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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: 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

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Article
Publication date: 7 December 2015

Igor Varfolomeev, Michael Windisch and Gerben Sinnema

The purpose of this paper is to validate the strain-based failure assessment diagram (SB-FAD) approach for surface cracks in components subjected to displacement…

Abstract

Purpose

The purpose of this paper is to validate the strain-based failure assessment diagram (SB-FAD) approach for surface cracks in components subjected to displacement controlled boundary conditions.

Design/methodology/approach

Numerical analyses are performed for several crack geometries and materials representative for aerospace applications. The performance of the SB-FAD is judged by comparing numerically calculated J-integrals to respective analytical estimates, using both Options 1 and 2 approximations.

Findings

In the most cases, both Options 1 and 2 SB-FAD method results in reasonably conservative J-estimates. Exceptions are for surface cracks in a pressurized vessel made of a material with low-strain hardening, for which Option 2 assessment produces non-conservative results. In contrast, Option 1 assessment is conservative for all geometries considered. In general, Option 1 results in a considerable overestimation of the crack driving force, whereas Option 2 produces rather accurate results in many cases.

Originality/value

The results demonstrate both the potential of the SB-FAD method and needs for its further improvements.

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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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: 7 December 2015

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

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

Naoya Tada and Manabu Nohara

Local wall thinning is one of serious problems in aged power generating plants. As the thinning grows inside the pipes, it is difficult to detect and evaluate it from the…

Abstract

Purpose

Local wall thinning is one of serious problems in aged power generating plants. As the thinning grows inside the pipes, it is difficult to detect and evaluate it from the outer surface of pipe. The purpose of this paper is to evaluate the method of semi-ellipsoidal wall thinning geometry on the back surface of flat plate by direct-current potential difference method (DC-PDM) was proposed as a preliminary research for the pipe wall thinning evaluation. The evaluation was performed for the potential difference numerically obtained by finite element method and the results were discussed.

Design/methodology/approach

A number of electric field analyses are necessary to evaluate the geometry of local wall thinning. In this study, defect-current modification method (DCMM), which is very fast analysis method based on the formulated solution for the similar thinning geometry, was used. The DCMM enabled the repeated electric field analyses necessary for the evaluation.

Findings

The potential difference on the front surface of plate was higher than the other part because of the electric current disturbance by a wall thinning on the back surface. In addition, the distribution depended on the geometry of the wall thinning. In this study, the shape of the thinning was assumed to be ellipsoid, and the width, depth, and length of the thinning were successfully evaluated based on the potential difference distribution on the front surface.

Originality/value

Evaluation of local wall thinning geometry was carried out by repeated analyses using DCMM, and the results were successful. This fact suggests that the evaluation of local wall thinning is possible by DC-PDM. The proposed method is going to be extended to the local wall thinning on the inner surface of pipe by geometrical conversion.

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

Peter Horst

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…

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.

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

Artur Szewieczek, Christian Willberg, Daniel Schmidt and Michael Sinapius

A design of sensor networks for structural health monitoring (SHM) with guided waves poses a hard challenge. Therefore different approaches are possible. A known one is…

Abstract

Purpose

A design of sensor networks for structural health monitoring (SHM) with guided waves poses a hard challenge. Therefore different approaches are possible. A known one is the usage of probability of detection (POD) criteria. Here, areas of potential impact sensitivity are calculated for every sensor which leads to a POD. The number of sensors is increased until a demanded POD is reached. However, these calculations are usually based on finite element methods and underlie different assumptions and approximations which can cause different inaccuracies. These limitations are avoided by using an experimental data basis for virtual sensors in this paper. The paper aims to discuss these issues.

Design/methodology/approach

An air-coupled ultrasound scanning technique is used for guided wave investigations. Recorded displacements of a structure surface are used as stimulation of virtual sensors which can be designed by software and positioned within available data field. For the calculation of sensor signals an isogeometric finite element model is used. The virtually bonded layer of the virtual piezoceramic sensor interpolates with non-uniform rational B-Splines (NURBS) the measured nodal data for each time step. This interpolation corresponds to a displacement boundary condition and is used to calculate the electrical potential at the free surface of the sensor.

Findings

Experimental data based on air-coupled ultrasound scanning technique can be used for elimination of disadvantages in numerical simulations by developing sensor networks for SHM. In combination with a transfer matrix method (TM) a three-dimensional displacement of specimen surface for complex composites can be calculated. To obtain the sensor signal a surface-bonded sensor is modeled by an isogeometric finite element approach. A good accordance is found between calculated virtual sensor signal and its experimental verification.

Research limitations/implications

Some deviations between calculated signal and its experimental verification are mainly justified by different spectral transfer functions between wave field scanning technique and signal recording of applied sensors. Furthermore, sensor influence on wave propagation is neglected in the presented method.

Originality/value

In this paper, the principle of virtual sensors is applied on anisotropic multilayered lamina by using isogeometric finite elements for piezoelectric sensors. This enables any sensor dimension, layout and position on complex composites. Furthermore a bonding layer between specimen and sensor is considered. The method allows a detailed analysis of sensor behavior on a specimen surface and the design and optimization of entire sensor networks for SHM.

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

José L. Ocaña, Carlos Correa, Juan A Porro, Marcos Díaz, Leonardo Ruiz de Lara and David Peral

With the aid of the calculational system developed by the authors, the analysis of the problem of laser shock processing (LSP) treatment for induction of residual stress…

Abstract

Purpose

With the aid of the calculational system developed by the authors, the analysis of the problem of laser shock processing (LSP) treatment for induction of residual stress (RS) fields for fatigue life enhancement in relatively thin sheets in a way compatible with reduced overall workpiece deformation due to spring-back self-equilibration has been envisaged. Numerical results directly tested against experimental results have been obtained confirming the critical influence of the laser energy and irradiation geometry parameters. The paper aims to discuss these issues.

Design/methodology/approach

Plane rectangular specimens (160 mm×100 mm×2 mm) of Al-cladded (∼80 μm) Al2024-T351 were considered both for LSP experimental treatment and for corresponding numerical simulation. The test piece is fixed on a holder and is driven along X and Y directions by means of an anthropomorphic robot. The predefined pulse overlapping strategy is used for the irradiation of extended areas of material. From the geometrical point of view, a full 3D configuration for the real geometry and for the sequential overlapping strategy of pulses has been considered. The FEM elements used for the simulation are an eight-node brick reduced integration with hourglass control in the treated area, namely C3D8RT, and a six-node trainer prism in the rest of the geometry, where there is no applied load, namely C3D6T, that ease meshing complex partitions. The element size in the nearest of the treated surface is 100×100×25 µm, being the maximum element size which allows to maintain calculation convergence.

Findings

Numerical results directly tested against experimental results have been obtained confirming: first, the critical influence of the laser energy and irradiation geometry parameters on the possible thin sheets deformation, both at local and global scales. Second, the possibility of finding LSP treatment parameter regimes that, maintaining the requirements relative to in-depth RSs fields, are able to reduce the relative importance of sheet deformation. Third, the possibility of finding LSP treatment parameter regimes able to provide through-thickness compressive RSs fields at levels compatible with an effective fatigue life enhancement. Fourth, the possibility of improving this through-thickness compressive RSs fields by double-side treatments. Fifth, the capability of the experimental LSP treatment system at the authors site (CLUPM) of practically achieve the referred through-thickness compressive RSs fields in excellent agreement with the predictive assessment obtained by the used numerical code (SHOCKLAS®).

Practical implications

The referred results provide a firm basis for the design of LSP treatments able to confer a broad range of RSs fields to thin components aiming the extension of their fatigue life, an enormously relevant field in which the authors are currently working.

Originality/value

The LSP treatment of relatively thin specimens brings, as an additional consequence, the possible bending in a process of laser shock forming. This effect poses a new class of problems regarding the attainment of specified RS’s depth profiles in the mentioned type of sheets, and, what can be more critical, an overall deformation of the treated component. The analysis of the problem of LSP treatment for induction of tentatively through-thickness RS’s fields for fatigue life enhancement in relatively thin sheets in a way compatible with reduced overall workpiece deformation due to spring-back self-equilibration is envisaged in this paper for the first time to the authors knowledge. The coupled theoretical-experimental predictive approach developed by the authors has been applied to the specification of LSP treatments for achievement of RS’s fields tentatively able to retard crack propagation on normalized specimens.

Details

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

Keywords

1 – 10 of 114