection applications. The approach was proposed by Shell personnel in a Shell-NASA "speed-matching" session in early 2011 after ISAG personnel described challenges inherent in the inspection of MMOD damage deep within spacecraft thermal protection system (TPS) tiles. The approach leveraged Shell's relevant sensor and analytical expertise. The research addressed the difficulties associated with producing 3D models of MMOD damage cavities under the surface of a TPS tile, given that simple image-based sensing is constrained by line of sight through entry holes that have diameters considerably smaller than the underlying damage cavities. Damage cavity characterization is needed as part of a vehicle inspection and risk reduction capability for long-duration, human-flown space missions. It was hoped that cavity characterization could be accomplished through the use of ultrasonic techniques that allow for signal penetration through solid material.
Damage modeling for Taylor impact simulations
NASA Astrophysics Data System (ADS)
Anderson, C. E., Jr.; Chocron, I. S.; Nicholls, A. E.
2006-08-01
G. I. Taylor showed that dynamic material properties could be deduced from the impact of a projectile against a rigid boundary. The Taylor anvil test became very useful with the advent of numerical simulations and has been used to infer and/or to validate material constitutive constants. A new experimental facility has been developed to conduct Taylor anvil impacts to support validation of constitutive constants used in simulations. Typically, numerical simulations are conducted assuming 2-D cylindrical symmetry, but such computations cannot hope to capture the damage observed in higher velocity experiments. A computational study was initiated to examine the ability to simulate damage and subsequent deformation of the Taylor specimens. Three-dimensional simulations, using the Johnson-Cook damage model, were conducted with the nonlinear Eulerian wavecode CTH. The results of the simulations are compared to experimental deformations of 6061-T6 aluminum specimens as a function of impact velocity, and conclusions regarding the ability to simulate fracture and reproduce the observed deformations are summarized.
Dynamic rupture in a damage-breakage rheology model
NASA Astrophysics Data System (ADS)
Lyakhovsky, Vladimir; Ben-Zion, Yehuda; Ilchev, Assen; Mendecki, Aleksander
2016-05-01
We present a thermodynamically-based formulation for modeling dynamic rupture processes in the brittle crust using a continuum damage-breakage rheology. The model combines aspects of a continuum viscoelastic damage framework for brittle solids with a continuum breakage mechanics for granular flow within dynamically generated slip zones. The formulation accounts for the density of distributed cracking and other internal flaws in damaged rocks with a scalar damage parameter, and addresses the grain size distribution of a granular phase in the slip zone with a breakage parameter. A dynamic brittle instability is associated with a critical level of damage in the solid, leading to loss of convexity of the solid strain energy, localization, and transition to a granular phase associated with lower energy level. The continuum damage-breakage rheology model treats the localization to a slip zone at the onset of dynamic rupture and post-failure recovery process as phase transitions between solid and granular states. The model generates sub- and super-shear rupture velocities and pulse-type ruptures seen also in frictional models, and additional important features such as strong dynamic changes of volumetric strain near the rupture front and diversity of nucleation mechanisms. The propagation of rupture front and slip accumulation at a point are correlated with sharp dynamic dilation followed by a gradual decay to a level associated with the final volumetric change associated with the granular phase transition in the slipping zone. The local brittle failure process associated with the solid-granular transition is expected to produce isotropic radiation in addition to the deviatoric terms. The framework significantly extends the ability to model brittle processes in complex geometrical structures and allows analyzing the roles of gouge thickness and other parameters on nucleation, rupture and radiation characteristics.
Dynamic rupture in a damage-breakage rheology model
NASA Astrophysics Data System (ADS)
Lyakhovsky, Vladimir; Ben-Zion, Yehuda; Ilchev, Assen; Mendecki, Aleksander
2016-08-01
We present a thermodynamically based formulation for modelling dynamic rupture processes in the brittle crust using a continuum damage-breakage rheology. The model combines aspects of a continuum viscoelastic damage framework for brittle solids with a continuum breakage mechanics for granular flow within dynamically generated slip zones. The formulation accounts for the density of distributed cracking and other internal flaws in damaged rocks with a scalar damage parameter, and addresses the grain size distribution of a granular phase in the slip zone with a breakage parameter. A dynamic brittle instability is associated with a critical level of damage in the solid, leading to loss of convexity of the solid strain energy, localization and transition to a granular phase associated with lower energy level. The continuum damage-breakage rheology model treats the localization to a slip zone at the onset of dynamic rupture and post-failure recovery process as phase transitions between solid and granular states. The model generates sub- and supershear rupture velocities and pulse-type ruptures seen also in frictional models, and additional important features such as strong dynamic changes of volumetric strain near the rupture front and diversity of nucleation mechanisms. The propagation of rupture front and slip accumulation at a point are correlated with sharp dynamic dilation followed by a gradual decay to a level associated with the final volumetric change associated with the granular phase transition in the slipping zone. The local brittle failure process associated with the solid-granular transition is expected to produce isotropic radiation in addition to the deviatoric terms. The framework significantly extends the ability to model brittle processes in complex geometrical structures and allows analysing the roles of gouge thickness and other parameters on nucleation, rupture and radiation characteristics.
NASA Astrophysics Data System (ADS)
Li, L. C.; Tang, C. A.; Li, G.; Wang, S. Y.; Liang, Z. Z.; Zhang, Y. B.
2012-09-01
The failure mechanism of hydraulic fractures in heterogeneous geological materials is an important topic in mining and petroleum engineering. A three-dimensional (3D) finite element model that considers the coupled effects of seepage, damage, and the stress field is introduced. This model is based on a previously developed two-dimensional (2D) version of the model (RFPA2D-Rock Failure Process Analysis). The RFPA3D-Parallel model is developed using a parallel finite element method with a message-passing interface library. The constitutive law of this model considers strength and stiffness degradation, stress-dependent permeability for the pre-peak stage, and deformation-dependent permeability for the post-peak stage. Using this model, 3D modelling of progressive failure and associated fluid flow in rock are conducted and used to investigate the hydro-mechanical response of rock samples at laboratory scale. The responses investigated are the axial stress-axial strain together with permeability evolution and fracture patterns at various stages of loading. Then, the hydraulic fracturing process inside a rock specimen is numerically simulated. Three coupled processes are considered: (1) mechanical deformation of the solid medium induced by the fluid pressure acting on the fracture surfaces and the rock skeleton, (2) fluid flow within the fracture, and (3) propagation of the fracture. The numerically simulated results show that the fractures from a vertical wellbore propagate in the maximum principal stress direction without branching, turning, and twisting in the case of a large difference in the magnitude of the far-field stresses. Otherwise, the fracture initiates in a non-preferred direction and plane then turns and twists during propagation to become aligned with the preferred direction and plane. This pattern of fracturing is common when the rock formation contains multiple layers with different material properties. In addition, local heterogeneity of the rock
A 3D Orthotropic Strain-Rate Dependent Elastic Damage Material Model.
English, Shawn Allen
2014-09-01
A three dimensional orthotropic elastic constitutive model with continuum damage and cohesive based fracture is implemented for a general polymer matrix composite lamina. The formulation assumes the possibility of distributed (continuum) damage followed b y localized damage. The current damage activation functions are simply partially interactive quadratic strain criteria . However, the code structure allows for changes in the functions without extraordinary effort. The material model formulation, implementation, characterization and use cases are presented.
Damage Propagation Modeling for Aircraft Engine Prognostics
NASA Technical Reports Server (NTRS)
Saxena, Abhinav; Goebel, Kai; Simon, Don; Eklund, Neil
2008-01-01
This paper describes how damage propagation can be modeled within the modules of aircraft gas turbine engines. To that end, response surfaces of all sensors are generated via a thermo-dynamical simulation model for the engine as a function of variations of flow and efficiency of the modules of interest. An exponential rate of change for flow and efficiency loss was imposed for each data set, starting at a randomly chosen initial deterioration set point. The rate of change of the flow and efficiency denotes an otherwise unspecified fault with increasingly worsening effect. The rates of change of the faults were constrained to an upper threshold but were otherwise chosen randomly. Damage propagation was allowed to continue until a failure criterion was reached. A health index was defined as the minimum of several superimposed operational margins at any given time instant and the failure criterion is reached when health index reaches zero. Output of the model was the time series (cycles) of sensed measurements typically available from aircraft gas turbine engines. The data generated were used as challenge data for the Prognostics and Health Management (PHM) data competition at PHM 08.
Investigating the Effect of Damage Progression Model Choice on Prognostics Performance
NASA Technical Reports Server (NTRS)
Daigle, Matthew; Roychoudhury, Indranil; Narasimhan, Sriram; Saha, Sankalita; Saha, Bhaskar; Goebel, Kai
2011-01-01
The success of model-based approaches to systems health management depends largely on the quality of the underlying models. In model-based prognostics, it is especially the quality of the damage progression models, i.e., the models describing how damage evolves as the system operates, that determines the accuracy and precision of remaining useful life predictions. Several common forms of these models are generally assumed in the literature, but are often not supported by physical evidence or physics-based analysis. In this paper, using a centrifugal pump as a case study, we develop different damage progression models. In simulation, we investigate how model changes influence prognostics performance. Results demonstrate that, in some cases, simple damage progression models are sufficient. But, in general, the results show a clear need for damage progression models that are accurate over long time horizons under varied loading conditions.
Vadhavkar, Nikhil; Pham, Christopher; Georgescu, Walter; Deschamps, Thomas; Heuskin, Anne-Catherine; Tang, Jonathan; Costes, Sylvain V.
2014-09-01
In contrast to the classic view of static DNA double-strand breaks (DSBs) being repaired at the site of damage, we hypothesize that DSBs move and merge with each other over large distances (m). As X-ray dose increases, the probability of having DSB clusters increases as does the probability of misrepair and cell death. Experimental work characterizing the X-ray dose dependence of radiation-induced foci (RIF) in nonmalignant human mammary epithelial cells (MCF10A) is used here to validate a DSB clustering model. We then use the principles of the local effect model (LEM) to predict the yield of DSBs at the submicron level. Two mechanisms for DSB clustering, namely random coalescence of DSBs versus active movement of DSBs into repair domains are compared and tested. Simulations that best predicted both RIF dose dependence and cell survival after X-ray irradiation favored the repair domain hypothesis, suggesting the nucleus is divided into an array of regularly spaced repair domains of ~;;1.55 m sides. Applying the same approach to high-linear energy transfer (LET) ion tracks, we are able to predict experimental RIF/m along tracks with an overall relative error of 12percent, for LET ranging between 30 350 keV/m and for three different ions. Finally, cell death was predicted by assuming an exponential dependence on the total number of DSBs and of all possible combinations of paired DSBs within each simulated RIF. Relative biological effectiveness (RBE) predictions for cell survival of MCF10A exposed to high-LET showed an LET dependence that matches previous experimental results for similar cell types. Overall, this work suggests that microdosimetric properties of ion tracks at the submicron level are sufficient to explain both RIF data and survival curves for any LET, similarly to the LEM assumption. Conversely, high-LET death mechanism does not have to infer linear-quadratic dose formalism as done in the LEM. In addition, the size of repair domains derived in our model
Magnetic measurement of creep damage: modeling and measurement
NASA Astrophysics Data System (ADS)
Sablik, Martin J.; Jiles, David C.
1996-11-01
Results of inspection of creep damage by magnetic hysteresis measurements on Cr-Mo steel are presented. It is shown that structure-sensitive parameters such as coercivity, remanence and hysteresis loss are sensitive to creep damage. Previous metallurgical studies have shown that creep changes the microstructure of he material by introducing voids, dislocations, and grain boundary cavities. As cavities develop, dislocations and voids move out to grain boundaries; therefore, the total pinning sources for domain wall motion are reduced.This, together with the introduction of a demagnetizing field due to the cavities, results in the decrease of both coercivity, remanence and hence, concomitantly, hysteresis loss. Incorporating these structural effects into a magnetomechanical hysteresis model developed previously by us produces numerical variations of coercivity, remanence and hysteresis loss consistent with what is measured. The magnetic model has therefore been used to obtain appropriately modified magnetization curves for each element of creep-damaged material in a finite element (FE) calculation. The FE calculation has been used to simulate magnetic detection of non-uniform creep damage around a seam weld in a 2.25 Cr 1Mo steam pipe. In particular, in the simulation, a magnetic C-core with primary and secondary coils was placed with its pole pieces flush against the specimen in the vicinity of the weld. The secondary emf was shown to be reduced when creep damage was present inside the pipe wall at the cusp of the weld and in the vicinity of the cusp. The calculation showed that the C- core detected creep damage best if it spanned the weld seam width and if the current in the primary was such that the C- core was not magnetically saturated. Experimental measurements also exhibited the dip predicted in emf, but the measurements are not yet conclusive because the effects of magnetic property changes of weld materials, heat- affected material, and base material have
Theoretical model of impact damage in structural ceramics
NASA Technical Reports Server (NTRS)
Liaw, B. M.; Kobayashi, A. S.; Emery, A. G.
1984-01-01
This paper presents a mechanistically consistent model of impact damage based on elastic failures due to tensile and shear overloading. An elastic axisymmetric finite element model is used to determine the dynamic stresses generated by a single particle impact. Local failures in a finite element are assumed to occur when the primary/secondary principal stresses or the maximum shear stress reach critical tensile or shear stresses, respectively. The succession of failed elements thus models macrocrack growth. Sliding motions of cracks, which closed during unloading, are resisted by friction and the unrecovered deformation represents the 'plastic deformation' reported in the literature. The predicted ring cracks on the contact surface, as well as the cone cracks, median cracks, radial cracks, lateral cracks, and damage-induced porous zones in the interior of hot-pressed silicon nitride plates, matched those observed experimentally. The finite element model also predicted the uplifting of the free surface surrounding the impact site.
NASA Astrophysics Data System (ADS)
Bielefeldt, Brent R.; Benzerga, A. Amine; Hartl, Darren J.
2016-04-01
The ability to monitor and predict the structural health of an aircraft is of growing importance to the aerospace industry. Currently, structural inspections and maintenance are based upon experiences with similar aircraft operating in similar conditions. While effective, these methods are time-intensive and unnecessary if the aircraft is not in danger of structural failure. It is imagined that future aircraft will utilize non-destructive evaluation methods, allowing for the near real-time monitoring of structural health. A particularly interesting method involves utilizing the unique transformation response of shape memory alloy (SMA) particles embedded in an aircraft structure. By detecting changes in the mechanical and/or electromagnetic responses of embedded particles, operators could detect the formation or propagation of fatigue cracks in the vicinity of these particles. This work focuses on a finite element model of SMA particles embedded in an aircraft wing using a substructure modeling approach in which degrees of freedom are retained only at specified points of connection to other parts or the application of boundary conditions, greatly reducing computational cost. Previous work evaluated isolated particle response to a static crack to numerically demonstrate and validate this damage detection method. This paper presents the implementation of a damage model to account for crack propagation and examine for the first time the effect of particle configuration and/or relative placement with respect to the ability to detect damage.
A prediction model for ocular damage - Experimental validation.
Heussner, Nico; Vagos, Márcia; Spitzer, Martin S; Stork, Wilhelm
2015-08-01
With the increasing number of laser applications in medicine and technology, accidental as well as intentional exposure of the human eye to laser sources has become a major concern. Therefore, a prediction model for ocular damage (PMOD) is presented within this work and validated for long-term exposure. This model is a combination of a raytracing model with a thermodynamical model of the human and an application which determines the thermal damage by the implementation of the Arrhenius integral. The model is based on our earlier work and is here validated against temperature measurements taken with porcine eye samples. For this validation, three different powers were used: 50mW, 100mW and 200mW with a spot size of 1.9mm. Also, the measurements were taken with two different sensing systems, an infrared camera and a fibre optic probe placed within the tissue. The temperatures were measured up to 60s and then compared against simulations. The measured temperatures were found to be in good agreement with the values predicted by the PMOD-model. To our best knowledge, this is the first model which is validated for both short-term and long-term irradiations in terms of temperature and thus demonstrates that temperatures can be accurately predicted within the thermal damage regime. PMID:26267496
NASA Astrophysics Data System (ADS)
Gou, Xiaofan; Shen, Qiang
2012-05-01
An analysis model of the bending strain dependence of the critical current in multifilamentary Bi2223/Ag composite tapes is presented. To investigate the effect of the mechanical properties of the Bi2223 superconducting filament, the actual part for carrying current, its damage stress and elastic modulus are introduced. The calculated result of the variation of the critical current with the bending strain is well agreed with the experimental one. The further studies find that the mechanical properties of the filament have a remarkable effect on the bending strain dependence of the critical current. Specifically, the larger the damage stress and elastic modulus of the filament are, the higher the critical current is, when the bending strain increases to a larger value beyond the critical one.
NASA Astrophysics Data System (ADS)
Zhang, Muyu; Schmidt, Rüdiger
2014-12-01
Structural damage detection using time domain vibration responses has advantages such as simplicity in calculation and no requirement of a finite element model, which attracts more and more researchers in recent years. In present paper, a new approach to detect the damage based on the auto correlation function is proposed. The maximum values of the auto correlation function of the vibration response signals from different measurement points are formulated as a vector called Auto Correlation Function at Maximum Point Value Vector, AMV for short. The relative change of the normalized AMV before and after damage is used as the damage index to locate the damage. Sensitivity analysis of the normalized AMV with respect to the local stiffness shows that the normalized AMV has a sharp change around the local stiffness change location, which means the normalized AMV is a good indicator to detect the damage even when the damage is very small. Stiffness reduction detection of a 12-story frame structure is provided to illustrate the validity, effectiveness and the anti-noise ability of the proposed method. Comparison of the normalized AMV and the other correlation-function-based damage detection method shows the normalized AMV has a better detectability.
Damage and fatigue described by a fractional derivative model
NASA Astrophysics Data System (ADS)
Caputo, Michele; Fabrizio, Mauro
2015-07-01
As in [1], damage is associated with fatigue that a material undergoes. In this paper, because we work with viscoelastic solids represented by a fractional model, damage is described by the order of the fractional derivative, which represents the phase field satisfying Ginzburg-Landau equation, which describes the evolution of damage. Finally, in our model, damage is caused, not only by fatigue, but also directly by a source related to environmental factors and described by a positive time function.
A stochastic model of radiation-induced bone marrow damage
Cotlet, G.; Blue, T.E.
2000-03-01
A stochastic model, based on consensus principles from radiation biology, is used to estimate bone-marrow stem cell pool survival (CFU-S and stroma cells) after irradiation. The dose response model consists of three coupled first order linear differential equations which quantitatively describe time dependent cellular damage, repair, and killing of red bone marrow cells. This system of differential equations is solved analytically through the use of a matrix approach for continuous and fractionated irradiations. The analytic solutions are confirmed through the dynamical solution of the model equations using SIMULINK. Rate coefficients describing the cellular processes of radiation damage and repair, extrapolated to humans from animal data sets and adjusted for neutron-gamma mixed fields, are employed in a SIMULINK analysis of criticality accidents. The results show that, for the time structures which may occur in criticality accidents, cell survival is established mainly by the average dose and dose rate.
Sandia/Stanford Unified Creep Plasticity Damage Model for ANSYS
2006-09-03
A unified creep plasticity (UCP) model was developed, based upon the time-dependent and time-independent deformation properties of the 95.5Sn-3.9Ag-0.6Cu (wt.%) soldier that were measured at Sandia. Then, a damage parameter, D, was added to the equation to develop the unified creep plasticity damage (UCPD) model. The parameter, D, was parameterized, using data obtained at Sandia from isothermal fatigue experiments on a double-lap shear test. The softwae was validated against a BGA solder joint exposed tomore » thermal cycling. The UCPD model was put into the ANSYS finite element as a subroutine. So, the softwae is the subroutine for ANSYS 8.1.« less
Modeling and characterization of recompressed damaged materials
Becker, R; Cazamias, J U; Kalantar, D H; LeBlanc, M M; Springer, H K
2004-02-11
Experiments have been performed to explore conditions under which spall damage is recompressed with the ultimate goal of developing a predictive model. Spall is introduced through traditional gas gun techniques or with laser ablation. Recompression techniques producing a uniaxial stress state, such as a Hopkinson bar, do not create sufficient confinement to close the porosity. Higher stress triaxialities achieved through a gas gun or laser recompression can close the spall. Characterization of the recompressed samples by optical metallography and electron microscopy reveal a narrow, highly deformed process zone. At the higher pressures achieved in the gas gun, little evidence of spall remains other than differentially etched features in the optical micrographs. With the very high strain rates achieved with laser techniques there is jetting from voids and other signs of turbulent metal flow. Simulations of spall and recompression on micromechanical models containing a single void suggest that it might be possible to represent the recompression using models similar to those employed for void growth. Calculations using multiple, randomly distributed voids are needed to determine if such models will yield the proper behavior for more realistic microstructures.
An integrated physiology model to study regional lung damage effects and the physiologic response
2014-01-01
Background This work expands upon a previously developed exercise dynamic physiology model (DPM) with the addition of an anatomic pulmonary system in order to quantify the impact of lung damage on oxygen transport and physical performance decrement. Methods A pulmonary model is derived with an anatomic structure based on morphometric measurements, accounting for heterogeneous ventilation and perfusion observed experimentally. The model is incorporated into an existing exercise physiology model; the combined system is validated using human exercise data. Pulmonary damage from blast, blunt trauma, and chemical injury is quantified in the model based on lung fluid infiltration (edema) which reduces oxygen delivery to the blood. The pulmonary damage component is derived and calibrated based on published animal experiments; scaling laws are used to predict the human response to lung injury in terms of physical performance decrement. Results The augmented dynamic physiology model (DPM) accurately predicted the human response to hypoxia, altitude, and exercise observed experimentally. The pulmonary damage parameters (shunt and diffusing capacity reduction) were fit to experimental animal data obtained in blast, blunt trauma, and chemical damage studies which link lung damage to lung weight change; the model is able to predict the reduced oxygen delivery in damage conditions. The model accurately estimates physical performance reduction with pulmonary damage. Conclusions We have developed a physiologically-based mathematical model to predict performance decrement endpoints in the presence of thoracic damage; simulations can be extended to estimate human performance and escape in extreme situations. PMID:25044032
Frequency Response Function Based Damage Identification for Aerospace Structures
NASA Astrophysics Data System (ADS)
Oliver, Joseph Acton
Structural health monitoring technologies continue to be pursued for aerospace structures in the interests of increased safety and, when combined with health prognosis, efficiency in life-cycle management. The current dissertation develops and validates damage identification technology as a critical component for structural health monitoring of aerospace structures and, in particular, composite unmanned aerial vehicles. The primary innovation is a statistical least-squares damage identification algorithm based in concepts of parameter estimation and model update. The algorithm uses frequency response function based residual force vectors derived from distributed vibration measurements to update a structural finite element model through statistically weighted least-squares minimization producing location and quantification of the damage, estimation uncertainty, and an updated model. Advantages compared to other approaches include robust applicability to systems which are heavily damped, large, and noisy, with a relatively low number of distributed measurement points compared to the number of analytical degrees-of-freedom of an associated analytical structural model (e.g., modal finite element model). Motivation, research objectives, and a dissertation summary are discussed in Chapter 1 followed by a literature review in Chapter 2. Chapter 3 gives background theory and the damage identification algorithm derivation followed by a study of fundamental algorithm behavior on a two degree-of-freedom mass-spring system with generalized damping. Chapter 4 investigates the impact of noise then successfully proves the algorithm against competing methods using an analytical eight degree-of-freedom mass-spring system with non-proportional structural damping. Chapter 5 extends use of the algorithm to finite element models, including solutions for numerical issues, approaches for modeling damping approximately in reduced coordinates, and analytical validation using a composite
Vibration-Based Damage Detection in Rotating Machinery
Farrar, C.R.; Duffey, T.A.
1999-06-28
Damage detection as determined from changes in the vibration characteristics of a system has been a popular research topic for the last thirty years. Numerous damage identification algorithms have been proposed for detecting and locating damage in structural and mechanical systems. To date, these damage-detection methods have shown mixed results. A particular application of vibration-based damage detection that has perhaps enjoyed the greatest success is that of damage detection in rotating machinery. This paper summarizes the state of technology in vibration-based damage detection applied to rotating machinery. The review interprets the damage detection process in terms of a statistical pattern recognition paradigm that encompasses all vibration-based damage detection methods and applications. The motivation for the study reported herein is to identify the reasons that vibration-based damage detection has been successfully applied to rotating machinery, but has yet to show robust applications to civil engineering infrastructure. The paper concludes by comparing and contrasting the vibration-based damage detection applied to rotating machinery with large civil engineering infrastructure applications.
The relationship between observed fatigue damage and life estimation models
NASA Technical Reports Server (NTRS)
Kurath, Peter; Socie, Darrell F.
1988-01-01
Observations of the surface of laboratory specimens subjected to axial and torsional fatigue loadings has resulted in the identification of three damage fatigue phenomena: crack nucleation, shear crack growth, and tensile crack growth. Material, microstructure, state of stress/strain, and loading amplitude all influence which of the three types of fatigue damage occurs during a dominant fatigue life fraction. Fatigue damage maps are employed to summarize the experimental observations. Appropriate bulk stress/strain damage parameters are suggested to model fatigue damage for the dominant fatigue life fraction. Extension of the damage map concept to more complex loadings is presented.
An empirical modified fatigue damage model for impacted GFRP laminates
NASA Astrophysics Data System (ADS)
Naderi, S.; Hassan, M. A.; Bushroa, A. R.
2014-10-01
The aim of the present paper is to evaluate the residual strength of GFRP laminates following a low-velocity impact event under cyclic loading. The residual strength is calculated using a linear fatigue damage model. According to an investigation into the effect of low-velocity impact on the fatigue behavior of laminates, it seems laminate fatigue life decreases after impact. By normalizing the fatigue stress against undamaged static strength, the Fatigue Damage parameter “FD” is presented with a linear relationship as its slope which is a linear function of the initial impact energy; meanwhile, the constants were attained from experimental data. FD is implemented into a plane-stress continuum damage mechanics based model for GFRP composite laminates, in order to predict damage threshold in composite structures. An S-N curve is implemented to indicate the fatigue behavior for 2 mm thickness encompassing both undamaged and impacted samples. A decline in lifespan is evident when the impact energy level increases. Finally, the FD is intended to capture the unique GFRP composite characteristics.
Damage Identification in Cable-Stayed Bridge Based on Modal Analysis and Neural Networks
NASA Astrophysics Data System (ADS)
Zhang, Xiedong; Zhang, Zhiguo; Li, Xiaofan; Zhan, Hao
2007-03-01
A damage-detection-oriented finite element model of a cable-stayed highway bridge is established and the modal analysis is then carried out. Modal frequency, displacement modal shape and curvature modal shape are included in BP neural network input vector. BP neural network models are established for bridge damage detection. The result indicates that the method based on vibration modal analysis theory and BP neural networks can detect both the position and degree of the damage.
NASA Astrophysics Data System (ADS)
Sung, S. H.; Koo, K. Y.; Jung, H. J.
2014-09-01
This paper presents a new damage detection approach for cantilever beam-type structures using the damage-induced inter-storey deflection (DIID) estimated by modal flexibility matrix. This approach can be utilized for damage detection of cantilever beam-type structures such as super high-rise buildings, high-rise apartment buildings, etc. Analytical studies on the DIID of cantilever beam-type structures have shown that the DIID abruptly occurs from damage location. Baseline modification concept was newly introduced to detect multiple damages in cantilever beam-type structures by changing the baseline to the prior damage location. This approach has a clear theoretical base and directly identifies damage location(s) without the use of a finite element (FE) model. For validating the applicability of the proposed approach to cantilever beam-type structures, a series of numerical and experimental studies on a 10-storey building model were carried out. From the tests, it was found that the damage locations can be successfully identified by the proposed approach for multiple damages as well as a single damage. In order to confirm the superiority of the proposed approach, a comparative study was carried out on two well-known damage metrics such as modal strain-based damage index approach and uniform load surface curvature approach.
Towards Industrial Application of Damage Models for Sheet Metal Forming
NASA Astrophysics Data System (ADS)
Doig, M.; Roll, K.
2011-05-01
Due to global warming and financial situation the demand to reduce the CO2-emission and the production costs leads to the permanent development of new materials. In the automotive industry the occupant safety is an additional condition. Bringing these arguments together the preferable approach for lightweight design of car components, especially for body-in-white, is the use of modern steels. Such steel grades, also called advanced high strength steels (AHSS), exhibit a high strength as well as a high formability. Not only their material behavior but also the damage behavior of AHSS is different compared to the performances of standard steels. Conventional methods for the damage prediction in the industry like the forming limit curve (FLC) are not reliable for AHSS. Physically based damage models are often used in crash and bulk forming simulations. The still open question is the industrial application of these models for sheet metal forming. This paper evaluates the Gurson-Tvergaard-Needleman (GTN) model and the model of Lemaitre within commercial codes with a goal of industrial application.
NASA Astrophysics Data System (ADS)
Aminjikarai Vedagiri, Srinivasa Babu
An active field of research that has developed due to the increasing use of computational techniques like finite element simulations for analysis of highly complex structural mechanics problems and the increasing use of composite laminates in varied industries such as aerospace, automotive, bio-medical, etc. is the development of numerical models to capture the behavior of composite materials. One of the big challenges not yet overcome convincingly in this field is the modeling of delamination failure which is one of the primary modes of damage in composite laminates. Hence, the primary aim of this work is to develop two numerical models for finite element simulations of delamination failure in composite laminates and implement them in the explicit finite element software DYNA3D/LS-DYNA. Dynamic fracture mechanics is an example of a complex structural analysis problem for which finite element simulations seem to be the only possible way to extract detailed information on sophisticated physical quantities of the crack-tip at any instant of time along a highly transient history of fracture. However, general purpose, commercial finite element software which have capabilities to do fracture analyses are still limited in their use to stationary cracks and crack propagation along trajectories known a priori. Therefore, an automated dynamic fracture procedure capable of simulating dynamic propagation of through-thickness cracks in arbitrary directions in linear, isotropic materials without user-intervention is first developed and implemented in DYNA3D for its default 8-node solid (brick) element. Dynamic energy release rate and stress intensity factors are computed in the model using integral expressions particularly well-suited for the finite element method. Energy approach is used to check for crack propagation and the maximum circumferential stress criterion is used to determine the direction of crack growth. Since the re-meshing strategy used to model crack growth
NASA Astrophysics Data System (ADS)
Patra, Anirban; McDowell, David L.
2015-01-01
A continuum damage framework is developed and coupled with an existing crystal plasticity framework, to model failure initiation in irradiated bcc polycrystalline materials at intermediate temperatures. Constitutive equations for vacancy generation due to inelastic deformation, void nucleation due to vacancy condensation, and diffusion-assisted void growth are developed. The framework is used to simulate failure initiation at dislocation channel interfaces and grain boundaries ahead of a sharp notch. Evolution of the microstructure is considered in terms of the evolution of inelastic deformation, vacancy concentration, and void number density and radius. Evolution of the damage, i.e., volume fraction of the voids, is studied as a function of applied deformation. Effects of strain rate and temperature on failure initiation are also studied. The framework is used to compute the fracture toughness of irradiated specimens for various loading histories and notch geometries. Crack growth resistance of the irradiated specimens are computed and compared to that of virgin specimens. Results are compared to available experimental data.
Kinetic Modeling of Damage Repair, Genome Instability, and Neoplastic Transformation
Stewart, Robert D
2007-03-17
Inducible repair and pathway interactions may fundamentally alter the shape of dose-response curves because different mechanisms may be important under low- and high-dose exposure conditions. However, the significance of these phenomena for risk assessment purposes is an open question. This project developed new modeling tools to study the putative effects of DNA damage induction and repair on higher-level biological endpoints, including cell killing, neoplastic transformation and cancer. The project scope included (1) the development of new approaches to simulate the induction and base excision repair (BER) of DNA damage using Monte Carlo methods and (2) the integration of data from the Monte Carlo simulations with kinetic models for higher-level biological endpoints. Methods of calibrating and testing such multiscale biological simulations were developed. We also developed models to aid in the analysis and interpretation of data from experimental assays, such as the pulsed-field gel electrophoresis (PFGE) assay used to quantity the amount of DNA damage caused by ionizing radiation.
Dynamic based damage detection in composite structures
NASA Astrophysics Data System (ADS)
Banerjee, Sauvik; Ricci, Fabrizio; Baid, Harsh; Mal, Ajit K.
2009-03-01
Advanced composites are being used increasingly in state-of-the-art aircraft and aerospace structures. In spite of their many advantages, composite materials are highly susceptible to hidden flaws that may occur at any time during the life cycle of a structure, and if undetected, may cause sudden and catastrophic failure of the entire structure. This paper is concerned with the detection and characterization of hidden defects in composite structures before they grow to a critical size. A methodology for automatic damage identification and localization is developed using a combination of vibration and wave propagation data. The structure is assumed to be instrumented with an array of actuators and sensors to excite and record its dynamic response, including vibration and wave propagation effects. A damage index, calculated from the measured dynamical response of the structure in a previous (reference) state and the current state, is introduced as a determinant of structural damage. The indices are used to identify low velocity impact damages in increasingly complex composite structural components. The potential application of the approach in developing health monitoring systems in defects-critical structures is indicated.
Borg, J.; Bibring, J.P.; Cowsik, G.; Langevin, Y.; Maurette, M.
1983-02-15
In this paper we present our most recent results on ion implantation and erosion effects, intended to reproduce the superficial amorphous layers of radiation damage observed with a high voltage electron microscope on ..mu..m-sized grains extracted from the lunar regolith and which result from the exposure of the grains to the solar wind. We next outline theoretical computations which yield the thickness distribution of such amorphous layers as a function of the exposure time of the grains at the surface of the moon, the He/H ratio, and the speed distribution in the solar wind. From this model, the position of the peak in the solar wind speed distribution is the major parameter controlling the thickness of the amorphous layer.
Discrete Element Modeling of Impact Damage on Thermal Barrier Coatings
NASA Astrophysics Data System (ADS)
Minor, Peter Michel
Natural gas turbines have become an increasingly important part of the energy landscape in the United States, currently accounting for 19% of all electricity production. Efforts to increase thermal efficiency in gas turbines has led to the adoption of highly porous ceramic thermal barrier coatings (TBCs), which are susceptible to erosion and foreign object impact damage. Despite significant investment to improve the design of TBCs, few numerical tools exist which are capable of both accurately capturing the specific failure mechanisms inherent to TBCs and iterating design parameters without the requirement for coupled experimental data. To overcome these limitations, a discrete element model (DEM) was created to simulate the microstructure of a TBC using a large-scale assembly of bonded particles. Acting as Lagrangian nodes, the particles can be combined to create accurate representations of TBC geometry and porosity. The inclusion of collision-driven particle dynamics and bonds derived from displacement-dependent force functions endow the microstructure model with the ability to deform and reproduce damage in a highly physical manner. Typical TBC damage mechanisms such as compaction, fracture and spallation occur automatically, without having to tune the model based on experimental observation. Therefore, the first order performance of novel TBC designs and materials can be determined numerically, greatly decreasing the cost of development. To verify the utility and effectiveness of the proposed damage model framework, a nanoindentation materials test simulation was developed to serve as a test case. By varying model parameters, such as the porosity of the TBC and maximum applied indenter force, nanoindentation data from more than one hundred distinct permutations was gathered and analyzed. This data was used to calculate the elastic modulus (E) and hardness (H) of the simulated microstructure, which could then be compared to known experimental material property
Mitochondrial DNA damage and efficiency of ATP biosynthesis: mathematical model.
Beregovskaya, N; Maiboroda, R
1995-01-21
The role of mitochondrial DNA (mtDNA) damage in ageing processes and in malignant transformation of a cell is discussed. A mathematical model of the mtDNA population in a cell and in tissue is constructed. The model describes the effects of mtDNA damages accumulated during ageing and some features of malignant transformation and regeneration. PMID:7891454
A damage mechanics based approach to structural deterioration and reliability
Bhattcharya, B.; Ellingwood, B.
1998-02-01
Structural deterioration often occurs without perceptible manifestation. Continuum damage mechanics defines structural damage in terms of the material microstructure, and relates the damage variable to the macroscopic strength or stiffness of the structure. This enables one to predict the state of damage prior to the initiation of a macroscopic flaw, and allows one to estimate residual strength/service life of an existing structure. The accumulation of damage is a dissipative process that is governed by the laws of thermodynamics. Partial differential equations for damage growth in terms of the Helmholtz free energy are derived from fundamental thermodynamical conditions. Closed-form solutions to the equations are obtained under uniaxial loading for ductile deformation damage as a function of plastic strain, for creep damage as a function of time, and for fatigue damage as function of number of cycles. The proposed damage growth model is extended into the stochastic domain by considering fluctuations in the free energy, and closed-form solutions of the resulting stochastic differential equation are obtained in each of the three cases mentioned above. A reliability analysis of a ring-stiffened cylindrical steel shell subjected to corrosion, accidental pressure, and temperature is performed.
Identification of structural damage using wavelet-based data classification
NASA Astrophysics Data System (ADS)
Koh, Bong-Hwan; Jeong, Min-Joong; Jung, Uk
2008-03-01
Predicted time-history responses from a finite-element (FE) model provide a baseline map where damage locations are clustered and classified by extracted damage-sensitive wavelet coefficients such as vertical energy threshold (VET) positions having large silhouette statistics. Likewise, the measured data from damaged structure are also decomposed and rearranged according to the most dominant positions of wavelet coefficients. Having projected the coefficients to the baseline map, the true localization of damage can be identified by investigating the level of closeness between the measurement and predictions. The statistical confidence of baseline map improves as the number of prediction cases increases. The simulation results of damage detection in a truss structure show that the approach proposed in this study can be successfully applied for locating structural damage even in the presence of a considerable amount of process and measurement noise.
Modeling the viscoplastic and damage behavior in deep argillaceous rocks
NASA Astrophysics Data System (ADS)
Souley, Mountaka; Armand, Gilles; Su, Kun; Ghoreychi, Mehdi
In order to demonstrate the feasibility of a radioactive waste repository in the Callovo-Oxfordian claystone formation, the French national radioactive waste management agency (ANDRA) started in 2000 to build an underground research laboratory at Bure (East of France). One of the key issues is to understand long term behavior of the drifts. More than 400 m horizontal galleries at the main level of -490 m have been instrumented since April 2005. The continuous measurements of convergence of the galleries are available, allowing a better understanding of the time-dependent response of the claystone at natural scale. Results indicate that the viscoplastic strain rates observed in the undamaged area far from the gallery walls are of the same order of magnitude as those obtained on rock samples, whereas those recorded in the damaged or fractured zone near the gallery walls are one to two orders of magnitude higher, indicating the significant influence of damage or/and macro-fractures on the viscoplastic strains. Based on these observations, a macroscopic viscoplastic model which aims to improve the viscoplastic strain prediction in the EDZ is proposed and implemented in FLAC3 D©. Both the instantaneous and the time-dependent behavior are considered in the model. The short term response is assumed to be elactoplastic with strain hardening/softening whereas the time-dependent behavior is based on the concepts of viscoplasticity (Lemaıˆtre’s model). Finally, the damage-induced viscoplastic strains changes is examined through the plastic deformation (assumed to approach the damage rate). In order to verify both constitutive equations and their implementations, several simulations are performed: (a) triaxial tests at different confining pressures; (b) single- and multi-stage creep tests; (c) relaxation tests with different total axial strain levels, etc. Finally, an example of a blind prediction of the excavation of a drift parallel to the horizontal minor stress,
Elastic-plastic models for multi-site damage
NASA Technical Reports Server (NTRS)
Actis, Ricardo L.; Szabo, Barna A.
1994-01-01
This paper presents recent developments in advanced analysis methods for the computation of stress site damage. The method of solution is based on the p-version of the finite element method. Its implementation was designed to permit extraction of linear stress intensity factors using a superconvergent extraction method (known as the contour integral method) and evaluation of the J-integral following an elastic-plastic analysis. Coarse meshes are adequate for obtaining accurate results supported by p-convergence data. The elastic-plastic analysis is based on the deformation theory of plasticity and the von Mises yield criterion. The model problem consists of an aluminum plate with six equally spaced holes and a crack emanating from each hole. The cracks are of different sizes. The panel is subjected to a remote tensile load. Experimental results are available for the panel. The plasticity analysis provided the same limit load as the experimentally determined load. The results of elastic-plastic analysis were compared with the results of linear elastic analysis in an effort to evaluate how plastic zone sizes influence the crack growth rates. The onset of net-section yielding was determined also. The results show that crack growth rate is accelerated by the presence of adjacent damage, and the critical crack size is shorter when the effects of plasticity are taken into consideration. This work also addresses the effects of alternative stress-strain laws: The elastic-ideally-plastic material model is compared against the Ramberg-Osgood model.
Multiscale modeling of damage in multidirectional composite laminates
NASA Astrophysics Data System (ADS)
Singh, Chandra Veer
90°-plies. The predictions agree well with published experimental data as well as independent FE computations. Limited parametric studies are performed to show usability of SDM for more general laminates. To predict the initiation and growth of intralaminar cracks, an energy based model is proposed in which these cracks initiate and multiply when the work required to form new set of cracks exceeds a laminate dependent critical energy release rate. The approach requires determination of average crack opening and sliding displacements at varying crack spacing. This task is performed through a suitable 3-D FE analysis. In case of off-axis ply cracking, a mixed mode fracture criterion is utilized, where the critical energy release rates in normal and shear modes are determined by fitting the damage model with the experimental data for a reference laminate. The predictions from the model for [0/+/-theta4/01/2]s and [0/90/∓45]s laminates show remarkable agreement with the experimental results. The methodology and the results covered in this dissertation will be of interest to mechanics of materials researchers as well as to engineers in industry where composite materials for structural applications are of interest.
Micromechanics Modeling of Composites Subjected to Multiaxial Progressive Damage in the Constituents
NASA Technical Reports Server (NTRS)
Bednarcyk, Brett A.; Aboudi, Jacob; Amold, Steven M.
2010-01-01
The high-fidelity generalized method of cells composite micromechanics model is extended to include constituent-scale progressive damage via a proposed damage model. The damage model assumes that all material nonlinearity is due to damage in the form of reduced stiffness, and it uses six scalar damage variables (three for tension and three for compression) to track the damage. Damage strains are introduced that account for interaction among the strain components and that also allow the development of the damage evolution equations based on the constituent material uniaxial stress strain response. Local final-failure criteria are also proposed based on mode-specific strain energy release rates and total dissipated strain energy. The coupled micromechanics-damage model described herein is applied to a unidirectional E-glass/epoxy composite and a proprietary polymer matrix composite. Results illustrate the capability of the coupled model to capture the vastly different character of the monolithic (neat) resin matrix and the composite in response to far-field tension, compression, and shear loading.
Modeling Fatigue Damage in Long-Fiber Thermoplastics
Nguyen, Ba Nghiep; Kunc, Vlastimil; Bapanapalli, Satish K.
2009-10-30
This paper applies a fatigue damage model recently developed for injection-molded long-fiber thermoplastics (LFTs) to predict the modulus reduction and fatigue lifetime of glass/polyamide 6,6 (PA6,6) specimens. The fatigue model uses a multiscale mechanistic approach to describe fatigue damage accumulation in these materials subjected to cyclic loading. Micromechanical modeling using a modified Eshelby-Mori-Tanaka approach combined with averaging techniques for fiber length and orientation distributions is performed to establish the stiffness reduction relation for the composite as a function of the microcrack volume fraction. Next, continuum damage mechanics and a thermodynamic formulation are used to derive the constitutive relations and the damage evolution law. The fatigue damage model has been implemented in the ABAQUS finite element code and has been applied to analyze fatigue of the studied glass/PA6,6 specimens. The predictions agree well with the experimental results.
Aerodynamic Effects and Modeling of Damage to Transport Aircraft
NASA Technical Reports Server (NTRS)
Shah, Gautam H.
2008-01-01
A wind tunnel investigation was conducted to measure the aerodynamic effects of damage to lifting and stability/control surfaces of a commercial transport aircraft configuration. The modeling of such effects is necessary for the development of flight control systems to recover aircraft from adverse, damage-related loss-of-control events, as well as for the estimation of aerodynamic characteristics from flight data under such conditions. Damage in the form of partial or total loss of area was applied to the wing, horizontal tail, and vertical tail. Aerodynamic stability and control implications of damage to each surface are presented, to aid in the identification of potential boundaries in recoverable stability or control degradation. The aerodynamic modeling issues raised by the wind tunnel results are discussed, particularly the additional modeling requirements necessitated by asymmetries due to damage, and the potential benefits of such expanded modeling.
Continuum damage model for ferroelectric materials and its application to multilayer actuators
NASA Astrophysics Data System (ADS)
Gellmann, Roman; Ricoeur, Andreas
2016-05-01
In this paper a micromechanical continuum damage model for ferroelectric materials is presented. As a constitutive law it is implemented into a finite element (FE) code. The model is based on micromechanical considerations of domain switching and its interaction with microcrack growth and coalescence. A FE analysis of a multilayer actuator is performed, showing the initiation of damage zones at the electrode tips during the poling process. Further, the influence of mechanical pre-stressing on damage evolution and actuating properties is investigated. The results provided in this work give useful information on the damage of advanced piezoelectric devices and their optimization.
Unsupervised Structural Damage Diagnosis Based on Change of Response Surface Using Statistical Tool
NASA Astrophysics Data System (ADS)
Iwasaki, Atsushi; Todoroki, Akira; Shimamura, Yoshinobu; Kobayashi, Hideo
Most structural health monitoring systems adopt parametric methods based on modeling or non-parametric methods such as artificial neural networks. The former methods require modeling of each structure, and the latter methods require a large number of data for training. These methods demand high costs, and it is impossible to obtain training data of the damaged state of an in-service structure. By the present method, damage is detected by judging the statistical difference between data of the intact state and the current state. The method requires data of the undamaged state, but does not require complicated modeling or data for training. As an example, the present study deals with the detection of delamination of a composite beam. Damage is detected from the change of strain data using statistical tools such as the response surface and F-statistics. As a result, the new method successfully diagnoses the damage without the need to use modeling or data of the damaged state.
NASA Astrophysics Data System (ADS)
Zhang, Muyu; Schmidt, Rüdiger
2015-12-01
The damage index based on the auto correlation function to detect the damage of the structure under white noise excitation is studied in detail in this paper. The maximum values of the auto correlation function of the vibration response signals (displacement, velocity and acceleration) from different measurement points of the structure are collected and formulated as a vector called Auto Correlation Function at Maximum Point Value Vector (AMV), which is expressed as a weighted combination of the Hadamard product of two mode shapes. AMV is normalized by its root mean square value so that the influence of the excitation can be eliminated. Sensitivity analysis for the different parts of the normalized AMV shows that the sensitivity of the normalized AMV to the local stiffness is dependent most on the sensitivity of the Hadamard product of the two lower order mode shapes to the local stiffness, which has a sudden change of the value around the local stiffness change position. The sensitivity of the normalized AMV has the similar shape and same trend that shows it is a very good damage indicator even for the very small damage. The relative change of the normalized AMV before and after damage occurs in the structure is adopted as the damage index to show the damage location. Several examples of the stiffness reduction detection of a 12-story shear frame structure are utilized to validate the results in sensitivity analysis, illustrate the effectiveness and anti-noise ability of the AMV-based damage detection method and compare the effect of the response type on the detectability of the normalized AMV.
Damage identification in beam type structures based on statistical moment using a two step method
NASA Astrophysics Data System (ADS)
Wang, Dansheng; Xiang, Wei; Zhu, Hongping
2014-02-01
This paper defines a novel damage index-strain statistical moment, and formulates the fourth strain statistical moment (FSSM) of beam-type structures under white noise excitation. Based on this newly defined strain statistical moment index and the least square optimization algorithm, a two-step damage identification method is proposed. This two-step method is operated like this: first use the difference curves of FSSMs before and after damage to locate damage elements; then for those identified damage elements, employ the model updating method based on the least square algorithm to assess their damage severity. Numerical studies on a simply supported beam and a two-span continuous beam are performed and the study results show that the newly defined index is effective to locate damages, even when the noise intensity is as high as 15 percent. Integrating with the least square-based model updating technique, the damage severities of beam-type structures can also be determined quantitatively. In this way, the proposed two-step method is verified and found to be capable of identifying damage positions and severities of beam-type structures and insensitive to measurement noise.
MRAC Control with Prior Model Knowledge for Asymmetric Damaged Aircraft
Xu, Xieyu; Yang, Lingyu; Zhang, Jing
2015-01-01
This paper develops a novel state-tracking multivariable model reference adaptive control (MRAC) technique utilizing prior knowledge of plant models to recover control performance of an asymmetric structural damaged aircraft. A modification of linear model representation is given. With prior knowledge on structural damage, a polytope linear parameter varying (LPV) model is derived to cover all concerned damage conditions. An MRAC method is developed for the polytope model, of which the stability and asymptotic error convergence are theoretically proved. The proposed technique reduces the number of parameters to be adapted and thus decreases computational cost and requires less input information. The method is validated by simulations on NASA generic transport model (GTM) with damage. PMID:26180839
Damage assessment framework for landslide disaster based on very high-resolution images
NASA Astrophysics Data System (ADS)
Sun, Bo; Xu, Qihua; He, Jun; Liu, Zhen; Wang, Ying; Ge, Fengxiang
2016-04-01
It is well known that rapid building damage assessment is necessary for postdisaster emergency relief and recovery. Based on an analysis of very high-resolution remote-sensing images, we propose an automatic building damage assessment framework for rainfall- or earthquake-induced landslide disasters. The framework consists of two parts that implement landslide detection and the damage classification of buildings, respectively. In this framework, an approach based on modified object-based sparse representation classification and morphological processing is used for automatic landslide detection. Moreover, we propose a building damage classification model, which is a classification strategy designed for affected buildings based on the spectral characteristics of the landslide disaster and the morphological characteristics of building damage. The effectiveness of the proposed framework was verified by applying it to remote-sensing images from Wenchuan County, China, in 2008, in the aftermath of an earthquake. It can be useful for decision makers, disaster management agencies, and scientific research organizations.
Track structure model of cell damage in space flight
NASA Technical Reports Server (NTRS)
Katz, Robert; Cucinotta, Francis A.; Wilson, John W.; Shinn, Judy L.; Ngo, Duc M.
1992-01-01
The phenomenological track-structure model of cell damage is discussed. A description of the application of the track-structure model with the NASA Langley transport code for laboratory and space radiation is given. Comparisons to experimental results for cell survival during exposure to monoenergetic, heavy-ion beams are made. The model is also applied to predict cell damage rates and relative biological effectiveness for deep-space exposures.
Direct Detection and Sequencing of Damaged DNA Bases
2011-01-01
Products of various forms of DNA damage have been implicated in a variety of important biological processes, such as aging, neurodegenerative diseases, and cancer. Therefore, there exists great interest to develop methods for interrogating damaged DNA in the context of sequencing. Here, we demonstrate that single-molecule, real-time (SMRT®) DNA sequencing can directly detect damaged DNA bases in the DNA template - as a by-product of the sequencing method - through an analysis of the DNA polymerase kinetics that are altered by the presence of a modified base. We demonstrate the sequencing of several DNA templates containing products of DNA damage, including 8-oxoguanine, 8-oxoadenine, O6-methylguanine, 1-methyladenine, O4-methylthymine, 5-hydroxycytosine, 5-hydroxyuracil, 5-hydroxymethyluracil, or thymine dimers, and show that these base modifications can be readily detected with single-modification resolution and DNA strand specificity. We characterize the distinct kinetic signatures generated by these DNA base modifications. PMID:22185597
Structural Damage Identification Based on Rough Sets and Artificial Neural Network
Liu, Chengyin; Wu, Xiang; Wu, Ning; Liu, Chunyu
2014-01-01
This paper investigates potential applications of the rough sets (RS) theory and artificial neural network (ANN) method on structural damage detection. An information entropy based discretization algorithm in RS is applied for dimension reduction of the original damage database obtained from finite element analysis (FEA). The proposed approach is tested with a 14-bay steel truss model for structural damage detection. The experimental results show that the damage features can be extracted efficiently from the combined utilization of RS and ANN methods even the volume of measurement data is enormous and with uncertainties. PMID:25013847
Structural damage identification based on rough sets and artificial neural network.
Liu, Chengyin; Wu, Xiang; Wu, Ning; Liu, Chunyu
2014-01-01
This paper investigates potential applications of the rough sets (RS) theory and artificial neural network (ANN) method on structural damage detection. An information entropy based discretization algorithm in RS is applied for dimension reduction of the original damage database obtained from finite element analysis (FEA). The proposed approach is tested with a 14-bay steel truss model for structural damage detection. The experimental results show that the damage features can be extracted efficiently from the combined utilization of RS and ANN methods even the volume of measurement data is enormous and with uncertainties. PMID:25013847
Localized planarization of optical damage using laser-based chemical vapor deposition
NASA Astrophysics Data System (ADS)
Matthews, Manyalibo J.; Elhadj, Selim; Guss, Gabe M.; Sridharan, Arun; Nielsen, Norman D.; Yoo, Jae-Hyuck; Lee, Daeho; Grigoropoulos, Costas
2013-11-01
We present a method to repair damaged optics using laser-based chemical vapor deposition (L-CVD). A CO2 laser is used to heat damaged silica regions and polymerize a gas precursor to form SiO2. Measured deposition rates and morphologies agree well with finite element modeling of a two-phase reaction. Along with optimizing deposition rates and morphology, we also show that the deposited silica is structurally identical to high-grade silica substrate and possesses high UV laser damage thresholds. Successful application of such a method could reduce processing costs, extend optic lifetime, and lead to more damage resistant laser optics used in high power applications.
Categorizing natural disaster damage assessment using satellite-based geospatial techniques
Myint, S.W.; Yuan, M.; Cerveny, R.S.; Giri, C.
2008-01-01
Remote sensing of a natural disaster's damage offers an exciting backup and/or alternative to traditional means of on-site damage assessment. Although necessary for complete assessment of damage areas, ground-based damage surveys conducted in the aftermath of natural hazard passage can sometimes be potentially complicated due to on-site difficulties (e.g., interaction with various authorities and emergency services) and hazards (e.g., downed power lines, gas lines, etc.), the need for rapid mobilization (particularly for remote locations), and the increasing cost of rapid physical transportation of manpower and equipment. Satellite image analysis, because of its global ubiquity, its ability for repeated independent analysis, and, as we demonstrate here, its ability to verify on-site damage assessment provides an interesting new perspective and investigative aide to researchers. Using one of the strongest tornado events in US history, the 3 May 1999 Oklahoma City Tornado, as a case example, we digitized the tornado damage path and co-registered the damage path using pre- and post-Landsat Thematic Mapper image data to perform a damage assessment. We employed several geospatial approaches, specifically the Getis index, Geary's C, and two lacunarity approaches to categorize damage characteristics according to the original Fujita tornado damage scale (F-scale). Our results indicate strong relationships between spatial indices computed within a local window and tornado F-scale damage categories identified through the ground survey. Consequently, linear regression models, even incorporating just a single band, appear effective in identifying F-scale damage categories using satellite imagery. This study demonstrates that satellite-based geospatial techniques can effectively add spatial perspectives to natural disaster damages, and in particular for this case study, tornado damages.
Electrical impedance tomography-based sensing skin for quantitative imaging of damage in concrete
NASA Astrophysics Data System (ADS)
Hallaji, Milad; Seppänen, Aku; Pour-Ghaz, Mohammad
2014-08-01
This paper outlines the development of a large-area sensing skin for damage detection in concrete structures. The developed sensing skin consists of a thin layer of electrically conductive copper paint that is applied to the surface of the concrete. Cracking of the concrete substrate results in the rupture of the sensing skin, decreasing its electrical conductivity locally. The decrease in conductivity is detected with electrical impedance tomography (EIT) imaging. In previous works, electrically based sensing skins have provided only qualitative information on the damage on the substrate surface. In this paper, we study whether quantitative imaging of the damage is possible. We utilize application-specific models and computational methods in the image reconstruction, including a total variation (TV) prior model for the damage and an approximate correction of the modeling errors caused by the inhomogeneity of the painted sensing skin. The developed damage detection method is tested experimentally by applying the sensing skin to polymeric substrates and a reinforced concrete beam under four-point bending. In all test cases, the EIT-based sensing skin provides quantitative information on cracks and/or other damages on the substrate surface: featuring a very low conductivity in the damage locations, and a reliable indication of the lengths and shapes of the cracks. The results strongly support the applicability of the painted EIT-based sensing skin for damage detection in reinforced concrete elements and other substrates.
Detection of Damaged DNA Bases by DNA Glycosylase Enzymes†
Friedman, Joshua I.; Stivers, James T.
2010-01-01
A fundamental and shared process in all forms of life is the use of DNA glycosylase enzymes to excise rare damaged bases from genomic DNA. Without such enzymes, the highly-ordered primary sequences of genes would rapidly deteriorate. Recent structural and biophysical studies are beginning to reveal a fascinating multistep mechanism for damaged base detection that begins with short-range sliding of the glycosylase along the DNA chain in a distinct conformation we refer to as the search complex (SC). Sliding is frequently punctuated by the formation of a transient “interrogation” complex (IC) where the enzyme extrahelically inspects both normal and damaged bases in an exosite pocket that is distant from the active site. When normal bases are presented in the exosite, the IC rapidly collapses back to the SC, while a damaged base will efficiently partition forward into the active site to form the catalytically competent excision complex (EC). Here we review the unique problems associated with enzymatic detection of rare damaged DNA bases in the genome, and emphasize how each complex must have specific dynamic properties that are tuned to optimize the rate and efficiency of damage site location. PMID:20469926
Micro-mechanical modeling of perforating shock damage
Swift, R.P.; Krogh, K.E.; Behrmann, L.A.; Halleck, P.M.
1997-11-17
Shaped charge jet induced formation damage from perforation treatments hinders productivity. Manifestation of this damage is in the form of grain fragmentation resulting in fines that plug up pore throats along with the breakdown of inter-grain cementation. The authors use the Smooth Particle Hydrodynamic (SPH) computational method as a way to explicitly model, on a grain pore scale, the dynamic interactions of grains and grain/pores to calculate the damage resulting from perforation type stress wave loading. The SPH method is a continuum Lagrangian, meshless approach that features particles. Clusters of particles are used for each grain to provide representation of a grain pore structure that is similar to x-ray synchrotron microtomography images. Numerous damage models are available to portray fracture and fragmentation. In this paper the authors present the results of well defined impact loading on a grain pore structure that illustrate how the heterogeneity affects stress wave behavior and damage evolution. The SPH approach easily accommodates the coupling of multi-materials. Calculations for multi-material conditions with the pore space treated as a void, fluid filled, and/or clay filled show diverse effects on the stress wave propagation behavior and damage. SPH comparisons made with observed damage from recovered impacted sandstone samples in gas gun experiments show qualitatively the influence of stress intensity. The modeling approach presented here offers a unique way in concert with experiments to define a better understanding of formation damage resulting from perforation completion treatments.
NASA Astrophysics Data System (ADS)
Saada, Mohamed M.; Arafa, Mustafa H.; Nassef, Ashraf O.
2013-06-01
The use of vibration-based techniques in damage identification has recently received considerable attention in many engineering disciplines. While various damage indicators have been proposed in the literature, those relying only on changes in the natural frequencies are quite appealing since these quantities can conveniently be acquired. Nevertheless, the use of natural frequencies in damage identification is faced with many obstacles, including insensitivity and non-uniqueness issues. The aim of this article is to develop a viable damage identification scheme based only on changes in the natural frequencies and to attempt to overcome the challenges typically encountered. The proposed methodology relies on building a finite element model (FEM) of the structure under investigation. An improved particle swarm optimization algorithm is proposed to facilitate updating the FEM in accordance with experimentally determined natural frequencies in order to predict the damage location and extent. The method is tested on beam structures and was shown to be an effective tool for damage identification.
Gonzalez-Hunt, Claudia P; Rooney, John P; Ryde, Ian T; Anbalagan, Charumathi; Joglekar, Rashmi; Meyer, Joel N
2016-01-01
Because of the role that DNA damage and depletion play in human disease, it is important to develop and improve tools to assess these endpoints. This unit describes PCR-based methods to measure nuclear and mitochondrial DNA damage and copy number. Long amplicon quantitative polymerase chain reaction (LA-QPCR) is used to detect DNA damage by measuring the number of polymerase-inhibiting lesions present based on the amount of PCR amplification; real-time PCR (RT-PCR) is used to calculate genome content. In this unit, we provide step-by-step instructions to perform these assays in Homo sapiens, Mus musculus, Rattus norvegicus, Caenorhabditis elegans, Drosophila melanogaster, Danio rerio, Oryzias latipes, Fundulus grandis, and Fundulus heteroclitus, and discuss the advantages and disadvantages of these assays. PMID:26828332
Gonzalez-Hunt, Claudia P.; Rooney, John P.; Ryde, Ian T.; Anbalagan, Charumathi; Joglekar, Rashmi
2016-01-01
Because of the role DNA damage and depletion play in human disease, it is important to develop and improve tools to assess these endpoints. This unit describes PCR-based methods to measure nuclear and mitochondrial DNA damage and copy number. Long amplicon quantitative polymerase chain reaction (LA-QPCR) is used to detect DNA damage by measuring the number of polymerase-inhibiting lesions present based on the amount of PCR amplification; real-time PCR (RT-PCR) is used to calculate genome content. In this unit we provide step-by-step instructions to perform these assays in Homo sapiens, Mus musculus, Rattus norvegicus, Caenorhabditis elegans, Drosophila melanogaster, Danio rerio, Oryzias latipes, Fundulus grandis, and Fundulus heteroclitus, and discuss the advantages and disadvantages of these assays. PMID:26828332
Stender, Michael E; Regueiro, Richard A; Klisch, Stephen M; Ferguson, Virginia L
2015-08-01
Traumatic injuries and gradual wear-and-tear of articular cartilage (AC) that can lead to osteoarthritis (OA) have been hypothesized to result from tissue damage to AC. In this study, a previous equilibrium constitutive model of AC was extended to a constitutive damage articular cartilage (CDAC) model. In particular, anisotropic collagen (COL) fibril damage and isotropic glycosaminoglycan (GAG) damage were considered in a 3D formulation. In the CDAC model, time-dependent effects, such as viscoelasticity and poroelasticity, were neglected, and thus all results represent the equilibrium response after all time-dependent effects have dissipated. The resulting CDAC model was implemented in two different finite-element models. The first simulated uniaxial tensile loading to failure, while the second simulated spherical indentation with a rigid indenter displaced into a bilayer AC sample. Uniaxial tension to failure simulations were performed for three COL fibril Lagrangian failure strain (i.e., the maximum elastic COL fibril strain) values of 15%, 30%, and 45%, while spherical indentation simulations were performed with a COL fibril Lagrangian failure strain of 15%. GAG damage parameters were held constant for all simulations. Our results indicated that the equilibrium postyield tensile response of AC and the macroscopic tissue failure strain are highly dependent on COL fibril Lagrangian failure strain. The uniaxial tensile response consisted of an initial nonlinear ramp region due to the recruitment of intact fibrils followed by a rapid decrease in tissue stress at initial COL fibril failure, as a result of COL fibril damage which continued until ultimate tissue failure. In the spherical indentation simulation, damage to both the COL fibril and GAG constituents was located only in the superficial zone (SZ) and near the articular surface with tissue thickening following unloading. Spherical indentation simulation results are in agreement with published experimental
A procedure for utilization of a damage-dependent constitutive model for laminated composites
NASA Technical Reports Server (NTRS)
Lo, David C.; Allen, David H.; Harris, Charles E.
1992-01-01
Described here is the procedure for utilizing a damage constitutive model to predict progressive damage growth in laminated composites. In this model, the effects of the internal damage are represented by strain-like second order tensorial damage variables and enter the analysis through damage dependent ply level and laminate level constitutive equations. The growth of matrix cracks due to fatigue loading is predicted by an experimentally based damage evolutionary relationship. This model is incorporated into a computer code called FLAMSTR. This code is capable of predicting the constitutive response and matrix crack damage accumulation in fatigue loaded laminated composites. The structure and usage of FLAMSTR are presented along with sample input and output files to assist the code user. As an example problem, an analysis of crossply laminates subjected to two stage fatigue loading was conducted and the resulting damage accumulation and stress redistribution were examined to determine the effect of variations in fatigue load amplitude applied during the first stage of the load history. It was found that the model predicts a significant loading history effect on damage evolution.
Damage detection in turbine wind blades by vibration based methods
NASA Astrophysics Data System (ADS)
Doliński, L.; Krawczuk, M.
2009-08-01
The paper describes results of numerical simulation for damage localization in the composite coat of a wind turbine blade using modal parameters and a modern damage detection method (wavelet transform). The presented results were obtained in the first period of research on the diagnostic method, which is aimed at detecting damage in the blades of large wind turbines during normal operation. A blade-modelling process including the geometry, loads and failures has been introduced in the paper. A series of simulations has been carried out for different localizations and size of damage for finding the method's limits. To verify the results of numeric simulations a subscale blade has been built which has geometric features and mechanical properties similar to the computer model.
A microstructurally inspired damage model for early venous thrombus.
Rausch, Manuel K; Humphrey, Jay D
2015-03-01
Accumulative damage may be an important contributor to many cases of thrombotic disease progression. Thus, a complete understanding of the pathological role of thrombus requires an understanding of its mechanics and in particular mechanical consequences of damage. In the current study, we introduce a novel microstructurally inspired constitutive model for thrombus that considers a non-uniform distribution of microstructural fibers at various crimp levels and employs one of the distribution parameters to incorporate stretch-driven damage on the microscopic level. To demonstrate its ability to represent the mechanical behavior of thrombus, including a recently reported Mullins type damage phenomenon, we fit our model to uniaxial tensile test data of early venous thrombus. Our model shows an agreement with these data comparable to previous models for damage in elastomers with the added advantages of a microstructural basis and fewer model parameters. We submit that our novel approach marks another important step toward modeling the evolving mechanics of intraluminal thrombus, specifically its damage, and hope it will aid in the study of physiological and pathological thrombotic events. PMID:26523784
Two-phase Damage Models of Magma Fracturing
NASA Astrophysics Data System (ADS)
Cai, Z.; Bercovici, D.
2011-12-01
pulse-like shock waves may prove effective at promoting fluid migration through hydro- and magma-fracturing. Our model of damage-enhanced solitary waves includes the onset of fast moving porosity pulses associated with the generation of micro-fractures, which may explain the transition from porous flow to fracturing and diking during magma migration.
A Contribution to Time-Dependent Damage Modeling of Composite Structures
NASA Astrophysics Data System (ADS)
Treasurer, Paul; Poirette, Yann; Perreux, Dominique; Thiebaud, Frédéric
2014-08-01
The paper presents a new damage model for predicting stiffness loss due to creep loading and cyclic fatigue. The model, developed within a continuum damage mechanics framework, is based on the idea of a time-dependent damage spectrum, some elements of which occur rapidly and others slowly. The use of this spectrum allows a single damage kinematic to model creep and fatigue damage and to take into account the effect of stress amplitude, R ratio, and frequency. The evolution equations are based on similar equation than the one describing the viscoelasticity model and are relatively easy to implement. The new model is compared to the experimental results on carbon fiber/epoxy tubes. Quasi-static, creep and fatigue tests are performed on filament-wound tubular specimens to characterize the elastic, viscoelastic and plastic behavior of the composite material. Varying amounts of damage are observed and discussed depending on stress level and R ratio. The experimental work aims to develop and validate the damage model for predicting stiffness loss due to creep loading and cyclic fatigue.
Simulation Based Investigation of Hidden Delamination Damage Detection in CFRP Composites
NASA Technical Reports Server (NTRS)
Leckey, Cara A. C.; Parker, F. Raymond
2013-01-01
Guided wave (GW) based damage detection methods have shown promise in structural health monitoring (SHM) and hybrid SHM-nondestructive evaluation (NDE) techniques. Much previous GW work in the aerospace field has been primarily focused on metallic materials, with a growing focus on composite materials. The work presented in this paper demonstrates how realistic three-dimensional (3D) GW simulations can aid in the development of GW based damage characterization techniques for aerospace composites. 3D elastodynamic finite integration technique is implemented to model GW interaction with realistic delamination damage. A local wavenumber technique is applied to simulation data in order to investigate the detectability of hidden delamination damage to enable accurate characterization of damage extent.
NASA Astrophysics Data System (ADS)
Terentyev, V. S.; Simonov, V. A.
2016-02-01
Numerical modelling demonstrates the possibility of fabricating an all-fibre multibeam two-mirror reflection interferometer based on a metal-dielectric diffraction structure in its front mirror. The calculations were performed using eigenmodes of a double-clad single-mode fibre. The calculation results indicate that, using a metallic layer in the structure of the front mirror of such an interferometer and a diffraction effect, one can reduce the Ohmic loss by a factor of several tens in comparison with a continuous thin metallic film.
Continuum Fatigue Damage Modeling for Critical Design, Control, and Fault Prognosis
NASA Technical Reports Server (NTRS)
Lorenzo, Carl F.
1996-01-01
This paper develops a simplified continuum (continuous with respect to time, stress, etc.) fatigue damage model for use in critical design, Life Extending Control and fault prognosis. The work is based on the local strain cyclic damage modeling method. New nonlinear explicit equation forms of cyclic damage in terms of stress amplitude are derived to facilitate the continuum modelling. Stress based continuum models are derived. Extension to plastic strain-strain rate models is also presented. Progress toward a non-zero mean stress based is presented. Also new nonlinear explicit equation forms in terms of stress amplitude are derived for this case. Application of the various models to design, control, and fault prognosis is considered.
A model for damage of microheterogeneous kidney stones
NASA Astrophysics Data System (ADS)
Szeri, Andrew J.; Zohdi, Tarek I.; Blake, John R.
2005-04-01
In this paper, a theoretical framework is developed for the mechanics of kidney stones with an isotropic, random microstructure-such as those comprised of cystine or struvite. The approach is based on a micromechanical description of kidney stones comprised of crystals in a binding matrix. Stress concentration functions are developed to determine load sharing of the particle phase and the binding matrix phase. As an illustration of the theory, the fatigue of kidney stones subject to shock wave lithotripsy is considered. Stress concentration functions are used to construct fatigue life estimates for each phase, as a function of the volume fraction and of the mechanical properties of the constituents, as well as the loading from SWL. The failure of the binding matrix is determined explicitly in a model for the accumulation of distributed damage. Also considered is the amount of material damaged in a representative non-spherical collapse of a cavitation bubble near the stone surface. The theory can be used to assess the importance of microscale heterogeneity on the comminution of renal calculi and to estimate the number of cycles to failure in terms of measurable material properties.
ASPH modeling of Material Damage and Failure
Owen, J M
2010-04-30
We describe our new methodology for Adaptive Smoothed Particle Hydrodynamics (ASPH) and its application to problems in modeling material failure. We find that ASPH is often crucial for properly modeling such experiments, since in most cases the strain placed on materials is non-isotropic (such as a stretching rod), and without the directional adaptability of ASPH numerical failure due to SPH nodes losing contact in the straining direction can compete with or exceed the physical process of failure.
Observation and Modeling of Fault Damage Zones at Reservoir Depths
NASA Astrophysics Data System (ADS)
Johri, M.; Zoback, M. D.; Dunham, E. M.; Hennings, P.
2011-12-01
We report a study of sub-surface fault damage zones adjacent to the San Andreas Fault in central California and series of first- and second-order faults in a gas field in Southeast Asia. We compare the observations with theoretically-predicted damage zones from dynamic rupture propagation modeling. The importance of characterizing damage zones arises from the important role that damage zones and natural fractures play in governing fluid flow in low permeability rocks. While there are many published studies of exposed damage zones, there is an absence of studies utilizing subsurface data that characterizes damage zones at depth. Damage zones associated with second-order faults adjacent to the San Andreas Fault are studied in well-cemented arkosic sandstones immediately southwest of the fault at the SAFOD site using electrical image logs and physical property measurements. The peak fracture intensity is between three and six fractures per meter in thee damage zones which persist about 50-80 meters from the second-order faults. Fracture intensity in these damage zones in both the regions of study decreases according to a power law where the rate of decrease is approximately -0.8 . The gas reservoir in Southeast Asia is associated with a large, basement master fault and twenty-seven seismically resolvable second-order faults. Four to seven fractures per meter are observed in electrical image logs from five wells in the 50-80m wide damage zones of the second-order faults. The second part of this work involves predicting damage zone widths utilizing two-dimensional plane-strain dynamic rupture models with strong rate-weakening fault friction and off-fault Drucker-Prager plasticity. The number of induced third-order faults and fractures are calculated by assuming that the dilatational plastic strain is manifested in the form of discrete fault planes. The theoretical results suggest that the damage zones are approximately 60-100 meters wide and the fracture intensity
Modelling blast induced damage from a fully coupled explosive charge
Onederra, Italo A.; Furtney, Jason K.; Sellers, Ewan; Iverson, Stephen
2015-01-01
This paper presents one of the latest developments in the blasting engineering modelling field—the Hybrid Stress Blasting Model (HSBM). HSBM includes a rock breakage engine to model detonation, wave propagation, rock fragmentation, and muck pile formation. Results from two controlled blasting experiments were used to evaluate the code’s ability to predict the extent of damage. Results indicate that the code is capable of adequately predicting both the extent and shape of the damage zone associated with the influence of point-of-initiation and free-face boundary conditions. Radial fractures extending towards a free face are apparent in the modelling output and matched those mapped after the experiment. In the stage 2 validation experiment, the maximum extent of visible damage was of the order of 1.45 m for the fully coupled 38-mm emulsion charge. Peak radial velocities were predicted within a relative difference of only 1.59% at the nearest history point at 0.3 m from the explosive charge. Discrepancies were larger further away from the charge, with relative differences of −22.4% and −42.9% at distances of 0.46 m and 0.61 m, respectively, meaning that the model overestimated particle velocities at these distances. This attenuation deficiency in the modelling produced an overestimation of the damage zone at the corner of the block due to excessive stress reflections. The extent of visible damage in the immediate vicinity of the blasthole adequately matched the measurements. PMID:26412978
Machine learning algorithms for damage detection: Kernel-based approaches
NASA Astrophysics Data System (ADS)
Santos, Adam; Figueiredo, Eloi; Silva, M. F. M.; Sales, C. S.; Costa, J. C. W. A.
2016-02-01
This paper presents four kernel-based algorithms for damage detection under varying operational and environmental conditions, namely based on one-class support vector machine, support vector data description, kernel principal component analysis and greedy kernel principal component analysis. Acceleration time-series from an array of accelerometers were obtained from a laboratory structure and used for performance comparison. The main contribution of this study is the applicability of the proposed algorithms for damage detection as well as the comparison of the classification performance between these algorithms and other four ones already considered as reliable approaches in the literature. All proposed algorithms revealed to have better classification performance than the previous ones.
NASA Astrophysics Data System (ADS)
Carrier, Aurore; Got, Jean-Luc; Peltier, Aline; Ferrazzini, Valérie; Staudacher, Thomas; Kowalski, Philippe; Boissier, Patrice
2015-01-01
Monitoring of large basaltic volcanoes, such as Piton de la Fournaise (La Réunion Island, France), has revealed preeruptive accelerations in surface displacements and seismicity rate over a period of between 1 h and several weeks before magma reaches the surface. Such eruptions are attributed to ruptures of pressurized magma reservoirs. Elastic models used to describe surface deformation would assume that accelerations in surface deformation are due to increases in reservoir pressure. This assumption requires changes in magma or pressure conditions at the base of the magma feeding system that are unrealistic over the observed timescale. Another possible cause for these accelerations is magma pressure in the reservoir weakening the volcanic edifice. In the present study, we modeled such weakening by progressive damage to an initially elastic edifice. We used an incremental damage model, with seismicity as a damage variable with daily increments. Elastic moduli decrease linearly with each damage increment. Applied to an initially elastic edifice with constant pressure at the base of the system, this damage model reproduces surface displacement accelerations quite well when damage is sufficient. Process dynamics is controlled by the damage parameter, taken as the ratio between the incremental rupture surface and the surface to be ruptured. In this case, edifice strength and magma reservoir pressure decrease with decreasing elastic moduli, whereas surface displacement accelerates. We discuss the consequences of pressure decreases in magma reservoirs.
Dealing with uncertainty in model updating for damage assessment: A review
NASA Astrophysics Data System (ADS)
Simoen, Ellen; De Roeck, Guido; Lombaert, Geert
2015-05-01
In structural engineering, model updating is often used for non-destructive damage assessment: by calibrating stiffness parameters of finite element models based on experimentally obtained (modal) data, structural damage can be identified, quantified and located. However, the model updating problem is an inverse problem prone to ill-posedness and ill-conditioning. This means the problem is extremely sensitive to small errors, which may potentially detract from the method's robustness and reliability. As many errors or uncertainties are present in model updating, both regarding the measurements as well as the employed numerical model, it is important to take these uncertainties suitably into account. This paper aims to provide an overview of the available approaches to this end, where two methods are treated in detail: a non-probabilistic fuzzy approach and a probabilistic Bayesian approach. These methods are both elaborated for the specific case of vibration-based finite element model updating for damage assessment purposes.
Regional flood impact assessment based on local land use patterns and sample damage records
NASA Astrophysics Data System (ADS)
Aubrecht, Christoph; Steinnocher, Klaus; Köstl, Mario
2011-10-01
Increasing land consumption and land demand particularly in mountainous regions entail further expansion of settlements to known hazard-prone areas. Potential impacts as well as regionally defined levels of 'acceptable risk' are often not transparently communicated and residual risks are not perceived by the public. Analysing past events and assessing regional damage potentials can help planners on all levels to improve comprehensive and sustainable risk management. In this letter, a geospatial and statistical approach to regional damage cost assessment is presented, integrating information on actual conditions in terms of land use disparities and recorded damage data from a documented severe flooding event. In a first step building objects are categorized according to their function and use. Tabular company information is linked to the building model via geocoded postal address data, enabling classification of building types in terms of predominant uses. For the disaster impact assessment the flood plain is delineated based on post-disaster aerial imagery and a digital terrain model distinguishing areas of long and short term flooding. Finally, four regional damage cost assessment scenarios on different levels of detail are calculated. The damage cost projection relies on available sample building-level damage records, allowing rough damage averaging for distinct building uses. Results confirm that consideration of local land use patterns is essential for optimizing regional damage cost projections.
Continuum damage modeling and simulation of hierarchical dental enamel
NASA Astrophysics Data System (ADS)
Ma, Songyun; Scheider, Ingo; Bargmann, Swantje
2016-05-01
Dental enamel exhibits high fracture toughness and stiffness due to a complex hierarchical and graded microstructure, optimally organized from nano- to macro-scale. In this study, a 3D representative volume element (RVE) model is adopted to study the deformation and damage behavior of the fibrous microstructure. A continuum damage mechanics model coupled to hyperelasticity is developed for modeling the initiation and evolution of damage in the mineral fibers as well as protein matrix. Moreover, debonding of the interface between mineral fiber and protein is captured by employing a cohesive zone model. The dependence of the failure mechanism on the aspect ratio of the mineral fibers is investigated. In addition, the effect of the interface strength on the damage behavior is studied with respect to geometric features of enamel. Further, the effect of an initial flaw on the overall mechanical properties is analyzed to understand the superior damage tolerance of dental enamel. The simulation results are validated by comparison to experimental data from micro-cantilever beam testing at two hierarchical levels. The transition of the failure mechanism at different hierarchical levels is also well reproduced in the simulations.
Prostaglandin ethanolamides attenuate damage in a human explant colitis model.
Nicotra, Lauren L; Vu, Megan; Harvey, Benjamin S; Smid, Scott D
2013-01-01
Endocannabinoids are protective in animal colitis models. As endocannabinoids also form novel prostaglandin ethanolamides (prostamides) via COX-2, we investigated the effects of prostamides and other COX-2 mediators on tissue damage in an ex vivo human mucosal explant colitis model. Healthy human colonic mucosae were incubated with pro-inflammatory cytokines TNF-α and IL-1β to elicit colitis-like tissue damage. The PGF-ethanolamide analogue, bimatoprost decreased colitis scores which were reversed by a prostamide-specific antagonist AGN 211334, but not the FP receptor antagonist AL-8810. PGF-ethanolamide and PGE-ethanolamide also reduced cytokine-evoked epithelial damage. Anandamide was protective in the explant colitis model; however COX-2 inhibition did not alter its effects, associated with a lack of COX-2 induction in explant mucosal tissue. These findings support an anti-inflammatory role for prostamides and endocannabinoids in the human colon. PMID:23380599
Flight Dynamics Modeling and Simulation of a Damaged Transport Aircraft
NASA Technical Reports Server (NTRS)
Shah, Gautam H.; Hill, Melissa A.
2012-01-01
A study was undertaken at NASA Langley Research Center to establish, demonstrate, and apply methodology for modeling and implementing the aerodynamic effects of MANPADS damage to a transport aircraft into real-time flight simulation, and to demonstrate a preliminary capability of using such a simulation to conduct an assessment of aircraft survivability. Key findings from this study include: superpositioning of incremental aerodynamic characteristics to the baseline simulation aerodynamic model proved to be a simple and effective way of modeling damage effects; the primary effect of wing damage rolling moment asymmetry may limit minimum airspeed for adequate controllability, but this can be mitigated by the use of sideslip; combined effects of aerodynamics, control degradation, and thrust loss can result in significantly degraded controllability for a safe landing; and high landing speeds may be required to maintain adequate control if large excursions from the nominal approach path are allowed, but high-gain pilot control during landing can mitigate this risk.
Probabilistic, multi-variate flood damage modelling using random forests and Bayesian networks
NASA Astrophysics Data System (ADS)
Kreibich, Heidi; Schröter, Kai
2015-04-01
Decisions on flood risk management and adaptation are increasingly based on risk analyses. Such analyses are associated with considerable uncertainty, even more if changes in risk due to global change are expected. Although uncertainty analysis and probabilistic approaches have received increased attention recently, they are hardly applied in flood damage assessments. Most of the damage models usually applied in standard practice have in common that complex damaging processes are described by simple, deterministic approaches like stage-damage functions. This presentation will show approaches for probabilistic, multi-variate flood damage modelling on the micro- and meso-scale and discuss their potential and limitations. Reference: Merz, B.; Kreibich, H.; Lall, U. (2013): Multi-variate flood damage assessment: a tree-based data-mining approach. NHESS, 13(1), 53-64. Schröter, K., Kreibich, H., Vogel, K., Riggelsen, C., Scherbaum, F., Merz, B. (2014): How useful are complex flood damage models? - Water Resources Research, 50, 4, p. 3378-3395.
The current state of eukaryotic DNA base damage and repair.
Bauer, Nicholas C; Corbett, Anita H; Doetsch, Paul W
2015-12-01
DNA damage is a natural hazard of life. The most common DNA lesions are base, sugar, and single-strand break damage resulting from oxidation, alkylation, deamination, and spontaneous hydrolysis. If left unrepaired, such lesions can become fixed in the genome as permanent mutations. Thus, evolution has led to the creation of several highly conserved, partially redundant pathways to repair or mitigate the effects of DNA base damage. The biochemical mechanisms of these pathways have been well characterized and the impact of this work was recently highlighted by the selection of Tomas Lindahl, Aziz Sancar and Paul Modrich as the recipients of the 2015 Nobel Prize in Chemistry for their seminal work in defining DNA repair pathways. However, how these repair pathways are regulated and interconnected is still being elucidated. This review focuses on the classical base excision repair and strand incision pathways in eukaryotes, considering both Saccharomyces cerevisiae and humans, and extends to some important questions and challenges facing the field of DNA base damage repair. PMID:26519467
The current state of eukaryotic DNA base damage and repair
Bauer, Nicholas C.; Corbett, Anita H.; Doetsch, Paul W.
2015-01-01
DNA damage is a natural hazard of life. The most common DNA lesions are base, sugar, and single-strand break damage resulting from oxidation, alkylation, deamination, and spontaneous hydrolysis. If left unrepaired, such lesions can become fixed in the genome as permanent mutations. Thus, evolution has led to the creation of several highly conserved, partially redundant pathways to repair or mitigate the effects of DNA base damage. The biochemical mechanisms of these pathways have been well characterized and the impact of this work was recently highlighted by the selection of Tomas Lindahl, Aziz Sancar and Paul Modrich as the recipients of the 2015 Nobel Prize in Chemistry for their seminal work in defining DNA repair pathways. However, how these repair pathways are regulated and interconnected is still being elucidated. This review focuses on the classical base excision repair and strand incision pathways in eukaryotes, considering both Saccharomyces cerevisiae and humans, and extends to some important questions and challenges facing the field of DNA base damage repair. PMID:26519467
Progressive Damage Modeling of Durable Bonded Joint Technology
NASA Technical Reports Server (NTRS)
Leone, Frank A.; Davila, Carlos G.; Lin, Shih-Yung; Smeltzer, Stan; Girolamo, Donato; Ghose, Sayata; Guzman, Juan C.; McCarville, Duglas A.
2013-01-01
The development of durable bonded joint technology for assembling composite structures for launch vehicles is being pursued for the U.S. Space Launch System. The present work is related to the development and application of progressive damage modeling techniques to bonded joint technology applicable to a wide range of sandwich structures for a Heavy Lift Launch Vehicle. The joint designs studied in this work include a conventional composite splice joint and a NASA-patented Durable Redundant Joint. Both designs involve a honeycomb sandwich with carbon/epoxy facesheets joined with adhesively bonded doublers. Progressive damage modeling allows for the prediction of the initiation and evolution of damage. For structures that include multiple materials, the number of potential failure mechanisms that must be considered increases the complexity of the analyses. Potential failure mechanisms include fiber fracture, matrix cracking, delamination, core crushing, adhesive failure, and their interactions. The joints were modeled using Abaqus parametric finite element models, in which damage was modeled with user-written subroutines. Each ply was meshed discretely, and layers of cohesive elements were used to account for delaminations and to model the adhesive layers. Good correlation with experimental results was achieved both in terms of load-displacement history and predicted failure mechanisms.
An in vitro model for retinal laser damage
NASA Astrophysics Data System (ADS)
Denton, Michael L.; Foltz, Michael S.; Schuster, Kurt J.; Estlack, Larry E.; Hodnett, Harvey M.; Noojin, Gary D.; Thomas, Robert J.
2007-02-01
Ocular laser exposures resulting in damage at the retina typically involve cellular alterations in the retinal pigment epithelial (RPE) layer. To provide guidelines for eye-safe exposure to lasers, the laser safety community has relied on damage assessment in nonhuman primate studies. Simple and reliable model systems for laser bioeffects that use cultured RPE cells, rather than animals, are thus desirable. We have characterized our artificially pigmented hTERT-RPE1 model by identifying ED 50 thresholds over a wide range of laser parameters and cell culture conditions. When summarized as action spectra and temporal action profiles (log threshold fluence versus log exposure duration), trends (pigment-dependent) in our cell model data are strikingly similar to the threshold trends reported for animal models (literature). In addition, the rapidity and flexibility (laser delivery) with which studies are performed in our culture model has benefited computational modeling efforts.
Neurocomputational models of the remote effects of focal brain damage.
Reggia, James A
2004-11-01
Sudden localized brain damage, such as occurs in stroke, produces neurological deficits directly attributable to the damaged site. In addition, other clinical deficits occur due to secondary "remote" effects that functionally impair the remaining intact brain regions (e.g., due to their sudden disconnection from the damaged area), a phenomenon known as diaschisis. The underlying mechanisms of these remote effects, particularly those involving interactions between the left and right cerebral hemispheres, have proven somewhat difficult to understand in the context of current theories of hemispheric specialization. This article describes some recent neurocomputational models done in the author's research group that try to explain diaschisis qualitatively. These studies show that both specialization and diaschisis can be accounted for with a single model of hemispheric interactions. Further, the results suggest that left-right subcortical influences may be much more important in influencing hemispheric specialization than is generally recognized. PMID:15564108
Thermomechanics of damageable materials under diffusion: modelling and analysis
NASA Astrophysics Data System (ADS)
Roubíček, Tomáš; Tomassetti, Giuseppe
2015-12-01
We propose a thermodynamically consistent general-purpose model describing diffusion of a solute or a fluid in a solid undergoing possible phase transformations and damage, beside possible visco-inelastic processes. Also heat generation/consumption/transfer is considered. Damage is modelled as rate-independent. The applications include metal-hydrogen systems with metal/hydride phase transformation, poroelastic rocks, structural and ferro/para-magnetic phase transformation, water and heat transport in concrete, and if diffusion is neglected, plasticity with damage and viscoelasticity, etc. For the ensuing system of partial differential equations and inclusions, we prove existence of solutions by a carefully devised semi-implicit approximation scheme of the fractional-step type.
A statistical damage model with implications for precursory seismicity
NASA Astrophysics Data System (ADS)
Lee, Ya-Ting; Turcotte, Donald; Rundle, John; Chen, Chien-Chih
2012-06-01
Acoustic emissions prior to rupture indicate precursory damage. Laboratory studies of frictional sliding on model faults feature accelerating rates of acoustic emissions prior to rupture. Precursory seismic emissions are not generally observed prior to earthquakes. To address the problem of precursory damage, we consider failure in a fiber-bundle model. We observe a clearly defined nucleation phase followed by a catastrophic rupture. The fibers are hypothesized to represent asperities on a fault. Two limiting behaviors are the equal load sharing p = 0 (stress from a failed fiber is transferred equally to all surviving fibers) and the local load sharing p = 1 (stress from a failed fiber is transferred to adjacent fibers). We show that precursory damage in the nucleation phase is greatly reduced in the local-load sharing limit. The local transfer of stress from an asperity concentrates nucleation, restricting precursory acoustic emissions (seismic activity).
Constitutive modeling of solid propellant materials with evolving microstructural damage
NASA Astrophysics Data System (ADS)
Xu, F.; Aravas, N.; Sofronis, P.
Solid propellants are composite materials with complex microstructure. In a generic form, the material consists of polymeric binder, crystal oxidizer (e.g., ammonium perchlorate), and fuel particles (e.g., aluminum). Severe stressing and extreme temperatures induce damage which is manifested in particle cracking, dewetting along particle/polymer interfaces, void nucleation and growth. Damage complicates the overall constitutive response of a solid propellant over and above the complexities associated with the differing constitutive properties of the particle and binder phases. Using rigorous homogenization theory for composite materials, we propose a general 3-D nonlinear macroscopic constitutive law that models microstructural damage evolution upon straining through continuous void formation and growth. The law addresses the viscous deformation rate within the framework of additive decomposition of the deformation rate and the concept of back stress is used to improve the model performance in stress relaxation. No restriction is placed on the magnitude of the strains. Experimental data from the standard relaxation and uniaxial tension tests are used to calibrate the model parameters in the case of a high elongation solid propellant. It is emphasized that the model parameters are descriptors of individual phase constitutive response and criticality conditions for particle decohesion which can systematically be determined through experiment. The model is used to predict the response of the material under more complex loading paths and to investigate the effect of crack tip damage on the mechanical behavior of a compact tension fracture specimen.
Capacitance-based damage detection sensing for aerospace structural composites
NASA Astrophysics Data System (ADS)
Bahrami, P.; Yamamoto, N.; Chen, Y.; Manohara, H.
2014-04-01
Damage detection technology needs improvement for aerospace engineering application because detection within complex composite structures is difficult yet critical to avoid catastrophic failure. Damage detection is challenging in aerospace structures because not all the damage detection technology can cover the various defect types (delamination, fiber fracture, matrix crack etc.), or conditions (visibility, crack length size, etc.). These defect states are expected to become even more complex with future introduction of novel composites including nano-/microparticle reinforcement. Currently, non-destructive evaluation (NDE) methods with X-ray, ultrasound, or eddy current have good resolutions (< 0.1 mm), but their detection capabilities is limited by defect locations and orientations and require massive inspection devices. System health monitoring (SHM) methods are often paired with NDE technologies to signal out sensed damage, but their data collection and analysis currently requires excessive wiring and complex signal analysis. Here, we present a capacitance sensor-based, structural defect detection technology with improved sensing capability. Thin dielectric polymer layer is integrated as part of the structure; the defect in the structure directly alters the sensing layer's capacitance, allowing full-coverage sensing capability independent of defect size, orientation or location. In this work, capacitance-based sensing capability was experimentally demonstrated with a 2D sensing layer consisting of a dielectric layer sandwiched by electrodes. These sensing layers were applied on substrate surfaces. Surface indentation damage (~1mm diameter) and its location were detected through measured capacitance changes: 1 to 250 % depending on the substrates. The damage detection sensors are light weight, and they can be conformably coated and can be part of the composite structure. Therefore it is suitable for aerospace structures such as cryogenic tanks and rocket
NASA Astrophysics Data System (ADS)
Shang, Shen; Yun, Gun Jin; Qiao, Pizhong
2010-05-01
In this paper, a new model-based delamination detection methodology is presented for laminated composite plates and its performance is studied both numerically and experimentally. This methodology consists of two main parts: (1) modal analysis of an undamaged baseline finite element (FE) model and experimental modal testing of panels with delamination damage at single or multiple locations and (2) a sensitivity based subset selection technique for single or multiple delamination damage localizations. As an identification model, a higher-order finite element model is combined with a rational micromechanics-based CDM model which defines the delamination damage parameter as a ratio of delaminated area to entire area. The subset selection technique based on sensitivity of the dynamic residual force has been known to be capable of detecting multiple damage locations. However, there has been no experimental study specifically for the applications in laminated composite structures. To implement the methodology, a sensitivity matrix for the laminated composite plate model has been derived. Applications of the proposed methodology to an E-glass/epoxy symmetric composite panel composed of 16 plies [CSM/UM1208/3 layers of C1800]s = [CSM/0/(90/0)3]s with delamination damage are demonstrated both numerically and experimentally. A non-contact scanning laser vibrometer (SLV), a lead zirconate titanate (PZT) actuator and a polyvinylidene fluoride (PVDF) sensor are used to conduct experimental modal testing. From the experimental example, capabilities of the proposed methodology for damage identification are successfully demonstrated for a 2D laminated composite panel. Furthermore, various damage scenarios are considered to show its performance and detailed results are discussed for future improvements.
Modeling of viscoelasticity and damage in composite laminates by continuum thermodynamics
NASA Astrophysics Data System (ADS)
Ahci, Elif
Time dependent analysis of fiber reinforced polymer matrix composites is essential if these materials are used in applications involving the effect of severe environmental conditions such as high temperature and humidity in addition to mechanical loading. The present research is focused on understanding and modeling the overall nonlinear viscoelastic response of polymer matrix composites incorporating the effects of distributed damage. A constitutive framework incorporating the effect of high temperature and distributed damage is developed for polymer matrix composite laminates. The use of this framework for woven fabric composites is illustrated. The viscoelastic material response and the material properties under severe environmental conditions are studied both theoretically and experimentally. The approach uses continuum thermodynamics based formulation in which stress and temperature are allowed as independent variables along with the so-called hidden variables associated with viscous flow and internal variables representing damage. The damage variables incorporate time-dependent crack separation response as well crack surface orientation. The material coefficients in the polynomial expansion of the free energy are evaluated by a computational model. A user defined material subroutine is developed to include the nonlinear viscoelastic constitutive relations into ABAQUS finite element analysis package in computational study. A combined analytical and numerical procedure to determine the unknown constants in the theoretical model is also presented. The effect of damage on the residual viscoelastic response of the material is studied by experiments to get a satisfactory and complete model. The effect of high temperature on the damage initiation and evolution is studied by microscopic observations of the undamaged and damaged specimen edges, which are exposed to high temperature. A systematic experimental procedure is followed to determine the critical temperature
Role of interactions and damage in a cohesive fracture model
NASA Astrophysics Data System (ADS)
Gran, Josesph; Rundle, John; Turcotte, Donald; Klein, William
2012-02-01
We study the influences of local and long range interactions in a numerical model of tensile fracture. Our model simulates fracture events on a 2D square lattice plane with a Metropolis algorithm. We chose a Hamiltonian that is written as a function of the crack separation (offset field) and includes contributions from an external field, interactions, as well as a cohesive energy across the crack surfaces. Included in our study is both a ferromagnetic-type (attractive) and antiferromagnetic-type (repulsive) interactions. We test both of these interactions individually as well as a hybrid interaction in which over a short range the interaction is antiferromagnetic and in the long range the interaction becomes ferromagnetic. This dual interaction approximates a Lennard-Jones potential. We also propose a characterization of damage and investigate the increase of damage in time for fractures occurring by a static-load as well as a time-dependent load. Damaged sites do not interact with neighboring sites and cannot hold any load. We compare our damage model to previous studies of fiber-bundle models.
Laser-based structural sensing and surface damage detection
NASA Astrophysics Data System (ADS)
Guldur, Burcu
Damage due to age or accumulated damage from hazards on existing structures poses a worldwide problem. In order to evaluate the current status of aging, deteriorating and damaged structures, it is vital to accurately assess the present conditions. It is possible to capture the in situ condition of structures by using laser scanners that create dense three-dimensional point clouds. This research investigates the use of high resolution three-dimensional terrestrial laser scanners with image capturing abilities as tools to capture geometric range data of complex scenes for structural engineering applications. Laser scanning technology is continuously improving, with commonly available scanners now capturing over 1,000,000 texture-mapped points per second with an accuracy of ~2 mm. However, automatically extracting meaningful information from point clouds remains a challenge, and the current state-of-the-art requires significant user interaction. The first objective of this research is to use widely accepted point cloud processing steps such as registration, feature extraction, segmentation, surface fitting and object detection to divide laser scanner data into meaningful object clusters and then apply several damage detection methods to these clusters. This required establishing a process for extracting important information from raw laser-scanned data sets such as the location, orientation and size of objects in a scanned region, and location of damaged regions on a structure. For this purpose, first a methodology for processing range data to identify objects in a scene is presented and then, once the objects from model library are correctly detected and fitted into the captured point cloud, these fitted objects are compared with the as-is point cloud of the investigated object to locate defects on the structure. The algorithms are demonstrated on synthetic scenes and validated on range data collected from test specimens and test-bed bridges. The second objective of
A creep-damage model for mesoscale simulations of concrete expansion-degradation phenomena
Giorla, Alain B; Le Pape, Yann
2015-01-01
Long-term performance of aging concrete in nuclear power plants (NPPs) requires a careful examination of the physical phenomena taking place in the material. Concrete under high neutron irradiation is subjected to large irreversible deformations as well as mechanical damage, caused by a swelling of the aggregates. However, these results, generally obtained in accelerated conditions in test reactors, cannot be directly applied to NPP irradiated structures, i.e., the biological shield, operating conditions due to difference in time scale and environmental conditions (temperature, humidity). Mesoscale numerical simulations are performed to separate the underlying mechanisms and their interactions. The cement paste creep-damage model accounts for the effect of the loading rate on the apparent damage properties of the material and uses an event-based approach to capture the competition between creep and damage. The model is applied to the simulation of irradiation experiments from the literature and shows a good agreement with the experimental data.
Multiscale Modeling of Advanced Materials for Damage Prediction and Structural Health Monitoring
NASA Astrophysics Data System (ADS)
Borkowski, Luke
Advanced aerospace materials, including fiber reinforced polymer and ceramic matrix composites, are increasingly being used in critical and demanding applications, challenging the current damage prediction, detection, and quantification methodologies. Multiscale computational models offer key advantages over traditional analysis techniques and can provide the necessary capabilities for the development of a comprehensive virtual structural health monitoring (SHM) framework. Virtual SHM has the potential to drastically improve the design and analysis of aerospace components through coupling the complementary capabilities of models able to predict the initiation and propagation of damage under a wide range of loading and environmental scenarios, simulate interrogation methods for damage detection and quantification, and assess the health of a structure. A major component of the virtual SHM framework involves having micromechanics-based multiscale composite models that can provide the elastic, inelastic, and damage behavior of composite material systems under mechanical and thermal loading conditions and in the presence of microstructural complexity and variability. Quantification of the role geometric and architectural variability in the composite microstructure plays in the local and global composite behavior is essential to the development of appropriate scale-dependent unit cells and boundary conditions for the multiscale model. Once the composite behavior is predicted and variability effects assessed, wave-based SHM simulation models serve to provide knowledge on the probability of detection and characterization accuracy of damage present in the composite. The research presented in this dissertation provides the foundation for a comprehensive SHM framework for advanced aerospace materials. The developed models enhance the prediction of damage formation as a result of ceramic matrix composite processing, improve the understanding of the effects of architectural and
Interpretation of the Superpave IDT strength test using a viscoelastic-damage constitutive model
NASA Astrophysics Data System (ADS)
Onifade, Ibrahim; Balieu, Romain; Birgisson, Bjorn
2016-03-01
This paper presents a new interpretation for the Superpave IDT strength test based on a viscoelastic-damage framework. The framework is based on continuum damage mechanics and the thermodynamics of irreversible processes with an anisotropic damage representation. The new approach introduces considerations for the viscoelastic effects and the damage accumulation that accompanies the fracture process in the interpretation of the Superpave IDT strength test for the identification of the Dissipated Creep Strain Energy (DCSE) limit from the test result. The viscoelastic model is implemented in a Finite Element Method (FEM) program for the simulation of the Superpave IDT strength test. The DCSE values obtained using the new approach is compared with the values obtained using the conventional approach to evaluate the validity of the assumptions made in the conventional interpretation of the test results. The result shows that the conventional approach over-estimates the DCSE value with increasing estimation error at higher deformation rates.
Interpretation of the Superpave IDT strength test using a viscoelastic-damage constitutive model
NASA Astrophysics Data System (ADS)
Onifade, Ibrahim; Balieu, Romain; Birgisson, Bjorn
2016-08-01
This paper presents a new interpretation for the Superpave IDT strength test based on a viscoelastic-damage framework. The framework is based on continuum damage mechanics and the thermodynamics of irreversible processes with an anisotropic damage representation. The new approach introduces considerations for the viscoelastic effects and the damage accumulation that accompanies the fracture process in the interpretation of the Superpave IDT strength test for the identification of the Dissipated Creep Strain Energy (DCSE) limit from the test result. The viscoelastic model is implemented in a Finite Element Method (FEM) program for the simulation of the Superpave IDT strength test. The DCSE values obtained using the new approach is compared with the values obtained using the conventional approach to evaluate the validity of the assumptions made in the conventional interpretation of the test results. The result shows that the conventional approach over-estimates the DCSE value with increasing estimation error at higher deformation rates.
Nonlinear ultrasound modelling and validation of fatigue damage
NASA Astrophysics Data System (ADS)
Fierro, G. P. Malfense; Ciampa, F.; Ginzburg, D.; Onder, E.; Meo, M.
2015-05-01
Nonlinear ultrasound techniques have shown greater sensitivity to microcracks and they can be used to detect structural damages at their early stages. However, there is still a lack of numerical models available in commercial finite element analysis (FEA) tools that are able to simulate the interaction of elastic waves with the materials nonlinear behaviour. In this study, a nonlinear constitutive material model was developed to predict the structural response under continuous harmonic excitation of a fatigued isotropic sample that showed anharmonic effects. Particularly, by means of Landau's theory and Kelvin tensorial representation, this model provided an understanding of the elastic nonlinear phenomena such as the second harmonic generation in three-dimensional solid media. The numerical scheme was implemented and evaluated using a commercially available FEA software LS-DYNA, and it showed a good numerical characterisation of the second harmonic amplitude generated by the damaged region known as the nonlinear response area (NRA). Since this process requires only the experimental second-order nonlinear parameter and rough damage size estimation as an input, it does not need any baseline testing with the undamaged structure or any dynamic modelling of the fatigue crack growth. To validate this numerical model, the second-order nonlinear parameter was experimentally evaluated at various points over the fatigue life of an aluminium (AA6082-T6) coupon and the crack propagation was measured using an optical microscope. A good correlation was achieved between the experimental set-up and the nonlinear constitutive model.
NASA Technical Reports Server (NTRS)
Ranatunga, Vipul; Bednarcyk, Brett A.; Arnold, Steven M.
2010-01-01
A method for performing progressive damage modeling in composite materials and structures based on continuum level interfacial displacement discontinuities is presented. The proposed method enables the exponential evolution of the interfacial compliance, resulting in unloading of the tractions at the interface after delamination or failure occurs. In this paper, the proposed continuum displacement discontinuity model has been used to simulate failure within both isotropic and orthotropic materials efficiently and to explore the possibility of predicting the crack path, therein. Simulation results obtained from Mode-I and Mode-II fracture compare the proposed approach with the cohesive element approach and Virtual Crack Closure Techniques (VCCT) available within the ABAQUS (ABAQUS, Inc.) finite element software. Furthermore, an eccentrically loaded 3-point bend test has been simulated with the displacement discontinuity model, and the resulting crack path prediction has been compared with a prediction based on the extended finite element model (XFEM) approach.
Damage identification by multi-model updating in the modal and in the time domain
NASA Astrophysics Data System (ADS)
Link, Michael; Weiland, Matthias
2009-08-01
size damage. Time domain response data from impact tests carry high-frequency information which usually is lost when experimental modal data are utilized for damage identification. Even so only little literature was found addressing the utilization of experimental time histories for model updating in conjunction with damage identification. In the present paper we summarize the methodology of computational model updating and report about our experience with damage identification using two different model updating techniques. The first is based on classical modal residuals (natural frequencies and mode shapes) which is extended to allow for simultaneous updating of two models, one for the initial undamaged structure and the second for the damaged structure using the test data of both states (multi-model updating). The second technique uses residuals composed of measured and analytical time histories. Time histories have the advantage of carrying high-frequency information which is beneficial for the detection of local damage and which usually is lost when modal residuals are used. Both techniques have been applied to the same beam structure consisting of two thin face sheets which were bonded together by an adhesive layer. It was the aim of this application to study the performance of the two techniques to localize and quantify the damage which was introduced locally in the adhesive layer.
Bread dough rheology: Computing with a damage function model
NASA Astrophysics Data System (ADS)
Tanner, Roger I.; Qi, Fuzhong; Dai, Shaocong
2015-01-01
We describe an improved damage function model for bread dough rheology. The model has relatively few parameters, all of which can easily be found from simple experiments. Small deformations in the linear region are described by a gel-like power-law memory function. A set of large non-reversing deformations - stress relaxation after a step of shear, steady shearing and elongation beginning from rest, and biaxial stretching, is used to test the model. With the introduction of a revised strain measure which includes a Mooney-Rivlin term, all of these motions can be well described by the damage function described in previous papers. For reversing step strains, larger amplitude oscillatory shearing and recoil reasonable predictions have been found. The numerical methods used are discussed and we give some examples.
Damage and Plastic Deformation Modeling of Beishan Granite Under Compressive Stress Conditions
NASA Astrophysics Data System (ADS)
Chen, L.; Wang, C. P.; Liu, J. F.; Liu, J.; Wang, J.; Jia, Y.; Shao, J. F.
2015-07-01
Based on experimental investigations, we propose a coupled elastoplastic damage model to simulate the mechanical behavior of granite under compressive stress conditions. The granite is taken from the Beishan area, a preferable region for China's high-level radioactive waste repository. Using a 3D acoustic emission monitoring system in mechanical tests, we focus on the cracking process and its influence on the macroscopic mechanical behavior of the granite samples. It is verified that the crack propagation coupled with fractional sliding along the cracks is the principal mechanism controlling the failure process and nonlinear mechanical behavior of granite under compressive stress conditions. Based on this understanding, the coupled elastoplastic damage model is formulated in the framework of the thermodynamics theory. In the model, the coupling between damage and plastic deformation is simulated by introducing the independent damage variable in the plastic yield surface. As a preliminary validation of the model, a series of numerical simulations are performed for compressive tests conducted under different confining pressures. Comparisons between the numerical and simulated results show that the proposed model can reproduce the main features of the mechanical behavior of Beishan granite, particularly the damage evolution under compressive stress conditions.
Physics-based damage predictions for simulating testing and evaluation (T and E) experiments
Addessio, F.L.; Schraad, M.W.; Lewis, M.W.
1999-03-01
This is the final report of a two-year, Laboratory-Directed Research and Development (LDRD) project at the Los Alamos National Laboratory (LANL). This report addresses the need to develop computational techniques and physics-based material models for simulating damage to weapons systems resulting from ballistic threats. Modern weapons systems, such as fighter aircraft, are becoming more dependent upon composite materials to reduce weight, to increase strength and stiffness, and to resist adverse conditions resulting from high temperatures and corrosion. Unfortunately, damaged components can have severe and detrimental effects, as evidenced by statistics from Desert Storm indicating that 75% of aircraft losses were attributable to fuel system vulnerability with hydrodynamic ram being the primary kill mechanism. Therefore, this project addresses damage predictions for composite systems that are subjected to ballistic threats involving hydrodynamic ram. A computational technique for simulating fluid-solid interaction phenomena and physics-based material models have been developed for this purpose.
Prediction of feather damage in laying hens using optical flows and Markov models
Lee, Hyoung-joo; Roberts, Stephen J.; Drake, Kelly A.; Dawkins, Marian Stamp
2011-01-01
Feather pecking in laying hens is a major welfare and production problem for commercial egg producers, resulting in mortality, loss of production as well as welfare issues for the damaged birds. Damaging outbreaks of feather pecking are currently impossible to control, despite a number of proposed interventions. However, the ability to predict feather damage in advance would be a valuable research tool for identifying which management or environmental factors could be the most effective interventions at different ages. This paper proposes a framework for forecasting the damage caused by injurious pecking based on automated image processing and statistical analysis. By frame-by-frame analysis of video recordings of laying hen flocks, optical flow measures are calculated as indicators of the movement of the birds. From the optical flow datasets, measures of disturbance are extracted using hidden Markov models. Based on these disturbance measures and age-related variables, the levels of feather damage in flocks in future weeks is predicted. Applying the proposed method to real-world datasets, it is shown that the disturbance measures offer improved predictive values for feather damage thus enabling an identification of flocks with probable prevalence of damage and injury later in lay. PMID:20659929
Modeling and Characterization of Damage Processes in Metallic Materials
NASA Technical Reports Server (NTRS)
Glaessgen, E. H.; Saether, E.; Smith, S. W.; Hochhalter, J. D.; Yamakov, V. I.; Gupta, V.
2011-01-01
This paper describes a broad effort that is aimed at understanding the fundamental mechanisms of crack growth and using that understanding as a basis for designing materials and enabling predictions of fracture in materials and structures that have small characteristic dimensions. This area of research, herein referred to as Damage Science, emphasizes the length scale regimes of the nanoscale and the microscale for which analysis and characterization tools are being developed to predict the formation, propagation, and interaction of fundamental damage mechanisms. Examination of nanoscale processes requires atomistic and discrete dislocation plasticity simulations, while microscale processes can be examined using strain gradient plasticity, crystal plasticity and microstructure modeling methods. Concurrent and sequential multiscale modeling methods are being developed to analytically bridge between these length scales. Experimental methods for characterization and quantification of near-crack tip damage are also being developed. This paper focuses on several new methodologies in these areas and their application to understanding damage processes in polycrystalline metals. On-going and potential applications are also discussed.
Modeling the Study of DNA Damage Responses in Mice
Specks, Julia; Nieto-Soler, Maria; Lopez-Contreras, Andres J; Fernandez-Capetillo, Oscar
2016-01-01
Summary Damaged DNA has a profound impact on mammalian health and overall survival. In addition to being the source of mutations that initiate cancer, the accumulation of toxic amounts of DNA damage can cause severe developmental diseases and accelerate ageing. Therefore, understanding how cells respond to DNA damage has become one of the most intense areas of biomedical research in the recent years. However, whereas most mechanistic studies derive from in vitro or in cellulo work, the impact of a given mutation on a living organism is largely unpredictable. For instance, why BRCA1 mutations preferentially lead to breast cancer whereas mutations compromising mismatch repair drive colon cancer is still not understood. In this context, evaluating the specific physiological impact of mutations that compromise genome integrity has become crucial for a better dimensioning of our knowledge. We here describe the various technologies that can be used for modeling mutations in mice, and provide a review of the genes and pathways that have been modeled so far in the context of DNA damage responses. PMID:25636482
NASA Astrophysics Data System (ADS)
Sbarufatti, C.; Manes, A.; Giglio, M.
2013-11-01
The work presented hereafter is about the development of a diagnostic system for crack damage detection, localization and quantification on a typical metallic aeronautical structure (skin stiffened through riveted stringers). Crack detection and characterization are based upon strain field sensitivity to damage. The structural diagnosis is carried out by a dedicated smart algorithm (Artificial Neural Network) which is trained on a database of Finite Element simulations relative to damaged and undamaged conditions, providing the system with an accurate predictor at low overall cost. The algorithm, trained on numerical damage experience, is used in a simulated environment to provide reliable preliminary information concerning the algorithm performances for damage diagnosis, thus further reducing the experimental costs and efforts associated with the development and optimization of such systems. The same algorithm has been tested on real experimental strain patterns acquired during real fatigue crack propagation, thus verifying the capability of the numerically trained algorithm for anomaly detection, damage assessment and localization on a real complex structure. The load variability, the discrepancy between the Finite Element Model and the real structure, and the uncertainty in the algorithm training process have been addressed in order to enhance the robustness of the system inference process. Some further algorithm training strategies are discussed, aimed at minimizing the risk for false alarms while maintaining a high probability of damage detection.
Evolution of damage and plasticity in titanium-based, fiber-reinforced composites
Majumdar, B.S. ); Newaz, G.M. ); Ellis, J.R. . Fatigue and Failure Branch)
1993-07-01
The inelastic deformation mechanisms were evaluated for a model titanium-based, fiber-reinforced composite: a beta titanium alloy (Ti-15V-3Al-3Cr-3Sn) reinforced with SiC (SCS-6) fibers. The primary emphasis of this article is to illustrate the sequence in which damage and plasticity evolved for this system. The mechanical responses and the results of detailed microstructural evaluations for the [0][sub 8], [90][sub 8], and [[plus minus]45][sub 2s] laminates are provided. It is shown that the characteristics of the reaction zone around the fiber play a very important role in the way damage and plasticity evolve, particularly in the microyield regime of deformation, and must be included in any realistic constitutive model. Fiber-matrix debonding was a major damage mode for the off-axis systems. The tension test results are also compared with the predictions of a few constitutive models.
Evolution of damage and plasticity in titanium-based, fiber-reinforced composites
NASA Technical Reports Server (NTRS)
Majumdar, B. S.; Newaz, G. M.; Ellis, J. R.
1993-01-01
The inelastic deformation mechanisms were evaluated for a model titanium-based, fiber-reinforced composite: a beta titanium alloy (Ti-15V-3Al-3Cr-3Sn) reinforced with SiC (SCS-6) fibers. The primary emphasis of this article is to illustrate the sequence in which damage and plasticity evolved for this system. The mechanical responses and the results of detailed microstructural evaluations for the 0(8), 90(8), and +/- 45(2s) line oriented laminates are provided. It is shown that the characteristics of the reaction zone around the fiber play a very important role in the way damage and plasticity evolve, particularly in the microyield regime of deformation, and must be included in any realistic constitutive model. Fiber-matrix debonding was a major damage mode for the off-axis systems. The tension test results are also compared with the predictions of a few constitutive models.
Aircraft ground damage and the use of predictive models to estimate costs
NASA Astrophysics Data System (ADS)
Kromphardt, Benjamin D.
Aircraft are frequently involved in ground damage incidents, and repair costs are often accepted as part of doing business. The Flight Safety Foundation (FSF) estimates ground damage to cost operators $5-10 billion annually. Incident reports, documents from manufacturers or regulatory agencies, and other resources were examined to better understand the problem of ground damage in aviation. Major contributing factors were explained, and two versions of a computer-based model were developed to project costs and show what is possible. One objective was to determine if the models could match the FSF's estimate. Another objective was to better understand cost savings that could be realized by efforts to further mitigate the occurrence of ground incidents. Model effectiveness was limited by access to official data, and assumptions were used if data was not available. However, the models were determined to sufficiently estimate the costs of ground incidents.
Predictability of formation damage: An assessment study and generalized models
Civan, F.
1991-01-01
The project objective is to develop improved generalized predictive models to be used for investigation of reservoir formation damage and control for various fluid and rock conditions and to account for these effects in reservoir simulation. To accomplish its objective the proposed study will first critically study and evaluate the previous modeling efforts and the experimental studies reported in the literature. Then, generalized predictive models will be formulated by combining the previous attempts and by improving and generalizing the modeling approaches to accommodate for a wide variety of conditions encountered in actual field applications. A critical review of the previous work addressing their theoretical basis, assumptions and limitations, and the generalized and improved model developed in this study will be presented in a systematic manner in terms of a standardized definition and nomenclature for direct comparison. Case studies with the generalized model will be presented to demonstrate its capacity and validity. User friendly computer programs implementing the improved modeling approaches will also be supplied. This study will form an assessment of the presently available models and methods for evaluating and predicting formation damage and present improved models. Therefore, it will be an important reference for the petroleum industry. 1 tab.
Rastgou Talemi, Soheil; Kollarovic, Gabriel; Lapytsko, Anastasiya; Schaber, Jörg
2015-01-01
Mathematical modelling has been instrumental to understand kinetics of radiation-induced DNA damage repair and associated secondary cancer risk. The widely accepted two-lesion kinetic (TLK) model assumes two kinds of double strand breaks, simple and complex ones, with different repair rates. Recently, persistent DNA damage associated with telomeres was reported as a new kind of DNA damage. We therefore extended existing versions of the TLK model by new categories of DNA damage and re-evaluated those models using extensive data. We subjected different versions of the TLK model to a rigorous model discrimination approach. This enabled us to robustly select a best approximating parsimonious model that can both recapitulate and predict transient and persistent DNA damage after ionizing radiation. Models and data argue for i) nonlinear dose-damage relationships, and ii) negligible saturation of repair kinetics even for high doses. Additionally, we show that simulated radiation-induced persistent telomere-associated DNA damage foci (TAF) can be used to predict excess relative risk (ERR) of developing secondary leukemia after fractionated radiotherapy. We suggest that TAF may serve as an additional measure to predict cancer risk after radiotherapy using high dose rates. This may improve predicting risk-dose dependency of ionizing radiation especially for long-term therapies. PMID:26359627
Rastgou Talemi, Soheil; Kollarovic, Gabriel; Lapytsko, Anastasiya; Schaber, Jörg
2015-01-01
Mathematical modelling has been instrumental to understand kinetics of radiation-induced DNA damage repair and associated secondary cancer risk. The widely accepted two-lesion kinetic (TLK) model assumes two kinds of double strand breaks, simple and complex ones, with different repair rates. Recently, persistent DNA damage associated with telomeres was reported as a new kind of DNA damage. We therefore extended existing versions of the TLK model by new categories of DNA damage and re-evaluated those models using extensive data. We subjected different versions of the TLK model to a rigorous model discrimination approach. This enabled us to robustly select a best approximating parsimonious model that can both recapitulate and predict transient and persistent DNA damage after ionizing radiation. Models and data argue for i) nonlinear dose-damage relationships, and ii) negligible saturation of repair kinetics even for high doses. Additionally, we show that simulated radiation-induced persistent telomere-associated DNA damage foci (TAF) can be used to predict excess relative risk (ERR) of developing secondary leukemia after fractionated radiotherapy. We suggest that TAF may serve as an additional measure to predict cancer risk after radiotherapy using high dose rates. This may improve predicting risk-dose dependency of ionizing radiation especially for long-term therapies. PMID:26359627
Impedance-based damage detection for civil infrastructures
NASA Astrophysics Data System (ADS)
Park, Seunghee; Roh, YongRae; Yi, JinHak; Yun, Chung-Bang; Kwak, Hyo-Gyoung; Lee, SangHan
2004-07-01
The objective of this study is to investigate the feasibility of an impedance-based damage detection technique using piezoelectric (PZT) transducers for civil infrastructures such as steel bridges. The basic concept of the technique is to monitor the changes in the electrical impedance to detect structural damages. Those changes in the electrical impedance are due to the electro-mechanical coupling property of piezoelectric materials. The smart PZT transducers which act as both actuators and sensors in a self-analyzing manner are emerging to be effective in non-parametric health monitoring of structural systems. This health monitoring technique can be easily adapted to existing structures, since only a small number of PZT patches are needed for continuous monitoring of their structural integrity. This impedance-based method operates at high frequencies (above 100 kHz), which enables it to detect incipient-type damage. It is not interfered by normal operating conditions, vibrations of the host structure, and changes in the host external body. The results of the experimental study on three kinds of structural members indicate that cracks or loosened bolts/nuts near the PZT sensors may be effectively detected by monitoring the shifts of the resonant frequencies of the impedance functions.
Modeling polyethylene wear acceleration due to femoral head dislocation damage.
Kruger, Karen M; Tikekar, Nishant M; Heiner, Anneliese D; Lannutti, John J; Callaghan, John J; Brown, Thomas D
2014-08-01
Scratching, scraping, and metal transfer to femoral heads commonly accompany acetabular shell contact during dislocation and closed reduction maneuvers. While head damage conceptually leads to accelerated wear, reports on this subject are mainly anecdotal, and differ widely on the potency of such effect. Towards better understanding this relationship, a physically validated finite element (FE) model was used to compute polyethylene wear acceleration propensity of specific head damage patterns on thirteen retrievals. These FE models estimated wear increases averaging half an order of magnitude when compared to simulations for undamaged heads. There was no correlation between the number of dislocations sustained and wear acceleration. These results underscore the importance of implant-gentle closed reduction, and heightened wear monitoring of successfully reduced dislocation patients. PMID:24851789
A Mathematical Model for Estimating Biological Damage Caused by Radiation
NASA Astrophysics Data System (ADS)
Manabe, Yuichiro; Ichikawa, Kento; Bando, Masako
2012-10-01
We propose a mathematical model for estimating biological damage caused by low-dose irradiation. We understand that the linear non threshold (LNT) hypothesis is realized only in the case of no recovery effects. In order to treat the realistic living objects, our model takes into account various types of recovery as well as proliferation mechanism, which may change the resultant damage, especially for the case of lower dose rate irradiation. It turns out that the lower the radiation dose rate, the safer the irradiated system of living object (which is called symbolically ``tissue'' hereafter) can have chances to survive, which can reproduce the so-called dose and dose-rate effectiveness factor (DDREF).
Analytical modeling for gamma radiation damage on silicon photodiodes
NASA Astrophysics Data System (ADS)
Jafari, H.; Feghhi, S. A. H.
2016-04-01
Radiation-induced damage in PIN silicon photodiode induces degradation of the photodiode parameters. In this work, by presenting an analytical model, the effect of gamma dose on the dark current in a PIN photodiode array was investigated. Geant4 was used to obtain the damage constant as a result of primary incident particle fluence and NIEL distribution calculations. Experimental measurements as well as numerical simulation of the semiconductor with ATLAS were carried out to verify and parameterize the analytical model calculations. A reasonable agreement has been found between analytical results and experimental data for BPX65 silicon photodiodes irradiated by a Co-60 gamma source at total doses up to 500 krad under different reverse voltages. Moreover, the results showed that the dark current of each photodiode array pixel has considerably increased by gamma dose irradiation.
Direct Radiation Damage to Crystalline DNA: What is the Source of Unaltered Base Release?
Razskazovskiy, Yuriy; Debije, Michael G.; Bernhard, William A.
2008-01-01
The radiation chemical yields of unaltered base release have been measured in three crystalline double-stranded DNA oligomers after X irradiation at 4 K. The yields of released bases are between 10 and 20% of the total free radical yields measured at 4 K. Using these numbers, we estimate that the yield of DNA strand breaks due to the direct effect is about 0.1 μmol J−1. The damage responsible for base release is independent of the base type (C, G, A or T) and is not scavenged by anthracycline drugs intercalated in the DNA. For these reasons, reactions initiated by the hydroxyl radical have been ruled out as the source of base release. Since the intercalated anthracycline scavenges electrons and holes completely but does not inhibit base release, the possibility for damage transfer from the bases to the sugars can also be ruled out. The results are consistent with a model in which primary radical cations formed directly on the sugar-phosphate backbone react by two competing pathways: deprotonation, which localizes the damage on the sugar, and hole tunneling, which transfers the damage to the base stack. Quantitative estimates indicate that these two processes are approximately equally efficient. PMID:10761004
Residual stresses and damage in unidirectional model composites
Chatterjee, A.; Moschler, J.W.; Mall, S.; Kerans, R.J.; Pagano, N.J.
1989-10-01
Unidirectional model composites were fabricated with SiC fibers and different borosilicate glasses to study the effect of residual stress states on the damage progression in these composites. A specially designed straining stage was employed to study the failure modes in these materials under stepwise loading. Although both fiber and matrix cracks were observed in all specimens, the mechanisms of failure were found to be different and strongly dependent on the residual stress state in these materials. 15 refs.
NASA Astrophysics Data System (ADS)
Hoell, Simon; Omenzetter, Piotr
2016-03-01
Data-driven vibration-based damage detection techniques can be competitive because of their lower instrumentation and data analysis costs. The use of autoregressive model coefficients (ARMCs) as damage sensitive features (DSFs) is one such technique. So far, like with other DSFs, either full sets of coefficients or subsets selected by trial-and-error have been used, but this can lead to suboptimal composition of multivariate DSFs and decreased damage detection performance. This study enhances the selection of ARMCs for statistical hypothesis testing for damage presence. Two approaches for systematic ARMC selection, based on either adding or eliminating the coefficients one by one or using a genetic algorithm (GA) are proposed. The methods are applied to a numerical model of an aerodynamically excited large composite wind turbine blade with disbonding damage. The GA out performs the other selection methods and enables building multivariate DSFs that markedly enhance early damage detectability and are insensitive to measurement noise.
Copper oxide nanoparticle mediated DNA damage in terrestrial plant models.
Atha, Donald H; Wang, Huanhua; Petersen, Elijah J; Cleveland, Danielle; Holbrook, R David; Jaruga, Pawel; Dizdaroglu, Miral; Xing, Baoshan; Nelson, Bryant C
2012-02-01
Engineered nanoparticles, due to their unique electrical, mechanical, and catalytic properties, are presently found in many commercial products and will be intentionally or inadvertently released at increasing concentrations into the natural environment. Metal- and metal oxide-based nanomaterials have been shown to act as mediators of DNA damage in mammalian cells, organisms, and even in bacteria, but the molecular mechanisms through which this occurs are poorly understood. For the first time, we report that copper oxide nanoparticles induce DNA damage in agricultural and grassland plants. Significant accumulation of oxidatively modified, mutagenic DNA lesions (7,8-dihydro-8-oxoguanine; 2,6-diamino-4-hydroxy-5-formamidopyrimidine; 4,6-diamino-5-formamidopyrimidine) and strong plant growth inhibition were observed for radish (Raphanus sativus), perennial ryegrass (Lolium perenne), and annual ryegrass (Lolium rigidum) under controlled laboratory conditions. Lesion accumulation levels mediated by copper ions and macroscale copper particles were measured in tandem to clarify the mechanisms of DNA damage. To our knowledge, this is the first evidence of multiple DNA lesion formation and accumulation in plants. These findings provide impetus for future investigations on nanoparticle-mediated DNA damage and repair mechanisms in plants. PMID:22201446
NASA Astrophysics Data System (ADS)
Sharafat, S.; El-Awady, J.; Liu, S.; Diegele, E.; Ghoniem, N. M.
2007-08-01
Large-scale finite element modeling (FEM) of the US Dual Coolant Lead Lithium ITER Test Blanket Module including damage evolution is under development. A comprehensive rate-theory based radiation damage creep deformation code was integrated with the ABACUS FEM code. The advantage of this approach is that time-dependent in-reactor deformations and radiation damage can now be directly coupled with 'material properties' of FEM analyses. The coupled FEM-Creep damage model successfully simulated the simultaneous microstructure and stress evolution in small tensile test-bar structures. Applying the integrated Creep/FEM code to large structures is still computationally prohibitive. Instead, for thermo-structural analysis of the DCLL TBM structure the integrated FEM-creep damage model was used to develop true stress-strain behavior of F82H ferritic steel. Based on this integrated damage evolution-FEM approach it is proposed to use large-scale FEM analysis to identify and isolate critical stress areas for follow up analysis using detailed and fully integrated creep-FEM approach.
Viscoelastic/damage modeling of filament-wound spherical pressure vessels
NASA Technical Reports Server (NTRS)
Hackett, Robert M.; Dozier, Jan D.
1987-01-01
A model of the viscoelastic/damage response of a filament-wound spherical vessel used for long-term pressure containment is developed. The matrix material of the composite system is assumed to be linearly viscoelastic. Internal accumulated damage based upon a quadratic relationship between transverse modulus and maximum circumferential strain is postulated. The resulting nonlinear problem is solved by an iterative routine. The elastic-viscoelastic correspondence is employed to produce, in the Laplace domain, the associated elastic solution for the maximum circumferential strain which is inverted by the method of collocation to yield the time-dependent solution. Results obtained with the model are compared to experimental observations.
NASA Technical Reports Server (NTRS)
Arnold, S. M.; Kruch, S.
1991-01-01
Three multiaxial isothermal continuum damage mechanics models for creep, fatigue, and creep/fatigue interaction of a unidirectional metal matrix composite volume element are presented, only one of which will be discussed in depth. Each model is phenomenological and stress based, with varying degrees of complexity to accurately predict the initiation and propagation of intergranular and transgranular defects over a wide range of loading conditions. The development of these models is founded on the definition of an initially transversely isotropic fatigue limit surface, static fracture surface, normalized stress amplitude function and isochronous creep damage failure surface, from which both fatigue and creep damage evolutionary laws can be obtained. The anisotropy of each model is defined through physically meaningful invariants reflecting the local stress and material orientation. All three transversely isotropic models have been shown, when taken to their isotropic limit, to directly simplify to previously developed and validated creep and fatigue continuum damage theories. Results of a nondimensional parametric study illustrate (1) the flexibility of the present formulation when attempting to characterize a large class of composite materials, and (2) its ability to predict anticipated qualitative trends in the fatigue behavior of unidirectional metal matrix composites. Additionally, the potential for the inclusion of various micromechanical effects (e.g., fiber/matrix bond strength, fiber volume fraction, etc.), into the phenomenological anisotropic parameters is noted, as well as a detailed discussion regarding the necessary exploratory and characterization experiments needed to utilize the featured damage theories.
SHOCK INITIATION EXPERIMENTS PLUS IGNITION AND GROWTH MODELING OF DAMAGED LX-04 CHARGES
Chidester, S K; Garcia, F; Vandersall, K S; Tarver, C M
2009-06-23
Shock initiation experiments were performed on mechanically and thermally damaged LX-04 (85% HMX and 15% Viton by weight) to obtain in-situ manganin pressure gauge data and run distances to detonation at various shock pressures. The LX-04 charges were damaged mechanically by applying a compressive load of 600 psi for 20,000 cycles, thus creating many small narrow cracks, or by cutting wedge shaped parts that were then loosely reassembled, thus creating a few large cracks. The thermal damaged LX-04 charges were heated to 190 C for a long enough time for the beta to delta phase transition to occur and then cooled to ambient temperature. Mechanically damaged LX-04 exhibited only slightly increased shock sensitivity, while the thermally damaged LX-04 was much more shock sensitive. The pristine LX-04 Ignition and Growth model, modified only by igniting a larger amount of explosive during shock compression based on the damaged charge density, accurately calculated the increased shock sensitivity of the three damaged charges.
Unified continuum damage model for matrix cracking in composite rotor blades
Pollayi, Hemaraju; Harursampath, Dineshkumar
2015-03-10
This paper deals with modeling of the first damage mode, matrix micro-cracking, in helicopter rotor/wind turbine blades and how this effects the overall cross-sectional stiffness. The helicopter/wind turbine rotor system operates in a highly dynamic and unsteady environment leading to severe vibratory loads present in the system. Repeated exposure to this loading condition can induce damage in the composite rotor blades. These rotor/turbine blades are generally made of fiber-reinforced laminated composites and exhibit various competing modes of damage such as matrix micro-cracking, delamination, and fiber breakage. There is a need to study the behavior of the composite rotor system under various key damage modes in composite materials for developing Structural Health Monitoring (SHM) system. Each blade is modeled as a beam based on geometrically non-linear 3-D elasticity theory. Each blade thus splits into 2-D analyzes of cross-sections and non-linear 1-D analyzes along the beam reference curves. Two different tools are used here for complete 3-D analysis: VABS for 2-D cross-sectional analysis and GEBT for 1-D beam analysis. The physically-based failure models for matrix in compression and tension loading are used in the present work. Matrix cracking is detected using two failure criterion: Matrix Failure in Compression and Matrix Failure in Tension which are based on the recovered field. A strain variable is set which drives the damage variable for matrix cracking and this damage variable is used to estimate the reduced cross-sectional stiffness. The matrix micro-cracking is performed in two different approaches: (i) Element-wise, and (ii) Node-wise. The procedure presented in this paper is implemented in VABS as matrix micro-cracking modeling module. Three examples are presented to investigate the matrix failure model which illustrate the effect of matrix cracking on cross-sectional stiffness by varying the applied cyclic load.
Crack diagnosis of metallic profiles based on structural damage indicators
NASA Astrophysics Data System (ADS)
Preisler, A.; Steenbock, C.; Schröder, K.-U.
2015-07-01
Structural Health Monitoring (SHM) faces several challenges before large-scale industrial application. First of all damage diagnosis has to be reliable. Therefore, common SHM approaches use highly advanced sensor techniques to monitor the whole structure on all possible failures. This results in an enormous amount of data gathered during service. The general effort can be drastically reduced, if the knowledge achieved during the sizing process is used. During sizing, potential failure modes and critical locations, so called hot spots, are already evaluated. A very sensitive SHM system can be developed, when the monitoring effort shifts from the damage to its impact on the structural behaviour and the so called damage indicators. These are the two main components of the SmartSHM approach, which reduces the monitoring effort significantly. Not only the amount of data is minimized, but also reliability and robustness are ensured by the SmartSHM approach. This contribution demonstrates the SmartSHM approach by a cracked four point bending beam. To show general applicability a parametric study considering different profiles (bar, box, I, C, T, L, Z), crack positions and lengths has been performed. Questions of sensitivity and minimum size of the sensor network are discussed based on the results of the parametric study.
Molecular dynamics modelling of radiation damage in zircon
NASA Astrophysics Data System (ADS)
Grechanovsky, A. E.
2009-04-01
Zircon (ZrSiO4) is among actinide-bearing phases which has been proposed as a crystalline confinement matrix for nuclear waste management, especially for weapon-grade plutonium and UO2 spent fuel in the USA. Zircon is also widely used in geochronology. But, with accumulating α-decay damage, zircon undergoes a radiation induced transition to an amorphous (or metamict) state. So, in the present work molecular dynamics simulations (MD simulations) of zircon structure have been performed to study radiation damage in zircon. In this technique, one simulates the propagation of an energetic particle in a system of atoms interacting via model potentials, by integrating the Newton equations of motion. Author has used version 3.09 of the DL_POLY molecular simulation package. Zircon structure containing 181944 atoms (19x19x21 unit cells) was equilibrated at 300 K for 10 ps, and one Zr atom (usually called the primary knock-on atom, PKA) was given a velocity corresponding to an implantation energy of about 20 keV. MD simulations were performed in the microcanonical ensemble that is under conditions of constant particle number, volume and energy. Results of the MD simulations show that the number of interstitials is equal to 840 atoms. This is very close (4000-5000 atoms for 70 keV recoil atom 234Th) to what is measured in the diffuse x-ray scattering and NMR experiments on amorphous metamict samples (damaged by natural irradiation) of geological age. It has been shown that the damaged structure contains several depleted regions with characteristic sized up to 2,5 nm after single event and up to 4,5 nm after three overlapping events. Furthermore, these events produce channels of depleted matter between the overlapping damaged regions. These channels provide a high-diffusivity path for radiogenic Pb (percolation effect). Loss of radiogenic Pb may result in to incorrect dating of rocks.
Implementation of the TEPLA Damage Model in a 3D Eulerian Hydrocode
NASA Astrophysics Data System (ADS)
Holian, Kathleen S.; Clancy, Sean P.; Maudlin, Paul J.
2007-06-01
A sophisticated damage model (TEPLA) has been implemented into a three-dimensional (Cartesian) computer code (Pagosa) used here at Los Alamos National Laboratory. TEPLA was originally an isotropic damage model based upon the Gurson flow surface (a potential function used in conjunction with the associated flow law) that models damage due to both porosity growth and plastic strain. It has since been modified to model anisotropic elastoplastic material strength as well. Pagosa is an Eulerian hydrodynamics code that has the following special features: a predictor-corrector Lagrangian step that advances the state variables in time, a high-order advection algorithm that remaps the problem back to the original mesh every time step, and a material interface tracking scheme with van Leer monotonic advection. It also includes a variety of equation of state, strength, fracture, and high explosive burn models. We will describe the physics of the TEPLA model (that models both strength and damage) and will show preliminary results of test problems that are used to validate the model. The four test problems (simple shear, stretching rod, Taylor anvil, and plate impact) can be compared with either analytic solutions or with experimental data.
A generalized law for aftershock rates in a damage rheology model
NASA Astrophysics Data System (ADS)
Ben Zion, Y.; Lyakhovsky, V.
2003-12-01
Aftershocks are the response of a damaged rock surrounding large earthquake ruptures to the stress perturbations produced by the large events. Lyakhovsky et al. [JGR, 1997] developed a damage rheology model that provides a quantitative treatment for macroscopic effects of evolving distributed cracking with local density represented by a state variable a. The equation for damage evolution, based on the balance equations of energy and entropy and generalization of linear elasticity, accounts for both degradation and healing as a function of the existing strain tensor and material properties that may be constrained by lab data (rate coefficients and ratio of strain invariants separating states of degradation and healing). Analyses of stress-strain and acoustic emission laboratory data during deformation leading to brittle failure indicate further [Liu et al., AGU, F01; Hamiel et al., this meeting] that the fit between model predictions and observations improves if we also incorporate gradual accumulation of a non-reversible deformation with a rate proportional to the rate of damage increase. For analysis of aftershocks, we consider the relaxation process of a material following the application of a strain step associated with the occurrence of a mainshock. The coupled differential equations governing the damage evolution and stress relaxation can be written in non-dimensional form by scaling the elastic stress to its initial value and the time to characteristic time of damage evolution td. With this, the system behavior is controlled by a single non-dimensional ratio R = td/tM representing the ratio between the damage time scale to the Maxwell relaxation time tM. For very small R there is no relaxation and the response consists of constant rate of damage increase until failure. For very large R there is rapid relaxation without significant change to the level of damage. For intermediate cases the equations are strongly coupled and nonlinear. The analytical solution
Real-time sensing of fatigue crack damage for information-based decision and control
NASA Astrophysics Data System (ADS)
Keller, Eric Evans
Information-based decision and control for structures that are subject to failure by fatigue cracking is based on the following notion: Maintenance, usage scheduling, and control parameter tuning can be optimized through real time knowledge of the current state of fatigue crack damage. Additionally, if the material properties of a mechanical structure can be identified within a smaller range, then the remaining life prediction of that structure will be substantially more accurate. Information-based decision systems can rely one physical models, estimation of material properties, exact knowledge of usage history, and sensor data to synthesize an accurate snapshot of the current state of damage and the likely remaining life of a structure under given assumed loading. The work outlined in this thesis is structured to enhance the development of information-based decision and control systems. This is achieved by constructing a test facility for laboratory experiments on real-time damage sensing. This test facility makes use of a methodology that has been formulated for fatigue crack model parameter estimation and significantly improves the quality of predictions of remaining life. Specifically, the thesis focuses on development of an on-line fatigue crack damage sensing and life prediction system that is built upon the disciplines of Systems Sciences and Mechanics of Materials. A major part of the research effort has been expended to design and fabricate a test apparatus which allows: (i) measurement and recording of statistical data for fatigue crack growth in metallic materials via different sensing techniques; and (ii) identification of stochastic model parameters for prediction of fatigue crack damage. To this end, this thesis describes the test apparatus and the associated instrumentation based on four different sensing techniques, namely, traveling optical microscopy, ultrasonic flaw detection, Alternating Current Potential Drop (ACPD), and fiber
Core damage frequency (reactor design) perspectives based on IPE results
Camp, A.L.; Dingman, S.E.; Forester, J.A.
1996-12-31
This paper provides perspectives gained from reviewing 75 Individual Plant Examination (IPE) submittals covering 108 nuclear power plant units. Variability both within and among reactor types is examined to provide perspectives regarding plant-specific design and operational features, and C, modeling assumptions that play a significant role in the estimates of core damage frequencies in the IPEs. Human actions found to be important in boiling water reactors (BWRs) and in pressurized water reactors (PWRs) are presented and the events most frequently found important are discussed.
Core damage frequency perspectives based on IPE results
Dingman, S.E.; Camp, A.L.; LaChance, J.L.; Drouin, M.T.
1996-08-01
In November 1988, the US Nuclear Regulatory Commission (NRC) issued Generic Letter 88-20 requesting that all licensees perform an individual Plant Examination (IPE) to identify any plant-specific vulnerability to severe accidents and report the results to the Commission. This paper provides perspectives gained from reviewing 75 Individual Plant Examination (IPE) submittals covering 108 nuclear power plant units. Variability both within and among reactor types is examined to provide perspectives regarding plant-specific design and operational features, and modeling assumptions that play a significant role in the estimates of core damage frequencies in the IPEs.
Damage Identification of Piles Based on Vibration Characteristics
Zhang, Xiaozhong; Yao, Wenjuan; Chen, Bo; Liu, Dewen
2014-01-01
A method of damage identification of piles was established by using vibration characteristics. The approach focused on the application of the element strain energy and sensitive modals. A damage identification equation of piles was deduced using the structural vibration equation. The equation contained three major factors: change rate of element modal strain energy, damage factor of pile, and sensitivity factor of modal damage. The sensitive modals of damage identification were selected by using sensitivity factor of modal damage firstly. Subsequently, the indexes for early-warning of pile damage were established by applying the change rate of strain energy. Then the technology of computational analysis of wavelet transform was used to damage identification for pile. The identification of small damage of pile was completely achieved, including the location of damage and the extent of damage. In the process of identifying the extent of damage of pile, the equation of damage identification was used in many times. Finally, a stadium project was used as an example to demonstrate the effectiveness of the proposed method of damage identification for piles. The correctness and practicability of the proposed method were verified by comparing the results of damage identification with that of low strain test. The research provided a new way for damage identification of piles. PMID:25506062
A damage model for the absence of significant precursory seismicity
NASA Astrophysics Data System (ADS)
Lee, Y.; Turcotte, D. L.; Rundle, J.; Chen, C.
2010-12-01
Acoustic emissions prior to rupture indicate precursory damage. Laboratory studies of frictional sliding on model faults feature accelerating rates of acoustic emissions prior to rupture. Precursory seismic emissions are not generally observed prior to earthquakes. To address the problem of precursory damage we consider failure in a fiber-bundle model. We observe a clearly defined nucleation phase followed by a catastrophic rupture. The fibers are hypothesized to represent asperities on a fault. Two limiting behaviors are equal load sharing (stress from a failed fiber is transferred equally to all surviving fibers) and local load sharing (stress from a failed fiber is transferred to adjacent fibers). We show that precursory damage in the nucleation phase is greatly reduced in the local-load sharing limit. We argue that laboratory experiments on fracture involve near-uniform load sharing whereas actual faults involve local load sharing. When one asperity fails on a fault the force carried by the asperity is transferred to adjacent asperities. We argue that this explains the absence of a well defined nucleation phase prior to an earthquake.
Ye, L.; Afaghi-Khatibi, A.; Mai, Y.W.
1997-12-31
The main objective of this study was to evaluate the residual strength of fiber reinforced metal laminates (FRMLs) and polymer matrix composite laminates (PMCLs) with a circular hole or sharp notch using an effective crack growth model (ECGM). Damage is assumed to initiate when the local normal stress at the hole edge/notch tip reaches the tensile strength or yield strength of the composite and metal layers, respectively. The damage in the constituent materials was modelled by fictitious cracks with cohesive stress acting on the crack surfaces, and the damage growth was simulated by extension of the fictitious cracks step by step and reduction of the cohesive stress with crack opening. The apparent fracture energy of composite layers and fracture toughness of metal layers were used to define the relationships between the tensile/yield strength and the critical crack opening. Based on the global equilibrium, an iterative technique was developed to evaluate the applied load required to produce the damage growth. The residual strength of notched composite laminates was defined by instability of the applied load and damage growth. The effect of hole/notch size on the residual strength was studied and the stress redistribution with damage growth was discussed. The residual strength simulated from ECGM correlated well with experimental data in the open literature.
Multi-damage localization in plate structure using frequency response function-based indices
NASA Astrophysics Data System (ADS)
Gao, Hai-yang; Guo, Xing-lin; Ouyang, Huajiang; Yang, Xiu-ming
2015-07-01
Vibration signal and its derivative have shown some promise in structural damage detection in previous research. However, the theoretical and practical difficulties of multi-damage detection in plate structures based on dynamic responses remain. In this paper, an efficient damage localization index based on frequency response function (FRF) is presented. The imaginary part of FRF (IFRF) is extracted to derive the new localization index due to its relation to modal flexibility. For avoiding the finite element model error, two-dimensional gapped smoothing method (GSM) is employed without the need for baseline data from a presumably undamaged structure. Experimental studies on a steel plate with two localized defects in different boundary conditions are performed. The results are compared with some typical damage indices in the literature, such as mode shapes, uniform load surface and IFRF. In order to mitigate the inherent disadvantages of GSM in anti-noise ability, a simple statistical treatment based on Thompson outlier analysis is finally used for noise suppression. The effect of damage level and boundary condition on the detection results is also investigated.
Re-assessment of chronic radio-induced tissue damage in a rat hindlimb model
PHULPIN, BÉRENGÈRE; DOLIVET, GILLES; MARIE, PIERRE-YVES; POUSSIER, SYLVAIN; GALLET, PATRICE; LEROUX, AGNÈS; GRAFF, PIERRE; GROUBACH, FREDERIQUE; BRAVETTI, PIERRE; MERLIN, JEAN-LOUIS; TRAN, NGUYEN
2010-01-01
Radiotherapy is successfully used to treat neoplastic lesions, but may adversely affect normal tissues within the irradiated volume. However, additional clinical and para-clinical data are required for a comprehensive understanding of the pathogenesis of this damage. We assessed a rat model using clinical records and medical imaging to gain a better understanding of irradiation-induced tissue damage. The hindlimbs of the rats in this model were irradiated with a single dose of 30 or 50 Gy. Sequential analysis was based on observation records of stage and planar scintigraphy. Additional radiography, radiohistology and histology studies were performed to detect histological alterations. All animals developed acute and late effects, with an increased severity after a dose of 50 Gy. The bone uptake of 99mTc-HDP was significantly decreased in a dose- and time-dependent manner. Histologically, significant tissue damage was observed. After the 50 Gy irradiation, the animals developed lesions characteristic of osteoradionecrosis (ORN). Radiographic and histological studies provided evidence of lytic bone lesions. Our rat model developed tissue damage characteristic of radiation injury after a single 30 Gy irradiation and tissue degeneration similar to that which occurs during human ORN after a 50 Gy irradiation. The development of this animal model is an essential step in exploring the pathogenesis of irradiation-induced tissue damage, and may be used to test the efficacy of new treatments. PMID:22993575
Relevance of a mesoscopic modeling for the coupling between creep and damage in concrete
NASA Astrophysics Data System (ADS)
Saliba, J.; Grondin, F.; Matallah, M.; Loukili, A.; Boussa, H.
2013-08-01
In its service-life concrete is loaded and delayed strains appear due to creep phenomenon. Some theories suggest that micro-cracks nucleate and grow when concrete is submitted to a high sustained loading, thereby contributing to the weakening of concrete. Thus, it is important to understand the interaction between the viscoelastic deformation and damage in order to design reliable civil engineering structures. Several creep-damage theoretical models have been proposed in the literature. However, most of these models are based on empirical relations applied at the macroscopic scale. Coupling between creep and damage is mostly realized by adding some parameters to take into account the microstructure effects. In the authors' opinion, the microstructure effects can be modeled by taking into account the effective interactions between the concrete matrix and the inclusions. In this paper, a viscoelastic model is combined with an isotropic damage model. The material volume is modeled by a Digital Concrete Model which takes into account the "real" aggregate size distribution of concrete. The results show that stresses are induced by strain incompatibilities between the matrix and aggregates at mesoscale under creep and lead to cracking.
Feasibility study on an angular velocity-based damage detection method using gyroscopes
NASA Astrophysics Data System (ADS)
Sung, S. H.; Lee, J. H.; Park, J. W.; Koo, K. Y.; Jung, H. J.
2014-07-01
This paper proposes an angular velocity-based damage detection method using gyroscopes and investigates its feasibility. This study basically intends to enhance the performance of the existing modal flexibility-based methods by replacing accelerations measured from accelerometers with angular velocities measured from gyroscopes. In order to verify the superiority of a gyroscope in damage detection, numerical studies were performed by changing optional parameters such as damage location, severity, and measurement noise. From parametric studies, it was shown that the damage detection results using gyroscopes are more sensitive to damage and more robust to noise generated from the curvature estimation than those using accelerometers. Experimental validations were also carried out to investigate the feasibility of a gyroscope in damage detection. From the results, it was shown that the gyroscope-based damage detection method can successfully identify damage location. In conclusion, it was numerically and experimentally verified that a new damage detection approach using gyroscopes could improve damage detection ability significantly.
Damage and fracture of brittle viscoelastic solids with application to ice load models
NASA Astrophysics Data System (ADS)
Xiao, Jing
1997-12-01
In this work a multiaxial constitutive theory for brittle, viscoelastic materials is presented based on viscoelasticity, continuum damage theory and fracture mechanics. The microstructural nature of the material and micromechanical processes have been modelled by damage mechanics using averaging procedures with a finite collection of state variables. The change in the state variable is directly related to the individual deformation process. The constitutive model includes the effects of damage including microcracking, dynamic recrystallization and pressure melting on the reduction in elastic modulus and the enhancement in creep deformation. Damage evolution is based on Schapery's approach using the generalized J integral theory. The influence of confining pressure on damage progress is included. Volumetric deformation under compression is also investigated which is mostly dilatation due to microstructural changes (damage). A triaxial test program has been carried out in the laboratory at Memorial University. A description of the test program, specimen preparation, test equipment and procedure used has been presented. The experimental observations and results have been discussed and are summarized. Triaxial tests were designed to investigate the deformation of ice and the influence of damage on the mechanical properties of ice. These tests have also served to verify the constitutive modelling. The theoretical model provides good agreement with test results. The role of fracture and spalling in ice-structure interaction has been investigated. Fracture analysis, using the J-integral, has been carried out in the numerical scheme, which is based on finite elements and the computer program ABAQUS. This analysis is consistent with the damage mechanics and has been carried out on the basis of plane strain assumptions and the direction of crack propagation was calculated by maximizing the strain energy release rate. The direction of maximum tensile stress was also
Finite element based damage assessment of composite tidal turbine blades
NASA Astrophysics Data System (ADS)
Fagan, Edward M.; Leen, Sean B.; Kennedy, Ciaran R.; Goggins, Jamie
2015-07-01
With significant interest growing in the ocean renewables sector, horizontal axis tidal current turbines are in a position to dominate the marketplace. The test devices that have been placed in operation so far have suffered from premature failures, caused by difficulties with structural strength prediction. The goal of this work is to develop methods of predicting the damage level in tidal turbines under their maximum operating tidal velocity. The analysis was conducted using the finite element software package Abaqus; shell models of three representative tidal turbine blades are produced. Different construction methods will affect the damage level in the blade and for this study models were developed with varying hydrofoil profiles. In order to determine the risk of failure, a user material subroutine (UMAT) was created. The UMAT uses the failure criteria designed by Alfred Puck to calculate the risk of fibre and inter-fibre failure in the blades. The results show that degradation of the stiffness is predicted for the operating conditions, having an effect on the overall tip deflection. The failure criteria applied via the UMAT form a useful tool for analysis of high risk regions within the blade designs investigated.
Unified Creep Plasticity Damage (UCPD) Model for Rigid Polyurethane Foams.
Neilsen, Michael K.; Lu, Wei-Yang; Scherzinger, William M.; Hinnerichs, Terry D.; Lo, Chi S.
2015-06-01
Numerous experiments were performed to characterize the mechanical response of several different rigid polyurethane foams (FR3712, PMDI10, PMDI20, and TufFoam35) to large deformation. In these experiments, the effects of load path, loading rate, and temperature were investigated. Results from these experiments indicated that rigid polyurethane foams exhibit significant volumetric and deviatoric plasticity when they are compressed. Rigid polyurethane foams were also found to be very strain-rate and temperature dependent. These foams are also rather brittle and crack when loaded to small strains in tension or to larger strains in compression. Thus, a new Unified Creep Plasticity Damage (UCPD) model was developed and implemented into SIERRA with the name Foam Damage to describe the mechanical response of these foams to large deformation at a variety of temperatures and strain rates. This report includes a description of recent experiments and experimental findings. Next, development of a UCPD model for rigid, polyurethane foams is described. Selection of material parameters for a variety of rigid polyurethane foams is then discussed and finite element simulations with the new UCPD model are compared with experimental results to show behavior that can be captured with this model.
Strong earthquakes knowledge base for calibrating fast damage assessment systems
NASA Astrophysics Data System (ADS)
Frolova, N.; Kozlov, M.; Larionov, V.; Nikolaev, A.; Suchshev, S.; Ugarov, A.
2003-04-01
At present Systems for fast damage and loss assessment due to strong earthquakes may use as input data: (1) information about event parameters (magnitude, depth and coordinates) issued by Alert Seismological Surveys; (2) wave-form data obtained by strong-motion seismograph network; (3) high resolution space images of the affected area obtained before and after the event. When data about magnidute, depth and location of event are used to simulate possible consequences, the reliability of estimations depends on completeness and reliability of databases on elements at risk (population and built environment); reliability of vulnerability functions of elements at risk; and errors in strong earthquakes' parameters determination by Alert Seismological Surveys. Some of these factors may be taken into account at the expense of the System calibration with usage of well documented past strong earthquakes. The paper is describing the structure and content of the knowledge base about well documented strong events, which occurred in last century. It contains the description of more than 1000 events. The data are distributed almost homogeneously as the losses due to earthquakes are concerned; the most events are in the magnitude range 6.5 -7.9. Software is created to accumulate and analyze the information about these events source parameters and social consequences. Created knowledge base is used for calibration the Fast Damage Assessment Tool, which is at present on duty with the framework of EDRIM Program. It is also used as additional information by experts who analyses the results of computations.
A damage-softening statistical constitutive model considering rock residual strength
NASA Astrophysics Data System (ADS)
Wang, Zhi-liang; Li, Yong-chi; Wang, J. G.
2007-01-01
Under stress, the microcracks in rock evolve (initiation, growth and coalescence) from damage to fracture with a continuous process. In order to describe this continuous process, a damage-softening statistical constitutive model for rock was proposed based on the Weibull distribution of mesoscopic element strength. This model usually adopts the Drucker-Prager criterion as its distribution parameter of mesoscopic element strength, which may produce larger damage zone in numerical simulations. This paper mainly studies the effects of strength criteria and residual strength on the performance of this damage-softening statistical constitutive model of rock. Main works include following three aspects: Firstly, the mechanical behaviors of rock are comparatively studied when the Drucker-Prager and the Mohr-Coulomb criteria are employed, respectively, as the distribution parameter. Then, a coefficient is introduced to make this constitutive model be capable of describing the residual strength of rock. Finally, a user-defined subroutine is concisely developed for this model and checked through typical strain paths. The current work lays a good foundation for further application of this model in geotechnics and geosciences.
Guided wave propagation based damage detection in welded rectangular tubular structures
NASA Astrophysics Data System (ADS)
Lu, Xi; Lu, M. Y.; Zhou, L. M.; Su, Z. Q.; Cheng, Li; Ye, Lin; Meng, Guang
2009-07-01
Guided wave based methods have shown great potential to practical use and have been the object of many researches for structural health monitoring (SHM). In this paper, a welded steel structure with rectangular section, which is almost 1:1 scale model for a bogie frame segment of train, is investigated by using both finite element method (FEM) and experimental analysis for the purpose of damage detection. Finite element models are established to simulate the propagation behavior of guided waves in the structure. An active actuator/sensor network is employed to generate guided waves propagating in the structures and collect response signals. Excitations at selected frequency are used to minimize the effect of the intrinsic multi-mode phenomenon of guided waves on the consequent signal interpretation. Modern signal processing approaches, such as continuous wavelet transform (CWT) and Hilbert transform (HT), are applied to all collected signals. An algorithm based on the concept of damage presence probability (DPP) is proposed for estimation of damage location. The results indicate that the recommended guided wave propagation based approach is reasonable for damage detection in such kind of structures.
NASA Astrophysics Data System (ADS)
Khatir, S.; Belaidi, I.; Serra, R.; Benaissa, B.; Ait Saada, A.
2015-07-01
The detection techniques based on non-destructive testing (NDT) defects are preferable because of their low cost and operational aspects related to the use of the analyzed structure. In this study, we used the genetic algorithm (GA) for detecting and locating damage. The finite element was used for diagnostic beams. Different structures considered may incur damage to be modelled by a loss of rigidity supposed to represent a defect in the structure element. Identification of damage is formulated as an optimization problem using three objective functions (change of natural frequencies, Modal Assurance Criterion MAC and MAC natural frequency). The results show that the best objective function is based on the natural frequency and MAC while the method of the genetic algorithm present its efficiencies in indicating and quantifying multiple damage with great accuracy. Three defects have been created to enhance damage depending on the elements 2, 5 and 8 with a percentage allocation of 50% in the beam structure which has been discretized into 10 elements. Finally the defect with noise was introduced to test the stability of the method against uncertainty.
Progressive delamination analysis of composite materials using XFEM and a discrete damage zone model
NASA Astrophysics Data System (ADS)
Wang, Yongxiang; Waisman, Haim
2015-01-01
The modeling of progressive delamination by means of a discrete damage zone model within the extended finite element method is investigated. This framework allows for both bulk and interface damages to be conveniently traced, regardless of the underlying mesh alignment. For discrete interfaces, a new mixed-mode force-separation relation, which accounts for the coupled interaction between opening and sliding modes, is proposed. The model is based on the concept of Continuum Damage Mechanics and is shown to be thermodynamically consistent. An integral-type nonlocal damage is adopted in the bulk to regularize the softening material response. The resulting nonlinear equations are solved using a Newton scheme with a dissipation-based arc-length constraint, for which an analytical Jacobian is derived. Several benchmark delamination studies, as well as failure analyses of a fiber/epoxy unit cell, are presented and discussed in detail. The proposed model is validated against available analytical/experimental data and is found to be robust and mesh insensitive.
Bottom-up modeling of damage in heterogeneous quasi-brittle solids
NASA Astrophysics Data System (ADS)
Rinaldi, Antonio
2013-03-01
The theoretical modeling of multisite cracking in quasi-brittle materials is a complex damage problem, hard to model with traditional methods of fracture mechanics due to its multiscale nature and to strain localization induced by microcracks interaction. Macroscale "effective" elastic models can be conveniently applied if a suitable Helmholtz free energy function is identified for a given material scenario. Del Piero and Truskinovsky (Continuum Mech Thermodyn 21:141-171, 2009), among other authors, investigated macroscale continuum solutions capable of matching—in a top-down view—the phenomenology of the damage process for quasi-brittle materials regardless of the microstructure. On the contrary, this paper features a physically based solution method that starts from the direct consideration of the microscale properties and, in a bottom-up view, recovers a continuum elastic description. This procedure is illustrated for a simple one-dimensional problem of this type, a bar modeled stretched by an axial displacement, where the bar is modeled as a 2D random lattice of decohesive spring elements of finite strength. The (microscale) data from simulations are used to identify the "exact" (macro-) damage parameter and to build up the (macro-) Helmholtz function for the equivalent elastic model, bridging the macroscale approach by Del Piero and Truskinovsky. The elastic approach, coupled with microstructural knowledge, becomes a more powerful tool to reproduce a broad class of macroscopic material responses by changing the convexity-concavity of the Helmholtz energy. The analysis points out that mean-field statistics are appropriate prior to damage localization but max-field statistics are better suited in the softening regime up to failure, where microstrain fluctuation needs to be incorporated in the continuum model. This observation is of consequence to revise mean-field damage models from literature and to calibrate Nth gradient continuum models.
Experimental models of perinatal hypoxic-ischemic brain damage.
Vannucci, R C
1993-01-01
Animal research has provided important information on the pathogenesis of and neuropathologic responses to perinatal cerebral hypoxia-ischemia. In experimental animals, structural brain damage from hypoxia-ischemia has been produced in immature rats, rabbits, guinea pigs, sheep and monkeys (18, 20, 24, 25, 38). Of the several available animal models, the fetal and newborn rhesus monkey and immature rat have been studied most extensively because of their similarities to humans in respect to the physiology of reproduction and their neuroanatomy at or shortly following birth. Given the frequency of occurrence of human perinatal hypoxic-ischemic brain damage and the multiple, often severe neurologic handicaps which ensue in infants and children, it is not surprising that the above described animal models have been developed. These models have provided the basis for investigations to clarify not only physiologic and biochemical mechanisms of tissue injury but also the efficacy of specific management strategies. Hopefully, such animal research will continue to provide important information regarding how best to prevent or minimize the devastating consequences of perinatal cerebral hypoxia-ischemia. PMID:8311995
A radiation damage repair model for normal tissues
NASA Astrophysics Data System (ADS)
Partridge, Mike
2008-07-01
A cellular Monte Carlo model describing radiation damage and repair in normal epithelial tissues is presented. The deliberately simplified model includes cell cycling, cell motility and radiation damage response (cell cycle arrest and cell death) only. Results demonstrate that the model produces a stable equilibrium system for mean cell cycle times in the range 24-96 h. Simulated irradiation of these stable equilibrium systems produced a range of responses that are shown to be consistent with experimental and clinical observation, including (i) re-epithelialization of radiation-induced lesions by a mixture of cell migration into the wound and repopulation at the periphery; (ii) observed radiosensitivity that is quantitatively consistent with both rate of induction of irreparable DNA lesions and, independently, with the observed acute oral and pharyngeal mucosal reactions to radiotherapy; (iii) an observed time between irradiation and maximum toxicity that is consistent with experimental data for skin; (iv) quantitatively accurate predictions of low-dose hyper-radiosensitivity; (v) Gomperzian repopulation for very small lesions (~2000 cells) and (vi) a linear rate of re-epithelialization of 5-10 µm h-1 for large lesions (>15 000 cells).
A thermochemical model of radiation damage and annealing applied to GaAs solar cells
NASA Technical Reports Server (NTRS)
Conway, E. J.; Walker, G. H.; Heinbockel, J. H.
1981-01-01
Calculations of the equilibrium conditions for continuous radiation damage and thermal annealing are reported. The calculations are based on a thermochemical model developed to analyze the incorporation of point imperfections in GaAs, and modified by introducing the radiation to produce native lattice defects rather than high-temperature and arsenic atmospheric pressure. The concentration of a set of defects, including vacancies, divacancies, and impurity vacancy complexes, are calculated as a function of temperature. Minority carrier lifetimes, short circuit current, and efficiency are deduced for a range of equilibrium temperatures. The results indicate that GaAs solar cells could have a mission life which is not greatly limited by radiation damage.
Manifold learning-based subspace distance for machinery damage assessment
NASA Astrophysics Data System (ADS)
Sun, Chuang; Zhang, Zhousuo; He, Zhengjia; Shen, Zhongjie; Chen, Binqiang
2016-03-01
Damage assessment is very meaningful to keep safety and reliability of machinery components, and vibration analysis is an effective way to carry out the damage assessment. In this paper, a damage index is designed by performing manifold distance analysis on vibration signal. To calculate the index, vibration signal is collected firstly, and feature extraction is carried out to obtain statistical features that can capture signal characteristics comprehensively. Then, manifold learning algorithm is utilized to decompose feature matrix to be a subspace, that is, manifold subspace. The manifold learning algorithm seeks to keep local relationship of the feature matrix, which is more meaningful for damage assessment. Finally, Grassmann distance between manifold subspaces is defined as a damage index. The Grassmann distance reflecting manifold structure is a suitable metric to measure distance between subspaces in the manifold. The defined damage index is applied to damage assessment of a rotor and the bearing, and the result validates its effectiveness for damage assessment of machinery component.
NASA Astrophysics Data System (ADS)
Treutenaere, S.; Lauro, F.; Bennani, B.; Matsumoto, T.; Mottola, E.
2015-09-01
The use of fabric reinforced polymers in the automotive industry is growing significantly. The high specific stiffness and strength, the ease of shaping as well as the great impact performance of these materials widely encourage their diffusion. The present model increases the predictability of explicit finite element analysis and push the boundaries of the ongoing phenomenological model. Carbon fibre composites made up various preforms were tested by applying different mechanical load up to dynamic loading. This experimental campaign highlighted the physical mechanisms affecting the initial mechanical properties, namely intra- and interlaminar matrix damage, viscoelasticty and fibre failure. The intralaminar behaviour model is based on the explicit formulation of the matrix damage model developed by the ONERA as the given damage formulation correlates with the experimental observation. Coupling with a Maxwell-Wiechert model, the viscoelasticity is included without losing the direct explicit formulation. Additionally, the model is formulated under a total Lagrangian scheme in order to maintain consistency for finite strain. Thus, the material frame-indifference as well as anisotropy are ensured. This allows reorientation of fibres to be taken into account particularly for in-plane shear loading. Moreover, fall within the framework of the total Lagrangian scheme greatly makes the parameter identification easier, as based on the initial configuration. This intralaminar model thus relies upon a physical description of the behaviour of fabric composites and the numerical simulations show a good correlation with the experimental results.
Pyrimidine base damage is increased in women with BRCA mutations.
Budzinski, Edwin E; Patrzyc, Helen B; Dawidzik, Jean B; Freund, Harold G; Frederick, Peter; Godoy, Heidi E; Voian, Nicoleta C; Odunsi, Kunle; Box, Harold C
2013-09-28
Oxidatively-induced DNA damage was measured in the DNA of WBC from two groups of women: carriers of a BRCA mutation, but asymptomatic for disease, and healthy controls. Two oxidatively induced lesions were measured: a formamide remnant of pyrimidine base and the glycol modification of thymine. These lesions, employed previously in studies of the effects of smoking, antioxidant usage and ovarian cancer, are proving valuable indicators of oxidative stress. The BRCA carriers of mutations, with no overt sign of cancer, nevertheless had significantly higher levels of DNA damage than the controls. The level measured for the formamide lesion was 5.9 ± 1.0 (femtomoles/μg of DNA ± SEM) compared with 2.4 ± 0.3 in controls. The level of the glycol lesion was 2.9 ± 0.4 compared with 1.8 ± 0.2 in controls. The experimental design utilized DNA from WBC and employed LC-MS/MS to detect the lesions. PMID:23583677
Modeling and simulation for collateral damage estimation in combat
NASA Astrophysics Data System (ADS)
Gordon, Steven C.; Martin, Douglas D.
2005-05-01
Modeling and simulation (M&S) is increasingly used for decision support during combat operations: M&S is going to war! One of the key operational uses of M&S in combat is collateral damage estimation (CDE). Reducing undesired collateral damage (CD) in war and in operations other than war is important to the United States of America. Injuries to noncombatants and damage to protected sites are uniformly avoided by our forces whenever possible in planning and executing combat operations. This desire to limit unwanted CD presents unique challenges to command and control (C2), especially for time-sensitive targeting (TST). The challenges begin the moment a target is identified because CD estimates must meet specified criteria before target approval is granted. Therefore, CDE tools must be accurate, responsive, and human-factored, with graphics that aid C2 decisions. This paper will describe how CDE tools are used to build three-dimensional models of potential target areas and select appropriate munitions, fusing, and delivery in order to minimize predicted CD. The paper will cover the evolution of CDE from using only range rings around the target to improvements through Operation Allied Force, Operation Enduring Freedom, and Operation Iraqi Freedom. Positive CDE feedback from various sources, including the Secretary of Defense, lessons learned, and warfighters will be presented. Current CDE tools in the field and CDE tools used in reachback are being improved, and short-term and long-term improvements in those tools and in the CDE methodology will be described in this paper.
Modelling the shock response of a damageable anisotropic composite material
NASA Astrophysics Data System (ADS)
Lukyanov, Alexander A.
2012-09-01
The purpose of this paper is the investigation of the effect of fibre orientation on the shock response of a damageable carbon fibre-epoxy composite (CFEC). A carbon fibre-epoxy composite (CFEC) shock response in the through-thickness orientation and in one of the fibre directions is significantly different. Modelling the effect of fibre orientation on the shock response of a CFEC has been performed using a generalised decomposition of the stress tensor [A.A. Lukyanov, Int. J. Plasticity 24, 140 (2008)] and an accurate extrapolation of high-pressure shock Hugoniot states to other thermodynamics states for shocked CFEC materials. The analysis of the experimental data subject to the linear relation between shock velocities and particle velocities has shown that damage softening process produces discontinuities both in value and slope in the generalized bulk shock velocity and particle velocity relation [A.A. Lukyanov, Eur Phys J B 74, 35 (2010)]. Therefore, in order to remove these discontinuities, the three-wave structure (non-linear anisotropic, fracture and isotropic elastic waves) that accompanies damage softening process is proposed in this work for describing CFEC behavior under shock loading. A numerical calculation shows that Hugoniot Stress Levels (HELs) agree with the experimental data for selected CFEC material in different directions at low and at high intensities. In the through-thickness orientation, the material behaves similar to a simple polymer. In the fibre direction, the proposed model explains a pronounced ramp, before at sufficiently high stresses, and a much faster rising shock above it. The results are presented and discussed, and future studies are outlined.
A visco-poroelastic damage model for modelling compaction and brittle failure of porous rocks
NASA Astrophysics Data System (ADS)
Jacquey, Antoine B.; Cacace, Mauro; Blöcher, Guido; Milsch, Harald; Scheck-Wenderoth, Magdalena
2016-04-01
Hydraulic stimulation of geothermal wells is often used to increase heat extraction from deep geothermal reservoirs. Initiation and propagation of fractures due to pore pressure build-up increase the effective permeability of the porous medium. Understanding the processes controlling the initiation of fractures, the evolution of their geometries and the hydro-mechanical impact on transport properties of the porous medium is therefore of great interest for geothermal energy production. In this contribution, we will present a thermodynamically consistent visco-poroelastic damage model which can deal with the multi-scale and multi-physics nature of the physical processes occurring during deformation of a porous rock. Deformation of a porous medium is crucially influenced by the changes in the effective stress. Considering a strain-formulated yield cap and the compaction-dilation transition, three different regimes can be identified: quasi-elastic deformation, cataclastic compaction with microcracking (damage accumulation) and macroscopic brittle failure with dilation. The governing equations for deformation, damage accumulation/healing and fluid flow have been implemented in a fully-coupled finite-element-method based framework (MOOSE). The MOOSE framework provides a powerful and flexible platform to solve multiphysics problems implicitly and in a tightly coupled manner on unstructured meshes which is of interest for such non-linear context. To validate and illustrate the model, simulations of the deformation behaviour of cylindrical porous Bentheimer sandstone samples under different confining pressures are compared to experiments. The first experiment under low confining pressure leads to shear failure, the second for high confining pressure leads to cataclastic compaction and the third one with intermediate confining pressure correspond to a transitional regime between the two firsts. Finally, we will demonstrate that this approach can also be used at the field
HF-based etching processes for improving laser damage resistance of fused silica optical surfaces
Suratwala, T I; Miller, P E; Bude, J D; Steele, R A; Shen, N; Monticelli, M V; Feit, M D; Laurence, T A; Norton, M A; Carr, C W; Wong, L L
2010-02-23
The effect of various HF-based etching processes on the laser damage resistance of scratched fused silica surfaces has been investigated. Conventionally polished and subsequently scratched fused silica plates were treated by submerging in various HF-based etchants (HF or NH{sub 4}F:HF at various ratios and concentrations) under different process conditions (e.g., agitation frequencies, etch times, rinse conditions, and environmental cleanliness). Subsequently, the laser damage resistance (at 351 or 355 nm) of the treated surface was measured. The laser damage resistance was found to be strongly process dependent and scaled inversely with scratch width. The etching process was optimized to remove or prevent the presence of identified precursors (chemical impurities, fracture surfaces, and silica-based redeposit) known to lead to laser damage initiation. The redeposit precursor was reduced (and hence the damage threshold was increased) by: (1) increasing the SiF{sub 6}{sup 2-} solubility through reduction in the NH4F concentration and impurity cation impurities, and (2) improving the mass transport of reaction product (SiF{sub 6}{sup 2-}) (using high frequency ultrasonic agitation and excessive spray rinsing) away from the etched surface. A 2D finite element crack-etching and rinsing mass transport model (incorporating diffusion and advection) was used to predict reaction product concentration. The predictions are consistent with the experimentally observed process trends. The laser damage thresholds also increased with etched amount (up to {approx}30 {micro}m), which has been attributed to: (1) etching through lateral cracks where there is poor acid penetration, and (2) increasing the crack opening resulting in increased mass transport rates. With the optimized etch process, laser damage resistance increased dramatically; the average threshold fluence for damage initiation for 30 {micro}m wide scratches increased from 7 to 41 J/cm{sup 2}, and the statistical
49 CFR 1133.2 - Statement of claimed damages based on Board findings.
Code of Federal Regulations, 2014 CFR
2014-10-01
... 49 Transportation 8 2014-10-01 2014-10-01 false Statement of claimed damages based on Board findings. 1133.2 Section 1133.2 Transportation Other Regulations Relating to Transportation (Continued) SURFACE TRANSPORTATION BOARD, DEPARTMENT OF TRANSPORTATION RULES OF PRACTICE RECOVERY OF DAMAGES § 1133.2 Statement of claimed damages based on...
Extended Kalman filter based structural damage detection for MR damper controlled structures
NASA Astrophysics Data System (ADS)
Jin, Chenhao; Jang, Shinae; Sun, Xiaorong; Jiang, Zhaoshuo; Christenson, Richard
2016-04-01
The Magneto-rheological (MR) dampers have been widely used in many building and bridge structures against earthquake and wind loadings due to its advantages including mechanical simplicity, high dynamic range, low power requirements, large force capacity, and robustness. However, research about structural damage detection methods for MR damper controlled structures is limited. This paper aims to develop a real-time structural damage detection method for MR damper controlled structures. A novel state space model of MR damper controlled structure is first built by combining the structure's equation of motion and MR damper's hyperbolic tangent model. In this way, the state parameters of both the structure and MR damper are added in the state vector of the state space model. Extended Kalman filter is then used to provide prediction for state variables from measurement data. The two techniques are synergistically combined to identify parameters and track the changes of both structure and MR damper in real time. The proposed method is tested using response data of a three-floor MR damper controlled linear building structure under earthquake excitation. The testing results show that the adaptive extended Kalman filter based approach is capable to estimate not only structural parameters such as stiffness and damping of each floor, but also the parameters of MR damper, so that more insights and understanding of the damage can be obtained. The developed method also demonstrates high damage detection accuracy and light computation, as well as the potential to implement in a structural health monitoring system.
2011-01-01
Background Irreversible electroporation (IRE) is a new minimally invasive technique to kill undesirable tissue in a non-thermal manner. In order to maximize the benefits from an IRE procedure, the pulse parameters and electrode configuration must be optimized to achieve complete coverage of the targeted tissue while preventing thermal damage due to excessive Joule heating. Methods We developed numerical simulations of typical protocols based on a previously published computed tomographic (CT) guided in vivo procedure. These models were adapted to assess the effects of temperature, electroporation, pulse duration, and repetition rate on the volumes of tissue undergoing IRE alone or in superposition with thermal damage. Results Nine different combinations of voltage and pulse frequency were investigated, five of which resulted in IRE alone while four produced IRE in superposition with thermal damage. Conclusions The parametric study evaluated the influence of pulse frequency and applied voltage on treatment volumes, and refined a proposed method to delineate IRE from thermal damage. We confirm that determining an IRE treatment protocol requires incorporating all the physical effects of electroporation, and that these effects may have significant implications in treatment planning and outcome assessment. The goal of the manuscript is to provide the reader with the numerical methods to assess multiple-pulse electroporation treatment protocols in order to isolate IRE from thermal damage and capitalize on the benefits of a non-thermal mode of tissue ablation. PMID:21529373
Flood damage maps: ranking sources of uncertainty with variance-based sensitivity analysis
NASA Astrophysics Data System (ADS)
Saint-Geours, N.; Grelot, F.; Bailly, J.-S.; Lavergne, C.
2012-04-01
In order to increase the reliability of flood damage assessment, we need to question the uncertainty associated with the whole flood risk modeling chain. Using a case study on the basin of the Orb River, France, we demonstrate how variance-based sensitivity analysis can be used to quantify uncertainty in flood damage maps at different spatial scales and to identify the sources of uncertainty which should be reduced first. Flood risk mapping is recognized as an effective tool in flood risk management and the elaboration of flood risk maps is now required for all major river basins in the European Union (European directive 2007/60/EC). Flood risk maps can be based on the computation of the Mean Annual Damages indicator (MAD). In this approach, potential damages due to different flood events are estimated for each individual stake over the study area, then averaged over time - using the return period of each flood event - and finally mapped. The issue of uncertainty associated with these flood damage maps should be carefully scrutinized, as they are used to inform the relevant stakeholders or to design flood mitigation measures. Maps of the MAD indicator are based on the combination of hydrological, hydraulic, geographic and economic modeling efforts: as a result, numerous sources of uncertainty arise in their elaboration. Many recent studies describe these various sources of uncertainty (Koivumäki 2010, Bales 2009). Some authors propagate these uncertainties through the flood risk modeling chain and estimate confidence bounds around the resulting flood damage estimates (de Moel 2010). It would now be of great interest to go a step further and to identify which sources of uncertainty account for most of the variability in Mean Annual Damages estimates. We demonstrate the use of variance-based sensitivity analysis to rank sources of uncertainty in flood damage mapping and to quantify their influence on the accuracy of flood damage estimates. We use a quasi
Origin and magma pathways for intraplate volcanism: a new damage mechanics model
NASA Astrophysics Data System (ADS)
Regenauer-Lieb, K.; Rosenbaum, G.; Weinberg, R. F.; Lyakhovsky, V.; Segev, A.; Weinstein, Y.
2013-12-01
We address the question of melting at the base of the lithosphere and the opening of pathways capable of transferring melt to the surface in an intraplate setting of an extending continental lithosphere. We study the initial stage of melting and the onset of the melting instability. The aim of this study thus is to understand: (i) the ubiquitous appearance of alkali-basaltic volcanic provinces that appear without identifiable heat source in intraplate settings; (ii) the apparent relation between melting and localization of deformation under such extremely low intraplate strain rates; (iii) the challenge of generating efficient pathways for the propagation of melt to the surface; (iv) the generation of melt at the base of a lithosphere with low regional heat flow in a thermodynamically consistent model; (iv) as a minor aspect, we also investigate the effect of a pre-existing structure at the surface of the lithosphere. We use a novel method for calculating the effect of melt on lithosphere deformation, which includes damage mechanics and feedback effects between melt generation and rock deformation. We show that it is possible to nucleate melt damage shear bands at the bottom of initially cold lithosphere in slow extensional setting. We conducted numerical models for common continental lithosphere with 50mW/m2 heat flow and a slow asymmetric extension velocity of 1 mm/y, and allowed three different damage mechanisms: (1) classical brittle damage with a Drucker-Prager type rheology; (2) creep damage with a crustal fluid assisted diffusional/dislocation mechanism; and (3) melt damage with a melt-supported diffusional/ dislocation mechanism. The melt conditions were calculated with a Gibbs energy minimization method (Melts; http://melts.ofm-research.org/), and the energy equation solved self-consistently for latent heat and shear heating effects. Our results show that within a short timeframe (~2 Ma), melt damage can propagate from the bottom of the lithosphere upwards
NASA Astrophysics Data System (ADS)
Kerschbaum, M.; Hopmann, C.
2016-06-01
The computationally efficient simulation of the progressive damage behaviour of continuous fibre reinforced plastics is still a challenging task with currently available computer aided engineering methods. This paper presents an original approach for an energy based continuum damage model which accounts for stress-/strain nonlinearities, transverse and shear stress interaction phenomena, quasi-plastic shear strain components, strain rate effects, regularised damage evolution and consideration of load reversal effects. The physically based modelling approach enables experimental determination of all parameters on ply level to avoid expensive inverse analysis procedures. The modelling strategy, implementation and verification of this model using commercially available explicit finite element software are detailed. The model is then applied to simulate the impact and penetration of carbon fibre reinforced cross-ply specimens with variation of the impact speed. The simulation results show that the presented approach enables a good representation of the force-/displacement curves and especially well agreement with the experimentally observed fracture patterns. In addition, the mesh dependency of the results were assessed for one impact case showing only very little change of the simulation results which emphasises the general applicability of the presented method.
Bammann, Douglas J.; Johnson, G. C. (University of California, Berkeley, CA); Marin, Esteban B.; Regueiro, Richard A.
2006-01-01
In this report we present the formulation of the physically-based Evolving Microstructural Model of Inelasticity (EMMI) . The specific version of the model treated here describes the plasticity and isotropic damage of metals as being currently applied to model the ductile failure process in structural components of the W80 program . The formulation of the EMMI constitutive equations is framed in the context of the large deformation kinematics of solids and the thermodynamics of internal state variables . This formulation is focused first on developing the plasticity equations in both the relaxed (unloaded) and current configurations. The equations in the current configuration, expressed in non-dimensional form, are used to devise the identification procedure for the plasticity parameters. The model is then extended to include a porosity-based isotropic damage state variable to describe the progressive deterioration of the strength and mechanical properties of metals induced by deformation . The numerical treatment of these coupled plasticity-damage constitutive equations is explained in detail. A number of examples are solved to validate the numerical implementation of the model.
NASA Astrophysics Data System (ADS)
Kerschbaum, M.; Hopmann, C.
2016-01-01
The computationally efficient simulation of the progressive damage behaviour of continuous fibre reinforced plastics is still a challenging task with currently available computer aided engineering methods. This paper presents an original approach for an energy based continuum damage model which accounts for stress-/strain nonlinearities, transverse and shear stress interaction phenomena, quasi-plastic shear strain components, strain rate effects, regularised damage evolution and consideration of load reversal effects. The physically based modelling approach enables experimental determination of all parameters on ply level to avoid expensive inverse analysis procedures. The modelling strategy, implementation and verification of this model using commercially available explicit finite element software are detailed. The model is then applied to simulate the impact and penetration of carbon fibre reinforced cross-ply specimens with variation of the impact speed. The simulation results show that the presented approach enables a good representation of the force-/displacement curves and especially well agreement with the experimentally observed fracture patterns. In addition, the mesh dependency of the results were assessed for one impact case showing only very little change of the simulation results which emphasises the general applicability of the presented method.
Two-phase damage models of magma-fracturing
NASA Astrophysics Data System (ADS)
Cai, Zhengyu; Bercovici, David
2013-04-01
Damage and fracturing in two-phase and porous flows are relevant for geological process such as magma-fracturing during melt migration, which is associated with the propagation of a pore-generating damage front ahead of high-pressure fluid injection. We therefore examine the propagation of porous flow in a damageable matrix by applying the two-phase theory for compaction and damage proposed by Bercovici et al. (2001a) and Bercovici and Ricard (2003). The movement of the fluid and the solid is governed by the two-phase flow laws, while damage (void generation and microcracking) is treated by considering the generation of interfacial surface energy by deformational work. Calculations of one-dimensional (1-D) flow of fluid migrating buoyantly through compacting and damageable matrix show that damage is mitigated in steady-state largely because of the loss of the velocity gradient at the fluid front. However, in time-dependent flows, linear stability analysis shows that the propagation velocity of porosity waves is strongly dependent on damage. In the damage-free case porosity waves are dispersive in that wave-speed decreases with wavenumber (inverse wavelength); however with damage the dispersion flattens and beyond a critical damage reverses (the wave speed increases with wavenumber). Since normal dispersive behavior balances breaking in the nonlinear wave case, such reversed dispersion implies that damage has a profound effect in the nonlinear limit by facilitating wave front steepening and higher wave velocities. Nonlinear solitary wave solutions are obtained numerically and show that the transmission of porosity waves induces high stress and damage that can push the damage front forward. With damage the porosity waves sharpen and calculations suggest that they can transform from shape-conserving solitary waves into faster high amplitude waves, which is also predicted by the linear theory. Such pulse-like sharper waves may prove effective at promoting fluid
Physically-based Assessment of Tropical Cyclone Damage and Economic Losses
NASA Astrophysics Data System (ADS)
Lin, N.
2012-12-01
Estimating damage and economic losses caused by tropical cyclones (TC) is a topic of considerable research interest in many scientific fields, including meteorology, structural and coastal engineering, and actuarial sciences. One approach is based on the empirical relationship between TC characteristics and loss data. Another is to model the physical mechanism of TC-induced damage. In this talk we discuss about the physically-based approach to predict TC damage and losses due to extreme wind and storm surge. We first present an integrated vulnerability model, which, for the first time, explicitly models the essential mechanisms causing wind damage to residential areas during storm passage, including windborne-debris impact and the pressure-debris interaction that may lead, in a chain reaction, to structural failures (Lin and Vanmarcke 2010; Lin et al. 2010a). This model can be used to predict the economic losses in a residential neighborhood (with hundreds of buildings) during a specific TC (Yau et al. 2011) or applied jointly with a TC risk model (e.g., Emanuel et al 2008) to estimate the expected losses over long time periods. Then we present a TC storm surge risk model that has been applied to New York City (Lin et al. 2010b; Lin et al. 2012; Aerts et al. 2012), Miami-Dade County, Florida (Klima et al. 2011), Galveston, Texas (Lickley, 2012), and other coastal areas around the world (e.g., Tampa, Florida; Persian Gulf; Darwin, Australia; Shanghai, China). These physically-based models are applicable to various coastal areas and have the capability to account for the change of the climate and coastal exposure over time. We also point out that, although made computationally efficient for risk assessment, these models are not suitable for regional or global analysis, which has been a focus of the empirically-based economic analysis (e.g., Hsiang and Narita 2012). A future research direction is to simplify the physically-based models, possibly through
NASA Technical Reports Server (NTRS)
Allen, David H.; Groves, Scott E.; Harris, Charles E.
1988-01-01
The present cumulative damage model for the prediction of stiffness loss in graphite/epoxy laminates applies a thermomechanical constitutive theory for elastic composites with distributed damage. The model proceeds from a continuum mechanics and thermodynamics approach in which the distributed damage is characterized by a set of second-order tensor-valued internal state variables. A set of damage-dependent laminated plate equations is obtained; this is developed by modifying classical Kirchhoff plate theory.
A robust operational model for predicting where tropical cyclone waves damage coral reefs.
Puotinen, Marji; Maynard, Jeffrey A; Beeden, Roger; Radford, Ben; Williams, Gareth J
2016-01-01
Tropical cyclone (TC) waves can severely damage coral reefs. Models that predict where to find such damage (the 'damage zone') enable reef managers to: 1) target management responses after major TCs in near-real time to promote recovery at severely damaged sites; and 2) identify spatial patterns in historic TC exposure to explain habitat condition trajectories. For damage models to meet these needs, they must be valid for TCs of varying intensity, circulation size and duration. Here, we map damage zones for 46 TCs that crossed Australia's Great Barrier Reef from 1985-2015 using three models - including one we develop which extends the capability of the others. We ground truth model performance with field data of wave damage from seven TCs of varying characteristics. The model we develop (4MW) out-performed the other models at capturing all incidences of known damage. The next best performing model (AHF) both under-predicted and over-predicted damage for TCs of various types. 4MW and AHF produce strikingly different spatial and temporal patterns of damage potential when used to reconstruct past TCs from 1985-2015. The 4MW model greatly enhances both of the main capabilities TC damage models provide to managers, and is useful wherever TCs and coral reefs co-occur. PMID:27184607
A robust operational model for predicting where tropical cyclone waves damage coral reefs
Puotinen, Marji; Maynard, Jeffrey A.; Beeden, Roger; Radford, Ben; Williams, Gareth J.
2016-01-01
Tropical cyclone (TC) waves can severely damage coral reefs. Models that predict where to find such damage (the ‘damage zone’) enable reef managers to: 1) target management responses after major TCs in near-real time to promote recovery at severely damaged sites; and 2) identify spatial patterns in historic TC exposure to explain habitat condition trajectories. For damage models to meet these needs, they must be valid for TCs of varying intensity, circulation size and duration. Here, we map damage zones for 46 TCs that crossed Australia’s Great Barrier Reef from 1985–2015 using three models – including one we develop which extends the capability of the others. We ground truth model performance with field data of wave damage from seven TCs of varying characteristics. The model we develop (4MW) out-performed the other models at capturing all incidences of known damage. The next best performing model (AHF) both under-predicted and over-predicted damage for TCs of various types. 4MW and AHF produce strikingly different spatial and temporal patterns of damage potential when used to reconstruct past TCs from 1985–2015. The 4MW model greatly enhances both of the main capabilities TC damage models provide to managers, and is useful wherever TCs and coral reefs co-occur. PMID:27184607
A robust operational model for predicting where tropical cyclone waves damage coral reefs
NASA Astrophysics Data System (ADS)
Puotinen, Marji; Maynard, Jeffrey A.; Beeden, Roger; Radford, Ben; Williams, Gareth J.
2016-05-01
Tropical cyclone (TC) waves can severely damage coral reefs. Models that predict where to find such damage (the ‘damage zone’) enable reef managers to: 1) target management responses after major TCs in near-real time to promote recovery at severely damaged sites; and 2) identify spatial patterns in historic TC exposure to explain habitat condition trajectories. For damage models to meet these needs, they must be valid for TCs of varying intensity, circulation size and duration. Here, we map damage zones for 46 TCs that crossed Australia’s Great Barrier Reef from 1985–2015 using three models – including one we develop which extends the capability of the others. We ground truth model performance with field data of wave damage from seven TCs of varying characteristics. The model we develop (4MW) out-performed the other models at capturing all incidences of known damage. The next best performing model (AHF) both under-predicted and over-predicted damage for TCs of various types. 4MW and AHF produce strikingly different spatial and temporal patterns of damage potential when used to reconstruct past TCs from 1985–2015. The 4MW model greatly enhances both of the main capabilities TC damage models provide to managers, and is useful wherever TCs and coral reefs co-occur.
Farrar, Charles; Figueiredo, Eloi; Todd, Michael; Flynn, Eric
2010-01-01
A nonlinear time series approach is presented to detect damage in systems by using a state-space reconstruction to infer the geometrical structure of a deterministic dynamical system from observed time series response at multiple locations. The unique contribution of this approach is using a Multivariate Autoregressive (MAR) model of a baseline condition to predict the state space, where the model encodes the embedding vectors rather than scalar time series. A hypothesis test is established that the MAR model will fail to predict future response if damage is present in the test condition, and this test is investigated for robustness in the context of operational and environmental variability. The applicability of this approach is demonstrated using acceleration time series from a base-excited 3-story frame structure.
Improvements in Modeling Thruster Plume Erosion Damage to Spacecraft Surfaces
NASA Technical Reports Server (NTRS)
Soares, Carlos; Olsen, Randy; Steagall, Courtney; Huang, Alvin; Mikatarian, Ron; Myers, Brandon; Koontz, Steven; Worthy, Erica
2015-01-01
Spacecraft bipropellant thrusters impact spacecraft surfaces with high speed droplets of unburned and partially burned propellant. These impacts can produce erosion damage to optically sensitive hardware and systems (e.g., windows, camera lenses, solar cells and protective coatings). On the International Space Station (ISS), operational constraints are levied on the position and orientation of the solar arrays to mitigate erosion effects during thruster operations. In 2007, the ISS Program requested evaluation of erosion constraint relief to alleviate operational impacts due to an impaired Solar Alpha Rotary Joint (SARJ). Boeing Space Environments initiated an activity to identify and remove sources of conservatism in the plume induced erosion model to support an expanded range of acceptable solar array positions ? The original plume erosion model over-predicted plume erosion and was adjusted to better correlate with flight experiment results. This paper discusses findings from flight experiments and the methodology employed in modifying the original plume erosion model for better correlation of predictions with flight experiment data. The updated model has been successful employed in reducing conservatism and allowing for enhanced flexibility in ISS solar array operations.
Phase field modeling of damage in glassy polymers
NASA Astrophysics Data System (ADS)
Xie, Yuesong; Kravchenko, Oleksandr G.; Pipes, R. Byron; Koslowski, Marisol
2016-08-01
Failure mechanisms in amorphous polymers are usually separated into two types, shear yielding and crazing due to the differences in the yield surface. Experiments show that the yield surface follows a pressure modified von Mises relation for shear yielding but this relation does not hold during crazing failure. In the past different yield conditions were used to represent each type of failure. Here, we show that the same damage model can be used to study failure under shear yielding and crazing conditions. The simulations show that different yield surfaces are obtained for craze and shear yielding if the microstructure is included explicitly in the simulations. In particular the breakdown of the pressure modified von Mises relation during crazing can be related to the presence of voids and other defects in the sample.
Damage Spreading in the Bak-Sneppen Model:
NASA Astrophysics Data System (ADS)
Tirnakli, Ugur; Lyra, Marcelo L.
The short-time and long-time dynamics of the Bak-Sneppen model of biological evolution are investigated using the damage spreading technique. By defining a proper Hamming distance measure, we are able to make it exhibit an initial power-law growth which, for finite size systems, is followed by a decay towards equilibrium. In this sense, the dynamics of self-organized critical states is shown to be similar to the one observed at the usual critical point of continuous phase transitions and at the onset of chaos of nonlinear low-dimensional dynamical maps. The transient, pre-asymptotic and asymptotic exponential relaxation of the Hamming distance between two initially uncorrelated equilibrium configurations is also shown to be fit within a single mathematical framework.
A procedure for damage detection and localization of framed buildings based on curvature variation
NASA Astrophysics Data System (ADS)
Ditommaso, Rocco; Carlo Ponzo, Felice; Auletta, Gianluca; Iacovino, Chiara; Mossucca, Antonello; Nigro, Domenico; Nigro, Antonella
2014-05-01
Structural Health Monitoring and Damage Detection are topics of current interest in civil, mechanical and aerospace engineering. Damage Detection approach based on dynamic monitoring of structural properties over time has received a considerable attention in recent scientific literature of the last years. The basic idea arises from the observation that spectral properties, described in terms of the so-called modal parameters (eigenfrequencies, mode shapes, and modal damping), are functions of the physical properties of the structure (mass, energy dissipation mechanisms and stiffness). Structural damage exhibits its main effects in terms of stiffness and damping variation. As a consequence, a permanent dynamic monitoring system makes it possible to detect and, if suitably concentrated on the structure, to localize structural and non-structural damage occurred on the structure during a strong earthquake. In the last years many researchers are working to set-up new methodologies for Non-destructive Damage Evaluation (NDE) based on the variation of the dynamic behaviour of structures under seismic loads. Pandey et al. (1991) highlighted on the possibility to use the structural mode shapes to extract useful information for structural damage localization. In this paper a new procedure for damage detection on framed structures based on changes in modal curvature is proposed. The proposed approach is based on the use of Stockwell Transform, a special kind of integral transformation that become a powerful tool for nonlinear signal analysis and then to analyse the nonlinear behaviour of a general structure. Using this kind of approach, it is possible to use a band-variable filter (Ditommaso et al., 2012) to extract from a signal recorded on a structure (excited by an earthquake) the response related to a single mode of vibration for which the related frequency changes over time (if the structure is being damaged). İn general, by acting simultaneously in both frequency and
Damage detection technique by measuring laser-based mechanical impedance
Lee, Hyeonseok; Sohn, Hoon
2014-02-18
This study proposes a method for measurement of mechanical impedance using noncontact laser ultrasound. The measurement of mechanical impedance has been of great interest in nondestructive testing (NDT) or structural health monitoring (SHM) since mechanical impedance is sensitive even to small-sized structural defects. Conventional impedance measurements, however, have been based on electromechanical impedance (EMI) using contact-type piezoelectric transducers, which show deteriorated performances induced by the effects of a) Curie temperature limitations, b) electromagnetic interference (EMI), c) bonding layers and etc. This study aims to tackle the limitations of conventional EMI measurement by utilizing laser-based mechanical impedance (LMI) measurement. The LMI response, which is equivalent to a steady-state ultrasound response, is generated by shooting the pulse laser beam to the target structure, and is acquired by measuring the out-of-plane velocity using a laser vibrometer. The formation of the LMI response is observed through the thermo-mechanical finite element analysis. The feasibility of applying the LMI technique for damage detection is experimentally verified using a pipe specimen under high temperature environment.
Damage detection technique by measuring laser-based mechanical impedance
NASA Astrophysics Data System (ADS)
Lee, Hyeonseok; Sohn, Hoon
2014-02-01
This study proposes a method for measurement of mechanical impedance using noncontact laser ultrasound. The measurement of mechanical impedance has been of great interest in nondestructive testing (NDT) or structural health monitoring (SHM) since mechanical impedance is sensitive even to small-sized structural defects. Conventional impedance measurements, however, have been based on electromechanical impedance (EMI) using contact-type piezoelectric transducers, which show deteriorated performances induced by the effects of a) Curie temperature limitations, b) electromagnetic interference (EMI), c) bonding layers and etc. This study aims to tackle the limitations of conventional EMI measurement by utilizing laser-based mechanical impedance (LMI) measurement. The LMI response, which is equivalent to a steady-state ultrasound response, is generated by shooting the pulse laser beam to the target structure, and is acquired by measuring the out-of-plane velocity using a laser vibrometer. The formation of the LMI response is observed through the thermo-mechanical finite element analysis. The feasibility of applying the LMI technique for damage detection is experimentally verified using a pipe specimen under high temperature environment.
NASA Astrophysics Data System (ADS)
Astroza, Rodrigo; Ebrahimian, Hamed; Conte, Joel P.
2015-03-01
This paper describes a novel framework that combines advanced mechanics-based nonlinear (hysteretic) finite element (FE) models and stochastic filtering techniques to estimate unknown time-invariant parameters of nonlinear inelastic material models used in the FE model. Using input-output data recorded during earthquake events, the proposed framework updates the nonlinear FE model of the structure. The updated FE model can be directly used for damage identification and further used for damage prognosis. To update the unknown time-invariant parameters of the FE model, two alternative stochastic filtering methods are used: the extended Kalman filter (EKF) and the unscented Kalman filter (UKF). A three-dimensional, 5-story, 2-by-1 bay reinforced concrete (RC) frame is used to verify the proposed framework. The RC frame is modeled using fiber-section displacement-based beam-column elements with distributed plasticity and is subjected to the ground motion recorded at the Sylmar station during the 1994 Northridge earthquake. The results indicate that the proposed framework accurately estimate the unknown material parameters of the nonlinear FE model. The UKF outperforms the EKF when the relative root-mean-square error of the recorded responses are compared. In addition, the results suggest that the convergence of the estimate of modeling parameters is smoother and faster when the UKF is utilized.
NASA Technical Reports Server (NTRS)
Goldberg, Robert K.; Carney, Kelly S.; DuBois, Paul; Hoffarth, Canio; Rajan, Subramaniam; Blankenhorn, Gunther
2016-01-01
The need for accurate material models to simulate the deformation, damage and failure of polymer matrix composites under impact conditions is becoming critical as these materials are gaining increased usage in the aerospace and automotive communities. In order to address a series of issues identified by the aerospace community as being desirable to include in a next generation composite impact model, an orthotropic, macroscopic constitutive model incorporating both plasticity and damage suitable for implementation within the commercial LS-DYNA computer code is being developed. The plasticity model is based on extending the Tsai-Wu composite failure model into a strain hardening-based orthotropic plasticity model with a non-associative flow rule. The evolution of the yield surface is determined based on tabulated stress-strain curves in the various normal and shear directions and is tracked using the effective plastic strain. To compute the evolution of damage, a strain equivalent semi-coupled formulation is used in which a load in one direction results in a stiffness reduction in multiple material coordinate directions. A detailed analysis is carried out to ensure that the strain equivalence assumption is appropriate for the derived plasticity and damage formulations that are employed in the current model. Procedures to develop the appropriate input curves for the damage model are presented and the process required to develop an appropriate characterization test matrix is discussed
NASA Technical Reports Server (NTRS)
Goldberg, Robert K.; Carney, Kelly S.; DuBois, Paul; Hoffarth, Canio; Rajan, Subramaniam; Blankenhorn, Gunther
2016-01-01
The need for accurate material models to simulate the deformation, damage and failure of polymer matrix composites under impact conditions is becoming critical as these materials are gaining increased usage in the aerospace and automotive communities. In order to address a series of issues identified by the aerospace community as being desirable to include in a next generation composite impact model, an orthotropic, macroscopic constitutive model incorporating both plasticity and damage suitable for implementation within the commercial LS-DYNA computer code is being developed. The plasticity model is based on extending the Tsai-Wu composite failure model into a strain hardening-based orthotropic plasticity model with a non-associative flow rule. The evolution of the yield surface is determined based on tabulated stress-strain curves in the various normal and shear directions and is tracked using the effective plastic strain. To compute the evolution of damage, a strain equivalent semi-coupled formulation is used in which a load in one direction results in a stiffness reduction in multiple material coordinate directions. A detailed analysis is carried out to ensure that the strain equivalence assumption is appropriate for the derived plasticity and damage formulations that are employed in the current model. Procedures to develop the appropriate input curves for the damage model are presented and the process required to develop an appropriate characterization test matrix is discussed.
A damage mechanics based approach for developing a quantitative understanding of ductile fracture.
Thissell, W. R.; Tonks, D. L.; Schwartz, D. S.
2004-01-01
A self-consistent damage mechanics approach for describing ductile fracture is introduced. This approach consists of damage quantification of incipiently failed specimens resulting from well-controlled and diagnosed experiments that span a wide parameter space of stress triaxiality, strain rate, and equivalent plastic strain. Numerical simulations are performed of these experiments using damage constitutive models and the simulation predictions are compared with the experimental measurements and post-mortem damage quantification, with the goal of developing, validating, and calibrating the damage constitutive models. New developments are described, such as the coupling between void and deformation bands.
Ferrando-May, Elisa; Tomas, Martin; Blumhardt, Philipp; Stöckl, Martin; Fuchs, Matthias; Leitenstorfer, Alfred
2013-01-01
Our understanding of the mechanisms governing the response to DNA damage in higher eucaryotes crucially depends on our ability to dissect the temporal and spatial organization of the cellular machinery responsible for maintaining genomic integrity. To achieve this goal, we need experimental tools to inflict DNA lesions with high spatial precision at pre-defined locations, and to visualize the ensuing reactions with adequate temporal resolution. Near-infrared femtosecond laser pulses focused through high-aperture objective lenses of advanced scanning microscopes offer the advantage of inducing DNA damage in a 3D-confined volume of subnuclear dimensions. This high spatial resolution results from the highly non-linear nature of the excitation process. Here we review recent progress based on the increasing availability of widely tunable and user-friendly technology of ultrafast lasers in the near infrared. We present a critical evaluation of this approach for DNA microdamage as compared to the currently prevalent use of UV or VIS laser irradiation, the latter in combination with photosensitizers. Current and future applications in the field of DNA repair and DNA-damage dependent chromatin dynamics are outlined. Finally, we discuss the requirement for proper simulation and quantitative modeling. We focus in particular on approaches to measure the effect of DNA damage on the mobility of nuclear proteins and consider the pros and cons of frequently used analysis models for FRAP and photoactivation and their applicability to non-linear photoperturbation experiments. PMID:23882280
NASA Astrophysics Data System (ADS)
Bodeux, J. B.; Golinval, J. C.
2001-06-01
In this paper, the application of auto-regressive moving average vector models to system identification and damage detection is investigated. These parametric models have already been applied for the analysis of multiple input-output systems under ambient excitation. Their main advantage consists in the capability of extracting modal parameters from the recorded time signals, without the requirement of excitation measurement. The excitation is supposed to be a stationary Gaussian white noise. The method also allows the estimation of modal parameter uncertainties. On the basis of these uncertainties, a statistically based damage detection scheme is performed and it becomes possible to assess whether changes of modal parameters are caused by, e.g. some damage or simply by estimation inaccuracies. The paper reports first an example of identification and damage detection applied to a simulated system under random excitation. The `Steel-Quake' benchmark proposed in the framework of COST Action F3 `Structural Dynamics' is also analysed. This structure was defined by the Joint Research Centre in Ispra (Italy) to test steel building performance during earthquakes. The proposed method gives an excellent identification of frequencies and mode shapes, while damping ratios are estimated with less accuracy.
Multi-variate flood damage assessment: a tree-based data-mining approach
NASA Astrophysics Data System (ADS)
Merz, B.; Kreibich, H.; Lall, U.
2013-01-01
The usual approach for flood damage assessment consists of stage-damage functions which relate the relative or absolute damage for a certain class of objects to the inundation depth. Other characteristics of the flooding situation and of the flooded object are rarely taken into account, although flood damage is influenced by a variety of factors. We apply a group of data-mining techniques, known as tree-structured models, to flood damage assessment. A very comprehensive data set of more than 1000 records of direct building damage of private households in Germany is used. Each record contains details about a large variety of potential damage-influencing characteristics, such as hydrological and hydraulic aspects of the flooding situation, early warning and emergency measures undertaken, state of precaution of the household, building characteristics and socio-economic status of the household. Regression trees and bagging decision trees are used to select the more important damage-influencing variables and to derive multi-variate flood damage models. It is shown that these models outperform existing models, and that tree-structured models are a promising alternative to traditional damage models.
NASA Astrophysics Data System (ADS)
Wang, Kai; Su, Zhongqing
2016-04-01
Targeting quantitative estimate of fatigue damage, a dedicated analytical model was developed based on the modal decomposition method and the variational principle. The model well interprets the contact acoustic nonlinearity induced by a "breathing" crack in a two-dimensional scenario, and the nonlinear characteristics of guided ultrasonic waves (GUWs) (e.g., reflection, transmission, mode conversion and high-order generation) when GUWs traversing the crack. Based on the model, a second-order reflection index was defined. Using the index, a fatigue damage evaluation framework was established, showing demonstrated capacity of estimating the severity of fatigue damage in a quantitative manner. The approach, in principle, does not entail a benchmarking process against baseline signals pre-acquired from pristine counterparts. The results obtained using the analytical modeling were compared with those from finite element simulation, showing good coincidence. Limitations of the model were also discussed.
Modeling of Laser Induced Damage in NIF UV Optics
Feit, M D; Rubenchik, A M
2001-02-21
Controlling damage to nominally transparent optical elements such as lenses, windows and frequency conversion crystals on high power lasers is a continuing technical problem. Scientific understanding of the underlying mechanisms of laser energy absorption, material heating and vaporization and resultant mechanical damage is especially important for UV lasers with large apertures such as NIF. This LDRD project was a single year effort, in coordination with associated experimental projects, to initiate theoretical descriptions of several of the relevant processes. In understanding laser damage, we distinguish between damage initiation and the growth of existent damage upon subsequent laser irradiation. In general, the effect of damage could be ameliorated by either preventing its initiation or by mitigating its growth. The distinction comes about because initiation is generally due to extrinsic factors such as contaminants, which provide a means of local laser energy absorption. Thus, initiation tends to be local and stochastic in nature. On the other hand, the initial damaging event appears to modify the surrounding material in such a way that multiple pulse damage grows more or less regularly. More exactly, three ingredients are necessary for visible laser induced damage. These are adequate laser energy, a mechanism of laser energy absorption and mechanical weakness. For damage growth, the material surrounding a damage site is already mechanically weakened by cracks and probably chemically modified as well. The mechanical damage can also lead to electric field intensification due to interference effects, thus increasing the available laser energy density. In this project, we successfully accounted for the pulselength dependence of damage threshold in bulk DKDP crystals with the hypothesis of small absorbers with a distribution of sizes. We theoretically investigated expected scaling of damage initiation craters both to baseline detailed numerical simulations
NASA Astrophysics Data System (ADS)
Wang, Xiao-Jun; Yang, Chen; Qiu, Zhi-Ping
2013-04-01
Based on measured natural frequencies and acceleration responses, a non-probabilistic information fusion technique is proposed for the structural damage detection by adopting the set-membership identification (SMI) and two-step model updating procedure. Due to the insufficiency and uncertainty of information obtained from measurements, the uncertain problem of damage identification is addressed with interval variables in this paper. Based on the first-order Taylor series expansion, the interval bounds of the elemental stiffness parameters in undamaged and damaged models are estimated, respectively. The possibility of damage existence (PoDE) in elements is proposed as the quantitative measure of structural damage probability, which is more reasonable in the condition of insufficient measurement data. In comparison with the identification method based on a single kind of information, the SMI method will improve the accuracy in damage identification, which reflects the information fusion concept based on the non-probabilistic set. A numerical example is performed to demonstrate the feasibility and effectiveness of the proposed technique.
Mechanical damage to Escherichia coli cells in a model of amino-acid crystal fermentation.
Okutani, Satoshi; Iwai, Takayoshi; Iwatani, Shintaro; Kondo, Kazuya; Osumi, Tsuyoshi; Tsujimoto, Nobuharu; Matsuno, Kiyoshi
2012-04-01
We investigated the mechanical damage to the Escherichia coli cell caused by polyvinyl chloride particles as a model of amino-acid crystal fermentation. Our results indicated that the glucose-consumption rate and the intracellular ATP concentration temporarily increased by the mechanical damage, and decreased after considerable damage had occurred on cell membrane. PMID:22153714
Optimal selection of artificial boundary conditions for model update and damage detection
NASA Astrophysics Data System (ADS)
Gordis, Joshua H.; Papagiannakis, Konstantinos
2011-07-01
Sensitivity-based model error localization and damage detection is hindered by the relative differences in modal sensitivity magnitude among updating parameters. The method of artificial boundary conditions is shown to directly address this limitation, resulting in the increase of the number of updating parameters at which errors can be accurately localized. Using a single set of FRF data collected from a modal test, the artificial boundary conditions (ABC) method identifies experimentally the natural frequencies of a structure under test for a variety of different boundary conditions, without having to physically apply the boundary conditions, hence the term "artificial". The parameter-specific optimal ABC sets applied to the finite element model will produce increased sensitivities in the updating parameter, yielding accurate error localization and damage detection solutions. A method is developed for identifying the parameter-specific optimal ABC sets for updating or damage detection, and is based on the QR decomposition with column pivoting. Updating solution residuals, such as magnitude error and false error location, are shown to be minimized when the updating parameter set is limited to those corresponding to the QR pivot columns. The existence of an optimal ABC set for a given updating parameter is shown to be dependent on the number of modes used, and hence the method developed provides a systematic determination of the minimum number of modes required for localization in a given updating parameter. These various concepts are demonstrated on a simple model with simulated test data.
Cellular track model of biological damage to mammalian cell cultures from galactic cosmic rays
NASA Technical Reports Server (NTRS)
Cucinotta, Francis A.; Katz, Robert; Wilson, John W.; Townsend, Lawrence W.; Nealy, John E.; Shinn, Judy L.
1991-01-01
The assessment of biological damage from the galactic cosmic rays (GCR) is a current interest for exploratory class space missions where the highly ionizing, high-energy, high-charge ions (HZE) particles are the major concern. The relative biological effectiveness (RBE) values determined by ground-based experiments with HZE particles are well described by a parametric track theory of cell inactivation. Using the track model and a deterministic GCR transport code, the biological damage to mammalian cell cultures is considered for 1 year in free space at solar minimum for typical spacecraft shielding. Included are the effects of projectile and target fragmentation. The RBE values for the GCR spectrum which are fluence-dependent in the track model are found to be more severe than the quality factors identified by the International Commission on Radiological Protection publication 26 and seem to obey a simple scaling law with the duration period in free space.
On Using Residual Voltage to Estimate Electrode Model Parameters for Damage Detection
Krishnan, Ashwati; Kelly, Shawn K.
2016-01-01
Current technology has enabled a significant increase in the number of electrodes for electrical stimulation. For large arrays of electrodes, it becomes increasingly difficult to monitor and detect failures at the stimulation site. In this paper, we propose the idea that the residual voltage from a biphasic electrical stimulation pulse can serve to recognize damage at the electrode-tissue interface. We use a simple switch circuit approach to estimate the relaxation time constant of the electrode model, which essentially models the residual voltage in biphasic electrical stimulation, and compare it with standard electrode characterization techniques. Out of 15 electrodes in a polyimide-based SIROF array, our approach highlights 3 damaged electrodes, consistent with measurements made using cyclic voltammetry and electrode impedance spectroscopy.
Failure Predictions for VHTR Core Components using a Probabilistic Contiuum Damage Mechanics Model
Fok, Alex
2013-10-30
The proposed work addresses the key research need for the development of constitutive models and overall failure models for graphite and high temperature structural materials, with the long-term goal being to maximize the design life of the Next Generation Nuclear Plant (NGNP). To this end, the capability of a Continuum Damage Mechanics (CDM) model, which has been used successfully for modeling fracture of virgin graphite, will be extended as a predictive and design tool for the core components of the very high- temperature reactor (VHTR). Specifically, irradiation and environmental effects pertinent to the VHTR will be incorporated into the model to allow fracture of graphite and ceramic components under in-reactor conditions to be modeled explicitly using the finite element method. The model uses a combined stress-based and fracture mechanics-based failure criterion, so it can simulate both the initiation and propagation of cracks. Modern imaging techniques, such as x-ray computed tomography and digital image correlation, will be used during material testing to help define the baseline material damage parameters. Monte Carlo analysis will be performed to address inherent variations in material properties, the aim being to reduce the arbitrariness and uncertainties associated with the current statistical approach. The results can potentially contribute to the current development of American Society of Mechanical Engineers (ASME) codes for the design and construction of VHTR core components.
NASA Astrophysics Data System (ADS)
Maresca, F.; Kouznetsova, V. G.; Geers, M. G. D.
2016-02-01
Metallic composite phases, like martensite present in conventional steels and new generation high strength steels exhibit microscale, locally lamellar microstructures characterized by alternating layers of phases or crystallographic variants. The layers can be sub-micron down to a few nanometers thick, and they are often characterized by high contrasts in plastic properties. As a consequence, fracture in these lamellar microstructures generally occurs along the layer interfaces or within one of the layers, typically parallel to the interface. This paper presents a computational framework that addresses the lamellar nature of these microstructures, by homogenizing the plastic deformation at the mesoscale by using the microscale response of the laminates. Failure is accounted for by introducing a family of damaging planes that are parallel to the layer interface. Mode I, mode II and mixed-mode opening are incorporated. The planes along which failure occurs are captured using a smeared damage approach. Coupling of damage with isotropic or anisotropic plasticity models, like crystal plasticity, is straightforward. The damaging planes and directions do not need to correspond to crystalline slip planes, and normal opening is also included. Focus is given on rate-dependent formulations of plasticity and damage, i.e. converged results can be obtained without further regularization techniques. The validation of the model using experimental observations in martensite-austenite lamellar microstructures in steels reveals that the model correctly predicts the main features of the onset of failure, e.g. the necking point, the failure initiation region and the failure mode. Finally, based on the qualitative results obtained, some material design guidelines are provided for martensitic and multi-phase steels.
NASA Technical Reports Server (NTRS)
Lo, David C.; Coats, Timothy W.; Harris, Charles E.; Allen, David H.
1996-01-01
A method for analysis of progressive failure in the Computational Structural Mechanics Testbed is presented in this report. The relationship employed in this analysis describes the matrix crack damage and fiber fracture via kinematics-based volume-averaged variables. Damage accumulation during monotonic and cyclic loads is predicted by damage evolution laws for tensile load conditions. The implementation of this damage model required the development of two testbed processors. While this report concentrates on the theory and usage of these processors, a complete list of all testbed processors and inputs that are required for this analysis are included. Sample calculations for laminates subjected to monotonic and cyclic loads were performed to illustrate the damage accumulation, stress redistribution, and changes to the global response that occur during the load history. Residual strength predictions made with this information compared favorably with experimental measurements.
Application of cyclic damage accumulation life prediction model to high temperature components
NASA Technical Reports Server (NTRS)
Nelson, Richard S.
1989-01-01
A high temperature, low cycle fatigue life prediction method was developed. This method, Cyclic Damage Accumulation (CDA), was developed for use in predicting the crack initiation lifetime of gas turbine engine materials, but it can be applied to other materials as well. The method is designed to account for the effects on creep-fatigue life of complex loading such as thermomechanical fatigue, hold periods, waveshapes, mean stresses, multiaxiality, cumulative damage, coatings, and environmental attack. Several features of this model were developed to make it practical for application to actual component analysis, such as the ability to handle nonisothermal loading (including TMF), arbitrary cycle paths, and multiple damage modes. The CDA life prediction model was derived from extensive specimen tests conducted on cast nickel-base superalloy B1900 + Hf. These included both monotonic tests (tensile and creep) and strain-controlled fatigue experiments (uniaxial, biaxial, TMF, mixed creep-fatigue, and controlled mean stress). Additional specimen tests were conducted on wrought INCO 718 to verify the applicability of the final CDA model to other high-temperature alloys. The model will be available to potential users in the near future in the form of a FORTRAN-77 computer program.
NASA Technical Reports Server (NTRS)
Song, Kyonchan; Li, Yingyong; Rose, Cheryl A.
2011-01-01
The performance of a state-of-the-art continuum damage mechanics model for interlaminar damage, coupled with a cohesive zone model for delamination is examined for failure prediction of quasi-isotropic open-hole tension laminates. Limitations of continuum representations of intra-ply damage and the effect of mesh orientation on the analysis predictions are discussed. It is shown that accurate prediction of matrix crack paths and stress redistribution after cracking requires a mesh aligned with the fiber orientation. Based on these results, an aligned mesh is proposed for analysis of the open-hole tension specimens consisting of different meshes within the individual plies, such that the element edges are aligned with the ply fiber direction. The modeling approach is assessed by comparison of analysis predictions to experimental data for specimen configurations in which failure is dominated by complex interactions between matrix cracks and delaminations. It is shown that the different failure mechanisms observed in the tests are well predicted. In addition, the modeling approach is demonstrated to predict proper trends in the effect of scaling on strength and failure mechanisms of quasi-isotropic open-hole tension laminates.
Insights into the damage zones in fault-bend folds from geomechanical models and field data
NASA Astrophysics Data System (ADS)
Ju, Wei; Hou, Guiting; Zhang, Bo
2014-01-01
Understanding the rock mass deformation and stress states, the fracture development and distribution are critical to a range of endeavors including oil and gas exploration and development, and geothermal reservoir characterization and management. Geomechanical modeling can be used to simulate the forming processes of faults and folds, and predict the onset of failure and the type and abundance of deformation features along with the orientations and magnitudes of stresses. This approach enables the development of forward models that incorporate realistic mechanical stratigraphy (e.g., the bed thickness, bedding planes and competence contrasts), include faults and bedding-slip surfaces as frictional sliding interfaces, reproduce the geometry of the fold structures, and allow tracking strain and stress through the whole deformation process. In this present study, we combine field observations and finite element models to calibrate the development and distribution of fractures in the fault-bend folds, and discuss the mechanical controls (e.g., the slip displacement, ramp cutoff angle, frictional coefficient of interlayers and faults) that are able to influence the development and distribution of fractures during fault-bend folding. A linear relationship between the slip displacement and the fracture damage zone, the ramp cutoff angle and the fracture damage zone, and the frictional coefficient of interlayers and faults and the fracture damage zone was established respectively based on the geomechanical modeling results. These mechanical controls mentioned above altogether contribute to influence and control the development and distribution of fractures in the fault-bend folds.
An automatic damage detection algorithm based on the Short Time Impulse Response Function
NASA Astrophysics Data System (ADS)
Auletta, Gianluca; Carlo Ponzo, Felice; Ditommaso, Rocco; Iacovino, Chiara
2016-04-01
Structural Health Monitoring together with all the dynamic identification techniques and damage detection techniques are increasing in popularity in both scientific and civil community in last years. The basic idea arises from the observation that spectral properties, described in terms of the so-called modal parameters (eigenfrequencies, mode shapes, and modal damping), are functions of the physical properties of the structure (mass, energy dissipation mechanisms and stiffness). Damage detection techniques traditionally consist in visual inspection and/or non-destructive testing. A different approach consists in vibration based methods detecting changes of feature related to damage. Structural damage exhibits its main effects in terms of stiffness and damping variation. Damage detection approach based on dynamic monitoring of structural properties over time has received a considerable attention in recent scientific literature. We focused the attention on the structural damage localization and detection after an earthquake, from the evaluation of the mode curvature difference. The methodology is based on the acquisition of the structural dynamic response through a three-directional accelerometer installed on the top floor of the structure. It is able to assess the presence of any damage on the structure providing also information about the related position and severity of the damage. The procedure is based on a Band-Variable Filter, (Ditommaso et al., 2012), used to extract the dynamic characteristics of systems that evolve over time by acting simultaneously in both time and frequency domain. In this paper using a combined approach based on the Fourier Transform and on the seismic interferometric analysis, an useful tool for the automatic fundamental frequency evaluation of nonlinear structures has been proposed. Moreover, using this kind of approach it is possible to improve some of the existing methods for the automatic damage detection providing stable results
Lau, Albert Y.; Wyatt, Michael D.; Glassner, Brian J.; Samson, Leona D.; Ellenberger, Tom
2000-01-01
The human 3-methyladenine DNA glycosylase [alkyladenine DNA glycosylase (AAG)] catalyzes the first step of base excision repair by cleaving damaged bases from DNA. Unlike other DNA glycosylases that are specific for a particular type of damaged base, AAG excises a chemically diverse selection of substrate bases damaged by alkylation or deamination. The 2.1-Å crystal structure of AAG complexed to DNA containing 1,N6-ethenoadenine suggests how modified bases can be distinguished from normal DNA bases in the enzyme active site. Mutational analyses of residues contacting the alkylated base in the crystal structures suggest that the shape of the damaged base, its hydrogen-bonding characteristics, and its aromaticity all contribute to the selective recognition of damage by AAG. PMID:11106395
Automated 3D Damaged Cavity Model Builder for Lower Surface Acreage Tile on Orbiter
NASA Technical Reports Server (NTRS)
Belknap, Shannon; Zhang, Michael
2013-01-01
The 3D Automated Thermal Tool for Damaged Acreage Tile Math Model builder was developed to perform quickly and accurately 3D thermal analyses on damaged lower surface acreage tiles and structures beneath the damaged locations on a Space Shuttle Orbiter. The 3D model builder created both TRASYS geometric math models (GMMs) and SINDA thermal math models (TMMs) to simulate an idealized damaged cavity in the damaged tile(s). The GMMs are processed in TRASYS to generate radiation conductors between the surfaces in the cavity. The radiation conductors are inserted into the TMMs, which are processed in SINDA to generate temperature histories for all of the nodes on each layer of the TMM. The invention allows a thermal analyst to create quickly and accurately a 3D model of a damaged lower surface tile on the orbiter. The 3D model builder can generate a GMM and the correspond ing TMM in one or two minutes, with the damaged cavity included in the tile material. A separate program creates a configuration file, which would take a couple of minutes to edit. This configuration file is read by the model builder program to determine the location of the damage, the correct tile type, tile thickness, structure thickness, and SIP thickness of the damage, so that the model builder program can build an accurate model at the specified location. Once the models are built, they are processed by the TRASYS and SINDA.
NASA Astrophysics Data System (ADS)
Taşkin Kaya, Gülşen
2013-10-01
Recently, earthquake damage assessment using satellite images has been a very popular ongoing research direction. Especially with the availability of very high resolution (VHR) satellite images, a quite detailed damage map based on building scale has been produced, and various studies have also been conducted in the literature. As the spatial resolution of satellite images increases, distinguishability of damage patterns becomes more cruel especially in case of using only the spectral information during classification. In order to overcome this difficulty, textural information needs to be involved to the classification to improve the visual quality and reliability of damage map. There are many kinds of textural information which can be derived from VHR satellite images depending on the algorithm used. However, extraction of textural information and evaluation of them have been generally a time consuming process especially for the large areas affected from the earthquake due to the size of VHR image. Therefore, in order to provide a quick damage map, the most useful features describing damage patterns needs to be known in advance as well as the redundant features. In this study, a very high resolution satellite image after Iran, Bam earthquake was used to identify the earthquake damage. Not only the spectral information, textural information was also used during the classification. For textural information, second order Haralick features were extracted from the panchromatic image for the area of interest using gray level co-occurrence matrix with different size of windows and directions. In addition to using spatial features in classification, the most useful features representing the damage characteristic were selected with a novel feature selection method based on high dimensional model representation (HDMR) giving sensitivity of each feature during classification. The method called HDMR was recently proposed as an efficient tool to capture the input
Validation of an empirical damage model for aging and in vivo injury of the murine patellar tendon.
Buckley, Mark R; Dunkman, Andrew A; Reuther, Katherine E; Kumar, Akash; Pathmanathan, Lydia; Beason, David P; Birk, David E; Soslowsky, Louis J
2013-04-01
While useful models have been proposed to predict the mechanical impact of damage in tendon and other soft tissues, the applicability of these models for describing in vivo injury and age-related degeneration has not been investigated. Therefore, the objective of this study was to develop and validate a simple damage model to predict mechanical alterations in mouse patellar tendons after aging, injury, or healing. To characterize baseline properties, uninjured controls at age 150 days were cyclically loaded across three strain levels and five frequencies. For comparison, damage was induced in mature (120 day-old) mice through either injury or aging. Injured mice were sacrificed at three or six weeks after surgery, while aged mice were sacrificed at either 300 or 570 days old. Changes in mechanical properties (relative to baseline) in the three week post-injury group were assessed and used to develop an empirical damage model based on a simple damage parameter related to the equilibrium stress at a prescribed strain (6%). From the derived model, the viscoelastic properties of the 300 day-old, 570 day-old, and six week post-injury groups were accurately predicted. Across testing conditions, nearly all correlations between predicted and measured parameters were statistically significant and coefficients of determination ranged from R² = 0.25 to 0.97. Results suggest that the proposed damage model could exploit simple in vivo mechanical measurements to predict how an injured or aged tendon will respond to complex physiological loading regimens. PMID:24231900
Evaluating the Human Damage of Tsunami at Each Time Frame in Aggregate Units Based on GPS data
NASA Astrophysics Data System (ADS)
Ogawa, Y.; Akiyama, Y.; Kanasugi, H.; Shibasaki, R.; Kaneda, H.
2016-06-01
Assessments of the human damage caused by the tsunami are required in order to consider disaster prevention at such a regional level. Hence, there is an increasing need for the assessments of human damage caused by earthquakes. However, damage assessments in japan currently usually rely on static population distribution data, such as statistical night time population data obtained from national census surveys. Therefore, human damage estimation that take into consideration time frames have not been assessed yet. With these backgrounds, the objectives of this study are: to develop a method for estimating the population distribution of the for each time frame, based on location positioning data observed with mass GPS loggers of mobile phones, to use a evacuation and casualties models for evaluating human damage due to the tsunami, and evaluate each time frame by using the data developed in the first objective, and 3) to discuss the factors which cause the differences in human damage for each time frame. By visualizing the results, we clarified the differences in damage depending on time frame, day and area. As this study enables us to assess damage for any time frame in and high resolution, it will be useful to consider provision for various situations when an earthquake may hit, such as during commuting hours or working hours and week day or holiday.
NASA Astrophysics Data System (ADS)
Nie, Zhenhua; Hao, Hong; Ma, Hongwei
2013-02-01
In this paper, a parameter based on geometry changes of the reconstructed multidimensional phase space of the measured vibration signals for structural damage identification is proposed. The choice of the proper delay time steps and embedding dimensions for phase space reconstruction of linear systems is discussed. Using the determined delay time and embedding dimensions, an index Changes of Phase Space Topology (CPST) with multiple embedding dimensions is calculated and then used to identify the structural damage. To demonstrate the reliability of the proposed method, vibration test data corresponding to different damage states of a continuous reinforced concrete slab is used to calculate the CPST value for damage identification. The results indicate that except the measurement points at structural supports, the CPST values at all the measurement points on the structure increase with structural damage level irrespective of the damage location, indicating that using a single or a minimum number of measurement points and their CPST value can effectively identify damage existence in the structure. The traditional modal-based indices are also calculated using the same vibration data for comparison. It is found that the proposed method with CPST is the most sensitive to structural damage than any modal-based index. The results demonstrate that the proposed method with CPST value is very effective in identifying damage existence in the structure. Although it cannot quantify the damage, it can be a good candidate for continuous structural health monitoring because it needs only a few sensors to detect damage existence in the entire structure.
Satellite-based damage mapping following the 2006 Indonesia earthquake—How accurate was it?
NASA Astrophysics Data System (ADS)
Kerle, Norman
2010-12-01
The Yogyakarta area in Indonesia suffered a devastating earthquake on 27 May 2006. There was an immediate international response, and the International Charter "Space and Major Disasters" was activated, leading to a rapid production of image-based damage maps and other assistance. Most of the acquired images were processed by UNOSAT and DLR-ZKI, while substantial damage mapping also occurred on the ground. This paper assesses the accuracy and completeness of the damage maps produced based on Charter data, using ground damage information collected during an extensive survey by Yogyakarta's Gadjah Mada University in the weeks following the earthquake and that has recently become available. More than 54,000 buildings or their remains were surveyed, resulting in an exceptional validation database. The UNOSAT damage maps outlining clusters of severe damage are very accurate, while earlier, more detailed results underestimated damage and missed larger areas. Damage maps produced by DLR-ZKI, using a damage-grid approach, were found to underestimate the extent and severity of the devastation. Both mapping results also suffer from limited image coverage and extensive cloud contamination. The ground mapping gives a more accurate picture of the extent of the damage, but also illustrates the challenge of mapping a vast area. The paper concludes with a discussion on ways to improve Charter-based damage maps by integration of local knowledge, and to create a wider impact through generation of customised mapping products using web map services.
A comprehensive model of catastrophic optical-damage in broad-area laser diodes
NASA Astrophysics Data System (ADS)
Chin, A. K.; Bertaska, R. K.; Jaspan, M. A.; Flusberg, A. M.; Swartz, S. D.; Knapczyk, M. T.; Petr, R.; Smilanski, I.; Jacob, J. H.
2009-02-01
The present model of formation and propagation of catastrophic optical-damage (COD), a random failure-mode in laser diodes, was formulated in 1974 and has remained substantially unchanged. We extend the model of COD phenomena, based on analytical studies involving EBIC (electron-beam induced current), STEM (scanning transmission-electron microscopy) and sophisticated optical-measurements. We have determined that a ring-cavity mode, whose presence has not been previously reported, significantly contributes to COD initiation and propagation in broad-area laser-diodes.
Rate sensitive continuum damage models and mesh dependence in finite element analyses.
Ljustina, Goran; Fagerström, Martin; Larsson, Ragnar
2014-01-01
The experiences from orthogonal machining simulations show that the Johnson-Cook (JC) dynamic failure model exhibits significant element size dependence. Such mesh dependence is a direct consequence of the utilization of local damage models. The current contribution is an investigation of the extent of the possible pathological mesh dependence. A comparison of the resulting JC model behavior combined with two types of damage evolution is considered. The first damage model is the JC dynamic failure model, where the development of the "damage" does not affect the response until the critical state is reached. The second one is a continuum damage model, where the damage variable is affecting the material response continuously during the deformation. Both the plasticity and the damage models are rate dependent, and the damage evolutions for both models are defined as a postprocessing of the effective stress response. The investigation is conducted for a series of 2D shear tests utilizing different FE representations of the plane strain plate with pearlite material properties. The results show for both damage models, using realistic pearlite material parameters, that similar extent of the mesh dependence is obtained and that the possible viscous regularization effects are absent in the current investigation. PMID:25530994
NASA Astrophysics Data System (ADS)
Safaei, Farinaz; Castorena, Cassie; Kim, Y. Richard
2016-08-01
Fatigue cracking is a major form of distress in asphalt pavements. Asphalt binder is the weakest asphalt concrete constituent and, thus, plays a critical role in determining the fatigue resistance of pavements. Therefore, the ability to characterize and model the inherent fatigue performance of an asphalt binder is a necessary first step to design mixtures and pavements that are not susceptible to premature fatigue failure. The simplified viscoelastic continuum damage (S-VECD) model has been used successfully by researchers to predict the damage evolution in asphalt mixtures for various traffic and climatic conditions using limited uniaxial test data. In this study, the S-VECD model, developed for asphalt mixtures, is adapted for asphalt binders tested under cyclic torsion in a dynamic shear rheometer. Derivation of the model framework is presented. The model is verified by producing damage characteristic curves that are both temperature- and loading history-independent based on time sweep tests, given that the effects of plasticity and adhesion loss on the material behavior are minimal. The applicability of the S-VECD model to the accelerated loading that is inherent of the linear amplitude sweep test is demonstrated, which reveals reasonable performance predictions, but with some loss in accuracy compared to time sweep tests due to the confounding effects of nonlinearity imposed by the high strain amplitudes included in the test. The asphalt binder S-VECD model is validated through comparisons to asphalt mixture S-VECD model results derived from cyclic direct tension tests and Accelerated Loading Facility performance tests. The results demonstrate good agreement between the asphalt binder and mixture test results and pavement performance, indicating that the developed model framework is able to capture the asphalt binder's contribution to mixture fatigue and pavement fatigue cracking performance.
NASA Astrophysics Data System (ADS)
Safaei, Farinaz; Castorena, Cassie; Kim, Y. Richard
2016-04-01
Fatigue cracking is a major form of distress in asphalt pavements. Asphalt binder is the weakest asphalt concrete constituent and, thus, plays a critical role in determining the fatigue resistance of pavements. Therefore, the ability to characterize and model the inherent fatigue performance of an asphalt binder is a necessary first step to design mixtures and pavements that are not susceptible to premature fatigue failure. The simplified viscoelastic continuum damage (S-VECD) model has been used successfully by researchers to predict the damage evolution in asphalt mixtures for various traffic and climatic conditions using limited uniaxial test data. In this study, the S-VECD model, developed for asphalt mixtures, is adapted for asphalt binders tested under cyclic torsion in a dynamic shear rheometer. Derivation of the model framework is presented. The model is verified by producing damage characteristic curves that are both temperature- and loading history-independent based on time sweep tests, given that the effects of plasticity and adhesion loss on the material behavior are minimal. The applicability of the S-VECD model to the accelerated loading that is inherent of the linear amplitude sweep test is demonstrated, which reveals reasonable performance predictions, but with some loss in accuracy compared to time sweep tests due to the confounding effects of nonlinearity imposed by the high strain amplitudes included in the test. The asphalt binder S-VECD model is validated through comparisons to asphalt mixture S-VECD model results derived from cyclic direct tension tests and Accelerated Loading Facility performance tests. The results demonstrate good agreement between the asphalt binder and mixture test results and pavement performance, indicating that the developed model framework is able to capture the asphalt binder's contribution to mixture fatigue and pavement fatigue cracking performance.
Case-based damage assessment of storm events in near real-time
NASA Astrophysics Data System (ADS)
Möhrle, Stella; Mühr, Bernhard
2015-04-01
Damage assessment in times of crisis is complex due to a highly dynamic environment and uncertainty in respect of available information. In order to assess the extent of a disaster in near real-time, historic events and their consequences may facilitate first estimations. Events of the past, which are in the same category or which have similar frame conditions like imminent or just occurring storms, might give preliminary information about possible damages. The challenge here is to identify useful historic events based on little information regarding the current event. This work investigates the potential of drawing conclusions about a current event based on similar historic disasters, exemplarily for storm events in Germany. Predicted wind speed and area affected can be used for roughly classifying a storm event. For this purpose, a grid of equidistant points can be used to split up the area of Germany. In combination with predicted wind speed at these points and the predicted number of points affected, respectively, a storm can be categorized in a fast manner. In contrast to investigate only data taken by the observation network, the grid approach is more objective, since stations are not equally distributed. Based on model data, the determined storm class provides one key factor for identifying similar historic events. Further aspects, such as region or specific event characteristics, complete knowledge about the potential storm scale and result in a similarity function, which automatically identifies useful events from the past. This work presents a case-based approach to estimate damages in the event of an extreme storm event in Germany. The focus in on the similarity function, which is based on model storm classes, particularly wind speed and area affected. In order to determine possible damages more precisely, event specific characteristics and region will be included. In the frame of determining similar storm events, neighboring storm classes will be
NASA Astrophysics Data System (ADS)
Vetrivel, Anand; Gerke, Markus; Kerle, Norman; Vosselman, George
2015-07-01
Point clouds generated from airborne oblique images have become a suitable source for detailed building damage assessment after a disaster event, since they provide the essential geometric and radiometric features of both roof and façades of the building. However, they often contain gaps that result either from physical damage or from a range of image artefacts or data acquisition conditions. A clear understanding of those reasons, and accurate classification of gap-type, are critical for 3D geometry-based damage assessment. In this study, a methodology was developed to delineate buildings from a point cloud and classify the present gaps. The building delineation process was carried out by identifying and merging the roof segments of single buildings from the pre-segmented 3D point cloud. This approach detected 96% of the buildings from a point cloud generated using airborne oblique images. The gap detection and classification methods were tested using two other data sets obtained with Unmanned Aerial Vehicle (UAV) images with a ground resolution of around 1-2 cm. The methods detected all significant gaps and correctly identified the gaps due to damage. The gaps due to damage were identified based on the surrounding damage pattern, applying Gabor wavelets and a histogram of gradient orientation features. Two learning algorithms - SVM and Random Forests were tested for mapping the damaged regions based on radiometric descriptors. The learning model based on Gabor features with Random Forests performed best, identifying 95% of the damaged regions. The generalization performance of the supervised model, however, was less successful: quality measures decreased by around 15-30%.
Schindler, Dirk; Grebhan, Karin; Albrecht, Axel; Schönborn, Jochen
2009-11-01
The wind damage probability (P (DAM)) in the forests in the federal state of Baden-Wuerttemberg (Southwestern Germany) was calculated using weights of evidence (WofE) methodology and a logistic regression model (LRM) after the winter storm 'Lothar' in December 1999. A geographic information system (GIS) was used for the area-wide spatial prediction and mapping of P (DAM). The combination of the six evidential themes forest type, soil type, geology, soil moisture, soil acidification, and the 'Lothar' maximum gust field predicted wind damage best and was used to map P (DAM) in a 50 x 50 m resolution grid. GIS software was utilised to produce probability maps, which allowed the identification of areas of low, moderate, and high P (DAM) across the study area. The highest P (DAM) values were calculated for coniferous forest growing on acidic, fresh to moist soils on bunter sandstone formations-provided that 'Lothar' maximum gust speed exceeded 35 m s(-1) in the areas in question. One of the most significant benefits associated with the results of this study is that, for the first time, there is a GIS-based area-wide quantification of P (DAM) in the forests in Southwestern Germany. In combination with the experience and expert knowledge of local foresters, the probability maps produced can be used as an important tool for decision support with respect to future silvicultural activities aimed at reducing wind damage. One limitation of the P (DAM)-predictions is that they are based on only one major storm event. At the moment it is not possible to relate storm event intensity to the amount of wind damage in forests due to the lack of comprehensive long-term tree and stand damage data across the study area. PMID:19562383
A local damage detection approach based on restoring force method
NASA Astrophysics Data System (ADS)
Zhan, Chao; Li, Dongsheng; Li, Hongnan
2014-09-01
Chain-like systems have been studied by many researchers for their simple structure and wide range of application. Previously, the damage in a chain-like system was detected by the reduction of the mass-normalized stiffness coefficient for certain elements as reported by Nayeri et al. (2008 [16]). However, some shortcomings exist in that approach and for overcoming them; an improved approach is derived and presented in this paper. In our improved approach, the mass normalized stiffness coefficients under two states (baseline state and potentially damaged state) are first estimated by a least square method, then these mass-stiffness coupled coefficients are decoupled to derive stiffness and mass relative change ratios for individual elements. These ratios are assembled in a vector, which is defined as damage indication vector (DIV). Each component in DIV is normalized individually to one to get multiple solutions. These solutions are averaged for estimating relative system changes, while abnormal solutions are discarded. The work of judging a solution as normal or abnormal is done by a cluster analysis algorithm. The most intriguing merit of this improved approach is that the relative stiffness and mass changes, which are coupled in the previous approach, can be separately identified. By this approach, the damage (single or multiple) extent and location can be correctly detected under operational conditions, meanwhile the proposed damage index has a clear physical meaning and is directly related to the stiffness reduction of corresponding structural elements. For illustrating the effectiveness and robustness of the improved approach, numerical simulation of a four floor building was carried out and experimental data from a structure tested at the Los Alamos National Laboratory was employed. Identified structural changes with both simulation and experimental data properly indicated the location and extent of actual structural damage, which validated the proposed
Methodology for a GIS-based damage assessment for researchers following large scale disasters
NASA Astrophysics Data System (ADS)
Crawford, Patrick Shane
The 1990s were designated the International Decade for Natural Disaster Reduction by the United Nations General Assembly. This push for decrease of loss of life, property destruction, and social and economic disruption brought advancements in disaster management, including damage assessment. Damage assessment in the wake of natural and manmade disasters is a useful tool for government agencies, insurance companies, and researchers. As technologies evolve damage assessment processes constantly evolve as well. Alongside the advances in Geographic Information Systems (GIS), remote sensing, and Global Positioning System (GPS) technology, as well as the growing awareness of the needs of a standard operating procedure for GIS-based damage assessment and a need to make the damage assessment process as quick and accurate as possible, damage assessment procedures are becoming easier to execute and the results are becoming more accurate and robust. With these technological breakthroughs, multi-disciplinary damage assessment reconnaissance teams have become more efficient in their assessment methods through better organization and more robust through addition of new datasets. Damage assessment personnel are aided by software tools that offer high-level analysis and increasingly rapid damage assessment methods. GIS software has advanced the damage assessment methods of these teams by combining remotely sensed aerial imagery, GPS, and other technologies to expand the uses of the data. GIS allows researchers to use aerial imagery to show field collected data in the geographic location that it was collected so that information can be revisited, measurements can be taken, and data can be disseminated to other researchers and the public. The GIS-based data available to the reconnaissance team includes photographs of damage, worksheets, calculations, voice messages collected while studying the affected area, and many other datasets which are based on the type of disaster and the
Vertebrate POLQ and POLβ Cooperate in Base Excision Repair of Oxidative DNA Damage
Yoshimura, Michio; Kohzaki, Masaoki; Nakamura, Jun; Asagoshi, Kenjiro; Sonoda, Eiichiro; Hou, Esther; Prasad, Rajendra; Wilson, Samuel H.; Tano, Keizo; Yasui, Akira; Lan, Li; Seki, Mineaki; Wood, Richard D.; Arakawa, Hiroshi; Buerstedde, Jean-Marie; Hochegger, Helfrid; Okada, Takashi; Hiraoka, Masahiro; Takeda, Shunichi
2007-01-01
Summary Base excision repair (BER) plays an essential role in protecting cells from mutagenic base damage caused by oxidative stress, hydrolysis, and environmental factors. POLQ is a DNA polymerase, which appears to be involved in translesion DNA synthesis (TLS) past base damage. We disrupted POLQ, and its homologs HEL308 and POLN in chicken DT40 cells, and also created polq/hel308 and polq/poln double mutants. We found that POLQ-deficient mutants exhibit hypersensitivity to oxidative base damage induced by H2O2, but not to UV or cisplatin. Surprisingly, this phenotype was synergistically increased by concomitant deletion of the major BER polymerase, POLβ. Moreover, extracts from a polq null mutant cell line show reduced BER activity, and POLQ, like POLβ, accumulated rapidly at sites of base damage. Accordingly, POLQ and POLβ share an overlapping function in the repair of oxidative base damage. Taken together, these results suggest a role for vertebrate POLQ in BER. PMID:17018297
Salajegheh, Nima; Abedrabbo, Nader; Pourboghrat, Farhang
2005-08-05
An efficient integration algorithm for continuum damage based elastoplastic constitutive equations is implemented in LS-DYNA. The isotropic damage parameter is defined as the ratio of the damaged surface area over the total cross section area of the representative volume element. This parameter is incorporated into the integration algorithm as an internal variable. The developed damage model is then implemented in the FEM code LS-DYNA as user material subroutine (UMAT). Pure stretch experiments of a hemispherical punch are carried out for copper sheets and the results are compared against the predictions of the implemented damage model. Evaluation of damage parameters is carried out and the optimized values that correctly predicted the failure in the sheet are reported. Prediction of failure in the numerical analysis is performed through element deletion using the critical damage value. The set of failure parameters which accurately predict the failure behavior in copper sheets compared to experimental data is reported as well.
NASA Astrophysics Data System (ADS)
Salajegheh, Nima; Abedrabbo, Nader; Pourboghrat, Farhang
2005-08-01
An efficient integration algorithm for continuum damage based elastoplastic constitutive equations is implemented in LS-DYNA. The isotropic damage parameter is defined as the ratio of the damaged surface area over the total cross section area of the representative volume element. This parameter is incorporated into the integration algorithm as an internal variable. The developed damage model is then implemented in the FEM code LS-DYNA as user material subroutine (UMAT). Pure stretch experiments of a hemispherical punch are carried out for copper sheets and the results are compared against the predictions of the implemented damage model. Evaluation of damage parameters is carried out and the optimized values that correctly predicted the failure in the sheet are reported. Prediction of failure in the numerical analysis is performed through element deletion using the critical damage value. The set of failure parameters which accurately predict the failure behavior in copper sheets compared to experimental data is reported as well.
Developments in impact damage modeling for laminated composite structures
NASA Technical Reports Server (NTRS)
Dost, Ernest F.; Avery, William B.; Swanson, Gary D.; Lin, Kuen Y.
1991-01-01
Damage tolerance is the most critical technical issue for composite fuselage structures studied in the Advanced Technology Composite Aircraft Structures (ATCAS) program. The objective here is to understand both the impact damage resistance and residual strength of the laminated composite fuselage structure. An understanding of the different damage mechanisms which occur during an impact event will support the selection of materials and structural configurations used in different fuselage quadrants and guide the development of analysis tools for predicting the residual strength of impacted laminates. Prediction of the damage state along with the knowledge of post-impact response to applied loads will allow for engineered stacking sequencies and structural configurations; intelligent decisions on repair requirements will also result.
NASA Astrophysics Data System (ADS)
Xin, Qiang; Su, Xing; Wang, Bo
2016-09-01
Plasma processing has been widely reported as an effective tool in relieving or removing surface/subsurface damage induced by previous mechanical machining process. However, the surface morphology evolution during removing the damage using plasma processing is rarely reported. In this research, this procedure is studied based on experiments and robust numerical models developed on the basis of Level Set Method (LSM). Even if some unique properties of plasma etching are observed, such as particle redistribution, the dominant role of isotropic etching of plasma processing is verified based on experiments and 2D LSM simulations. With 2D LSM models, the damage removal process under various damage characteristics is explored in detail. Corresponding peak-to-valley roughness evolution is investigated as well. Study on morphology evolution is also conducted through the comparison between experiments and 3D LSM computations. The modeling results and experiments show good agreement with each other. The trends of simulated roughness evolution agree with the experiments as well. It is revealed that the plasma processing may end up with a planar surface depending on the damage characteristics. The planarization procedure can be divided into four parts: crack opening and pit formation; pit coalescing and shallow pits subsumed by deep ones; morphology duplicate etching; and finally a planar and damage free surface.
Online damage diagnosis for civil infrastructure employing a flexibility-based approach
NASA Astrophysics Data System (ADS)
Gao, Y.; Spencer, B. F., Jr.
2006-02-01
Structural health monitoring (SHM) and damage detection have recently emerged as a new research area in civil engineering. Continuous and long-term monitoring of civil infrastructure is desirable, because it allows the damage in the structure to be detected at an early stage so that necessary measures can be carried out to prolong and optimize the associated service life and cost. In this paper, an approach which extends a flexibility-based damage detection technique, the damage locating vector (DLV) method, for continuous online SHM is presented. The essence of the proposed approach is to construct an approximate flexibility matrix for the damaged structure utilizing the modal normalization constants from the undamaged structure. This extended DLV method can then be applied for online damage diagnosis. Numerical simulation has been conducted using a 14-bay planar truss structure, with the results showing that the proposed approach works well for both single- and multiple-damage scenarios.
NASA Technical Reports Server (NTRS)
Lua, Yuan J.; Liu, Wing K.; Belytschko, Ted
1992-01-01
A stochastic damage model for predicting the rupture of a brittle multiphase material is developed, based on the microcrack-macrocrack interaction. The model, which incorporates uncertainties in locations, orientations, and numbers of microcracks, characterizes damage by microcracking and fracture by macrocracking. A parametric study is carried out to investigate the change of the stress intensity at the macrocrack tip by the configuration of microcracks. The inherent statistical distribution of the fracture toughness arising from the intrinsic random nature of microcracks is explored using a statistical approach. For this purpose, a computer simulation model is introduced, which incorporates a statistical characterization of geometrical parameters of a random microcrack array.
Active destabilization of base pairs by a DNA glycosylase wedge initiates damage recognition
Kuznetsov, Nikita A.; Bergonzo, Christina; Campbell, Arthur J.; Li, Haoquan; Mechetin, Grigory V.; de los Santos, Carlos; Grollman, Arthur P.; Fedorova, Olga S.; Zharkov, Dmitry O.; Simmerling, Carlos
2015-01-01
Formamidopyrimidine-DNA glycosylase (Fpg) excises 8-oxoguanine (oxoG) from DNA but ignores normal guanine. We combined molecular dynamics simulation and stopped-flow kinetics with fluorescence detection to track the events in the recognition of oxoG by Fpg and its mutants with a key phenylalanine residue, which intercalates next to the damaged base, changed to either alanine (F110A) or fluorescent reporter tryptophan (F110W). Guanine was sampled by Fpg, as evident from the F110W stopped-flow traces, but less extensively than oxoG. The wedgeless F110A enzyme could bend DNA but failed to proceed further in oxoG recognition. Modeling of the base eversion with energy decomposition suggested that the wedge destabilizes the intrahelical base primarily through buckling both surrounding base pairs. Replacement of oxoG with abasic (AP) site rescued the activity, and calculations suggested that wedge insertion is not required for AP site destabilization and eversion. Our results suggest that Fpg, and possibly other DNA glycosylases, convert part of the binding energy into active destabilization of their substrates, using the energy differences between normal and damaged bases for fast substrate discrimination. PMID:25520195
Rate Sensitive Continuum Damage Models and Mesh Dependence in Finite Element Analyses
Fagerström, Martin
2014-01-01
The experiences from orthogonal machining simulations show that the Johnson-Cook (JC) dynamic failure model exhibits significant element size dependence. Such mesh dependence is a direct consequence of the utilization of local damage models. The current contribution is an investigation of the extent of the possible pathological mesh dependence. A comparison of the resulting JC model behavior combined with two types of damage evolution is considered. The first damage model is the JC dynamic failure model, where the development of the “damage” does not affect the response until the critical state is reached. The second one is a continuum damage model, where the damage variable is affecting the material response continuously during the deformation. Both the plasticity and the damage models are rate dependent, and the damage evolutions for both models are defined as a postprocessing of the effective stress response. The investigation is conducted for a series of 2D shear tests utilizing different FE representations of the plane strain plate with pearlite material properties. The results show for both damage models, using realistic pearlite material parameters, that similar extent of the mesh dependence is obtained and that the possible viscous regularization effects are absent in the current investigation. PMID:25530994
A biophysical model of cell evolution after cytotoxic treatments: Damage, repair and cell response.
Tomezak, M; Abbadie, C; Lartigau, E; Cleri, F
2016-01-21
We present a theoretical agent-based model of cell evolution under the action of cytotoxic treatments, such as radiotherapy or chemotherapy. The major features of cell cycle and proliferation, cell damage and repair, and chemical diffusion are included. Cell evolution is based on a discrete Markov chain, with cells stepping along a sequence of discrete internal states from 'normal' to 'inactive'. Probabilistic laws are introduced for each type of event a cell can undergo during its life: duplication, arrest, senescence, damage, reparation, or death. We adjust the model parameters on a series of cell irradiation experiments, carried out in a clinical LINAC, in which the damage and repair kinetics of single- and double-strand breaks are followed. Two showcase applications of the model are then presented. In the first one, we reconstruct the cell survival curves from a number of published low- and high-dose irradiation experiments. We reobtain a very good description of the data without assuming the well-known linear-quadratic model, but instead including a variable DSB repair probability. The repair capability of the model spontaneously saturates to an exponential decay at increasingly high doses. As a second test, we attempt to simulate the two extreme possibilities of the so-called 'bystander' effect in radiotherapy: the 'local' effect versus a 'global' effect, respectively activated by the short-range or long-range diffusion of some factor, presumably secreted by the irradiated cells. Even with an oversimplified simulation, we could demonstrate a sizeable difference in the proliferation rate of non-irradiated cells, the proliferation acceleration being much larger for the global than the local effect, for relatively small fractions of irradiated cells in the colony. PMID:26549470
NASA Astrophysics Data System (ADS)
Lin, Y. Q.; Ren, W. X.; Fang, S. E.
2011-11-01
Although most vibration-based damage detection methods can acquire satisfactory verification on analytical or numerical structures, most of them may encounter problems when applied to real-world structures under varying environments. The damage detection methods that directly extract damage features from the periodically sampled dynamic time history response measurements are desirable but relevant research and field application verification are still lacking. In this second part of a two-part paper, the robustness and performance of the statistics-based damage index using the forward innovation model by stochastic subspace identification of a vibrating structure proposed in the first part have been investigated against two prestressed reinforced concrete (RC) beams tested in the laboratory and a full-scale RC arch bridge tested in the field under varying environments. Experimental verification is focused on temperature effects. It is demonstrated that the proposed statistics-based damage index is insensitive to temperature variations but sensitive to the structural deterioration or state alteration. This makes it possible to detect the structural damage for the real-scale structures experiencing ambient excitations and varying environmental conditions.
Damage Detection on Sudden Stiffness Reduction Based on Discrete Wavelet Transform
Chen, Bo; Chen, Zhi-wei; Wang, Gan-jun; Xie, Wei-ping
2014-01-01
The sudden stiffness reduction in a structure may cause the signal discontinuity in the acceleration responses close to the damage location at the damage time instant. To this end, the damage detection on sudden stiffness reduction of building structures has been actively investigated in this study. The signal discontinuity of the structural acceleration responses of an example building is extracted based on the discrete wavelet transform. It is proved that the variation of the first level detail coefficients of the wavelet transform at damage instant is linearly proportional to the magnitude of the stiffness reduction. A new damage index is proposed and implemented to detect the damage time instant, location, and severity of a structure due to a sudden change of structural stiffness. Numerical simulation using a five-story shear building under different types of excitation is carried out to assess the effectiveness and reliability of the proposed damage index for the building at different damage levels. The sensitivity of the damage index to the intensity and frequency range of measurement noise is also investigated. The made observations demonstrate that the proposed damage index can accurately identify the sudden damage events if the noise intensity is limited. PMID:24991647
Vibration-based damage detection for filament wound pressure vessel filled with fluid
NASA Astrophysics Data System (ADS)
Zhou, W.; Wu, Z.; Li, H.
2008-03-01
Filament wound pressure vessels have been extensively used in industry and engineering. The existing damage detection and health monitoring methods for these vessels, such as X-ray and ultrasonic scan, can not meet the requirement of online damage detection; moreover optical grating fibre can only sense the local damage, but not the damage far away from the location of sensors. Vibration-based damage detection methods have the potential to meet such requirements. There methods are based on the fact that damages in a structure results in a change in structural dynamic characteristics. A damage detection method based on a residual associated with output-only subspace-based modal identification and global or focused chi^2-tests built on that residual has been proposed and successfully experimented on a variety of test cases. The purpose of this work is to describe the damage detection method and apply this method to assess the composite structure filled with fluid. The results of identification and damage detection will be presented.
Modal macro-strain vector based damage detection methodology with long-gauge FBG sensors
NASA Astrophysics Data System (ADS)
Xu, Bin; Liu, Chongwu W.; Masri, Sami F.
2009-07-01
Advances in optic fiber sensing technology provide easy and reliable way for the vibration-based strain measurement of engineering structures. As a typical optic fiber sensing techniques with high accuracy and resolution, long-gauge Fiber Bragg Grating (FBG) sensors have been widely employed in health monitoring of civil engineering structures. Therefore, the development of macro strain-based identification methods is crucial for damage detection and structural condition evaluation. In the previous study by the authors, a damage detection algorithm for a beam structure with the direct use of vibration-based macro-strain measurement time history with neural networks had been proposed and validated with experimental measurements. In this paper, a damage locating and quantifying method was proposed using modal macrostrain vectors (MMSVs) which can be extracted from vibration induced macro-strain response measurement time series from long-gage FBG sensors. The performance of the proposed methodology for damage detection of a beam with different damage scenario was studied with numerical simulation firstly. Then, dynamic tests on a simply-supported steel beam with different damage scenarios were carried out and macro-strain measurements were employed to detect the damage severity. Results show that the proposed MMSV based structural identification and damage detection methodology can locate and identify the structural damage severity with acceptable accuracy.
Creep damage characterization using nonlinear ultrasonic guided wave method: A mesoscale model
NASA Astrophysics Data System (ADS)
Xiang, Yanxun; Deng, Mingxi; Xuan, Fu-Zhen
2014-01-01
The early deformations in materials such as creep, plasticity, and fatigue damages have been proved to have a close relationship with the nonlinear effect of ultrasonic waves propagating in them. In the present paper, a theoretical mesoscale model of an ultrasonic non-destructive method has been proposed to evaluate creep deformed states based on nonlinear guided waves. The model developed here considers the nonlinear generation of Lamb waves response from precipitates variation in the dislocation network, which can be applicable to all precipitate stages including coherent and semi-coherent precipitates in the metallic alloy undergoing creep degradation. To verify the proposed model, experiments of titanium alloy Ti60 plates were carried out with different creep strains. An "increase-decrease" change of the acoustic nonlinearity of guided wave versus the creep life fraction has been observed. Based on microscopic images analyses, the mesoscale model was then applied to these creep damaged Ti60 specimens, which revealed a good accordance with the measured results of the nonlinear guided waves. It is shown that the change of the nonlinear Lamb wave depends on the variations of the α2 precipitation volume fraction, the dislocation density, the growth of the creep-voids, and the increasing mismatch of the phase velocities during the creep deformation process. The results indicate that the effect of the precipitate-dislocation interactions on the nonlinear guided wave is likely the dominant mechanism responsible for the change of nonlinear guided wave propagation in the crept materials.
Comparative study of performance of neutral axis tracking based damage detection
NASA Astrophysics Data System (ADS)
Soman, R.; Malinowski, P.; Ostachowicz, W.
2015-07-01
This paper presents a comparative study of a novel SHM technique for damage isolation. The performance of the Neutral Axis (NA) tracking based damage detection strategy is compared to other popularly used vibration based damage detection methods viz. ECOMAC, Mode Shape Curvature Method and Strain Flexibility Index Method. The sensitivity of the novel method is compared under changing ambient temperature conditions and in the presence of measurement noise. Finite Element Analysis (FEA) of the DTU 10 MW Wind Turbine was conducted to compare the local damage identification capability of each method and the results are presented. Under the conditions examined, the proposed method was found to be robust to ambient condition changes and measurement noise. The damage identification in some is either at par with the methods mentioned in the literature or better under the investigated damage scenarios.
Inspection of the Math Model Tools for On-Orbit Assessment of Impact Damage Report
NASA Technical Reports Server (NTRS)
Harris, Charles E.; Raju, Ivatury S.; Piascik, Robert S>
2007-01-01
In Spring of 2005, the NASA Engineering Safety Center (NESC) was engaged by the Space Shuttle Program (SSP) to peer review the suite of analytical tools being developed to support the determination of impact and damage tolerance of the Orbiter Thermal Protection Systems (TPS). The NESC formed an independent review team with the core disciplines of materials, flight sciences, structures, mechanical analysis and thermal analysis. The Math Model Tools reviewed included damage prediction and stress analysis, aeroheating analysis, and thermal analysis tools. Some tools are physics-based and other tools are empirically-derived. Each tool was created for a specific use and timeframe, including certification, real-time pre-launch assessments. In addition, the tools are used together in an integrated strategy for assessing the ramifications of impact damage to tile and RCC. The NESC teams conducted a peer review of the engineering data package for each Math Model Tool. This report contains the summary of the team observations and recommendations from these reviews.
Structural damage identification based on substructure sensitivity and l1 sparse regularization
NASA Astrophysics Data System (ADS)
Zhou, Shumei; Bao, Yuequan; Li, Hui
2013-04-01
Sparsity constraints are now very popular to regularize inverse problems in the field of applied mathematics. Structural damage identification is a typical inverse problem of structural dynamics and Structural damage is a spatial sparse phenomenon, i.e., structural damage occurs, only part of elements or substructures are damaged. In this paper, a structural damage identification method based on the substructure-based sensitivity analysis and the sparse constraints regularization is proposed. Substructure sensitivity analysis, the establishment of structural damage stiffness parameter variation and change of modal parameters of linear equations between the measured degrees of freedom is limited, the equations for a morbid equation. The introduction of structural damage sparsity conditions, to minimize the l1 norm optimization solution. The numerical example of the 20 bay-truss structure with considering measurement noise, incomplete of measurements and multi-damage cases are carried out. The effects of number sensor and layout to the identification results are also investigated. The results indicated that the damage locations and extents can be effectively identified by the proposed method. Additionally, the sensor location can be random arrangement, which has great significance to the sensor placement of the actual structural health monitoring because robust structural damage identification also can be obtained even a few of sensor are failure.
Fatigue damage modeling for coated single crystal superalloys
NASA Technical Reports Server (NTRS)
Nissley, David M.
1988-01-01
A high temperature, low-cycle fatigue life prediction method for coated single crystal nickel-base superalloys is being developed. The method is being developed for use in predicting crack initiation life of coated single crystal turbine airfoils. Although the models are being developed using coated single crystal PWA 1480, they should be readily adaptable to other coated nickel-base single crystal materials. The coatings choosen for this effort were of two generic types: a low pressure plasma sprayed NiCoCrAlY overlay, designated PWA 286, and an aluminide diffusion, designated PWA 273. In order to predict the useful crack initiation life of airfoils, the constitutive and failure behavior of the coating/substrate combination must be taken into account. Coatings alter the airfoil surface microstructure and are a primary source from which cracks originate. The adopted life prediction approach addresses this complexity by separating the coating and single crystal crack initiation regimes. This provides a flexible means for using different life model formulations for the coating and single crystal materials. At the completion of this program, all constitutive and life model formulations will be available in equation form and as software. The software will use the MARC general purpose finite element code to drive the constitutive models and calculate life parameters.
Optimal ozone reduction policy design using adjoint-based NOx marginal damage information.
Mesbah, S Morteza; Hakami, Amir; Schott, Stephan
2013-01-01
Despite substantial reductions in nitrogen oxide (NOx) emissions in the United States, the success of emission control programs in optimal ozone reduction is disputable because they do not consider the spatial and temporal differences in health and environmental damages caused by NOx emissions. This shortcoming in the current U.S. NOx control policy is explored, and various methodologies for identifying optimal NOx emission control strategies are evaluated. The proposed approach combines an optimization platform with an adjoint (or backward) sensitivity analysis model and is able to examine the environmental performance of the current cap-and-trade policy and two damage-based emissions-differentiated policies. Using the proposed methodology, a 2007 case study of 218 U.S. electricity generation units participating in the NOx trading program is examined. The results indicate that inclusion of damage information can significantly enhance public health performance of an economic instrument. The net benefit under the policy that minimizes the social cost (i.e., health costs plus abatement costs) is six times larger than that of an exchange rate cap-and-trade policy. PMID:24144173
High-energy radiation damage in zirconia: Modeling results
NASA Astrophysics Data System (ADS)
Zarkadoula, E.; Devanathan, R.; Weber, W. J.; Seaton, M. A.; Todorov, I. T.; Nordlund, K.; Dove, M. T.; Trachenko, K.
2014-02-01
Zirconia is viewed as a material of exceptional resistance to amorphization by radiation damage, and consequently proposed as a candidate to immobilize nuclear waste and serve as an inert nuclear fuel matrix. Here, we perform molecular dynamics simulations of radiation damage in zirconia in the range of 0.1-0.5 MeV energies with account of electronic energy losses. We find that the lack of amorphizability co-exists with a large number of point defects and their clusters. These, importantly, are largely isolated from each other and therefore represent a dilute damage that does not result in the loss of long-range structural coherence and amorphization. We document the nature of these defects in detail, including their sizes, distribution, and morphology, and discuss practical implications of using zirconia in intense radiation environments.
High-energy radiation damage in zirconia: modeling results
Zarkadoula, Evangelia; Devanathan, Ram; Weber, William J; Seaton, M; Todorov, I T; Nordlund, Kai; Dove, Martin T; Trachenko, Kostya
2014-01-01
Zirconia is viewed as a material of exceptional resistance to amorphization by radiation damage, and consequently proposed as a candidate to immobilize nuclear waste and serve as an inert nuclear fuel matrix. Here, we perform molecular dynamics simulations of radiation damage in zirconia in the range of 0.1-0.5 MeV energies with account of electronic energy losses. We nd that the lack of amorphizability co-exists with a large number of point defects and their clusters. These, importantly, are largely isolated from each other and therefore represent a dilute damage that does not result in the loss of long-range structural coherence and amorphization. We document the nature of these defects in detail, including their sizes, distribution and morphology, and discuss practical implications of using zirconia in intense radiation environments.
High-energy radiation damage in zirconia: modeling results
Zarkadoula, Eva; Devanathan, Ram; Weber, William J.; Seaton, Michael; Todorov, Ilian; Nordlund, Kai; Dove, Martin T.; Trachenko, Kostya
2014-02-28
Zirconia has been viewed as a material of exceptional resistance to amorphization by radiation damage, and was consequently proposed as a candidate to immobilize nuclear waste and serve as a nuclear fuel matrix. Here, we perform molecular dynamics simulations of radiation damage in zirconia in the range of 0.1-0.5 MeV energies with the account of electronic energy losses. We find that the lack of amorphizability co-exists with a large number of point defects and their clusters. These, importantly, are largely disjoint from each other and therefore represent a dilute damage that does not result in the loss of long-range structural coherence and amorphization. We document the nature of these defects in detail, including their sizes, distribution and morphology, and discuss practical implications of using zirconia in intense radiation environments.
High-energy radiation damage in zirconia: Modeling results
Zarkadoula, E.; Devanathan, R.; Weber, W. J.; Seaton, M. A.; Todorov, I. T.; Nordlund, K.; Dove, M. T.; Trachenko, K.
2014-02-28
Zirconia is viewed as a material of exceptional resistance to amorphization by radiation damage, and consequently proposed as a candidate to immobilize nuclear waste and serve as an inert nuclear fuel matrix. Here, we perform molecular dynamics simulations of radiation damage in zirconia in the range of 0.1–0.5 MeV energies with account of electronic energy losses. We find that the lack of amorphizability co-exists with a large number of point defects and their clusters. These, importantly, are largely isolated from each other and therefore represent a dilute damage that does not result in the loss of long-range structural coherence and amorphization. We document the nature of these defects in detail, including their sizes, distribution, and morphology, and discuss practical implications of using zirconia in intense radiation environments.
Discrete fracture modeling of hydro-mechanical damage processes in geological systems
NASA Astrophysics Data System (ADS)
Kim, K.; Rutqvist, J.; Houseworth, J. E.; Birkholzer, J. T.
2014-12-01
This study presents a modeling approach for investigating coupled thermal-hydrological-mechanical (THM) behavior, including fracture development, within geomaterials and structures. In the model, the coupling procedure consists of an effective linkage between two codes: TOUGH2, a simulator of subsurface multiphase flow and mass transport based on the finite volume approach; and an implementation of the rigid-body-spring network (RBSN) method, a discrete (lattice) modeling approach to represent geomechanical behavior. One main advantage of linking these two codes is that they share the same geometrical mesh structure based on the Voronoi discretization, so that a straightforward representation of discrete fracture networks (DFN) is available for fluid flow processes. The capabilities of the TOUGH-RBSN model are demonstrated through simulations of hydraulic fracturing, where fluid pressure-induced fracturing and damage-assisted flow are well represented. The TOUGH-RBSN modeling methodology has been extended to enable treatment of geomaterials exhibiting anisotropic characteristics. In the RBSN approach, elastic spring coefficients and strength parameters are systematically formulated based on the principal bedding direction, which facilitate a straightforward representation of anisotropy. Uniaxial compression tests are simulated for a transversely isotropic material to validate the new modeling scheme. The model is also used to simulate excavation fracture damage for the HG-A microtunnel in the Opalinus Clay rock, located at the Mont Terri underground research laboratory (URL) near Saint-Ursanne, Switzerland. The Opalinus Clay has transversely isotropic material properties caused by natural features such as bedding, foliation, and flow structures. Preferential fracturing and tunnel breakouts were observed following excavation, which are believed to be strongly influenced by the mechanical anisotropy of the rock material. The simulation results are qualitatively
Chen, Z.; Schreyer, H.L.
1995-09-01
The response of underground structures and transportation facilities under various external loadings and environments is critical for human safety as well as environmental protection. Since quasi-brittle materials such as concrete and rock are commonly used for underground construction, the constitutive modeling of these engineering materials, including post-limit behaviors, is one of the most important aspects in safety assessment. From experimental, theoretical, and computational points of view, this report considers the constitutive modeling of quasi-brittle materials in general and concentrates on concrete in particular. Based on the internal variable theory of thermodynamics, the general formulations of plasticity and damage models are given to simulate two distinct modes of microstructural changes, inelastic flow and degradation of material strength and stiffness, that identify the phenomenological nonlinear behaviors of quasi-brittle materials. The computational aspects of plasticity and damage models are explored with respect to their effects on structural analyses. Specific constitutive models are then developed in a systematic manner according to the degree of completeness. A comprehensive literature survey is made to provide the up-to-date information on prediction of structural failures, which can serve as a reference for future research.
Creep damage in a localized load sharing fibre bundle model with additional ageing
NASA Astrophysics Data System (ADS)
Lennartz-Sassinek, Sabine; Danku, Zsuzsa; Main, Ian; Kun, Ferenc
2013-04-01
Many fields of science are interested in the damage growth in earth materials. Often the damage propagates not in big avalanches like the crack growth measured by acoustic emissions. Also "silent" damage may occur whose emissions are either to small to be detected or mix with back ground noise. These silent emissions may carry the majority of the over all damage in a system until failure. One famous model for damage growth is the fibre bundle model. Here we consider an extended version of a localized load sharing fibre bundle model which incorporates additional time dependent ageing of each fibre motivated by a chemically active environment. We present the non-trivial time dependent damage growth in this model in the low load limit representing creep damage far away from failure. We show both numerical simulations and analytical equations describing the damage rate of silent events and the corresponding amount of triggered "acoustic" damage. The analytical description is in agreement with the numerical results.
Multi-physics modeling of multifunctional composite materials for damage detection
NASA Astrophysics Data System (ADS)
Sujidkul, Thanyawalai
This study presents a modeling of multifunction composite materials for damage detection with its verification and validation to mechanical behavior predictions of Carbon Fibre Reinforced Polymer composites (CFRPs), CFRPs laminated composites, and woven SiC/SiC matrix composites that are subjected to fracture damage. Advantages of those materials are low cost, low density, high strength-to-weight ratio, and comparable specific tensile properties, the special of SiC/SiC is good environmental stability at high temperature. Resulting in, the composite has been used for many important structures such as helicopter rotors, aerojet engines, gas turbines, hot control surfaces, sporting goods, and windmill blades. Damage or material defect detection in a mechanical component can provide vital information for the prediction of remaining useful life, which will result in the prevention of catastrophic failures. Thus the understanding of the mechanical behavior have been challenge to the prevent damage and failure of composites in different scales. The damage detection methods in composites have been investigated widely in recent years. Non-destructive techniques are the traditional methods to detect the damage such as X-ray, acoustic emission and thermography. However, due to the invisible damage in composite can be occurred, to prevent the failure in composites. The developments of damage detection methods have been considered. Due to carbon fibers are conductive materials, in resulting CFRPs can be self-sensing to detect damage. As is well known, the electrical resistance has been shown to be a sensitive measure of internal damage, and also this work study in thermal resistance can detect damage in composites. However, there is a few number of different micromechanical modeling schemes has been proposed in the published literature for various types of composites. This works will provide with a numerical, analytical, and theoretical failure models in different damages to
NASA Astrophysics Data System (ADS)
Wiebe, D. M.; Cox, D. T.; Chen, Y.; Weber, B. A.; Chen, Y.
2012-12-01
Building damage from a hypothetical Cascadia Subduction Zone tsunami was estimated using two methods and applied at the community scale. The first method applies proposed guidelines for a new ASCE 7 standard to calculate the flow depth, flow velocity, and momentum flux from a known runup limit and estimate of the total tsunami energy at the shoreline. This procedure is based on a potential energy budget, uses the energy grade line, and accounts for frictional losses. The second method utilized numerical model results from previous studies to determine maximum flow depth, velocity, and momentum flux throughout the inundation zone. The towns of Seaside and Canon Beach, Oregon, were selected for analysis due to the availability of existing data from previously published works. Fragility curves, based on the hydrodynamic features of the tsunami flow (inundation depth, flow velocity, and momentum flux) and proposed design standards from ASCE 7 were used to estimate the probability of damage to structures located within the inundations zone. The analysis proceeded at the parcel level, using tax-lot data to identify construction type (wood, steel, and reinforced-concrete) and age, which was used as a performance measure when applying the fragility curves and design standards. The overall probability of damage to civil buildings was integrated for comparison between the two methods, and also analyzed spatially for damage patterns, which could be controlled by local bathymetric features. The two methods were compared to assess the sensitivity of the results to the uncertainty in the input hydrodynamic conditions and fragility curves, and the potential advantages of each method discussed. On-going work includes coupling the results of building damage and vulnerability to an economic input output model. This model assesses trade between business sectors located inside and outside the induction zone, and is used to measure the impact to the regional economy. Results highlight
NASA Astrophysics Data System (ADS)
Lu, Xi; Lu, Mingyu; Zhou, Li-Min; Su, Zhongqing; Cheng, Li; Ye, Lin; Meng, Guang
2011-01-01
Welded tubular steel structures (WTSSs) are widely used in various engineering sectors, serving as major frameworks for many mechanical systems. There has been increasing awareness of introducing effective damage identification and up-to-the-minute health surveillance to WTSSs, so as to enhance structural reliability and integrity. In this study, propagation of guided waves (GWs) in a WTSS of rectangular cross-section, a true-scale model of a train bogie frame segment, was investigated using the finite element method (FEM) and experimental analysis with the purpose of evaluating welding damage in the WTSS. An active piezoelectric sensor network was designed and surface-bonded on the WTSS, to activate and collect GWs. Characteristics of GWs at different excitation frequencies were explored. A signal feature, termed 'time of maximal difference' (ToMD) in this study, was extracted from captured GW signals, based on which a concept, damage presence probability (DPP), was established. With ToMD and DPP, a probability-based damage imaging approach was developed. To enhance robustness of the approach to measurement noise and uncertainties, a two-level image fusion scheme was further proposed. As validation, the approach was employed to predict presence and location of slot-like damage in the welding zone of a WTSS. Identification results have demonstrated the effectiveness of the developed approach for identifying damage in WTSSs and its large potential for real-time health monitoring of WTSSs.
A model for predicting damage induced fatigue life of laminated composite structural components
NASA Technical Reports Server (NTRS)
Allen, David H.; Lo, David C.; Georgiou, Ioannis T.; Harris, Charles E.
1990-01-01
This paper presents a model for predicting the life of laminated composite structural components subjected to fatigue induced microstructural damage. The model uses the concept of continuum damage mechanics, wherein the effects of microcracks are incorporated into a damage dependent lamination theory instead of treating each crack as an internal boundary. Internal variables are formulated to account for the effects of both matrix cracks and internal delaminations. Evolution laws for determining the damage variables as functions of ply stresses are proposed, and comparisons of predicted damage evolution are made to experiment. In addition, predicted stiffness losses, as well as ply stresses are shown as functions of damage state for a variety of stacking sequences.
Transgenic Mouse Model for Reducing Oxidative Damage in Bone
NASA Technical Reports Server (NTRS)
Schreurs, A.-S.; Torres, S.; Truong, T.; Kumar, A.; Alwood, J. S.; Limoli, C. L.; Globus, R. K.
2014-01-01
Exposure to musculoskeletal disuse and radiation result in bone loss; we hypothesized that these catabolic treatments cause excess reactive oxygen species (ROS), and thereby alter the tight balance between bone resorption by osteoclasts and bone formation by osteoblasts, culminating in bone loss. To test this, we used transgenic mice which over-express the human gene for catalase, targeted to mitochondria (MCAT). Catalase is an anti-oxidant that converts the ROS hydrogen peroxide into water and oxygen. MCAT mice were shown previously to display reduced mitochondrial oxidative stress and radiosensitivity of the CNS compared to wild type controls (WT). As expected, MCAT mice expressed the transgene in skeletal tissue, and in marrow-derived osteoblasts and osteoclast precursors cultured ex vivo, and also showed greater catalase activity compared to wildtype (WT) mice (3-6 fold). Colony expansion in marrow cells cultured under osteoblastogenic conditions was 2-fold greater in the MCAT mice compared to WT mice, while the extent of mineralization was unaffected. MCAT mice had slightly longer tibiae than WT mice (2%, P less than 0.01), although cortical bone area was slightly lower in MCAT mice than WT mice (10%, p=0.09). To challenge the skeletal system, mice were treated by exposure to combined disuse (2 wk Hindlimb Unloading) and total body irradiation Cs(137) (2 Gy, 0.8 Gy/min), then bone parameters were analyzed by 2-factor ANOVA to detect possible interaction effects. Treatment caused a 2-fold increase (p=0.015) in malondialdehyde levels of bone tissue (ELISA) in WT mice, but had no effect in MCAT mice. These findings indicate that the transgene conferred protection from oxidative damage caused by treatment. Unexpected differences between WT and MCAT mice emerged in skeletal responses to treatment.. In WT mice, treatment did not alter osteoblastogenesis, cortical bone area, moment of inertia, or bone perimeter, whereas in MCAT mice, treatment increased these
Bailey, Aaron D; Zhang, Guiru; Murphy, Bryan P
2014-01-01
The number of Level 3 hair color products that substitute 2-aminoethanol [monoethanolamine (MEA)] for ammonia is increasing. There is some anecdotal evidence that higher levels of MEA can be more damaging to hair and more irritating than a corresponding equivalent level of the typical alkalizer, ammonia (in the form of ammonium hydroxide). Our interest was to understand in more quantitative terms the relative hair damage from the two alkalizers, particularly at the upper limits of MEA on-head use. Limiting investigations of oxidative hair damage to increases in cysteic acid content (from cystine oxidation) can underreport the extent of total damage. Hence, we complemented Fourier transform infrared spectroscopy (FTIR) cysteic acid level measurement with scanning electron microscopy (SEM) photomicrographs to visualize cuticle damage, and protein loss to understand not only the oxidative damage but also the damage caused by other damage pathways, e.g., reaction of the more nucleophilic (than ammonia) MEA with hair protein. In fact, all methods show an increase in damage from MEA-based formulations, up to 85% versus ammonia in the most extreme case. Hence, if the odor of ammonia is a concern, a better approach may be to minimize the volatility of ammonia in specific chassis rather than replacing it with high levels of a potentially more damaging alkalizer such as MEA. PMID:24602818
An Assessment of Radiation Damage Models and Methods
Stoller, Roger E; Mansur, Louis K
2005-05-01
The current state of development of the primary models used for investigating and simulating irradiation effects in structural alloys of interest to the U.S. DOE's Generation-IV reactor program are discussed. The underlying theory that supports model development is also described where appropriate. First, the key processes that underlie radiation-induced changes in material properties are summarized, and the types of radiation effects that subsequently arise are described. Future development work needed in order for theory, modeling, and computational materials science to support and add value to the Gen IV reactor materials program are then outlined. The expected specific outcomes and overall benefits of the required effort are: the knowledge to extrapolate material behavior to conditions for which there are no experimental data; systematic understanding of mechanisms and processes to enable confident interpolation between point-by-point experimental observations; acceleration of the development, selection, and qualification of materials for reactor service; and prediction of material response to real-world operating load histories which often involve a complicated superposition of time, temperature, radiation dose rate, and mechanical loading conditions. Opportunities for international collaboration to accelerate progress in all of the required research areas are briefly discussed, particularly in the context of two well coordinated, broad-based research projects on modeling and simulation of radiation effects on materials that are currently funded in Europe. In addition to providing the opportunity for substantial leveraging of the DOE-funded activities in this area, these projects may serve as models for future development within the Gen-IV program. The larger of these two projects, which involves 12 European research laboratories and 16 universities, is called PERFECT and is funded by the European Union. A smaller effort focusing on developing predictive
Damage detection in rotating machinery by means of entropy-based parameters
NASA Astrophysics Data System (ADS)
Tocarciuc, Alexandru; Bereteu, Liviu; ǎgǎnescu, Gheorghe Eugen, Dr
2014-11-01
The paper is proposing two new entropy-based parameters, namely Renyi Entropy Index (REI) and Sharma-Mittal Entropy Index (SMEI), for detecting the presence of failures (or damages) in rotating machinery, namely: belt structural damage, belt wheels misalignment, failure of the fixing bolt of the machine to its baseplate and eccentricities (i.e.: due to detaching a small piece of material or bad mounting of the rotating components of the machine). The algorithms to obtain the proposed entropy-based parameters are described and test data is used in order to assess their sensitivity. A vibration test bench is used for measuring the levels of vibration while artificially inducing damage. The deviation of the two entropy-based parameters is compared in two states of the vibration test bench: not damaged and damaged. At the end of the study, their sensitivity is compared to Shannon Entropic Index.
Airframe structural damage detection: a non-linear structural surface intensity based technique.
Semperlotti, Fabio; Conlon, Stephen C; Barnard, Andrew R
2011-04-01
The non-linear structural surface intensity (NSSI) based damage detection technique is extended to airframe applications. The selected test structure is an upper cabin airframe section from a UH-60 Blackhawk helicopter (Sikorsky Aircraft, Stratford, CT). Structural damage is simulated through an impact resonator device, designed to simulate the induced vibration effects typical of non-linear behaving damage. An experimental study is conducted to prove the applicability of NSSI on complex mechanical systems as well as to evaluate the minimum sensor and actuator requirements. The NSSI technique is shown to have high damage detection sensitivity, covering an extended substructure with a single sensing location. PMID:21476618
Moore, John R; Watt, Michael S
2015-08-01
Wind is the major abiotic disturbance in New Zealand's planted forests, but little is known about how the risk of wind damage may be affected by future climate change. We linked a mechanistic wind damage model (ForestGALES) to an empirical growth model for radiata pine (Pinus radiata D. Don) and a process-based growth model (cenw) to predict the risk of wind damage under different future emissions scenarios and assumptions about the future wind climate. The cenw model was used to estimate site productivity for constant CO2 concentration at 1990 values and for assumed increases in CO2 concentration from current values to those expected during 2040 and 2090 under the B1 (low), A1B (mid-range) and A2 (high) emission scenarios. Stand development was modelled for different levels of site productivity, contrasting silvicultural regimes and sites across New Zealand. The risk of wind damage was predicted for each regime and emission scenario combination using the ForestGALES model. The sensitivity to changes in the intensity of the future wind climate was also examined. Results showed that increased tree growth rates under the different emissions scenarios had the greatest impact on the risk of wind damage. The increase in risk was greatest for stands growing at high stand density under the A2 emissions scenario with increased CO2 concentration. The increased productivity under this scenario resulted in increased tree height, without a corresponding increase in diameter, leading to more slender trees that were predicted to be at greater risk from wind damage. The risk of wind damage was further increased by the modest increases in the extreme wind climate that are predicted to occur. These results have implications for the development of silvicultural regimes that are resilient to climate change and also indicate that future productivity gains may be offset by greater losses from disturbances. PMID:25703827
Miehe, C; Teichtmeister, S; Aldakheel, F
2016-04-28
This work outlines a novel variational-based theory for the phase-field modelling of ductile fracture in elastic-plastic solids undergoing large strains. The phase-field approach regularizes sharp crack surfaces within a pure continuum setting by a specific gradient damage modelling. It is linked to a formulation of gradient plasticity at finite strains. The framework includes two independent length scales which regularize both the plastic response as well as the crack discontinuities. This ensures that the damage zones of ductile fracture are inside of plastic zones, and guarantees on the computational side a mesh objectivity in post-critical ranges. PMID:27002069
Strain-Based Damage Determination Using Finite Element Analysis for Structural Health Management
NASA Technical Reports Server (NTRS)
Hochhalter, Jacob D.; Krishnamurthy, Thiagaraja; Aguilo, Miguel A.
2016-01-01
A damage determination method is presented that relies on in-service strain sensor measurements. The method employs a gradient-based optimization procedure combined with the finite element method for solution to the forward problem. It is demonstrated that strains, measured at a limited number of sensors, can be used to accurately determine the location, size, and orientation of damage. Numerical examples are presented to demonstrate the general procedure. This work is motivated by the need to provide structural health management systems with a real-time damage characterization. The damage cases investigated herein are characteristic of point-source damage, which can attain critical size during flight. The procedure described can be used to provide prognosis tools with the current damage configuration.
A damage identification technique based on embedded sensitivity analysis and optimization processes
NASA Astrophysics Data System (ADS)
Yang, Chulho; Adams, Douglas E.
2014-07-01
A vibration based structural damage identification method, using embedded sensitivity functions and optimization algorithms, is discussed in this work. The embedded sensitivity technique requires only measured or calculated frequency response functions to obtain the sensitivity of system responses to each component parameter. Therefore, this sensitivity analysis technique can be effectively used for the damage identification process. Optimization techniques are used to minimize the difference between the measured frequency response functions of the damaged structure and those calculated from the baseline system using embedded sensitivity functions. The amount of damage can be quantified directly in engineering units as changes in stiffness, damping, or mass. Various factors in the optimization process and structural dynamics are studied to enhance the performance and robustness of the damage identification process. This study shows that the proposed technique can improve the accuracy of damage identification with less than 2 percent error of estimation.
A FLUORESCENCE BASED ASSAY FOR DNA DAMAGE INDUCED BY STYRENE OXIDE
A rapid and simple assay to detect DNA damage to calf thymus DNA caused by styrene oxide (SO) is reported. This assay is based on changes observed in the melting and annealing behavior of the damaged DNA. The melting annealing process was monitored using a fluorescence indicat...
A FLUORESCENCE BASED ASSAY FOR DNA DAMAGE: INDUCED BY RADIATION, CHEMICALS AND ENZYMES
A simple and rapid assay to detect DNA damage is reported. This assay is based on the ability of certain dyes to fluoresce upon intercalation with dsDNA. Damage caused by ultraviolet (UV) radiation, chemicals or restriction enzymes is detected using this assay. UV radiation at...
A FLUORESCENCE BASED ASSAY FOR DNA DAMAGE INDUCED BY RADIATION, CHEMICAL MUTAGENS AND ENZYMES
A simple and rapid assay to detect DNA damage is reported. This novel assay is based on changes in melting/annealing behavior and facilitated using certain dyes that increase their fluorescence upon association with double stranded (ds)DNA. Damage caused by ultraviolet (UV) ra...
A New In Vitro Model to Study Cellular Responses after Thermomechanical Damage in Monolayer Cultures
Hettler, Alice; Werner, Simon; Eick, Stefan; Laufer, Stefan; Weise, Frank
2013-01-01
Although electrosurgical instruments are widely used in surgery to cut tissue layers or to achieve hemostasis by coagulation (electrocautery), only little information is available concerning the inflammatory or immune response towards the debris generated. Given the elevated local temperatures required for successful electrocautery, the remaining debris is likely to contain a plethora of compounds entirely novel to the intracorporal setting. A very common in vitro method to study cell migration after mechanical damage is the scratch assay, however, there is no established model for thermomechanical damage to characterise cellular reactions. In this study, we established a new in vitro model to investigate exposure to high temperature in a carefully controlled cell culture system. Heatable thermostat-controlled aluminium stamps were developed to induce local damage in primary human umbilical vein endothelial cells (HUVEC). The thermomechanical damage invoked is reproducibly locally confined, therefore allowing studies, under the same experimental conditions, of cells affected to various degrees as well as of unaffected cells. We show that the unaffected cells surrounding the thermomechanical damage zone are able to migrate into the damaged area, resulting in a complete closure of the ‘wound’ within 48 h. Initial studies have shown that there are significant morphological and biological differences in endothelial cells after thermomechanical damage compared to the mechanical damage inflicted by using the unheated stamp as a control. Accordingly, after thermomechanical damage, cell death as well as cell protection programs were activated. Mononuclear cells adhered in the area adjacent to thermomechanical damage, but not to the zone of mechanical damage. Therefore, our model can help to understand the differences in wound healing during the early phase of regeneration after thermomechanical vs. mechanical damage. Furthermore, this model lends itself to study the
Hettler, Alice; Werner, Simon; Eick, Stefan; Laufer, Stefan; Weise, Frank
2013-01-01
Although electrosurgical instruments are widely used in surgery to cut tissue layers or to achieve hemostasis by coagulation (electrocautery), only little information is available concerning the inflammatory or immune response towards the debris generated. Given the elevated local temperatures required for successful electrocautery, the remaining debris is likely to contain a plethora of compounds entirely novel to the intracorporal setting. A very common in vitro method to study cell migration after mechanical damage is the scratch assay, however, there is no established model for thermomechanical damage to characterise cellular reactions. In this study, we established a new in vitro model to investigate exposure to high temperature in a carefully controlled cell culture system. Heatable thermostat-controlled aluminium stamps were developed to induce local damage in primary human umbilical vein endothelial cells (HUVEC). The thermomechanical damage invoked is reproducibly locally confined, therefore allowing studies, under the same experimental conditions, of cells affected to various degrees as well as of unaffected cells. We show that the unaffected cells surrounding the thermomechanical damage zone are able to migrate into the damaged area, resulting in a complete closure of the 'wound' within 48 h. Initial studies have shown that there are significant morphological and biological differences in endothelial cells after thermomechanical damage compared to the mechanical damage inflicted by using the unheated stamp as a control. Accordingly, after thermomechanical damage, cell death as well as cell protection programs were activated. Mononuclear cells adhered in the area adjacent to thermomechanical damage, but not to the zone of mechanical damage. Therefore, our model can help to understand the differences in wound healing during the early phase of regeneration after thermomechanical vs. mechanical damage. Furthermore, this model lends itself to study the
NASA Technical Reports Server (NTRS)
Leser, Patrick E.; Hochhalter, Jacob D.; Newman, John A.; Leser, William P.; Warner, James E.; Wawrzynek, Paul A.; Yuan, Fuh-Gwo
2015-01-01
Utilizing inverse uncertainty quantification techniques, structural health monitoring can be integrated with damage progression models to form probabilistic predictions of a structure's remaining useful life. However, damage evolution in realistic structures is physically complex. Accurately representing this behavior requires high-fidelity models which are typically computationally prohibitive. In the present work, a high-fidelity finite element model is represented by a surrogate model, reducing computation times. The new approach is used with damage diagnosis data to form a probabilistic prediction of remaining useful life for a test specimen under mixed-mode conditions.
Structural kinematics based damage zone prediction in gradient structures using vibration database
NASA Astrophysics Data System (ADS)
Talha, Mohammad; Ashokkumar, Chimpalthradi R.
2014-05-01
To explore the applications of functionally graded materials (FGMs) in dynamic structures, structural kinematics based health monitoring technique becomes an important problem. Depending upon the displacements in three dimensions, the health of the material to withstand dynamic loads is inferred in this paper, which is based on the net compressive and tensile displacements that each structural degree of freedom takes. These net displacements at each finite element node predicts damage zones of the FGM where the material is likely to fail due to a vibration response which is categorized according to loading condition. The damage zone prediction of a dynamically active FGMs plate have been accomplished using Reddy's higher-order theory. The constituent material properties are assumed to vary in the thickness direction according to the power-law behavior. The proposed C0 finite element model (FEM) is applied to get net tensile and compressive displacement distributions across the structures. A plate made of Aluminum/Ziconia is considered to illustrate the concept of structural kinematics-based health monitoring aspects of FGMs.
Ratigan, J.L.; Nieland, J.D.; Devries, K.L.
1998-12-31
Geomechanical analyses were made to determine the minimum gas pressure allowable based on an existing stress-based criterion (Damage Potential) and an advanced constitutive model (MDCF model) capable of quantifying the level of damage and healing in rock salt. The MDCF model is a constitutive model developed for the WIPP to provide a continuum description of the dislocation and damage deformation of salt. The purpose of this study was to determine if the MDCF model is applicable for evaluating the minimum gas pressure of CNG storage caverns. Specifically, it was to be determined if this model would predict that the minimum gas pressure in the caverns could be lowered without compromising the stability of the cavern. Additionally, the healing behavior of the salt was analyzed to determine if complete healing of the damaged rock zone would occur during the period the cavern was at maximum gas pressure. Significant findings of this study are reported.
Cross-country transferability of flood damage models for residential buildings
NASA Astrophysics Data System (ADS)
Kreibich, H.; Neuhold, C.
2012-04-01
The estimation of flood damage is an important component for risk-oriented flood design, risk mapping, financial appraisals and comparative risk analyses. However, existing damage models are hardly validated and inherent to substantial uncertainty. Many damage models are currently transferred in space and time, e.g. from region to region or from one flood event to another. Though, it is still unknown to what extent and under which conditions this transfer is possible and reliable. Model validations in different countries could provide valuable insights into the transferability of damage models. Therefore, the German flood damage model FLEMOps has been applied and validated in Austria and an Austrian flood damage model has been applied and validated in Germany. The Austrian municipality of Gleisdorf and the German city of Eilenburg are analysed as test cases. Flood damage data collected after the flood in 2005 in Tyrol, Austria and Bavaria, Germany are used for validation purposes. Results of model validations and comparisons in both countries as well as model sensitivities with respect to flood and resistance characteristics are discussed.
Damage modeling of small-scale experiments on dental enamel with hierarchical microstructure.
Scheider, I; Xiao, T; Yilmaz, E; Schneider, G A; Huber, N; Bargmann, S
2015-03-01
Dental enamel is a highly anisotropic and heterogeneous material, which exhibits an optimal reliability with respect to the various loads occurring over years. In this work, enamel's microstructure of parallel aligned rods of mineral fibers is modeled and mechanical properties are evaluated in terms of strength and toughness with the help of a multiscale modeling method. The established model is validated by comparing it with the stress-strain curves identified by microcantilever beam experiments extracted from these rods. Moreover, in order to gain further insight in the damage-tolerant behavior of enamel, the size of crystallites below which the structure becomes insensitive to flaws is studied by a microstructural finite element model. The assumption regarding the fiber strength is verified by a numerical study leading to accordance of fiber size and flaw tolerance size, and the debonding strength is estimated by optimizing the failure behavior of the microstructure on the hierarchical level above the individual fibers. Based on these well-grounded properties, the material behavior is predicted well by homogenization of a representative unit cell including damage, taking imperfections (like microcracks in the present case) into account. PMID:25484332
Modelling electron distributions within ESA's Gaia satellite CCD pixels to mitigate radiation damage
NASA Astrophysics Data System (ADS)
Seabroke, G. M.; Holland, A. D.; Burt, D.; Robbins, M. S.
2009-08-01
The Gaia satellite is a high-precision astrometry, photometry and spectroscopic ESA cornerstone mission, currently scheduled for launch in 2012. Its primary science drivers are the composition, formation and evolution of the Galaxy. Gaia will achieve its unprecedented positional accuracy requirements with detailed calibration and correction for radiation damage. At L2, protons cause displacement damage in the silicon of CCDs. The resulting traps capture and emit electrons from passing charge packets in the CCD pixel, distorting the image PSF and biasing its centroid. Microscopic models of Gaia's CCDs are being developed to simulate this effect. The key to calculating the probability of an electron being captured by a trap is the 3D electron density within each CCD pixel. However, this has not been physically modelled for the Gaia CCD pixels. In Seabroke, Holland & Cropper (2008), the first paper of this series, we motivated the need for such specialised 3D device modelling and outlined how its future results will fit into Gaia's overall radiation calibration strategy. In this paper, the second of the series, we present our first results using Silvaco's physics-based, engineering software: the ATLAS device simulation framework. Inputting a doping profile, pixel geometry and materials into ATLAS and comparing the results to other simulations reveals that ATLAS has a free parameter, fixed oxide charge, that needs to be calibrated. ATLAS is successfully benchmarked against other simulations and measurements of a test device, identifying how to use it to model Gaia pixels and highlighting the affect of different doping approximations.
Modeling of damage in ductile cast iron - The effect of including plasticity in the graphite nodules
NASA Astrophysics Data System (ADS)
Andriollo, T.; Thorborg, J.; Tiedje, N. S.; Hattel, J.
2015-06-01
In the present paper a micro-mechanical model for investigating the stress-strain relation of ductile cast iron subjected to simple loading conditions is presented. The model is based on a unit cell containing a single spherical graphite nodule embedded in a uniform ferritic matrix, under the assumption of infinitesimal strains and plane-stress conditions. Despite the latter being a limitation with respect to full 3D models, it allows a direct comparison with experimental investigations of damage evolution on the surface of ductile cast iron components, where the stress state is biaxial in nature. In contrast to previous works on the subject, the material behaviour in both matrix and nodule is assumed to be elasto-plastic, described by the classical J2-flow theory of plasticity, and damage evolution in the matrix is taken into account via Lemaitre's isotropic model. The effects of residual stresses due to the cooling process during manufacturing are also considered. Numerical solutions are obtained using an in-house developed finite element code; proper comparison with literature in the field is given.
Hong, Ming; Su, Zhongqing; Wang, Qiang; Cheng, Li; Qing, Xinlin
2014-03-01
A dedicated modeling technique for comprehending nonlinear characteristics of ultrasonic waves traversing in a fatigued medium was developed, based on a retrofitted constitutive relation of the medium by considering the nonlinearities originated from material, fatigue damage, as well as the "breathing" motion of fatigue cracks. Piezoelectric wafers, for exciting and acquiring ultrasonic waves, were integrated in the model. The extracted nonlinearities were calibrated by virtue of an acoustic nonlinearity parameter. The modeling technique was validated experimentally, and the results showed satisfactory consistency in between, both revealing: the developed modeling approach is able to faithfully simulate fatigue crack-incurred nonlinearities manifested in ultrasonic waves; a cumulative growth of the acoustic nonlinearity parameter with increasing wave propagation distance exists; such a parameter acquired via a sensing path is nonlinearly related to the offset distance from the fatigue crack to that sensing path; and neither the incidence angle of the probing wave nor the length of the sensing path impacts on the parameter significantly. This study has yielded a quantitative characterization strategy for fatigue cracks using embeddable piezoelectric sensor networks, facilitating deployment of structural health monitoring which is capable of identifying small-scale damage at an embryo stage and surveilling its growth continuously. PMID:24156928
NASA Astrophysics Data System (ADS)
Revil-Baudard, Benoit; Cazacu, Oana; Flater, Philip; Chandola, Nitin; Alves, J. L.
2016-03-01
In this paper, we present an experimental study on plastic deformation and damage of polycrystalline pure HCP Ti, as well as modeling of the observed behavior. Mechanical characterization data were conducted, which indicate that the material is orthotropic and displays tension-compression asymmetry. The ex-situ and in-situ X-ray tomography measurements conducted reveal that damage distribution and evolution in this HCP Ti material is markedly different than in a typical FCC material such as copper. Stewart and Cazacu (2011) anisotropic elastic/plastic damage model is used to describe the behavior. All the parameters involved in this model have a clear physical significance, being related to plastic properties, and are determined from very few simple mechanical tests. It is shown that this model predicts correctly the anisotropy in plastic deformation, and its strong influence on damage distribution and damage accumulation. Specifically, for a smooth axisymmetric specimen subject to uniaxial tension, damage initiates at the center of the specimen, and is diffuse; the level of damage close to failure being very low. On the other hand, for a notched specimen subject to the same loading the model predicts that damage initiates at the outer surface of the specimen, and further grows from the outer surface to the center of the specimen, which corroborates with the in-situ tomography data.
Offline and online detection of damage using autoregressive models and artificial neural networks
NASA Astrophysics Data System (ADS)
Omenzetter, Piotr; de Lautour, Oliver R.
2007-04-01
Developed to study long, regularly sampled streams of data, time series analysis methods are being increasingly investigated for the use of Structural Health Monitoring. In this research, Autoregressive (AR) models are used in conjunction with Artificial Neural Networks (ANNs) for damage detection, localisation and severity assessment. In the first reported experimental exercise, AR models were used offline to fit the acceleration time histories of a 3-storey test structure in undamaged and various damaged states when excited by earthquake motion simulated on a shake table. Damage was introduced into the structure by replacing the columns with those of a thinner thickness. Analytical models of the structure in both damaged and undamaged states were also developed and updated using experimental data in order to determine structural stiffness. The coefficients of AR models were used as damage sensitive features and input into an ANN to build a relationship between them and the remaining structural stiffness. In the second, analytical exercise, a system with gradually progressing damage was numerically simulated and acceleration AR models with exogenous inputs were identified recursively. A trained ANN was then required to trace the structural stiffness online. The results for the offline and online approach showed the efficiency of using AR coefficient as damage sensitive features and good performance of the ANNs for damage detection, localization and quantification.
NASA Astrophysics Data System (ADS)
Wang, Yanfeng; Liang, Ming; Xiang, Jiawei
2014-10-01
Blades are among the key components of wind turbines. Blade damage is one of the most common types of structural defects and can cause catastrophic structural failure. Therefore, it is highly desirable to detect and diagnose blade damage as early as possible. In this paper, we propose a method for blade damage detection and diagnosis. This method incorporates finite element method (FEM) for dynamics analysis (modal analysis and response analysis) and the mode shape difference curvature (MSDC) information for damage detection/diagnosis. Finite element models of wind turbine blades have been built and modified via frequency comparison with experimental data and the formula for the model updating technique. Our numerical simulation results have demonstrated that the proposed technique can detect the spatial locations of damages for wind turbine blades. Changes in natural frequencies and modes for smaller size blades with damage are found to occur at lower frequencies and lower modes than in the larger sized blade case. The relationship between modal parameters and damage information (location, size) is very complicated especially for larger size blades. Moreover, structure and dynamic characters for larger size blades are different from those for smaller sized blades. Therefore, dynamic response analysis for a larger sized wind turbine blade with a multi-layer composite material based on aerodynamic loads’ (including lift forces and drag forces) calculation has been carried out and improved the efficiency and precision to damage detection by combining (MSDC) information. This method provides a low cost and efficient non-destructive tool for wind turbine blade condition monitoring.
Physical modeling of animal cell damage by hydrodynamic forces in suspension cultures.
Lu, G Z; Gray, M R; Thompson, B G
1992-12-01
Physical damage of animal cells in suspension culture, due to stirring and sparging, is coupled with complex metabolic responses. Nylon microcapsules, therefore, were used as a physical model to study the mechanisms of damage in a stirred bioreactor and in a bubble column. Microcapsule breaskage folowed first-order kinetices in all experiments Entrainment of bubbles into the liquid phase in the stirred bioreactor gave more microcapsule breakage. In the bubble column, the bubble bursting zone at gas-liquid interface was primarily responsible for microcapsule breakage. The forces on the microcapsules were equivalent to an external pressure of approximately 4 x 10(4) N. m(-2), based on the critical microcapsule diameter for survival of 190 microm. A stable foam layer, however, was found to be effective in protecting microcapsules from damage. The microcapsule transport to the gas-liquid interface and entrainment into the foam phase was consistent with flotation by air bubbles. This result implies that additives and operation of bioreactors should be selected to minimize flotation of cells. PMID:18601080
1995-12-31
The Stand-Damage Model (a component of the Gypsy Moth Life System Model) simulates the growth of a mixed hardwood forest and incorporates the effects of defoliation by gypsy moth or tree harvesting as prescribed by the user. It can be used to assess the damage from expected defoliation, view the differences between various degrees of defoliation, and describe the effects of defoliation on a standard under user-defined silvicultural prescriptions and defoliation scenarios. The user`s guide provides the information necessary to install and use the model software on DOS microcomputers. A reference section provides a more experienced user with a structure map of the system.
Damage mechanics in engineering materials
Voyiadjis, G.Z.; Woody Ju, J.W.; Chaboche, J.L.
1998-12-31
This book contains thirty peer-reviewed papers that are based on the presentations made at the symposium on Damage Mechanics in Engineering Materials on the occasion of the Joint ASME/ASCE/SES Mechanics Conference (McNU97), held in Evanston, Illinois, June 28--July 2, 1997. The key area of discussion was on the constitutive modeling of damage mechanics in engineering materials encompassing the following topics: macromechanics/micromechanical constitutive modeling, experimental procedures, numerical modeling, inelastic behavior, interfaces, damage, fracture, failure, computational methods. The book is divided into six parts: study of damage mechanics; localization and damage; damage in brittle materials; damage in metals and metal matrix composites; computational aspects of damage models; damage in polymers and elastomers.
Burnett, G.C.
2000-04-28
Until recently, attempts to update Finite Element Models (FEM) of large structures based upon recording structural motions were mostly ad hoc, requiring a large amount of engineering experience and skill. Studies have been undertaken at LLNL to use state-space based signal processing techniques to locate the existence and type of model mismatches common in FEM. Two different methods (Gauss-Newton gradient search and extended Kalman filter) have been explored, and the progress made in each type of algorithm as well as the results from several simulated and one actual building model will be discussed. The algorithms will be examined in detail, and the computer programs written to implement the algorithms will be documented.
DAMAGE MODELING OF INJECTION-MOLDED SHORT- AND LONG-FIBER THERMOPLASTICS
Nguyen, Ba Nghiep; Kunc, Vlastimil; Bapanapalli, Satish K.; Phelps, Jay; Tucker III, Charles L.
2009-10-30
This article applies the recent anisotropic rotary diffusion – reduced strain closure (ARD-RSC) model for predicting fiber orientation and a new damage model for injection-molded long-fiber thermoplastics (LFTs) to analyze progressive damage leading to total failure of injection-molded long-glass-fiber/polypropylene (PP) specimens. The ARD-RSC model was implemented in a research version of the Autodesk Moldflow Plastics Insight (MPI) processing code, and it has been used to simulate injection-molding of a long-glass-fiber/PP plaque. The damage model combines micromechanical modeling with a continuum damage mechanics description to predict the nonlinear behavior due to plasticity coupled with damage in LFTs. This model has been implemented in the ABAQUS finite element code via user-subroutines and has been used in the damage analyses of tensile specimens removed from the injection-molded long-glass-fiber/PP plaques. Experimental characterization and mechanical testing were performed to provide input data to support and validate both process modeling and damage analyses. The predictions are in agreement with the experimental results.
NASA Astrophysics Data System (ADS)
Lee, Keejoo
2005-11-01
A damage model for ceramic materials is developed and incorporated into the geometrically nonlinear solid shell element formulation for dynamic analyses of multi-layered ceramic armor panels under blast wave pressure loading. The damage model takes into account material behaviors observed from multi-axial dynamic tests on Aluminum Nitride (AlN) ceramic. The ceramic fails in a brittle or gradual fashion, depending upon the hydrostatic pressure and applied strain-rate. In the model, the gradual failure is represented by two states: the initial and final failure states. These states are described by two separate failure surfaces that are pressure-dependent and strain-rate-dependent. A scalar damage parameter is defined via using the two failure surfaces, based on the assumption that the local stress state determines material damage and its level. In addition, the damage model accounts for the effect of existing material damage on the new damage. The multi-layered armor panel of interest is comprised of an AlN-core sandwich with unidirectional composite skins and a woven composite back-plate. To accommodate the material damage effect of composite layers, a composite failure model in the open literature is adopted and modified into two separate failure models to address different failure mechanisms of the unidirectional and woven composites. In addition, the effect of strain-rates on the material strengths is incorporated into the composite failure models. For finite element modeling, multiple eighteen-node elements are used in the thickness direction to properly describe mechanics of the multi-layered panel. Dynamic analyses of a multi-layered armor panel are conducted under blast wave pressure loadings. The resulting dynamic responses of the panel demonstrate that dynamic analyses that do not take into account material damage and failure significantly under-predict the peak displacement. The under-prediction becomes more pronounced as the blast load level increases
NASA Astrophysics Data System (ADS)
Gaitan, Santiago; ten Veldhuis, Marie-Claire; van de Giesen, Nick
2013-04-01
Extreme weather events such as floods and storms are expected to cause severe economic losses in The Netherlands. Cumulative damage due to pluvial flooding can be considerable, especially in lowland areas where this type of floods occurs relatively frequently. Currently, in The Netherlands, water-related damages to property and contents are covered through private insurance. As pluvial flooding is becoming heavier and more likely to occur, sound modelling of damages is required to ensure that insurance systems are able to stand as an adaptation measure. Current damage models based on rainfall intensity, registries of insurance claims, and classifications of building types are unable to fully explain damage variability. Further developments assessing additional explanatory factors and reducing uncertainties, are required in order to significantly explain damage. In this study, urban topography is used as an explanatory factor for modelling of urban pluvial flooding. Flood damage is evaluated based on complaints data, a valuable resource for assessing vulnerability to urban pluvial flooding. Though previous research has shown coincidences between the localization of high complaint counts and large size catchments areas in Rotterdam, additional research is needed to establish the precise spatial relationship of those two variables. This additional task is the focus of the presented work. To that end a data base of complaints, that was made available by the Municipality Administration of the City, will be analysed. It comprises close to 36800 complaints from 2004 to 2011. The geographical position of the registries is aggregated into 4 to 6-digit Postal Code zones, which represents entire streets or relative positions along a street, respectively. The Municipality also provided the DEM, characterized by a spatial resolution of 0.5 m × 0.5 m, a vertical precision of 5 cm, and an accuracy better than two standard deviations of 15 cm. First the localization of complaints
Application of a damage model for rock fragmentation to the Straight Creek Mine blast experiments
Thorne, B.J.
1991-09-01
Early attempts at estimation of stress wave damage due to blasting by use of finite element calculations met with limited success due to numerical instabilities that prevented calculations from being carried past the fragmentation limit. More recently, the improved damage model PRONTO has allowed finite element calculations which remain stable and yield good agreement between calculated fragmented regions and excavated crater profiles for blasting experiments in granite. Application of this damage model to blast experiments at the Straight Creek Mine in Bell County, Kentucky were complicated by anisotropic conditions and uncertainties in material properties. It appears that significant modifications to the damage model and extensive material testing may be necessary in order to estimate damage in these anisotropic materials. 18 refs., 18 figs.
Indentation experiments and simulation of ovine bone using a viscoelastic-plastic damage model
Zhao, Yang; Wu, Ziheng; Turner, Simon; MacLeay, Jennifer; Niebur, Glen L.; Ovaert, Timothy C.
2015-01-01
Indentation methods have been widely used to study bone at the micro- and nanoscales. It has been shown that bone exhibits viscoelastic behavior with permanent deformation during indentation. At the same time, damage due to microcracks is induced due to the stresses beneath the indenter tip. In this work, a simplified viscoelastic-plastic damage model was developed to more closely simulate indentation creep data, and the effect of the model parameters on the indentation curve was investigated. Experimentally, baseline and 2-year postovariectomized (OVX-2) ovine (sheep) bone samples were prepared and indented. The damage model was then applied via finite element analysis to simulate the bone indentation data. The mechanical properties of yielding, viscosity, and damage parameter were obtained from the simulations. The results suggest that damage develops more quickly for OVX-2 samples under the same indentation load conditions as the baseline data. PMID:26136623
Schmidt, Thomas; Balzani, Daniel
2016-05-01
In this paper, a three-dimensional relaxed incremental variational damage model is proposed, which enables the description of complex softening hysteresis as observed in supra-physiologically loaded arterial tissues, and which thereby avoids a loss of convexity of the underlying formulation. The proposed model extends the relaxed formulation of Balzani and Ortiz [2012. Relaxed incremental variational formulation for damage at large strains with application to fiber-reinforced materials and materials with truss-like microstructures. Int. J. Numer. Methods Eng. 92, 551-570], such that the typical stress-hysteresis observed in arterial tissues under cyclic loading can be described. This is mainly achieved by constructing a modified one-dimensional model accounting for cyclic loading in the individual fiber direction and numerically homogenizing the response taking into account a fiber orientation distribution function. A new solution strategy for the identification of the convexified stress potential is proposed based on an evolutionary algorithm which leads to an improved robustness compared to solely Newton-based optimization schemes. In order to enable an efficient adjustment of the new model to experimentally observed softening hysteresis, an adjustment scheme using a surrogate model is proposed. Therewith, the relaxed formulation is adjusted to experimental data in the supra-physiological domain of the media and adventitia of a human carotid artery. The performance of the model is then demonstrated in a finite element example of an overstretched artery. Although here three-dimensional thick-walled atherosclerotic arteries are considered, it is emphasized that the formulation can also directly be applied to thin-walled simulations of arteries using shell elements or other fiber-reinforced biomembranes. PMID:26341795
NASA Astrophysics Data System (ADS)
Vanli, O. Arda; Jung, Sungmoon
2014-01-01
Health monitoring of large structures with embedded, distributed sensor systems is gaining importance. This study proposes a new probabilistic model updating method in order to improve the damage prediction capability of a finite element analysis (FEA) model with experimental observations from a Lamb-wave sensing system. The approach statistically calibrates unknown parameters of the FEA model and estimates a bias-correcting function to achieve a good match between the model predictions and sensor observations. An experimental validation study is presented in which a set of controlled damages are generated on a composite panel. Time-series signals are collected with the damage condition using a Lamb-wave sensing system and a one dimensional FEA model of the panel is constructed to quantify the damages. The damage indices from both the experiments and the computational model are used to calibrate assumed parameters of the FEA model and to estimate a bias-correction function. The updated model is used to predict the size (extent) and location of damage. It is shown that the proposed model updating approach achieves a prediction accuracy that is superior to a purely statistical approach or a deterministic model calibration approach.
Validating finite element models of composite aerospace structures for damage detection applications
NASA Astrophysics Data System (ADS)
Oliver, J. A.; Kosmatka, J. B.; Hemez, François M.; Farrar, Charles R.
2006-03-01
Carbon-fiber-reinforced-polymer (CFRP) composites represent the future for advanced lightweight aerospace structures. However, reliable and cost-effective techniques for structural health monitoring (SHM) are needed. Modal and vibration-based analysis, when combined with validated finite element (FE) models, can provide a key tool for SHM. Finite element models, however, can easily give spurious and misleading results if not finely tuned and validated. These problems are amplified in complex structures with numerous joints and interfaces. A small series of all-composite test pieces emulating wings from a lightweight all-composite Unmanned Aerial Vehicle (UAV) have been developed to support damage detection and SHM research. Each wing comprises two CFRP prepreg and Nomex honeycomb co-cured skins and two CFRP prepreg spars bonded together in a secondary process using a structural adhesive to form the complete wings. The first of the set is fully healthy while the rest have damage in the form of disbonds built into the main spar-skin bondline. Detailed FE models were created of the four structural components and the assembled structure. Each wing component piece was subjected to modal characterization via vibration testing using a shaker and scanning laser Doppler vibrometer before assembly. These results were then used to correlate the FE model on a component-basis, through fitting and optimization of polynomial meta-models. Assembling and testing the full wing provided subsequent data that was used to validate the numerical model of the entire structure, assembled from the correlated component models. The correlation process led to the following average percent improvement between experimental and FE frequencies of the first 20 modes for each piece: top skin 10.98%, bottom skin 45.62%, main spar 25.56%, aft spar 10.79%. The assembled wing model with no further correlation showed an improvement of 32.60%.
Some remarks on a model for rate-independent damage in thermo-visco-elastodynamics
NASA Astrophysics Data System (ADS)
Lazzaroni, Giuliano; Rossi, Riccarda; Thomas, Marita; Toader, Rodica
2016-06-01
This note deals with the analysis of a model for partial damage, where the rate- independent, unidirectional flow rule for the damage variable is coupled with the rate-dependent heat equation, and with the momentum balance featuring inertia and viscosity according to Kelvin-Voigt rheology. The results presented here combine the approach from Roubicek [1, 2] with the methods from Lazzaroni/Rossi/Thomas/Toader [3]. The present analysis encompasses, differently from [2], the monotonicity in time of damage and the dependence of the viscous tensor on damage and temperature, and, unlike [3], a nonconstant heat capacity and a time-dependent Dirichlet loading.
Testing and numerical modeling of hypervelocity impact damaged Space Station multilayer insulation
NASA Technical Reports Server (NTRS)
Rule, William K.
1992-01-01
Results are presented of experiments measuring the degradation of the insulating capabilities of the multilayer insulation (MLI) of the Space Station Freedom, when subjected to hypervelocity impact damage. A simple numerical model was developed for use in an engineering design environment for quick assessment of thermal effect of the impact. The model was validated using results from thermal vacuum tests on MLI with simulated damage. The numerical model results agreed with experimental data.
L.H. Toburen, Principal Investigator; J.L. Shinpaugh; M. Dingfelder; and G. Lapicki; Co-Investigators
2007-01-07
Modern tools of radiobiology are leading to many new discoveries regarding how cells and tissues respond to radiation exposure. We can now irradiate single cells and observe responses in adjacent cells. We can also measure clusters of radiation damage produced in DNA. Our primary objective has been to understand the underling physics associated with these new biological responses. The primary tools available to describe the initial spatial pattern of damage formed by the absorption of ionizing radiation are based on Monte Carlo simulation of the structure of charged particle tracks. Although many Monte Carlo codes exist and considerable progress is being made in the incorporation of detailed macromolecular target structures into these codes, much of the interaction physics is still based on gas phase measurements and/or untested theoretical calculations that focus on water as the transport medium. Our objectives were threefold, (1) to expand the applicability of Monte Carlo track structure simulation to tissue-like material beyond the current focus on water, (2) to incorporate the most recent experimental information on electron interactions in biologically relevant material, and (3) to compare recent measurements of electron emissions induced by charged particles in thin foils with Monte Carlo predictions. We addressed these research objectives in three ways. First we applied theoretical techniques, similar to those used to derive data for water, to obtain cross sections for other condensed phase materials. This served two purposes. One was to provide testability of the theoretical technique by comparison to existing experimental data for electron transport (similar data does not exist for water), and the other was to expand the target database for use in modeling tissue. Second, we carefully reviewed published data, and ongoing experiments, for electron interaction cross-sections in biologically relevant condensed phase material. Results for low-energy electron
Prediction Of Formability In Sheet Metal Forming Processes Using A Local Damage Model
Teixeira, P.; Santos, Abel; Cesar Sa, J.; Andrade Pires, F.; Barata da Rocha, A.
2007-05-17
The formability in sheet metal forming processes is mainly conditioned by ductile fracture resulting from geometric instabilities due to necking and strain localization. The macroscopic collapse associated with ductile failure is a result of internal degradation described throughout metallographic observations by the nucleation, growth and coalescence of voids and micro-cracks. Damage influences and is influenced by plastic deformation and therefore these two dissipative phenomena should be coupled at the constitutive level. In this contribution, Lemaitre's ductile damage model is coupled with Hill's orthotropic plasticity criterion. The coupling between damaging and material behavior is accounted for within the framework of Continuum Damage Mechanics (CDM). The resulting constitutive equations are implemented in the Abaqus/Explicit code, for the prediction of fracture onset in sheet metal forming processes. The damage evolution law takes into account the important effect of micro-crack closure, which dramatically decreases the rate of damage growth under compressive paths.
Modeling crater formation in femtosecond-pulse laser damage from basic principles.
Mitchell, Robert A; Schumacher, Douglass W; Chowdhury, Enam A
2015-05-15
We present the first fundamental simulation method for the determination of crater morphology due to femtosecond-pulse laser damage. To this end we have adapted the particle-in-cell (PIC) method commonly used in plasma physics for use in the study of laser damage and developed the first implementation of a pair potential for PIC codes. We find that the PIC method is a complementary approach to modeling laser damage, bridging the gap between fully ab-initio molecular dynamics approaches and empirical models. We demonstrate our method by modeling a femtosecond-pulse laser incident on a flat copper slab for a range of intensities. PMID:26393696
Assessment of crop damage and hail risk based on radar hail signature information
NASA Astrophysics Data System (ADS)
Tani, Satyanarayana; Paulitsch, Helmut; Teschl, Reinhard; Süsser-Rechberger, Barbara
2016-04-01
Hail storm damage is a major concern to the farmers in the province of Styria, Austria. Each year severe hail storms are causing damages to crops, resulting in losses of millions of euros. High spatiotemporal resolution data are essential to properly assess crop damage information for the insurance sector and also for the better risk assessment. Radar data offer high spatial and temporal resolutions, resulting in very promising option for crop damage assessment and hail risk analysis. This study focuses on the combined analysis of hail signature information from radar and ground measurements for crop hail damage assessment. The days with the high crop hail damage claims were selected for the investigation. Total 16 hail days were assigned to examine the relation between radar-derived products and damages produced by hail in Styria during 2015. 3D single polarization C-band weather radar data and radiosonde freezing level data were used to derive hail kinetic energy flux as well as flux integrated over the whole event. Hail events from ESWD (European Severe Weather Database) and crop damage reports from the Austrian Hail Insurance System were allotted for validation. The spatial distribution maps of total hail kinetic energy were developed to capture the swath and intensity of the hail storms to identify potential hail damage areas. The results show that in most cases radar-based hail signature information well corresponds to the areas where hail events and damage footprints were reported. The radar-based hail signature information is a useful detection option for the assessment of crop damage and hail risk.
Smart aggregate based damage detection of circular RC columns under cyclic combined loading
NASA Astrophysics Data System (ADS)
Moslehy, Yashar; Gu, Haichang; Belarbi, Abdeldjelil; Mo, Y. L.; Song, Gangbing
2010-06-01
Structural health monitoring is an important issue for the maintenance of large-scale civil infrastructures, especially for bridge columns. In this paper, an innovative piezoceramic-based approach is developed for the structural health monitoring of reinforced concrete columns. An innovative piezoceramic-based device, the smart aggregate, is utilized as a transducer for the purpose of health monitoring. To investigate the seismic behavior of reinforced concrete (RC) bridge columns, structural health monitoring tests were performed on two bridge columns under combined reversed cyclic loading at the Missouri University of Science and Technology. The proposed smart aggregate based approach successfully evaluated the health status of concrete columns during the loading procedure. Sensor energy plots and 3D normalized sensor energy plots demonstrated that the damage inside attenuated the transmitted energy. The wavelet packet based damage index and sensor history damage index evaluate the damage development in concrete columns under cyclic loading.
Modeling of thermal wave propagation in damaged composites with internal source
NASA Astrophysics Data System (ADS)
Ciampa, Francesco; Angioni, Stefano L.; Pinto, Fulvio; Scarselli, Gennaro; Almond, Darrel P.; Meo, Michele
2015-04-01
SMArt Thermography exploits the electrothermal properties of multifunctional smart structures, which are created by embedding shape memory alloy (SMA) wires in traditional carbon fibre reinforced composite laminates (known as SMArt composites), in order to detect the structural flaws using an embedded source. Such a system enables a built-in, fast, cost-effective and in-depth assessment of the structural damage as it overcomes the limitations of standard thermography techniques. However, a theoretical background of the thermal wave propagation behaviour, especially in the presence of internal structural defects, is needed to better interpret the observations/data acquired during the experiments and to optimise those critical parameters such as the mechanical and thermal properties of the composite laminate, the depth of the SMA wires and the intensity of the excitation energy. This information is essential to enhance the sensitivity of the system, thus to evaluate the integrity of the medium with different types of damage. For this purpose, this paper aims at developing an analytical model for SMArt composites, which is able to predict the temperature contrast on the surface of the laminate in the presence of in-plane internal damage (delamination-like) using pulsed thermography. Such a model, based on the Green's function formalism for one-dimensional heat equation, takes into account the thermal lateral diffusion around the defect and it can be used to compute the defect depth within the laminate. The results showed good agreement between the analytical model and the measured thermal waves using an infrared (IR) camera. Particularly, the contrast temperature curves were found to change significantly depending on the defect opening.
Modelling long term damage in rock slopes and impact of deglaciation
NASA Astrophysics Data System (ADS)
Amitrano, D.; Lacroix, P.
2014-12-01
Long-term observations of large active rockslides show accelerating deformation over many thousands of years since the last deglaciation. The effect of deglaciation on slope stability is however poorly understood due to (1) limited long-term observations and (2) a complex interaction between glacier retreat and hydrogeological, mechanical, and morphological processes. To assess the sensitivity of rockslide dynamics to these different processes, a model of progressive damage through intact rock mass is developed in this study, based on the finite element method. This model uses time-to-failure laws based on rock laboratory creep experiments. It is able to reproduce progressive damage localization along shear bands associated with strain rate acceleration as observed during tertiary creep. The model reproduces the different phases of deformation associated with morphologies typical of large rockslides. This model is thus suitable for simulating the dynamics of large rockslides and the transition from initiation to rapid sliding. The sensitivity of rockslide kinematics and morphology to different mechanical properties is analyzed. This analysis shows that the time evolution of the rockslide can be inferred with the knowledge of only one time parameter, independent of the knowledge of the mechanical properties of the rock mass. This parameter is here chosen as the time when the summit slope displacement has reached 10 m, a parameter that can be estimated with cosmogenic dating. The model is then used to study the effects of deglaciation on the valley flank stability and the formation of large rockslides. This study shows that the deglaciation velocity can affect the morphology of the rockslide, with the shear band of the rockslide emerging at higher elevation as the velocity decreases.We also show that the response to the deglaciation can last several thousands of years after the glacier retreat.
The study of target damage assessment system based on image change detection
NASA Astrophysics Data System (ADS)
Zhao, Ping; Yang, Fan; Feng, Xinxi
2009-10-01
Target Damage Assessment (TDA) system is an important component of the intelligent command and control system. The method of building TDA based on Image Change Detection can greatly improve the system efficiency and accuracy, thus get a fast and precise assessment results. This paper firstly analyzes the structure of TDA system. Then studies the key technology in this system. Finally, gives an evaluation criteria based on image change detection of the target damage assessment system.
Modeling continuous-fiber reinforced polymer composites for exploration of damage tolerant concepts
NASA Astrophysics Data System (ADS)
Matthews, Peter J.
This work aims to improve the predictive capability for fiber-reinforced polymer matrix composite laminates using the finite element method. A new tool for modeling composite damage was developed which considers important modes of failure. Well-known micromechanical models were implemented to predict material values for material systems of interest to aerospace applications. These generated material values served as input to intralaminar and interlaminar damage models. A three-dimensional in-plane damage material model was implemented and behavior verified. Deficiencies in current state-of-the-art interlaminar capabilities were explored using the virtual crack closure technique and the cohesive zone model. A user-defined cohesive element was implemented to discover the importance of traction-separation material constitutive behavior. A novel method for correlation of traction-separation parameters was created. This new damage modeling tool was used for evaluation of novel material systems to improve damage tolerance. Classical laminate plate theory was used in a full-factorial study of layerwise-hybrid laminates. Filament-wound laminated composite cylindrical shells were subjected to quasi-static loading to validate the finite element computational composite damage model. The new tool for modeling provides sufficient accuracy and generality for use on a wide-range of problems.
An Elastic-Plastic Damage Model for Long-Fiber Thermoplastics
Nguyen, Ba Nghiep; Kunc, Vlastimil
2009-08-11
This article proposes an elastic-plastic damage model that combines micromechanical modeling with continuum damage mechanics to predict the stress-strain response of injection-molded long-fiber thermoplastics. The model accounts for distributions of orientation and length of elastic fibers embedded in a thermoplastic matrix whose behavior is elastic-plastic and damageable. The elastic-plastic damage behavior of the matrix is described by the modified Ramberg-Osgood relation and the three-dimensional damage model in deformation assuming isotropic hardening. Fiber/matrix debonding is accounted for using a parameter that governs the fiber/matrix interface compliance. A linear relationship between this parameter and the matrix damage variable is assumed. First, the elastic-plastic damage behavior of the reference aligned-fiber composite containing the same fiber volume fraction and length distribution as the actual composite is computed using an incremental Eshelby-Mori-Tanaka mean field approach. The incremental response of the latter is then obtained from the solution for the aligned-fiber composite by averaging over all fiber orientations. The model is validated against the experimental stress-strain results obtained for long-glass-fiber/polypropylene specimens.
A simple 2-D inundation model for incorporating flood damage in urban drainage planning
NASA Astrophysics Data System (ADS)
Pathirana, A.; Tsegaye, S.; Gersonius, B.; Vairavamoorthy, K.
2008-11-01
In this paper a new inundation model code is developed and coupled with Storm Water Management Model, SWMM, to relate spatial information associated with urban drainage systems as criteria for planning of storm water drainage networks. The prime objective is to achive a model code that is simple and fast enough to be consistently be used in planning stages of urban drainage projects. The formulation for the two-dimensional (2-D) surface flow model algorithms is based on the Navier Stokes equation in two dimensions. An Alternating Direction Implicit (ADI) finite difference numerical scheme is applied to solve the governing equations. This numerical scheme is used to express the partial differential equations with time steps split into two halves. The model algorithm is written using C++ computer programming language. This 2-D surface flow model is then coupled with SWMM for simulation of both pipe flow component and surcharge induced inundation in urban areas. In addition, a damage calculation block is integrated within the inundation model code. The coupled model is shown to be capable of dealing with various flow conditions, as well as being able to simulate wetting and drying processes that will occur as the flood flows over an urban area. It has been applied under idealized and semi-hypothetical cases to determine detailed inundation zones, depths and velocities due to surcharged water on overland surface.
Wilkins, M.L.; Streit, R.D.; Reaugh, J.E.
1980-10-03
A cumulative-strain-damage criterion is used to predict the initiation and propagation of fracture in ductile materials. The model is consistent with a model of ductile rupture that involves void growth and coalescence. Two- and three-dimensional finite difference computer codes, which use incremental-plasticity theory to describe large strains with rotation, are used to trace the history of damage in a material due to external forces. Fracture begins when the damage exceeds a critical value over a critical distance and proceeds as the critical-damage state is reached elsewhere. This unified approach to failure prediction can be applied to an arbitrary geometry if the material behavior has been adequately characterized. The damage function must be calibrated for a particular material using various material property tests. The fracture toughness of 6061-T651 aluminum is predicted.
Brain damage in a new hemorrhagic shock model in the rat using long-term recovery
Yamauchi, Y.; Kato, H.; Kogure, K. )
1990-03-01
A new shock model in the rat using hemorrhagic hypotension for production of brain damage is described. Hemorrhagic shock was induced by lowering arterial blood pressure with bleeding. The MABP was maintained at approximately 25 mm Hg, accompanied by isoelectric EEG, and then shed blood was retransfused. At 1 week of recovery, morphological and 45Ca autoradiographic changes were examined. No brain damage was observed in rats after 1 min of isoelectric EEG. Mild neuronal damage in the hippocampal CA1 subfield was seen in some animals after 2 min of isoelectric EEG. Severe and consistent neuronal loss in the hippocampal CA1 subfield was recognized after 3 min of isoelectric EEG. Additional damage was also seen in the dentate hilus and the thalamus in some animals. This model can be used to study the pathophysiology of postshock brain damage and to assess new therapies following shock.
NASA Astrophysics Data System (ADS)
Eriguchi, Koji
2014-10-01
An increasing demand for high performance field-effect transistors (FETs) leads to the aggressive critical dimension shrinkage and the currently-emerging three dimensional (3D) geometry. Plasma processing is widely used also in the scaled- and 3D-FET (e.g. FinFET) manufacturing, where precise control of the reaction on the (sidewall) surfaces is a prime issue. In this study, damage creation mechanism during plasma etching--plasma-induced physical damage (PPD)--was investigated in such structures on the basis of the PPD range theory, atomistic simulations, and experiments. Compared to PPD in planar FETs (e.g. Si recess [2,3]), a stochastic modeling and atomistic simulations predicted that, during etching of ``fins'' in a 3D-FET, the following two mechanisms are responsible for damage creation in addition to an ion impact on the sidewall at an oblique incident angle: 1) incoming ions penetrate into the Si substrate and undergo scattering by Si atoms in the lateral direction even if the incident angle is normal to the surface and 2) some of Si atoms and ions sputtered at the surface being etched impact on the sidewall with energies sufficient to break Si-Si bonds. These straggling and sputtering processes are stochastic and fundamental, thus, result in 3D structure damage (``fin-damage''). The ``fin-damage'' induced by straggling was modeled by the PPD range theory. Molecular dynamics simulations clarified the mechanisms under the various plasma conditions. Quantum mechanical calculations showed that created defect structures play the role of a carrier trap site, which was experimentally verified by an electrical measurement. Since they are intrinsic natures of etching, both straggling and sputtering noted here should be implemented to design a low-damage etching process. This work was supported in part by Grant-in-Aid for Scientific Research (B) 23360321 from JSPS and STARC project.
Stereology-based fabric analysis of microcracks in damaged granite
NASA Astrophysics Data System (ADS)
Takemura, Takato; Oda, Masanobu
2004-08-01
Crack-related fabric analyses were carried out in terms of crack tensors using Inada granite deformed inelastically in a triaxial vessel up to post-failure, focusing on the fabric changes during brittle failure. Complementarily, numerical simulation tests were conducted to determine the representative volume element (RVE) required for crack surveying. Numerical simulation tests show that the window size for crack surveying should be at least six times the mean trace length in order to obtain a statistically meaningful crack tensor. A larger window is needed to estimate the distribution of crack radii. In quartz, cracks grow preferentially parallel to the major loading axis. Crack tensors in quartz can provide a measure of damage reflecting inelastic deformation under differential stress in past geological events. During the first stage of inelastic deformation, the number density of cracks decreases with a rather sharp increase in crack diameters. This happens because pre-existing cracks in intact rock join together to make longer cracks. However, the density remains almost constant during the second stage of loading from 90% to 100% of the peak stress. The crack diameter gradually increases due to the stable propagation of cracks. When granite is further deformed beyond the peak stress, the number density decreases again while sharp increases in crack diameters appear as a result of the forking and coalescence of cracks. It is also suggested that load-normal grain boundary cracks are generated as a result of the rolling and sliding of disintegrated blocks in the post-failure stage.
The use of strain gauges in vibration-based damage detection
NASA Astrophysics Data System (ADS)
Marques dos Santos, Fabio Luis; Peeters, Bart; Lau, Jenny; Desmet, Wim; Sandoval Goes, Luiz Carlos
2015-07-01
Strain gauges and strain measurements have been widely used in structural health monitoring (SHM) systems as a means of detecting and localizing damage, due to their higher sensitivity to local damage. These damage identification techniques normally use strain related measurements such as the mode curvature, strain frequency response function or strain energy as the main parameter to detect damage. However, damage detection techniques based on acceleration measurements have also been investigated in the past, using modal parameter comparison and other methodologies. In this paper, the use of vibration-based strain measurements for use in SHM systems will be evaluated, with the purpose of characterizing their higher sensitivity in damage detection, when compared to other vibration measurements, such as acceleration-based measurements. Since the choice and use of the most damage sensitive parameter can lead to a more sensitive and robust system, the assessment of the more suitable sensor and processing of information is very important. For this purpose, numerical and experimental examples will be discussed to evaluate the higher performance of the strain gauges.
NASA Astrophysics Data System (ADS)
Sabuncu, A.; Uca Avci, Z. D.; Sunar, F.
2016-06-01
Earthquakes are the most destructive natural disasters, which result in massive loss of life, infrastructure damages and financial losses. Earthquake-induced building damage detection is a very important step after earthquakes since earthquake-induced building damage is one of the most critical threats to cities and countries in terms of the area of damage, rate of collapsed buildings, the damage grade near the epicenters and also building damage types for all constructions. Van-Ercis (Turkey) earthquake (Mw= 7.1) was occurred on October 23th, 2011; at 10:41 UTC (13:41 local time) centered at 38.75 N 43.36 E that places the epicenter about 30 kilometers northern part of the city of Van. It is recorded that, 604 people died and approximately 4000 buildings collapsed or seriously damaged by the earthquake. In this study, high-resolution satellite images of Van-Ercis, acquired by Quickbird-2 (Digital Globe Inc.) after the earthquake, were used to detect the debris areas using an object-based image classification. Two different land surfaces, having homogeneous and heterogeneous land covers, were selected as case study areas. As a first step of the object-based image processing, segmentation was applied with a convenient scale parameter and homogeneity criterion parameters. As a next step, condition based classification was used. In the final step of this preliminary study, outputs were compared with streetview/ortophotos for the verification and evaluation of the classification accuracy.
Dislocation dynamics modelling of radiation damage in thin films
NASA Astrophysics Data System (ADS)
Ferroni, Francesco; Tarleton, Edmund; Fitzgerald, Steven
2014-06-01
Transmission electron microscopy is a key tool for the extraction of information on radiation damage, the understanding of which is critical for materials development for nuclear fusion and fission reactors. Dislocations in TEM samples are subject to strong image forces, owing to the nanometric sample thicknesses, which may introduce artifacts in the damage analysis. Using dislocation dynamics, we elucidate the roles played by dislocation-surface interactions, dislocation-dislocation interactions and self-interactions due to climb for loop types observed in TEM. Comparisons with analytic solutions for a dislocation loop and an edge dislocation in a half-space are included, and the relationship between glide force and loop tilt examined. The parameters for convergence of the zero-traction boundary conditions are obtained, after which the evolution of dislocation structures in a thin film is studied. It is found that three main length scales govern the physical processes: the image force is governed by the distance of the loop from the surface and scales with the film thickness; the glide force is governed by the image stress as well as the loop-loop interaction stress which is in turn governed by the loop spacing L\\sim 1/\\sqrt{\\rho} , where ρ is the loop density; finally, the climb force depends on the loop size. The three forces compete and their relative magnitudes define the evolution pathway of the dislocation structure.
Furda, Amy; Santos, Janine H.; Meyer, Joel N.; Van Houten, Bennett
2015-01-01
In this chapter, we describe a gene-specific quantitative PCR (QPCR)-based assay for the measurement of DNA damage, using amplification of long DNA targets. This assay has been used extensively to measure the integrity of both nuclear and mitochondrial genomes exposed to different genotoxins and has proven to be particularly valuable in identifying reactive oxygen species-mediated mitochondrial DNA damage. QPCR can be used to quantify both the formation of DNA damage as well as the kinetics of damage removal. One of the main strengths of the assay is that it permits monitoring the integrity of mtDNA directly from total cellular DNA without the need for isolating mitochondria or a separate step of mitochondrial DNA purification. Here we discuss advantages and limitations of using QPCR to assay DNA damage in mammalian cells. In addition, we give a detailed protocol of the QPCR assay that helps facilitate its successful deployment in any molecular biology laboratory. PMID:24623245
Structural damage identification based on change in geometric modal strain energy–eigenvalue ratio
NASA Astrophysics Data System (ADS)
Nguyen, Khac-Duy; Chan, Tommy HT; Thambiratnam, David P.
2016-07-01
This study presents a new damage identification method to locate and quantify damage using measured mode shapes and natural frequencies. A new vibration parameter, ratio of geometric modal strain energy to eigenvalue (GMSEE), has been developed and its change due to stiffness reduction has been formulated using a sensitivity matrix. This sensitivity matrix is estimated with measured modal parameters and basic information of the structure. For damage identification, firstly, the locations of damage and the correlative damage extents are identified by maximizing the correlation level between an analytical GMSEE change vector and a measured one. Herein, the genetic algorithm, which is a powerful evolutionary optimization algorithm, is utilized to solve this optimization problem. Secondly, the size of damage can be estimated using the proposed GMSEE technique and compared with a conventional technique using frequency change. A numerical 2D Truss bridge is used to demonstrate the performance of the proposed method in identifying single and multiple damage cases. Also, practicality of the method is tested with a laboratory eight degree-of-freedom system and a real bridge. Results illustrate the high capability of the method to identify structural damage with less modeling efforts.
Warnecke, Lisa; Turner, James M; Bollinger, Trent K; Misra, Vikram; Cryan, Paul M; Blehert, David S; Wibbelt, Gudrun; Willis, Craig K R
2013-08-23
White-nose syndrome is devastating North American bat populations but we lack basic information on disease mechanisms. Altered blood physiology owing to epidermal invasion by the fungal pathogen Geomyces destructans (Gd) has been hypothesized as a cause of disrupted torpor patterns of affected hibernating bats, leading to mortality. Here, we present data on blood electrolyte concentration, haematology and acid-base balance of hibernating little brown bats, Myotis lucifugus, following experimental inoculation with Gd. Compared with controls, infected bats showed electrolyte depletion (i.e. lower plasma sodium), changes in haematology (i.e. increased haematocrit and decreased glucose) and disrupted acid-base balance (i.e. lower CO2 partial pressure and bicarbonate). These findings indicate hypotonic dehydration, hypovolaemia and metabolic acidosis. We propose a mechanistic model linking tissue damage to altered homeostasis and morbidity/mortality. PMID:23720520
Pathophysiology of white-nose syndrome in bats: a mechanistic model linking wing damage to mortality
Warnecke, Lisa; Turner, James M.; Bollinger, Trent K.; Misra, Vikram; Cryan, Paul M.; Blehert, David S.; Wibbelt, Gudrun; Willis, Craig K.R.
2013-01-01
White-nose syndrome is devastating North American bat populations but we lack basic information on disease mechanisms. Altered blood physiology owing to epidermal invasion by the fungal pathogen Geomyces destructans (Gd) has been hypothesized as a cause of disrupted torpor patterns of affected hibernating bats, leading to mortality. Here, we present data on blood electrolyte concentration, haematology and acid–base balance of hibernating little brown bats, Myotis lucifugus, following experimental inoculation with Gd. Compared with controls, infected bats showed electrolyte depletion (i.e. lower plasma sodium), changes in haematology (i.e. increased haematocrit and decreased glucose) and disrupted acid–base balance (i.e. lower CO2 partial pressure and bicarbonate). These findings indicate hypotonic dehydration, hypovolaemia and metabolic acidosis. We propose a mechanistic model linking tissue damage to altered homeostasis and morbidity/mortality.
NASA Astrophysics Data System (ADS)
Bech, Joan; Gayà, Miquel; Aran, Montserrat; Figuerola, Francesc; Amaro, Jéssica; Arús, Joan
This paper deals with the application of a methodology to characterize tornado damage in forests based on a simple two dimensional stationary tornado vortex to describe the surface wind field. The basic vortex model is built over the traditional approach of a combined Rankine velocity profile with radial and azimuthal components plus a constant translational field. Several additions are considered such as producing theoretical swath patterns including absolute velocity values (to compare more easily with Fujita damage rating) or using radar data to estimate the translational speed of the vortex. The methodology is demonstrated with the Castellcir tornado that took place in Catalonia (NE Spain) on the 18th October 2006. The site survey indicated a 4 km path and 260 m maximum width as well as F2 damage. Further analysis suggests the existence of three stages in the tornado life cycle: 1) an organising stage with predominantly inflow pattern; 2) a mature stage with predominant tangential circulation of the vortex and maximum damage and width path -possibly influenced by the complex topography of the terrain-, and 3) a dissipating stage showing weakening and narrowing of the damage path but no outflow patterns. The methodology also helped to confirm the tornadic character of the damage discarding possible microbursts in some parts of the area surveyed.
NASA Technical Reports Server (NTRS)
Ponomarev, A. L.; Huff, J. L.; Cucinotta, F. A.
2011-01-01
Future long-tem space travel will face challenges from radiation concerns as the space environment poses health risk to humans in space from radiations with high biological efficiency and adverse post-flight long-term effects. Solar particles events may dramatically affect the crew performance, while Galactic Cosmic Rays will induce a chronic exposure to high-linear-energy-transfer (LET) particles. These types of radiation, not present on the ground level, can increase the probability of a fatal cancer later in astronaut life. No feasible shielding is possible from radiation in space, especially for the heavy ion component, as suggested solutions will require a dramatic increase in the mass of the mission. Our research group focuses on fundamental research and strategic analysis leading to better shielding design and to better understanding of the biological mechanisms of radiation damage. We present our recent effort to model DNA damage and tissue damage using computational models based on the physics of heavy ion radiation, DNA structure and DNA damage and repair in human cells. Our particular area of expertise include the clustered DNA damage from high-LET radiation, the visualization of DSBs (DNA double strand breaks) via DNA damage foci, image analysis and the statistics of the foci for different experimental situations, chromosomal aberration formation through DSB misrepair, the kinetics of DSB repair leading to a model-derived spectrum of chromosomal aberrations, and, finally, the simulation of human tissue and the pattern of apoptotic cell damage. This compendium of theoretical and experimental data sheds light on the complex nature of radiation interacting with human DNA, cells and tissues, which can lead to mutagenesis and carcinogenesis later in human life after the space mission.
NASA Technical Reports Server (NTRS)
Pineda, Evan Jorge; Waas, Anthony M.
2013-01-01
A thermodynamically-based work potential theory for modeling progressive damage and failure in fiber-reinforced laminates is presented. The current, multiple-internal state variable (ISV) formulation, referred to as enhanced Schapery theory (EST), utilizes separate ISVs for modeling the effects of damage and failure. Consistent characteristic lengths are introduced into the formulation to govern the evolution of the failure ISVs. Using the stationarity of the total work potential with respect to each ISV, a set of thermodynamically consistent evolution equations for the ISVs are derived. The theory is implemented into a commercial finite element code. The model is verified against experimental results from two laminated, T800/3900-2 panels containing a central notch and different fiber-orientation stacking sequences. Global load versus displacement, global load versus local strain gage data, and macroscopic failure paths obtained from the models are compared against the experimental results.
Multiscale Model Predicts Tissue-Level Failure From Collagen Fiber-Level Damage
Hadi, Mohammad F.; Sander, Edward A.; Barocas, Victor H.
2013-01-01
Excessive tissue-level forces communicated to the microstructure and extracellular matrix of soft tissues can lead to damage and failure through poorly understood physical processes that are multiscale in nature. In this work, we propose a multiscale mechanical model for the failure of collagenous soft tissues that incorporates spatial heterogeneity in the microstructure and links the failure of discrete collagen fibers to the material response of the tissue. The model, which is based on experimental failure data derived from different collagen gel geometries, was able to predict the mechanical response and failure of type I collagen gels, and it demonstrated that a fiber-based rule (at the micrometer scale) for discrete failure can strongly shape the macroscale failure response of the gel (at the millimeter scale). The model may be a useful tool in predicting the macroscale failure conditions for soft tissues and engineered tissue analogs. In addition, the multiscale model provides a framework for the study of failure in complex fiber-based mechanical systems in general. PMID:22938372
Empirical modeling of the cross section of damage formation in ion implanted III-V semiconductors
Wendler, E.; Wendler, L.
2012-05-07
In this letter, the cross section of damage formation per individual ion is measured for III-V compound semiconductors ion implanted at 15 K, applying Rutherford backscattering spectrometry. An empirical model is proposed that explains the measured cross sections in terms of quantities representing the primary energies deposited in the displacement of lattice atoms and in electronic interactions. The resulting formula allows the prediction of damage formation for low temperatures and low ion fluences in these materials and can be taken as a starting point for further quantitative modeling of damage formation including secondary effects such as temperature and ion flux.
Acousto-ultrasonics-based fatigue damage characterization: Linear versus nonlinear signal features
NASA Astrophysics Data System (ADS)
Su, Zhongqing; Zhou, Chao; Hong, Ming; Cheng, Li; Wang, Qiang; Qing, Xinlin
2014-03-01
Engineering structures are prone to fatigue damage over service lifespan, entailing early detection and continuous monitoring of the fatigue damage from its initiation through growth. A hybrid approach for characterizing fatigue damage was developed, using two genres of damage indices constructed based on the linear and the nonlinear features of acousto-ultrasonic waves. The feasibility, precision and practicability of using linear and nonlinear signal features, for quantitatively evaluating multiple barely visible fatigue cracks in a metallic structure, was compared. Miniaturized piezoelectric elements were networked to actively generate and acquire acousto-ultrasonic waves. The active sensing, in conjunction with a diagnostic imaging algorithm, enabled quantitative evaluation of fatigue damage and facilitated embeddable health monitoring. Results unveiled that the nonlinear features of acousto-ultrasonic waves outperform their linear counterparts in terms of the detectability. Despite the deficiency in perceiving small-scale damage and the possibility of conveying false alarms, linear features show advantages in noise tolerance and therefore superior practicability. The comparison has consequently motivated an amalgamation of linear and nonlinear features of acousto-ultrasonic waves, targeting the prediction of multi-scale damage ranging from microscopic fatigue cracks to macroscopic gross damage.
Comparison of Model Calculations of Biological Damage from Exposure to Heavy Ions with Measurements
NASA Technical Reports Server (NTRS)
Kim, Myung-Hee Y.; Hada, Megumi; Cucinotta, Francis A.; Wu, Honglu
2014-01-01
The space environment consists of a varying field of radiation particles including high-energy ions, with spacecraft shielding material providing the major protection to astronauts from harmful exposure. Unlike low-LET gamma or X rays, the presence of shielding does not always reduce the radiation risks for energetic charged-particle exposure. Dose delivered by the charged particle increases sharply at the Bragg peak. However, the Bragg curve does not necessarily represent the biological damage along the particle path since biological effects are influenced by the track structures of both primary and secondary particles. Therefore, the ''biological Bragg curve'' is dependent on the energy and the type of the primary particle and may vary for different biological end points. Measurements of the induction of micronuclei (MN) have made across the Bragg curve in human fibroblasts exposed to energetic silicon and iron ions in vitro at two different energies, 300 MeV/nucleon and 1 GeV/nucleon. Although the data did not reveal an increased yield of MN at the location of the Bragg peak, the increased inhibition of cell progression, which is related to cell death, was found at the Bragg peak location. These results are compared to the calculations of biological damage using a stochastic Monte-Carlo track structure model, Galactic Cosmic Ray Event-based Risk Model (GERM) code (Cucinotta, et al., 2011). The GERM code estimates the basic physical properties along the passage of heavy ions in tissue and shielding materials, by which the experimental set-up can be interpreted. The code can also be used to describe the biophysical events of interest in radiobiology, cancer therapy, and space exploration. The calculation has shown that the severely damaged cells at the Bragg peak are more likely to go through reproductive death, the so called "overkill".
Validation of formability of laminated sheet metal for deep drawing process using GTN damage model
NASA Astrophysics Data System (ADS)
Lim, Yongbin; Cha, Wan-gi; Ko, Sangjin; Kim, Naksoo
2013-12-01
In this study, we studied formability of PET/PVC laminated sheet metal which named VCM (Vinyl Coated Metal). VCM offers various patterns and good-looking metal steel used for appliances such as refrigerator and washing machine. But, this sheet has problems which are crack and peeling of film when the material is formed by deep drawing process. To predict the problems, we used finite element method and GTN (Gurson-Tvergaard-Needleman) damage model to represent damage of material. We divided the VCM into 3 layers (PET film, adhesive and steel added PVC) in finite element analysis model to express the crack and peeling phenomenon. The material properties of each layer are determined by reverse engineering based on tensile test result. Furthermore, we performed the simple rectangular deep drawing and simulated it. The simulation result shows good agreement with drawing experiment result in position, punch stroke of crack occurrence. Also, we studied the fracture mechanism of PET film on VCM by comparing the width direction strain of metal and PET film.
Validation of formability of laminated sheet metal for deep drawing process using GTN damage model
Lim, Yongbin; Cha, Wan-gi; Kim, Naksoo; Ko, Sangjin
2013-12-16
In this study, we studied formability of PET/PVC laminated sheet metal which named VCM (Vinyl Coated Metal). VCM offers various patterns and good-looking metal steel used for appliances such as refrigerator and washing machine. But, this sheet has problems which are crack and peeling of film when the material is formed by deep drawing process. To predict the problems, we used finite element method and GTN (Gurson-Tvergaard-Needleman) damage model to represent damage of material. We divided the VCM into 3 layers (PET film, adhesive and steel added PVC) in finite element analysis model to express the crack and peeling phenomenon. The material properties of each layer are determined by reverse engineering based on tensile test result. Furthermore, we performed the simple rectangular deep drawing and simulated it. The simulation result shows good agreement with drawing experiment result in position, punch stroke of crack occurrence. Also, we studied the fracture mechanism of PET film on VCM by comparing the width direction strain of metal and PET film.
NASA Technical Reports Server (NTRS)
Sinha, Neeraj; Brinckman, Kevin; Jansen, Bernard; Seiner, John
2011-01-01
A method was developed of obtaining propulsive base flow data in both hot and cold jet environments, at Mach numbers and altitude of relevance to NASA launcher designs. The base flow data was used to perform computational fluid dynamics (CFD) turbulence model assessments of base flow predictive capabilities in order to provide increased confidence in base thermal and pressure load predictions obtained from computational modeling efforts. Predictive CFD analyses were used in the design of the experiments, available propulsive models were used to reduce program costs and increase success, and a wind tunnel facility was used. The data obtained allowed assessment of CFD/turbulence models in a complex flow environment, working within a building-block procedure to validation, where cold, non-reacting test data was first used for validation, followed by more complex reacting base flow validation.
Vogel, Nicolas; Belisle, Rebecca A.; Hatton, Benjamin; Wong, Tak-Sing; Aizenberg, Joanna
2013-07-31
A transparent coating that repels a wide variety of liquids, prevents staining, is capable of self-repair and is robust towards mechanical damage can have a broad technological impact, from solar cell coatings to self-cleaning optical devices. Here we employ colloidal templating to design transparent, nanoporous surface structures. A lubricant can be firmly locked into the structures and, owing to its fluidic nature, forms a defect-free, self-healing interface that eliminates the pinning of a second liquid applied to its surface, leading to efficient liquid repellency, prevention of adsorption of liquid-borne contaminants, and reduction of ice adhesion strength. We further show howmore » this method can be applied to locally pattern the repellent character of the substrate, thus opening opportunities to spatially confine any simple or complex fluids. The coating is highly defect-tolerant due to its interconnected, honeycomb wall structure, and repellency prevails after the application of strong shear forces and mechanical damage. The regularity of the coating allows us to understand and predict the stability or failure of repellency as a function of lubricant layer thickness and defect distribution based on a simple geometric model.« less
Vogel, Nicolas; Belisle, Rebecca A.; Hatton, Benjamin; Wong, Tak-Sing; Aizenberg, Joanna
2013-07-31
A transparent coating that repels a wide variety of liquids, prevents staining, is capable of self-repair and is robust towards mechanical damage can have a broad technological impact, from solar cell coatings to self-cleaning optical devices. Here we employ colloidal templating to design transparent, nanoporous surface structures. A lubricant can be firmly locked into the structures and, owing to its fluidic nature, forms a defect-free, self-healing interface that eliminates the pinning of a second liquid applied to its surface, leading to efficient liquid repellency, prevention of adsorption of liquid-borne contaminants, and reduction of ice adhesion strength. We further show how this method can be applied to locally pattern the repellent character of the substrate, thus opening opportunities to spatially confine any simple or complex fluids. The coating is highly defect-tolerant due to its interconnected, honeycomb wall structure, and repellency prevails after the application of strong shear forces and mechanical damage. The regularity of the coating allows us to understand and predict the stability or failure of repellency as a function of lubricant layer thickness and defect distribution based on a simple geometric model.
Vogel, Nicolas; Belisle, Rebecca A; Hatton, Benjamin; Wong, Tak-Sing; Aizenberg, Joanna
2013-01-01
A transparent coating that repels a wide variety of liquids, prevents staining, is capable of self-repair and is robust towards mechanical damage can have a broad technological impact, from solar cell coatings to self-cleaning optical devices. Here we employ colloidal templating to design transparent, nanoporous surface structures. A lubricant can be firmly locked into the structures and, owing to its fluidic nature, forms a defect-free, self-healing interface that eliminates the pinning of a second liquid applied to its surface, leading to efficient liquid repellency, prevention of adsorption of liquid-borne contaminants, and reduction of ice adhesion strength. We further show how this method can be applied to locally pattern the repellent character of the substrate, thus opening opportunities to spatially confine any simple or complex fluids. The coating is highly defect-tolerant due to its interconnected, honeycomb wall structure, and repellency prevails after the application of strong shear forces and mechanical damage. The regularity of the coating allows us to understand and predict the stability or failure of repellency as a function of lubricant layer thickness and defect distribution based on a simple geometric model. PMID:23900310
A coupled mechanical and chemical damage model for concrete affected by alkali–silica reaction
Pignatelli, Rossella; Comi, Claudia; Monteiro, Paulo J.M.
2013-11-15
To model the complex degradation phenomena occurring in concrete affected by alkali–silica reaction (ASR), we formulate a poro-mechanical model with two isotropic internal variables: the chemical and the mechanical damage. The chemical damage, related to the evolution of the reaction, is caused by the pressure generated by the expanding ASR gel on the solid concrete skeleton. The mechanical damage describes the strength and stiffness degradation induced by the external loads. As suggested by experimental results, degradation due to ASR is considered to be localized around reactive sites. The effect of the degree of saturation and of the temperature on the reaction development is also modeled. The chemical damage evolution is calibrated using the value of the gel pressure estimated by applying the electrical diffuse double-layer theory to experimental values of the surface charge density in ASR gel specimens reported in the literature. The chemo-damage model is first validated by simulating expansion tests on reactive specimens and beams; the coupled chemo-mechanical damage model is then employed to simulate compression and flexure tests results also taken from the literature. -- Highlights: •Concrete degradation due to ASR in variable environmental conditions is modeled. •Two isotropic internal variables – chemical and mechanical damage – are introduced. •The value of the swelling pressure is estimated by the diffuse double layer theory. •A simplified scheme is proposed to relate macro- and microscopic properties. •The chemo-mechanical damage model is validated by simulating tests in literature.
A new conceptual model for damage zone evolution with fault growth
NASA Astrophysics Data System (ADS)
de Joussineau, G.; Aydin, A.
2006-12-01
Faults may either impede or enhance fluid flow in the subsurface, which is relevant to a number of economic issues (hydrocarbon migration and entrapment, formation and distribution of mineral deposits) and environmental problems (movement of contaminants). Fault zones typically comprise a low-permeability core made up of intensely deformed fault rock and a high-permeability damage zone defined by fault-related fractures. The geometry, petrophysical properties and continuity of both the fault core and the damage zone have an important influence on the mechanical properties of the fault systems and on subsurface fluid flow. Information about fault components from remote seismic methods is limited and is available only for large faults (slip larger than 20-100m). It is therefore essential to characterize faults and associated damage zones in field analogues, and to develop conceptual models of how faults and related structures form and evolve. Here we present such an attempt to better understand the evolution of fault damage zones in the Jurassic Aztec Sandstone of the Valley of Fire State Park (SE Nevada). We document the formation and evolution of the damage zone associated with strike-slip faults through detailed field studies of faults of increasing slip magnitudes. The faults initiate as sheared joints with discontinuous pockets of damage zone located at fault tips and fault surface irregularities. With increasing slip (slip >5m), the damage zone becomes longer and wider by progressive fracture infilling, and is organized into two distinct components with different geometrical and statistical characteristics. The first component of the damage zone is the inner damage zone, directly flanking the fault core, with a relatively high fracture frequency and a thickness that scales with the amount of fault slip. Parts of this inner zone are integrated into the fault core by the development of the fault rock, contributing to the core's progressive widening. The second
Predictive modeling techniques for nanosecond-laser damage growth in fused silica optics.
Liao, Zhi M; Abdulla, Ghaleb M; Negres, Raluca A; Cross, David A; Carr, Christopher W
2012-07-01
Empirical numerical descriptions of the growth of laser-induced damage have been previously developed. In this work, Monte-Carlo techniques use these descriptions to model the evolution of a population of damage sites. The accuracy of the model is compared against laser damage growth observations. In addition, a machine learning (classification) technique independently predicts site evolution from patterns extracted directly from the data. The results show that both the Monte-Carlo simulation and machine learning classification algorithm can accurately reproduce the growth of a population of damage sites for at least 10 shots, which is extremely valuable for modeling optics lifetime in operating high-energy laser systems. Furthermore, we have also found that machine learning can be used as an important tool to explore and increase our understanding of the growth process. PMID:22772252
A micro to macro approach to polymer matrix composites damage modeling : final LDRD report.
English, Shawn Allen; Brown, Arthur A.; Briggs, Timothy M.
2013-12-01
Capabilities are developed, verified and validated to generate constitutive responses using material and geometric measurements with representative volume elements (RVE). The geometrically accurate RVEs are used for determining elastic properties and damage initiation and propagation analysis. Finite element modeling of the meso-structure over the distribution of characterizing measurements is automated and various boundary conditions are applied. Plain and harness weave composites are investigated. Continuum yarn damage, softening behavior and an elastic-plastic matrix are combined with known materials and geometries in order to estimate the macroscopic response as characterized by a set of orthotropic material parameters. Damage mechanics and coupling effects are investigated and macroscopic material models are demonstrated and discussed. Prediction of the elastic, damage, and failure behavior of woven composites will aid in macroscopic constitutive characterization for modeling and optimizing advanced composite systems.
Multiscale Modeling of Damage Processes in Aluminum Alloys: Grain-Scale Mechanisms
NASA Technical Reports Server (NTRS)
Hochhalter, J. D.; Veilleux, M. G.; Bozek, J. E.; Glaessgen, E. H.; Ingraffea, A. R.
2008-01-01
This paper has two goals related to the development of a physically-grounded methodology for modeling the initial stages of fatigue crack growth in an aluminum alloy. The aluminum alloy, AA 7075-T651, is susceptible to fatigue cracking that nucleates from cracked second phase iron-bearing particles. Thus, the first goal of the paper is to validate an existing framework for the prediction of the conditions under which the particles crack. The observed statistics of particle cracking (defined as incubation for this alloy) must be accurately predicted to simulate the stochastic nature of microstructurally small fatigue crack (MSFC) formation. Also, only by simulating incubation of damage in a statistically accurate manner can subsequent stages of crack growth be accurately predicted. To maintain fidelity and computational efficiency, a filtering procedure was developed to eliminate particles that were unlikely to crack. The particle filter considers the distributions of particle sizes and shapes, grain texture, and the configuration of the surrounding grains. This filter helps substantially reduce the number of particles that need to be included in the microstructural models and forms the basis of the future work on the subsequent stages of MSFC, crack nucleation and microstructurally small crack propagation. A physics-based approach to simulating fracture should ultimately begin at nanometer length scale, in which atomistic simulation is used to predict the fundamental damage mechanisms of MSFC. These mechanisms include dislocation formation and interaction, interstitial void formation, and atomic diffusion. However, atomistic simulations quickly become computationally intractable as the system size increases, especially when directly linking to the already large microstructural models. Therefore, the second goal of this paper is to propose a method that will incorporate atomistic simulation and small-scale experimental characterization into the existing multiscale
A multi-stage approach for damage detection in structural systems based on flexibility
NASA Astrophysics Data System (ADS)
Grande, E.; Imbimbo, M.
2016-08-01
The paper proposes a fusion approach for damage detection in structural applications in the case of multiple damage locations and three-dimensional systems. Based on the Dempster-Shafer evidence theory, a multi-stage approach is proposed with the mode shapes assumed as primary sources and local decisions based on a flexibility method. The proposed approach has been applied to two case studies, a a fixed end beam analyzed in other papers and a three dimensional structures codified in a Benchmark problem. Both the case studies have shown the ability and the efficiency of the proposed approach to detect damage also in the case of multiple damage, limited number of identified parameters and noise measurements.
Experimental verification and comparison of mode shape-based damage detection methods
NASA Astrophysics Data System (ADS)
Radzieński, M.; Krawczuk, M.
2009-08-01
This paper presents experimental verification and comparison of damage detection methods based on changes in mode shapes such as: mode shape curvature (MSC), modal assurance criterion (MAC), strain energy (SE), modified Laplacian operator (MLO), generalized fractal dimension (GFD) and Wavelet Transform (WT). The object of the investigation is to determine benefits and drawbacks of the aforementioned methods and to develop data preprocessing algorithms for increasing damage assessment effectiveness by using signal processing techniques such as interpolation and extrapolation of measured points. Noise reduction algorithms based on moving average, median filter, and wavelet decomposition are also tested. The experiments were performed on an aluminium plate with riveted stiffeners. Damage was introduced in a form of damaged rivets and a saw cut in the angle bar. Measurements were made using a non-contact Scanning Laser Doppler Vibrometer (SLDV) at 101 points in two rows, distributed over the structure height and positioned along two reinforcing ribs.
A Dynamic Damage Mechanics Source Model for Explosions in Crystalline Rock
NASA Astrophysics Data System (ADS)
Mihaly, J. M.; Bhat, H. S.; Sammis, C. G.; Rosakis, A.
2011-12-01
The micromechanical damage mechanics formulated by Ashby and Sammis [PAGEOPH, 1990] and generalized by Deshpande and Evans [J. Mech. Phys. Solids, 2008] has been extended to allow for a more generalized stress state and to incorporate an experimentally motivated crack growth (damage evolution) law that is valid over a wide range of loading rates. This law is sensitive to both the crack tip stress field and its time derivative, and thus produces strain-rate sensitivity in the constitutive response. The model is experimentally verified by predicting the failure strength of Dionysus-Pentelicon marble over strain rates ranging from to . This rate-dependent damage mechanics has been implemented in the ABAQUS dynamic finite element code and used to explore the effects of burn rate (loading rate) and lithostatic stress on the spatial extent of fracture damage and S waves generated by explosions in crystalline rock. Slower rise times and longer pressure pulses produce more damage and stronger S waves.
NASA Astrophysics Data System (ADS)
Zhu, Cheng; Pouya, Ahmad; Arson, Chloé
2015-11-01
This paper aims to gain fundamental understanding of the microscopic mechanisms that control the transition between secondary and tertiary creep around salt caverns in typical geological storage conditions. We use a self-consistent inclusion-matrix model to homogenize the viscoplastic deformation of halite polycrystals and predict the number of broken grains in a Representative Elementary Volume of salt. We use this micro-macro modeling framework to simulate creep tests under various axial stresses, which gives us the critical viscoplastic strain at which grain breakage (i.e., tertiary creep) is expected to occur. The comparison of simulation results for short-term and long-term creep indicates that the initiation of tertiary creep depends on the stress and the viscoplastic strain. We use the critical viscoplastic deformation as a yield criterion to control the transition between secondary and tertiary creep in a phenomenological viscoplastic model, which we implement into the Finite Element Method program POROFIS. We model a 850-m-deep salt cavern of irregular shape, in axis-symmetric conditions. Simulations of cavern depressurization indicate that a strain-dependent damage evolution law is more suitable than a stress-dependent damage evolution law, because it avoids high damage concentrations and allows capturing the formation of a damaged zone around the cavity. The modeling framework explained in this paper is expected to provide new insights to link grain breakage to phenomenological damage variables used in Continuum Damage Mechanics.
Doebling, S.W.
1996-04-01
A new optimal update method for the correlation of dynamic structural finite element models with modal data is presented. The method computes a minimum-rank solution for the perturbations of the elemental stiffness parameters while constraining the connectivity of the global stiffness matrix. The resulting model contains a more accurate representation of the dynamics of the test structure. The changes between the original model and the updated model can be interpreted as modeling errors or as changes in the structure resulting from damage. The motivation for the method is presented in the context of existing optimal matrix update procedures. The method is demonstrated numerically on a spring-mass system and is also applied to experimental data from the NASA Langley 8-bay truss damage detection experiment. The results demonstrate that the proposed procedure may be useful for updating elemental stiffness parameters in the context of damage detection and model refinement.
NASA Astrophysics Data System (ADS)
Burkett, Michael W.; Clancy, Sean P.; Maudlin, Paul J.; Holian, Kathleen S.
2004-07-01
Previously developed constitutive models and solution algorithms for continuum-level anisotropic elastoplastic material strength and an isotropic damage model TEPLA have been implemented in the three-dimensional Eulerian hydrodynamics code known as CONEJO. The anisotropic constitutive modeling is posed in an unrotated material frame of reference using the theorem of polar decomposition to compute rigid-body rotation. TEPLA is based upon the Gurson flow surface (a potential function used in conjunction with the associated flow law). The original TEPLA equation set has been extended to include anisotropic elastoplasticity and has been recast into a new implicit solution algorithm based upon an eigenvalue scheme to accommodate the anisotropy. This algorithm solves a two-by-two system of nonlinear equations using a Newton-Raphson iteration scheme. Simulations of a shaped-charge jet formation, a Taylor cylinder impact, and an explosively loaded hemishell were selected to demonstrate the utility of this modeling capability. The predicted deformation topology, plastic strain, and porosity distributions are shown for the three simulations.
Huang, Hong-Zhong; Yuan, Rong
2014-01-01
Many structures are subjected to variable amplitude loading in engineering practice. The foundation of fatigue life prediction under variable amplitude loading is how to deal with the fatigue damage accumulation. A nonlinear fatigue damage accumulation model to consider the effects of load sequences was proposed in earlier literature, but the model cannot consider the load interaction effects, and sometimes it makes a major error. A modified nonlinear damage accumulation model is proposed in this paper to account for the load interaction effects. Experimental data of two metallic materials are used to validate the proposed model. The agreement between the model prediction and experimental data is observed, and the predictions by proposed model are more possibly in accordance with experimental data than that by primary model and Miner's rule. Comparison between the predicted cumulative damage by the proposed model and an existing model shows that the proposed model predictions can meet the accuracy requirement of the engineering project and it can be used to predict the fatigue life of welded aluminum alloy joint of Electric Multiple Units (EMU); meanwhile, the accuracy of approximation can be obtained from the proposed model though more simple computing process and less material parameters calling for extensive testing than the existing model. PMID:24574866
NASA Technical Reports Server (NTRS)
Coats, Timothy W.; Harris, Charles E.; Lo, David C.; Allen, David H.
1998-01-01
A method for analysis of progressive failure in the Computational Structural Mechanics Testbed is presented in this report. The relationship employed in this analysis describes the matrix crack damage and fiber fracture via kinematics-based volume-averaged damage variables. Damage accumulation during monotonic and cyclic loads is predicted by damage evolution laws for tensile load conditions. The implementation of this damage model required the development of two testbed processors. While this report concentrates on the theory and usage of these processors, a complete listing of all testbed processors and inputs that are required for this analysis are included. Sample calculations for laminates subjected to monotonic and cyclic loads were performed to illustrate the damage accumulation, stress redistribution, and changes to the global response that occurs during the loading history. Residual strength predictions made with this information compared favorably with experimental measurements.
Full-scale testing and progressive damage modeling of sandwich composite aircraft fuselage structure
NASA Astrophysics Data System (ADS)
Leone, Frank A., Jr.
A comprehensive experimental and computational investigation was conducted to characterize the fracture behavior and structural response of large sandwich composite aircraft fuselage panels containing artificial damage in the form of holes and notches. Full-scale tests were conducted where panels were subjected to quasi-static combined pressure, hoop, and axial loading up to failure. The panels were constructed using plain-weave carbon/epoxy prepreg face sheets and a Nomex honeycomb core. Panel deformation and notch tip damage development were monitored during the tests using several techniques, including optical observations, strain gages, digital image correlation (DIC), acoustic emission (AE), and frequency response (FR). Additional pretest and posttest inspections were performed via thermography, computer-aided tap tests, ultrasound, x-radiography, and scanning electron microscopy. The framework to simulate damage progression and to predict residual strength through use of the finite element (FE) method was developed. The DIC provided local and full-field strain fields corresponding to changes in the state-of-damage and identified the strain components driving damage progression. AE was monitored during loading of all panels and data analysis methodologies were developed to enable real-time determination of damage initiation, progression, and severity in large composite structures. The FR technique has been developed, evaluating its potential as a real-time nondestructive inspection technique applicable to large composite structures. Due to the large disparity in scale between the fuselage panels and the artificial damage, a global/local analysis was performed. The global FE models fully represented the specific geometries, composite lay-ups, and loading mechanisms of the full-scale tests. A progressive damage model was implemented in the local FE models, allowing the gradual failure of elements in the vicinity of the artificial damage. A set of modifications
Munson, D.E.; Jensen, A.L.; Webb, S.W.; DeVries, K.L.
1996-02-01
In a large in situ experimntal circular room, brine inflow was measured over 5 years. After correcting for evaporation losses into mine ventilation air, the measurements gave data for a period of nearly 3 years. Predicted brine accumulation based on a mechanical ``snow plow`` model of the volume swept by creep-induced damage as calculated with the Multimechanism Deformation Coupled Fracture model was found to agree with experiment. Calculation suggests the damage zone at 5 years effectively exends only some 0.7 m into the salt around the room. Also, because the mecahnical model of brine release gives an adequate explanation of the measured data, the hydrological process of brine flow appears to be rapid compared to the mechanical process of brine release.
Oxidative Damage in the Aging Heart: an Experimental Rat Model
Marques, Gustavo Lenci; Neto, Francisco Filipak; Ribeiro, Ciro Alberto de Oliveira; Liebel, Samuel; de Fraga, Rogério; Bueno, Ronaldo da Rocha Loures
2015-01-01
Introduction: Several theories have been proposed to explain the cause of ‘aging’; however, the factors that affect this complex process are still poorly understood. Of these theories, the accumulation of oxidative damage over time is among the most accepted. Particularly, the heart is one of the most affected organs by oxidative stress. The current study, therefore, aimed to investigate oxidative stress markers in myocardial tissue of rats at different ages. Methods: Seventy-two rats were distributed into 6 groups of 12 animals each and maintained for 3, 6, 9, 12, 18 and 24 months. After euthanasia, the heart was removed and the levels of non-protein thiols, lipid peroxidation, and protein carbonylation, as well as superoxide dismutase and catalase activities were determined. Results: Superoxide dismutase, catalase activity and lipid peroxidation were reduced in the older groups of animals, when compared with the younger group. However, protein carbonylation showed an increase in the 12-month group followed by a decrease in the older groups. In addition, the levels of non-protein thiols were increased in the 12-month group and not detected in the older groups. Conclusion: Our data showed that oxidative stress is not associated with aging in the heart. However, an increase in non-protein thiols may be an important factor that compensates for the decrease of superoxide dismutase and catalase activity in the oldest rats, to maintain appropriate antioxidant defenses against oxidative insults. PMID:27006709
A Two-State Cell Damage Model Under Hyperthermic Conditions: Theory and In Vitro Experiments
Feng, Yusheng; Oden, J. Tinsley; Rylander, Marissa Nichole
2010-01-01
The ultimate goal of cancer treatment utilizing thermotherapy is to eradicate tumors and minimize damage to surrounding host tissues. To achieve this goal, it is important to develop an accurate cell damage model to characterize the population of cell death under various thermal conditions. The traditional Arrhenius model is often used to characterize the damaged cell population under the assumption that the rate of cell damage is proportional to exp(−Ea/RT), where Ea is the activation energy, R is the universal gas constant, and T is the absolute temperature. However, this model is unable to capture transition phenomena over the entire hyperthermia and ablation temperature range, particularly during the initial stage of heating. Inspired by classical statistical thermodynamic principles, we propose a general two-state model to characterize the entire cell population with two distinct and measurable subpopulations of cells, in which each cell is in one of the two microstates, viable (live) and damaged (dead), respectively. The resulting cell viability can be expressed as C(τ, T) = exp(−Φ(τ, T)/kT)/(1+exp(−Φ(τ, T)/kT)), where k is a constant. The in vitro cell viability experiments revealed that the function Φ(τ, T) can be defined as a function that is linear in exposure time τ when the temperature T is fixed, and linear as well in terms of the reciprocal of temperature T when the variable τ is held as constant. To determine parameters in the function Φ(τ, T), we use in vitro cell viability data from the experiments conducted with human prostate cancerous (PC3) and normal (RWPE-1) cells exposed to thermotherapeutic protocols to correlate with the proposed cell damage model. Very good agreement between experimental data and the derived damage model is obtained. In addition, the new two-state model has the advantage that is less sensitive and more robust due to its well behaved model parameters. PMID:18601458
NASA Astrophysics Data System (ADS)
dot Zak, A.; Ostachowicz, W.; Krawczuk, M.
2011-07-01
Damage of aircraft structural elements in any form always present high risks. Failures of these elements can be caused by various reasons including material fatigue or impact leading to damage initiation and growth. Detection of these failures at their earliest stage of development, estimation of their size and location, are one of the most crucial factors for each damage detection method. Structural health monitoring strategies based on propagation of guided elastic waves in structures and wave interaction with damage related discontinuities are very promising tools that offer not only damage detection capabilities, but are also meant to provide precise information about the state of the structures and their remaining lifetime. Because of that various techniques are employed to simulate and mimic the wave-discontinuity interactions. The use of various types of sensors, their networks together with sophisticated contactless measuring techniques are investigated both numerically and experimentally. Certain results of numerical simulations obtained by the use of the spectral finite element method are presented by the authors and related with propagation of guided elastic waves in shell-type aircraft structures. Two types of structures are considered: flat 2D panels with or without stiffeners and 3D shell structures. The applicability of two different damage detection approaches is evaluated in order to detect and localise damage in these structures. Selected results related with the use of laser scanning vibrometry are also presented and discussed by the authors.
NASA Astrophysics Data System (ADS)
Chaabane, Makram; Chaabane, Makram; Dalverny, Olivier; Deramecourt, Arnaud; Mistou, Sébastien
The super-pressure balloons developed by CNES are a great challenge in scientific ballooning. Whatever the balloon type considered (spherical, pumpkin...), it is necessary to have good knowledge of the mechanical behavior of the envelope regarding to the flight level and the lifespan of the balloon. It appears during the working stages of the super pressure balloons that these last can exploded prematurely in the course of the first hours of flight. For this reason CNES and LGP are carrying out research programs about experimentations and modelling in order to predict a good stability of the balloons flight and guarantee a life time in adequacy with the technical requirement. This study deals with multilayered polymeric film damage which induce balloons failure. These experimental and numerical study aims, are a better understanding and predicting of the damage mechanisms bringing the premature explosion of balloons. The following damages phenomena have different origins. The firsts are simple and triple wrinkles owed during the process and the stocking stages of the balloons. The second damage phenomenon is associated to the creep of the polymeric film during the flight of the balloon. The first experimental results we present in this paper, concern the mechanical characterization of three different damage phenomena. The severe damage induced by the wrinkles of the film involves a significant loss of mechanical properties. In a second part the theoretical study, concerns the choice and the development of a non linear viscoelastic coupled damage behavior model in a finite element code.
Simulation and modeling of the electronic structure of GaAs damage clusters
NASA Astrophysics Data System (ADS)
Moussa, Jonathan E.; Foiles, Stephen M.; Schultz, Peter A.
2013-03-01
In an effort to build a stronger microscopic foundation for radiation damage models in gallium arsenide (GaAs), the electronic properties of radiation-induced damage clusters are studied with atomistic simulations. Molecular dynamics simulations are used to access the time and length scales required for direct simulation of a collision cascade, and density functional theory simulations are used to calculate the electronic properties of isolated damaged clusters that are extracted from these cascades. To study the physical properties of clusters, we analyze the statistics of a randomly generated ensemble of damage clusters because no single cluster adequately represents this class of defects. The electronic properties of damage clusters are accurately described by a classical model of the electrical charging of a semiconducting sphere embedded in a uniform dielectric. The effective band gap of the cluster depends on the degree of internal structural damage, and the gap closes to form a metal in the high-damage limit. We estimate the Fermi level of this metallic state, which corresponds to high-energy amorphous GaAs, to be 0.46±0.07 eV above the valence band edge of crystalline GaAs.
Ma, Songyun; Scheider, Ingo; Bargmann, Swantje
2016-09-01
An anisotropic constitutive model is proposed in the framework of finite deformation to capture several damage mechanisms occurring in the microstructure of dental enamel, a hierarchical bio-composite. It provides the basis for a homogenization approach for an efficient multiscale (in this case: multiple hierarchy levels) investigation of the deformation and damage behavior. The influence of tension-compression asymmetry and fiber-matrix interaction on the nonlinear deformation behavior of dental enamel is studied by 3D micromechanical simulations under different loading conditions and fiber lengths. The complex deformation behavior and the characteristics and interaction of three damage mechanisms in the damage process of enamel are well captured. The proposed constitutive model incorporating anisotropic damage is applied to the first hierarchical level of dental enamel and validated by experimental results. The effect of the fiber orientation on the damage behavior and compressive strength is studied by comparing micro-pillar experiments of dental enamel at the first hierarchical level in multiple directions of fiber orientation. A very good agreement between computational and experimental results is found for the damage evolution process of dental enamel. PMID:27294283
Evaluation of microcrack thermal shock damage in ceramics: Modeling and experiment
NASA Technical Reports Server (NTRS)
Chu, Y. C.; Hefetz, M.; Rokhlin, S. I.
1992-01-01
In this paper we present an experimental and theoretical study of the effect of microcrack damage on ceramic properties. For the experimental investigation, ceramic samples of aluminum oxide and reaction bonded silicon nitride (RBSN) are used. Thermal shock treatment from different temperatures up to 1000 C is applied to produce the microcracks. Both surface and bulk ultrasonic wave methods are used to correlate the change of elastic constants to microstructural degradation and to determine the change in elastic anisotropy induced by microcrack damage. For the theoretical investigation, damage mechanics, which relates microstructural damage to material service life and mechanical failure, is used. The change in elastic properties due to microcrack damage calculated from the theoretical model is compared with the experimental results for determination of the applicability of damage theory. It is shown that two independent experimental methods (bulk wave and surface wave) give the same results for shear moduli of damaged ceramics. The experimental results aagree reasonably well with the moduli predicted from the cracked solid model.
Creep crack growth predictions in INCO 718 using a continuum damage model
NASA Technical Reports Server (NTRS)
Walker, K. P.; Wilson, D. A.
1985-01-01
Creep crack growth tests have been carried out in compact type specimens of INCO 718 at 1200 F (649 C). Theoretical creep crack growth predictions have been carried out by incorporating a unified viscoplastic constitutive model and a continuum damage model into the ARAQUS nonlinear finite element program. Material constants for both the viscoplastic model and the creep continuum damage model were determined from tests carried out on uniaxial bar specimens of INCO 718 at 1200 F (649 C). A comparison of the theoretical creep crack growth rates obtained from the finite element predictions with the experimentally observed creep crack growth rates indicates that the viscoplastic/continuum damage model can be used to successfully predict creep crack growth in compact type specimens using material constants obtained from uniaxial bar specimens of INCO 718 at 1200 F (649 C).
Repair of ionizing radiation DNA base damage in ataxia-telangiectasia cells
Fornace, A.J. Jr.; Kinsella, T.J.; Dobson, P.P.; Mitchell, J.B.
1986-04-01
Micrococcus luteus endonuclease sensitive sites were measured by alkaline elution in normal human and ataxia-telangiectasia (AT) fibroblasts after ionizing radiation. Due to the sensitivity of this assay, repair of base damage after 3 to 6 kilorads has been measured after oxic or hypoxic radiation. With 5.5 kilorads of oxic radiation, more than 50% of the base damage was removed after 1.5 h of repair incubation in all cells, including exr+ and exr- AT cells, and approximately 75% was removed by 4 h. After 3 or 4.5 kilorads of hypoxic X-irradiation, repair was equivalent in normal and exr- AT cells. This study included three exr- AT strains which have been reported to be deficient in the removal of gamma-ray base damage at higher doses. Since these strains repaired ionizing radiation base damage normally at lower doses, which are more relevant to survival, it is concluded that the X-ray hypersensitivity of AT cells is probably not related to the repair of base damage.
Comparison of Model Calculations of Biological Damage from Exposure to Heavy Ions with Measurements
NASA Astrophysics Data System (ADS)
Kim, Myung-Hee Y.; Wu, Honglu; Hada, Megumi; Cucinotta, Francis
The space environment consists of a varying field of radiation particles including high-energy ions, with spacecraft shielding material providing the major protection to astronauts from harmful exposure. Unlike low-LET g or X rays, the presence of shielding does not always reduce the radiation risks for energetic charged-particle exposure. Dose delivered by the charged particle increases sharply at the Bragg peak. However, the Bragg curve does not necessarily represent the biological damage along the particle path since biological effects are influenced by the track structures of both primary and secondary particles. Therefore, the ‘‘biological Bragg curve’’ is dependent on the energy and the type of the primary particle and may vary for different biological end points. Measurements of the induction of micronuclei (MN) have made across the Bragg curve in human fibroblasts exposed to energetic silicon and iron ions in vitro at two different energies, 300 MeV/nucleon and 1 GeV/nucleon. Although the data did not reveal an increased yield of MN at the location of the Bragg peak, the increased inhibition of cell progression, which is related to cell death, was found at the Bragg peak location. These results are compared to the calculations of biological damage using a stochastic Monte-Carlo track structure model, Galactic Cosmic Ray Event-based Risk Model (GERM) code (Cucinotta et al., 2011). The GERM code estimates the basic physical properties along the passage of heavy ions in tissue and shielding materials, by which the experimental set-up can be interpreted. The code can also be used to describe the biophysical events of interest in radiobiology, cancer therapy, and space exploration. The calculation has shown that the severely damaged cells at the Bragg peak are more likely to go through reproductive death, the so called “overkill”. F. A. Cucinotta, I. Plante, A. L. Ponomarev, and M. Y. Kim, Nuclear Interactions in Heavy Ion Transport and Event-based
Reduced-order modeling for mistuned centrifugal impellers with crack damages
NASA Astrophysics Data System (ADS)
Wang, Shuai; Zi, Yanyang; Li, Bing; Zhang, Chunlin; He, Zhengjia
2014-12-01
An efficient method for nonlinear vibration analysis of mistuned centrifugal impellers with crack damages is presented. The main objective is to investigate the effects of mistuning and cracks on the vibration features of centrifugal impellers and to explore effective techniques for crack detection. Firstly, in order to reduce the input information needed for component mode synthesis (CMS), the whole model of an impeller is obtained by rotation transformation based on the finite element model of a sector model. Then, a hybrid-interface method of CMS is employed to generate a reduced-order model (ROM) for the cracked impeller. The degrees of freedom on the crack surfaces are retained in the ROM to simulate the crack breathing effects. A novel approach for computing the inversion of large sparse matrix is proposed to save memory space during model order reduction by partitioning the matrix into many smaller blocks. Moreover, to investigate the effects of mistuning and cracks on the resonant frequencies, the bilinear frequency approximation is used to estimate the resonant frequencies of the mistuned impeller with a crack. Additionally, statistical analysis is performed using the Monte Carlo simulation to study the statistical characteristics of the resonant frequencies versus crack length at different mistuning levels. The results show that the most significant effect of mistuning and cracks on the vibration response is the shift and split of the two resonant frequencies with the same nodal diameters. Finally, potential quantitative indicators for detection of crack of centrifugal impellers are discussed.
NASA Astrophysics Data System (ADS)
Hoang, Tuan L.; Marian, Jaime; Bulatov, Vasily V.; Hosemann, Peter
2015-11-01
An improved version of a recently developed stochastic cluster dynamics (SCD) method (Marian and Bulatov, 2012) [6] is introduced as an alternative to rate theory (RT) methods for solving coupled ordinary differential equation (ODE) systems for irradiation damage simulations. SCD circumvents by design the curse of dimensionality of the variable space that renders traditional ODE-based RT approaches inefficient when handling complex defect population comprised of multiple (more than two) defect species. Several improvements introduced here enable efficient and accurate simulations of irradiated materials up to realistic (high) damage doses characteristic of next-generation nuclear systems. The first improvement is a procedure for efficiently updating the defect reaction-network and event selection in the context of a dynamically expanding reaction-network. Next is a novel implementation of the τ-leaping method that speeds up SCD simulations by advancing the state of the reaction network in large time increments when appropriate. Lastly, a volume rescaling procedure is introduced to control the computational complexity of the expanding reaction-network through occasional reductions of the defect population while maintaining accurate statistics. The enhanced SCD method is then applied to model defect cluster accumulation in iron thin films subjected to triple ion-beam (Fe3+, He+ and H+) irradiations, for which standard RT or spatially-resolved kinetic Monte Carlo simulations are prohibitively expensive.
NASA Astrophysics Data System (ADS)
Girolamo, D.; Girolamo, L.; Yuan, F. G.
2015-03-01
Nondestructive evaluation (NDE) for detection and quantification of damage in composite materials is fundamental in the assessment of the overall structural integrity of modern aerospace systems. Conventional NDE systems have been extensively used to detect the location and size of damages by propagating ultrasonic waves normal to the surface. However they usually require physical contact with the structure and are time consuming and labor intensive. An automated, contactless laser ultrasonic imaging system for barely visible impact damage (BVID) detection in advanced composite structures has been developed to overcome these limitations. Lamb waves are generated by a Q-switched Nd:YAG laser, raster scanned by a set of galvano-mirrors over the damaged area. The out-of-plane vibrations are measured through a laser Doppler Vibrometer (LDV) that is stationary at a point on the corner of the grid. The ultrasonic wave field of the scanned area is reconstructed in polar coordinates and analyzed for high resolution characterization of impact damage in the composite honeycomb panel. Two methodologies are used for ultrasonic wave-field analysis: scattered wave field analysis (SWA) and standing wave energy analysis (SWEA) in the frequency domain. The SWA is employed for processing the wave field and estimate spatially dependent wavenumber values, related to discontinuities in the structural domain. The SWEA algorithm extracts standing waves trapped within damaged areas and, by studying the spectrum of the standing wave field, returns high fidelity damage imaging. While the SWA can be used to locate the impact damage in the honeycomb panel, the SWEA produces damage images in good agreement with X-ray computed tomographic (X-ray CT) scans. The results obtained prove that the laser-based nondestructive system is an effective alternative to overcome limitations of conventional NDI technologies.
Girolamo, D. Yuan, F. G.; Girolamo, L.
2015-03-31
Nondestructive evaluation (NDE) for detection and quantification of damage in composite materials is fundamental in the assessment of the overall structural integrity of modern aerospace systems. Conventional NDE systems have been extensively used to detect the location and size of damages by propagating ultrasonic waves normal to the surface. However they usually require physical contact with the structure and are time consuming and labor intensive. An automated, contactless laser ultrasonic imaging system for barely visible impact damage (BVID) detection in advanced composite structures has been developed to overcome these limitations. Lamb waves are generated by a Q-switched Nd:YAG laser, raster scanned by a set of galvano-mirrors over the damaged area. The out-of-plane vibrations are measured through a laser Doppler Vibrometer (LDV) that is stationary at a point on the corner of the grid. The ultrasonic wave field of the scanned area is reconstructed in polar coordinates and analyzed for high resolution characterization of impact damage in the composite honeycomb panel. Two methodologies are used for ultrasonic wave-field analysis: scattered wave field analysis (SWA) and standing wave energy analysis (SWEA) in the frequency domain. The SWA is employed for processing the wave field and estimate spatially dependent wavenumber values, related to discontinuities in the structural domain. The SWEA algorithm extracts standing waves trapped within damaged areas and, by studying the spectrum of the standing wave field, returns high fidelity damage imaging. While the SWA can be used to locate the impact damage in the honeycomb panel, the SWEA produces damage images in good agreement with X-ray computed tomographic (X-ray CT) scans. The results obtained prove that the laser-based nondestructive system is an effective alternative to overcome limitations of conventional NDI technologies.
Farrar, C.R.; Doebling, S.W.; Prime, M.B.; Cornwell, P.; Kam, M.; Straser, E.G.; Hoerst, B.C.
1998-11-01
This is the final report of a three-year, Laboratory Directed Research and Development (LDRD) project at the Los Alamos National Laboratory (LANL). Recent advances in wireless, remotely monitored data acquisition systems coupled with the development of vibration-based damage detection algorithms make the possibility of self- or remotely-monitored structures and mechanical systems appear to be within the capabilities of current technology. However, before such a system can be relied upon to perform this monitoring, the variability of the vibration properties that are the basis for the damage detection algorithm must be understood and quantified. This understanding is necessary so that the artificial intelligence/expert system that is employed to discriminate when changes in modal properties are indicative of damage will not yield false indications of damage. To this end, this project has focused on developing statistical methods for quantifying variability in identified vibration proper ties of structural and mechanical systems.
Damage Evaluation Based on a Wave Energy Flow Map Using Multiple PZT Sensors
Liu, Yaolu; Hu, Ning; Xu, Hong; Yuan, Weifeng; Yan, Cheng; Li, Yuan; Goda, Riu; Alamusi; Qiu, Jinhao; Ning, Huiming; Wu, Liangke
2014-01-01
A new wave energy flow (WEF) map concept was proposed in this work. Based on it, an improved technique incorporating the laser scanning method and Betti's reciprocal theorem was developed to evaluate the shape and size of damage as well as to realize visualization of wave propagation. In this technique, a simple signal processing algorithm was proposed to construct the WEF map when waves propagate through an inspection region, and multiple lead zirconate titanate (PZT) sensors were employed to improve inspection reliability. Various damages in aluminum and carbon fiber reinforced plastic laminated plates were experimentally and numerically evaluated to validate this technique. The results show that it can effectively evaluate the shape and size of damage from wave field variations around the damage in the WEF map. PMID:24463430
3D-DIP-Chip: a microarray-based method to measure genomic DNA damage
Powell, James Rees; Bennett, Mark Richard; Evans, Katie Ellen; Yu, Shirong; Webster, Richard Michael; Waters, Raymond; Skinner, Nigel; Reed, Simon Huw
2015-01-01
Genotoxins cause DNA damage, which can result in genomic instability. The genetic changes induced have far-reaching consequences, often leading to diseases such as cancer. A wide range of genotoxins exists, including radiations and chemicals found naturally in the environment, and in man-made forms created by human activity across a variety of industries. Genomic technologies offer the possibility of unravelling the mechanisms of genotoxicity, including the repair of genetic damage, enhancing our ability to develop, test and safely use existing and novel materials. We have developed 3D-DIP-Chip, a microarray-based method to measure the prevalence of genomic genotoxin-induced DNA damage. We demonstrate the measurement of both physical and chemical induced DNA damage spectra, integrating the analysis of these with the associated changes in histone acetylation induced in the epigenome. We discuss the application of the method in the context of basic and translational sciences. PMID:25609656
Modeling Damage Complexity-Dependent Non-Homologous End-Joining Repair Pathway
Li, Yongfeng; Reynolds, Pamela; O'Neill, Peter; Cucinotta, Francis A.
2014-01-01
Non-homologous end joining (NHEJ) is the dominant DNA double strand break (DSB) repair pathway and involves several repair proteins such as Ku, DNA-PKcs, and XRCC4. It has been experimentally shown that the choice of NHEJ proteins is determined by the complexity of DSB. In this paper, we built a mathematical model, based on published data, to study how NHEJ depends on the damage complexity. Under an appropriate set of parameters obtained by minimization technique, we can simulate the kinetics of foci track formation in fluorescently tagged mammalian cells, Ku80-EGFP and DNA-PKcs-YFP for simple and complex DSB repair, respectively, in good agreement with the published experimental data, supporting the notion that simple DSB undergo fast repair in a Ku-dependent, DNA-PKcs-independent manner, while complex DSB repair requires additional DNA-PKcs for end processing, resulting in its slow repair, additionally resulting in slower release rate of Ku and the joining rate of complex DNA ends. Based on the numerous experimental descriptions, we investigated several models to describe the kinetics for complex DSB repair. An important prediction of our model is that the rejoining of complex DSBs is through a process of synapsis formation, similar to a second order reaction between ends, rather than first order break filling/joining. The synapsis formation (SF) model allows for diffusion of ends before the synapsis formation, which is precluded in the first order model by the rapid coupling of ends. Therefore, the SF model also predicts the higher number of chromosomal aberrations observed with high linear energy transfer (LET) radiation due to the higher proportion of complex DSBs compared to low LET radiation, and an increased probability of misrejoin following diffusion before the synapsis is formed, while the first order model does not provide a mechanism for the increased effectiveness in chromosomal aberrations observed. PMID:24520318
Modeling damage complexity-dependent non-homologous end-joining repair pathway.
Li, Yongfeng; Reynolds, Pamela; O'Neill, Peter; Cucinotta, Francis A
2014-01-01
Non-homologous end joining (NHEJ) is the dominant DNA double strand break (DSB) repair pathway and involves several repair proteins such as Ku, DNA-PKcs, and XRCC4. It has been experimentally shown that the choice of NHEJ proteins is determined by the complexity of DSB. In this paper, we built a mathematical model, based on published data, to study how NHEJ depends on the damage complexity. Under an appropriate set of parameters obtained by minimization technique, we can simulate the kinetics of foci track formation in fluorescently tagged mammalian cells, Ku80-EGFP and DNA-PKcs-YFP for simple and complex DSB repair, respectively, in good agreement with the published experimental data, supporting the notion that simple DSB undergo fast repair in a Ku-dependent, DNA-PKcs-independent manner, while complex DSB repair requires additional DNA-PKcs for end processing, resulting in its slow repair, additionally resulting in slower release rate of Ku and the joining rate of complex DNA ends. Based on the numerous experimental descriptions, we investigated several models to describe the kinetics for complex DSB repair. An important prediction of our model is that the rejoining of complex DSBs is through a process of synapsis formation, similar to a second order reaction between ends, rather than first order break filling/joining. The synapsis formation (SF) model allows for diffusion of ends before the synapsis formation, which is precluded in the first order model by the rapid coupling of ends. Therefore, the SF model also predicts the higher number of chromosomal aberrations observed with high linear energy transfer (LET) radiation due to the higher proportion of complex DSBs compared to low LET radiation, and an increased probability of misrejoin following diffusion before the synapsis is formed, while the first order model does not provide a mechanism for the increased effectiveness in chromosomal aberrations observed. PMID:24520318
NASA Astrophysics Data System (ADS)
Lafon, Jose J.
(FOD) Foreign Object Debris/Damage has been a costly issue for the commercial and military aircraft manufacturers at their production lines every day. FOD can put pilots, passengers and other crews' lives into high-risk. FOD refers to any type of foreign object, particle, debris or agent in the manufacturing environment, which could contaminate/damage the product or otherwise undermine quality standards. Nowadays, FOD is currently addressed with prevention programs, elimination techniques, and designation of FOD areas, controlled access to FOD areas, restrictions of personal items entering designated areas, tool accountability, etc. All of the efforts mentioned before, have not shown a significant reduction in FOD occurrence in the manufacturing processes. This research presents a Decision Making Model approach based on a logistic regression predictive model that was previously made by other researchers. With a general idea of the FOD expected, elimination plans can be put in place and start eradicating the problem minimizing the cost and time spend on the prediction, detection and/or removal of FOD.
Accounting for damage to model the influence of a pinning point on the grounding line dynamics
NASA Astrophysics Data System (ADS)
Brondex, Julien; Gagliardini, Olivier; Gillet-Chaulet, Fabien; Krug, Jean; Durand, Gaël
2015-04-01
The ice released from Greenland and Antarctic ice sheets into the ocean is the main cause of the current observed sea-level rise. Using the open-source finite-element code Elmer/Ice, a previous study (Favier et al., 2012) investigated the impact of a localised contact point between a floating ice shelf and the bedrock and showed its stabilizing effect on ice discharge. The large amount of friction introduced locally by a pinning point induces a rapid decrease of ice velocities upstream the contact leading to an advance of the grounding line seaward until the grounded ice-sheet and the ice rise merge together. This causes a slow down of ice discharge which is consistent with observations on real ice-shelves. However, highly crevassed zones surrounding those pinning points are commonly observed, highlighting strong damage patterns which were not taken into account in Favier et al. (2012). Damage has a strong influence on ice rheology as ice gets softer when damaged, therefore accelerating the ice flow. Recently, a damage model has been implemented within Elmer/Ice (Krug et al., 2014). In this model, damage is created in areas where the maximum principal Cauchy stress is higher than a stress threshold. Damage is then advected with ice flow and its impact on viscosity is taken into account by modifying the enhancement factor of Glen's flow law. Since high shear stresses predominate in the vicinity of pinning points, damage is likely to appear in those areas, making ice more fluid and thus lessening the stabilizing effect previously observed. To check the validity of this hypothesis, the pinning point experiment is repeated taking damage into account. The impact of basal crevasses filled with sea water, which tend to counteract the compressive stresses due to cryostatic pressure and thus to promote damage formation under the shelf, is investigated as well.
Construction of homogeneous loading functions for elastoplastic damage models for concrete
NASA Astrophysics Data System (ADS)
Zhang, Ji; Li, Jie
2014-03-01
Over the past 2 decades, tight restriction has been imposed on strength criteria of concrete by the combination of plasticity and damage in one theory. The present study aims at constructing plastic/damage loading functions for elastoplastic damage models for concrete that can perform more satisfactorily in 3D stress states. Numerous strength criteria of concrete are reorganized according to their simplest representations as Cartesian, cylindrical, mixed cylindrical-Cartesian, and other forms, and the homogeneity of loading functions discussed. It is found that under certain supplementary conditions from physical meanings, an unambiguous definition of the cohesion in a strength criterion, which is demanded in an elastoplastic damage model, is usually available in an explicit or implicit form, and in each case the loading function is still homogeneous. To apply and validate the presented theory, we construct the respective homogeneous damage and plastic loading functions and implant them into some widely used elastoplastic damage models for concrete, and their performances in triaxial compression prove to have improved significantly.
Leith, S.D.; Reddy, M.M.; Irez, W.F.; Heymans, M.J.
1996-01-01
The pore structure of Salem limestone is investigated, and conclusions regarding the effect of the pore geometry on modeling moisture and contaminant transport are discussed based on thin section petrography, scanning electron microscopy, mercury intrusion porosimetry, and nitrogen adsorption analyses. These investigations are compared to and shown to compliment permeability and capillary pressure measurements for this common building stone. Salem limestone exhibits a bimodal pore size distribution in which the larger pores provide routes for convective mass transfer of contaminants into the material and the smaller pores lead to high surface area adsorption and reaction sites. Relative permeability and capillary pressure measurements of the air/water system indicate that Salem limestone exhibits high capillarity end low effective permeability to water. Based on stone characterization, aqueous diffusion and convection are believed to be the primary transport mechanisms for pollutants in this stone. The extent of contaminant accumulation in the stone depends on the mechanism of partitioning between the aqueous and solid phases. The described characterization techniques and modeling approach can be applied to many systems of interest such as acidic damage to limestone, mass transfer of contaminants in concrete and other porous building materials, and modeling pollutant transport in subsurface moisture zones.
Application of Laser Based Ultrasound for NDE of Damage in Thick Stitched Composites
NASA Technical Reports Server (NTRS)
Anastasi, Robert F.; Friedman, Adam D.; Hinders, Mark K.; Madaras, Eric I.
1997-01-01
As design engineers implement new composite systems such as thick, load bearing composite structures, they must have certifiable confidence in structure s durability and worthiness. This confidence builds from understanding the structural response and failure characteristics of simple components loaded in testing machines to tests on full scale sections. Nondestructive evaluation is an important element which can provide quantitative information on the damage initiation, propagation, and final failure modes for the composite structural components. Although ultrasound is generally accepted as a test method, the use of conventional ultrasound for in-situ monitoring of damage during tests of large structures is not practical. The use of lasers to both generate and detect ultrasound extends the application of ultrasound to in- situ sensing of damage in a deformed structure remotely and in a non-contact manner. The goal of the present research is to utilize this technology to monitor damage progression during testing. The present paper describes the application of laser based ultrasound to quantify damage in thick stitched composite structural elements to demonstrate the method. This method involves using a Q-switched laser to generate a rapid, local linear thermal strain on the surface of the structure. This local strain causes the generation of ultrasonic waves into the material. A second laser used with a Fabry-Perot interferometer detects the surface deflections. The use of fiber optics provides for eye safety and a convenient method of delivering the laser over long distances to the specimens. The material for these structural elements is composed of several stacks of composite material assembled together by stitching through the laminate thickness that ranging from 0.5 to 0.8 inches. The specimens used for these nondestructive evaluation studies had either impact damage or skin/stiffener interlaminar failure. Although little or no visible surface damage existed
NASA Astrophysics Data System (ADS)
Arrieta, Albert Joseph
2001-07-01
Damage tolerance analysis (DTA) was considered in the global design optimization of an aircraft wing structure. Residual strength and fatigue life requirements, based on the damage tolerance philosophy, were investigated as new design constraints. In general, accurate fatigue prediction is difficult if the load environment is not known with a high degree of certainty. To address this issue, a probabilistic approach was used to describe the uncertain load environment. Probabilistic load spectra models were developed from flight recorder data. The global/local finite element approach allowed local fatigue requirements to be considered in the global design optimization. AFGROW fatigue crack growth analysis provided a new strength criterion for satisfying damage tolerance requirements within a global optimization environment. Initial research with the ASTROS program used the probabilistic load model and this damage tolerance constraint to optimize cracked skin panels on the lower wing of a fighter/attack aircraft. For an aerodynamic and structural model similar to an F-16, ASTROS simulated symmetric and asymmetric maneuvers during the optimization. Symmetric maneuvers, without underwing stores, produced the highest stresses and drove the optimization of the inboard lower wing skin. Asymmetric maneuvers, with underwing stores, affected the optimum thickness of the outboard hard points. Subsequent design optimizations included von Mises stress, aileron effectiveness, and lift effectiveness constraints simultaneously. This optimization was driven by the DTA and von Mises stress constraints and, therefore, DTA requirements can have an active role to play in preliminary aircraft design.
Computational Model of Alpha-Decay Damage Accumulation in Zircon
Heinisch, Howard L.; Weber, William J.
2005-01-01
Atomic-scale computer simulations are used to study defect accumulation and amorphization due to alpha decay in zircon (ZrSiO4). The displacement cascades, which represent 234U recoil nuclei from alpha-decay of 238Pu in zircon, are generated using a crystalline binary collision model, and the stochastic production of defects in the crystal lattice, recombination of defects, and the identification of amorphous regions are followed within the framework of a kinetic Monte Carlo simulation. Within the model, amorphous regions are identified as those having a critical density of Zr vacancies. The simulation predicts the interstitial content and amorphous fraction as functions of dose that are consistent with experimental data at 300 K for 238Pu-doped zircon, which indicate that the kinetic Monte Carlo model for behavior in zircon at 300 K is reasonable.
An anisotropic thermomechanical damage model for concrete at transient elevated temperatures.
Baker, Graham; de Borst, René
2005-11-15
The behaviour of concrete at elevated temperatures is important for an assessment of integrity (strength and durability) of structures exposed to a high-temperature environment, in applications such as fire exposure, smelting plants and nuclear installations. In modelling terms, a coupled thermomechanical analysis represents a generalization of the computational mechanics of fracture and damage. Here, we develop a fully coupled anisotropic thermomechanical damage model for concrete under high stress and transient temperature, with emphasis on the adherence of the model to the laws of thermodynamics. Specific analytical results are given, deduced from thermodynamics, of a novel interpretation on specific heat, evolution of entropy and the identification of the complete anisotropic, thermomechanical damage surface. The model is also shown to be stable in a computational sense, and to satisfy the laws of thermodynamics. PMID:16243703
NASA Astrophysics Data System (ADS)
Urrutia, J. D.; Bautista, L. A.; Baccay, E. B.
2014-04-01
The aim of this study was to develop mathematical models for estimating earthquake casualties such as death, number of injured persons, affected families and total cost of damage. To quantify the direct damages from earthquakes to human beings and properties given the magnitude, intensity, depth of focus, location of epicentre and time duration, the regression models were made. The researchers formulated models through regression analysis using matrices and used α = 0.01. The study considered thirty destructive earthquakes that hit the Philippines from the inclusive years 1968 to 2012. Relevant data about these said earthquakes were obtained from Philippine Institute of Volcanology and Seismology. Data on damages and casualties were gathered from the records of National Disaster Risk Reduction and Management Council. The mathematical models made are as follows: This study will be of great value in emergency planning, initiating and updating programs for earthquake hazard reductionin the Philippines, which is an earthquake-prone country.
Crash Simulation of Roll Formed Parts by Damage Modelling Taking Into Account Preforming Effects
NASA Astrophysics Data System (ADS)
Till, Edwin T.; Hackl, Benjamin; Schauer, Hermann
2011-08-01
Complex phase steels of strength levels up to 1200 MPa are suitable to roll forming. These may be applied in automotive structures for enhancing the crashworthiness, e. g. as stiffeners in doors. Even though the strain hardening of the material is low there is considerable bending formability. However ductility decreases with the strength level. Higher strength requires more focus to the structural integrity of the part during the process planning stage and with respect to the crash behavior. Nowadays numerical simulation is used as a process design tool for roll-forming in a production environment. The assessment of the stability of a roll forming process is quite challenging for AHSS grades. There are two objectives of the present work. First to provide a reliable assessment tool to the roll forming analyst for failure prediction. Second to establish simulation procedures in order to predict the part's behavior in crash applications taking into account damage and failure. Today adequate ductile fracture models are available which can be used in forming and crash applications. These continuum models are based on failure strain curves or surfaces which depend on the stress triaxiality (e. g. Crach or GISSMO) and may additionally include the Lode angle (extended Mohr Coulomb or extended GISSMO model). A challenging task is to obtain the respective failure strain curves. In the paper the procedure is described in detail how these failure strain curves are obtained using small scale tests within voestalpine Stahl, notch tensile-, bulge and shear tests. It is shown that capturing the surface strains is not sufficient for obtaining reliable material failure parameters. The simulation tool for roll-forming at the site of voestalpine Krems is Copra® FEA RF, which is a 3D continuum finite element solver based on MSC.Marc. The simulation environment for crash applications is LS-DYNA. Shell elements are used for this type of analyses. A major task is to provide results of
A bone remodelling model including the effect of damage on the steering of BMUs.
Martínez-Reina, J; Reina, I; Domínguez, J; García-Aznar, J M
2014-04-01
Bone remodelling in cortical bone is performed by the so-called basic multicellular units (BMUs), which produce osteons after completing the remodelling sequence. Burger et al. (2003) hypothesized that BMUs follow the direction of the prevalent local stress in the bone. More recently, Martin (2007) has shown that BMUs must be somehow guided by microstructural damage as well. The interaction of both variables, strain and damage, in the guidance of BMUs has been incorporated into a bone remodelling model for cortical bone. This model accounts for variations in porosity, anisotropy and damage level. The bone remodelling model has been applied to a finite element model of the diaphysis of a human femur. The trajectories of the BMUs have been analysed throughout the diaphysis and compared with the orientation of osteons measured experimentally. Some interesting observations, like the typical fan arrangement of osteons near the periosteum, can be explained with the proposed remodelling model. Moreover, the efficiency of BMUs in damage repairing has been shown to be greater if BMUs are guided by damage. PMID:24445006
Chao, Lin; Rang, Camilla Ulla; Proenca, Audrey Menegaz; Chao, Jasper Ubirajara
2016-01-01
Non-genetic phenotypic variation is common in biological organisms. The variation is potentially beneficial if the environment is changing. If the benefit is large, selection can favor the evolution of genetic assimilation, the process by which the expression of a trait is transferred from environmental to genetic control. Genetic assimilation is an important evolutionary transition, but it is poorly understood because the fitness costs and benefits of variation are often unknown. Here we show that the partitioning of damage by a mother bacterium to its two daughters can evolve through genetic assimilation. Bacterial phenotypes are also highly variable. Because gene-regulating elements can have low copy numbers, the variation is attributed to stochastic sampling. Extant Escherichia coli partition asymmetrically and deterministically more damage to the old daughter, the one receiving the mother’s old pole. By modeling in silico damage partitioning in a population, we show that deterministic asymmetry is advantageous because it increases fitness variance and hence the efficiency of natural selection. However, we find that symmetrical but stochastic partitioning can be similarly beneficial. To examine why bacteria evolved deterministic asymmetry, we modeled the effect of damage anchored to the mother’s old pole. While anchored damage strengthens selection for asymmetry by creating additional fitness variance, it has the opposite effect on symmetry. The difference results because anchored damage reinforces the polarization of partitioning in asymmetric bacteria. In symmetric bacteria, it dilutes the polarization. Thus, stochasticity alone may have protected early bacteria from damage, but deterministic asymmetry has evolved to be equally important in extant bacteria. We estimate that 47% of damage partitioning is deterministic in E. coli. We suggest that the evolution of deterministic asymmetry from stochasticity offers an example of Waddington’s genetic
Chao, Lin; Rang, Camilla Ulla; Proenca, Audrey Menegaz; Chao, Jasper Ubirajara
2016-01-01
Non-genetic phenotypic variation is common in biological organisms. The variation is potentially beneficial if the environment is changing. If the benefit is large, selection can favor the evolution of genetic assimilation, the process by which the expression of a trait is transferred from environmental to genetic control. Genetic assimilation is an important evolutionary transition, but it is poorly understood because the fitness costs and benefits of variation are often unknown. Here we show that the partitioning of damage by a mother bacterium to its two daughters can evolve through genetic assimilation. Bacterial phenotypes are also highly variable. Because gene-regulating elements can have low copy numbers, the variation is attributed to stochastic sampling. Extant Escherichia coli partition asymmetrically and deterministically more damage to the old daughter, the one receiving the mother's old pole. By modeling in silico damage partitioning in a population, we show that deterministic asymmetry is advantageous because it increases fitness variance and hence the efficiency of natural selection. However, we find that symmetrical but stochastic partitioning can be similarly beneficial. To examine why bacteria evolved deterministic asymmetry, we modeled the effect of damage anchored to the mother's old pole. While anchored damage strengthens selection for asymmetry by creating additional fitness variance, it has the opposite effect on symmetry. The difference results because anchored damage reinforces the polarization of partitioning in asymmetric bacteria. In symmetric bacteria, it dilutes the polarization. Thus, stochasticity alone may have protected early bacteria from damage, but deterministic asymmetry has evolved to be equally important in extant bacteria. We estimate that 47% of damage partitioning is deterministic in E. coli. We suggest that the evolution of deterministic asymmetry from stochasticity offers an example of Waddington's genetic assimilation
[Modeling and characteristics of liver damage in herpes infection].
Tereshko, A B; Kolomiets, A G; Grits, M A; Duboĭskaia, G P
1999-01-01
An experimental model of herpetic hepatitis is developed, levels and time course of changes in transaminases, the main indicators of lipid metabolism, are characterized, and morphologic features of hepatocyte injury by herpes simplex virus are shown. Liver involvement in herpetic infection is described in detail. PMID:10392435
The EST Model for Predicting Progressive Damage and Failure of Open Hole Bending Specimens
NASA Technical Reports Server (NTRS)
Joseph, Ashith P. K.; Waas, Anthony M.; Pineda, Evan J.
2016-01-01
Progressive damage and failure in open hole composite laminate coupons subjected to flexural loading is modeled using Enhanced Schapery Theory (EST). Previous studies have demonstrated that EST can accurately predict the strength of open hole coupons under remote tensile and compressive loading states. This homogenized modeling approach uses single composite shell elements to represent the entire laminate in the thickness direction and significantly reduces computational cost. Therefore, when delaminations are not of concern or are active in the post-peak regime, the version of EST presented here is a good engineering tool for predicting deformation response. Standard coupon level tests provides all the input data needed for the model and they are interpreted in conjunction with finite element (FE) based simulations. Open hole bending test results of three different IM7/8552 carbon fiber composite layups agree well with EST predictions. The model is able to accurately capture the curvature change and deformation localization in the specimen at and during the post catastrophic load drop event.
Model-Trained Neural Networks and Electronic Holography Demonstrated to Detect Damage in Blades
NASA Technical Reports Server (NTRS)
Decker, Arthur J.; Fite, E. Brian; Mehmed, Oral; Thorp, Scott A.
1998-01-01
Detect Damage in Blades Electronic holography can show damaged regions in fan blades at 30 frames/sec. The electronic holograms are transformed by finite-element-model-trained artificial neural networks to visualize the damage. The trained neural networks are linked with video and graphics to visualize the bending-induced strain distribution, which is very sensitive to damage. By contrast, it is very difficult to detect damage by viewing the raw, speckled, characteristic fringe patterns. For neural-network visualization of damage, 2 frames or 2 fields are used, rather than the 12 frames normally used to compute the displacement distribution from electronic holograms. At the NASA Lewis Research Center, finite element models are used to compute displacement and strain distributions for the vibration modes of undamaged and cracked blades. A model of electronic time-averaged holography is used to transform the displacement distributions into finite-element-resolution characteristic fringe patterns. Then, a feedforward neural network is trained with the fringe-pattern/strain-pattern pairs, and the neural network, electronic holography, and video are implemented on a workstation. Now that the neural networks have been tested successfully at 30 frames/sec on undamaged and cracked cantilevers, the electronic holography and neural-network processing are being adapted for onsite damage inspection of twisted fan blades and rotormounted blades. Our conclusion is that model-trained neural nets are effective when they are trained with good models whose application is well understood. This work supports the aeromechanical testing portion of the Advanced Subsonic Technology Project.
Lim, Ji Hwan; Kim, Joo-Hyun; Lee, Byoung Hwan; Seo, Pyoung Ju; Kang, Jung Mook; Jo, So Young; Park, Ji Hyun; Nam, Ryoung Hee; Chang, Hyun; Kwon, Jin-Won; Lee, Dong Ho
2014-01-01
Background/Aims The major compounds of Cochinchina momordica seed extract (SK-MS10) include momordica saponins. We report that the gastroprotective effect of SK-MS10 in an ethanol-induced gastric damage rat model is mediated by suppressing proinflammatory cytokines and downregulating cytosolic phospholipase A2 (cPLA2), 5-lipoxygenase (5-LOX), and the activation of calcitonin gene-related peptide. In this study, we evaluated the gastroprotective effects of SK-MS10 in the nonsteroidal anti-inflammatory drug (NSAID)-induced gastric damage rat model. Methods The pretreatment effect of SK-MS10 was evaluated in the NSAID-induced gastric damage rat model using aspirin, indomethacin, and diclofenac in 7-week-old rats. Gastric damage was evaluated based on the gross ulcer index by gastroenterologists, and the damage area (%) was measured using the MetaMorph 7.0 video image analysis system. Myeloperoxidase (MPO) was measured by enzyme-linked immunosorbent assay, and Western blotting was used to analyze the levels of cyclooxygenase (COX)-1, COX-2, cPLA2, and 5-LOX. Results All NSAIDs induced gastric damage based on the gross ulcer index and damage area (p<0.05). Gastric damage was significantly attenuated by SK-MS10 pretreatment compared with NSAID treatment alone (p<0.05). The SK-MS10 pretreatment group exhibited lower MPO levels than the diclofenac group. The expression of cPLA2 and 5-LOX was decreased by SK-MS10 pretreatment in each of the three NSAID treatment groups. Conclusions SK-MS10 exhibited a gastroprotective effect against NSAID-induced acute gastric damage in rats. However, its protective mechanism may be different across the three types of NSAID-induced gastric damage models in rats. PMID:24516701
NASA Astrophysics Data System (ADS)
Escalona, Luis; Díaz-Montiel, Paulina; Venkataraman, Satchi
2016-04-01
Laminated carbon fiber reinforced polymer (CFRP) composite materials are increasingly used in aerospace structures due to their superior mechanical properties and reduced weight. Assessing the health and integrity of these structures requires non-destructive evaluation (NDE) techniques to detect and measure interlaminar delamination and intralaminar matrix cracking damage. The electrical resistance change (ERC) based NDE technique uses the inherent changes in conductive properties of the composite to characterize internal damage. Several works that have explored the ERC technique have been limited to thin cross-ply laminates with simple linear or circular electrode arrangements. This paper investigates a method of optimum selection of electrode configurations for delamination detection in thick cross-ply laminates using ERC. Inverse identification of damage requires numerical optimization of the measured response with a model predicted response. Here, the electrical voltage field in the CFRP composite laminate is calculated using finite element analysis (FEA) models for different specified delamination size and locations, and location of ground and current electrodes. Reducing the number of sensor locations and measurements is needed to reduce hardware requirements, and computational effort needed for inverse identification. This paper explores the use of effective independence (EI) measure originally proposed for sensor location optimization in experimental vibration modal analysis. The EI measure is used for selecting the minimum set of resistance measurements among all possible combinations of selecting a pair of electrodes among the n electrodes. To enable use of EI to ERC required, it is proposed in this research a singular value decomposition SVD to obtain a spectral representation of the resistance measurements in the laminate. The effectiveness of EI measure in eliminating redundant electrode pairs is demonstrated by performing inverse identification of
Model based manipulator control
NASA Technical Reports Server (NTRS)
Petrosky, Lyman J.; Oppenheim, Irving J.
1989-01-01
The feasibility of using model based control (MBC) for robotic manipulators was investigated. A double inverted pendulum system was constructed as the experimental system for a general study of dynamically stable manipulation. The original interest in dynamically stable systems was driven by the objective of high vertical reach (balancing), and the planning of inertially favorable trajectories for force and payload demands. The model-based control approach is described and the results of experimental tests are summarized. Results directly demonstrate that MBC can provide stable control at all speeds of operation and support operations requiring dynamic stability such as balancing. The application of MBC to systems with flexible links is also discussed.