1,720,966 research outputs found
Uniaxial static mechanical properties of regular, irregular and random additively manufactured cellular materials: Nominal vs. real geometry
Get PDFThe present work investigates cellular materials that can be potentially used as a replacement of solid implants owing to their mechanical properties and biocompatibility. More specifically, titanium alloy (Ti6Al4V) cellular materials of three different topologies were considered to study the effect of the degree of irregularity. Cubic regular, cubic irregular and trabecular structures were manufactured using Laser based powder bed fusion (LB-PBF) process. The LB-PBF process had an impact on the strut thickness of the samples. Samples were subjected to micro computed tomography to understand the geometrical deviations and to use the actual geometry for finite element analysis. Mechanical properties such as Young's modulus and strength were derived from compression and tensile testing. The results indicate that the Young's modulus was between 6 and 17 GPa, which were closer to the values of human cortical bone. The finite element analysis results showed a good correlation with the tensile test results as well. Furthermore, Gibson–Ashby model is used to study the effect of cell topology on the structural behavior. The model indicated that the misalignment of nodes of cubic regular structures to form irregular structure, transformed the stretching dominated behavior of cubic structures to bending dominated behavior like trabecular structures. Finally, the regular structures appeared to be much more prone to catastrophic failure than irregular and trabecular structures. Both visual observation of experimental testing and FE analysis explained this difference as result of different modes and zones of failures
Evaluating radiographic characteristics of polymeric implant with osseointegrative coatings by a tissue-equivalent phantom
No full textNew prosthetic implants can nowadays be realized with high performance polymers such as polyetheretherketone (PEEK) and its carbon-fiber reinforced composite (CFR-PEEK). These materials can be plasma-spray coated with titanium (Ti) or hydroxyapatite (HA) to improve osseointegration (1). Checking the location of the implanted device intraoperatively and assessing loosening or migration in the early and late postoperative periods are critical issues in orthopaedics and radiology. The most frequently used technique to perform the follow up assessment is plain radiography (2). However, PEEK polymers are radiolucent to X-ray and the addition of a radiopaque osseointegrative coating may enhance the visualization of the implanted device in clinical X-ray imaging. This work aimed at evaluating the radiological characteristics of polymeric samples coated with an osseointegrative layer for application in hip arthroprosthesis
Characterization of compressive fatigue behavior and acoustic emission analysis of Ti6Al4V cellular lattice materials fabricated by laser powder bed fusion
No full textThis study investigates the mechanical properties and fatigue performance of Ti6Al4V cellular lattice materials (CLMs) featuring five distinct unit cell types (BCC-Z, BCC, Octet, Truncated cuboctahedron [TCO], and Trabecular) at a relative density of 25%. Compression tests were conducted to assess static properties, including Young's modulus and yield strength. Subsequently, compression–compression fatigue tests (R = 0.1) were performed to evaluate fatigue behavior. Acoustic emission analysis was employed during static and fatigue tests to explore the potential for failure prediction. Results reveal that BCC-Z and TCO exhibit slightly higher Young's moduli, surpassing 20 GPa, while BCC, Octet, and Trabecular display moduli ranging from 6 to 12 GPa. Regarding normalized fatigue behavior, BCC-Z demonstrates superior fatigue resistance, followed by TCO. Notably, the acoustic emission parameters significantly correlate with the unit cell type. Lastly, a strong relationship between the initiation of failure and changes in acoustic emission parameters is observed, establishing a meaningful link between the static and fatigue curves and acoustic emission results
Additively manufactured Ti–6Al–4V thin struts via laser powder bed fusion: Effect of building orientation on geometrical accuracy and mechanical properties
No full textPorous metal lattice structures have a very high potential in biomedical applications, setting as innovative new generation prosthetic devices. Laser powder bed fusion (L-PBF) is one of the most widely used additive manufacturing (AM) techniques involved in the production of Ti6Al4V lattice structures. The mechanical and failure behavior of lattice structures is strongly affected by geometrical imperfections and defects occurring during L-PBF process. Due to the influence of multiple process parameters and to their combined effect, the mechanical properties of these structures are not yet properly understood. Despite the major commitment to characterize and better comprehend lattice structures, little attention has been paid to the impact that single struts have on the overall lattice properties. In this work, the authors have investigated the tensile strength and fatigue behavior of thin L-PBF Ti6Al4V lattice struts at different building orientations (0°, 15°, 45°, and 90°). This investigation has been focused on the effect that microstructural defects (particularly porosity) and actual surface geometry (including surface texture and geometrical errors such as varying cross-section shape and size) have on the mechanical performances of the struts in relation to their building direction. The results have shown that there is a tendency, particularly for low printing angles, of fatigue life to decrease with decreasing of the building angle. This is mainly due to the surge in surface texture and loss in cross-sectional regularity. On the other hand, the monotonic tensile test results have shown a low sensitivity to these factors. The strut failure behavior has been examined employing dynamic digital image correlation (DIC) of tensile tests and scanning electron imaging (SEM) of the fracture surfaces
Comparative metrological characterization of Ti6Al4V lattice structures produced by laser powder bed fusion
No full textThe advancement of Additive Manufacturing (AM) technologies, such as Laser Powder Bed Fusion (LPBF), enables the fabrication of metallic lattice materials with a wide range of topologies and size scales. The possibility to manufacture these materials into complex shapes with good property-to-weight ratio stimulates a growing interest in several industrial sectors, including biomedical, aerospace, and automotive. Nevertheless, such structural features printed at a small-scale often suffer from a wide range of morphological defects that can lead to a marked deviation from the nominal geometry and consequently impact the mechanical, transport and thermal properties. An accurate metrological characterization of the lattice is thus of paramount importance for a more reliable prediction of the properties of the lattice.
The most common characterization techniques used for as-built lattice materials are scanning electron microscopy (SEM), optical microscopy (OM) and X-ray computed tomography (CT). CT, contrary to the other methods, provides full 3D data including inaccessible geometries and features, in a non-destructive way, but it requires expensive equipment and considerable expertise. SEM and OM can be faster and less expensive, but can be non-destructive only when limited to the outer surface of the lattice. When combined with metallographic analysis, instead, they require destructive, careful and time-consuming specimen preparation, and the analysis is confined to selected sections.
In this work, the three above-mentioned techniques are applied to the metrological characterization of LBPF Ti6Al4V regular cubic lattices of 4 mm unit cell size and struts with circular cross-section of diameter 0.760 mm. The results in terms of strut cross-section parameters and junction fillet radius are compared and the effect of the size of the analysis domain on the accuracy of the results is investigated by comparing lattice sub-volumes of different size. Via a thorough statistical analysis it is shown that CT and metallographic characterization are compatible, while microscope imaging can lead to an overestimation of the strut thickness
Quantifying radiographic contrast of polymeric orthopedic implants with osseointegrative coating by a tissue-equivalent phantom
No full textGoing Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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