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Thermal expansion molding process (TEMP) is a sophisticated molding technique for creating complex sandwich composites. The core key of TEMP is a high‐performance, thermally expandable resin film. In this study, the epoxy resin is used to create a specific crosslinking network that can provide the support force required for the stable molding of the vesicles during the expansion process of the foaming agent. The curing process of the resin was determined by analyzing the change in the exothermic amount of the epoxy resin during the curing process and the flow behavior of the resin. The pore size distribution of the epoxy foam was investigated, and the expansion force of the thermally expandable resin was tested. The TEMP molding process was compared with the vacuum bag press molding (VBPM) process. The TEMP molding technique increased tensile and compressive strength by about 25%, flexural strength by 34.5%, and shear strength by 54.5%. Finally, the section on microanalysis of the comparative materials and the short beam bending experiments of the sandwich structure provides a theoretical foundation for developing complicated sandwich structures. Highlights: Preparation of thermally expandable epoxy prepregs with stabilized foaming by means of pre‐curing.The effects of curing temperature, foaming agent content and expansion multiplicity on the thermal expansion force of epoxy prepreg adhesives were investigated.Thermally expandable epoxy prepreg molding composites with different expansion multiplicities and analysis of the mechanical properties of the composites.Preparation of foam core sandwich composites by thermal expansion in‐mold monolithic molding process and their verification by bending experiments. [ABSTRACT FROM AUTHOR]

In this work, a dicyclopentadiene monomer/Grubbs 2 catalyst was added to a mixture of epoxy oligomers and methyl nadic anhydride to obtain a poly‐dicyclopentadiene (DCPD) modified epoxy cross‐linked network via sequential curing. The hybrid resin was used as a matrix for preparing carbon fiber composites. The results indicated that the addition of DCPD monomers significantly reduced the viscosity of the epoxy resin. The toughness and heat resistance of the co‐cured resin was improved without significant loss of strength, which was attributed to the high compatibility between epoxy and the modifier polymer. Regarding the composites, the flexural strength of the hybrid resin‐derived composite first increased and then diminished slightly. Meanwhile, the mode‐I interlaminar fracture toughness continued to increase with the increase of PDCPD content compared to the non‐modified composites. Generally, the change trend of the above properties in the composites was consistent with the change trend of the strength and toughness exhibited in the bulk resin with increasing PDCPD contents, while the change extent was inconsistent due to factors such as fiber volume content and interfacial bonding. Highlights: The epoxy/PDCPD hybrid resin system was obtained via sequential curing.The PDCPD as modifier can reduce the viscosity of the epoxy curing system.The toughness and heat resistance of the PDCPD modified epoxy resin was improved.The loss in flexural strength of the hybrid resin system was insignificant.The GIC of the epoxy composites modified with PDCPD improved appreciably. [ABSTRACT FROM AUTHOR]