The structure-permeability relation of textile reinforcements

The limits of production processes of composites are explored increasingly. A higher performance and a higher quality are demanded at lower cost prices. Inevitably, a thorough understanding of the processes occurring during the production is essential to meet the imposed demands. The research presented here aims to increase the fundamental knowledge on a crucial part of the Resin Transfer Moulding (RTM) production technology: the impregnation behaviour of textile reinforcements. In RTM, a near-net-shaped, dry, textile preform is manufactured and placed in a closely fitting mould. Resin is subsequently injected, typically at a pressure varying between 2 and 10 bars relative to the atmospheric pressure. The textile reinforcement is made of a fibre bundle structure, which can either be a preform made of (a stack of) woven fabrics or Non¿Crimp Fabrics (NCF), or be a preform manufactured employing automated preforming technologies such as braiding and fibre placement technologies

Smart Autonomous Sensor Network for Multilevel Damage Identification

If there is anything industrial application can learn from nature, then it is flexibility and adaptiveness. Humanity has invented, designed and implemented a increasingly complex set of technological solutions to achieve more, make life more easy and reach further than our natural capacity allows us. However, only recently developments started to hand over the control to systems. While not disregarding the potentially negative sides of this, the concept of autonomous operation systems does exhibit a significant positive contribution to for example monitoring systems. Control of these systems includes the decision on what to monitor when and how and ultimately which action is to be taken based on the outcome of the monitoring. Normally, this is a task assigned to humans, which are generally considered as trustworthy and sufficiently flexible to recognize out of the ordinary responses. The objectiveness of the human judgment is however a weak point and the inability to recognize new, yet unknown outliers in a signal is increasingly pushed back by new technologies to resolve or circumvent this issue. Bringing this line of thought to the application of an actual application of a damage identification system for a safety critical composite structure, results in the concept of a smart autonomous sensor network using piezo-electric sensors. The use of piezo-electric sensors is crucial, due to their chameleon characteristic: they can be used as sensor, actuator and harvester. Focusing on the first two functionalities, a given set of piezo-electric transducers (PZTs) is embedded in a composite skin stiffener structure, which is excited by a shaker mimicking an operational, vibrating condition. In normal mode, the transducers measure the dynamic response of the system. Depending on several possible triggers, such as time, an impact event or anomaly identification based on the dynamic response, the mode of operation switches to a specific form of active, for example, Vibro-Acoustic Modulation (VAM) or acousto-ultrasonic (AU) measurement at a specific location in the network. All without human interference: all decisions on what to do when and how are taken by the control unit of the network. Ultimately, the outcome of the analysis of the system includes an operational control action, such as stopping the system (shut down) or limiting the maximum power. A leaner version simply issues a warning to the user that a specific component needs attention

Aligning PHM, SHM and CBM by understanding the physical system failure behaviour

In this work the three disciplines of condition based maintenance (CBM), structural health monitoring (SHM) and prognostics and health management (PHM) are described and the characteristics of the disciplines are compared. The three approaches are then demonstrated using three different case studies on bearing vibration monitoring, composite panel structural health monitoring and helicopter landing gear prognostics, respectively. After a discussion on the benefits of understanding the system (failure) behaviour, an integrated approach is proposed in\ud which the three disciplines are aligned. This approach starts from defining an appropriate monitoring strategy and eventually leads to decision support in taking the decisions that lead to an optimal maintenance process throughout the life cycle of the asset

Actuators for smart applications

Actuator manufacturers are developing promising technologies\ud which meet high requirements in performance, weight and\ud power consumption. Conventionally, actuators are characterized\ud by their displacement and load performance. This hides the\ud dynamic aspects of those actuation solutions. Work per weight\ud performed by an actuation mechanism and the time needed to\ud develop this mechanical energy are by far more relevant figures.\ud Based on these figures, a selection process was developed.\ud With time and energy constraints, it highlights the most\ud weight efficient actuators. This process has been applied to the\ud Gurney flap technology used as a morphing concept for rotorblades.\ud Three control schemes were considered and simulations\ud were performed to investigate the mechanical work required. It\ud brought forward piezoelectric stack actuators as the most effective\ud solution in the case of an actively controlled rotorblade. The\ud generic nature of the procedure allows to use it for a wide range\ud of applications

Development of a multigrid finite difference solver for benchmark permeability analysis

A finite difference solver, dedicated to flow around fibre architectures is currently being developed. The complexity of the internal geometry of textile reinforcements results in extreme computation times, or inaccurate solutions. A compromise between the two is found by implementing a multigrid algorithm and analytical solutions at the coarsest level of discretisation. Hence, the computational load of the solver is drastically reduced.\ud This paper discusses the main features of the 3D multigrid algorithm implemented as well as the implementation of the analytical solution in the finite difference scheme. The first tests of the solver on the permeability benchmark lithographic reference geometry are discussed.\ud Several tests were performed to assess the accuracy and the reduction in calculation time. The methods prove to be both accurate and efficient. However, the code is developed in Matlab© and hence is relatively slow. A C++ code is currently under development to achieve acceptable calculation times

Geometric Optimisation of Hinge-less Deployment System for an Active Rotorblade

The Green Rotorcraft project (part of Clean Sky JTI) is\ud studying the Gurney flap as a demonstrator of a smart adaptive\ud rotorblade. Deployment systems for the Gurney flap need to\ud sustain large centrifugal loads and vibrations while maintaining\ud precisely the displacement under aerodynamic loading. Designing\ud such a mechanism relies on both the actuation technology\ud and the link which transmits motion to the control surface. Flexible\ud beams and piezoelectric patch actuators have been chosen as\ud components to design this mechanism. Flexible beams are providing\ud an hinge-less robust structure onto which the piezoelectric\ud actuators are bonded. A candidate topology is determined\ud by investigating the compliance of a simple wire structure with\ud beam elements. A parametrized finite element model is then built\ud and optimized for displacement and force through surrogate optimization.\ud The whole process does not requires many finite element\ud analyses and quickly converge to an optimized mechanism

The Detection of Fatigue Damage Accumulation in a Thick Composite Beam Using Acousto Ultrasonics

The Acousto Ultrasonics (AU) technique is a Non-Destructive Testing (NDT) technique, widely used for thin, plate-like composite structures. The application of this technique to thick structures, such as the spar cap of rotor blades of wind turbines is considered promising. A problem for the spar caps is fatigue damage. This paper therefore focusses on the fatigue damage detection in a thick composite beam. Two laboratory specimens with a thickness of 56 mm, width of 60 mm and length of 900 mm are equipped with piezo-electric transducers on the top and bottom surface. Short ultrasonic burst waves with varying actuation frequencies are sent by one transducer and measured with the other transducers. Preliminary tests are executed to assess the damage detection capability. The damage is initially simulated by drilling a hole at one location with a stepwise increasing depth of 10 to 56 mm. The number of actuator-sensor paths crossing the simulated damage increases for increasing hole depth. Various Damage Indicator (DI) algorithms and the Reconstruction Algorithm for Probabilistic Inspection of Damage (RAPID) are used for damage assessment and visualisation. A correlation between the DI values and the severity and location of the damage is found. This result is a positive indication for the applicability of AU for damage detection in thick composite structures. A second identical beam is currently placed in a three-point bending fatigue setup