Assessment of the influences of fiber volume fraction gradients on cure-induced residual stresses and shape deformations in U-shaped CFRP laminates

Accurate prediction of cure-induced deformations (CIDs) and residual stresses (RSs) is essential for manufacturing high-precision carbon fiber reinforced polymer (CFRP) components. However, prevailing models for composites curing analysis rest on the simplified assumption of a uniform fiber volume fraction (FVF), which is often physically inaccurate. Such a simplification becomes particularly problematic in complex geometries like U-shaped laminates, where the through-thickness fiber volume fraction gradient (FVFG) can interact with curvature more significantly, causing undesirable stress distributions. Given that FVFG is a proven experimental reality, this study moves beyond the uniform-FVF paradigm by developing an advanced modeling framework that explicitly incorporates the through-thickness FVFG alongside a path-dependent constitutive model. Based on the proposed framework, we quantitatively evaluated the influence of FVFG on the CIDs and RSs in U-shaped CFRP laminates. Results demonstrate that models neglecting FVFG are fundamentally inadequate: they produce spring-in angle mis-predictions ranging from −77.9% to +45.9% and severely underestimate residual stresses. Moreover, the FVFG-integrated models capture interlaminar stress jumps—a potential delamination driver absent in uniform-FVF models. This work establishes FVFG as a significant source of material heterogeneity. Its explicit integration is essential for reliable predictions of cure-induced quantities and thus a critical step towards improving manufacturing quality.