Failure‐Mode Transition in CFRP Axial Compression Testing: Coupled Effects of Tab Thickness and Clamping Pressure

The axial compression testing of CFRP laminates requires stable load introduction, which is governed by the coupled constraints imposed by the tabs and fixture. This study investigates the coupled effect of tab thickness and clamping pressure on failure‐mode transition in CFRP laminates tested using a hydraulic composites compression fixture. A 4 × 4 experimental matrix combining tab thicknesses (1–4 mm) and clamping‐pressure levels (5–20 MPa) was examined. The experiments revealed a transition from end‐crushing, through a mixed compression‐shear stage, to shear‐dominated fracture as the combined tab‐fixture constraint increased. Increasing clamping pressure raised S 33 of working region, indicating stronger through‐thickness confinement that suppressed end instability and facilitated load transfer into working region. The value of S 12 of working region also increased with clamping pressure, but its amplification was spatially nonuniform and concentrated near the tab terminations. Increasing tab thickness improved end stabilization but also strengthened the mechanical transition between the constrained tabbed region and the free working region. Consequently, insufficient constraint promotes end‐crushing, intermediate constraint enables stable working‐region loading, whereas excessive combined constraint shifts the governing mechanism toward shear fracture. These results demonstrate that reliable CFRP compression testing requires balancing end stabilization against localized shear transfer.