A series of tensile tests has been performed to determine the effect of specimen size on the mechanical response of composite laminates that were scaled at the sublaminate level. The two material systems studied were AS4/3502 and APC-2. In the case of AS4/3502, three generic layups were considered: [±30/90 2 L,, [±45/0/90]™, and [90/0/90/0]™ deg, where n = 1, 2, 3, or 4. For the APC-2 system, only the [±45/0/90],,.? deg layup was studied with n = 1 and 4. The effect of specimen size was examined with respect to first-ply failure strain, delamination onset strain, and ultimate stress and strain. In general, the strength of scaled specimens increased with increasing specimen size. Models from the literature were applied to attempt to explain the variations observed. It was found that the effect of ply constraint is not addressed properly in existing theories.

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It has been demonstrated by several researchers that composite materials exhibit scaling effects both in unidirectional and multidirectional specimens. This has an important impact on the design and manufacture of full scale structures. In the current work, the authors present a wide range of experimental data for scaled composite laminates under tensile, flexural and compressive loading. Data for both blocked ply (so-called ply-level) and distributed ply (so-called sublaminate-level) thickness scaling are presented. Laminates studied include the following stacking sequences: [45/-45/45/-45]s, [45/-45/0/90]s, [45/-45/90/0]s, [45/90/-45/0]s, [45/-45/45/-45/0]s, [45/-45/0/0]s, [90/0/90/0]s. In general, ply-level scaling leads to degraded performance with increased specimen size in all stacking sequences, under all loading conditions. Sublaminate-level scaling also leads to a lowering of strength and strain to failure, although the effect is much less pronounced than in ply-level scaling. Typically, the strength of these specimens decreases by about 5% as the size of the specimens is quadrupled.

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