In this work, single-curvature V-bending experiments are carried out on pre-consolidated Carbon Fibre/Poly Ether Ketone (CF/PEKK) composites to determine their formability during thermo-forming operations. A Design of Experiments (DoE) approach is used to investigate the spring-back by varying forming parameters systematically. The formed sample is examined under an optical microscope to visualise inter-ply and intra-ply deformations that occurred during the forming operation. The DoE results indicate the contribution of the bending radius factor on the spring-back of CF/PEKK composites to be the greatest. Image analysis shows inter-ply slip to be the primary mode of deformation during the forming operation, followed by intra-ply movement, causing a negligible decrease in the laminate thickness.
The compaction plays a major role in characterizing the behavior of prepreg. Prepregs are known to exhibit viscoelastic behavior. This study will investigate the compaction rate effect of uncured glass/epoxy prepreg. The results showed that as the rate decreases the prepreg can achieve higher volume fraction. A non-linear elastic model was used to capture the compaction results. However, a viscoelastic model is needed to predict the behavior more accurately.
Prepregs have been widely used in composite manufacturing of advance aero structure. Compaction of prepreg in its uncured state is a key step in the manufacturing process techniques such as autoclave, out-of-autoclave, and automated tape layup processing. Prepreg are known to exhibit viscoelastic behaviour because of the presence of resin and fabric reinforcement. Modelling the compaction of prepreg in such process would enable to develop process models. In this paper, a hyper-viscoelastic model based on QLV approach is utilized to model the time dependent response of prepreg. Experimental data at different compaction were used and the model parameters were determined using the least square fitting
This paper involves an investigation of the ability of steady, quasi-steady and unsteady aerodynamic models to predict aeroelastic flutter in incompressible subsonic flow on aircraft wings. The wing structure is modelled as a Euler-Bernoulli cantilever beam, with shape functions incorporated for bending and torsional modes via Rayeligh-Ritz method, and aerodynamic models are constructed using strip theory. The equations of motion for the 2 degrees of freedom wing in pitch and plunge are developed using Lagrangian method. Three aerodynamic models in frequency domain and one unsteady model in time-domain are presented and all results are compared to available literature data. It is shown that quasi-steady models possess inadequate accuracy in determination of flutter phenomena. Steady aerodynamic model underpredicts flutter velocity, however, can be used for initial design stages. Unsteady flow models are the most reliable either in frequency or time-domain and predict the flutter velocity with highest accuracy.
This article presents the compression response and energy absorption capabilities of novel carbon fiber reinforced thermoplastic honeycombs manufactured through vacuum assisted resin transfer molding technique. The composite honeycombs were fabricated in a steel mold having removable hexagonal rings inside each honeycomb cell. The novel honeycombs exhibited compressive strength as high as 39.5 MPa and specific energy absorption values in excess of 50 kJ/kg. It was observed that increasing the fiber weight fraction significantly improved the compressive response of the honeycomb cores. Furthermore, the results showed that the thermoplastic honeycombs exhibited better energy absorption capabilities compared to their epoxy counterparts.
This study explores the potential of Sweeping Jet Actuators as effective flow control devices for bluff body drag reduction. A baseline actuator design installed on Ahmed body in mid plane configuration provides a decrease in base suction resulting in reduced drag. Slight variations in maximum suction pressure reduction are also observed for different internal geometries of the actuator. Sweeping Jet Actuators may be applied as an alternative to steady jet base blowing, provided the location of actuator is such that the detrimental interaction of blown jet with global shear layers is kept minimized.
Our knowledge about Uranus and its moons is scarce. To gain insight into the features of this planet and its satellites, an exploration mission is needed. Uranus axial tilt of 98? requires a prohibitive amount of propellant for insertion into an equatorial orbit. To minimize the cost of the orbit insertion maneuver, a combination of low-thrust (LT) propulsion and gravity assist (GA) at Jupiter is explored. GA is applied at Jupiter en route to Uranus followed by a LT direct optimization approach that minimizes the inclination angle relative to the Uranus equator upon arrival at Uranus. This approach lowers the orbit insertion impulse significantly for the capture into a near-equatorial orbit around Uranus which is required for observation of the features of the planet and its major moons. The LT optimization method, the control-law algorithm, the benefits to the propellant budget, and areas for further progress are presented and discussed.
The recent discoveries made by the Cassini spacecraft have greatly heightened the urge of the scientific community and space agencies in proposing scientific missions to explore Saturn and its moons. This work builds upon the results of two prior contributions regarding the Earth-to-Saturn interplanetary transfer characterized by a low relative arrival speed (1 km/s) and the concept of the lunar cycler to perform an observational tour of the Inner Large Moons of Saturn (Mimas, Enceladus, Tethys, Dione). The main objective here is to minimize propellant cost during the complete mission from the interplanetary arrival at Saturn to the final orbits around the inner moons. In this work, a novel scenario is proposed where a capture around Saturn via gravity assist with Titan is made possible. A sequence of swingbys with Titan, Rhea, and the Inner Large Moons (ILMs) is proposed to bridge between interplanetary space and the lunar tour.
Osteoporosis is the fourth most common chronic disease in the world. Adopting preventative measures and effective self-management interventions helps in improving bone health. Mobile health (mHealth) technologies can play a key role in osteoporosis patient care and self- management. Presently, there is a limited number of mHealth applications available for supporting patients with osteoporosis or healthcare professionals in the research field and in the market place. These applications are in most of the cases poorly designed, have weak performance, and lack evidence-based validation. In this work, we review the available osteoporosis-related mHealth apps and we suggest some guidelines for the development of new, more comprehensive mHealth apps that facilitate self-management of osteoporosis in addition to the decision support and the shared-decision making.
Three-dimensional bioprinting is an emerging fabrication technique in the field of tissue engineering. Extrusion-based bioprinting is one of the widely employed biofabrication techniques; researchers tend to use it because of its simplicity, affordability and scalability. During the extrusion-based bioprinting process, cells are subjected to mechanical forces of different kinds. Among these mechanical forces, shear stress is of a special significance and concern as it is considered the main cause of cell damage/death. This paper covers the principle of extrusion-based bioprinting and the bioinks used. Moreover, it highlights extrusion-based bioprinting induced shear stress, and the relationship between shear stress, cell viability and different material properties and process parameters.
