Microstructural Evolution Of LPBF AlSiMg – Effect Of Water Quenching Vs Furnace Cooling Vs Direct Aging

The heat treatment response of AlSi10Mg via laser powder bed fusion (LPBF) has been studied via detailed microstructural characterization. The effect of solutioning (S) and water quenching (WQ) vs furnace cooling (FC), and direct aging (DA) vs solutioning and aging (SA), has been analysed, for microstructure and tensile properties. 11 heat treatments were carried out to map the partitioning of Si, starting with stress relieving at 200 °C vs 300 °C, followed by solution heat treatment at 430°C vs 530 °C, water quenching vs furnace cooling, aging at 160 °C vs direct aging at 160 °C, to establish the microstructure of LPBF AlSi10Mg alloys for potential applications. The microstructure at 430 °C and 530 °C shows Si precipitate fractions of 25% and 14%, respectively. Room temperature mechanical properties, revealed the 300 °C, 2 h stress relieved sample with the highest strength and ductility (YS of 230 MPa and 16%). At 430 °C, both water quenching and furnace cooling showed similar strengths and 16% elongation, while at 530 °C, there was a much lower elongation (8–9%) with the T6 (53 °C, WQ, SA) showing higher strength and elongation. This study brings out the importance of being able to choose the heat treatments suitable to AlSiMg part geometry, via LPBF additive manufacturing for various applications.

Lignin reinforced, water resistant, and biodegradable cassava starch/PBAT sandwich composite pieces

Following the stipulation to replace nondegradable plastics with biodegradable materials in China, cost-effective and water-resistant packaging materials have become increasingly necessary. In this work, lignin reinforced thermoplastic cassava starch (TPS) pieces were prepared by filling glycerol and lignin powder into starch via a melt blending process and then being pressed into thin pieces. A mechanical properties test showed that following the addition of 3 wt% lignin, the tensile strength of the TPS piece was improved to 16.15 MPa from 3.71 MPa of the original TPS piece. The porous structures of the lignin powder tie the TPS macromolecular chains, induce higher crystallization, and thus provide higher tensile strength and lower elongation at break. After sandwiching two pieces of poly (butylene adipateco-terephthalate) (PBAT)/peanut shell powder composite thin film to each side of the TPS piece, the PBAT/TPS/PBAT sandwich gains excellent water resistance properties. However, as soon as the sandwich piece is cut into smaller ones, they absorb water quickly, implying such pieces can be biodegraded rapidly. These characteristics make it especially suitable for use in the preparation of cabinet waste bags, which are generally stirred into organic fertilizer with the cabinet waste. Slow degradation may negatively affect soil health and farm production.

Functionalizable coaxial PLLA/PDLA nanofibers with stereocomplexes at the internal interface

Multifunctionality of electrospun polylactic acid (PLA) nonwovens was generated by the morphological design of nanofibers. Coaxial fibers with a lower number average molar mass Mn PLLA core and a higher Mn PDLA shell form PDLA–PLLA stereocrystals at the interface, induced by annealing. In tensile tests under physiological conditions, the core–shell fibers with higher crystallinity (22% compared to 11–14%) had lower Young’s moduli E (9 ± 1 MPa) and lower elongation at break εb (26 ± 3%) than PDLA alone (E = 31 ± 9 MPa, εb = 80 ± 5%), which can be attributed to simultaneous crystallization and relaxation effects. Gelatin incorporated in the PDLA phase was presented on the outer surface providing a biointerface putatively favorable for cell adherence. Gelatin incorporation did not influence the crystallization behavior but slightly lowered Tg (60 → 54 °C). Employing exclusively polymers established in the clinic, multifunctionality was generated by design. Graphic abstract

Post-fire performance of structural steel

Carbon steel is widely used in building industry. The different structural element might be exposed to high temperature during fire. The structural safety of steel buildings must be evaluated after they have suffered a fire. The assessment requires understanding the behaviour of carbon steel after heating. Therefore, this paper is aimed at studying the post-fire behaviour of carbon steel. A total of seventeen coupon specimens were tested by uniaxial tensile test. One of them was tested without heating and considered as a reference. Sixteen specimens were heated at a temperature of either 400°C or 700°C for different durations. Eight specimens were cooled in air and the others cooled in water. Heating durations were 30 min, 60 min, 90 min and 120 min. Results showed that the high-temperature has a great influence on decreasing the ultimate and yield stress and elongation for specimens cooled in the air. For specimens cooled in water, the decreased in yield and ultimate stress was minor comparing to the reference specimen. The ductility of water-cooled specimens showed a noticeable reduction comparing to specimens cooled in air. Increasing the heating time results in higher elongation for specimens heated to 400oC and lower elongation for specimens heated to 700oC, but the specimen loses strength in both cases

Effects of Fabrication Conditions on Structure and Properties of Mechanically Prepared Natural Silk Web and Non-Woven Fabrics

In this study, natural silk web and natural silk non-woven fabric were prepared mechanically using the binding character of the sericin in silk. The effect of process variables on the preparation, structure, and properties of the silk web and the non-woven fabric was examined. The reeling velocity affected the morphology and mechanical properties of the web but had almost no influence on the crystalline structure of the silk. From the viewpoint of reel-ability and the mechanical properties (work of rupture) of silk web, a reeling velocity of 39.2 m/min represented the optimal processing velocity. The porosity and swelling ratio of the silk web decreased slightly with increasing reeling velocity. Furthermore, the reeling bath temperature had a significant effect on the reel-ability of silk filaments from a silkworm cocoon. Bath temperatures ≥50 °C yielded good reel-ability (>900 m reeling length). The porosity, swelling ratio in water, and mechanical properties of the silk web and silk non-woven fabric changed only slightly with the reeling bath temperature but changed significantly with the hot press treatment. The hot-pressed silk web (i.e., silk non-woven fabric) exhibited higher tensile strength as well as lower elongation at break, porosity, and swelling ratio than the silk web.

Microstructure and Mechanical Properties of Laser-Welded DP Steels Used in the Automotive Industry

The aim of this work was to investigate the microstructure and the mechanical properties of laser-welded joints combined of Dual Phase DP800 and DP1000 high strength thin steel sheets. Microstructural and hardness measurements as well as tensile and fatigue tests have been carried out. The welded joints (WJ) comprised of similar/dissimilar steels with similar/dissimilar thickness were consisted of different zones and exhibited similar microstructural characteristics. The trend of microhardness for all WJs was consistent, characterized by the highest value at hardening zone (HZ) and lowest at softening zone (SZ). The degree of softening was 20 and 8% for the DP1000 and DP800 WJ, respectively, and the size of SZ was wider in the WJ combinations of DP1000 than DP800. The tensile test fractures were located at the base material (BM) for all DP800 weldments, while the fractures occurred at the fusion zone (FZ) for the weldments with DP1000 and those with dissimilar sheet thicknesses. The DP800-DP1000 weldment presented similar yield strength (YS, 747 MPa) and ultimate tensile strength (UTS, 858 MPa) values but lower elongation (EI, 5.1%) in comparison with the DP800-DP800 weldment (YS 701 MPa, UTS 868 MPa, EI 7.9%), which showed similar strength properties as the BM of DP800. However, the EI of DP1000-DP1000 weldment was 1.9%, much lower in comparison with the BM of DP1000. The DP800-DP1000 weldment with dissimilar thicknesses showed the highest YS (955 MPa) and UTS (1075 MPa) values compared with the other weldments, but with the lowest EI (1.2%). The fatigue fractures occurred at the WJ for all types of weldments. The DP800-DP800 weldment had the highest fatigue limit (348 MPa) and DP800-DP1000 with dissimilar thicknesses had the lowest fatigue limit (<200 MPa). The fatigue crack initiated from the weld surface.

Characterization and Optimization of Elastomeric Electrodes for Dielectric Elastomer Artificial Muscles

Dielectric elastomer actuators (DEAs) are an emerging type of soft actuation technology. As a fundamental unit of a DEA, the characteristics of compliant electrodes play a crucial role in the actuation performances of DEAs. Generally, the compliant electrodes can be categorized into uncured and cured types, of which the cured one commonly involves mixing conductive particles into an elastomeric matrix before curing, thus demonstrating a better long-term performance. Along with the increasing proportion of conductive particles, the electrical conductivity increases at the cost of a stiffer electrode and lower elongation at break ratio. For different DEA applications, it can be more desirable to minimize the electrode stiffness or to maximize its conductivity. In examination of the papers published in recent years, few works have characterized the effects of elastomeric electrodes on the outputs of DEAs, or of their optimizations under different application scenarios. In this work, we propose an experimental framework to characterize the performances of elastomeric electrodes with different formulas based on the two key parameters of stiffness and conductivity. An optimizing method is developed and verified by two different application cases (e.g., quasi-static and dynamic). The findings and the methods developed in this work can offer potential approaches for developing high-performance DEAs.

Influence of Powder Particle Morphology on the Static and Fatigue Properties of Laser Powder Bed-Fused Ti-6Al-4V Components

In this work, two Ti-6Al-4V powder lots were produced using two different techniques: plasma atomization and gas atomization, with the first producing more spherical particles than the second. Testing specimens were then manufactured with these powder lots using an identical set of printing parameters and the same laser powder bed fusion system. Next, the porosity levels and distributions as well as the static and fatigue properties of the specimens from both powder lots were compared. Regarding the static mechanical properties, a noticeable difference was observed between the plasma-atomized powder specimens and their gas-atomized equivalents (7% greater ultimate and 4% greater yield strengths, but 3% lower elongation to failure, respectively). However, with regard to the fatigue resistance, the advantages of the plasma-atomized powder specimens in terms of their mechanical resistance were somewhat counterbalanced by the presence of pores aligned in the direction perpendicular to that of applied load. Conversely, specimens printed with the gas-atomized powder manifested a similar level of porosity, but a uniform pore distribution, which reduced the impact of the processing-induced porosity on fatigue cracks initiation and propagation.

Functional MgO–Lignin Hybrids and Their Application as Fillers for Polypropylene Composites

Inorganic–organic hybrids are a group of materials that have recently become the subject of intense scientific research. They exhibit some of the specific properties of both highly durable inorganic materials (e.g., titanium dioxide, zinc) and organic products with divergent physicochemical traits (e.g., lignin, chitin). This combination results in improved physicochemical, thermal or mechanical properties. Hybrids with defined characteristics can be used as fillers for polymer composites. In this study, three types of filler with different MgO/lignin ratio were used as fillers for polypropylene (PP). The effectiveness of MgO-lignin binding was confirmed using Fourier transform infrared spectroscopy. The fillers were also tested in terms of thermal stability, dispersive-morphological properties as well as porous structure. Polymer composites containing 3 wt.% of each filler were subjected to wide angle X-ray diffraction tests, differential scanning calorimetry and microscopic studies to define their structure, morphology and thermal properties. Additionally, tensile tests of the composites were performed. It was established that the composition of the filler has a significant influence on the crystallization of polypropylene—either spherulites or transcrystalline layers were formed. The value of Young’s modulus and tensile strength remained unaffected by filler type. However, composites with hybrid fillers exhibited lower elongation at break than unfilled polypropylene.

Development and performance study of a natural silk fiber facial mask paper

Facial masks are beauty products which composed of a facial mask paper and beauty solution. Silk contains the amino acid structure closest to the human skin, and has the skin-friendly, cosmetic and antibacterial functions, but the common method for making nonwoven facial mask paper is not suitable for silk. In this paper, the silkworm’s spinning path is intervened manually to obtain a smart silk facial mask paper (SMC) of controllable thickness, so that the sericin on the silk fiber is well preserved. In the experiment where the SMC is compared with the nonwoven 384-cuprammonium rayon facial mask paper (CRMC) which is the most widely used in the market, it is found that the ways of forming the two facial mask paper are completely different, and therefore the morphologies under SEM are obviously different. The thickness of the SMC is 0.183 mm and the areal weight of it is 38.0 g/m2. It is very close to the CRMC (0.187 mm, 38.4 g/m2). The porosity of the SMC is 84.0%, which is slightly lower than that of the CRMC (86.3%), but its pores are well distributed. Compared with the CRMC, the smart SMC has higher dry and wet strength, lower elongation, slightly lower air permeability and liquid entrainment rate, and better antibacterial performance.