Acoustic and Elastic Waves: Recent Trends in Science and Engineering

The present Special Issue intends to explore new directions in the field of acoustics and ultrasonics. The interest includes, but is not limited to, the use of acoustic technology for condition monitoring of materials and structures. Topics of interest (among others): • Acoustic emission in materials and structures (without material limitation) • Innovative cases of ultrasonic inspection • Wave dispersion and waveguides • Monitoring of innovative materials • Seismic waves • Vibrations, damping and noise control • Combination of mechanical wave techniques with other types for structural health monitoring purposes. Experimental and numerical studies are welcome

Texture and Colour in Image Analysis

Research in colour and texture has experienced major changes in the last few years. This book presents some recent advances in the field, specifically in the theory and applications of colour texture analysis. This volume also features benchmarks, comparative evaluations and reviews

Cork structural characteristics and their influence on the oxygen ingress through wine stoppers

Doutoramento em Engenharia Florestal e dos Recursos Naturais - Instituto Superior de Agronomia - ULCork structural characteristics and their influence on the oxygen ingress through wine stoppers were studied aiming to contribute to an increased added-value of the natural cork stoppers. The surface porosity features of cork stoppers can differentiate the three main commercial classes used nowadays: the porosity coefficient was 2.4%, 4.0% and 5.5% for premium, good and standard stoppers, respectively. Image analysis also distinguished defects in the cork structure: empty ant gallery; Coroebus undatus F. larvae gallery; and wetcork. Several predictive classification models of stoppers into quality classes were built using the results from cork stoppers surface characterization and a simplified model using the main discriminant features i.e. porosity coefficient and the RGB colour-type variables was presented. X-ray tomography was used as a non-destructive technique to study the internal structure of natural cork stoppers, allowing the visualization of some defects inside the cork stopper. After characterization, the natural cork stoppers were used as closure of bottles and oxygen diffusion measurements were made along time. The kinetics of oxygen transfer was similar and could be adjusted to logarithmic models. On average 35% of the overall oxygen ingress occurred in the first 5 days, 59% in the 1st month and 78% in the first 3 months. Microtomography images (voxel size of 50 µm) allowed the observation of lenticular channels development and geometry, and the quantification of void and high density regions (HDR) fractions. The evidence that the void fraction of lenticular channels in the innermost part of the cork stopper inserted in the bottle was strongly related to the oxygen ingress in the first month after bottling can be used for quality enhancement of natural cork stoppers with incorporation of performance requirement

Friction stir processing : simulation and experimental characterizations of aluminium metal matrix composites

Abstract: Aluminum (Al) and its alloys have been the prime materials of construction for many industries. The Al alloys are readily weldable and have excellent formability, good strength and excellent resistance to corrosion. While Al alloys are very strong and exhibit a high strength to weight ratio, they exhibit limited capabilities for wear and abrasion applications. The reinforcement of Aluminum and its alloys with various reinforcing powders has engineered a new type of material regarded as metal-matrix composites. The reinforcement of pure Al and its alloys with ceramic particles is expected to result in an improved mechanical property-to-weight ratio, as well as a superior resistance to wear, and to a high specific hardness. However, these composites suffer from a great loss in ductility and toughness due to the incorporation of non-deformable ceramic reinforcements as a result of inappropriate fabrication process and process parameters. The fabrication process used in this study is known as the friction stir processing technique ...D.Phil. (Mechanical Engineering Science

Magnetic Hysteretic Characterization of Ferromagnetic Materials with Objectives towards Non-Destructive Evaluation of Material Degradation

Structurele componenten en machineonderdelen vervaardigd uit staal worden vaak onder veeleisende omstandigheden uitgebaat. Dit kan aanleiding geven tot materiaaldegradatieprocessen zoals verbrossing en metaalvermoeiing. Mettertijd kunnen deze microstructurele processen leiden tot een graduele verslechtering van de mechanische eigenschappen, en eventueel tot scheurgroei en breuk. Om dit te vermijden is het monitoren van de materiaalintegriteit van groot belang, wat uitgevoerd kan worden met behulp van niet-destructieve evaluatietechnieken. In dit doctoraatsonderzoek bestuderen we de mogelijkheden van magnetische hysteretische karakteriseringstechnieken voor het niet-destructief monitoren van toenemende materiaaldegradatie van ferromagnetisch constructiestaal. Dergelijke aanpak is gemotiveerd door de kennis dat magnetisch hysteretisch gedrag beïnvloed is door microstructurele materiaaleigenschappen. Anders geformuleerd, de verandering in de vorm van de magnetische hysteresislussen, experimenteel waargenomen op verschillende momenten tijdens de materiaaldegradatie, reflecteert de onderliggende microstructurele veranderingen en de degradatie van de mechanische eigenschappen. Een van de onderzochte onderwerpen is de verbrossing van ferritisch staal door neutronenbestraling. Dit effect kan schadelijk zijn voor het drukvat van een nucleaire reactor. De maximum-permeabiliteit vertoont een significante dalende trend met stijgende neutronendosis en met stijgende vloeigrens, hetgeen het potentieel aangeeft van de magnetische hysteretische evaluatie van verbrossing door neutronenbestraling. Een andere topic is het continu monitoren van metaalvermoeiing aan de hand van een magnetomechanische methode. Deze methode resulteert in informatie over de verschillende vermoeiingsstadia, alsook over het finale vermoeiingsstadium. De ontwikkelde magnetische en magnetomechanische karakteriseringstechnieken kunnen gebruikt worden voor de niet-destructieve evaluatie van mechanische en microstructurele eigenschappen, met als doelstelling de beoordeling van de materiaalintegriteit tijdens uitbating en/of voor de kwaliteitscontrole tijdens materiaalproductieprocessen

Manufacturing and characterisation of a fibre optic acoustic emission sensor

The value of Remote Condition Monitoring for the real-time evaluation of the structural integrity of critical components is undeniable. Fibre-reinforced polymer composites are a class of materials which offer significant advantages over conventional metal alloys used for manufacturing load bearing structures in cases where weight and/or energy consumption need to be kept to a minimum, for example automotive and aerospace applications. This is due to the excellent strength to weight ratio that FRPCs exhibit. However, their strongly anisotropic microstructure of poses significant challenges for Non-Destructive Evaluation of the actual structural health of components made from such materials. Acoustic Emission is a passive condition monitoring technique based on the detection of elastic stress waves emitted when damage evolves in a structure. Conventional piezoelectric AE sensors need to be surface-mounted as their embedding in FRPCs is impractical. Fibre Optic Acoustic Emission Sensors (FOAES) offer a distinct advantage since they are light weight, have small size and can be effectively embedded in composite laminates. Moreover, they can be multiplexed with the entire structure being monitored more effectively. This study has focused in the evaluation of the manufacturing process and characterisation of FOAES. Comparison of their performance with conventional commercial sensors was carried out

The effect of molybdenum on precipitation behaviour in low-carbon strip-cast steels containing niobium

This study addresses the effects of molybdenum on phase transformation and precipitation behaviour in low-carbon niobium-containing strip-cast steels, which is beneficial for the development of new high-strength low-alloy (HSLA) steels, designed specifically for production by direct strip casting

A new mixed model based on the enhanced-Refined Zigzag Theory for the analysis of thick multilayered composite plates

The Refined Zigzag Theory (RZT) has been widely used in the numerical analysis of multilayered and sandwich plates in the last decay. It has been demonstrated its high accuracy in predicting global quantities, such as maximum displacement, frequencies and buckling loads, and local quantities such as through-the-thickness distribution of displacements and in-plane stresses [1,2]. Moreover, the C0 continuity conditions make this theory appealing to finite element formulations [3]. The standard RZT, due to the derivation of the zigzag functions, cannot be used to investigate the structural behaviour of angle-ply laminated plates. This drawback has been recently solved by introducing a new set of generalized zigzag functions that allow the coupling effect between the local contribution of the zigzag displacements [4]. The newly developed theory has been named enhanced Refined Zigzag Theory (en- RZT) and has been demonstrated to be very accurate in the prediction of displacements, frequencies, buckling loads and stresses. The predictive capabilities of standard RZT for transverse shear stress distributions can be improved using the Reissner’s Mixed Variational Theorem (RMVT). In the mixed RZT, named RZT(m) [5], the assumed transverse shear stresses are derived from the integration of local three-dimensional equilibrium equations. Following the variational statement described by Auricchio and Sacco [6], the purpose of this work is to implement a mixed variational formulation for the en-RZT, in order to improve the accuracy of the predicted transverse stress distributions. The assumed kinematic field is cubic for the in-plane displacements and parabolic for the transverse one. Using an appropriate procedure enforcing the transverse shear stresses null on both the top and bottom surface, a new set of enhanced piecewise cubic zigzag functions are obtained. The transverse normal stress is assumed as a smeared cubic function along the laminate thickness. The assumed transverse shear stresses profile is derived from the integration of local three-dimensional equilibrium equations. The variational functional is the sum of three contributions: (1) one related to the membrane-bending deformation with a full displacement formulation, (2) the Hellinger-Reissner functional for the transverse normal and shear terms and (3) a penalty functional adopted to enforce the compatibility between the strains coming from the displacement field and new “strain” independent variables. The entire formulation is developed and the governing equations are derived for cases with existing analytical solutions. Finally, to assess the proposed model’s predictive capabilities, results are compared with an exact three-dimensional solution, when available, or high-fidelity finite elements 3D models. References: [1] Tessler A, Di Sciuva M, Gherlone M. Refined Zigzag Theory for Laminated Composite and Sandwich Plates. NASA/TP- 2009-215561 2009:1–53. [2] Iurlaro L, Gherlone M, Di Sciuva M, Tessler A. Assessment of the Refined Zigzag Theory for bending, vibration, and buckling of sandwich plates: a comparative study of different theories. Composite Structures 2013;106:777–92. https://doi.org/10.1016/j.compstruct.2013.07.019. [3] Di Sciuva M, Gherlone M, Iurlaro L, Tessler A. A class of higher-order C0 composite and sandwich beam elements based on the Refined Zigzag Theory. Composite Structures 2015;132:784–803. https://doi.org/10.1016/j.compstruct.2015.06.071. [4] Sorrenti M, Di Sciuva M. An enhancement of the warping shear functions of Refined Zigzag Theory. Journal of Applied Mechanics 2021;88:7. https://doi.org/10.1115/1.4050908. [5] Iurlaro L, Gherlone M, Di Sciuva M, Tessler A. A Multi-scale Refined Zigzag Theory for Multilayered Composite and Sandwich Plates with Improved Transverse Shear Stresses, Ibiza, Spain: 2013. [6] Auricchio F, Sacco E. Refined First-Order Shear Deformation Theory Models for Composite Laminates. J Appl Mech 2003;70:381–90. https://doi.org/10.1115/1.1572901