The Effect of Deformation Heating on Restoration and Constitutive Equation of a Wrought Equi-Atomic NiTi Alloy

In this study, a set of constitutive equation corrected for deformation heating is proposed for a near equi-atomic NiTi shape memory alloy using isothermal hot compression tests in temperature range of 700 to 1000 °C and strain rate of 0.001 to 1 s⁻¹. In order to determine the temperature rise due to deformation heating, Abaqus simulation was employed and varied thermal properties were considered in the simulation. The results of hot compression tests showed that at low pre-set temperatures and high strain rates the flow curves exhibit a softening, while after correction of deformation heating the softening is vanished. Using the corrected flow curves, the power-law constitutive equation of the alloy was established and the variation of constitutive constants with strain was determined. Moreover, it was found that deformation heating introduces an average relative error of about 9.5% at temperature of 800 °C and strain rate of 0.1 s⁻¹. The very good agreement between the fitted flow stress (by constitutive equation) and the measured ones indicates the accuracy of the constitutive equation in analyzing the hot deformation behavior of equi-atomic NiTi alloy.     

Creep response of glued-laminated beam reinforced with pre-stressed sub-laminated composite

In the past decades, the use of fibre-reinforced polymer (FRP) for enhancement of strength and stiffness of wood-based structural members has been established as an economical method. New developments have been ongoing to further improve the structural performance of glued-laminate beams. Recently, a novel integral sub-laminated composite, referred to as pre-stressed FRP–wood composite laminate (PWCL), was patented (KarisAllen and Tynes, 2000 [1]). This system is comprised of pre-stressed high performance fibres, sandwiched and glued within layers of pre-compressed wood strands. The resulting sub-laminated system may be attached to the tension zone of timber/glulam beams. A concern involved with the use of such pre-stressing scheme has been the issue of creep, which could affect the long-term performance of such composite beams. This paper presents the results of a study conducted to investigate the long-term performance of glulam beams reinforced with PWCL sub-laminate. Experimental investigations were conducted to determine the creep parameters of FRP composites and wood species employed in the fabrication of PWCL. The main objective was to develop a finite element model (FEM) to simulate the pre-stressing process and to predict the creep response of an entire reinforced glulam system, including the PWCL, under an externally applied load and constant environmental condition. The FEM was constructed in the Abaqus environment and the residual stress distribution was modeled in a step-wise scheme, corresponding to each step of PWCL and beam fabrication as well as the in situ response of the composite beam. The integrity of the creep model used in the simulation was verified by the experimental results obtained from tests performed on FRP reinforced small-size wood.     

High temperature deformation and processing map of a NiTi intermetallic alloy

The deformation behavior of a 49.8 Ni-50.2 Ti (at pct) alloy was investigated using the hot compression test in the temperature range of 700 °C–1100 °C, and strain rate of 0.001 s^?1 to 1 s^?1. The hot tensile test of the alloy was also considered to assist explaining the related deformation mechanism within the same temperature range and the strain rate of 0.1 s^?1. The processing map of the alloy was developed to evaluate the efficiency of hot deformation and to identify the instability regions of the flow. The peak efficiency of 24–28% was achieved at temperature range of 900 °C–1000 °C, and strain rates higher than 0.01 s^?1 in the processing map. The hot ductility and the deformation efficiency of the alloy exhibit almost similar variation with temperature, showing maximum at temperature range of 900 °C–1000 °C and minimum at 700 °C and 1100 °C. Besides, the minimum hot ductility lies in the instability regions of the processing map. The peak efficiency of 28% and microstructural analysis suggests that dynamic recovery (DRV) can occur during hot working of the alloy. At strain rates higher than 0.1 s^?1, the peak efficiency domain shifts from the temperature range of 850 °C–1000 °C to lower temperature range of 800 °C–950 °C which is desirable for hot working of the NiTi alloy. The regions of flow instability have been observed at high Z values and at low temperature of 700 °C and low strain rate of 0.001 s^?1. Further instability region has been found at temperature of 1000 °C and strain rates higher than 1 s^?1 and at temperature of 1100 °C and all range of strain rates.     

Lasing in a three-dimensional photonic crystal of the liquid crystal blue phase II

Photonic-bandgap materials, with periodicity in one, two or three dimensions, offer control of spontaneous emission and photon localization. Low-threshold lasing has been demonstrated in two-dimensional photonic-bandgap materials, both with distributed feedback and defect modes. Liquid crystals with chiral constituents exhibit mesophases with modulated ground states. Helical cholesterics are one-dimensional, whereas blue phases are three-dimensional self-assembled photonic-bandgap structures. Although mirrorless lasing was predicted and observed in one-dimensional helical cholesteric materials and chiral ferroelectric smectic materials, it is of great interest to probe light confinement in three dimensions. Here, we report the first observations of lasing in three-dimensional photonic crystals, in the cholesteric blue phase II. Our results show that distributed feedback is realized in three dimensions, resulting in almost diffraction-limited lasing with significantly lower thresholds than in one dimension. In addition to mirrorless lasing, these self-assembled soft photonic-bandgap materials may also be useful for waveguiding, switching and sensing applications.     

Tolerances in self-cohering antenna arrays of arbitrary geometry

In a conventional array, the location of each element must be known to an accuracy of aboutlambda/10for phasing and scanning purposes. A larger tolerance on the element location results in the loss of gain and deterioration of the radiation pattern. In a self-cohering phased array, the phasing of the array elements is accomplished closed-loop and adaptively; therefore, no information on the element location is necessary. On the other hand, to scan the adaptively formed beam about the direction of the received wave, which has to be performed open-loop, one requires information on the element locations. In this paper, basic relations pertaining to the open-loop scanning of adaptive antenna arrays of arbitrary geometry are derived for both far-field and near-field scanning problems, and the transition between the two cases and the required accuracy in the knowledge of the same distance are explored. It is shown that the tolerance requirement on the element locations is the conventional tolerance divided by the maximum scan angle. In large systems designed for target imaging, it is shown that the tolerance on element location can be two or more orders of magnitude larger than that in a conventional array.     

Analysis of deformations and stresses in balanced and unbalanced adhesively bonded single-strap joints

Adhesively bonded joints are increasingly being used in joining various structural components. Adequate understanding of the behaviour of adhesively bonded joints is necessary to ensure efficiency, safety and reliability of such joints. While several joint configurations, such as the single- and double-lap joints have received considerable consideration, the single-strap joint configuration has received little attention, partly because earlier studies have shown it to be the least efficient.

One of the objectives of this paper is to demonstrate that strap joints can be as efficient as lap joints, as long as they are properly designed. This will be done through a detailed analytical investigation into influence of the parameters that govern peak stresses in the adhesive. The next objective is to produce simple equations by which the design of strap joint could be facilitated in an effective manner. For this, the developed analytical expressions are simplified and shown to provide accurate results. The derived solutions provide better insight into understanding the parameters that most influence the edge forces.     

In situ synthesis of hydroxyapatite-grafted titanium nanotube composite

ABSTRACT

The present study is an investigation to demonstrate the effectiveness of in situ approach in the synthesis of hydroxyapatite-grafted titanium nanotube composite (HA-TNT). This method involves combining the process of HA sol–gel and rapid breakdown anodisation of titanium in a novel solution consisting of NaCl and N₃PO₄. This new synthesis approach produced a uniform dispersion of Anatase and Rutile phases of TiO₂ nanotubes with minimal agglomeration in the matrix of crystalline HA. The characterisation of homogenised HA-TNT composite was investigated via field emission scanning electron microscopy (FESEM), energy dispersive spectroscopy (EDS), transmission electron microscope (TEM) and X-ray diffraction (XRD). FESEM and TEM images indicated the nanostructure of composite with TiO₂ nanotube diameter of approximately 10 nm. XRD and EDS analyses confirmed the formation of HA crystalline with the Ca/P ratio of 1.58 and formation of Anatase and Rutile phase of TiO₂ nanotubes.     

A Unified Approach to Similarity Measures Between Intuitionistic Fuzzy Sets

Two general classes of similarity measures between intuitionistic fuzzy sets (hereafter IFSs) are introduced. Some properties of these measures are investigated with respect to some well‐known reasonable axioms. It is shown that several similarity measures between IFSs introduced elsewhere can be expressed by these definitions as special cases. Some illustrative and practical examples from the areas of pattern recognition, fuzzy clustering analysis, and decision making will be used to investigate the performance of the proposed measures with respect to some common measures. The results indicate that these measures can provide a useful way for measuring the degree of similarity between IFSs and that the proposed approach performs well in pattern recognition, fuzzy clustering, and decision making.     

Landsat ETM+ imaging for mineral potential mapping: application to Avaj area,Qazvin, Iran

The Avaj area is located in the northwestern part of Iran, on the boundary between the Orumieh-Dokhtar and Sanandaj-Sirjan geological zones. It corresponds to two different geological sub-zones:Abe-Garm, to the north, which is related to the volcanic belt of Orumieh-Dokhtar; and the Razan sub-zone, to the south, which is related to the Sanandaj-Sirjan zone. Lithological aspects of different rock units indicate the presence of four distinct volcanic groups of andesite, basalt, tuff, and dacite. The present research utilizes various Landsat Enhanced Thematic Mapper Plus (ETM+) image-processing techniques, including false colour composite images, colour composite ratio images, and standard principal component (PC) image analysis on six bands and colour composite selective PC images, filtering and supervised classification. Nonetheless, colour composite selective images may be the most reliable method for enhancement of areas with hydrothermal alteration. All the techniques used clearly show the pervasive alteration of kaolinite-argillite in the area. These alterations are mainly related to the andesite, and tuffs have the same trend as fault directions.     

A low-overhead scheme for testing a bit-level finite ring systolic array

Testing large VLSI circuits is a difficult and challenging problem for designers. Large unstructured circuits are often impossible to test. The number of test vectors also tend to be large and difficult to generate using automated tools for testing. In this paper, we have investigated the testing of systolic arrays built from a finite ring cell that has been proposed recently for digital signal processing functions. The cell has been shown to allow encoding, decoding and general inner product type computations for residue number system applications, with considerable advantages over equivalent binary implementation. As a further feature, we show, in this paper, that an array of such cells is remarkably easy to test for stuck-at faults. Generating test vectors for these arrays is also straightforward.