Fiber-reinforced composite material and sandwich structure

A fiber-reinforced composite material comprising:

• a resin (A);
• and reinforcing fibers (B), and including:
• a porous structure portion having micropores with an average pore diameter of 500 μm or less as measured by a mercury intrusion method;
• and a tunnel-shaped coarse cavity portion defined by the porous structure portion and having a maximum length of more than 500 μm as a cross-sectional opening portion, wherein the tunnel-shaped coarse cavity portion extends in an in-plane direction of the fiber reinforced composite material, wherein the in-plane direction is orthogonal to a thickness direction of the fiber reinforced composite material, wherein the reinforcing fibers (B) are discontinuous fibers having a number average fiber length of 1 mm or more and 50 mm or less, wherein the reinforcing fibers (B) are randomly dispersed in the porous structure portion, wherein the fiber-reinforced composite material is molded by using a folded prepreg of resin-impregnated sheet-shaped reinforcing fiber, wherein the tunnel-shaped coarse cavity portion extends in an in-plane direction of the folded prepreg, and wherein the fiber-reinforced composite material comprises a plurality of tunnel-shaped coarse cavity portions extending in an in-plane direction, wherein the opening portions of the tunnel-shaped coarse cavity portions are aligned in the in-plane direction in a cross section orthogonal to an extending direction of the tunnel-shaped coarse cavity portions.