Key Engineering Materials Vol. 1026

Abstract: The widespread adoption of integral stiffened panel in the aviation industry due to its valuable advantages lead to constant research with focus in the improvements in the crack-growth analysis and its numerical modelling. In this context, the experimental characterization of the mechanical behavior of such structures is an essential demand for a proper usage. The current work intends to describe the characterization of one aluminum integral stiffened panel through experimental fatigue crack-growth tests and numerical analysis. The work describes the finite element model approach to assess the behavior of the stiffened panel under tensile load and describes the fatigue crack-growth tests setup and corresponding results. Additionally, the work describes some findings about the instrumentation adopted in the laboratory tests. The results presented an overall good correlation between the numerical and experimental test results, verifying the proposed numerical model approach.

Abstract: The purpose of this study is to investigate the effectiveness of laser peening (LP) and shot peening (SP) on the fatigue strength and harmless crack size ( of 3D additively manufactured maraging steel. LP and SP was performed under random condition and pre-optimal condition, respectively. Compressive residual stresses of 510MPa and 1650MPa could be introduced on the surface by LP and SP, respectively. Bending fatigue tests were conducted using base metal (BM) specimen, LP specimen and SP specimen. The fatigue strength of the LP and SP specimens were about 57 and 47% higher than that of BM specimen, respectively. Fatigue fracture was initiated from internal by LP and SP. The semicircular cracks less than 0.3mm and 0.1mm in the depth could be rendered harmless by LP and SP, respectively. The estimated based on fracture mechanics were similar to experimental result. The fatigue strength and was affected by the distribution of the compressive residual stress induced by LP and SP. Thus, the LP and SP process can contribute to improving the reliability of 3D additively manufactured maraging steel. Compressive residual stress is the dominant factor in improving fatigue strength and rendering surface defects harmless.

Abstract: This work aims to prepare an epoxy basalt powder and apply it as a protective coating for steel. Basalt powder was dispersed in epoxy resin with different doses of 3, 6, 9, and 12% of the epoxy weight. The prepared modified epoxy coatings were applied to the surfaces of carbon steel plates, and the coated samples were evaluated as follows: dry film thickness (DFT), adhesion strength, impact resistance, bending test, abrasion resistance, and fire and chemical resistance. The study revealed that using basalt powder improves the protective performance of epoxy. The obtained results showed that the optimum basalt content is 9%, and the enhancing coating performance of epoxy modified with 9% basalt as compared to neat epoxy was as follows: DFT increased by 50%, adhesion strength enhanced by 85%, and impact resistance increased by 95%. Abrasion and fire resistance were improved by 13% and 30%, respectively. Lastly, the chemical resistance of coatings was changed from fair to excellent. Keywords: epoxy, epoxy basalt coating, steel protection, basalt powder

Abstract: Electronic equipment is exposed to rough vibrations throughout its life cycle. Electronic components can be damaged by these vibrations and could lead to device failure. The conventional Printed Circuit Boards (PCBs) that form the foundation of numerous electronic devices are predominantly constructed from copper films that are bound to fiber epoxy laminates, such as FR4, which is composed of glass fibers, and FR1, which is composed of paper. Being biodegradable makes cellulose a more sustainable choice. Nonetheless, it is imperative to uphold performance criteria, and this work aims to contribute to this assessment. Using simulation studies, we compare the behavior of these two PCBs under vibrational stress. The finite element analysis (FEA) of the vibrations for the PCB samples was modelled using the Ansys software. The FEA simulations show that both types of PCBs have similar movements and accelerations at certain places on the board.

Abstract: Investigating how two different ceramic additives affect the microstructure and nanomechanical characteristics of the Ti6Al4V matrix forms the goal of this work. Under 50 MPa pressure, 10 min dwell time, and 100 °C/min sintering rate at 950 °C, a pulsed electric current sintering process, or PECS, was used. An XRD spectrometer was used to examine the phases, and SEM-EDS was used to examine the bulk morphology of the starting powders and sintered composites. The fabricated Cs1, Cs2, and Cs3 composites attained theoretical densities of 99.74, 98.90, and 96.7%, respectively, above 96.22% of unreinforced Ti-alloy. The SEM analysis showed an even dispersion of the ceramic reinforcements in the matrix of Ti6Al4V, with the characteristics of porous craters in all the samples. Of the three composite samples, Cs1 showed the highest elastic modulus, micro, and nanohardness absolute values of 173 GPa, 796 MPa, and 8942 MPa, respectively, as compared to the unreinforced titanium alloy of 114 GPa, 589 MPa, and 6466 MPa. It was thought that the improved mechanical properties of the sintered composites were due to the production of intermediate phases of Ti₂N and SiO₂ during the sintering process. The materials improvement stands at approximately 30% of the unreinforced Ti-alloy.

Abstract: This research improves the mechanical properties of laminates in ship hulls made of glass fiber reinforced plastics (GFRP) with the design of auxetic sheets, to take advantage of the property in their geometry to reduce the damage energy due to surface impacts absorbed by the laminate. 3D printing of second generation auxetic components to produce modified specimens. Laboratory reproductions of mechanical damage were compared with those of specimens extracted from a ship under construction. The mechanical properties of the bending and tensile tests demonstrated that the insertion of the core in the laminate protected the matrix from damaged energy, prolonging its useful life. Comparative results are presented, which will allow GFRP hull designers to insert auxetic sheet cores into their design. Mechanical tests allowed us to compare the progress of delamination.

Abstract: Computational methods provide effective tools for the prediction of the failure behavior of structures, especially for composites with complex failure modes. The effect of manufacturing process defects on the delamination behavior of composites receives insufficient attention in current studies. In this work, an interlaminar model for composite curved beams considering inter-ply voids was established. A classification and calculation method for calculating inter-ply porosity and intra-ply porosity is proposed based on geometry and location characteristics of voids. Then, an interlaminar model is established based on cohesive zone model with the inter-ply porosity as an input parameter. L-shaped composites with balanced and symmetry layups were cured and subjected to four-point bending tests to validate the proposed method. The numerically predicted location of initial crack generation and final delamination pattern are in great agreement with the experimental results. Besides, the prediction accuracy of the model considering inter-ply voids improves compared with the model without defects, the prediction error of the failure load is reduced from 12.8% to 2.1%. The overall framework provides an accurate and promising tool for the prediction of the delamination behavior and assessing the effects of pore defects of composite curve beams.

Abstract: Hybrid magnets integrate permanent and soft magnetic materials, resulting in enhanced magnetic performance suitable for a variety of applications. Neodymium-iron-boron (NdFeB) magnets, known for their high energy output, exhibit limitations at elevated frequencies due to eddy current effects. To address this problem, it is beneficial to combine NdFeB with high-resistivity nickel zinc ferrites (NZF) to optimize their magnetic properties. This study focuses on the synthesis of NZF and the fabrication of NdFeB/NZF hybrid composites with varying ratios of NdFeB-to-NZF (40:60, 50:50, and 60:40) and different configurations. Their structural, microstructural, and magnetic characteristics were analyzed to identify the optimum fraction for the hybrid composite formulations. In this work, a commercially available NdFeB and NZF were synthesized via high-energy ball milling while NdFeB was used for the composite’s fabrication. Among the synthesized samples, the mixture-composites of a 60:40 ratio exhibited the highest saturation magnetization of 43.01 emu/g with a notable Curie temperature of 390 °C. The results indicate that increasing the hard phase of NdFeB enhances both saturation magnetization and Curie temperature in all composite samples. Conversely, the stacked-composites with a 40:60 ratio displayed the highest resistivity at 7.96x10⁶ Ωm, suggesting that a higher proportion of NZF significantly contributes to increased resistivity. The observed enhancements in magnetic properties can be attributed to the exchange spring mechanism between the soft and hard magnetic phases, as well as the larger grain size in the samples, which promotes a greater number of magnetic domains and reduction of the grain boundaries. Thus, it facilitates more efficient domain wall movement in response to the external magnetic field.

Abstract: Lead hydroxyapatite (PbHAP, chemical formula Pb₁₀(PO₄)₆(OH)₂) has been synthesized by ceramic (solid-state reaction) and semi-ceramic (precipitation) methods. The samples were prepared through a solid-state reaction conducted at 830 °C for 60 hours, with the y values ranging from 0.95 to 1.00. We have developed and created the most efficient preparation methods. The well-known technique was used - semi-ceramic (precipitation) deposition of lead and hydroxyapatite. For this purpose, several advanced devices were used to obtain an accurate structural structure of lead hydroxyapatite compounds. It has been observed, as in the case of chemical synthesis, that the elements (lead, phosphorus, and oxygen) appear to be distributed homogeneously within the crystals, regardless of the method of composition, which indicates that the samples are homogeneous. More importantly, the "solid-state reaction" method favored a specific composition range, while the "precipitation" method performed well for other composition ranges. The above methods indicate an ideal method, according to the desired structure, that should be developed for lead hydroxyapatite, depending on its composition. This research aims to establish the first steps in developing a new method for preparing lead hydroxyapatite compounds with the desired properties to improve their purity and crystal structure for potential uses in the future.