Roman Ruzek, Martin Kadlec, Konstantinos Tserpes and Evaggelos Karachalios
Compression is critical loading condition for composite airframes. Compression behaviour of structures with or without damages is a weak point for composite fuselage panels. This…
Abstract
Purpose
Compression is critical loading condition for composite airframes. Compression behaviour of structures with or without damages is a weak point for composite fuselage panels. This is one of the reasons for need of continuous in-service health monitoring of composite structures. The purpose of this paper is to characterize the compression panel behaviour on the base of a developed and implemented structural health monitoring (SHM) system.
Design/methodology/approach
The SHM system based on fibre optic Bragg grating (FOBG) sensors and standard resistance strain gauges (SGs) was placed onto/into (embedded or bonded) three stiffened carbon fibre reinforced polymer (CFRP) fuselage panels. The FOBG sensor system was used to monitor the structural integrity of the reference, impacted, and fatigued panels under compression loading. Both barely visible impact damage and visible impact damage were created to evaluate their influence on the panel behaviour. The functionality of the SHM system was verified through mechanical testing.
Findings
Experimental data showed the presence of impact damages significantly changes the buckling modes development and deformation behaviour of the panels. Some differences between the optical and SG sensors during buckling were observed. The buckling waves and failure development were very well indicated during loading by all sensors located on the panel surface but not by the embedded sensors. Good agreement between the data from the SGs and FOBG sensors was achieved for all sensors placed on the stringers, which did not buckle. The good reliability of FOBG sensors during the fatigue and static testing up to panel failure was verified.
Originality/value
The paper gives information about different buckling behaviour of CFRP fuselage stiffened panels in compression. The paper gives detailed information about measured signals from different sensors based on their location on/in the panel structure for realistic loading scenario of composite aerostructures. The paper gives an integrated overview of sensors placement considering possibilities to predicate structure behaviour.
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Defects can be caused by a number of factors, such as maintenance damage, ground handling and foreign objects thrown up from runways during an in-service use of composite…
Abstract
Purpose
Defects can be caused by a number of factors, such as maintenance damage, ground handling and foreign objects thrown up from runways during an in-service use of composite aerospace structures. Sandwich structures are capable of absorbing large amounts of energy under impact loads, resulting in high structural crashworthiness. This situation is one of the many reasons why sandwich structures are extensively used in many aerospace applications nowadays. Their non-destructive inspection is often more complex. Hence, the choice of a suitable non-destructive testing (NDT) method can play a key role in successful damage detection. The paper aims to discuss these issues.
Design/methodology/approach
A comparison of detection capabilities of selected C-scan NDT methods applicable for inspections of sandwich structures was performed using water-squirt, air-coupled and pitch-catch (PC) ultrasonic techniques, supplemented by laser shearography (LS).
Findings
Test results showed that the water-squirt and PC techniques are the most suitable methods for core damage evaluation. Meanwhile, the air-coupled method showed lower sensitivity for the detection of several artificial defects and impact damage in honeycomb sandwiches when unfocussed transducers were used. LS can detect most of the defects in the panels, but it has lower sensitivity and resolution for honeycomb core-type sandwiches.
Originality/value
This study quantitatively compared the damage size indication capabilities of sandwich structures by using various NDT techniques. Results of the realised tests can be used for successful selection of a suitable NDT method. Combinations of the presented methods revealed most defects.
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Martin Kadlec, Robin Hron and Liberata Guadagno
The purpose of this paper is to present the mechanical and morphological characterization of new multifunctional carbon fibre-reinforced composites (CFRCs) that are able to…
Abstract
Purpose
The purpose of this paper is to present the mechanical and morphological characterization of new multifunctional carbon fibre-reinforced composites (CFRCs) that are able to overcome two of the main drawbacks of aeronautical composite materials: reduced electrical conductivity and poor flame resistance. Multiwall carbon nanotubes and glycidyl POSS (GPOSS) were used to simultaneously enhance electrical conductivity and flame resistance. The effect of these two combined components on the mechanical and morphological properties of the manufactured CFRCs was analysed.
Design/methodology/approach
This paper describes the mechanical test results obtained for interlaminar shear strength, three-point bending, and tensile and fracture toughness in mode I tests. Carbon fibre-reinforced epoxy resin plates were manufactured in two series with blank resin and CNT+flame retardant GPOSS-enhanced resin.
Findings
The mechanical properties were decreased by no more than 10 per cent by combined influence of CNTs and GPOSS. Agglomerates of CNTs were observed using scanning electron microscopy. The agglomerates were large enough to be visible to the naked eye as black spots on the delaminated fracture surface. The decrease of the mechanical properties could be caused by these agglomerates or by a changed fibre volume content that was affected by the difficult infusion procedure due to high resin viscosity.
Originality/value
If we consider the benefit of CNTs as a nanofiller to increase electrical conductivity and the GPOSS as a component to increase the flame resistance of the resin, the decrease of strength seems to be insignificant.
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Martin Kadlec, Robin Hron and Timo Grieser
T-sections of carbon fibre-reinforced composites are prone to delamination because they lack reinforcement through their thicknesses. The purpose of this paper is to present the…
Abstract
Purpose
T-sections of carbon fibre-reinforced composites are prone to delamination because they lack reinforcement through their thicknesses. The purpose of this paper is to present the structural response of cost-effective laminated T-sections when subjected to various types of loads and impacts.
Design/methodology/approach
The core of the automated manufactured beams is analysed. Pull-off, flange tension, and flange bending were tested for specimens extracted from an I-beam. The failure processes for all of the specimens were investigated in detail, leading to the statistical evaluation of the failure modes.
Findings
A correlation is apparent between the impact damage energy and certain fracture patterns. These results can be used to assess damage tolerance when designing stiffeners, beams, and various complex structures. The increase in strength by 25 per cent was measured for the advanced stitching located in the web section for the flange tension test.
Originality/value
The resistance displayed by the T-sections toward impact damage was studied experimentally, as the literature describing this topic is limited. The prevalence of one fracture mode for higher impact energies shows a possible advantage of the cost-effective preforms for the damage tolerant philosophy.
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Martin Kadlec and Václav Kafka
Polymer composite panels are widely used in aeronautic and aerospace structures due to the high strength-to-weight ratios of these structures. The purpose of this paper is to…
Abstract
Purpose
Polymer composite panels are widely used in aeronautic and aerospace structures due to the high strength-to-weight ratios of these structures. The purpose of this paper is to determine the strain fields and failure mechanisms during the failure of the impacted composite laminates when subjected to compression.
Design/methodology/approach
A series of compression-after-impact (CAI) tests was performed on composite plates 150×100×4 mm3 made of a carbon-fibre-reinforced epoxy resin matrix. A digital image correlation and fractographic analysis by means of optical and electron microscopy are used for this purpose.
Findings
The full-field strain measurements indicate a concentrated band of compressive strain near the impact, where buckling occurs. The results indicate that the strain concentration factor can be considered to be a failure criterion. The shear strain visualisation around the impact reveals an area of heterogeneous deformation that is comparable to the detected delamination area acquired by an ultrasonic technique. Fibre and inter-fibre fractures are described for the particular impact site regions.
Originality/value
These experiments could improve numerical models for the CAI analyses and help to build a new criterion for this severe failure mode.
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Dewey, through his contributions to pragmatism (America’s sole original philosophy), has long been considered relative to symbolic interactionism (SI), which emerged from that…
Abstract
Dewey, through his contributions to pragmatism (America’s sole original philosophy), has long been considered relative to symbolic interactionism (SI), which emerged from that philosophy. His impact on SI, while falling short of those of Mead and Cooley, has mainly come from (and has been limited to) concepts and insights developed in Human Nature and Conduct: An Introduction to Social Psychology (1922/1957) and his earlier, seminal, article, “The Reflex Arc Concept in Psychology,” published in 1896 during his tenure at the University of Chicago (1894–1904). SI, however, has wrongly ignored Dewey’s political theory, especially his concept of domination. In order to rectify this inattention, I summarize the social and historical contexts that motivated Dewey’s turn toward domination; outline the radical nature of his political theory; illustrate similarities of his political theory with Marx’s; expatiate on his concept of domination, including his argument for social practices to reduce surplus domination; and explicate the theoretical and political implications of taking his political theory seriously.
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Sen Peng, Huiping Cui and Min Ji
The new campus of Tianjin University was designed, built and now operates following a green and sustainable concept. The campus’ eco-friendly water environment was formed by…
Abstract
The new campus of Tianjin University was designed, built and now operates following a green and sustainable concept. The campus’ eco-friendly water environment was formed by establishing a water recycling system. The campus is divided into three drainage sections based on the masterplan. Each drainage section adopts different methods of collecting, utilizing and discharging water according to specific conditions, aimed at achieving both high drainage capability and the efficient utilisation of rainwater. The campus was designed so runoff pollution is reduced through the utilisation of low-impact development methods, ensuring the quality of the recharge water. Through studying the fundamentals of treatment measures and models for simulating water quality, water circulation, constructed wetlands and pollution control of rain runoff, parameters for efficient water recycling could be mathematically forecast, ensuring that stakeholders can be continuously engaged in improving and preserving the water quality of landscaped water on campus. The overall system integrates a variety of measures being implemented into one cohesive entity, which contributes to establishing the sustainable and healthy water cycling system of the green campus.
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Nicholas Wonder and Claire Lending
The purpose of this paper is to study the impact of acquisitions on the number of shareholders of the acquirer (the shareholder base) and relate that effect to the method of…
Abstract
Purpose
The purpose of this paper is to study the impact of acquisitions on the number of shareholders of the acquirer (the shareholder base) and relate that effect to the method of payment and the ratio between the target’s and acquirer’s shareholder bases prior to the acquisition.
Design/methodology/approach
Using 348 acquisitions from 1993 to 2013 for which both parties are public, American firms, the paper measures changes in the acquirer’s shareholder base from before announcement through to four years after completion. OLS regressions, together with an instrumental variables approach addressing the endogeneity of acquisition payment, indicate the determinants of those changes.
Findings
Acquisitions completed partly or entirely in stock lead to large increases in the shareholder base, and the increases mostly endure over the four-year window examined in the study. Regression results indicate that the target to acquirer shareholder ratio has a much greater impact on the acquirer’s base for stock acquisitions than for cash acquisitions. The ratio is also associated with changes in beta.
Practical implications
Because existing theoretical and empirical literature shows that the shareholder base impacts the risk, liquidity, and market value of stock, managers evaluating potential targets and modes of payment may wish to consider the likely impact on their firms’ shareholder bases, as may investors contemplating the effects of an acquisition announcement.
Originality/value
This is the first work documenting both a short- and long-term impact of acquisitions on the shareholder base and the first to investigate the determinants of the change in the base.
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The purpose of this paper is to test the hypothesis that relative to a cash acquisition, a stock acquisition would increase the bidder’s investor base and lower Merton’s (1987…
Abstract
Purpose
The purpose of this paper is to test the hypothesis that relative to a cash acquisition, a stock acquisition would increase the bidder’s investor base and lower Merton’s (1987) shadow cost, which in turn contributes positively to the bidder announcement return.
Design/methodology/approach
Using the number of registered shareholders and measures of institutional ownership as the proxies for investor base and investor recognition, this paper compares their changes and the changes in shadow cost between bidders using different methods of payment. The authors examine the relation between the shadow cost reduction and bidder announcement return in a multivariate framework.
Findings
This paper finds that given the target type, bidders using stocks experience significantly larger increases in their investor bases and investor recognition than bidders using cash. Additionally, only bidders using stocks experience significant decreases in their shadow costs. In a multivariate framework, the change in the shadow cost has a negative and significant effect on the bidder announcement return in the sample of stock acquisitions and the subsample of bidders using stocks to acquire private targets. These findings support the authors’ hypothesis and suggest that the less established bidders acquiring private targets in particular benefit from the shadow cost reduction.
Originality/value
This paper provides the direct evidence that investor recognition matters in mergers and acquisitions. The findings also provide a complementary explanation for the documented positive bidder returns when bidders use stocks to acquire private targets.
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Guang Jin, A.J. Englande and Chih‐Yang Hu
The purpose of this paper is to describe the investigation of distribution of metals in water and sediment samples of Poydras‐Verret wetland, an area that has received…
Abstract
Purpose
The purpose of this paper is to describe the investigation of distribution of metals in water and sediment samples of Poydras‐Verret wetland, an area that has received approximately 40 years input of secondarily treated municipal effluent.
Design/methodology/approach
Water and sediment samples were analyzed for metals for a period of 18 months. These metals were also monitored for the secondarily treated effluent, and at a reference/control wetland that does not receive wastewater. Analysis of variance (ANOVA) and Student Newman‐Keuls post‐hoc ANOVA analysis were conducted to evaluate the pattern of metal distribution within the Poygras‐Verret wetland and compare results to the reference wetland. Heavy metal criteria established by United States Environmental Protection Agency (USEPA) and State of Louisiana were also used to assess the potential chronic and acute health impacts of heavy metals in the Poydras‐Verret wetland.
Findings
Concentrations of metals of the Poydras‐Verret wetland water are not different from those found in the reference wetland water, suggesting no observed accumulation of these metals within the receiving wetland water. All metals are below the acute criteria.
Originality/value
Historical data regarding metal accumulation in wetlands in the published literature is limited. This paper provides supporting evidence that using wetlands to assimilate wastewater could be a long‐term, practical solution with the side benefits including wetland restorations and protection from wave erosion and storm surge.