Sabu John

Longitudinal and transverse damage taxonomy in woven composite components

This work addresses the issue of micro-structural damage in the longitudinal direction of the woven during a deformation process, primarily in the tensile mode. This paper extends the insight into self-inflicted damage in dimensional multilayer woven composites subjected to uniaxial tensile and shear loading. Two composites made of multilayer woven architectures, hereby named: orthogonal and normal layer interlock forms the basis of this study. It identifies the physical characteristics which initiate the various damage modes, what these modes are and when they occur. This work complements the work already reported on the transverse direction in woven composites.

An improved z-buffer CSG rendering algorithm

We present an improved z-buffer based CSG rendering algorithm, based on previous techniques using z-buffer parity based surface clipping. We show that while this type of algorithm has been reported as requiring O( ), (where is the number of primitives), an O( ) (where is depth complexity) algorithm may be substituted. For cases where is less than this translates into a significant performance gain. CR Categories: I.3.5 [Computing Methodologies]: Computer Graphics—Constructive solid geometry (CSG) I.3.3 [Computing Methodologies]: Computer Graphics—Display Algorithms I.3.1 [Computing Methodologies]: Computer Graphics—Hardware Architecture

The Effect of Ply Orientation on the Performance of Antennas in or on Carbon Fiber Composites

In this paper, the anisotropic conductivity efiect of quasi- isotropic carbon flber laminates on conformal load-bearing antenna structures (CLAS) is presented. The conductivity of a quasi-isotropic IM7/977-3 CFRP laminate is measured using waveguide techniques. The results show that orientation of the surface ply relative to the polarization of the incident E-fleld has a major in∞uence on the re∞ectivity. This difierence is attributed to the fact that carbon flbres oriented parallel to the E-fleld plies behave as good conductors, while ofi-axis plies present as lossy dielectric layers with a flnite conductivity. This anisotropic behavior of the ply layers is shown to have a distinctive in∞uence on the operation of both microstrip patch and slot antennas.

Strain-based structural health monitoring of complex composite structures

The use of composite structures in engineering applications has proliferated over the past few decades due to its distinct advantages, namely: high structural performance, corrosion resistance, and high strength/weight ratio. However, they also come with a set of disadvantages, i.e., they are prone to fiber breakage, matrix cracking, and delaminations. These types of damage are often invisible and if undetected, could lead to catastrophic failures of structures. Although there are systems to detect such damage, the criticality assessment and prognosis of the damage is often much more difficult to achieve. This article discusses the research study conducted, which resulted in the development of a Structural Health Monitoring (SHM) system for a 2D polymeric composite T-joint, used in maritime structures. The SHM system was found to be capable of not only detecting the presence of multiple delaminations in a composite structure, but also capable of determining the location and extent of all the delaminations present in the T-joint structure, regardless of the load (angle and magnitude) acting on the structure. The system developed relies on the examination of the strain distribution of the structure under operational loading.

Utilising microstrip patch antenna strain sensors for structural health monitoring

In this article, the feasibility of using a circular microstrip patch antenna to measure strain and the effects of different materials on sensitivity of the patch antenna are investigated. Also, the effect of strain direction on the frequency shift is studied. The theoretical model shows a linear relationship between strain and the shift in the resonant frequency of the antenna in any material. Both finite element analysis (FEA) and experimental tests have been undertaken to corroborate the relationship between strain and frequency shift. In addition, a new antenna sensor based on a meandered microstrip patch antennas has been designed and tested to overcome the shortcomings of the circular patch. The meandered circular microstrip patch antenna exhibited a threefold increase in sensitivity and a fivefold reduction in its physical size, when compared to the simple circular patch. The ultimate intention of this work is to configure antennas for the detection of relatively small damage zones in structures and to do so wirelessly.

Improved CSG rendering using overlap graph subtraction sequences

The <i>Sequenced Convex Subtraction</i> (SCS) algorithm for <i>Constructive Solid Geometry</i> (CSG) sequentially subtracts convex volumes from the z-buffer. The performance of the algorithm is determined by the length of the subtraction sequence used. View-independent subtraction sequences are <i>O</i>(<i>n</i>²) in length. These can be reduced to <i>O</i>(<i>kn</i>) if the maximum depth complexity <i>k,</i> which ranges between 1 and <i>n,</i> is known or can be determined.We present an improvement to subtraction sequence generation which uses object space overlap information to give <i>O</i>(<i>n</i>) length sequences in the best case and (unchanged) <i>O</i>(<i>n</i>²) sequences in the worst case. The approach is based on what we term an <i>overlap graph.</i> We also discuss a unifying approach combining overlap graph based processing with the Sequenced Convex Subtraction (SCS) CSG rendering algorithm. Finally, we present experimental results which show performance improvements, depending on the spatial arrangements of objects.

The Effect of the Configuration of the Amplification Device on the Power Output of a Piezoelectric Strip

We investigated the behaviour of a polyvinylidene-fluoride piezoelectric strip (‘stalk’) clamped at the leading edge, and hinged to an amplification device (‘leaf’) at the trailing edge. Flutter of this cantilevered system was induced within smooth, parallel flow, and an AC voltage was generated from the PVDF strip. A polypropylene, triangle comprised the leaf. Two leaf parameters were varied so as to quantify their effect on the power output of the system: 1) the area, and 2) the aspect ratio. It was found that the highest power output was realised with the 2nd-largest leaf across a range of wind speeds, but the variation in power measurements was large. Thus, the 3rd-largest leaf was found to give the highest power output with the lowest power variation. This leaf area was then fixed and the aspect ratio varied. It was found that the largest aspect ratio-leaf rendered the highest power output, but had a relatively high start-up wind speed.Copyright

A slot spiral in carbon-fibre composite laminate as a conformal load-bearing antenna

Conformal load-bearing antenna structures, which afford load-bearing structures with radar capability, are a promising technology to reduce weight and drag of air vehicles. This article presents an investigation of the mechanical and electromagnetic performance of slot log-spiral antenna in carbon-fibre composite structures. Compared with traditional rectangular slots, equiangular slot spiral antenna is found to offer broader bandwidth and better mechanical strength. Through experimental testing and finite element analyses, a new tip design is proposed that can significantly reduce the stress concentration of the non-load-bearing log-spiral antenna. Results of mechanical tests also show that the compressive strength of a carbon-fibre composite plate featuring a spiral slot is comparable with that pertinent to a plate with a circular hole of the same size. Filling the slots with epoxy resin can further enhance the compressive strength.

The strong diamagnetic behaviour of unidirectional carbon fiber reinforced polymer laminates

Carbon fibers are finite conductors with a weak diamagnetic response in a static magnetic field. When illuminated with a high-frequency alternating electromagnetic wave such that the skin depth is greater than the fiber diameter, carbon-fiber composites are shown to exhibit a strong dynamic diamagnetic response. The magnetic susceptibility (χm) is controlled by the polarization angle (θ), which is the angle between the incident electric field and conductor direction. A closed form solution for this behaviour was derived using Maxwells equations and an understanding of the induced conductor currents. The equation was verified using simulation and free space “wall” and waveguide measurements on unidirectional IM7/977-3 carbon fiber reinforced polymer laminates. The measured responses ranged from non-magnetic at θ = 90°, χm = 0, up to strongly diamagnetic at θ = 30°, χm = −0.75, over the 8-18 GHz bandwidth. The experimental results are in good agreement with theoretical predictions and computational simulat...

The design and realization of uniplanar CPW fed PICA slot antennas

In modern wireless communication system design, antennas with wide impedance bandwidth are desirable for numerous reasons. An antenna with a wide impedance bandwidth may be used for transmission and reception of multiple narrowband services in a multi-purpose platform. Alternatively a single wideband service may be of interest for various radar and imaging applications, or for impulse based radio communications in the FCC ultra-wideband (UWB) regime from 3.1 GHz to 10.6 GHz.