Repercussions of powder contamination on the fatigue life of additive manufactured maraging steel

A wide range of materials is suitable for processing by powder bed fusion (PBF) techniques. Among the latest formulations, maraging steel 18Ni-300, which is a martensite-hardenable alloy, is often used when both high fracture toughness and high strength are required, or if dimensional changes need to be minimised. In direct tooling, 18Ni-300 can be successfully employed in numerous applications, for example in the production of dies for injection moulding and for casting of aluminium alloys; moreover, it is particularly valuable for high-performance engineering parts. Even though bibliographic data are available on the effects that parameters, employed in PBF processes, have on the obtained density, roughness, hardness and microstructure of 18Ni-300, there is still a lack of knowledge on the fatigue life of PBF manufactured parts. This paper describes the fatigue behaviour of 18Ni-300 steel manufactured by PBF, as compared by forging. Relevant negative effects of the cross-contamination of the raw material are originally identified in this paper, which emphasizes the inadequacy of current acceptability protocols for PBF powders. In the absence of contamination, endurance achieved by PBF is found equal to that by forging and consistent with tooling requirements as set out by industrial partners, based on injection moulding process modelling

Reinforcement effectiveness on mechanical performances of composites obtained by powder bed fusion

New material formulations to be used in Additive Manufacturing machines are one of the major interests in this fast growing field. The possibility to tune functional and mechanical properties, by the addition of reinforcements to a polymeric matrix, is hindered by the low provisional capability of the additive manufactured composite. The inherent anisotropy of layer manufacturing combines with mechanisms of filler dispersion and of filler/matrix adhesion in a complex scenario. The paper entails a critical evaluation of mechanical properties measured for several polymeric composites produced by Powder Bed Fusion, in the perspective of provisional models commonly accepted for composite materials. The models are reviewed versus experimental and literature data. The provisional effectiveness is generally good, except for the case of nanometric or surface treated fillers, or of specific anisotropic microstructures obtained by layer manufacturing

A statistical approach for modeling individual vertical walking forces

This paper proposes a statistical approach for modeling vertical walking forces induced by single pedestrians. To account for the random nature of human walking, the individual vertical walking force is modeled as a series of steps and the gait parameters are assumed to vary at each step. Walking parameters are statistically calibrated with respect to the results of experimental tests performed with a force plate system. Results showed that the walking parameters change during walking and are correlated with each other. The force model proposed in this paper is a step-by-step model based on the description of the multivariate distribution of the walking features through a Gaussian Mixture model. The performance of the proposed model is compared to that of a simplified load model and of two force models proposed in the literature in a numerical case study. Results demonstrate the importance of an accurate modeling of both the single step force and the variability of the individual walking force

Design for additive manufacturing and for machining in the automotive field

High cost, unpredictable defects and out-of-tolerance rejections in final parts are preventing the complete deployment of Laser-based Powder Bed Fusion (LPBF) on an industrial scale. Repeatability, speed and right-first-time manufacturing require synergistic design approaches. In addition, post-build finishing operations of LPBF parts are the object of increasing attention to avoid the risk of bottlenecks in the machining step. An aluminum component for automotive application was redesigned through topology optimization and Design for Additive Manufacturing. Simulation of the build process allowed to choose the orientation and the support location for potential lowest deformation and residual stresses. Design for Finishing was adopted in order to facilitate the machining operations after additive construction. The optical dimensional check proved a good correspondence with the tolerances predicted by process simulation and confirmed part acceptability. A cost and time comparison versus CNC alone attested to the convenience of LPBF unless single parts had to be produced

Herbs for voice database : developing a rational approach to the study of herbal remedies used in voice care

Herbs have been used for voice care since ancient times and many herbal remedies are still in use in every geographical areas and cultures, both as traditional medicine and as sources of botanicals used in commercial products. Many of these plants are used as extracts and other phytopreparates, and a full phytochemical analysis is sometimes incomplete or lacking. The mechanisms of action of these botanicals include antibacterial, antiinflammatory, mucolytic, and other general activities; nevertheless, mechanisms that could be specifically referred to voice are often unknown, as well as the corresponding molecular targets and therefore a rational approach in the use of these remedies is hard to be applied by phoniatricians. To address this problem, we collected information on plants used for voice care from several different geographical areas, using both literature data and a pool of contributors from an international network of artistic phoniatrics and vocologists. The plants have been organized in a database (Herbs for Voice Database) and classified according to the natural compounds contained in them, their molecular targets and the pathologies they are recommended for. This first database contains 44 plants, 101 phytocompounds, and 32 recognized molecular targets. The distribution of herbs and phytocompounds according to the botanical families, their known biological activity, traditional uses, and molecular targets were analyzed. In particular, data analysis shows that the somatosensory and pain receptor Transient Receptor Potential Ankyrin 1 ion channel is targeted by a large number of different phytochemicals contained in the herbs for voice, and could therefore be involved in a mechanism of action common to many plants

A trip in voice phytotheraphy: TRPA1 ion channel as a target for bioactive compounds in herbal remedies for voice care

Voice is the sound we produce to communicate meanings and ideas and has a capital importance in human social development. Herbs have been used for voice care since ancient times and many herbal remedies are still in use, both as folk medicine and as sources of botanicals used in commercial products. In Europe Sisymbrium officinale (L.) Scop (the "singers'plant\u201d) is the most popular herbal remedy for voice care, but many other plants are employed in phytopreparations. The mechanisms of action of these botanicals include anti-bacterial, anti-inflammatory, mucolytic, antinociceptive and other general activities; nevertheless, mechanisms that could be specifically referred to voice are often unknown. We collected information on plants used worldwide for voice care; the plants have been organized in a database (Herbs for Voice Database) and classified according to the bioactive compounds, their molecular targets and the pathologies they are recommended for. The data were analyzed with the aim to identify some possible common mechanism of action and the molecular targets involved. The analysis of data shows that an important pathway involves the somatosensory TRPA1 (Transient Receptor Potential Ankyrin type 1) ion channel, a well-known mediator of irritation, inflammatory and neurogenic pain. Agonists of this ion channel have been identified in 27 over 44 plants, corresponding to 61,3% of the plants in the database. Also TRPM8 (Transient Receptor Potential Melastatin type 8), involved in the perception of coolness, was identified among the molecular targets. This finding reinforces the hypothesis that these somatosensory ion channels could be involved in relevant mechanisms of action of these traditional remedies and open new perspectives in the rational study of voice phytopharmacology and therapy. This research was funded by FONDAZIONE CARIPLO (Milano, I), University of Milano (I) and Conservatorio di Musica G. Verdi (Milano, I), grant number 2017-1653

Solid-state phase transformations in thermally treated Ti-6Al-4V alloy fabricated via laser powder bed fusion

Laser Powder Bed Fusion (LPBF) technology was used to produce samples based on the Ti-6Al-4V alloy for biomedical applications. Solid-state phase transformations induced by thermal treatments were studied by neutron diffraction (ND), X-ray diffraction (XRD), scanning transmission electron microscopy (STEM) and energy-dispersive spectroscopy (EDS). Although, ND analysis is rather uncommon in such studies, this technique allowed evidencing the presence of retained \u3b2 in \u3b1' martensite of the as-produced (#AP) sample. The retained \u3b2 was not detectable byXRDanalysis, nor by STEM observations. Martensite contains a high number of defects, mainly dislocations, that anneal during the thermal treatment. Element diffusion and partitioning are the main mechanisms in the \u3b1 \u2194 \u3b2 transformation that causes lattice expansion during heating and determines the final shape and size of phases. The retained \u3b2 phase plays a key role in the \u3b1' \u2192 \u3b2 transformation kinetics

Biomedical Co-Cr-Mo Components Produced by Direct Metal Laser Sintering

Direct Metal Laser Sintering (DMLS) is an additive manufacturing technique based on a laser power source that sinters powdered materials using a 3D CAD model. The mechanical components produced by this procedure typically show higher residual porosity and poorer mechanical properties than those obtained by traditional manufacturing techniques. In this study, samples were produced by DMLS starting from a Co-Cr-Mo powder (in the \u3b3 phase) with a composition suitable for biomedical applications. Samples were submitted to hardness measurements and structural characterization. The samples showed a hardness value remarkably higher that those commonly obtained for the same cast or wrought alloys. In fact, the HRC value measured for the samples is 47 HRC, while the usual range for CAST Co-Cr-Mo is from 25 to 35 HRC. The samples microstructure was investigated by X-ray diffraction (XRD), electron microscopy (SEM and TEM) and energy dispersive microanalysis (EDX) in order to clarify the origin of this unexpected result. The laser treatment induced a melting of the metallic Co-Cr-Mo powder, generating a phase transformation from the \u3b3 (fcc) to the e (hcp) phase. The rapid cooling of the melted powder produced the formation of e (hcp) nano-lamellae inside the \u3b3 (fcc) phase. The nano-lamellae formed an intricate network responsible for the measured hardness increase. The results suggest possible innovative applications of the DMLS technique to the production of mechanical parts in the medical and dental fields, where a high degree of personalization is required