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

The accurate prediction of failure of load-bearing fiber-reinforced structures remains a challenge due to the complex interacting failure modes at multiple length scales. In recent years however, there has been considerable progress, in part due to the increasing sophistication of advanced numerical modelling technology and computational power. Advanced discrete crack and cohesive zone models enable interrogation of failure modes and patterns at high resolution but also come with high computational cost, thus limiting their application to coupons or small-sized components. Adaptively combining high-fidelity with lower fidelity techniques such as smeared crack modelling has been shown to reduce computational costs without sacrificing accuracy. On the other hand, machine learning (ML) technology has also seen an increasing contribution towards failure prediction in composites. Leveraging on large sets of experimental and simulation training data, appropriate application of ML techniques could speed up the failure prediction in composites. While ML has seen many uses in composites, its use in progressive damage is still nascent. Existing use of ML for the progressive damage of composites can be classified into three categories: (i) generation of directly verifiable results, (ii) generation of material input parameters for accurate FE simulations and (iii) uncertainty quantification. Current limitations, challenges and further developments related to ML for progressive damage of composites are expounded on in the discussion section.

Composite structures are susceptible to the combined effect of seawater aging and stress load in the marine environment. This paper investigates the moisture absorption and mechanical properties of CFRP immersed in seawater at 70 °C and subjected to sustained bending. The moisture absorption process of CFRP in a moisture-force coupling environment was characterized, and the effect of moisture-force coupling on the bending and tensile properties of laminates was studied. The results show that the maximum moisture content and diffusion coefficient of the sample decrease with the increase of the sustained bending stress level. It is found that the Fick model can better describe the water diffusion process of thicker samples than the Langmuir model. The bending stress causes the post-curing rate of the sample to slow down, and the duration becomes longer. The tensile strength of the sample at a 10.5% stress level exceeds the initial value of 8.62% after immersion for 2016 h. The sustained bending stress aggravated the degradation of the flexural properties. The sample under 30% bending stress decreased by 18.08% after immersion for 2016 h, while the unstressed sample only decreased by 11.90%. An empirical prediction model based on the Fick model and experimental data is proposed to describe the degradation of bending strength, verified by the existing literature data.

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.

In this work, a novel unsupervised machine learning (ML) method for automatic image segmentation of low velocity impact damage in carbon fiber reinforced polymer (CFRP) composites has been developed. The method relies on the use of non-parametric statistical models in conjunction with the so-called intensity-based segmentation, enabling one to determine the thresholds of image histograms and isolate the damage. Statistical distance metrics, including the Kullback–Leibler divergence, the Helling distance, and the Renyi divergence are used to formulate and solve optimization problems for finding the thresholds. The developed method enabled rigorous and rapid automatic image segmentation of the grayscale images from the micro computed tomography (micro-CT) scans of the impacted CFRP composites. Sensitivity of the segmentation results with respect to the thresholds obtained using different statistical distances has been investigated. Based on the analysis of the segmentation results, it is concluded that the Kullback-Leibler divergence is the most appropriate statistical measure and should be used for automatic image segmentation of impact damage in CFRP composites.

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.

Composites reinforced with fibres have a high specific strength and are very rigid, making them useful in the energy, aerospace, and automotive sectors. Composite constructions are susceptible to internal damage and residual strength loss due to unanticipated exterior impacts in the workplace. Addressing the disposal of composite materials sustainably is another persistent challenge. Low-velocity Impact at room temperature, -20 ^oC and -50 ^oC temperatures, and post-impact flexural (FAI) behaviour of glass/epoxy composite laminates are studied with the inclusion of recycled milled carbon (rmCF), recycled milled Kevlar (rmKF), and hybrid recycled fibres (rmHF) as fillers. Using ultra-sonication and mechanical stirring procedures, the glass/epoxy laminates were enhanced with 3.5% rmC Fillers, 0.375% rmK Fillers, and 0.375% rmH Fillers by weight of epoxy. The impact force, absorbed energy, residual flexural strength, and growth of damage area were used in investigations of surface roughness and hardness and the crash performances to evaluate the reaction of neat glass epoxy and glass epoxy composites loaded with recycled milled fillers to low-velocity impacts at sub-zero temperatures. With a peak force increase of 97.4%, a damaged area drop of 28%, and a reduction of 30.3% and 54.1% in surface roughness, respectively, the rmHF composites outperformed the baseline samples. The residual flexural strength of rmH filler samples was 14.2% more than that of raw glass epoxy composites during LVI testing, as measured in a 3-point bending test conducted at -20 ^oC. Recycled milled filler composite has better impact and FAI characteristics, making it a promising material for load-bearing uses in sub-zero temperatures.

Despite being invented several decades ago, fiber metal laminates (FMLs) still encounter challenges in large-scale manufacturing, especially in forming small and complex-shaped components. These challenges arise from the limited strain rate of the fiber layers compared to the metallic layers. Consequently, conventional approaches to form FML parts are often inadequate. To produce parts free of defects such as fractures and wrinkles, this study investigates the effects of Thermo-stamping (TH-S), in addition to fiber orientation, on the forming behavior of FMLs, employing two different aluminum layer thicknesses. A comprehensive approach combining finite element simulations and experimental analyses was employed. The study investigated thinning of aluminum alloy layers, stress distributions across different layers, and the influence of fiber orientation. The FML blanks are made of a middle woven glass fiber prepreg with a thickness of 0.2 mm, using a thermosetting epoxy system, and Al 2024-T3 alloy sheets with varying thicknesses of 0.3 mm and 0.5 mm. Material behavior was evaluated using Abaqus software, applying the Johnson-Cook criterion for damage initiation in ductile metals and Hashin’s theory for damage initiation in fiber-reinforced composites. These simulations were then compared with experimental results. The findings highlight the potential of the TH-S process to enhance the forming performance of FMLs, particularly evident in the case of the 0°/45° middle layer fiber, which exhibits a higher forming depth and a more uniform thickness distribution. Additionally, a greater flexibility of the glass fiber under the 0°/45° layup compared to the 0/90 layup was detected. This flexibility provides the aluminum layers with more freedom of deformation in the plastic domain. These advancements hold promise for widespread industrial applications of FMLs.