Currently, the mechanical performances of polylactic acid (PLA) samples prepared using the fused filament fabrication (FFF) technique are relatively poor. Hence, the carbon fiber (CF) is used to improve the thermal stability and mechanical property of FFF-ed PLA samples in this paper. The crystalline structure, thermal stability, melt flow rate, tensile strength and fractured surface morphology of PLA and PLA/CF samples were investigated with an X-ray diffraction device, differential scanning calorimeter, thermogravimetric analyzer, melt flow rate equipment, universal tensile test machine and scanning electron microscope, respectively. Meanwhile, the reinforcement mechanism of CF on the mechanical property of PLA samples was also analyzed. XRD results revealed that the diffraction peaks intensities of PLA/CF sample were obviously lower than those of PLA sample. TGA and DSC curves illustrated that the initial thermal decomposition temperature, thermal stability and crystallinity of the PLA/CF sample improved significantly. The tensile strength of the PLA/CF sample was 91.58 MPa, which was 42.49% higher than that of the PLA sample. Moreover, SEM images showed that the fractured behavior of the PLA sample varied from brittle fracture to ductile fracture after the introduction of CF. The results concluded the CF is a feasible fiber for enhancing the performances of the PLA sample.

Bit bounce and stick-slip vibration are detrimental to the service life of drillstring and down-hole equipment. A two degrees-of-freedom lumped parameters model is employed to account for bit-rock interaction and coupled vibration. Qualitative analysis to system parameters is performed through analyzing the influence of the angular speed of the rotary table and the length of drillstring on stick-slip vibration and bit bounce. After that, the suppression methods of stick-slip vibration and bit bounce are also given. The nonlinear motions predicted by the model are in agreement with the experimental observations. The study shows that increasing the weight-on-bit(WOB) and the angular speed of the rotary table effectively suppresses bit bounce and stick-slip vibration. What’s more, the posterior models can suppress stick-slip vibration. At the same time, bit bounce can be reduced through applying the models in the middle. When the drillstring is in a higher-length, the stick-slip frequency is at a lower level. However, the intensity of bit bounce is extremely high.

Natural gas hydrate (NGH) is a kind of unique resource among hydrocarbon fuels. It is stable within its sedimentary hosts and will only convert to its constituent gas and water phases relatively quickly if reservoir pressure-temperature conditions are artificially disturbed. The unwanted vibrations from the drill string with the complex external environment and excitation usually cause instability in the NGH. In this paper, a nonlinear mathematical model is presented taking into account the fluid–solid coupling vibration caused by the drilling fluid inside and outside the drill string, the non-smooth rub-impact between the drill string and borehole wall, and the influence of centralizer setting interval on nonlinear resonant vibration of the drill string. The relationship between the variable parameters of the drill string and the complex dynamics of the drill string is analyzed. Finally, the bifurcation diagram is given. The results show that the system response exhibits complex dynamic behavior due to rub-impact and nonlinear effects. However, there is always a suitable parameter in the bifurcation diagram of each parameter change, so that the amplitude of the system is small and the failure probability of the drill string is reduced. The research results have reference significance for exploring the nonlinear dynamic mechanism of a drill string under complex working conditions and reasonably optimizing drilling parameters.

At present, the improvement of anti-wear performance of piston rings remains a challenge. In this article, Ni-SiC composite coatings fabricated at 3, 9, and 15 g/L SiC were denoted as NSc-3, NSc-9, and NSc-15 coatings. Meanwhile, the influence of SiC concentration on the surface morphology, phase structure, microhardness, and anti-wear performance of electrodeposited Ni-SiC composite coatings were investigated utilizing scanning electron microscopy, X-ray diffraction, a microhardness tester, and a friction–wear tester, respectively. The SEM images presented NSc-9 coatings with a compact, flat, or cauliflower-like surface morphology. The cross-sectional morphology and EDS results showed that the Si and Ni elements were uniformly distributed in the NSc-9 coatings with dense and flat microstructures. Moreover, the average grain size of the NSc-9 coatings was only 429 nm. Furthermore, the microhardness and indentation path of the NSc-9 coatings were 672 Hv and 13.7 μm, respectively. Also, the average friction coefficient and worn weight loss of the NSc-9 coatings were 0.46 and 29.5 mg, respectively, which were lower than those of the NSc-3 and NSc-15 coatings. In addition, a few shallow scratches emerged on the worn surfaces of the NSc-9 coatings, demonstrating their outstanding anti-wear performance when compared to the NSc-3 and NSc-15 coatings.

In order to study nozzle angle on the abrasion resistance of nickel-titanium carbide (Ni-TiC) composites, the jet electrodeposited Ni-TiC composite coating was fabricated at nozzle angles of 30°, 45° and 60°. The jet velocity and kinetic energy of the electrolyte at different nozzle angles within the given range of 30°–60° were simulated by means of COMSOL software. Additionally, the surface morphology, phase structure, and abrasion resistance of the Ni-TiC composites prepared at various jet angles were investigated using a scanning electron microscopy, energy dispersive spectroscopy, X-ray diffraction analysis, and a friction-abrasion testing machine, respectively. The simulation results indicated that at a nozzle angle of 45°, the jet speed and spraying pressure of the electrolyte were 3.17 m/s and 3.18 × 10⁴ Pa, respectively. The Ni-TiC composites fabricated at nozzle angle of 45° had dense and smooth surface morphology with uniform distribution of TiC nanoparticles. Furthermore, at this nozzle angle, the composite demonstrated the smallest nanoparticle size (60.8 nm) and the highest TiC content (4.82 wt%). These findings confirm that the nozzle angle plays a crucial role in the distribution and incorporation of TiC nanoparticles, directly influencing the abrasion resistance of the composite. Notably, the Ni-TiC composite deposited at 45° exhibited the lowest friction coefficient and minimal mass loss, confirming its superior abrasion resistance.