Modern Physics Letters B

In this study, the mechanical properties and friction behavior of carbon/carbon (C/C) composites with and without stitching were investigated. The C/C composites were prepared via high-pressure liquid-phase infiltration, followed by carbonization and graphitization over several cycles. The unstitched C/C composites exhibited better comprehensive mechanical and friction properties and showed excellent application potential for the field of high-temperature friction.

This paper presents the research results on the microstructure changes of SKD61 steel after quenching at 1050${}^{\circ }$C and then tempering at 580${}^{\circ }$C. After quenching and tempering, the microstructure of this steel is determined by various moieties, including tempering martensite, residual austenite, and carbides dispersed within the matrix. Scanning electron microscopy, X-ray, and energy-dispersive spectroscopic analysis reveal that the presence of the carbides Cr₇C₃, Mo₃C₂ and MoC determines the mechanical properties of steel during high-temperature operations.

A machined surface study was performed according to the surface roughness post-process polishing operation on the aspheric mold core using a diamond turning machine. Machined surface features in the bokeh image must be removed with a subsequent surface polishing process after the aspheric glass molding pressing, as surface defects are caused by the mechanical resolution of ultraprecision diamond turning machines. Therefore, in this paper, we analyze the interrelationship between surface roughness, interference frequencies, and error-approximation aspherical error values to propose a baseline measure for machined surface removal. From the results of profilometer measurements, the form error accuracy before polishing is 1.3 $\mu$m, and after polishing is 0.2 $\mu$m. As a result of the LUPHOS, the root mean square (RMS) average of interference frequencies before polishing is 20 nm, and after polishing is 3 nm. The machining marks are removed from the bokeh image only when the RMS roughness is maintained at 5 nm or less.

Composite powders mixed with yttrium aluminum garnet (YAG:Ce) and SiO₂ powders were prepared in a tetraethyl orthosilicate solution of an alkali hydrolysis bath. The state of the composite powders varies depending on the reaction conditions: the amount of ammonium water and the reaction time. The photoluminescence property of the composite powder was the same as that of pure YAG powder, while the quantum efficiency varied depending on the morphologies of the composite powders. The quantum efficiency improved for the composite powder with nano-sized silica particles covering the YAG surface.

In powder-mixed electrical discharge machining (PMEDM), the application of low-frequency vibrations to a workpiece is considered beneficial to the machining quality. This study evaluates the average surface roughness (Ra) of SKD61 steel workpieces subjected to low-frequency vibrations during PMEDM using a Cu electrode and titanium powder. Specifically, Taguchi’s L25 experimental design method is used to evaluate the influence of the following process parameters: current, pulse-on time, concentration, push pressure, frequency, and amplitude. The analysis of variance technique is used to determine the minimum Ra (Ra${}_{min}$) value. The results show that Ra is most and least strongly influenced by $I$ and $A$, respectively. Further, Ra${}_{min}$ is found to be 1.03 $\mu$m.

The two-stage cumulative flexural fatigue behavior of sandwich beams with glass/polypropylene (PP) faces and aluminum (Al) foam core was experimentally analyzed to study the loading sequence effect of the studied innovative sandwich composites subjected to variable-amplitude cyclic loading. The constant amplitude load–life curve was established first for reference. Subsequently, the two-stage cumulative fatigue tests were performed, and the high/low loading sequence and cycle ratio of the first stage were used as experimental variables in the cumulative fatigue tests. Experimental results showed that the sum of the cycle ratios of the two stages for all cases was approximately 1.3. Furthermore, the loading sequence effect was slight. Because the interaction of damage evolution for the two stages was nonsignificant, the different failure modes for the high- and low-loading levels contributed to the high sums of cycle ratios.

A novel route planning method based on the RRT algorithm is proposed in this study. To enhance the structure of the state tree, a general-purpose pseudorandom number generator is inserted into RRT. In addition, the proposed method includes a distance restriction that helps reduce the number of possible candidate nodes. MATLAB has been utilized to examine the efficacy of the proposed technique using three different types of maps. The simulation results demonstrate that the revised method is advantageous for route planning due to its superior convergence and efficacy over the original.

Carbon fiber-reinforced polymer composites employed in practical aerospace applications are subjected to harsh temperature changes and preloads (PLs) simultaneously. Thus, it is important to analyze the mechanical behavior of carbon fiber/polyether-ketone-ketone (CF/PEKK) composites under such conditions. Therefore, this study first performed bending tests on CF/PEEK samples at room temperature (RT), 80${}^{\circ }$C, and 120${}^{\circ }$C. Subsequently, bending tests were performed on CF/PEEK samples preloaded with 30%, 50%, and 70% of the ultimate load for 24 h and 72 h. Finally, bending tests were conducted on CF/PEKK samples subjected to both temperature and PL variations. The results show that as temperature increased from RT to 120${}^{\circ }$C, the strain values increased, but the modulus ($E$) and strength ($\sigma$) decreased. As PL increased, the flexural stress, $E$, and strain ($𝜀$) decreased. The samples preloaded with 30% of the ultimate load at 80${}^{\circ }$C had the highest $E$, $\sigma$, and $𝜀$ values. However, the $E$, $\sigma$, and $𝜀$ values at 120${}^{\circ }$C were only slightly lower than those at 80${}^{\circ }$C. This proves that preloaded CF/PEKK composites maintain their high strength, toughness, and plastic behavior at high temperatures, and thus, they are suitable for aerospace applications.

This work used short carbon fibers (SCFs) of different lengths to manufacture epoxy bulk mold compound (BMC) composites. Drop-weight-impact tests were performed on the intact carbon-fiber-reinforced-polymers (CFRPs) laminates to generate artificial damage. The damaged CFRP laminates were then repaired using the SCF-BMC composites. Compression after impact (CAI) tests were conducted to measure the compressive strength of the repaired laminates. Tensile properties and compressive properties of the SCF-BMC composites were also measured. The results show that 48-mm carbon fibers result in the largest tensile modulus, tensile strength, and compressive strength, while 12-mm carbon fibers result in the largest compressive modulus. CAI test results show that the compressive strength of the repaired laminate can be restored to 80.3% of that of the undamaged laminate. Therefore, SCF-BMC composites significantly contribute to repairing damaged composite laminates.

This study investigated the effects of Nb addition on the glass formation ability, mechanical properties, and microstructural evolution of Fe–Y–B bulk metallic glass (BMG) alloys. The glass formation ability of the alloys with different Nb contents was evaluated by means of X-ray diffraction and differential scanning calorimetry. The mechanical properties of the various BMGs were examined using a universal testing machine (MTS 810) under quasi-static strain rates of 10${}^{-3}$–10${}^{-1}$ s${}^{-1}$. The high strain rate mechanical properties of the BMGs were tested using a split Hopkinson pressure bar system under strain rates of $2\times 10^3$ to $4\times 10^3$ s${}^{-1}$. Finally, the microstructures of the fracture surfaces of the alloys tested at different strain rates were observed by scanning electron microscopy (SEM).