Material Design & Processing Communications最新文献

Polycarbonate composites are widely spread in many industries, for product manufacturing. Although these materials are being used with high fidelity, their mechanical properties will highly depend on manufacturing processes, fiber orientations with respect to external loads, type of loading, environmental conditions, and so forth. This paper presents the Charpy impact behavior of three polycarbonate grades, in notched and unnotched conditions, as follows: Makrolon 2405—unreinforced polycarbonate, Makrolon 9415—polycarbonate with 10% glass fiber, and Makrolon 8035—polycarbonate with 30% glass fiber. The experimental measurements clearly demonstrated the effect of the fiber content on the impact strength of the material: as the fiber ratio increases, the impact strength decreases, exhibiting brittle behavior. The impact characterization of the notched specimens can facilitate the material selection for applications with higher geometrical complexities, where stress concentrators cannot be eliminated. In addition, the material models obtained through correlations could help increase simulation accuracy and speed up product development cycles.

Despite the great potential of additively manufactured (AM) metallic lattice materials, a comprehensive understanding of their mechanical behavior, particularly fatigue, has yet to be achieved. The role of the sub-unital lattice elements, that is, the struts and the nodes (or strut junctions), is rarely explored, even though it is well known that fatigue is a local phenomenon, determined by the small features of a structure (defects and local geometrical discontinuities).

In this work, the mechanical behavior of nodes and struts has been investigated by designing laser powder bed fusion (L-PBF) Ti6Al4V single strut specimens, with a node placed in the central part of the gauge length. The specimens were manufactured according to four different building orientations, namely, 90°, 45°, 15°, and 0° to the build plane. The influence of the fillet radius at the node and of the printing direction on the fatigue strength has been examined.

Laser powder bed fusion process is widely used in producing cellular materials for various applications. However, there are limitations in the process to produce high-porosity cellular materials with accuracy. A deviation is observed between the as-built and the as-designed geometrical parameters that lead to variation in the obtained stiffness of the cellular material. This study investigates the behavior of three cell topologies, cubic regular, cubic irregular, and trabecular under as-designed and as-built configurations to study their Young's modulus variation. The obtained results are compared with the ideal predictions of the Gibson–Ashby law to evaluate the deviation. Eventually, a linear correlation was developed between the as-designed and as-built Young's modulus to generate a database to select the as-designed geometry/properties to obtain the required as-built geometry/properties.

This study demonstrates the feasibility of fabricating by additive manufacturing composite objects based on acrylic hybrid photocurable formulations, containing 45% by weight of silica nanoparticles, with an average size of about 30 nm. A commercial stereolithography apparatus was used to selectively cure, layer by layer, the high-loaded acrylic resin. The presence of the filler determines an increase in the physical and mechanical properties of the samples that become significantly stiffer and stronger than the pristine matrix. Dynamic mechanical analysis performed on the printed samples gave promising results for the use of developed formulation in the realization of three-dimensional (3D) polymeric structures with improved mechanical properties.

Additive manufacturing (AM) is spreading in a wide range of industrial fields. The influence of the printing parameters on the mechanical performance is still an open issue among researchers, particularly when dealing with fatigue loads, which can lead to an unexpected failure. Classical fatigue tests require a large amount of time and materials to be consumed. Compared to the traditional fatigue assessment, the thermographic method (TM) is able to derive in a very rapid way the SN curve and fatigue limit of the material monitoring its energetic release during fatigue tests.

In this work, for the first time, the energetic release during fatigue test has been evaluated in specimens made of AISI 316L, obtained by SLM technique. Compared to literature data, the specimens show premature failure, even at low stress levels, with brittle fracture surfaces. The internal microstructure seems to be strictly related to the energetic release of the material.

Lightweight core topologies have been considered as an advanced alternative to improve the overall performance of sandwich structures in bending. Designed sandwich beams containing 3D printed cores as conventional honeycomb, re-entrant auxetic honeycomb with two positions of the cells, and chiral topologies were created with CATIA V5. The sandwich beams were manufactured from polylactic acid polymer (PLA) by fused deposition modeling (FDM) using the Ultimaker 3 Extended printer. Three-point bending testing was conducted on sandwich beams using an Instron 8872 testing machine and following ASTM C393-20, as to obtain the strength, bending stiffness, and energy absorption of the sandwich beams for these three designed core topologies. Comments on the cores' performance and sandwich beams response are done together with observations concerning their failure.

This paper presents manufacturing, testing, and computing steps for determining the fracture toughness property of polyamide PA 2200 processed by laser sintering using different process parameters. The design of the samples was conducted according to ASTM D5045-99 and ASTM D5528-01, and the fracture tests consist of four-point bending in symmetric and asymmetric configuration and double cantilever beam test. The process parameters selected as variables were in-plane orientation, spatial orientation, energy density of the process, and induced structural defects. The results provide an extended view regarding the variation of fracture properties when the manufacturing conditions in laser sintering are changed.

In this paper, the current state of the art of additive manufacturing (AM) in the construction industry to manufacture on large scales is reviewed. The central concept of AM was defined, and it has been highlighted in the large use in several sectors. The main advantages that AM offers in the construction industry were described with at the same time the most important challenges that need to be addressed for real use. The main AM technologies solutions on large scales were described from more compact solutions like gantry technology to more flexible and free technology solutions. The choice of an AM solution rather than another is closely linked to the materials to be used and the building component to be built. Regarding materials, the research focused on materials based on aggregates, metals, and polymers. The application of AM in the construction field requires more studies and further research.

The goal of the present study is to obtain a new structured material starting from a copper–polylactic acid (PLA) composite filament 3D printed using fused deposition modeling method, followed by a sintering process in vacuum atmosphere. Metal-reinforced filaments made of 80 wt.% copper encased in an environmentally friendly, biodegradable and carbon neutral PLA binder were used as feedstock materials. The thermal stability and the melting temperature of the filaments were evaluated through thermogravimetric analysis. The printing parameters were chosen according to the producer's specifications. Furthermore, the printed samples were submitted to a two-step sintering process in a vacuum furnace, assuring a complete removal of the polymeric material and the diffusion of the copper particles. The post-treatment revealed a porous structured material, similar to a cellular solid. Microstructural analysis and preliminary mechanical testing show that the porosity and hardness of the end product are heavily influenced by the initial polymer content.

The recycling of materials and the efficient use of resources are nowadays fundamental in a circular economy perspective. This concept also applies to additive manufacturing (AM) where waste can be reused to produce new material. Using mostly thermoplastic polymers, fused deposition modeling (FDM) is an AM technique that allows to melt waste materials and, successively, using a suitable extruder, obtain new filament. In the process, polymers are subject to multiple re-melting and polymer orientations by extrusion operations. The aim of this work is to evaluate the influence of the recycling process over polyethylene terephthalate glycol-modified (PETG) mechanical properties by tensile testing of samples produced using pure and recycled material. Furthermore, filament itself has been tested to evaluate recycle process influence before FDM printing.