Design and fabrication of variable stiffness composite laminates with enhanced dynamic behavior
Topic(s) : Material and Structural Behavior - Simulation & Testing
Co-authors :
Peiman KHANDAR SHAHABAD (TURKEY), Mirmeysam RAFIEI ANAMAGH (IRELAND), Gokhan SERHAT (BELGIUM), Ipek BASDOGAN , Bekir BEDIZ (TURKEY)Abstract :
Fiber-reinforced composites (FRC) find widespread application across various industries due to their exceptional mechanical properties such as a lower weight-to-stiffness ratio. Traditional constant stiffness (CS) composite laminates involve 0, +-45, 90 degree layers with straight fibers. However, advanced manufacturing technologies enable the use of long curvilinear fibers to produce variable stiffness (VS) composite structures with enhanced mechanical performance. Nevertheless, VS composite design encounters modeling difficulties such as non-convexity and high computational time as well as manufacturing problems such as wrinkles, gaps, and overlaps.
This study introduces a three-step design framework to design VS laminates: (i) optimization of lamination parameters, (ii) retrieval of discrete fiber distribution, and (iii) path-planning/determination of curvilinear fiber paths. To address the aforementioned challenges, a computationally efficient meshless/spectral modeling approach based on Chebyshev polynomials is employed. The stiffness distribution is expressed via lamination parameters (LPs) to avoid pre-constraining the lay-up configuration and obtain a convex design domain. The focus is on symmetric and balanced laminates, thus, two LPs are sufficient to model the stiffness properties. The optimal LP distributions are obtained by defining two independent LPs either at each sampling point or only at master points. In the latter case, the LP pairs anywhere on the domain can be found using interpolation/extrapolation methods.
The developed methodology is tested on different fundamental frequency maximization problems. The obtained optimal LP designs are validated via comparisons with the results from literature and finite element analysis. Then, employing the trigonometric relation between LPs and the number of layers with distinct fiber angles, discrete fiber angles at each sampling point are attained. To obtain manufacturable and continuous curvilinear fiber paths, streamline and normalized-cut segment techniques are adopted. The normalized segment method proves more efficient in overcoming manufacturing constraints (such as gaps and overlaps) compared to the streamline method.
Finally, using an automated fiber placement (AFP) machine, designed optimal CS and VS laminates are fabricated using 8 and 24 symmetric and balanced layers. Modal analysis results for free boundary conditions demonstrate that the VS composite panels provide up to 8% higher fundamental frequency compared to the CS panels. Experimentally observed natural frequencies are generally 10% lower than the computational results due to fabrication errors/limitations and/or simplifications in the modeling process.
This study introduces a three-step design framework to design VS laminates: (i) optimization of lamination parameters, (ii) retrieval of discrete fiber distribution, and (iii) path-planning/determination of curvilinear fiber paths. To address the aforementioned challenges, a computationally efficient meshless/spectral modeling approach based on Chebyshev polynomials is employed. The stiffness distribution is expressed via lamination parameters (LPs) to avoid pre-constraining the lay-up configuration and obtain a convex design domain. The focus is on symmetric and balanced laminates, thus, two LPs are sufficient to model the stiffness properties. The optimal LP distributions are obtained by defining two independent LPs either at each sampling point or only at master points. In the latter case, the LP pairs anywhere on the domain can be found using interpolation/extrapolation methods.
The developed methodology is tested on different fundamental frequency maximization problems. The obtained optimal LP designs are validated via comparisons with the results from literature and finite element analysis. Then, employing the trigonometric relation between LPs and the number of layers with distinct fiber angles, discrete fiber angles at each sampling point are attained. To obtain manufacturable and continuous curvilinear fiber paths, streamline and normalized-cut segment techniques are adopted. The normalized segment method proves more efficient in overcoming manufacturing constraints (such as gaps and overlaps) compared to the streamline method.
Finally, using an automated fiber placement (AFP) machine, designed optimal CS and VS laminates are fabricated using 8 and 24 symmetric and balanced layers. Modal analysis results for free boundary conditions demonstrate that the VS composite panels provide up to 8% higher fundamental frequency compared to the CS panels. Experimentally observed natural frequencies are generally 10% lower than the computational results due to fabrication errors/limitations and/or simplifications in the modeling process.