Massimiliano Avalle | Università degli Studi di Genova (original) (raw)
Papers by Massimiliano Avalle
International Journal of Crashworthiness, 2015
The microstructural analysis of many cellular materials may be performed by means of X-ray tomogr... more The microstructural analysis of many cellular materials may be performed by means of X-ray tomography (CT). This technique allows a 3-dimensional non-destructive visualization of the cellular microstructure of the examined materials. Starting from specimen images obtained from this technique it is possible to obtain detailed numerical FE model of it. Some techniques have been used in the past to perform this type of analysis on closed cell foams: the Groupe d’ Etudes de Metallurgie Physique et de Physique des Materiaux in France recently conducted some works [1], in the modeling of the actual structure of a cellular material. The group examined the microstructure of foams (polymeric and metallic) in a compression test. They discussed three different technique: the first one is based on a tetrahedrical mesh of the structure obtained by a triangularization of the CT volume (by using medical software like Amira); the second one is based on a direct transformation of CT voxel in cubic e...
This paper summarises the results of a CRAFT project investigating the influence of casting defec... more This paper summarises the results of a CRAFT project investigating the influence of casting defects on material properties for a high pressure die cast aluminium alloy. Defects consist in gas and shrinkage pores as well as cold fills, dross and alumina skins. Static and fatigue tests are run on standard specimens and production components. For the specimens, the influence is straightforward, while for components no significant difference was found between batches of components, judged as "acceptable" and "non acceptable" by the quality inspection within the foundry. Fatigue testing showed four different fracture regions; two corresponding to a region of high stress as indicated by a FEM simulation. For the other two regions of failure, voids or oxide layers of significant dimensions were observed on the fracture regions. These regions corresponded to regions of last solidification; moreover, for these regions, simulation of the casting process pointed out the pre...
The present work illustrates a procedure for the design and optimization of an elastic component ... more The present work illustrates a procedure for the design and optimization of an elastic component used in vibration welding machines for plastic materials. Vibration welding is a very effective technology, both technically and economically, to join plastic parts: welding is obtained by locally heating the material by means of the friction obtained by relative transverse vibration between the two parts. Since the vibration is obtained by resonance of one of the machine heads, there is an elastic element stressed in fatigue loading condition at high number of cycles. To increase the fatigue life of the component and minimize the mass and costs of it, one of the action that can be taken is to optimize the shape of the component to decrease stress concentrations. To design this spring element with the optimized shape a technique based on selection charts is proposed. Parole chiave: saldatura a vibrazioni, saldatura plastiche, ottimizzazione strutturale
Procedia Structural Integrity, 2018
Cellular materials, often referred as foams or structural foams when used for energy absorption, ... more Cellular materials, often referred as foams or structural foams when used for energy absorption, are largely used to protect people and goods in the case of shocks and impacts. The detailed knowledge of their behavior is fundamental to design components for this aim. Peroni et al. (2008)-(2009) proposed a model able to describe the mechanical compression behavior of some polymeric material. Such model, based on the work by Rusch (1970), described the stress-strain curve as a sum of two contributions, the first for the elastic part and the second for the densification. More recently Avalle and Belingardi (2018) presented a more general model where the stress is calculated as a sum of three terms, one for the elasto-plastic phase, the second for the plateau, and a third for the densification. The model could include effects like density and strain-rate. However, those models allow to describe only the monotonic compression behavior: in several situations repeated impacts can happen with unloading followed by further reloading. Unfortunately unloading cannot be described by a linear relation between stress and strain (as is usually considered for metals). Unloading follows a non-linear law with a variable relation between stress and strain in the successive cycles: this requires a particularly complex model. In this work, a new model able to effectively reproduce the compression behavior of some polymeric cellular materials is presented. The model is validated and tuned on the basis of experimental tests with specimen subject to complex cycles of repeated loading and unloading. The model describes both the loading from different levels of residual compression and unloading from any value of compression level. The application to several materials justifies the generality of the method.
Astroparticle, Particle and Space Physics, Detectors and Medical Physics Applications, 2010
Carcinoma of unknown primary (CUP) is occasionally encountered in clinical oncology. Wide variati... more Carcinoma of unknown primary (CUP) is occasionally encountered in clinical oncology. Wide variation exists in CUP. We herein report a rare case of CUP of a mediastinal lymph node. A 61-year-old man with dermatomyositis was referred to our hospital for treatment of mediastinal adenopathy and gastric cancer. Biopsy of both lesions showed that they were histologically different from each other. Mediastinal lymphadenectomy and total gastrectomy were performed for a definitive diagnosis and radical cure. Pathological examination revealed two distinctly different disease processes. The patient underwent postoperative chemotherapy for residual gastric cancer. Twenty months postoperatively, he is alive with cancer. Although CUP usually has a poor prognosis, surgical treatment of metastatic mediastinal lymph node CUP is a feasible therapeutic option.
The Journal of Strain Analysis for Engineering Design, 1997
This paper illustrates experimental results obtained by means of strain gauges applied on circula... more This paper illustrates experimental results obtained by means of strain gauges applied on circular tubes during static lateral crushing. The aim of the work is to obtain an experimental insight regarding the strain field during lateral compression and to verify the known theoretical models. The experimental activity involved aluminium tubes of 80 and 100 mm diameter and 2 mm wall thickness. Up to thirty strain gauges were applied on the internal and external surfaces of each tube. Additional theoretical results were obtained by means of numerical simulation performed using a non-linear finite element code. The measurements are well fitted, both qualitatively and quantitatively, by the Reid-Reddy theoretical model.
Advanced Engineering Materials, 2012
Using hollow particles as reinforcement, syntactic foams are a unique class of materials with fea... more Using hollow particles as reinforcement, syntactic foams are a unique class of materials with features of conventional foams as well as composites. Usually, the main role of the filler is to introduce porosity, and thus also change specifically the compressive response to that of a typical foam or cellular material. However, depending on which of the many variants of such syntactic foams is considered, hollow particles can also have a strengthening effect. In the way this is achieved, however, they are distinguished from the many kinds of metal foams that use ceramic particles first for stabilization during processing and secondly for some strengthening effect: [1-3] In syntactic foams, the reinforcement provides a stable inner lining of each pore, while in conventional particle-reinforced metal foams, the distribution of ceramic particles in the matrix effectively allows them to be understood as cellular MMCs in which matrix ductility is adversely affected by the otherwise strengthening addition. In syntactic foams of the type discussed here, the matrix is unaltered and can thus maintain considerable levels of ductility. So far, numerous materials differing in the size of structural elements, nature of filler, etc. have been realized, featuring both polymer [4,5] and metal [6] matrices. In the case of metals, reinforcing particles can be millimeter sized steel hollow spheres, [7] or, on another, micrometer length scale, cenospheres [8] as well as glass microspheres. [9] The present study concentrates on the latter variant. Main production methods for such materials are melt stirring, melt infiltration [9-12] or powder metallurgy processes. [13,14] When contrasted to metal foams based on the powder compact melting or the APM process [15-17] iron matrix syntactic foams combine lower maximum porosity and thus higher density with greatly improved performance under both quasi-static compressive and tensile load while showing the typical deformation characteristics of foams. [14] In comparison to other types of iron-based foams, such as the so-called lotus-type porous metals recently discussed in detail by Song et al. and Tane et al., [18-20] the present materials combine still higher strength with isotropic behavior and greater ease in manufacture of the
An important topic related to the use of advanced engineering ceramics is joining. Limited availa... more An important topic related to the use of advanced engineering ceramics is joining. Limited availability and knowledge of joining techniques, not yet available or at the preliminary research stage, often limit the utilization of these ceramics, especially when dealing with complex structures. Moreover, there is a lack of one widely accepted experimental method to evaluate the mechanical properties of the joints. In the present work, the methods to characterize the shear strength of joined ceramics are discussed and compared. The results of a large experimental campaign are shown in this work: a critical analysis of the main problems is presented, in order to suggest acceptable testing methods. Parole chiave: materiali ceramici, prove di resistenza a taglio, metodi di giunzione
In the design of vehicle structures for crashworthiness, there is a need for rigid subsystems tha... more In the design of vehicle structures for crashworthiness, there is a need for rigid subsystems that guarantee an undeformable survival cell for the passengers and deformable subsystems able to efficiently dissipate the kinetic energy. The front rail is the main deformable component dissipating energy in a frontal crash, which is the most dangerous crash situation, and for which the structural behaviour is mostly affecting. The design of the front rail, usually consisting of a thin walled prismatic column, requires definition of the geometry, that is, of the shape and dimension of the cross section, of the thickness of the material, and of the material itself. In this work the analysis of the effect of different cross sections of the front rail, and of the joining system is carried out. Furthermore, the collapse during crash is influenced by the loading rate since the loading speed has substantial influence on the mode of collapse and on the material behaviour. In fact, the structural...
Traffic Injury Prevention
Objective: The work aims at investigating the influence of some front-end design parameters of a ... more Objective: The work aims at investigating the influence of some front-end design parameters of a passenger vehicle on the behavior and damage occurring in the human lower limbs while impacted in an accident. Methods: The analysis is carried out by means of finite element analysis using a generic car model for the vehicle and the Lower Limbs Model for Safety (LLMS) for the purpose of pedestrian safety. Considering the pedestrian standardized impact procedure (as in the 2003/12/EC Directive) a parametric analysis, through a DOE plan, was done. Various material properties, bumper thickness, position of the higher and lower bumper beams and the position of pedestrian, were made variable in order to identify how they influence the injury occurrence. The injury prediction was evaluated from the knee lateral flexion, the ligaments elongation, and the state of stress in the bone structure. Results: The results highlighted that the offset between the higher and lower bumper beams is the most influencing parameter affecting the knee ligament response. The influence is smaller or absent considering the other responses and the other considered parameters. The stiffness characteristics of the bumper are, instead, more notable on the tibia. Even if an optimal value of the variables could not be identified trends were detected, with the potential of indicating strategies for improvement. Conclusions: The behavior of a vehicle front-end in the impact against a pedestrian can be improved optimizing its design. The work indicates potential strategies for improvement. In this work, each parameter was changed independently one at a time: in future works the interaction between the design parameters could be also investigated. Moreover, a similar parametric analysis can be carried out using a standard mechanical legform model in order to understand potential diversities or correlations between standard tools and human models.
Le saldature a punti sono il principale metodo di giunzione delle lamiere nelle scocche dei veico... more Le saldature a punti sono il principale metodo di giunzione delle lamiere nelle scocche dei veicoli terrestri. Esiste un'ampia letteratura sulla resistenza statica ed a fatica dei punti e sulla loro modellazione statica. Per simulare fedelmente le strutture puntate occorre conoscere le proprieta dei punti in condizioni di sollecitazione dinamica. Su questo problema non esistono molti risultati per cui in questo lavoro si propone un metodo di prova che permette di studiare la resistenza a differenti velocita di impatto ed in diverse condizioni di sollecitazione. I risultati permettono di definire un criterio di rottura del punto in funzione del tipo di carico
International Journal of Crashworthiness, 2015
The microstructural analysis of many cellular materials may be performed by means of X-ray tomogr... more The microstructural analysis of many cellular materials may be performed by means of X-ray tomography (CT). This technique allows a 3-dimensional non-destructive visualization of the cellular microstructure of the examined materials. Starting from specimen images obtained from this technique it is possible to obtain detailed numerical FE model of it. Some techniques have been used in the past to perform this type of analysis on closed cell foams: the Groupe d’ Etudes de Metallurgie Physique et de Physique des Materiaux in France recently conducted some works [1], in the modeling of the actual structure of a cellular material. The group examined the microstructure of foams (polymeric and metallic) in a compression test. They discussed three different technique: the first one is based on a tetrahedrical mesh of the structure obtained by a triangularization of the CT volume (by using medical software like Amira); the second one is based on a direct transformation of CT voxel in cubic e...
This paper summarises the results of a CRAFT project investigating the influence of casting defec... more This paper summarises the results of a CRAFT project investigating the influence of casting defects on material properties for a high pressure die cast aluminium alloy. Defects consist in gas and shrinkage pores as well as cold fills, dross and alumina skins. Static and fatigue tests are run on standard specimens and production components. For the specimens, the influence is straightforward, while for components no significant difference was found between batches of components, judged as "acceptable" and "non acceptable" by the quality inspection within the foundry. Fatigue testing showed four different fracture regions; two corresponding to a region of high stress as indicated by a FEM simulation. For the other two regions of failure, voids or oxide layers of significant dimensions were observed on the fracture regions. These regions corresponded to regions of last solidification; moreover, for these regions, simulation of the casting process pointed out the pre...
The present work illustrates a procedure for the design and optimization of an elastic component ... more The present work illustrates a procedure for the design and optimization of an elastic component used in vibration welding machines for plastic materials. Vibration welding is a very effective technology, both technically and economically, to join plastic parts: welding is obtained by locally heating the material by means of the friction obtained by relative transverse vibration between the two parts. Since the vibration is obtained by resonance of one of the machine heads, there is an elastic element stressed in fatigue loading condition at high number of cycles. To increase the fatigue life of the component and minimize the mass and costs of it, one of the action that can be taken is to optimize the shape of the component to decrease stress concentrations. To design this spring element with the optimized shape a technique based on selection charts is proposed. Parole chiave: saldatura a vibrazioni, saldatura plastiche, ottimizzazione strutturale
Procedia Structural Integrity, 2018
Cellular materials, often referred as foams or structural foams when used for energy absorption, ... more Cellular materials, often referred as foams or structural foams when used for energy absorption, are largely used to protect people and goods in the case of shocks and impacts. The detailed knowledge of their behavior is fundamental to design components for this aim. Peroni et al. (2008)-(2009) proposed a model able to describe the mechanical compression behavior of some polymeric material. Such model, based on the work by Rusch (1970), described the stress-strain curve as a sum of two contributions, the first for the elastic part and the second for the densification. More recently Avalle and Belingardi (2018) presented a more general model where the stress is calculated as a sum of three terms, one for the elasto-plastic phase, the second for the plateau, and a third for the densification. The model could include effects like density and strain-rate. However, those models allow to describe only the monotonic compression behavior: in several situations repeated impacts can happen with unloading followed by further reloading. Unfortunately unloading cannot be described by a linear relation between stress and strain (as is usually considered for metals). Unloading follows a non-linear law with a variable relation between stress and strain in the successive cycles: this requires a particularly complex model. In this work, a new model able to effectively reproduce the compression behavior of some polymeric cellular materials is presented. The model is validated and tuned on the basis of experimental tests with specimen subject to complex cycles of repeated loading and unloading. The model describes both the loading from different levels of residual compression and unloading from any value of compression level. The application to several materials justifies the generality of the method.
Astroparticle, Particle and Space Physics, Detectors and Medical Physics Applications, 2010
Carcinoma of unknown primary (CUP) is occasionally encountered in clinical oncology. Wide variati... more Carcinoma of unknown primary (CUP) is occasionally encountered in clinical oncology. Wide variation exists in CUP. We herein report a rare case of CUP of a mediastinal lymph node. A 61-year-old man with dermatomyositis was referred to our hospital for treatment of mediastinal adenopathy and gastric cancer. Biopsy of both lesions showed that they were histologically different from each other. Mediastinal lymphadenectomy and total gastrectomy were performed for a definitive diagnosis and radical cure. Pathological examination revealed two distinctly different disease processes. The patient underwent postoperative chemotherapy for residual gastric cancer. Twenty months postoperatively, he is alive with cancer. Although CUP usually has a poor prognosis, surgical treatment of metastatic mediastinal lymph node CUP is a feasible therapeutic option.
The Journal of Strain Analysis for Engineering Design, 1997
This paper illustrates experimental results obtained by means of strain gauges applied on circula... more This paper illustrates experimental results obtained by means of strain gauges applied on circular tubes during static lateral crushing. The aim of the work is to obtain an experimental insight regarding the strain field during lateral compression and to verify the known theoretical models. The experimental activity involved aluminium tubes of 80 and 100 mm diameter and 2 mm wall thickness. Up to thirty strain gauges were applied on the internal and external surfaces of each tube. Additional theoretical results were obtained by means of numerical simulation performed using a non-linear finite element code. The measurements are well fitted, both qualitatively and quantitatively, by the Reid-Reddy theoretical model.
Advanced Engineering Materials, 2012
Using hollow particles as reinforcement, syntactic foams are a unique class of materials with fea... more Using hollow particles as reinforcement, syntactic foams are a unique class of materials with features of conventional foams as well as composites. Usually, the main role of the filler is to introduce porosity, and thus also change specifically the compressive response to that of a typical foam or cellular material. However, depending on which of the many variants of such syntactic foams is considered, hollow particles can also have a strengthening effect. In the way this is achieved, however, they are distinguished from the many kinds of metal foams that use ceramic particles first for stabilization during processing and secondly for some strengthening effect: [1-3] In syntactic foams, the reinforcement provides a stable inner lining of each pore, while in conventional particle-reinforced metal foams, the distribution of ceramic particles in the matrix effectively allows them to be understood as cellular MMCs in which matrix ductility is adversely affected by the otherwise strengthening addition. In syntactic foams of the type discussed here, the matrix is unaltered and can thus maintain considerable levels of ductility. So far, numerous materials differing in the size of structural elements, nature of filler, etc. have been realized, featuring both polymer [4,5] and metal [6] matrices. In the case of metals, reinforcing particles can be millimeter sized steel hollow spheres, [7] or, on another, micrometer length scale, cenospheres [8] as well as glass microspheres. [9] The present study concentrates on the latter variant. Main production methods for such materials are melt stirring, melt infiltration [9-12] or powder metallurgy processes. [13,14] When contrasted to metal foams based on the powder compact melting or the APM process [15-17] iron matrix syntactic foams combine lower maximum porosity and thus higher density with greatly improved performance under both quasi-static compressive and tensile load while showing the typical deformation characteristics of foams. [14] In comparison to other types of iron-based foams, such as the so-called lotus-type porous metals recently discussed in detail by Song et al. and Tane et al., [18-20] the present materials combine still higher strength with isotropic behavior and greater ease in manufacture of the
An important topic related to the use of advanced engineering ceramics is joining. Limited availa... more An important topic related to the use of advanced engineering ceramics is joining. Limited availability and knowledge of joining techniques, not yet available or at the preliminary research stage, often limit the utilization of these ceramics, especially when dealing with complex structures. Moreover, there is a lack of one widely accepted experimental method to evaluate the mechanical properties of the joints. In the present work, the methods to characterize the shear strength of joined ceramics are discussed and compared. The results of a large experimental campaign are shown in this work: a critical analysis of the main problems is presented, in order to suggest acceptable testing methods. Parole chiave: materiali ceramici, prove di resistenza a taglio, metodi di giunzione
In the design of vehicle structures for crashworthiness, there is a need for rigid subsystems tha... more In the design of vehicle structures for crashworthiness, there is a need for rigid subsystems that guarantee an undeformable survival cell for the passengers and deformable subsystems able to efficiently dissipate the kinetic energy. The front rail is the main deformable component dissipating energy in a frontal crash, which is the most dangerous crash situation, and for which the structural behaviour is mostly affecting. The design of the front rail, usually consisting of a thin walled prismatic column, requires definition of the geometry, that is, of the shape and dimension of the cross section, of the thickness of the material, and of the material itself. In this work the analysis of the effect of different cross sections of the front rail, and of the joining system is carried out. Furthermore, the collapse during crash is influenced by the loading rate since the loading speed has substantial influence on the mode of collapse and on the material behaviour. In fact, the structural...
Traffic Injury Prevention
Objective: The work aims at investigating the influence of some front-end design parameters of a ... more Objective: The work aims at investigating the influence of some front-end design parameters of a passenger vehicle on the behavior and damage occurring in the human lower limbs while impacted in an accident. Methods: The analysis is carried out by means of finite element analysis using a generic car model for the vehicle and the Lower Limbs Model for Safety (LLMS) for the purpose of pedestrian safety. Considering the pedestrian standardized impact procedure (as in the 2003/12/EC Directive) a parametric analysis, through a DOE plan, was done. Various material properties, bumper thickness, position of the higher and lower bumper beams and the position of pedestrian, were made variable in order to identify how they influence the injury occurrence. The injury prediction was evaluated from the knee lateral flexion, the ligaments elongation, and the state of stress in the bone structure. Results: The results highlighted that the offset between the higher and lower bumper beams is the most influencing parameter affecting the knee ligament response. The influence is smaller or absent considering the other responses and the other considered parameters. The stiffness characteristics of the bumper are, instead, more notable on the tibia. Even if an optimal value of the variables could not be identified trends were detected, with the potential of indicating strategies for improvement. Conclusions: The behavior of a vehicle front-end in the impact against a pedestrian can be improved optimizing its design. The work indicates potential strategies for improvement. In this work, each parameter was changed independently one at a time: in future works the interaction between the design parameters could be also investigated. Moreover, a similar parametric analysis can be carried out using a standard mechanical legform model in order to understand potential diversities or correlations between standard tools and human models.
Le saldature a punti sono il principale metodo di giunzione delle lamiere nelle scocche dei veico... more Le saldature a punti sono il principale metodo di giunzione delle lamiere nelle scocche dei veicoli terrestri. Esiste un'ampia letteratura sulla resistenza statica ed a fatica dei punti e sulla loro modellazione statica. Per simulare fedelmente le strutture puntate occorre conoscere le proprieta dei punti in condizioni di sollecitazione dinamica. Su questo problema non esistono molti risultati per cui in questo lavoro si propone un metodo di prova che permette di studiare la resistenza a differenti velocita di impatto ed in diverse condizioni di sollecitazione. I risultati permettono di definire un criterio di rottura del punto in funzione del tipo di carico