Damage tolerance assessment by bend and shear tests of two multilayer composites: Glass fibre reinforced metal laminate and aluminium roll-bonded laminate

The damage tolerance of an aluminium roll-bonded laminate (ALH19) and a glass fibre reinforced laminate (GLARE) (both based in Al 2024-T3) has been studied. The composite laminates have been tested under 3-point bend and shear tests on the interfaces to analyze their fracture behaviour. During the bend tests different fracture mechanisms were activated for both laminates, which depend on the constituent materials and their interfaces. The high intrinsic toughness of the pure Al 1050 layers present in the aluminium roll-bonded laminate (ALH19), together with extrinsic toughening mechanisms such as crack bridging and interface delamination were responsible for the enhanced toughness of this composite laminate. On the other hand, crack deflection by debonding between the glass fibres and the plastic resin in GLARE, was the main extrinsic toughening mechanism present in this composite laminateFinancial support from CICYT (Project MAT2003-01172) is gratefully acknowledged. C.M. Cepeda-Jiménez thanks the Spanish Ministry of Education and Science for a Juan de la Cierva contract. Authors also thank Delft University of Technology for providing the GLARE.Peer reviewe

Effect of thermal treatment on the interfacial shear toughness of an aluminium composite laminate

The microstructure and mechanical properties in the interface region of a multilayer composite laminate based on Al-Zn (Al 7075) and Al-Cu (Al 2024) alloys have been mainly characterized by EBSD and shear tests. It is shown that varying solution heat treatments affect the microstructure of the constituent aluminium alloys in the bonding region and, as a consequence, the interfacial mechanical properties. The increase in the solution treatment time improves the interfacial toughness of the multilayer aluminium laminate due to higher intrinsic toughness of the constituent aluminium alloys.Financial support from CICYT (Project MAT2003-01172 and MAT2006-11202) is gratefully acknowledged. C.M. Cepeda-Jiménez thanks the Spanish National Research Council (CSIC) for a I3P contract. We also thank F.F. González-Rodríguez for assistance during hot rolling. Finally, an especial mention in memory of P.J. González-Aparicio for his help and assistance with electron microscopy during all these years is made.Peer reviewe

Evolution of the microstructure, texture and creep properties of the 7075 aluminium alloy during hot accumulative roll bonding

The 7075 Al alloy was severely deformed at 350 °C by a 3:1 thickness reduction per pass accumulative roll bonding (ARB) process up to six passes. It was found that discontinuous recrystallisation occurs during the inter-pass annealing stages from the third pass on, attributable to the increment of the mean particle size during processing. As a consequence, the mean crystallite size did not decrease, but remained approximately constant at 440 nm along the present ARB process and the mean boundary misorientation angle reached a maximum of 30° for the 3-passes sample. However, since nucleation of new grains takes place at the pre-existing grain boundaries, discontinuous recrystallisation results in slight changes in texture throughout the processing, being the orientations in the ARBed samples predominantly located along the typical rolling β-fibre. Uniaxial tests conducted at 300 °C and 350 °C revealed that the operating deformation mechanism in the processed alloy at such temperatures was grain boundary sliding; the optimum superplastic strain rate being 3×10−3–10−2 s−1. Boundary misorientation and thermal stability are the two main factors that contribute to high elongations to failureFinancial support from the CICYT (Projects MAT2009-14452 and MAT2012-38962)Peer reviewe

All-sky search for long-duration gravitational wave transients with initial LIGO

We present the results of a search for long-duration gravitational wave transients in two sets of data collected by the LIGO Hanford and LIGO Livingston detectors between November 5, 2005 and September 30, 2007, and July 7, 2009 and October 20, 2010, with a total observational time of 283.0 days and 132.9 days, respectively. The search targets gravitational wave transients of duration 10-500 s in a frequency band of 40-1000 Hz, with minimal assumptions about the signal waveform, polarization, source direction, or time of occurrence. All candidate triggers were consistent with the expected background; as a result we set 90% confidence upper limits on the rate of long-duration gravitational wave transients for different types of gravitational wave signals. For signals from black hole accretion disk instabilities, we set upper limits on the source rate density between 3.4×10-5 and 9.4×10-4 Mpc-3 yr-1 at 90% confidence. These are the first results from an all-sky search for unmodeled long-duration transient gravitational waves. © 2016 American Physical Society

All-sky search for long-duration gravitational wave transients with initial LIGO

We present the results of a search for long-duration gravitational wave transients in two sets of data collected by the LIGO Hanford and LIGO Livingston detectors between November 5, 2005 and September 30, 2007, and July 7, 2009 and October 20, 2010, with a total observational time of 283.0 days and 132.9 days, respectively. The search targets gravitational wave transients of duration 10-500 s in a frequency band of 40-1000 Hz, with minimal assumptions about the signal waveform, polarization, source direction, or time of occurrence. All candidate triggers were consistent with the expected background; as a result we set 90% confidence upper limits on the rate of long-duration gravitational wave transients for different types of gravitational wave signals. For signals from black hole accretion disk instabilities, we set upper limits on the source rate density between 3.4×10-5 and 9.4×10-4 Mpc-3 yr-1 at 90% confidence. These are the first results from an all-sky search for unmodeled long-duration transient gravitational waves. © 2016 American Physical Society

Search for Tensor, Vector, and Scalar Polarizations in the Stochastic Gravitational-Wave Background

The detection of gravitational waves with Advanced LIGO and Advanced Virgo has enabled novel tests of general relativity, including direct study of the polarization of gravitational waves. While general relativity allows for only two tensor gravitational-wave polarizations, general metric theories can additionally predict two vector and two scalar polarizations. The polarization of gravitational waves is encoded in the spectral shape of the stochastic gravitational-wave background, formed by the superposition of cosmological and individually unresolved astrophysical sources. Using data recorded by Advanced LIGO during its first observing run, we search for a stochastic background of generically polarized gravitational waves. We find no evidence for a background of any polarization, and place the first direct bounds on the contributions of vector and scalar polarizations to the stochastic background. Under log-uniform priors for the energy in each polarization, we limit the energy densities of tensor, vector, and scalar modes at 95% credibility to Ω0T<5.58×10-8, Ω0V<6.35×10-8, and Ω0S<1.08×10-7 at a reference frequency f0=25 Hz. © 2018 American Physical Society

Influence of the thermomechanical processing on the fracture mechanisms of high strength aluminium/pure aluminium multilayer laminate materials

The microstructure and mechanical properties, with emphasis in the impact fracture toughness behaviour, of two multilayer laminate materials have been investigated. The multilayer materials are constituted by alternated sheets of pure aluminium (Al 1200 or Al 1050) and high strength Al 7075 alloy. Stacked layers of these alloys have been successfully joined using two processing routes with different total hot rolling strains. Both laminates have been tested at room temperature under impact Charpy tests, 3-point bend tests and shear tests on the interfaces. Both laminates exhibited more than eight times improvement in impact fracture toughness over the monolithic Al 7075-T6. The toughness increase in the higher rolling strained laminate is almost entirely due to crack blunting mechanism, while in the lower strained laminate, crack deflection by delamination and crack renucleation processes were active.Financial support from CICYT (Project MAT2003-01172) is gratefully acknowledged. C.M. Cepeda-Jiménez thanks the Spanish Ministry of Education and Science for a Juan de la Cierva contract. We also thank L. del Real-Alarcón for the welding work, F.F. González-Rodríguez for assistance during hot rolling and J. Chao- Hermida for assistance with the Charpy impact test.Peer reviewe

Influence of the thermal treatment on the microstructure and hardness evolution of 7075 aluminium layers in a hot-rolled multilayer laminate composite

The microstructure and mechanical properties of the Al 7075 alloy present in a hot roll-bonded laminate consisting of Al 7075/Al 2024 layers have been characterized by high resolution electron backscattering diffraction (EBSD) analysis and Vickers microhardness, respectively. The as-rolled deformation structure consisted in lamellar bands aligned parallel to the rolling direction. It was found that a post-rolling tempering at 175ºC/6 h, prior to the T6 treatment has a profound effect on the microstructure and the mechanical properties of the Al 7075 alloy. This tempering reduces the driving force for recrystallization during the usual solution treatment of 30 min that is part of the T6 treatment. The performed procedures favour a more homogeneous precipitation during the following age hardening step and the achievement of a noticeable increase in Vickers microhardness.Financial support from CICYT (Projects MAT2003-01172 and MAT2006- 11202) is gratefully acknowledged. C.M. Cepeda-Jiménez thanks the Spanish National Research Council (CSIC) for a I3P contract.Peer reviewe

Study of hot deformation of an Al-Cu-Mg alloy using processing maps and microstructural characterization

The forming behaviour of an Al–Cu–Mg alloy (Al 2024-T351) has been studied by processing maps and microstructural characterization. Torsion tests were conducted in the range 278–467 ◦C, between 2.1 and 25.6 s−1. Stress–strain curves obtained from the experiment data were fitted using the Garofalo equation to obtain the constitutive parameters, obtaining a stress exponent of 6.1 and an activation energy of 180 kJ/mol. Electron backscatter diffraction (EBSD) was employed to characterize the microtexture and microstructure, before and after torsion testing, to evaluate the microstructural changes and instability phenomena. A peak ductility of the Al 2024 alloy was found at about 400 ◦C at all strain rates considered. According to the processing maps and microstructure observation, the optimum hot deformation condition for the Al 2024 alloy is in the range 360–410 ◦C and 2.1–4.5 s−1. Under these favourable conditions a uniform and fine grain size is obtained by extended dynamic recovery (DRV), which leads to the formation of subgrain boundaries that progressively transform at large strains into new high angle grain boundariesFinancial support from CICYT (Project MAT2009-14452)Peer reviewe