Stab resistance of smart polymer coated textiles reinforced with particle additives
Smart materials have attracted much attention due to their potential applications. Shear stiffening polymer is one of smart materials having increasing stiffness under loading. Although there are only few studies dealing with shear stiffening polymers, we developed a new concept by reinforcing this material with carbide particles for the first time. In this work, different amounts of carbide particles were included in a shear stiffening polymer and the influences of additives were investigated through rheological measurements. From the rheological results, it can be stated that carbide particles result in much stiffer properties in the polymers however, the composites still keep their viscous behavior at low shear rates. In addition to the rheological investigations, these smart materials were used as coatings on high performance textiles which were subjected to low velocity stab tests. According to the stab tests, shear stiffening polymer provides a substantial improvement in the energy absorption of the targets however, carbide reinforced ones take this development a step further by the effect of additional particles within the matrix.
Predictive analysis of stitched aerospace structures for advanced aircraft
In recent years, the aviation industry has taken a leading role in the integration of composite structures to develop lighter and more fuel efficient aircraft. Among the leading concepts to achieve this goal is the Pultruded Rod Stitched Efficient Unitized Structure (PRSEUS) concept. The focus of most PRSEUS studies has been on developing an hybrid wing body structure, with only a few discussing the application of PRSEUS to a tube-wing fuselage structure. Additionally, the majority of investigations for PRSEUS have focused on experimental validation of anticipated benefits rather than developing a methodology to capture the behavior of stitched structure analytically. This paper presents an overview of a numerical methodology capable of accurately describing PRSEUS' construction and how it may be implemented in a barrel fuselage platform resorting to high-fidelity mesoscale modeling techniques. The methodology benefits from fresh user defined strategies developed in a commercially available finite element analysis environment. It further proposes a new approach for improving the ability to predict deformation in stitched composites, allowing for a better understanding of the intricate behavior and subtleties of stitched aerospace structures.
The paper presents the design and experimental testing of the control system used in a new morphing wing application with a full-scaled portion of a real wing. The morphing actuation system uses four similar miniature brushless DC (BLDC) motors placed inside the wing, which execute a direct actuation of the flexible upper surface of the wing made from composite materials. The control system of each actuator uses three control loops (current, speed and position) characterised by five control gains. To tune the control gains, the Particle Swarm Optimisation (PSO) method is used. The application of the PSO method supposed the development of a MATLAB/Simulink (R) software model for the controlled actuator, which worked together with a software sub-routine implementing the PSO algorithm to find the best values for the five control gains that minimise the cost function. Once the best values of the control gains are established, the software model of the controlled actuator is numerically simulated in order to evaluate the quality of the obtained control system. Finally, the designed control system is experimentally validated in bench tests and wind-tunnel tests for all four miniature actuators integrated in the morphing wing experimental model. The wind-tunnel testing treats the system as a whole and includes, besides the evaluation of the controlled actuation system, the testing of the integrated morphing wing experimental model and the evaluation of the aerodynamic benefits brought by the morphing technology on this project. From this last perspective, the airflow on the morphing upper surface of the experimental model is monitored by using various techniques based on pressure data collection with Kulite pressure sensors or on infrared thermography camera visualisations.
Crashworthiness Analysis and Enhancement of Aircraft Structures Under Vertical Impact Scenarios
This research focuses on the crashworthiness study and enhancement of commercial aircraft structures by developing crushable energy absorbers to work as vertical struts (stanchions). To assess their contribution on a representative crash scenario, a numerical simulation of a Boeing 737-200 drop test developed and verified with experimental data is used as a benchmark. The numerical model is then enhanced with four hybrid energy absorbers designed for programmed and progressive collapse, which are added in the cargo compartment connecting the floor beams and the frames. These devices are composed of a square aluminum tube filled with a composite skeleton and foam extrusions for maximized energy absorption. The enhanced aircraft is later simulated under hard-landing and water-ditching scenarios, analyzing the benefits resulting from the absorbers according to structural efficiency and biometric criteria. The results show increased plastic dissipation values by the main structural components given the modified collapse mechanism obtained when adding the crushable absorbers. Peak acceleration values are also reduced, consequently lessening the passenger injury prediction at the studied locations.
This paper considers the effect of geometric nonlinearity on gust load analyses of high-aspect-ratio commercial aircraft. Three variants of a conceptual aircraft, featuring wing aspect ratios of 10, 18, and 26, are sized using an industrially inspired procedure to obtain realistic structures of existing and future designs. These aircraft are modeled in a nonlinear aeroelastic framework, featuring a geometrically exact beam formulation coupled with unsteady aerodynamics, and subjected to a gust loads process adapted for nonlinear systems. The gust analysis is also carried out using a linear approach (linearizing the equations of motion about an undeformed or trimmed geometry) to understand how nonlinearities influence the loads and dynamic behavior of aircraft as the aspect ratio increases. Load envelopes show that vertical shear and bending moments are predicted well by the linear analyses, even for the aspect-ratio-26 case, providing that the linearization is performed about the trimmed geometry. In contrast, the in-plane and axial loads are significantly underestimated using linear analyses. Torque behavior is problem specific and therefore difficult to generalize. Even on the aspect-ratio-10 case, which would traditionally be considered as a linear problem, it can be shown that the torque loads are considerably affected by nonlinearity.
Response surface characterization for biaxial tensile properties of envelope fabrics under multiple stress ratios
As the most frequently used material in stratospheric airship, the mechanical properties of envelope fabrics that are significant for the structural analysis have attracted widespread attention. Biaxial cyclic tensile load with eleven stress ratios were applied to estimate tensile properties of envelope fabrics. Based on the stress-strain curves of eleven stress ratios, polynomial fitting provided a reliable and convenient method to describe the biaxial tensile behavior of envelope fabrics. Besides, the response surfaces of stiffness and Poisson's ratios were calculated by the least-square method and fitted by binary quadratic polynomial. The accuracy of polynomial fitting method was analyzed, and the elastic properties of envelope fabrics provide reference for engineering application.
Airframe digital twin technology adaptability assessment and technology demonstration
The National Research Council of Canada (NRC) is currently reviewing and assessing the airframe digital twin (ADT) framework being developed by the United States Air Force (USAF). The goal is to investigate the adaptability and potential application of the ADT for reducing maintenance cost and maximize availability of the existing and future fleets of the Royal Canadian Air Force (RCAF). The USAF ADT framework is based on a probabilistic and prognostic individual aircraft tracking approach, which intends to improve the current individual aircraft tracking (IAT) program by quantifying and updating the uncertainties of some IAT parameters in airframe fatigue life assessment. This paper presents the results from recent work at NRC, including: (1) a review and evaluation of the digital twin and digital thread concepts, especially the USAF ADT framework, methodstool, (2) a brief survey of structural lifing methods and IAT systems of selected RCAF aircraft, (3) a feasibility and adaptability study of the ADT to RCAF aircraft, and (4) the development of NRC ADT technologies, including Bayesian updating algorithms and a demonstration case being developed based on a CF188 fullscale component test. In conclusion, the NRC review and assessment show that the USAF ADT framework can be adapted to support the RCAF fleets that are managed using IATbased programs. The NRC models and tools developed from previous projects can be expanded to serve as the core of an ADT framework that can be implemented for RCAF fleets. Some shortterm and longterm benefits are identified and discussed in this paper for future research and application.
Development of highly electrically conductive composites for aeronautical applications utilizing bi-functional composite interleaves
With the wide application of composite materials in modern aerospace industry, multifunctional carbon fibre composites are likely to play an important role in next generation aircraft. Here, carbon fibre reinforced epoxy composites were produced by using Functionalized Interleaf Technology (FIT). The electroless coppernickel plated polyester veils (CNPV) were used as the interleaves to replace the initial resinrich interlaminar regions with functional interlayers. The latter shows useful toughening efficiency, in which the G Ic and G IIc values for interleaved specimens increased by 59% and 31%, respectively. At the same time, the inplane ( xy ) and throughthickness ( z ) electrical conductivities were also improved from 74.12 Scm to 1079.6 Scm and 1.510 3 Scm to 5.29 Scm, respectively. Moreover, it is found that the effective electric contact area at electrodes was increased by incorporating additional functionalized veils. Therefore, the interleaf material can be characterized by its bifunctionality as it provides both toughening efficiency in the interlaminar region and the ability to form an electrically conductive path crossing the resinrich interlaminar layer, perpendicular to the laminate plane.
Towards a digital twin for mitigating void formation during debulking of autoclave composite parts
Highperformance polymeric composites are increasingly used in the design of aircraft structural components however, susceptibility to manufacturing irregularities, including porosityvoids, remains a primary challenge delaying the implementation of advanced composites in modern aircraft. Voids may be precursors to structural damage significantly affecting structural integrity and remaining useful life of the aircraft. Highperformance aerospace composite parts are commonly manufactured from resinsaturated preimpregnated plies of uncured material laidup over a rigid tool and consolidated and cured in an autoclave. In many applications, especially in thick and curved composite sections common in aerospace designs, autoclave consolidation alone is not sufficient to remove the air, or bulk, that might have been entrapped within the laminate during the layup process. Vacuum consolidation, or “debulking”, has been a standard practice extensively used by manufacturers to reduce the amount of bulk prior to autoclave curing. The debulking process typically takes a long time and requires intensive manual operations. The underlying physical principles governing the formation and evolution of voids during these early stages of the manufacturing process are not yet well understood, and controlling parameters remain largely determined empirically or based on prior experience. Driven by the need to improve such understanding, there has been a recent interest in using newly available highfidelity nondestructive inspection (NDI) techniques, such as Xray Computed Tomography, for in situ observations of composites internal structure during the early stages of manufacturing. In situ observations are allowing researchers to identify the driving mechanisms involved during defect formation and develop improved predictive models. The objective of this work is to show that highfidelity NDI data and new developments in numerical modeling can be combined to create a Digital Twin for mitigation of void formation in composite parts. In particular, Xray CT data is used to extract bulk content and distribution in uncured carbonepoxy curvedbeam specimens after manual layup, and such information is transferred into a finite element (FE) model for simulation of debulking. The FE model uses a fracturebased approach that relies on porepressure cohesive zone modeling recently proposed for the discrete representation of entrapped air pockets in uncured resinsaturated prepregs. Preliminary results support a promising ability of the Digital Twin concept for optimizing the debulking process of autoclave composites towards mitigating void formation.
Tensile properties of carbon nanotubes reinforced aluminum matrix composites: A review
Carbon nanotubes (CNT) have received huge attention from the scientific community in the last two decades due to their unique structure and properties. They have been considered for potential applications in various areas of science and technology. One of the major applications of CNT is as reinforcement for fabrication of light weight high strength composite materials for use in automobile and aerospace applications. Aluminium and its alloys are natural choices for such applications due to their low density, high specific strength and modulus. In the last decade, there have been significant advances in the processing of carbon nanotube reinforced aluminium matrix (AlCNT) composites. New understanding has emerged due to research on several aspects such as damage to CNTs during processing, interfacial phenomena, novel methods of processing for improving CNT dispersion, tensile behaviour, numerical modelling and in situ tensile testing. This review summarizes the present status of the tensile properties of pure AlCNT and Al alloyCNT composites. The various processing routes for fabrication of AlCNT composites have been compared in terms of the resulting microstructure, degree of CNT dispersion, extent of interfacial reaction and its effect on the tensile properties. Factors affecting strengthening efficiency and the strengthening mechanisms in AlCNT composites are discussed.