Determination of Composite Laminate B-Basis Values for Low-Altitude Aircraft Using Small-Sample Statistics

The long test cycle and high cost of generating composite design allowables constrain the development of low-altitude aircraft. This study investigates a calculation method for single-batch, small-sample B-basis values of multidirectional laminates. Eight variants of the lamina variability method (LVM) and the batch normal method (Ward method) were evaluated using 2622 specimens from five composite material systems, with multi-batch B-basis values calculated using the CMH-17-1G single-point method after the prescribed CV adjustment as the reference. Four materials were used to establish a method-selection rule, and the fifth was used for validation. The results show that the lamina coefficient of variation used by LVM-based methods should not be lower than the measured single-batch value, and the empirical upper limits for tensile, compressive, and bearing/damage-related tests are 6%, 8%, and 10%, respectively. When these conditions are satisfied, LVM with a Ward mean reduction is used; otherwise, the Ward method with stronger reduction is used. After applying the rule, 90.7% of 366 results were within 90–105% of the multi-batch B-basis values, 79.5% were lower than the reference by no more than 10%, and only 0.8% exceeded the reference by at least 5%. The proposed rule provides generally conservative small-sample estimates of multidirectional-laminate B-basis values relative to the reference, supporting strength assessment during the development of composite structures for low-altitude aircraft.