Modifying the impact toughness of carbon fiber‐reinforced epoxy composites by introducing thermoplastic inserts in the interlaminar layer is state‐of‐the‐art. This article compares the introduction of thermoplastics in continuous and discontinuous form. Test plate samples were produced using unidirectional noncrimp carbon fabrics with two different aircraft resin systems: HEXFLOW RTM6 (Hexcel) and Cycom 890 RTM (Cytec). In addition, Polyamide 12 (PA12) was laid in the interlaminar layer in the forms of two different laid scrims, as powder or as nonwoven fabric (NWF). The performance of the resulting combinations was assessed by testing the samples in Mode I and II interlaminar fracture toughness (GIc and GIIc), interlaminar shear strength (ILSS), and compression strength after impact (CAI). The results show that in nearly all the tests a fine‐mesh laid scrim performs similarly to a NWF with twice the weight per surface area. They show furthermore that the curing dynamics of the resin systems together with the melting characteristics of the thermoplastic during processing have an important effect on the performance of the test samples. Hardening of the resin before the PA12 reaches its melting point hinders the compacting of the thermoplastic. This limits the reduction in the original thickness of the insert, leading to an increase in the sample thickness and, thus, reducing the fiber volume content. Otherwise, the discrete arrangement of the laid scrim has positive effects on the material properties of the composite at elevated temperatures, considerably reducing the falloff in ILSS resulting from the temperature‐dependent Young's modulus of PA12. POLYM. COMPOS., 36:1249–1257, 2015. © 2014 Society of Plastics Engineers

Modifying the impact toughness of carbon composite by means of introducing thermoplastic inserts in the interlaminar layer is state of the art. However, these inlayers reduce the electrical conductivity through the thickness of the composite. Because the combination of good electrical conductivity and high fracture toughness is desirable, a detailed investigation was carried out into additive-enhanced polyamide 12 compound. The modification consisted in compounding graphite, graphene and carbon nanotubes with polyamide 12 in various proportions. After it was introduced into the interlaminar layer, the samples' electrical conductivity was measured and their mechanical properties assessed. Afterwards, these results were compared with various inserts made with unmodified polyamide 12. It turned out that the coarse-mesh laid scrim showed only a slight fall in conductivity. Furthermore, it provided promising results regarding the increase of the interlaminar toughness. Thus, the expensive modification of polyamide 12 can be avoided by using discrete laid scrim.

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