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Article
Publication date: 6 February 2017

António José Ramos Silva, P.M.G. Moreira, Mario A.P. Vaz and Joaquim Gabriel

Maintenance is one of the most critical and expensive operations during the life cycle of metallic structures, in particular in the aeronautic industry. However, early…

Abstract

Purpose

Maintenance is one of the most critical and expensive operations during the life cycle of metallic structures, in particular in the aeronautic industry. However, early detection of fatigue cracks is one of the most demanding operations in global maintenance procedures. In this context, non-destructive testing using image techniques may represent one of the best solutions in such situations, especially thermal stress analyses (TSA) using infrared thermography. The purpose of this paper is to access and characterize the main stress profile calculated through temperature variation, for different load frequencies.

Design/methodology/approach

In this paper, a cyclic load is applied to an aluminum sample component while infrared thermal image is being acquired. According to the literature and experiments, a cyclic load applied to a material results in cyclic temperature variation.

Findings

Frequency has been shown to be an important parameter in TSA evaluations, increasing the measured stress profile amplitude. The loading stimulation frequency and the maximum stress recorded show a good correlation (R2 higher than 0.995). It was verified that further tests and modeling should be performed to fully comprehend the influence of load frequency and to create a standard to conduct thermal stress tests.

Originality/value

This work revealed that the current infrared technology is capable of reaching far more detailed thermal and spatial resolution than the one used in the development of TSA models. Thus, for the first time the influence of mechanical load frequency in the thermal profiles of TSA is visible and consequentially the measured mechanical stress.

Details

International Journal of Structural Integrity, vol. 8 no. 1
Type: Research Article
ISSN: 1757-9864

Keywords

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Article
Publication date: 7 December 2015

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…

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

International Journal of Structural Integrity, vol. 6 no. 6
Type: Research Article
ISSN: 1757-9864

Keywords

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Article
Publication date: 25 May 2012

José A.F.O. Correia, Abilio M.P. de Jesus and Alfonso Fernández‐Canteli

Recently, a new class of fatigue crack growth models based on elastoplastic stress‐strain histories at the crack tip region and strain‐life fatigue damage models have been…

Abstract

Purpose

Recently, a new class of fatigue crack growth models based on elastoplastic stress‐strain histories at the crack tip region and strain‐life fatigue damage models have been proposed. The fatigue crack propagation is understood as a process of continuous crack initializations, over elementary material blocks, which may be governed by strain‐life data of the plain material. The residual stresses developed at the crack tip play a central role in these models, since they are used to assess the actual crack driving force, taking into account mean stresses and loading sequential effects. The UniGrow model fits this particular class of fatigue crack propagation models. The purpose of this paper is to propose an extension of the UniGrow model to derive probabilistic fatigue crack propagation data, in particular the derivation of the P–da/dN–ΔK–R fields.

Design/methodology/approach

An existing deterministic fatigue crack propagation model, based on local strain‐life data is first assessed. In particular, an alternative methodology for residual stress computation is proposed, based on elastoplastic finite element analysis, in order to overcome inconsistencies found in the analytical approximate approaches often used in literature. Then, using probabilistic strain‐life fields, a probabilistic output for the fatigue crack propagation growth rates is generated. A new probabilistic fatigue field is also proposed to take mean stress effects into account, using the Smith‐Watson‐Topper (SWT) damage parameter. The proposed models are assessed using experimental data available for two materials representative from old Portuguese bridges.

Findings

A new method to generate probabilistic fatigue crack propagation rates (P–da/dN–ΔK–R fields) is proposed and verified using puddle iron from old Portuguese bridges, usually characterized by significant scatter in fatigue properties. Also, a new probabilistic fatigue field for plain material is proposed to deal with mean stress effects.

Originality/value

A relation between the P–ε–N and the P–da/dN–ΔK–R fields is firstly proposed in this research. Furthermore, a new PSWTN field is proposed to deal with mean stress effects.

Details

International Journal of Structural Integrity, vol. 3 no. 2
Type: Research Article
ISSN: 1757-9864

Keywords

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Article
Publication date: 25 May 2012

C.M.C. Albuquerque, R.M.C. Miranda, V. Richter‐Trummer, M.A.V. de Figueiredo, R. Calçada and P.M.S.T. de Castro

The purpose of this paper is to study the fatigue crack growth (FCG) behaviour of the steel and weldments of a railway bridge.

Abstract

Purpose

The purpose of this paper is to study the fatigue crack growth (FCG) behaviour of the steel and weldments of a railway bridge.

Design/methodology/approach

Tests were carried out on compact tension (CT) specimens using the thickness (B=32 mm) of a structural detail. The test matrix included three R values and three material conditions: base material (BM), heat affected zone (HAZ) and weld metal (WM). An evaluation of opening load behavior was carried out. The full field measurement of the residual stress perpendicular to the crack plane was performed using the contour technique. A simplified finite element analysis supported the interpretation of the results. Scanning electron microscopy (SEM) observation of the fracture surface of BM and HAZ specimens was carried out.

Findings

Extensive crack closure effects were found in the welded specimens. Important through‐the‐thickness variation of residual stress was found using the contour technique. The residual stress fields of HAZ and WM specimens led to slowing down the FCG rate in the initial stages of crack propagation and to uncommon fracture surfaces. When the opening load effect was taken into consideration it was found that the da/dN vs ΔK of the different types of specimens are approximately identical. The ratio (striation spacing)/(da/dN) decreases up to approximately unity as a/W increases. In the specimens analyzed, FCG rates below approximately 2E‐7 to 3E‐7 m/cycle are associated with approximately constant striation spacing values, which could be considered a conservative upper bound of the real crack growth rate.

Originality/value

Fatigue crack growth behavior of thick welded steel CT specimens was analyzed on the basis of tests including full field residual stress measurements, crack closure behavior and striation spacing, allowing for the simultaneous consideration of all those aspects. It is shown that the striations spacing provides no more than a conservative upper bond of the real crack propagation rate.

Details

International Journal of Structural Integrity, vol. 3 no. 2
Type: Research Article
ISSN: 1757-9864

Keywords

Content available
Article
Publication date: 7 December 2015

P.M.G. Moreira and Paulo J Tavares

Abstract

Details

International Journal of Structural Integrity, vol. 6 no. 6
Type: Research Article
ISSN: 1757-9864

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Article
Publication date: 28 May 2010

Paulo M.S.T. de Castro, Pedro P. Camanho, Lucas F.M. da Silva and Pedro M.G.P. Moreira

The purpose of this paper is to describe the work of IDMEC, a not‐for‐profit R&D private association located in Porto and Lisbon, Portugal.

Abstract

Purpose

The purpose of this paper is to describe the work of IDMEC, a not‐for‐profit R&D private association located in Porto and Lisbon, Portugal.

Design/methodology/approach

The paper focuses on IDMEC's R&D activities, focusing on aeronautics.

Findings

Together IDMEC‐Porto and INEGI provide answers to R&D challenges in the broad area of aerostructures, from fracture and fatigue problems to advanced composites for space applications.

Originality/value

The paper offers a concise presentation of the IDMEC's R&D activities in the field of aeronautics.

Details

International Journal of Structural Integrity, vol. 1 no. 2
Type: Research Article
ISSN: 1757-9864

Keywords

Content available
Article
Publication date: 25 May 2012

Paulo M.S.T. de Castro, Pedro M.G.P. Moreira and Andreas Öchsner

Abstract

Details

International Journal of Structural Integrity, vol. 3 no. 2
Type: Research Article
ISSN: 1757-9864

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Article
Publication date: 1 August 2010

Pedro M.G.P. Moreira and Paulo M.S.T. de Castro

The purpose of this paper is to complement available macroscopic fatigue crack growth measurements in flat stiffened panels with scanning electron microscopy (SEM…

Abstract

Purpose

The purpose of this paper is to complement available macroscopic fatigue crack growth measurements in flat stiffened panels with scanning electron microscopy (SEM) measurements of striation spacing.

Design/methodology/approach

The paper's approach is fatigue testing of two‐stiffener flat panels manufactured using three different processes, with a central initial crack perpendicular to the stiffeners and load, in order to identify striation spacing during crack growth up to final fracture, using SEM.

Findings

An increase of striation spacing as cracks grow was quantified. Although when cracks approach the stiffeners the stress intensity factor decreases, there is no clear decrease of striation spacing in that region. Striation spacing is roughly similar to macroscopic crack‐propagation rate da/dN measured in the panels testing. This observation is no longer valid once the stiffeners are reached; this stage is characterized by fast acceleration of the cracking process until final complete rupture is verified, and macroscopic crack growth measurements are made difficult because of the “T” geometry in that region.

Originality/value

A complete picture of the striation spacing during the fatigue crack growth up to final fracture of a two‐stiffener flat panel is provided for three different manufacturing processes: high‐speed machining, laser beam welding and friction stir welding.

Details

International Journal of Structural Integrity, vol. 1 no. 3
Type: Research Article
ISSN: 1757-9864

Keywords

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Article
Publication date: 7 December 2015

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…

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

International Journal of Structural Integrity, vol. 6 no. 6
Type: Research Article
ISSN: 1757-9864

Keywords

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Article
Publication date: 7 December 2015

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…

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.

Details

International Journal of Structural Integrity, vol. 6 no. 6
Type: Research Article
ISSN: 1757-9864

Keywords

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