Size‐Dependent Central Notch Behavior of 3D Woven Composites Under Tensile Load

ABSTRACT This paper presents an experimental investigation of the size effect in 3D fiber‐reinforced composites (FRC) caused by a central notch. It highlights the influence of different notch shapes (circular and racetrack) and notch sizes (5, 7.5, and 10 mm) on the open‐hole tensile performance of 3D‐FRC. Four different configurations were investigated with both constant and variable notch size (hole diameter ( D ) or slot length ( H )) to width ( W ) ratios, that is, constant W and variable D , variable W and variable D , constant W and variable H , and variable W and variable H . As the notch size increases for a variable D / W ratio, the net strength remains nearly constant and close to the unnotched strength, while gross strength decreased by up to 46.0% and 38.3% in warp‐ and fill‐loaded specimens, respectively. In comparison, for a constant D / W ratio, net and gross strength decreased by up to 40% and 26%, respectively, for warp‐ and fill‐loaded specimens. For specimens with variable D / W or H / W ratios, the normalized strength is close to the straight notch insensitive line, indicating the notch insensitive response due to small net stress concentration factors (SCF). In contrast, for specimens with constant D / W or H / W ratios, the normalized strength is below the straight notch‐insensitive line, indicating a notch‐sensitive response due to relatively higher SCFs. This study provides valuable insights for the design and optimization of 3D woven composite structures, considering the effects of geometric features on stress concentration and failure mechanisms.