Distribution-Aware Estimation of A-/B-Basis Characteristic Values for Natural-Fiber Composite Laminates from Single-Source Tensile Data

Natural-fiber composites exhibit large property scatter, and multi-batch qualification data are rarely available. Using 590 tensile specimens from ten flax, jute, and carbon-fiber laminate groups in a single experimental program, we applied established one-sided lower tolerance limits as approximations of A-basis (99% coverage, 95% confidence) and B-basis (90%, 95%) values for strength, modulus, and failure strain, and compared normal-theory, bootstrap, family-specific pivotal, and selection-robust routes. A Monte Carlo study (eight scenarios, 5000 replicates) showed that the pivotal limit reached a mean A-basis confidence of 0.949 when the family was known but only 0.896 (minimum 0.805) when the family was selected by AIC; an envelope over all three families reached at least 0.944 at the cost of lower limits. An empirical bootstrap cannot exceed a confidence of 1–0.99n (0.311 at n = 37). Two jute-twill records with a zero video-strain reading at peak load were excluded from the strain analysis by a rule based solely on the measurement record, raising the A-basis failure strain by 45%. Retention rankings partly changed when the sample size was equalized. In the five groups that contain a second file-name series, tensile strength differed significantly between the series (Welch p ≤ 0.008), so the pooled limits for these groups assume identically distributed specimens. The values are screening approximations and not design allowables.