Paulo J Tavares, Tiago Ramos, Daniel Braga, Mario A P Vaz and Pedro Miguel Guimarães Pires Moreira
Hybrid methods, wherefore numerical and experimental data are used to calculate a critical parameter, have been used for several years with great success in Experimental Mechanics…
Abstract
Purpose
Hybrid methods, wherefore numerical and experimental data are used to calculate a critical parameter, have been used for several years with great success in Experimental Mechanics and, in particular, in fracture mechanics. The purpose of this paper is to report on the comparison of the strain field from numerical modelling forecasts against the experimental data obtained with the digital image correlation method under Mode II loading in fatigue testing. The numerical dual boundary element method has been established in the past as a very reliable method near singular regions where stresses tend to grow abruptly. The results obtained from the strain data near the crack tip were used in Williams expansion and agree fairly well with both the numerical results and the analytical solution proposed for pure Mode II testing.
Design/methodology/approach
The work presented in this note is experimental. The proposed methodology is of an hybrid experimental/numerical nature in that a numerical stress intensity factor calculation hinges upon a stress field obtained with an image method.
Findings
The obtained results are an important step towards the development of a practical tool for crack behaviour prediction in fatigue dominated events.
Research limitations/implications
The results also stress the necessity of improving the experimental techniques to a point where the methods can be applied in real-life solicitations outside of laboratory premises.
Originality/value
Although several research teams around the globe are presently working in this field, the present research topic is original and the proposed methodology has been presented initially by the research team years ago.
Details
Keywords
Francisco Barros, Susana Aguiar, Pedro J. Sousa, António Cachaço, Nuno V. Ramos, Paulo Tavares, P.M.G. Moreira, Luís Oliveira Santos, Min Xu and Elsa Franco
Part of the runway at Madeira Airport is a platform above the sea at a 60 m height, supported by a series of frames. When aircraft land on this section, a load is exerted on the…
Abstract
Purpose
Part of the runway at Madeira Airport is a platform above the sea at a 60 m height, supported by a series of frames. When aircraft land on this section, a load is exerted on the structure, resulting in bending of the beams which constitute the frames. A vision-based monitoring system was devised and implemented to measure the deflection of the runway's beams when a landing occurs.
Design/methodology/approach
An area on the midspan of two beams, located on the area where aircraft are most likely to land, was prepared with a speckle pattern, and a camera was assembled above a column on each of the adjacent frames, enabling the computation of displacements using digital image correlation (DIC). The camera continuously acquires images of the monitored area and compares them to a reference using DIC. If a displacement is detected, a number of frames before and after this event are saved for further DIC processing.
Findings
The installed systems successfully detected several events corresponding to landings and, for each of those events, measured the deflection of the beams over time and computed displacement fields for critical images, with strain values obtained up to this point being too small to measure using the current system.
Originality/value
This work provides novel insights into the behaviour of a unique structure and constitutes the first use of a vision system in its structural monitoring operations. It is also a valuable development in the implementation of automated DIC monitoring systems in locations of difficult access.
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João Da Rocha Lima Júnior and Claudio Tavares De Alencar
The office market in São Paulo has been in recession since the year 2000. This situation came up due to two main factors: [i] the very aggressive attitude of developers during…
Abstract
The office market in São Paulo has been in recession since the year 2000. This situation came up due to two main factors: [i] the very aggressive attitude of developers during the period that comprises the year 1999 until 2000. At that time there was a very strong perception among investors that a new expansion era for new office buildings in São Paulo was about to begin and, moreover the Brazilian economy had started its recovery; [ii] The intense retraction of the Brazilian economy along with the political transition in 2002, which was mainly caused by the deterioration of the expectations in relation to the economic policies that would be performed by the new government.The recovery of the economic activity in the office building market firstly depends on the macroeconomic growth in Brazil and within the São Paulo metropolitan area. On the other hand, the expansion of the activity in the office buildings sector relies not only on the developers’ expectations of how and when the current vacant units will be rented, but also on the potential risk‐return composition of new buildings to be developed in the next years. This paper describes the economic scenario in which investment decisions to build new office buildings for rent in our local market are made and we also simulated both the necessary period of time for investments in the São Paulo office market to recover attractiveness and the time interval for the increase in the occupation rate absorb the actual vacant spaces. These simulations have taken place based on projections for the Brazilian GNP increase and they showed that for an annual increment of 4.5%, in 3 years could be reached both, attractiveness for new investment and occupation of vacant areas. For a 2.0% annual growth, the absorption of vacant spaces will take 4 years from now and new investment would be attractive only in 2012. Besides, we discuss the market prices fluctuations on the inflexion point where the transition from one phase of the real estate cycle (recession‐non attractiveness) to another (recovery‐attractiveness) occurs.
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Carolina Faria Tavares, Marisa Lipi, Dirce Maria Lobo Marchioni and Maria Elisabeth Machado Pinto e Silva
The purpose of this paper is to evaluate the energy density (ED) of preparations served by a food service and develop and evaluate the acceptability of preparations in which the…
Abstract
Purpose
The purpose of this paper is to evaluate the energy density (ED) of preparations served by a food service and develop and evaluate the acceptability of preparations in which the ED was reduced by substitution and/or reduction of fat and sugar.
Design/methodology/approach
The preparations served most frequently by a food service were identified and described using datasheets. Nutritional assessment of the preparations was performed while the ED was estimated by the ratio of energy value to final weight of the preparations. The preparations were analyzed for their sensory characteristics and reproducibility. Sensory analysis was performed using acceptability and affective tests. The scores obtained on the hedonic scale (1‐9) were assessed by ANOVA and Tukey's test.
Findings
The percentage difference between the ED of traditional and modified preparations showed an ED reduction of 6 to 28 per cent in savory preparations and 5 to 63 per cent in sweet preparations. Preparations that had an average acceptance of greater than or equal to 7 were considered acceptable. All preparations were considered acceptable by the judges. Many preparations depend on ingredients with high ED for their success and removing these ingredients can undermine acceptance of the preparation. It is important to understand the role of each ingredient in recipes as a whole, in order to retain the characteristics and palatability of preparations.
Originality/value
The reduction of ED in preparations is an effective strategy for reducing energy intake and increasing weight loss, where ED of preparations can be reduced while maintaining the level of acceptability.
Details
Keywords
André F. B. P. Pinto, S.M.O. Tavares, José M. A. César de Sá and P.M.S.T. de Castro
The purpose of this paper is to use PAM-CRASH, a finite element analysis solver, to assess the performance of a mass production vehicle cross car beam (CCB) under an overlap…
Abstract
Purpose
The purpose of this paper is to use PAM-CRASH, a finite element analysis solver, to assess the performance of a mass production vehicle cross car beam (CCB) under an overlap frontal crash scenario (crashworthiness). Simulation results were reviewed according to what is plausible to register regarding some critical points displacements and, moreover, to identify its stress concentrations zones. Furthermore, it was also computed the CCB modal analysis (noise, vibration and harshness (NVH) assessment) in order to examine if its natural modes are within with the original equipment manufacturer (OEM) design targets.
Design/methodology/approach
The available data at the beginning of the present study consisted of the structure CAD file and performance requirements stated by the OEM for NVH. No technical information was available concerning crashworthiness. Taking into account these limitations, it was decided to adapt the requirements for other mass production cars of the same category, as regards dynamic loading. A dynamic explicit code finite element analysis was performed throughout the CCB structure simulating the 120e−3 s crash event. For the modal analysis, there were some necessary modifications to the explicit finite element model in order to perform the analysis in implicit code. In addition, the car body in white stiffness was assigned at the boundaries. These stiffness values are withdrawn from the points where the CCB is attached to the car body’s sheet metal components.
Findings
Although the unavailability of published results for this particular CCB model prevents a comparison of the present results, the trends and order of magnitude of the crash simulation results are within the expectations for this type of product. Concerning modal analysis, the steering column first natural frequency has a percent deviation from the design lower bound value of 5.09 percent when local body stiffness is considered and of 1.94 percent with fixed boundary conditions. The other requirement of the NVH assessment regarding a 5 Hz minimum interval between first vehicle CCB mode and the first mode of the steering column was indeed achieved with both boundary configurations.
Originality/value
This study is a further confirmation of the interest of numerical modeling as a first step before actual experimental testing, saving time and money in an automotive industry that has seen an enormous increase of the demand for new car models in the last decade.
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F.F. Duarte, Virgínia Isabel V. Infante, P.M.G. Moreira, M. de Freitas and P.M.S.T. de Castro
Friction stir welding lap joints of aluminum alloy AA6082-T6 were joined using two distinct configurations. The purpose of this paper is to study the effect of the welding line…
Abstract
Purpose
Friction stir welding lap joints of aluminum alloy AA6082-T6 were joined using two distinct configurations. The purpose of this paper is to study the effect of the welding line direction on the fatigue life of the specimens. For that purpose, specimens with the welding line parallel to the loading direction and with the welding line perpendicular to the loading direction were designed and manufactured. Fatigue tests were performed under constant amplitude load and stress ratio of R=0.1. As shown in previous studies, the hook defect plays a decisive role in the mechanical behavior of the joint, in particular when submitted to fatigue. The specimen geometry with the welding line parallel to the loading direction showed a superior fatigue behavior: for a given number of cycles to rupture, the level of stress is approximately twice as high as for the perpendicular configuration.
Design/methodology/approach
Two finite element models were created in order to study the behavior of the welded zone and, in particular, to compare influence of the hook defect in both configurations.
Findings
The specimen geometry with the welding line parallel to the loading direction showed a superior fatigue behavior: for a given number of cycles to rupture, the level of stress is approximately twice as high as for the perpendicular configuration.
Originality/value
The main objective of this work is to study the effect of the welding line direction on the fatigue life of the specimens. For that purpose, specimens with the welding line parallel to the loading direction and with the welding line perpendicular to the loading direction were designed and manufactured. Fatigue tests were performed under constant amplitude load and stress ratio of R=0.1. As shown in previous studies, the hook defect plays a decisive role in the mechanical behavior of the joint, in particular when submitted to fatigue.
Details
Keywords
Nikolai Kashaev, Stefan Riekehr, Kay Erdmann, Alexandre Amorim Carvalho, Maxim Nurgaliev, Nikolaos Alexopoulos and Alexandra Karanika
Composite materials and metallic structures already compete for the next generation of single-aisle aircraft. Despite the good mechanical properties of composite materials…
Abstract
Purpose
Composite materials and metallic structures already compete for the next generation of single-aisle aircraft. Despite the good mechanical properties of composite materials metallic structures offer challenging properties and high cost effectiveness via the automation in manufacturing, especially when metallic structures will be welded. In this domain, metallic aircraft structures will require weight savings of approximately 20 per cent to increase the efficiency and reduce the CO2 emission by the same amount. Laser beam welding of high-strength Al-Li alloy AA2198 represents a promising method of providing a breakthrough response to the challenges of lightweight design in aircraft applications. The key factor for the application of laser-welded AA2198 structures is the availability of reliable data for the assessment of their damage tolerance behaviour. The paper aims to discuss these issues.
Design/methodology/approach
In the presented research, the mechanical properties concerning the quasi-static tensile and fracture toughness (R-curve) of laser beam-welded AA2198 butt joints are investigated. In the next step, a systematic analysis to clarify the deformation and fracture behaviour of the laser beam-welded AA2198 four-stringer panels is conducted.
Findings
AA2198 offers better resistance against fracture than the well-known AA2024 alloy. It is possible to weld AA2198 with good results, and the welds also exhibit a higher fracture resistance than AA2024 base material (BM). Welded AA2198 four-stringer panels exhibit a residual strength behaviour superior to that of the flat BM panel.
Originality/value
The present study is undertaken on the third-generation airframe-quality Al-Li alloy AA2198 with the main emphasis to investigate the mechanical fracture behaviour of AA2198 BMs, laser beam-welded joints and laser beam-welded integral structures. Studies investigating the damage tolerance of welded integral structures of Al-Li alloys are scarce.
Details
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In general two main types of criteria are essential for the sizing of aircraft structural panels, namely, stability and damage tolerance. The way these criteria act and interact…
Abstract
Purpose
In general two main types of criteria are essential for the sizing of aircraft structural panels, namely, stability and damage tolerance. The way these criteria act and interact is very different for metallic and composite building blocks. While interaction of both types of criteria is relatively clear for composite parts, this is normally not the case for metallic ones. What is common for both is the fact that, if an interaction occurs, the impact is essential. The paper aims to discuss these issues.
Design/methodology/approach
This is a survey paper.
Findings
There is a strong mutual influence of buckling and damage in many cases.
Originality/value
It shows the significance of both, buckling and damage as a combined phenomenon.