scholarly journals Influence of Gradual Damage on the Structural Dynamic Behaviour of Composite Rotors: Simulation Assessment

Materials ◽  
2018 ◽  
Vol 11 (12) ◽  
pp. 2453 ◽  
Author(s):  
Angelos Filippatos ◽  
Albert Langkamp ◽  
Maik Gude
Keyword(s):  
Damage Evolution ◽  
Composite Structures ◽  
Damage Mechanics ◽  
Dynamic Behaviour ◽  
Damage Identification ◽  
Simulation Analysis ◽  
Element Model ◽  
Model Quality ◽  
Structural Dynamic ◽  
Damage Initiation

Fibre-reinforced composite structures under complex loads exhibit gradual damage behaviour with degradation of effective mechanical properties and change of their structural dynamic behaviour. In case of composite rotors, this can lead to catastrophic failure if an eigenfrequency is met by the rotational speed. The description and simulation analysis of the gradual damage behaviour of composite rotors therefore provides the fundamentals for a first understanding of complex and partially-unpredicted structural phenomena. Therefore, a simulation tool is developed using a finite element model, which calculates the damage-dependent structural dynamic behaviour of selected composite rotors considering both damage initiation and in-plane damage evolution due to a combination of out-of-plane and in-plane loads. Damage initiation is determined using failure criteria, whereas the gradual damage evolution using a validated continuum damage mechanics model. Numerical results are compared with experimental results for rotor-typical stress states to assess the model quality, which could be later used for damage identification approaches.

scholarly journals Structural Damage Identification of Composite Rotors Based on Fully Connected Neural Networks and Convolutional Neural Networks

Sensors ◽  
2021 ◽  
Vol 21 (6) ◽  
pp. 2005
Author(s):  
Veronika Scholz ◽  
Peter Winkler ◽  
Andreas Hornig ◽  
Maik Gude ◽  
Angelos Filippatos
Keyword(s):  
Neural Networks ◽  
Convolutional Neural Networks ◽  
Composite Structures ◽  
Damage Identification ◽  
Vibration Response ◽  
Damage Initiation ◽  
Matrix Cracks ◽  
Operational Life ◽  
Multiple Data Sets ◽  
Fully Connected

Damage identification of composite structures is a major ongoing challenge for a secure operational life-cycle due to the complex, gradual damage behaviour of composite materials. Especially for composite rotors in aero-engines and wind-turbines, a cost-intensive maintenance service has to be performed in order to avoid critical failure. A major advantage of composite structures is that they are able to safely operate after damage initiation and under ongoing damage propagation. Therefore, a robust, efficient diagnostic damage identification method would allow monitoring the damage process with intervention occurring only when necessary. This study investigates the structural vibration response of composite rotors by applying machine learning methods and the ability to identify, localise and quantify the present damage. To this end, multiple fully connected neural networks and convolutional neural networks were trained on vibration response spectra from damaged composite rotors with barely visible damage, mostly matrix cracks and local delaminations using dimensionality reduction and data augmentation. A databank containing 720 simulated test cases with different damage states is used as a basis for the generation of multiple data sets. The trained models are tested using k-fold cross validation and they are evaluated based on the sensitivity, specificity and accuracy. Convolutional neural networks perform slightly better providing a performance accuracy of up to 99.3% for the damage localisation and quantification.

scholarly journals Influence of Gradual Damage on the Structural Dynamic Behaviour of Composite Rotors: Experimental Investigations

Materials ◽  
2018 ◽  
Vol 11 (12) ◽  
pp. 2421 ◽  
Author(s):  
Angelos Filippatos ◽  
Maik Gude
Keyword(s):  
Mechanical Properties ◽  
Composite Structures ◽  
Dynamic Behaviour ◽  
Experimental Investigations ◽  
Catastrophic Failure ◽  
Structural Dynamic ◽  
Delamination Growth ◽  
Reinforced Composite ◽  
Out Of Plane ◽  
Effective Mechanical Properties

Fibre-reinforced composite structures subjected to complex loads exhibit gradual damage behaviour with the degradation of the effective mechanical properties and changes in their structural dynamic behaviour. Damage manifests itself as a spatial increase in inter-fibre failure and delamination growth, resulting in local changes in stiffness. These changes affect not only the residual strength but, more importantly, the structural dynamic behaviour. In the case of composite rotors, this can lead to catastrophic failure if an eigenfrequency coincides with the rotational speed. The description and analysis of the gradual damage behaviour of composite rotors, therefore, provide the fundamentals for a better understanding of unpredicted structural phenomena. The gradual damage behaviour of the example composite rotors and the resulting damage-dependent dynamic behaviour were experimentally investigated under propagating damage caused by a combination of out-of-plane and in-plane loads. A novel observation is the finding that a monotonic increase in damage results in a non-monotonic frequency shift of a significant number of eigenfrequencies.

scholarly journals A Sequence-Based Damage Identification Method for Composite Rotors by Applying the Kullback–Leibler Divergence, a Two-Sample Kolmogorov–Smirnov Test and a Statistical Hidden Markov Model

Entropy ◽  
2019 ◽  
Vol 21 (7) ◽  
pp. 690 ◽  
Author(s):  
Angelos Filippatos ◽  
Albert Langkamp ◽  
Pawel Kostka ◽  
Maik Gude
Keyword(s):  
Markov Model ◽  
Hidden Markov Model ◽  
Composite Structures ◽  
Damage Identification ◽  
Hidden Markov ◽  
Structural Dynamic ◽  
Identification Method ◽  
Leibler Divergence ◽  
Kolmogorov Smirnov ◽  
Smirnov Test

Composite structures undergo a gradual damage evolution from initial inter-fibre cracks to extended damage up to failure. However, most composites could remain in service despite the existence of damage. Prerequisite for a service extension is a reliable and component-specific damage identification. Therefore, a vibration-based damage identification method is presented that takes into consideration the gradual damage behaviour and the resulting changes of the structural dynamic behaviour of composite rotors. These changes are transformed into a sequence of distinct states and used as an input database for three diagnostic models, based on the Kullback–Leibler divergence, the two-sample Kolmogorov–Smirnov test and a statistical hidden Markov model. To identify the present damage state based on the damage-dependent modal properties, a sequence-based diagnostic system has been developed, which estimates the similarity between the present unclassified sequence and obtained sequences of damage-dependent vibration responses. The diagnostic performance evaluation delivers promising results for the further development of the proposed diagnostic method.

scholarly journals Modal Identification of Output-Only Systems of Composite Discs Using Zernike Modes and MAC

Sensors ◽  
2019 ◽  
Vol 19 (3) ◽  
pp. 660 ◽  
Author(s):  
Minh Nguyen ◽  
Angelos Filippatos ◽  
Albert Langkamp ◽  
Maik Gude
Keyword(s):  
Composite Structures ◽  
Dynamic Behaviour ◽  
Correlation Method ◽  
Modal Identification ◽  
Diagnostic Methods ◽  
Mode Shapes ◽  
Modal Assurance Criterion ◽  
Significant Information ◽  
Structural Dynamic ◽  
Modal Properties

The analysis of the structural dynamic behaviour of composite rotor–discs by a valid description of the eigenfrequencies and mode shapes can provide significant information for action-taking before a failure occurs. Specifically, vibration-based diagnostic methods, which are able to take into consideration the interdependencies and sequential changes of the modal properties could benefit from such an analysis. Here, on the example of composite rotors, a correlation method for experimentally determined mode shapes is developed. For this purpose the Zernike polynomials are used to enhance the identification of mode shapes. Furthermore, the modal assurance criterion (MAC) in combination with the frequency response criterion and a data processing approach are applied in order to characterize changing modal properties of composite rotors. In addition, the developed algorithms can be further extended in order to simplify the experimental evaluation of the complex dynamic behaviour of composite structures.

scholarly journals Application of discrete damage mechanics for determination of the crack density in composite laminates

2020 ◽  
Vol 310 ◽  
pp. 00002
Author(s):  
Milan Žmindák ◽  
Eva Kormaníková ◽  
Pavol Novák ◽  
Josef Soukup ◽  
Kamila Kotrasová
Keyword(s):  
Fracture Toughness ◽  
Composite Laminates ◽  
Composite Structures ◽  
Damage Mechanics ◽  
Crack Density ◽  
Matrix Cracking ◽  
Mapping Algorithm ◽  
Damage Initiation ◽  
Return Mapping

The finite element method (FEM) is one of the most widely and most popular numerical methods for analyzing damage of composite structures, In this paper discrete damage mechanics (DDM) is used to predict inter-laminar transverse and shear damage initiation and evolution in terms of the fracture toughness of the laminate. ANSYS commercial software is used for analysis of layered plate composite structure reinforced with long unidirectional fibers with Carbon/Epoxy material. Because ANSYS does not have a built-in capability for calculating crack density, we have to use plagin. A methodology for determination of the fracture toughness is based on fitting DDM model and these data are obtained from literature. Also, prediction of modulus vs. applied strain is contrasted with ply discount results and the effect of in situ correction of strength is highlighted. Evaluation of matrix cracking detected in lamina has been solved using return mapping algorithm.

scholarly journals A model of low-velocity impact damage assessment of laminated composite structures

2018 ◽  
Vol 188 ◽  
pp. 01012 ◽  
Author(s):  
Konstantinos P. Stamoulis ◽  
Stylianos K. Georgantzinos ◽  
Georgios I. Giannopoulos
Keyword(s):  
Composite Structures ◽  
Mechanical Performance ◽  
Impact Damage ◽  
Experimental Testing ◽  
Laminated Composite ◽  
Element Model ◽  
Low Velocity Impact ◽  
Low Velocity ◽  
Damage Initiation ◽  
Laminated Composite Structures

Laminated composites have important applications in modern aeronautical structures due to their extraordinary mechanical and environmental behaviour. Nevertheless, aircraft composite structures are highly vulnerable to impact damage, either by low-velocity sources during maintenance or high-velocity sources during in-flight events. Even barely visible impact damage induced by low-velocity loading, substantially reduces the residual mechanical performance and the safe-service life of the composites structures. Despite the extensive research already carried out, impact damage of laminated composite structures is still not well understood and it is an area of on-going research. Numerical modelling is considered as the most efficient tool as compared to the expensive and time-consuming experimental testing. In this paper, a finite element model based on explicit dynamics formulations is adopted. Hashin criterion is applied to predict the intra-laminar damage initiation and evolution. The numerical analysis is performed using the ABAQUS® programme. The employed modelling approach is validated using numerical results found in the literature and the presented results show an acceptable correlation to the available literature data. It is demonstrated that the presented model is able to capture force-time response as well as damage evolution map for a range of impact energies.

Influence of rough surface on damage evolution and fatigue life of M50-bearing steel containing a spherical inclusion

2019 ◽  
Vol 28 (10) ◽  
pp. 1580-1604 ◽  
Author(s):  
Jian Guan ◽  
Liqin Wang ◽  
Yunfeng Li ◽  
Chuanwei Zhang ◽  
Le Gu
Keyword(s):  
Fatigue Life ◽  
Damage Evolution ◽  
Damage Mechanics ◽  
Spherical Inclusion ◽  
Frictional Coefficient ◽  
Elastohydrodynamic Lubrication ◽  
Continuum Damage Mechanics ◽  
Element Model ◽  
Bearing Steel ◽  
Hydrodynamic Effect

In this paper, a continuum damage mechanics model is incorporated into the finite element model which contains a spherical inclusion to investigate damage evolution and predict fatigue life of M50-bearing steel. Quasi-dynamic method, isothermal elastohydrodynamic lubrication analysis and non-Gaussian surface simulating technique are combined to obtain the contact pressure. The damage evolution process of the micro-domain considering roughness texture is simulated and the fatigue life is predicted. The result shows that transverse texture can weaken the damage accumulation due to the strengthening of hydrodynamic effect. The effects of surface roughness parameters on fatigue life are also analyzed. It should be noted that transverse texture, small mean square root value and kurtosis, negative skewness are helpful for enhancing the fatigue life of bearing steel. Meanwhile, the increase of frictional coefficient and radius, negative position of local region will reduce the fatigue life.

Damage Mechanics-Finite Element Full-Couple Method to Predict the Fatigue Life of Metallic Material

2014 ◽  
Vol 707 ◽  
pp. 390-396
Author(s):  
Xian Min Chen ◽  
Di Guan ◽  
Feng Ping Yang
Keyword(s):  
Finite Element ◽  
Fatigue Life ◽  
Fatigue Test ◽  
Fatigue Damage ◽  
Damage Evolution ◽  
Damage Mechanics ◽  
Fatigue Tests ◽  
Damage Initiation ◽  
Strain Threshold ◽  
Couple Method

A damage accumulation model is presented for fatigue life prediction of metallic structures. Based on the energy theory and material fatigue test data, the plastic strain threshold for damage initiation was modified for HCF and LCF respectively. The damage evolution parameters were determined according to the fatigue test results of standard specimens. A damage mechanics-finite element full-couple method was adopted to simulate the process of fatigue damage evolution, incorporating elastic modulus reduction due to fatigue damage. Comparisons are made with the fatigue tests of 2A12-T4 open-hole plates and good agreement was obtained.

A Damage Mechanics Approach to Simulate Butterfly Wing Formation Around Nonmetallic Inclusions

2014 ◽  
Vol 137 (1) ◽  
Author(s):  
Sina Mobasher Moghaddam ◽  
Farshid Sadeghi ◽  
Nick Weinzapfel ◽  
Alexander Liebel
Keyword(s):  
Damage Evolution ◽  
Damage Mechanics ◽  
Nonmetallic Inclusions ◽  
Continuum Damage Mechanics ◽  
Element Model ◽  
Butterfly Wing ◽  
Microstructural Changes ◽  
Damage Evolution Equation ◽  
Wing Formation ◽  
Cyclic Damage

Nonmetallic inclusions such as sulfides and oxides are byproducts of the steel manufacturing process. For more than half a century, researchers have observed microstructural alterations around the inclusions commonly referred to as “butterfly wings.” This paper proposes a model to describe butterfly wing formation around nonmetallic inclusions. A 2D finite element model is developed to obtain the stress distribution in a domain subject to Hertzian loading with an embedded nonmetallic inclusion. It was found that mean stress due to surface traction has a significant effect on butterfly formation. Continuum damage mechanics (CDM) was used to investigate fatigue damage and replicate the observed butterfly wing formations. It is postulated that cyclic damage accumulation can be the reason for the microstructural changes in butterflies. A new damage evolution equation, which accounts for the effect of mean stresses, was introduced to capture the microstructural changes in the material. The proposed damage evolution law matches experimentally observed butterfly orientation, shape, and size successfully. The model is used to obtain S-N results for butterfly formation at different Hertzian load levels. The results corroborate well with the experimental data available in the open literature. The model is used to predict debonding at the inclusion/matrix interface and the most vulnerable regions for crack initiation on butterfly sides. The proposed model is capable of predicting the regions of interest in corroboration with experimental observations.

scholarly journals Influence of Gradual Damage on the Structural Dynamic Behaviour of Composite Rotors: Experimental Investigations

2018 ◽  
Author(s):  
Angelos Filippatos ◽  
Maik Gude
Keyword(s):  
Mechanical Properties ◽  
Composite Structures ◽  
Dynamic Behaviour ◽  
Experimental Investigations ◽  
Catastrophic Failure ◽  
Structural Dynamic ◽  
Delamination Growth ◽  
Reinforced Composite ◽  
Out Of Plane ◽  
Effective Mechanical Properties

Fibre-reinforced composite structures under complex loads exhibit gradual damage behaviour with a degradation of effective mechanical properties and change of their structural dynamic behaviour. Damage manifests itself as spatial increase of inter-fibre failure and delamination-growth, resulting in local changes of stiffness. These changes affect not only the residual strengths but more importantly the structural dynamic behaviour. In case of composite rotors, this can lead to catastrophic failure if an eigenfrequency coincides with the rotational speed. The description and analysis of the gradual damage behaviour of composite rotors therefore provides the fundamentals for a better understanding of unpredicted structural phenomena. The gradual damage behaviour on the example of composite rotors and the resulting damage-dependent dynamic behaviour is experimentally investigated under propagating damage for combined out-of-plane and in-plane loads. A novel observation is reported, where monotonic increase of damage results in non-monotonic frequency shift of significant amount of eigenfrequencies.

Sign in / Sign up

Export Citation Format

Share Document