Experimental characterization of fracture of glass fiber reinforced composites laminates subjected to freeze‐thaw cycles

The simultaneous effect of moisture and freeze‐thaw cycle on the mechanical behavior of glass/epoxy composites laminates is experimentally investigated. The study is planned in order to simulate the detrimental presence of humidity due to rainfall in surface damage of composite structures operating in cold weather. Different mechanisms governing the monotonic response of specimens subjected to freeze‐thaw cycles are pointed out by taking advantages of SEM images. Comparing SEM images taken from dry and wet specimens shows that the failure mechanisms such as matrix cracking and delamination are vastly activated around the notched region when the material is exposed to humidity and freeze‐thaw cycle. The load‐displacement response of examined specimens, namely the linear response, is remarkably altered under these conditions. A reduction of approximately 40% in ultimate load and 30% in slope of tangent line of load‐displacement curves is identified after 100 cycles of freeze‐thaw as well as more than 20% decrease of strain energy release rate.     

Two‐Microphone Binary Mask Speech Enhancement in Diffuse and Directional Noise Fields

Two‐microphone binary mask speech enhancement (2mBMSE) has been of particular interest in recent literature and has shown promising results. Current 2mBMSE systems rely on spatial cues of speech and noise sources. Although these cues are helpful for directional noise sources, they lose their efficiency in diffuse noise fields. We propose a new system that is effective in both directional and diffuse noise conditions. The system exploits two features. The first determines whether a given time–frequency (T‐F) unit of the input spectrum is dominated by a diffuse or directional source. A diffuse signal is certainly a noise signal, but a directional signal could correspond to a noise or speech source. The second feature discriminates between T‐F units dominated by speech or directional noise signals. Speech enhancement is performed using a binary mask, calculated based on the proposed features. In both directional and diffuse noise fields, the proposed system segregates speech T‐F units with hit rates above 85%. It outperforms previous solutions in terms of signal‐to‐noise ratio and perceptual evaluation of speech quality improvement, especially in diffuse noise conditions.     

The effect of Ti and Si on the mechanical and electrochemical behaviors of the AlCrN coating deposited by CAPVD on 304SS

This study aimed to investigate the effect of adding titanium (Ti) and silicon (Si) elements on the mechanical and electrochemical properties of the AlCrN-based coating. For this purpose, a cathodic arc physical vapor deposition machine was used. Scanning electron microscopy, X-ray diffraction, and nanoindentation tests were utilized for morphological, microstructural, and mechanical characterization of the coatings. The hardness value and plastic deformation index of CrAlN-based coating increase with the presence of Si element. The mechanical properties improvement is attributed to the reduction of crystallite size as well as to the tendency of the coating structure to become amorphous. The specimens were subjected to 3.5 wt% NaCl solution to electrochemical impedance corrosion and potentiodynamic polarization tests. The results showed that by increasing the coatings’ titanium content, the coatings’ corrosion resistance improved. Moreover, by adding 3% and 5% of Si elements to the coatings’ composition, the corrosion resistance of the AlCrTiSiN coatings was enhanced by 35% and 78%, respectively. Improving the corrosion resistance of the AlCrN-based coatings by adding the Si element is attributed to the change in the microstructure and reduction in the porosity of the coatings.     

Multilayered Electrospun/Electrosprayed Polyvinylidene Fluoride+Zinc Oxide Nanofiber Mats with Enhanced Piezoelectricity

Electrospun polyvinylidene fluoride (PVDF) nanofibers have been widely used in the fabrication of flexible piezoelectric sensors and nanogenerators, due to their excellent mechanical properties. However, their relatively low piezoelectricity is still a critical issue. Herein, a new and effective route to enhance the piezoelectricity of PVDF nanofiber mats by electrospraying zinc oxide (ZnO) nanoparticles between layers of PVDF nanofibers is demonstrated. As compared to the conventional way of dispersing ZnO nanoparticles into PVDF solution for electrospinning nanofiber mats, this approach results in multilayered PVDF+ZnO nanofiber mats with significantly increased piezoelectricity. For example, 6.2 times higher output is achieved when 100% of ZnO (relative to PVDF quantity) is electrosprayed between PVDF nanofibers. Moreover, this new method enables higher loading of ZnO without having processing challenges and the maximum peak voltage of ≈3 V is achieved, when ZnO content increases up to 150%. Additionally, it is shown that the samples with equal amount of material but consisting of different number of layers have no significant difference. This work demonstrates that the proposed multilayer design provides an alternative strategy to enhance the piezoelectricity of PVDF nanofibers, which can be readily scaled up for mass production.     

Effect of Intercritical Annealing Time on the Microstructure and Mechanical Properties of Dual-Phase Steel Processed by Large-Strain Asymmetric Cold-Rolling

Herein, the effect of intercritical annealing time on the microstructure and mechanical properties of dual-phase steel processed by large-strain asymmetric cold-rolling is studied. It is observed that the martensite islands are uniformly distributed in the ferrite phase in the microstructures of dual-phase steels due to performing the asymmetric cold-rolling before intercritical annealing treatment. As the intercritical annealing time increases up to 10 min, the fraction of martensite increases. By increasing the holding time and fraction of martensite, the carbon content of the martensite phase is decreased. The short-term intercritical annealing eliminates the yield point phenomenon. However, intercritical annealing at 860 °C for 20 min leads to the reoccurrence of a yield point phenomenon. Increasing the intercritical annealing time to 10 min improves the yield strength to 505 MPa and ultimate tensile strength to 834 MPa. However, the strength decreases sharply after the holding time of 20 min. There is a perfect linear relationship between the mechanical properties and the fraction of martensite. Ductile failure is observed at the center of the fracture surfaces of dual-phase steels while shear failure occurs at the edges of the fracture surfaces.     

The synergistic effect of texture and surface roughness on electrophoretic deposited bioactive glass coating

To improve the biocompatibility of AISI 316L, bioactive glass (BG) coating of SiO₂–CaO–P₂O₅ which helps bonding with bone implants was used by an electrophoretic deposition method. Before coating deposition, the samples were treated by shot peening, known as an efficient process for metal grain refinement and fatigue properties. The stainless steel 316L was investigated in terms of microstructure, texture, and roughness. This research covers the effects of chosen shot peening parameter on the BG-coating properties on the obtained results. Shot peening was carried using two different sets of parameters as conventional shot peening, and severe shot peening. Wettability, roughness, microstructure, coating thickness, and corrosion behavior of coated sample were investigated in terms of potentiodynamic polarization and electrochemical impedance spectroscopy in simulated body fluid (SBF) solutions at 37°C. The results indicated that the coating thickness decreased from 35.5 ± 10 µm for coated not peened (CNP) to 20 ± 5 and 17 ± 2 µm for coated conventionally shot-peened (CCSP) and coated severely shot-peened (CSSP), respectively. As well as, the water contact angle of CSSP sample was equal to 15.71° which is much lower than CNP (20.7°). The protection ability of the tested samples in the SBF was improved in the following order: CCSP < CNP < CSSP.