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.

Integration of functional elements into fibre-reinforced host structures provides the possibility for in situ monitoring of the structural integrity of critical components. In this study, a vibration-based monitoring function has been developed that allows the structural integrity identification of critical components. For this purpose, signal analysis algorithms were developed to enable the estimation of damage-dependent modal damping. The analysed smart structure was a carbon fibre–reinforced epoxy composite plate with an integrated actuating/sensing system. The local material damping is a parameter especially sensitive to different failure modes of composites. In order to characterise the changes of this parameter resulting from impact events, dynamical mechanical analysis on intact and damaged specimens made of the composite material was conducted. Based on the dynamical mechanical analysis results, a finite element model of the structure was developed. Then, modal damping ratios for different sizes and locations of damaged regions were numerically determined, and a relation between modal damping and damage-dependent local damping was identified. The deterministic decision trees describing the reverse relationship between online-measured modal damping and damage condition were determined. That was accomplished through the application of information entropy-based data-mining algorithms to the numerically generated learning dataset obtained using the developed finite element model.

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.

No abstract

Function-integrative lightweight engineering represents an essential element in modern design methods. Currently, there is a great need for the incorporation of sensors, actuators and electronics in novel, demand-oriented components. In contrast to a subsequent, mostly adhesive bonding, structural integration offers numerous advantages, for example in terms of space requirements and robustness. This paper demonstrates the potential of integrated sensors for various industrial sectors based on selected examples from mechanical engineering, aviation, mobility, sports, and medical technology.

No abstract

The unique potential to integrate functional elements into fibre-reinforced components combined with the recent progress in the simulation models of composite materials provides new perspectives for reliability improvement of the next generation components. Such combination is presented on the example of a carbon-fibre reinforced composite plate with integrated vibration measurement and excitation systems. The investigated structure was consolidated in an adapted resin transfer moulding process using additional layers for positioning, contacting and isolating of the active elements. The integrated elements enable an online estimation of the structural dynamic behaviour and its damage-dependent changes.The article considers the identification problem of diagnostic models enabling a precise interpretation of the measured vibration responses. An approach based on the generation of classifiers by means of inductive machine learning algorithms is applied. At the baseline phase, modal properties are measured that correspond to the undamaged state of the structure. Using these experimental data, a simulation model of the structure was fitted by means of a mixed numerical experimental technique and used for the generation of multiple vibration patterns resulting from different mass distributions. The unique combination of experimental and numerical results enables a generation of high resolved learning datasets for machine learning algorithms using a minimum amount of experimental data. The verification of the estimated classifiers by means of the achievable diagnostic performance is firstly conducted theoretically using standardised validation techniques and a high performance is identified. Then, at the inspection phase, the performance of the whole diagnostic system is additionally experimentally confirmed based on the dynamic response resulting from different unseen structural disturbances.

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.