Chensong Dong

Hybrid carbon/glass fibre reinforced polymer composites offer attractive opportunities for balancing structural performance, weight, and material cost in bending-dominated applications. However, the design of such laminates is challenging due to the mixed discrete–continuous nature of the design variables, comprising stacking sequence and fibre volume fraction, and the highly nonlinear influence of these variables on flexural strength. This study proposes a physics-informed machine learning framework for the multi-objective optimisation of hybrid composite laminates subjected to three-point bending. A finite element dataset consisting of 240 laminate configurations was generated to characterise the relationship between laminate architecture and flexural strength. Three ensemble learning algorithms, namely Random Forest, Extra Trees, and GB Regression, were evaluated as surrogate models. Among these, GB achieved the highest predictive performance, yielding a five-fold cross-validation coefficient of determination of (R2 = 0.899 ± 0.027) and an independent test-set coefficient of determination of (R2 = 0.946), with a root mean square error of 44.8 MPa. Unlike fully data-driven optimisation approaches, machine learning was employed exclusively for flexural strength prediction, while laminate cost and weight were evaluated analytically using rule-of-mixtures formulations derived from constituent properties. The surrogate model was integrated into a Pareto-based optimisation framework and applied to evaluate 500,000 candidate laminate configurations under minimum flexural strength requirements of 1000 MPa and 1300 MPa. The optimisation identified 236,692 and 29,982 feasible laminate configurations for the respective strength constraints and revealed clear trade-offs between structural weight and material cost. The results further demonstrated that hybrid laminate architectures provide cost-effective solutions at moderate strength requirements, whereas increasingly carbon-dominant designs become necessary as strength demands increase. The proposed framework combines the predictive capability of machine learning with the transparency of physics-based modelling, providing an efficient and interpretable tool for hybrid composite laminate design. The methodology offers practical guidance for balancing performance, weight, and cost and can be readily extended to incorporate additional performance criteria, manufacturing constraints, and sustainability objectives.

Intralayer hybridisation provides a powerful strategy for tailoring the stiffness–strength–ductility balance of fibre-reinforced composites through architecture control. This study investigates the flexural behaviour of carbon/glass intralayer hybrid composites with varying carbon-to-glass (C:G) ratios and degrees of dispersion using a finite element modelling framework supported by experimental validation against published flexural test data. Four hybrid ratios (C:G = 2:1, 1:1, 1:2, and 1:4) and multiple dispersion levels were examined under three-point bending to quantify the effects of intralayer architecture on flexural strength, modulus, and strain to failure. The results show that carbon-rich hybrids retain high flexural stiffness and strength while achieving substantial improvements in failure strain and damage tolerance compared with pure carbon laminates. In these systems, flexural strength is strongly influenced by dispersion, with moderate-to-high dispersion improving strain compatibility, delaying tensile-side carbon fibre fracture, and enhancing strength. In contrast, glass-dominated hybrids exhibit flexural behaviour that is largely insensitive to dispersion, with strength and modulus following near rule-of-mixtures trends and failure governed by progressive glass fibre and matrix damage. Across all hybrid ratios, flexural modulus is controlled primarily by fibre volume fraction, whereas flexural strength and failure strain depend sensitively on intralayer architecture when carbon fibres remain the dominant load-bearing phase. These findings clarify the respective roles of hybrid ratio and dispersion in governing flexural performance and extend recent studies by demonstrating a systematic transition from dispersion-dominated to ratio-dominated behaviour as glass content increases. The results provide mechanistic insight and practical design guidance for optimising intralayer hybrid composites for lightweight, damage-tolerant structural applications.

Fibre-reinforced hybrid composites offer an effective balance between strength, weight, and cost by combining multiple fibre types within a single matrix. This study focuses on optimising the design of carbon/glass fibre-reinforced hybrid composites under combined bending and torsional loading using finite element analysis (FEA) and response surface methodology. Twelve different layup configurations, including sandwich and non-sandwich hybrid designs, were analysed to identify the optimal ply angles and fibre volume fractions that maximise failure load while minimising material cost and density. The results reveal that sandwich-type layups, such as [C₃G]_S, [C₂G₂]_S, and [CG₃]_S, demonstrate superior strength-to-weight performance, achieving failure loads exceeding 300 N. The study also confirms that optimal ply angles range from 12° to 30°, depending on the layup configuration, and that increasing the carbon fibre volume fraction generally enhances failure load, though an optimal balance with glass fibres must be maintained. The findings provide valuable design guidelines for engineers seeking to tailor hybrid composites for aerospace, automotive, and structural applications. Future work should focus on experimental validation and extending the analysis to additional loading conditions, such as impact and fatigue, to further improve the robustness of hybrid composite structures.

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This study investigates the biodegradability and water absorption properties of Macadamia nutshell powder and poly(lactic acid) (PLA) biocomposites using a Design of Experiments (DOE) approach. The influences of processing methods, the Macadamia nutshell powder’s weight content, and the powder’s condition are studied. A biodegradability test is performed in accordance with the American Society for Testing and Materials (ASTM) D5338-11 by burying the test specimens in wet garden soil at a controlled temperature of 50 °C and 100% humidity. The specimens obtained by counter-rotating processing exhibit varying weight loss patterns with an increasing powder weight content, while the specimens obtained by co-rotating processing demonstrate consistent behaviour. This study highlights the complex nature of PLA biodegradation, which is affected by diverse factors such as test conditions and environments, thereby contributing to a deeper understanding of the sustainability implications. A water absorption test is carried out in accordance with ASTM D570-98. It is shown that the water absorption characteristics are predominantly determined by the hydrophilic nature of Macadamia nutshells, with an increased powder weight content leading to higher absorption. Pure PLA, due to its hydrophobic nature, exhibits minimal water absorption. By unravelling the complexities of PLA biodegradation and water absorption in Macadamia nutshell and PLA biocomposites, this study not only advances the understanding of materials’ behaviour but also underscores the potential sustainability implications of utilizing natural resources in composite materials. This research contributes valuable insights to the broader discourse on environmentally friendly materials and their role in promoting sustainable practices.

An eco-efficiency optimisation study on unidirectional carbon/glass fibre-reinforced hybrid composites with natural fibre (i.e., flax) and without flax is presented in this paper. The mechanical performance was assessed by determining the flexural properties obtained via finite element analysis (FEA)-based simulation. Given the required flexural strength, optimal candidate designs were found using a set of design rules and regression analysis, with minimising the cost and weight being the objectives. An eco-efficiency framework was applied to determine the eco-efficient hybrid composites. Life cycle assessment was an indispensable component of the framework as it helped determine the life cycle environmental impacts and costs of the hybrid composite materials. The environmental impacts and cost values were converted to the eco-efficiency portfolios of these composites for both comparison and selection purposes. The hybrid composites using bio-based flax fibre have been found to be eco-efficient in most of the cases due to the avoidance of energy-intensive and expensive reinforcing materials. The environmental impacts of the hybrid composites using flaxes are 12 to 13% less than the ones using no flaxes and the former are 7 to 13% cheaper than the latter, making the flax-based hybrid composites eco-efficient.