Compressive strength and wear properties of SiC/Al6061 composites reinforced with high contents of SiC fabricated by pressure-assisted infiltration

Pressure-assisted infiltration was used to synthesize SiC/Al 6061 composites containing high weight percentages of SiC. A combination of PEG and glass water was used to fabricate SiC preforms and the effect of the presence of glass water on the microstructure and mechanical properties of the preforms was evaluated by performing compression tests on the preforms. Also, the compressive strength and the hardness of the SiC/Al composites were investigated. The results revealed that the glass water improved the compressive strength of the preforms by about five times. The microstructural characterization of the composites showed that the penetration of the aluminum melt into the preforms was completed and almost no porosity could be seen in the microstructures of the composites. Moreover, the composite containing 75 wt% SiC exhibited the highest compressive strength as well as the maximum hardness. The results of the wear tests showed that increasing the SiC content reduces the wear rate so that the Al-75 wt% SiC composite has a lower wear rate and a lower coefficient of friction than those of Al-67 wt% SiC composite. This indicated higher wear resistance in these composites than the Al alloy due to the formation of a tribological layer on the surface of the composites.     

Exosomes derived from osteoclasts under compression stress inhibit osteoblast differentiation

Orthodontic tooth movement is triggered by orthodontic force loading on the periodontal ligament and is achieved by alveolar bone remodeling, which is regulated by intimate crosstalk between osteoclastogenesis and osteoblast differentiation. Whether the communication between osteoclasts and osteoblasts is influenced by orthodontic compression stress requires further clarification. In this study, osteoclasts were differentiated for 10 days. On day 4 of differentiation, the number of pre-osteoclasts peaked, as determined by the increased expression of RANK and the number of multinucleated cells. After 24 h of compression stress loading, on day 4, the number of osteoclasts increased, and the optimal magnitude of stress to promote osteoclastogenesis was determined as 1 g/cm2. Moreover, the results of RNA-sequencing analysis showed that the miRNA expression profile changed markedly after compression loading and that many of the altered miRNAs were associated with cell communication functions. A series of indirect co-culture experiments showed an inhibitory effect of osteoclasts on osteoblast differentiation, especially after compression. Next, we added osteoclast-derived exosomes to hPDLSCs during osteoblast differentiation. Exosomes derived from osteoclasts under compression (cEXO) showed a greater inhibitory effect on osteoblast differentiation, compared to exosomes from osteoclasts without compression (EXO). Therefore, we analyzed differentially expressed miRNAs associated with bone development functions in exosomes: miR-223-5p and miR-181a-5p were downregulated, whereas miR-133a-3p, miR-203a-3p, miR-106a-5p, and miR-331-3p were upregulated; these altered expressions may explain the enhanced inhibitory effect of compression stress.     

High strain rate compressive response of the Cf/SiC composite

Carbon fiber reinforced ceramic owns the properties of lightweight, high fracture toughness, excellent shock resistance, and thus overcomes ceramic's brittleness. The researches on the advanced structure of astronautics, marine have exclusively evaluated the quasi-static mechanical response of carbon fiber reinforced ceramics, while few investigations are available in the open literature regarding elastodynamics. This paper reports the dynamic compressive responses of a carbon fiber reinforced silicon carbide (C_f/SiC) composite (CFCMC) tested by the material test system 801 machine (MTS) and the split Hopkinson pressure bar (SHPB). These tests were to determine the rate dependent compression response and high strain rate failure mechanism of the C_f/SiC composite in in-plane and out-plane directions. The in-plane compressive strain rates are from 0.001 to 2200?s^?1, and that of the out-plane direction are from 0.001 to 2400?s^?1. The compressive stress-strain curves show the C_f/SiC composite has a property of strain rate sensitivity in both directions while under high strain rate loadings. Its compressive stiffness, compressive stress, and corresponding strain are also strain rate sensitive. The compressive damage morphologies after high strain rate impacting show different failure modes for each loading direction. This study provides knowledge about elastodynamics of fiber-reinforced ceramics and extends their design criterion with a reliable evaluation while applying in the scenario of loading high strain rate.     

高性能纤维的单纤维压缩弯曲性能

选取11种高性能纤维,包括PBO纤维、芳纶1313纤维、对位芳纶纤维、高强聚乙烯长丝和高强聚乙烯短纤等,采用单纤维压缩弯曲仪测试纤维的单纤维压缩弯曲性能,并对其压缩弯曲曲线进行对比分析。结果表明,11种高性能纤维中,Technora纤维的最大力和抗弯刚度最大,在相同条件下,Technora纤维更难被压弯;PBO纤维普通丝的抗弯刚度远大于高模量丝的抗弯刚度;直径相同的条件下,芳纶1414纤维的最大力、等效弯曲模量及抗弯刚度明显高于芳纶1313纤维;超高分子量聚乙烯纤维的压缩弯曲曲线变化趋势最明显。     

Material behavior of rubber sealing for proton exchange membrane fuel cells

Reliable sealing is necessary for the stable operation of proton exchange membrane fuel cell (PEMFC). In practical application, various materials have been tried in PEMFC sealing. However, the mechanical properties of these sealing materials, which play a key role in the sealing stability, have not been fully understood in PEMFC environment, especially after long-term operation. In this paper, according to the operating environment of PEMFC, sealing material experiments are carried out to explore the differences in mechanical behaviors of sealing materials, including silicone rubber (SR), fluororubber (FR), nitrile rubber (NBR) and ethylene-propylene-diene-terpolymer rubber (EPDM) and the variation of mechanical properties of these sealing materials is predicted as time goes on. The results indicate that compression rate has a great influence on sealing contact stress. SR and EPDM, with the variation of 0.15 MPa and 0.45 MPa in stress, show the best and worst mechanical stability at different compression rates, respectively. In terms of temperature, it is found that SR can adapt to different operating temperature of PEMFC and only 18% variation is found from 20 °C to 100 °C. Finally, based on Time-Temperature Superposition (TTS), high temperature experiments are conducted to predict long-term relaxation stress under PEMFC working condition. The analysis results are beneficial for choosing suitable sealing material, and it can also be applied to predict sealing ability in PEMFC.     

JPEG encryption for image rescaling in the encrypted domain

This work proposes a novel protocol of encrypting the JPEG image suitable for image rescaling in the encrypted domain. To protect the privacy of original content, the image owner perturbs the texture and randomizes the structure of the JPEG image by enciphering the quantized Discrete Cosine Transform (DCT) coefficients. After receiving the encrypted JPEG image, the service provider generates a rescaled JPEG image by down-sampling the encrypted DCT coefficients. On the recipient side, the encrypted JPEG image rescaled by the service provider can be decrypted to a plaintext image with a lower resolution with the aid of encryption keys. Experimental results show that the proposed method has a good capability of rescaling the privacy-protected JPEG file.     

The incorporation of low-substituted hydroxypropyl cellulose into solid dispersion systems

While the use of amorphous solid dispersions to improve aqueous solubility is well documented, little consideration has traditionally been given to the finished dosage form. The objective of this study was to evaluate the dissolution performance of amorphous solid dispersions containing a dispersed superdisintegrant with binding properties. KinetiSol® dispersing was used to thermally process hypromellose acetate succinate-based compositions containing the drug substance nifedipine (NIF) and a highly compressible grade of low-substituted hydroxypropyl cellulose (New Binder Disintegrants; NBD-grade). Solid-state analysis demonstrated that compositions were rendered amorphous during processing. Tablets containing intra-dispersion NBD were found to exhibit non-sink dissolution performance similar to milled intermediate, demonstrating excellent disintegration characteristics. Conversely, tablets without intra-dispersion NBD were found to release significantly less NIF during dissolution analysis due to particle agglomeration. It was determined that compressibility and particle wetting increased as the level of intra-dispersion NBD increased.     

Oriented total variation l1/2 regularization

Total Variation (TV) is a widely used image restoration/decomposition model. It is observed that the classical TV l1 and TV l2 regularization, on the one hand, do not favor higher-gradient structures over lower-gradient details as expected for structure preserving image processing, and on the other hand, tend to reduce the horizontal and vertical gradients, and thus inevitably blur the oblique edges in images. In this paper, we address these two problems by defining Oriented Total Variation l1/2 (OTV l1/2). It is theoretically and experimentally demonstrated that applying l1/2 regularization to the directional derivatives of images leads to superior structure preservation. OTV l1/2 regularization can be applied to image denoising and video compression, and the experimental results verify that OTV l1/2 outperforms other similar models.     

Microstructural toughening mechanisms in nanostructured Al2O3/GdAlO3 eutectic composite studied using in situ microscale fracture experiments

This work uses in situ transmission electron microscopy (TEM) based micromechanical testing to isolate and quantify the microstructural toughening mechanisms active in nanostructured Al₂O₃/GdAlO₃ eutectic samples. The effect of fracture direction across orthogonal sections of the rod-like eutectic was used to reveal the influence of different fracture paths and mechanisms on toughening. The average fracture toughnesses of the rod-like structures in the longitudinal cross-section and transverse cross-section are 2.4 MPa·m^1/2 and 2.7 MPa·m^1/2, respectively. Multiple samples tested in the longitudinal cross-section show significant R-curve toughening response, and obtain values greatly exceeding the initial values upon crack extension. It is concluded that nanoscale crack bridging induces deflection of the crack path, which leads extrinsic energy dissipation as the crack opens. Micropillar compressions are also performed to investigate the composite’s strength. Sample orientation strongly affects the deformation mode and interfacial sliding occurs when the maximal shear stress is parallel to the interface.     

Fabrication of multi-filler thermoset-based composite bipolar plates for PEMFCs applications: Molding defects and properties characterizations

The bipolar plate (BP) material should possess contradictory properties. They should also manufacture from low-cost methods and materials. In the current investigation, thermoset-based composite materials reinforced with conductive fillers, and the compression molding process is implemented. In addition to fabricating the bipolar plates (BPs) with and without the flowing channels, alleviating the defects during the molding process is performed. The channels are perfectly formed on the plates with the designed depth of 0.65 mm and 0.5 mm of width. In the meanwhile, we alleviate different molding defects, which spoil the surface appearance and part properties. Regarding the physical properties, the water contact angle is measured to be around 85°. The through-plane electrical conductivity of molded plates showed high values up to 38 S/cm, and the interfacial contact resistance measured to be 18–24 mΩ cm². The mean value of the flexural strength of the produced samples was equal to 47 MPa, which is almost twice the DOE target (>25 MPa).