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Adopting novel sandwich structures with FRP (Fibre Reinforced Polymer) skins and a metallic lattice core, both of which have high specific strength and stiffness, is one way to achieve better mechanical performance while remaining lightweight. Flexural stress is a load pattern that frequently occurs in the structural frame components of automobiles; nonetheless, while the in-plane load scheme has scarcely been examined, the out-of-plane load one has. As a result, the former configuration received consideration in this work. Moreover, short beam specimens were taken into account. The mechanical response of specimens with three different kinds of composite materials as skin material was analysed. The skins were made of CFRP (Carbon Fiber Reinforced Polymer), with two different weaving styles, and AFRP (Aramid Fiber Reinforced Polymer). All-titanium specimens were studied, too. Similar maximum loads and maximum displacement at break were recorded for both CFRP and AFRP specimens, while the all-titanium one resulted stronger. In terms of the load-displacement curves, the first section featured an initial linear phase, followed by a minor load drop, likely attributed to the breakage of fibres. The CFRP specimens showed a sharp fracture of the skin fibres, while for the AFRP, a fraying was observed.

Brake pad linings are an essential part of the correct functioning of braking systems based on the use of pads and discs. Generally, the compounds used to make the gaskets are characterised by the use of over 20 sintered components, which allow friction coefficients that vary between 0.2 and 0.6 at temperatures up to 200 °C. In this work, a traditional compound was investigated under close-to-real conditions in order to evaluate the tribological behaviour at different temperatures. Finally, a model based on the proportionality between temperature increase and relative variation of the friction coefficient was proposed. From the experimental test, it was evident that the friction coefficient increased with the temperature, passing from 0.4 to 0.6 in the temperature range of 100 °C to 180 °C; however, a further temperature increment until 350 °C caused a reduction in the friction coefficient to 0.2. The proposed model was able to anticipate the abovementioned trend, especially at high temperatures.

The core of the present work concerns the analysis of the failure mode and the fracture process induced by the flexural load in Fibre Metal Laminates (FMLs). The influence of the connection layer placed between the composite ones and the metal sheets on the fracture mode was analysed. The considered FML was made of aluminium sheets interposed with carbon fibre reinforced polymer (CFRP) layers, joined with two different types of interface: by using a structural adhesive, or by relying on the bonding capacity of the prepreg resin. Then, the mechanical performances of the produced laminates were determined through the three-point bending test procedure, and the support span was varied to investigate different loading conditions. Finally, the fracture surface morphology was analysed by using both optical and scanning electron microscopes. The type of interface was found to influence the strength of the studied FML, and different fracture modes were observed, depending on the loading condition

Lattice structures made of metal materials are very interesting since their structural efficiency is elevated, thanks to their good mechanical properties and light weight. Additive manufacturing processes are appropriate to produce those structures. However, the peculiar geometry of lattice structures causes the manufacturing process to create rather significant unconformities, affecting the structures’ mechanical properties. In this article, small trusses with different diameters were produced through electron beam melting (EBM) by varying the process parameters, like the orientation and the position in the build chamber. Then, their diameter was evaluated and compared with the nominal one. It was found that the orientation in the chamber was very influential on the geometrical error, as well as the nominal diameter, while the position in the building chamber was uninfluential. In particular, the highest deviation was found for the specimens oriented at 0° and those with a diameter of 1 mm. Moreover, a similar result was detected for the ovalisation of the truss section too.

The Smart Landing Gear system to be developed in the framework of the ANGELA project provides the strain measurements on landing gear structure at landings, and this system should be maintained efficiently under operational conditions. It is intended to assess the relevance of Fiber Bragg Gratings for in-flight testing. To assess the capabilities of the FBG bonding and to analyze the strain transmission conditions from the host structure to the FBG through the bonding layer during the operational phases of landing gears, a long-period cyclic loading test campaign on the bonding layer itself was performed. The primary objective of this fatigue-like test was to prove the ability of FBG sensors to withstand the operational life-cycle of landing gear while providing the same strain transfer function throughout the entire cycle; the secondary objective was to select the most suitable fiber-coating and bonding agents for this application. This document describes the execution and results of the fatigue-like test, intended as a preparatory test campaign to support the preliminary design activities of the Smart Landing System.

Metal lattice structures manufactured utilising additive techniques are attracting increasing attention thanks to the high structural efficiency they can offer. Although many studies exist on the characterisation of massive parts in Ti6Al4V processed by Electron Beam Melting (EBM), several investigations are necessary to characterise the Ti6Al4V lattice structures made by the EBM process. The objective of this paper is to develop a measurement method to assess the dimensional accuracy of Ti6Al4V octet truss lattice structures manufactured by EBM technology. Beam specimens with a 2 mm diameter and different growth orientations with respect to the build direction were analysed. The geometry differences between the designed and the manufactured beam specimens were highlighted. Two effects were identified: (i) The EBM-manufactured beams are generally thinner than the designed ones, and (ii) the shape of the section was found to be almost circular for the beam specimens oriented at 45° and 90°; on the contrary, the section of the horizontal beam (0°) cannot be considered circular.

In recent decades, designers have increasingly focused on the stability of assemblies in composite materials over time, particularly when used in structural applications. The use of structural adhesives allows for realising assemblies without mechanical fasteners. In fact, bonding is an assembly technique that prevent corrosion, ensures uniform stresses in the joint, and grows the specific resistance of the assembly. The knowledge of the behaviour of bonded joint is necessary to ensure the reliability of this technique over time, especially in aggressive environments. The aim of this work consists in investigating the combined effect of hydrothermal ageing and temperature test on the lap shear strength of single lap joints realised in CFRP. The results showed a higher influence of the ageing on paste adhesive compared to film adhesive. However, the ageing, combined with the operating temperature, played a fundamental role on the shear strength of the bonded joints.

The goal of this work is to improve the understanding of the relation between the microstructural characteristics of Intercritical Austempered Ductile Cast Iron (IADI) and the damage micromechanisms observed during its tensile loading. The experimental methodology involves heat treatments to obtain IADI and the assessment of the damage mechanisms (sequence and occurrence) during step by step tensile testing. The damage evaluation was carried out by observing the surface of the tensile test specimen with optical and scanning electron microscopy. The results show that small cracks start forming soon after the yield stress is surpassed. The crack initiation is preferentially located at matrix-nodule interface. As loading increases, cracks also develop at the ferritic grain boundaries and the ausferritic/ferritic interfaces. Consequently, at higher strain values, a competition between the plastic deformation on internodular zones and crack propagation along ausferritic phase is observed. Finally, the final fracture is produced by the propagation of cracks across the internodular ligaments and through the ausferritic/ferritic interface that later coalesce into a single dominant crack leading to the material failure.

FML (Fibre Metal Laminate) is a hybrid material that presents outstanding structural properties, such as resistance to cyclic and dynamic loads, together with low specific weight. This material consists of metal sheets alternating to composite material layers. In the present work, the ILSS (Interlaminar Shear Strength) was evaluated for different types of carbon fibre/aluminium FML, produced varying the layer thickness and the bonding solution of layers. In fact, FMLs consisting of one or two metal sheets (a parameter strictly connected to the layer thickness, as the metal/composite volume fraction was kept at constant value) and bonded with structural adhesive or prepreg resin were considered for this study. The ILSS was determined according to the three-point bending method with short beam specimens. The experimental tests evidenced an effect of the adhesion methodology on the ILSS value, while the layer thickness did not influence the interlaminar strength. The mechanical behaviour after the maximum load point was investigated too, evaluating the trend of the shear stress as a function of the loading nose displacement.

The thermomechanical interactions between the different materials constituting a hybrid laminate make residual stresses arise during the manufacturing process of such laminate. In turn, the residual stresses make the laminate deform as it is extracted from the mould. Cure induced deformation represent a problem for the assembly step, since additional operations are required for allowing the joining of the different components. Therefore, a tool suitable for the calculation of residual stresses and deformation is needed in order to predict them and to implement the necessary remedies. In the present work, a numerical model for the determination of residual stresses is presented and validated through experimental tests. The case study was a notched laminate, in order to emphasize the deformation without altering the thermal cycle experienced in the material. Both numerical and experimental runs highlighted a higher deformation near the vertex of the laminate.

Hot dip galvanizing is among the cheapest methods for protecting ferrous alloys against corrosion. The success is due to both the low cost of the process and the high degree of protection in many corrosive environments, where the coatings serve as sacrificial protection. The purpose of this analysis is to study the mechanical characteristics of steel plates, that have been hot dip coated with five different zinc alloy molten bath for different time periods. The mechanical tests performed is a non-standardized four-point bending test considering three distinct bending angles. Results are examined in terms of both mechanical behaviour and coating phase damage. The development of intermetallic phases and their damage are both influenced by the chemical compositions of the zinc bath, demonstrating that fractures arise mostly at the substrate-coating interface. All the coatings showed the arising of micro-cracks except for the Aluminium, which demonstrated its ductility. In addition, Zn-Ti coatings showed the arising of a new compact phase rich in iron, characterized by a great hardness. More research is needed to explore the aluminium impact on the zinc bath, the lack of tiny fractures in the phase, and the lesser thickness compared to the other coatings tested.

Using a finite element calculation code, this work analyses the influence of friction during a stamping test conducted on the AA6060 aluminium-based alloy. The study focuses on phenomena happening when the sheet necking appears. This condition, based on the Hill�s localized necking theory and the Swift�s diffuse necking theory, is dependent on the material hardening index. This work shows that the punch stroke at the necking condition point is maximum when the main strain measured on the sheet surface is unbalanced and close to a balanced biaxial tension condition.

Industry needs new materials that present very high structural characteristic, such as high strength, low weight and high damage tolerance. To obtain these characteristics a new class of materials has been introduced: Fibre Metal Laminate (FML); they consist in metal sheets alternated to composite material layers: in such manner, the good characteristics of each constituent material confer the utmost properties to the FMLs. However, the mechanical properties depend, among other factors, on the thickness and the numerousness of the layers constituting the FML, as well as the interface between metal and composite. Therefore, in this paper, the influence of the abovementioned factors on the material answer to flexural load was investigated. In particular, different kinds of laminates were produced varying the layers adhesion and the layers thickness, but maintaining unaltered the metal/composite volume ratio and the total laminate thickness. Then their structural behaviour was investigated through three-point bending test, and it was found that the flexural behaviour was affected by both the investigated factors; in fact, the maximum flexural load diminished incrementing the number of layers and inserting an adhesive layer at the metal/composite interface.

A new class of material characterized by mechanical properties close to the traditional low and medium carbon steel is the Ductile Cast Irons (DCIs). High castability and low production costs allow them to be used in many fields, ranging from automotive to piping. In this class of iron-based alloy the content of carbon is mainly localized in the graphite nodules, which are dispersed in a metallic matrix characterized by different phases: ferrite, austenite, pearlite, martensite or their mix, depending on the chemical composition and the heat treatment. Metallic matrix is subjected to the corrosion phenomenon, and, for this reason, the study and the development of traditional and innovative protection techniques are important, mainly in critical applications. Hot dip galvanizing is one of the investigated protections because the zinc is able to protect the iron-based alloys thanks to the reduction potential that is lower than the iron one. In this work, a ferritic-pearlitic DCI (GS500) is galvanized by using a pure Zn bath at 440�C in order to generate a zinc coating at different dipping time. The presence of thermal cracks is observed by means of a Scanning Electron Microscope (SEM).

Metal lattice structures produced by means of additive techniques are attracting increasing attention thanks to the high structural efficiency they can offer. In order to achieve the maximum structural performance, numerical design techniques are used almost exclusively, thus based on CAE-FEM codes. Nevertheless, the current manufacturing facilities do not yet guarantee defect-free components, and, therefore, such imperfections need to be introduced in the numerical models too. The present work aims to describe a FE modelling technique for lattice structures based on the use of beam and shell elements, and therefore with a very reduced computational cost. The main structural parameters, such as weight and stiffness and strength, are used to drive the model calibration. Simple mathematical relationships, based on Experimental-CAD-FEM comparisons, are provided to estimate the error related to the numerical model in a simple and fast way. The validation was performed by three-point bending test on flat specimen with regular octet-truss microstructure both with and without external skin. The test articles were produced in Ti6Al4V and by means of the electron beam melting (EBM) technology. The results obtained are in excellent agreement with the experimental ones, indeed the maximum error is about 3%. All this indicates these methodologies as possible tools for evaluating the performance of such kinds of high-tech structures.

Natural stone is a material that presents durableness over time and high aesthetic characteristic, but it is brittle and its tensile strength is significantly lower than compressive one: these peculiarities must be taken into account for material usage; in fact, for applications requiring high flexural and tensile strength, as thin sections or long spans, the particular mechanical behavior of the natural stone constitutes an issue to be overcome.A solution to the above mentioned problem is presented in the present paper: a natural stone tile is reinforced by bonding a sandwich structural laminate made of composite materials. In such manner, a double result is obtained: the mechanical strength increment and the and the tile specific weight decrement. In particular, two different types of sandwich structures, made of glass/epoxy laminates and honeycomb or foam core, were bonded to the lower surfaces of marble and granite tiles; then, 3-point bending tests were carried out on specimens extracted from the produced hybrid tiles. A performance index, considering both strength and weight of tiles, was introduced and the comparison with specimens extracted from traditional unreinforced tiles demonstrated that the considered reinforcement increases the structural characteristics of stone tiles up to an order of magnitude.

Lightening parts, maintaining also a high strength, is a request of the transport industry. Isogrid structures represent one of the best answer to face these issues, especially if composite materials are considered for their production. However, the fabrication of these structures is very complex, as defects can arise that cause the part discarding or the part failure during service. The properties of the fabricated structure depend on some process characteristics, as the forming technology, the process parameters and the tools that have to be wisely designed. Isogrid structures are characterized by the ribs, so the mould shape must be carefully planned. In fact, a common defect that usually occurs is a scarce compaction of the ribs, which involves porosity and low mechanical strength. In this paper, the manufacturing process peculiarities for GFRP (Glass Fibre Reinforced Polymer) isogrid structures were defined, then both the mould and the parts were produced. Structural tests were carried out on these structures in order to validate the process design methodology, paying particular attention to the structural properties of the ribs, as the compaction degree and the interlaminar shear strength. Finally, some actions were undertaken to avoid the problems found in the first production run.

Nowadays adhesive are widely used in structural applications, in particular for assembly composite materials. In fact, this technique allows to obtain a more uniform load in the joint, to realise a joint with an higher specific strength and to avoid drilling parts as in the case of bolted joints. However, the mechanical properties of bonded parts over time are not well understood if they are subjected to a more or less aggressive environment. Generally, the main factors of influence regarding the durability of bonded joints are humidity and temperature, but their effects are not always clear if these two factors act simultaneously. In this work the effect of hydrothermal ageing on the mechanical resistance of single lap bonded CFRP joints has been investigated. In particular two types of adhesives (AF 163-2K film and EA 9309NA paste) and three ageing environments (thermal cycles from -28 �C to 85 �C in air, distilled water and salt water) have been chosen for the activity.

This work analyses the results of a simple forming process of an AA6060 aluminium alloy sheet in order to validate the development of a simulation model based on the finite element method (FEM). This work represents the starting point of a broader study aimed at analysing the sheet formability. The FEM based model and the use of both the flow stress curve and the formability limit curve (FLC) were validated through the simulation of a simple forming process that required use of a hemispherical punch. The detailed analysis of the machining process by using FEM allows significant time and cost savings, avoiding "trial-and-error" operations that are normally used in the setup phase of the production process.