Applied Composite Materials最新文献

A multiscale model is developed for stress analysis and burst speed prediction of a titanium matrix composite (TMC) ring. The proposed multiscale model is based on finite-volume directly averaging micromechanics (FVDAM) to connect the TMC ring and the composite microstructure. Moreover, Bodner-Partom’s constitutive model is adopted to characterise the viscoplasticity of the titanium cladding and the matrix. The effects of viscoplasticity on the mechanical behaviour and burst speed of the TMC ring are presented and discussed for the first time via macromechanical and micromechanical analysis. The results suggest that considering the viscoplasticity of the titanium matrix and cladding leads to a decrease in the burst speed of the TMC ring, especially at elevated temperatures such as 315 ℃ and 482 ℃. Burst rupture of the TMC ring also occurs after a certain time in the load-holding stage at these elevated temperatures and a low, constant angular speed, even though no burst rupture is predicted in the loading stage. Hence, the newly defined load-holding burst speed, which is relative to the load-holding time, is predicted at elevated temperatures. The results of the load-holding burst speed provide more comprehensive information on the safety assessment of a TMC ring at elevated temperatures.

In this work, a numerical model was developed to investigate the layer wise temperature distribution during microwave curing to manufacture carbon fiber composites using COMSOL Multiphysics^® software package. A multivariable nonlinear regression analysis was conducted to acquire the cure kinetics parameters based on the heating rate. The resulting model demonstrated temperature and percentage degree of cure prediction accuracy within an error margin of 6% and 0.62%, respectively. In addition, a comparison was made between the contour of temperature distribution across different layers. The correlation with experimental and simulation data revealed that uniform heating occurred at 180 W due to a longer cycle time compared to power levels of 360 W, 540 W, and 720 W, in the presence of a standing wave. Conversely, the model indicated a temperature gradient of approximately 8.7 ℃, 10.2 ℃, 24.6 ℃, and 36.6 ℃ between the first and last layer for power levels of 180 W, 360 W, 540 W, and 720 W, respectively. Utilizing a dwell period of 65 s at a temperature of 100 ℃, the gradient between the first and last layer reduced to approximately 5.21 ℃, 7.97 ℃, 8.91 ℃, and 9.04 ℃ for power levels of 180 W, 360 W, 540 W, and 720 W, respectively, at the end of the curing process. Furthermore, a comparative examination of temperature distribution and degree of cure at 180 W revealed a higher degree of cure in regions where the temperature was elevated due to the standing wave.

Graphical Abstract

Poly(lactic acid) (PLA) was melt-blended separately with low concentrations of polypropylene (PP) and low-density polyethylene (LDPE) that maintained the total biopolymer content above 89 wt%. Additionally, a multifunctional reactive chain extender was also incorporated to assess the potential compatibility among the constituents. The blends were exposed up to five reprocessing cycles to simulate recycling, with material collection occurring at one and three recycling stages for characterization. Rheology, thermal, and mechanical properties were then evaluated to assess the processing – properties of the resulting materials. In addition, wood flour powder (≤ 250 μm) was compounded into two different system types (PLA: PP and PLA: LDPE) at 30 and 40 wt% to fabricate high-biopolymer content wood-plastic composites (WPCs). The entire composite was then subjected to up to five recycling cycles to elucidate the effects of recycling on different systems. The simulated recycling process induced crosslinking reactions in the case of LDPE, evidenced by an increase in melt viscosity and changes to the zero-shear viscosity ratio of the blended polymers. In the case of PP, recycling led to reduced viscosity likely attributed to temperature and shear mediated chain scission inducing changes in both the matrix and dispersed phase’s viscosity. The study provided valuable insights into the behavior of the materials and composites undergoing through recycling.

To ensure a strong adhesive bond, most standards and adhesive manufacturers specify a maximum adhesive gap of 1 mm when bonding fiber reinforced composite structures. In manufacturing large components, such as joining two halves of wind turbine blades, meeting this gap tolerance specification is impractical; gaps larger than 10 mm are common in large adhesively bonded composite structures using state-of-the-art manufacturing techniques. Currently, there is a lack of fundamental understanding of the failure mechanics of adhesive gaps larger than 3 mm. To create such understanding, glass fiber – acrylic thermoplastic composite panels bonded using different epoxy adhesives within single-lap joint samples with adhesive thicknesses of 0.1 mm, 0.3 mm, 1 mm, 3 mm, 5 mm, and 10 mm were sheared to failure. A transition from cohesive to adhesive failure was observed to occur about 1 mm to 3 mm joint thicknesses. Plotting the shear stress normalized by the ratio of the joint width to thickness as a function of the joint thickness normalized by the joint length is shown to result in the ability to fit simple empirically derived models of the cohesive-to-adhesive failure transition, regardless of the adhesive. Furthermore, using these normalized variables, all the observed cohesively failed specimens collapse to a single master curve, as do the adhesively failed specimens.

The structural design of the brake disc of urban rail trains, especially the design of the heat dissipation rib structure, affects the heat dissipation performance of the brake disc. Unreasonable design can lead to poor heat dissipation performance and generate energy consumption caused by large air-pumping resistance. However, the current structural design method for brake discs does not consider material characteristics and continues with materials such as steel and iron. There is no long-term service performance testing applicable to brake disc service conditions for lightweight and high-strength materials such as aluminum matrix composites. In addition, there is no comprehensive and systematic analysis of the structural design of cooling ribs. Therefore, a structure of SiCp/A356 brake discs for urban rail trains was designed in this work. Different from the previous design method, long-term performance testing of materials was conducted first, and then the heat dissipation performance and energy loss performance of different cooling rib structures were systematically analyzed to select the appropriate cooling rib structure. Based on long-term performance testing results, cooling rib optimization, and material forming process, a new brake disc structure was designed. The thermal-fluid–solid multi-field coupling simulation was conducted on the new structure brake disc under emergency braking and full round-trip conditions, and bench tests were conducted to verify the reliability of the simulation. Based on comprehensive simulation and bench test results, the new structure SiCp/A356 brake disc meets the established operating conditions. This design method considers material properties, multi-field coupling simulation, and engineering practice, which can a provide reference for the design of other brake discs and has high engineering application value.