Key Engineering Materials Vol. 994

Abstract: This study examines the feasibility of utilizing the press forming method on multi-layer, multi-orientation continuous CFRP preform produced by the additive manufacturing (AM) technique. The 5-layer preforms with fiber orientations of 45° and -45° impregnated in Nylon-6 resin layers were made by a 3D printer, and press-formed in varying temperatures and pressures. Optimal forming outcomes were determined by qualitative evaluations of the surface finish, fiber impregnation, resin flow, and quantitative observations on shape variations by comparison with the mold dimensions. Experimental results showed that the molding temperature of 220°C and pressure between 0.5MPa - 1MPa could produce preforms with optimal surface conditions. There was almost no void of bubble defects, no excess resin flow, and a smooth transition was established between the carbon fiber and the matrix resin layers while allowing the full mechanical strength properties to be realized. The formed preform evaluations confirmed that the press molding method is feasible on multi-layer, multi-orientation continuous CFRP with optimal surface conditions.

Abstract: Laminated composite beams are being used for many applications due to their high strength to weight ratio. To enhance the performance of laminated composites under dynamic loading, Magnetorheological (MR) and Electrorheological (ER) fluids have been considered to be added as embedded layers/segments to the conventional laminated structures. The present work focuses on the dynamic behavior of laminated composite beams incorporating MR fluid pockets (referred to as MR-laminated beams) under impulse loadings. A modified layerwise displacement theory is employed to account for the varying fluidity of MR pockets along the thickness direction. Four configurations of MR-laminated beams featuring multiple MR pockets distributed through the thickness and along the length have been examined. A parametric analysis explores the impact of magnetic field strength, number and placement of MR pockets, and boundary conditions on the dynamic response of the MR-laminated beams. The changes in natural frequencies concerning the size and location of activated MR pockets have been explored. Time-response analysis is conducted for MR-laminated beams subjected to impulse loading, considering various sizes and locations of activated MR pockets. The investigation highlights the significant influence of the MR pocket's location and size on the vibration response of MR-laminated beams. It is realized that the total stiffness, mass, and activation energy can be optimized according to the desired dynamic response of the beams. The proposed configuration for MR-laminated beam, results in a beam with 7% reduction in total mass while exhibiting fivefold increase in the corresponding natural frequencies, 40% increase in damping and 40% reduction in maximum amplitude.

Abstract: Carbon and glass fabric reinforced polymer (C/GFRP) composites are extensively used in aerospace and sports industry because of their exceptional properties. However, during service, static and dynamic bending loads can ensue damage in composites affecting their strength, stiffness and energy absorption. Carbon fiber composites, being inherently brittle, are prone to sudden catastrophic fracture without ductile-like behavior of metals. This study investigates mechanical behavior and damage mechanisms of woven C/GFRP composites in on- and off-axis orientations during bending. Initially, bending tests with quasi-static loading were performed, followed by dynamic ones using an Izod impact testing apparatus. Results showed distinct behavior in on-axis CFRP laminates with brittle fracture. Off-axis CFRP samples and both on- and off-axis GFRP laminates showed signs of damage and non-linear behavior, yet they retained their ability to bear loads. Significantly, off-axis specimens of both types and on-axis GFRP laminates exhibited enhanced energy absorption capabilities without experiencing fracture, undergoing pseudo-ductile deformation. CFRP specimens were analyzed with micro-computed tomography (micro-CT), provided insights into prevalent damage modes such as matrix mircocracking, debonding of tows, delamination and breakage of fabric. While on-axis CFRP laminates experienced brittle fracture, off-axis specimens exhibited a ductile-like response attributed to matrix plasticity, cracking and fiber trellising before eventual failure.

Abstract: In the present nanoscale regime, mixed carbon nanotube bundles (MCBs) are considered to be highly promising interconnect options. This research paper introduces a spatially arranged mixed carbon nanotubes (CNTs) bundle (MCB), wherein single-walled CNTs (SWCNTs) and multi-walled CNTs (MWCNTs) occupy equal halves in the MCB. An equivalent single conductor (ESC) model for MCB is employed to analyze the interconnect performances in terms of signal transmission delay and dynamic crosstalk delay at different technology nodes (i.e., 32nm, 22nm, and 16 nm). Encouragingly, a significant reduction in signal transmission delay and dynamic crosstalk induced delay are observed at 32 nm technology node. It is observed that at 32 nm technology node, the propagation delay and crosstalk induced delay significantly improves by 29.40% and 55.53%, respectively, compared to 22 nm technology node and 187.88% and 185.94%, respectively, compared to 16 nm technology node. The improvement in interconnect performances can primarily be attributed to the improvement in the number of conducting channels inside the MCB at 32 nm, which greatly impacted the interconnect parasitics such as quantum resistance, quantum capacitance, kinetic inductance etc.

Abstract: A thermally conductive silicone adhesive UB-5715 was prepared using vinyl silicone oil of medium viscosity, hydrogen-containing silicone oil and micron alumina powder. The results revealed that UB-5715 demonstrated superior thermal and mechanical properties. Specifically, its thermal decomposition temperature exceeded 400 °C, the thermal conductivity coefficient surpassed 1.80 W/m·K, the thermal resistance was under 12.0 °C·cm²/W, the shear strength reached achieved was over 5.00 MPa. Meanwhile, after being subjected to uHAST for 384 hours, thermal cycle for 1000 times and heat aging for 1000 hours respectively, UB-5715 still maintained its high thermal conductivity coefficient and mechanical properties. The thermal conductivity coefficient still exceeded 1.70 W/m·K, shear strength still surpassed 5.00 MPa, the tensile modulus remained below 100 MPa, the linear expansion coefficient was less than 160 ppm/°C, and its comprehensive performance met the reliability requirements for advanced packaging process substrates and heat dissipation cover assemblies.

Abstract: The amorphous silicon (a-Si) grown by plasma enhanced chemical vapor deposition (PECVD) has been widely applied in advanced semiconductor devices. However, it still suffers from the bubble defects when the deposition temperature goes above 450 °C. In this work, we have investigated the influence of underlying materials on the formation of bubbles of a-Si. The a-Si was deposited on different dielectric substrates, including silicon nitrides (SiN) and silicon dioxide (SiO₂), using PECVD technique at a substrate temperature of 500 °C. A large number of bubbles of the a-Si has been observed on the thermal ALD deposited SiN underlayer, and some of them even burst. In contrast, no bubble defects were observed at the a-Si grown on PECVD SiN and PECVD SiO₂ films. Such deviation may be attributed to the quality of the underlying material, which induces the H/H₂ diffusion during the growth of a-Si and results in bubbles. A solution based on the model has been used to suppress the formation of such bubbles. An inserting layer of SiO₂ was introduced in between SiN and a-Si to improve the density of the lower layer material and the adhesion between the two materials. As a result, there is no bubble defects at the surface of a-Si observed using optical microscope. Our work reveals the mechanism of the formation of bubble defects and paves a new method to eliminate the bubbles defects and to form high-quality a-Si, which shows potential in the manufacture of semiconductor devices.

Abstract: Considering solar energy is being used more and more frequently in recent years, numerous studies have been conducted in order to improve the performance of the solar cell. The application of anti-reflective coating (ARC) in the solar cell is one of the most effective techniques. It has been said that although single and double ARC layers are adequate, applying triple ARC layers would render them significantly more effective across a broad spectrum. Henceforth, in this study, different materials were recently designed to produce triple layers of ARC, which are SiO₂/Si₃N₄/TiO₂, SiO₂/ZnO/TiO₂, ZnO/Si₃N₄/TiO₂, SiO₂/Si₃N₄/ZnS, and SiO₂/ZnO/ZnS, which are then applied in silicon solar cells using PC1D simulation software. The outcomes of the simulation included the analysis of the I-V curve, efficiency (ŋ), and reflection, in addition to the results for short circuit current (I_sc), maximum power output (P_max), open circuit voltage (V_oc), and fill factor (FF), which have been compared to numerous other theoretical findings from other investigations and research projects. By that, the simulation revealed that SiO₂/ZnO/TiO₂ is the most suitable triple-layer ARC to be applied to a silicon solar cell, which exhibits the highest efficiency of 22.63% with an I_sc of 3.967A, P_max of 2.489W, a V_oc of 0.7389V, and a fill factor of 84.91 at a wavelength of 400 nm.

Abstract: Recently, researchers have developed the method as a harmless the crack by the surface modification. For the purpose of contributing to reliability improvement of the A6061-T6 structure by harmless method, the following research was carried out: The tensile residual stress of friction stir welding was added by shot peening, resulting in a more significant compressive residual stress than that of the base metal. The effect of the surface crack aspect ratio on the maximum harmless crack depth (a_hml) of A6061-T6 was evaluated for residual stress distribution. The detectable depth was evaluated in the relationship between a_hml and the maximum detectable crack depth (a_NDI) by non-destructive inspection (NDI).

Abstract: Friction stir welding is a research direction within ISIM Timisoara, with contributions and results obtained in several research projects carried out in this field. The paper presents results obtained by ISIM Timisoara regarding FSW welding in ambient environment and in liquid working environment (submerged friction stir welding SFSW) of EN AW 1200 aluminum alloy, using a welding tool made of steel, with threaded cylindrical pin. FSW welding in liquid working environment aims to avoid overheating of the welding tool and welding device during the joining process, as well as achieving better results compared to FSW welding in ambient environment. The evaluation of welded joints included structural analysis, hardness measurements, tensile and bending tests. A comparative analysis of the results obtained in the FSW / SFSW welding experiments carried out for the EN AW 1200 aluminum alloy is presented. The obtained results are useful for the outline of the future experimental research programs which will be carried out within the ongoing Nucleu project PN 23.37.01.02, regarding friction stir processing in ambient and in a liquid environment of this material.