The Effects of Core Machining Configurations on the Mechanical Properties of Cores and Sandwich Structures

Composite sandwich structures are widely used in the fields of aviation, marine, and energy due to their high specific stiffness and design flexibility. Improving the mechanical properties of the cores is significant to the strength, modulus, and stability of composite sandwich structures. Two kinds of core machining configurations were designed by combining thin grooves, perforated holes, and thick contour cuts as well as non-machining plain cores. The cores and sandwich structures with these configurations were fabricated using a vacuum-assistant infusion process. Static tensile, compressive, shear, and peeling tests were conducted on the infused cores and sandwich structures. The results showed that the tensile, compressive, and shear moduli, and compressive strength of the infused cores can be greatly improved. The tensile strength changed negligibly due to stress concentration induced by irregular foam cell and the shear-lag phenomenon of the resin column/foam interface. The shear strength of the infused cores increased slightly. The thick contour cuts and perforated holes can greatly improve the face sheet/core peel capacity of the sandwich structures, whereas the thin grooves can moderately improve the peel capacity. Both infused cores with the designed machining configurations exhibited positive effects on the compressive, tensile, and shear moduli, and compressive strength, considering the material costs. The study provides a comprehensive and quantitative insight into the effects of core machining configurations on mechanical properties of infused cores and composite sandwich structures.

Nano-hybridization effects of nano-silica and nano-graphene platelet on mechanical properties of E-glass/epoxy nanocomposites

This study reveals the nano-hybridization effects of nano-graphene platelets (NGPs) and nano-silica (SiO2 nanoparticle), having different structural geometries on the mechanical properties, nano and micro-scale failure behaviors, and nanoscale fracture mechanisms of E-glass/epoxy composites. Tensile, three-point bending, and Charpy impact experiments were applied to determine the mechanical behaviors of 0.5 wt.% NGPs, 4 wt.% nano-silica and 0.5 wt.% NGPs + 4 wt.% nano-silica nanohybrid filled E-glass/epoxy and neat E-glass/epoxy composite samples. Failure of composite samples was examined by microscopy and SEM analysis. FTIR analyses were conducted to interpret the chemical and physical interactions between the nanoparticles and epoxy resin. Nano-hybridization exhibited the highest tensile strength and three-point flexural force for the composite samples. However, the NGPs filled nanocomposites also exhibited the best static tensile toughness and impact energy absorption. The experimental data showed that it was statistically significant as a result of the one-way ANOVA analysis. Remarkably, nano-hybridization of nano-silica and NGPs showed different fracture mechanisms at the nano and micro-scales.

‎‏FINDING PERCENTAGE OF BREAKDOWN STIMULATION OF ALUMINUM WIRES THAT OPERATES IN A CORROSIVE MEDIUM

The study of the duration of mechanical resistance to static tensile stress (withstand time) for an aluminum wire that being suffers from the corrosion effect stimulated by stray currents at different temperatures. Test device was designed and produced locally "in advance" in accordance with the specification (ASTM G103 - 97) to create static tensile stress of (1 N) on an aluminum wire of type ASTM (B231/B231M) with particular dimensions and utilized in the transmission of electrical energy, and when the wire is surrounded by a corrosive environment (NaCl solution) (3.5 % NaCl) at three different temperatures (25, 50, and 75 ° C) without any external electrical current causing corrosion; this symbolizes stray currents. Then compare the findings of that example to the results of the same wire's withstand time in the presence of an external electrical current generated by corrosion of type (D.C) by (5V & 3A). Following that, the resulting diagrams were analyzed, and it was discovered that the wire resistivity time (without the existence of stray currents and at a temperature of 25 ° C) completed (17 days), which is the longest duration of endure, and the lowest time of resistivity or resistance period (in the existence of an external electric current) is (18 hr.).Impact of (stray currents) at (75 ° C), and this is an indicator of the stray currents with corrosive environment temperatures on the resistance period (withstand duration) in the existence of static stress. The total stimulation increase is 1.9% between corrosion at 75°C and 25°C.

Influence of Pressure and Temperature on the Strength Properties of a Laminate Produced by the RTM Method

This paper discusses the effect of pressure on the content of microvoids and defects inside laminates fabricated under different pressures, by vacuum methods. Two basic vacuum methods resin transfer molding (RTM) and vacuum bag method were used in this paper. A glass mat with an alignment angle of (0□/90□) and a mass of 450 g/cm2 was used to produce the laminate, and a polymer resin was used as the matrix. Special attention was paid to the technological parameters of both processes. A mathematical analysis of the most important parameters which include flow rate, permeability, and gelation temperature has been carried out. In addition, the resin temperature is used to reduce the viscosity of the resin to facilitate its flow through the reinforcement, and in the final stage of production to control the chemical reactions occurring in the mold. The pressure is chosen so that the resin flow is continuous. The synchronization of these two parameters and the measurement of the time in which they occur are called the “cure cycle”. In the final step of the study, the composite was subjected to a static tensile test, using specimens of two different dimensions (scale effect) to evaluate the effect of microvoids and microcracks created by the processes on the strength of the material.

Prevention of Postsurgical Abdominal Adhesion Using Electrospun TPU Nanofibers in Rat Model

Intra-abdominal adhesions following surgery are a challenging problem in surgical practice. This study fabricated different thermoplastic polyurethane (TPU) nanofibers with different average diameters using the electrospinning method. The conditions were evaluated by scanning electron microscopy (SEM), atomic force microscope (AFM), and Fourier transform infrared spectrometer (FTIR) analysis. A static tensile test was applied using a strength testing device to assess the mechanical properties of the electrospun scaffolds. By changing the effective electrospinning parameters, the best quality of nanofibers could be achieved with the lowest bead numbers. The electrospun nanofibers were evaluated in vivo using a rat cecal abrasion model. The macroscopic evaluation and the microscopic study, including the degree of adhesion and inflammation, were investigated after three and five weeks. The resultant electrospun TPU nanofibers had diameters ranging from about 200 to 1000 nm. The diameters and morphology of the nanofibers were significantly affected by the concentration of polymer. Uniform TPU nanofibers without beads could be prepared by electrospinning through reasonable control of the process concentration. These nanofibers’ biodegradability and antibacterial properties were investigated by weight loss measurement and microdilution methods, respectively. The purpose of this study was to provide electrospun nanofibers having biodegradability and antibacterial properties that prevent any adhesions or inflammation after pelvic and abdominal surgeries. The in vivo experiments revealed that electrospun TPU nanofibers reduced the degree of abdominal adhesions. The histopathological study confirmed only a small extent of inflammatory cell infiltration in the 8% and 10% TPU. Conclusively, nanofibers containing 8% TPU significantly decreased the incidence and severity of postsurgical adhesions, and it is expected to be used in clinical applications in the future.

A Comparative Analysis of Selected Methods for Determining Young’s Modulus in Polylactic Acid Samples Manufactured with the FDM Method

The objective of this study was to compare three methods for determining the Young’s modulus of polylactic acid (PLA) and acrylonitrile-butadiene-styrene (ABS) samples. The samples were manufactured viathe fused filament fabrication/fused deposition modeling (FFF/FDM) 3D printing technique. Samples for analysis were obtained at processing temperatures of 180 °C to 230 °C. Measurements were performed with the use of two nondestructive techniques: the impulse excitation technique (IET) and the ultrasonic (US) method. The results were compared with values obtained in static tensile tests (STT), which ranged from 2.06 ± 0.03 to 2.15 ± 0.05 GPa. Similar changes in Young’s modulus were observed in response to the processing temperatures of the compared methods. The values generated by the US method were closer to the results of the STT, but still diverged considerably, and the error exceeded 10% in all cases. Based on the present findings, it might be concluded that the results of destructive and nondestructive tests differ by approximately 1 GPa.

Ageing of climbing ropes with and without hydrophobic coating

The effects of 4 months of weather exposure on the ageing of dynamic climbing ropes made of polyamide 6 were studied and differences between ropes with and without hydrophobic coating were examined. The polyamide degradation of the rope yarns was studied using infrared spectroscopy and a quasi-static tensile test. The number of falls to failure and the maximum force on the climber in a fall were evaluated with a drop test according to the UIAA 101 standard. Moreover, changes in the length of the ropes due to weathering were measured. The following results were found. After 4 months of weathering, sheath yarns of the coated rope showed a greater decrease in breaking force than those of the uncoated rope, which might be due to reactions of polyamide with radicals formed during the photo-induced oxidation of the coating. In contrast, the core yarns from the uncoated rope showed a greater decrease in breaking force than those from the coated rope, probably due to prolonged exposure of the uncoated core to water with possibly dissolved atmospheric acids. Furthermore, the decrease in the number of falls to failure was greater in the uncoated than in the coated rope. This difference was explained by a mechanism of changes in radial pressure of the sheath on the core. Regarding the maximum force on the climber, no significant changes due to ageing were observed during the drop test. Thus, it was concluded that 4 months of weather exposure do not pose a safety risk for climbing ropes, but the negative effect of coating on the ageing of polyamide might be detrimental when it comes to static personal safety equipment, such as slings or accessory cords.

WAAM-Fabricated Laminated Metal Composites

Laminated metal composites are a promising design since the hybrid design enables superior and tailorable material properties compared with bulk material. The article introduces for the first time, laminated metal composites consisting of multiple bilayers of alternating layers of ductile and high-strength steel processed by wire arc additive manufacturing (WAAM). The layup of the laminated metal composites is built up by alternating deposits made of ductile steel and high-strength steel type wires. Governing parameters in the fabrication process affecting the material properties, such as dilution, are discussed. Enhanced material properties of the laminated metal composites fabricated by WAAM are investigated under static tensile, impact and tension-tension high-cycle-fatigue loading and compared to the relating homogenous weld metal. Potential reasons for the retardation of crack propagation in laminated metal composites fabricated by WAAM compared to findings in roll-bonded laminated metal composites are discussed. WAAM is conducted by a collaborative robot providing a high level of flexibility in respect to geometry and scalability. Tailorability of material properties through WAAM-fabricated laminated metal composites adds an important layer of flexibility which has not been explored yet.

Structure and Mechanical Properties of Shipbuilding Steel Obtained by Direct Laser Deposition and Cold Rolling

The study of the formation of microstructural features of low-alloy bainite-martensitic steel 09CrNi2MoCu are of particular interest in additive technologies. In this paper, we present a study of cold-rolled samples after direct laser deposition (DLD). We investigated deposited samples after cold plastic deformation with different degrees of deformation compression (50, 60 and 70%) of samples from steel 09CrNi2MoCu. The microstructure and mechanical properties of samples in the initial state and after heat treatment (HT) were analyzed and compared with the samples obtained after cold rolling. The effect on static tensile strength and impact toughness at −40 °C in the initial state and after cold rolling was investigated. The mechanical properties and characteristics of fracture in different directions were determined. Optimal modes and the degree of cold rolling deformation compression required to obtain balanced mechanical properties of samples obtained by additive method were determined. The influence of structural components and martensitic-austenitic phase on the microhardness and mechanical properties of the obtained samples was determined.