Influenza del processo produttivo sulla difettologia e sul danneggiamento a fatica di laminati compositi

in questo lavoro si è indagata l'influenza dei difetti indotti dal processo produttivo nei materiali compositi sulle loro proprietà meccaniche in presenza di carico mono e multi-assiale. Si è cercata inoltre una correlazione tra i parametri di processo dell'infusione con la morfologia e con il contenuto di vuotiope

Conventional or additive manufacturing for spare parts management: An extensive comparison for Poisson demand

Due to the main peculiarities of spare parts, i.e. intermittent demands, long procurement lead times and high downtime costs when the parts are not available on time, it is often difficult to find the optimal inventory level. Recently, Additive Manufacturing (AM) has emerged as a promising technique to improve spare parts inventory management thanks to a ‘print on demand’ approach. So far, however, the impact of AM on spare parts inventory management has been little considered, and it is not yet clear when the use of AM for spare parts inventory management would provide benefits over Conventional Manufacturing (CM) techniques. With this paper we thus aim to contribute to the field of AM spare parts inventory management by developing decision trees that can be of support to managers and practitioners. To this aim, we considered a Poisson-based inventory management system and we carried out a parametrical analysis considering different part sizes and complexity, backorder costs and part consumption. Moreover, we evaluated scenarios where the order-up-to level is limited to resemble applications with a limited storage capacity. For the first time, the analysis was not limited to just one AM and one CM technique, but several AM and CM techniques were considered, also combined with different post-process treatments, for a total of nine different sourcing alternatives. In addition, the economic and technical performance of the different sourcing options were obtained thanks to an interdisciplinary approach, where experts from production economics and material science were brought together

Assessment of tensile and fatigue behavior of PEEK specimens in a physiologically relevant environment

In the last decades the necessity of implant devices is continuously increasing. The researchers have thus focused their attentions on the development of new biocompatible materials, in particular polymers. Among them, polyetheretherketone (PEEK) has gained wide interest in loadbearing applications such as spinal cages due to its yielding behavior and its superior corrosion resistance. Since such applications are characterized by notches and other stress concentrators weakening the implant resistance, a design tool for assessing their tensile and fatigue behavior, in the presence of such discontinuities, is highly claimed. To this aim, tensile and fatigue data available in literature related to neat and differently notched PEEK samples, experimentally tested in a phosphate-buffered saline (PBS) at 37 �C have been analyzed using the strain energy density (SED) approach. The method is shown to provide accurate results regardless of the different notch geometries, both in terms of tensile and fatigue behavior. Concerning the former, the tensile strength was in fact estimated with an error lower than �10%, whereas for the latter the SED approach was able to summarize the experimental fatigue data in a single narrow scatter band, independently from the notch geometr

Decision Considerations for Securing and Managing Intellectual Property within Additive Manufacturing Supply Chains

Intellectual property is a crucial asset that generates debates about its effects on additive manufacturing supply chains. Actors within these supply chains must adapt to navigate intellectual property issues and decisions to sustain growth. However, no consensus exists among scholars and practitioners on “whether, why, or how” to secure and manage intellectual property, which complicates decision-making. This paper presents a quantitative survey of expert opinions from management, engineering, academia, and consultancy sectors on various decision considerations for securing and managing intellectual property in additive manufacturing supply chains. The findings indicate that decision-making remains significantly complex and non-uniform; this offers insights into crucial considerations when aiming to secure or manage intellectual property as a valued and balanced asset in additive manufacturing supply chains.</p

Decision considerations for securing and managing intellectual property within additive manufacturing supply chains

Intellectual property is a crucial asset that generates debates about its effects on additive manufacturing supply chains. Actors within these supply chains must adapt to navigate intellectual property issues and decisions to sustain growth. However, no consensus exists among scholars and practitioners on “whether, why, or how” to secure and manage intellectual property, which complicates decision-making. This paper presents a quantitative survey of expert opinions from management, engineering, academia, and consultancy sectors on various decision considerations for securing and managing intellectual property in additive manufacturing supply chains. The findings indicate that decision-making remains significantly complex and non-uniform; this offers insights into crucial considerations when aiming to secure or manage intellectual property as a valued and balanced asset in additive manufacturing supply chains

Relating stress corrosion cracking behavior to microstructural and surface properties of biocompatible AZ31 alloy

Magnesium (Mg) and its alloys have attracted significant attention as temporary implant materials due to their excellent biocompatibility with human physiology. In fact, Mg is essential to the human metabolism as a cofactor for many enzymes and Mg ions are well-known to facilitate tissue-healing. In addition, the mechanical properties (density, elastic modulus, yield strength and ultimate tensile strength) of Mg and its alloys resemble those of natural bone reducing the risk of the stress-shielding-related problems observed with other metallic implant materials such as stainless steel, titanium and Co-Cr alloys. However, despite their high potential, Mg and its alloys are not yet utilized in biomedical applications. This is due to the (1) rapid corrosion and degradation in the human body that leads to a loss of mechanical integrity before tissues have sufficient time to heal, (2) the evolution of hydrogen as corrosion product accompanied by hydrogen pocket formation that hampers healing or even cause the death of patients through the blockage of the blood stream and (3) the sudden fracture of implants due to the simultaneous action of the corrosive human-body-fluid and mechanical loads through corrosion-assisted cracking phenomena (stress corrosion cracking (SCC) and corrosion fatigue (CF)). In the past years, several approaches have been developed to improve the corrosion resistance of Mg and its alloys. These approaches can be divided into two main groups, one characterized by the modification of the bulk and the other by the modification of the surface. Among the former, Severe Plastic Deformation (SPD) techniques, such as Equal Channel Angular Pressing (ECAP), have attracted attention as possibility for inducing a very fine and homogeneous microstructure throughout all the samples. The latter group relies on surface modifications obtained by mechanical processing (e.g. cryogenic machining) or by the protection through coatings deposited by various techniques (e.g. sputter and Atomic Layer Deposition (ALD)). However, the assessment of the effectiveness of the different approaches in improving the resistance of Mg and its alloys to corrosion-assisted cracking phenomena is still underexplored. In an attempt to understand the fundamental mechanisms linking the microstructural and surface properties to the SCC susceptibility, this thesis investigates how selected procedures initially intended for improving the corrosion resistance of Mg and its alloys impact the SCC susceptibility of AZ31 alloys in Simulated Body Fluid (SBF) at 37 °C. The procedures selected from an extensive literature review investigating the different procedures used to improve the corrosion behavior and the mechanisms regulating the SCC phenomenon were ECAP, cryogenic machining and coatings obtained by means of ALD. 1, 2 and 4 passes of ECAP were carried out on an AZ31 alloy and samples subjected to one pass of ECAP have been shown to be less susceptible to SCC compared to the material in the as-received condition (the elongation to failure was increased by 150%) due to the improved corrosion resistance as a consequence of a reduced grain size. The reduced SCC susceptibility after one pass of ECAP was also confirmed by the morphology of the fracture surfaces that reveals an increased ductility compared to the as-received material. However further ECAP processing (2 and 4 passes) are reported to worsen the SCC susceptibility due to an increased brittleness of the material as a consequence of an increased amount of hydrogen evolved. This is due to the unfavorable texture evolution, as confirmed by the mechanical characterization (tensile tests and hardness measurements). AZ31 samples were machined under cryogenic cooling and afterwards subjected to Slow Strain Rate Tests (SSRTs) at a strain rate of 3.5·10-6 s-1 to evaluate the SCC susceptibility. Cryogenic machined samples were characterized by lower SCC susceptibility than dry cut samples (the elongation to failure was increased by 28%) as a consequence of their improved corrosion performances due to the presence of a wider nanocrystalline layer, resulting in a faster formation of passivating surface oxides, and to the presence of compressive residual stresses instead of tensile. Being ALD a recently developed technique still underexplored in terms of corrosion and biological properties, it was compared to sputter technique in terms of corrosion protectiveness and the induced biocompatibility of three different coatings were evaluated. The ALD technique has been shown to provide the better corrosion protection (assessed by means of potentiodynamic polarization curves and hydrogen evolution experiments) both in case of smooth and rough surfaces due to an increased surface integrity (observed by SEM and XPS analyses). In addition, in the case of 3D porous structures, the improvements provided by the ALD technique were even higher as a consequence of the line-of-sight limitation of sputtering (confirmed by means of SEM analyses). In addition, the biocompatibility of TiO2, ZrO2 and HfO2 coatings obtained by means of ALD have been investigated by means of MTS assay on L929 cells and the HfO2 coatings were shown to provide the best biocompatibility due to the highest corrosion resistance. This can be reasoned by their lower wettability and their higher electrochemical stability and surface integrity (in terms of cracks and pores). TiO2, though generally considered a biocompatible coating, was found to provide the lowest improvements in terms of corrosion resistance and cell viability. Interestingly, TiO2 coatings are characterized by grade 3 cytotoxicity after 5 days of culture due to their high corrosion rate, which does not meet the demands for cellular applications. These results indicate the strong link between biocompatibility and corrosion protection and signify the need of considering the latter when choosing a biocompatible coating to protect temporary Mg based alloys before implantation. Finally, the SCC susceptibility of TiO2 and ZrO2 ALDed coated AZ31 alloys have been evaluated and the ZrO2 coated samples were reported to have the lowest SCC susceptibility. In fact, the elongation to failure of the TiO2 coated samples were increased by 125% and that of ZrO2 coated samples by 220%. The different SCC susceptibility was attributed to the improved corrosion of the ZrO2 coated samples compared to the TiO2 coated samples as a consequence of four main aspects, i.e. different cohesive energies, different wettability, different defect densities and sizes and different mechanical properties

A Novel Approach for Assessing the Fatigue Behavior of PEEK in a Physiologically Relevant Environment

In recent years, the need of surgical procedures has continuously increased and, therefore, researchers and clinicians are broadly focusing on the development of new biocompatible materials. Among them, polyetheretherketone (PEEK) has gained wide interest in load-bearing applications due to its yielding behaviour and its superior corrosion resistance. To assure its reliability in these applications where notches and other stress concentrators weaken implants resistance, a design tool for assessing its tensile and fatigue behaviour in the presence of geometrical discontinuities is highly claimed. Herein, a new fatigue design method based on a local approach is proposed for PEEK implant, and the results are compared with those obtained using the two main biomaterial design approaches available in literature, i.e., the theory of critical distances (TCD) and the notch stress intensity factor (NSIF) approach. To this aim, previously published datasets of PEEK-notched specimens are used, and the proposed method is reported to provide more accurate results and to be robust for different notch geometries

Influenza del processo produttivo sulla difettologia e sul danneggiamento a fatica di laminati compositi

in questo lavoro si è indagata l'influenza dei difetti indotti dal processo produttivo nei materiali compositi sulle loro proprietà meccaniche in presenza di carico mono e multi-assiale. Si è cercata inoltre una correlazione tra i parametri di processo dell'infusione con la morfologia e con il contenuto di vuot

Additive Manufacturing and Spare Parts: Literature Review and Future Perspectives

The use of Additive Manufacturing (AM) for spare parts management has increasingly gained interest in the last years, thanks to the possibility provided by AM technologies to print-on-demand. In such a way, the high spare parts inventory level necessary with Conventional Manufacturing (CM) techniques could be reduced due to a faster responsiveness of AM. Recently, some researchers have investigated the profitability of the transition from CM to AM for the spare parts management, and these contributions are herein reviewed, highlighting the main novelties and limitations of these studies. Based on the output of the literature review and on interviews with experts and industrial partners, future research perspectives have been reported. Four main research areas have been identified, and a multidisciplinary approach is suggested to accomplish them all

Assessment of tensile and fatigue behavior of PEEK specimens in a physiologically relevant environment

In the last decades the necessity of implant devices is continuously increasing. The researchers have thus focused their attentions on the development of new biocompatible materials, in particular polymers. Among them, polyetheretherketone (PEEK) has gained wide interest in load-bearing applications such as spinal cages due to its yielding behavior and its superior corrosion resistance. Since such applications are characterized by notches and other stress concentrators weakening the implant resistance, a design tool for assessing their tensile and fatigue behavior in the presence of such discontinuities is highly claimed. To this aim, tensile and fatigue data available in literature of neat and differently notched PEEK samples (circumferentially cracked and U-notched specimens with different notch radii) experimentally tested in a phosphate-buffered saline (PBS) at 37 °C have been analyzed using the strain energy density (SED) approach. The method is shown to provide accurate results regardless of the different notch geometries, both for tensile and fatigue data. Concerning the former, the tensile strength was in fact estimated with an error lower than ±10%, regardless of the strain rate, while for the latter the SED approach was able to summarize the fatigue data with a single narrow scatter band independently from the notch geometr