Gianluca Chiappini

Università Telematica "E-Campus" · Faculty of Engineering

The metal additive manufacturing (AM) is a technology that is rapidly spreading in the industrial sector with its enormous potential in making components with complex shapes and low weight, ensuring a high structural strength. However, the mechanical properties of the components depend on the printing process, and the interactions between the proce...

CuCrZr alloys achieve high mechanical properties by thermal (e.g., supersaturated temper and aging), mechanical (e.g., ECAP), or thermomechanical treatments (solution annealing, cold working, and aging). This alloy can be considered a functional material, and it can be exploited in different application fields, thanks to a combination of thermal, e...

Shape memory polymers (SMPs) represent a materials class capable of recovering their initial shape, when submitted to deformations, through an external stimulus. This paper focuses on a Shape Memory Thermoplastic Polyurethane (SMPU), characterized by a one-way shape memory effect (SME) activated by temperature. The material was characterized by Dif...

The present work deals with the construction and verification of a 1:2 scale prototype of a modular system of a lightweight floor made of steel and glass with a tensegrity type load-bearing frame. In particular, the proposed study tests the applicability of the adhesive joint on the “Tensegrity Floor” (Patent No. 00014426973). The Tensegrity Floor...

In the last few decades, the shape memory polymers have gained growing interest and relevance in many application fields, which include textiles, aerospace, biomedical devices, etc. SMP are materials with stimuli-sensitive switches that are able to change their geometry from a primary shape to a secondary shape—and vice versa—in response to externa...

Additive manufacturing (AM) is undoubtedly the fastest-growing technology in the field of component productions. In particular, metal AM is rapidly emerging thanks to its enormous potentiality in manufacturing components with complex shapes and high structural performances. Although the precision and the rapidity of the production process is contin...

Tensegrity structures are interesting elements that can be used to create innovative building components. In this work, the deformation behavior of a new type of tensegrity floor (patent n. 0001426973) was investigated through image analysis and photogrammetry, using stereoscopic algorithms. The main innovation of the proposed tensegrity floor is t...

The use of reinforcements in adhesive joints makes the stress distribution more uniform, improving their mechanical performance and adhesion. The present paper aims to verify the effectiveness and efficiency of the insertion of nylon 6 fabric in the adhesive layer, to study their applicability and functionality in building components. The increase...

The use of glass elements in civil engineering is spreading in the last years beyond merely aesthetic functions for their ease of installation and production. Nonetheless, the structural performance of such materials in any condition of use is object of investigation. In this scenario, the paper analyses the performance of an innovative concept of...

Adhesive bonding technology make it possible to join different materials and to assemble lightweight joints with high mechanical performance. These advantages over conventional technologies have led to a growing interest in these joints in timber construction. This study reports the results of an experimental campaign on double-lap adhesive joints...

The use of large glass areas is a hallmark of modern architecture, and glass is also used as a structural element in many applications. Recent developments in the field of structural adhesives have led to the development of bonding solutions between steel and glass adherends that meet the structural and aesthetic requirements for high performance b...

The paper provides an evaluation of the nonlinear dynamic response of a cantilever beam made of composite material subjected to low-velocity impacts. The structure is assumed to respond in a quasi-static manner and modelled by a continuous beam in large displacement with a lumped mass attached. First, an analytical model was developed to study the...

The use of glass elements in civil engineering is spreading in the last years beyond merely aesthetic functions for their ease of installation and production. Nonetheless, the structural performance of such materials in any condition of use is object of investigation. In this scenario, the paper analyses the performance of an innovative concept of...

The aim of this research was to investigate the mechanical performance of an earthen massive cladding, recently used for external/internal layers in Platform Frame technology, through an extensive experimental campaign. The masonry is built with extruded unbaked earth blocks and characterized by dovetail horizontally staggered bed joints. The wall...

In this experimental study, a series of mechanical tests were conducted on double-lap joint specimens, where glass sheets were adhesively bonded on two different supports, namely aluminum and glass fiber reinforced polymer (GFRP). Five different types of adhesives (three epoxy and two acrylic) were compared and three temperature conditions (room te...

The virtual fields method is a well-known inverse technique used to identify the constitutive parameters of materials starting from full-field measurement. The method exploits the equilibrium equation, written in the form of the principle of virtual work, to extract the constitutive parameters directly from the measured data. Similar considerations...

This paper investigates the nonlinear dynamic behavior of a cantilever beam made of composite material without and with lumped mass fixed along its length. The analysis compares the results coming from analytical and numerical modeling with experimental observations. The first part focuses on the analytical model. The model takes into account the n...

The influence of high strain rate on the forming limit curves of AA6082-T6 aluminum alloy sheets, 1 mm in thickness, was investigated by means of dynamic tensile and hemispherical punch tests carried out until the onset of sample failure using a Split Hopkinson Bar (SHB) system, at a punch speed of 7500 and 12000 mm/s. The equipment used was design...

Ultra‐High Performance Fiber‐Reinforced Concrete (UHPFRC) is considered a promising material for many structural applications where high strength and high energy absorption capacity are required. The purpose of this work is to study the uniaxial tensile behavior of soft cast (flowable at casting time) UHPFRC by varying the amount of hooked steel fi...

Invisible orthodontic aligners (IOAs) have been introduced in the orthodontic field as an innovative alternative for fixed brackets, in relation to their ability to be easily inserted/removed from the oral cavity without affecting the chewing ability and the aesthetic of the patients. The paper provides a complete physicochemical and mechanical cha...

The aim of this research is to investigate, through the Digital Image Correlation (DIC) technique, the mechanical performance of a new type of earth masonry, built with extruded blocks and characterized by dovetail horizontally staggered bed joints. The experimental program consists of two levels of investigations: (i) preliminary phase on componen...

The use of Textile Reinforced Mortar (TRM) systems represent a valid alternative to traditional strengthening techniques, to improve mechanical strength and seismic performance of masonry buildings. Their effectiveness has been validated by several studies [1-4]. However, the TRM contribution in the mechanical behavior of masonry walls, subjected t...

In this experimental study, a series of tensile tests were conducted on double-lap specimens, where UV absorbance laminated glass was adhesively bonded on GFRP polyester pultruded support. Three different types of adhesives were compared, two epoxy and one polyurethane, and both un-aged and aged conditions were investigated. Three ageing conditions...

This study investigates the effects of the addition of two different types of particles on morphological, thermo-hygrometric and mechanical properties of thermal insulating sprayed polyurethane foams. Platelet nanoclay and spherical silicon dioxide microparticles were poured into two different foams with a density of 15 Kg/m³ and 30 Kg/m³, respecti...

The use of Fabric Reinforced Cementitious Matrix (FRCM) systems to reinforce existing masonry and concrete structures is nowadays a well-established practice. The mechanical characterization of FRCM systems is of fundamental importance to define the correct parameters needed to design a strengthening intervention. However, some aspects regarding FR...

The knowledge of formability is important for the success of sheet metal forming processes. Notwithstanding they can involve relatively high speeds, higher than the quasi-static regime ones, few studies considering the strain rate effect on formability are available in literature. In the present paper, a study on the effect of strain rate on formab...

Polymer nanocomposites synergistically combine the good thermal properties of the hosting polymer matrix with the high mechanical performance of the fillers, providing a new class of materials with superior properties. The present study aims to evaluate in a multidisciplinary way the enhancement in mechanical and thermal-hygrometric properties of l...

In this work, experimental compression tests have been performed on parallelepiped specimens cut from an agglomerated cork slab. The tests have been performed both using a quasi-static testing machine and a polymeric Split Hopkinson Bar, in order to assess the sensitivity of the material to the strain rate. A standard and a high-speed digital camer...

In this work, experimental compression tests have been performed on rectangular specimens cut from a cork slab. The tests have been performed both using a quasi-static testing machine and a Split Hopkinson Bar. The dynamic tests revealed a high sensitivity of the material to the strain rate, with stress strain curves significantly higher than in qu...

The aim of this paper is the systematic study of thermo-structural behavior of ceramic components, in particular, mixtures of refractory materials with high thermal and mechanical performance. Using 3-point bending tests, the elastic modulus, ultimate stress and elongation was obtained; measured values, also thanks to the use of DIC optical technol...

The yielding process of some aluminium alloys is often characterized by an inhomogeneous diffusion of shear bands during deformation, which cause oscillations in both the force level and the strain history. This phenomenon can be observed during a tensile test, however, in order to describe the mechanical behaviour of components at the continuum le...

The knowledge of the sheet metals formality is important for the success of the manufacturing processed based on plastic deformation. Even though many industrial processes take place at relatively high speeds, higher than the quasi-static regime ones, few studies are present in the literature on the evaluation of the formability at high speed. In t...

The present work describes a study carried out to characterize the constitutive and operating behavior of a rubber membrane, to be used as an air-oil separator in vibration dampers of helicopter rotor blades. The membrane is mounted inside the main damper tube through a manual reversal movement, has to withstand a differential pressure and elongati...

In this work, tension and compression tests have been carried out on aluminium samples at low and high strain rate, the latter performed by means of a direct tension Hopkinson bar equipment. The parameters of the Johnson-Cook constitutive model have been identified using different approaches; the first method consists in the classical Finite Elemen...

In this work, dynamic tension tests have been conducted by an SHB on sheet metals in order to characterize the plastic behaviour of the materials. Pictures of the samples were acquired during the test by means of a fast camera and were post-processed by a global approach 2D DIC software. On the one hand, this permitted to validate the strain measur...

In this paper, the stiffness increase obtained by coupling steel laminates to GFRP pultruded profiles is investigated, three different epoxy adhesives were used and compared. The objective is to verify the applicability of this hybrid system in structural members for curtain walls. Three types of test were used to investigate different properties o...

The paper deals with the accelerated tests to evaluate the effect of the on/off switching in the elastomeric diffusers used for the aeration in the biological processes for urban wastewater. Two types of commercial diffusers were subjected to consecutive cycles up to simulate more than 8 years of real working conditions. The pressure trends increme...

In order to simulate accurately the stamping process of sheet metals, their constitutive behaviour, as well as their formability limits, must be accurately evaluated. In this work, tensile and Nakazima tests are conducted at high temperature on aluminium alloys of the 5000 series. The tensile tests are mainly used to determine the flow stress curve...

2D and stereo Digital Image Correlation (DIC) allows to retrieve complex displacement and strain fields on a specimen’s surface. Although 2D DIC is strongly affected by out-of-plane motions, in many situations, it is preferred over stereo DIC because of its ease to use and because only one camera is required. The out-of-plane movements can be ascri...

The present work is an extension of the optical grid method for the experimental investigation of deformation in stamped sheet metals. The classical method presents difficulty or is inapplicable where the deformation has resulted in the tearing of the sheet. In these cases, the measurement result is not available right where the most interesting da...

This paper is concerned with an in-depth study of the interactions between full-field measurements errors and material identification. It is a further step in a research plan that aims to create a simulation procedure of actual experiments, with the final goal of using the simulator to optimise the test set-up in terms of specimen shape, measuremen...

The split Hopkinson bar is a well-known apparatus for performing tests at high strain-rate on engineering materials. The specimen is placed between two long bars and quickly loaded by a pressure wave, which travels at sound speed along the input bar, passes through the specimen, then is partly reflected and partly transmitted to the output bar. In...

In this paper Digital Image Correlation (DIC) is used to study the evolution of the plastic zone close to a crack tip. A modified CT-specimen was used in order to fulfill the plane stress condition. The strain field around the crack tip was measured using two cameras and stereo DIC, so that out-of-plane movements are taken into account. Then, the V...

The Virtual Fields Method (VFM) is an inverse method which allows to identify the constitutive parameters of materials from full-field measurements. The method relies on the principle of virtual work and, traditionally, is mainly used to characterize the material properties. Nonetheless the VFM can also be used as an inspection tool to compare cons...

In this work, the Virtual Fields Method is employed in order to identify the parameters of constitutive models describing the visco-pseudo-hyper elastic behavior of rubber-like materials; a cruciform specimen is subjected to several biaxial loading/unloading cycles at different strain amplitudes, while load and full-field strain histories are recor...

The present work describes the study carried out to characterize the constitutive and operating behavior of a rubber membrane; the application under examination consists of a air-oil separator for dampers of helicopter rotor blades. The main requirements are that the membrane must be mounted inside the main tube through a manual reversal movement,...

Full field measurements and inverse methods can be conveniently used to identify the constitutive properties of materials. Several methods are available in the literature which can be applied to many different types of materials and constitutive models (linear elasticity, elasto-plasticity, hyper-elasticity, etc.). The effectiveness of the identifi...

The use of rubber like materials has a number applications, from automotive to aeronautics and many other fields particular, as they are often used to make gaskets, hoses, separation membranes, vibration absorbers, etc. In order to optimize and enhance the performances of a rubber component, a FEA is frequently required. Although many models are av...

The aim of this work is the simultaneous use and comparison of two different techniques for measuring the three dimensional deformation of a sheet metal specimen subjected to a tensile load. Such measurements are useful for a correct analysis of the mechanical behavior and plastic damage of materials. The former is a hybrid technique based on the c...

This work aimed to implement and compare two competitive procedures for the identification of hyperelastic material parameters. Formerly, experimental tests have been conducted on fluorosilicone rubber specimens in equal-biaxial tension; the cruciform shaped-specimens underwent heterogeneous large strain distributions, which were captured by Digita...

  New methods are emerging in the material characterisation field with the aim of exploiting innovative full-field strain measurement techniques. Besides experimental issues, also numerical procedures for inverse problems should adapt to a new philosophy: the large amount of data referred to local strains should be used in an appropriate way to obt...

In the 2009 SEM Conference in Albuquerque, a measurement technique that combines the digital image correlation and the fringe projection was proposed by the authors to evaluate the 3D displacement of a specimen during a tensile test: the DIC is used to measure the in-plane displacement on both faces of the specimen while the fringe projection and p...

Besides the typical hyperelastic behaviour, large elastic deformations with non-linear stress–strain behaviour, rubber-like materials may also exhibit some inelastic effects, like hysteresis and permanent set. One of them is a particular damage phenomenon called Mullins effect. This is visible when cyclic tension tests are performed with increasing...

The aim in this work is the development of an image analysis technique for 3D shape acquisition, based on luminous fringe projections. In more detail, the method is based on the simultaneous use of several projectors, which is desirable whenever the surface under inspection has a complex geometry, with undercuts or shadow areas. In these cases, the...

Quasi-static tension tests are largely used in research and industry practice in order to evaluate the mechanical behavior of metals part. The stress-strain constitutive relationship are regularly obtained with standard testing machine, equipped with load cells for force measurement and with LVDTs, or preferably extensometers, for deformation evalu...

Several techniques for full-field strain measurement are nowadays available and reliable, and the topics of research should be to find well suited methods and procedures to use the great amount of data in an appropriate and sharp way. In this terms, one of the best and effective techniques developed in recent years is the Virtual Field Method (VFM)...

Visco-elastic properties of rubberlike materials are of fundamental importance to understand their mechanical behaviour, especially dealing with dynamic and vibration problems. In this paper the results of a series of tests performed on rubber specimens subjected to uniaxial cyclic loading at different frequencies are shown; tests are performed usi...

Rubber-like materials exhibit a particular stress–strain behaviour known as hyperelasticity. Several models are available in the literature for these materials, based on the definition of a particular expression of the specific potential deformation energy. Among these, Mooney–Rivlin and Ogden models are the most used. In both cases, at least uniax...

The aim of this work is the development of an image analysis technique for 3D shape acquisition, based on luminous fringes projections. More in detail the method is based on the simultaneous use of several projectors, which is desirable whenever the surface under inspection has a complex geometry, with undercuts or shadow areas. In these cases, the...

This paper represents the further development of a system recently presented by the authors in order to determine the mechanical properties of rubber-like materials. An elementary hydraulic circuit fed by a motor pump allows to inflate a thin disk of rubber with adjustable flow rate, thus controlling the speed of deformation of the specimen. The in...

Sommario L'obiettivo del presente lavoro è lo sviluppo di una tecnica di analisi di immagine per il rilievo di forma 3D basata sulla proiezione di frange luminose. In particolare lo scopo della ricerca è stato la realizzazione di una tecnica di acquisizione basata sull'utilizzo simultaneo di più proiettori. Questa necessità può scaturire qualora la...

Sommario Con il presente articolo gi autori propongono una tecnica di caratterizzazione meccanica di materiali iperelastici basata sull'applicazione della tecnica di correlazione digitale di immagini speckle (DIC) ad una prova di tensione planare su provini piatti rettangolari. Se si considera una sezione trasversale del provino, in base alle defor...