This study investigates the effect of static magnetic field exposure (~0.07 T, 30 min) during curing (TDC) and after full cure (TAC) on an unfilled epoxy resin, compared against untreated (UTS) and thermally treated (HTS) controls. Characterisation via modulated DSC, ATR-FTIR, TGA, and DMA revealed that chemical structure (FTIR) and thermal stability (TGA) remained unaffected. However, glass transition temperature (Tg) exhibited strong process-dependent variations. Calorimetric Tg ranged from 69.6 °C (TDC) to 74.4 °C (TAC) versus 72.9 °C (control) (p = 0.0007). Viscoelastic Tg (tan delta peak) peaked at 102.8 °C for TDC and dropped to 88.0 °C for TAC (F(3,8) = 94.4, p < 0.001), while storage modulus showed no significant change (p = 0.170). Because HTS controls did not replicate this response, the shift in Tg is attributed to spatially non-uniform thermal history during exposure rather than direct diamagnetic molecular alignment.
This study presents algorithms for additively manufacturing semi-woven carbon fiber composite skins over singly and doubly curved non-planar surfaces through an innovative remapping/wrapping algorithm. The algorithm efficiently generates 5-axis continuous fiber deposition paths from 2D fiber layout patterns in a way that reduces geometric distortion in fiber placement that normally occurs when planar 2D toolpaths are linearly projected onto non-planar surfaces. A customized 5-axis 3D printer equipped with a modified continuous carbon fiber deposition head is used to validate feasibility of the algorithm by printing a semi-woven carbon fiber skin onto a hemi-spherical surface. Toolpaths are smoothened prior to printing to reduce jerking motions in the 5-axis machine's A/B axes.
Composite winding processes offer the possibility to produce lightweight pressure vessels, a key element in hydrogen mobility, with the potential to reduce global carbon dioxide emissions. Digitizing winding processes has significantly gained attention because of the potential to improve the ecological and economic sustainability of both the process and the product. Numerous process parameters influence manufacturing performance and overall sustainability. This necessitates precise parameter adjustment. However, computing process parameters is not trivial and often imprecise, especially with regard to process-related fluctuations. Consequently, inline measurement systems are needed to acquire actual parameter values and enable process simulations, the generation of digital twins, and closed-loop controls. This paper provides an overview of measurement principles and sensors for monitoring composite winding processes, addressing their implementation, as well as studies on their general feasibility and accuracy. Presented are principles for monitoring the input material, fiber tension, temperature, length and speed, as well as methods for acquiring impregnation properties (resin or volatile content), tack, and fiber deposition geometry (winding angle, gaps, overlaps). The review critically compares the methods’ advantages and restrictions concerning inline use in composite winding and assesses their technology readiness levels as well as future potential for industrial inline process monitoring in composite winding. A decision aid is provided for selecting suitable sensor principles according to the targeted process or material parameters. The early publications presented in this overview address simple measurements and date back to the mid-1990s, while data-driven technologies such as artificial intelligence are the subject of current research.
Carbon fiber-reinforced polymers are increasingly employed in load-bearing structures such as thick reservoirs, pipes or flywheels where cure-induced defects can impair performance and dimensional accuracy. This study investigates whether interlaminar performance and microstructure quality are preserved in tow-wound composites fabricated via partial pre-curing and in situ compaction, which proved to mitigate the risk of thermal overshoot and stress build-up. A proof-of-concept manufacturing line is developed to produce wound rings under varying pre-cure and compaction conditions. Interlaminar performance is evaluated through short-beam and double cantilever beam tests, supported by microscopy. Results show void contents below 3%, although the fiber volume fraction (33%-41%) remains lower than for prepreg references (53%-58%). Interlaminar properties are comparable between tow-wound and prepreg laminates, with no significant degradation due to pre-curing or compaction. The results demonstrate that partial pre-curing combined with local compaction does not degrade interlaminar performance, supporting the feasibility of such strategies for efficient and automated manufacturing.
Precise control of gripping forces is essential for automated preforming of technical textiles to prevent material damage while ensuring reliable handling. This study investigates the holding force thresholds causing shear deformation in four glass fiber-based fabrics: one woven fabric and three non-crimp fabrics (NCFs). A novel experimental setup combining a universal testing machine, a coanda gripper, and a laser profile scanner was used to detect the onset of relative motion and determine the critical holding forces. Preforming tests with two coanda grippers evaluated the maximum forming height using two different pressure configurations. The results demonstrate a linear relationship between applied pressure and holding force, with critical forces inversely correlated to air permeability. The analysis shows that friction properties and flexural stiffness are critical factors for bond reliability, with flexural stiffness exhibiting a strong negative correlation (HR = 0.013) with the risk of failure. The regression analysis also shows that optimal alignment is crucial. These results underscore that strategic material selection and optimal fiber alignment can positively influence the forming height.
