Effect of specimen size and loading conditions on spalling of concrete

Different qualities of concrete have been fire tested using different geometries of the specimens as well as different load levels and load configurations. The main objective with the study was to examine a test methodology consisting of a full‐scale test and different small scale‐tests for determining the probability of spalling and the amount of spalling of fire exposed concrete structures. A reference specimen was defined as a one‐sided fire exposed slab with the dimensions 1800 × 1200 mm² giving an exposed area of 1500 × 1200 mm². A number of concrete qualities with different probabilities for spalling, were tested using the reference specimen. These tests showed that the reference specimens worked well giving the expected test results. Small specimens were manufactured in different shapes with the same concrete as the one used in the reference tests. These small specimens were tested either at the same time as the reference specimens in the large furnace or afterwards on a small‐scale furnace where the fire exposed surface was 450 × 360 mm². The test results clearly show the increased probability and the increased amount of spalling by using external compressive loading. The results also show that by using pre‐stress through bars or wires the load can be lost due to heating of the bars/wires which results in a decreased amount of spalling. The boundary of the specimen also affects the amount of spalling. The spalling around the edges was in all tests less than the spalling on the central parts of the exposed area. It could also be noted that the spalling did not pass completely through any of the specimens. The reason for this is probably that the water/vapour could migrate out from the unexposed surface of the specimen. Copyright © 2006 John Wiley & Sons, Ltd.     

A fast and noise resilient cluster-based anomaly detection

Clustering, while systematically applied in anomaly detection, has a direct impact on the accuracy of the detection methods. Existing cluster-based anomaly detection methods are mainly based on spherical shape clustering. In this paper, we focus on arbitrary shape clustering methods to increase the accuracy of the anomaly detection. However, since the main drawback of arbitrary shape clustering is its high memory complexity, we propose to summarize clusters first. For this, we design an algorithm, called Summarization based on Gaussian Mixture Model (SGMM), to summarize clusters and represent them as Gaussian Mixture Models (GMMs). After GMMs are constructed, incoming new samples are presented to the GMMs, and their membership values are calculated, based on which the new samples are labeled as “normal” or “anomaly.” Additionally, to address the issue of noise in the data, instead of labeling samples individually, they are clustered first, and then each cluster is labeled collectively. For this, we present a new approach, called Collective Probabilistic Anomaly Detection (CPAD), in which, the distance of the incoming new samples and the existing SGMMs is calculated, and then the new cluster is labeled the same as of the closest cluster. To measure the distance of two GMM-based clusters, we propose a modified version of the Kullback–Libner measure. We run several experiments to evaluate the performances of the proposed SGMM and CPAD methods and compare them against some of the well-known algorithms including ABACUS, local outlier factor (LOF), and one-class support vector machine (SVM). The performance of SGMM is compared with ABACUS using Dunn and DB metrics, and the results indicate that the SGMM performs superior in terms of summarizing clusters. Moreover, the proposed CPAD method is compared with the LOF and one-class SVM considering the performance criteria of (a) false alarm rate, (b) detection rate, and (c) memory efficiency. The experimental results show that the CPAD method is noise resilient, memory efficient, and its accuracy is higher than the other methods.     

Fabrication process of open surfaces by robotic fibre placement

Composite materials are being used extensively in many industrial sectors. They offer excellent material properties compared to other structural materials available. However, the traditional fabrication process using manual hand lay-up is time consuming and labour intensive. Therefore, robotic fibre placement has been introduced to overcome these drawbacks. This approach may greatly reduce cycle time and manufacturing costs. This paper describes the overall strategy for the establishment of a flexible robotic fibre placement technique. The fabrication process planning of this new technique is presented. Three different types of fibre placement for open surfaces are discussed. These include simulation-based fibre path generation, fibre steering, and sensory-based contour following methodologies. The system architecture for the process control is also presented.     

An experimental study on damage detection of structures using a timber beam

Using vibration methods for the damage detection and structural health monitoring in bridge structures is rapidly developing. However, very little work has so far been reported on timber bridges. This paper intends to address such shortcomings by experimental investigation on a timber beam using a vibration based method to detect damage. A promising damage detection algorithm based on modal strain energy was adopted and modified to locate/evaluate damage. A laboratory investigation was conducted on a timber beam inflicted with various damage scenarios using modal tests. The modal parameters obtained from the undamaged and damaged state of the test beam were used in the computation of damage index, were then applied using a damage detection algorithm utilising modal strain energy and a statistical approach to detect location of damage. A mode shape reconstruction technique was used to enhance the capability of the damage detection algorithm with limited number of sensors. The test results and analysis show that location of damage can be accurately identified with limited sensors. The modified method is less dependent on the number of modes selected and can detect damage with a higher degree of confidence.     

Development of a novel flexure-based microgripper for high precision micro-object manipulation

Micro-scaled parts with dimension below 1 mm need to be manipulated with high precision and consistency in order to guarantee successful microassembly process. Often these requirements are difficult to be achieved particularly due to the problems associated with the structural integrity of the grasping mechanism which will affect the accuracy of the manipulation. Furthermore, the object's texture and fragility imply that small perturbation by the grasping mechanism can result in substantial damage to the object and leads to the degradation of its geometry, shape, and quality. This paper focuses on the unification of two designing approaches to develop a compliant-based microgripper for performing high precision manipulation of micro-objects. A combination of Pseudo Rigid Body Model (PRBM) and Finite Element Analysis (FEA) technique has proven to improve the design efficiency by providing the essential guideline to expedite the prototyping procedure which effectively reduces the cost and modeling time. An Electro Discharge Machining (EDM) technique was utilized for the fabrication of the device. Series of experimental studies were conducted for performance verification and the results are compared with the computational analysis results. A high displacement amplification and maximum stroke of 100 μm can be achieved.     

A lumped parameter element for the analysis of hyperbolic paraboloid shells

This paper presents the derivation of the stiffness matrix for a lumped parameter hyperbolic paraboloid shell element. This element is used to obtain solutions to hyperbolic paraboloid shells with various edge conditions. Numerical example for three types of support conditions (a simple support, a clamped edge and a shell supported by concentric edge beams) are presented. To illustrate the applicability of the method, the results obtained by the lumped parameter element are compared with those obtained by well-known methods of analysis such as the variational procedure, the finite difference and the finite element method.     

On intuitionistic fuzzy sub-hyperquasigroups of hyperquasigroups

The notion of intuitionistic fuzzy sets was introduced by Atanassov as a generalization of the notion of fuzzy sets. In this paper, we consider the intuitionistic fuzzification of the concept of sub-hyperquasigroups in a hyperquasigroup and investigate some properties of such sub-hyperquasigroups. In particular, we investigate some natural equivalence relations on the set of all intuitionistic fuzzy sub-hyperquasigroups of a hyperquasigroup.     

Nanogrooved carbon microtubes for wet three‐dimensional printing of conductive composite structures

Recent advances in three‐dimensional (3D) printing have enabled the fabrication of interesting structures which are not achievable using traditional fabrication approaches. The 3D printing of carbon microtube composite inks allows fabrication of conductive structures for practical applications in soft robotics and tissue engineering. However, it is challenging to achieve 3D printed structures from solution‐based composite inks, which requires an additional process to solidify the ink. Here, we introduce a wet 3D printing technique which uses a coagulation bath to fabricate carbon microtube composite structures. We show that through a facile nanogrooving approach which introduces cavitation and channels on carbon microtubes, enhanced interfacial interactions with a chitosan polymer matrix are achieved. Consequently, the mechanical properties of the 3D printed composites improve when nanogrooved carbon microtubes are used, compared to untreated microtubes. We show that by carefully controlling the coagulation bath, extrusion pressure, printing distance and printed line distance, we can 3D print composite lattices which are composed of well‐defined and separated printed lines. The conductive composite 3D structures with highly customised design presented in this work provide a suitable platform for applications ranging from soft robotics to smart tissue engineering scaffolds. © 2019 Society of Chemical Industry     

Structural,morphological, and optical properties of W-doped VO2 thin films prepared by sol-gel spin coating method

Thermochromic VO₂ thin films were deposited on soda-lime glass via sol-gel method. Doping was done through adding tungstic acid solution to the vanadium solution precursor. Grazing incidence x-ray diffractometer (GIXRD) results showed that VO₂ and V₆O₁₃ phases were formed together in the heat-treated sample. According to the GIXRD result of the W-doped sample, only VO₂ remained. Field-emission scanning electron microscopy (FESEM) micrographs showed that the VO₂ grain size decreased from about 70 to about 25 nm for undoped film and 2 wt% W-doped films, respectively. Atomic force microscopy (AFM) results showed that the root mean square roughness for the film with 180 nm thickness was about 18 nm, and 2 wt% W-doped film had a smoother surface. Diffuse reflectance spectroscopy (DRS) results showed that the band gap energy for undoped, 1 wt% W- doped, and 2 wt% W-doped VO₂ thin films was 1.7, 1.3, and 0 eV, respectively. Four-point probe resistivity measurements showed a significant decrement, from approximately 1 MΩ at 15°C to <100 Ω at 80°C. Regarding Vis-NIR spectroscopy results, maximum optical transmission for undoped and W-doped films was approximately 75% and 35%, respectively.     

Swoop: A Web Ontology Editing Browser

In this paper, we describe Swoop, a hypermedia inspired Ontology Browser and Editor based on OWL, the recently standardized Web-oriented ontology language. After discussing the design rationale and architecture of Swoop, we focus mainly on its features, using illustrative examples to highlight its use. We demonstrate that with its Web-metaphor, adherence to OWL recommendations and key unique features, such as Collaborative Annotation using Annotea, Swoop acts as a useful and efficient Web Ontology development tool. We conclude with a list of future plans for Swoop, that should further increase its overall appeal and accessibility.