Investigation on tensile modulus of lumen-bast fiber reinforced composites using multiscale simulation method

Natural bast fibers offer comparable specific strength and stiffness to glass fibers, while being cost-effective, widely available, and eco-friendly. Consequently, bast fiber-reinforced composites show potential for extensive use in vehicles like cars, high-speed trains, and airplanes. The mechanical performance of these composites is crucial for their application, making the efficient design and development of bast fiber-reinforced composites a research focus. However, unlike synthetic fibers such as glass and carbon fibers, plant-based bast fibers have more complex microcavity structures. To accurately predict and control the tensile properties of bast fiber-reinforced composites, this study investigates the tensile modulus of ramie fiber reinforced polypropylene composites using a multi-scale simulation approach.

By integrating the rule of mixtures and Micro-CT technology, this study proposes a theoretical formula for calculating the effective elastic modulus of bast fibers based on their lumen structure characteristics. Using a multi-scale simulation approach, a representative volume element (RVE) model of ramie fiber-reinforced polymer composites (RFPC) is constructed. The elastic modulus of the composites is analyzed from micro/macro scales, and the RVE multi-scale modeling's validity and reliability are verified through tensile experiments on RFPCs. An orthogonal experimental design and polynomial fitting method are employed to derive a predictive formula for the elastic modulus of ramie fiber-reinforced composites, with fiber content, cavity fraction, fiber orientation, and fiber aspect ratio as independent variables. The study also systematically reveals the main effects and synergistic interactions of these fiber parameters on the tensile modulus of RFPCs.

An orthogonal experimental design was used to investigate the effects of ramie fiber parameters (fiber content, cavity fraction, fiber orientation tensor component, fiber aspect ratio) on the tensile modulus of ramie fiber-reinforced composites. Range and variance analyses identified the weight order of these parameters on the tensile modulus as follows: fiber content > fiber aspect ratio > fiber orientation tensor component > lumen volume fraction. The optimal parameter combination for maximum tensile modulus was determined to be A4B1C4D4: fiber content at 20wt%, cavity fraction at 16vol%, fiber orientation tensor factor λ1 at 1.0, and aspect ratio at 14. A polynomial fitting method was employed to derive a theoretical formula for quantitatively predicting the tensile modulus of ramie fiber-reinforced composites. Dimensional reduction identified fiber content and fiber aspect ratio as significant factors influencing the tensile modulus of composites. The tensile elastic modulus increases with rising fiber content (5-20wt%) and fiber aspect ratio (2-14). Surface plots facilitated the understanding of the synergistic effects between fiber parameters on the tensile modulus. Higher fiber content increases the composite's elastic modulus due to the higher stiffness of fibers compared to the matrix. A larger fiber aspect ratio correlates with more interfaces between fibers and the matrix, enhancing force transfer and thus increasing the elastic modulus. Larger fiber lumen volumes reduce fiber stiffness, slightly decreasing the composite's tensile modulus. Lastly, the fiber orientation tensor component value closer to 1 indicates the alignment of fibers with the load direction, resulting in a higher elastic modulus in that direction.Conclusions: This study develops a homogenized equivalent model for bast fibers with microstructural characteristics of lumens. Using ramie fiber-reinforced polypropylene composites as the research subject, a multi-scale RVE model based on lumen features was constructed. The elastic modulus of the composites was predicted under various fiber parameters. The proposed method for predicting the elastic modulus of plant-based bast fiber-reinforced composites based on lumen structure aims to provide new theoretical approaches and methods for more accurately predicting and controlling the performance of this class of composites.