A prepreg laminate is provided which includes: a woven fabric prepreg on at least one surface layer; and a discontinuous fiber prepreg; the woven fabric prepreg including reinforcing fibers R.sub.1 having a woven structure, and a thermosetting resin A, the discontinuous fiber prepreg including unidirectionally oriented discontinuous reinforcing fibers R.sub.2 and a thermosetting resin B, the thermosetting resin A and the thermosetting resin B satisfying the following calorific value condition: calorific value condition: when each of the thermosetting resin A and the thermosetting resin B is heated using a differential scanning calorimeter from 50° C. to 130° C. at 700° C./min under a nitrogen atmosphere followed by retention at 130° C. until completion of thermal curing reaction, Tb−Ta>30, wherein Ta (s): time required for the calorific value of the thermosetting resin A to reach 50% of the gross calorific value of the thermosetting resin A; Tb (s): time required for calorific value of the thermosetting resin B to reach 50% of gross calorific value of the thermosetting resin B.

A discontinuous fiber-reinforced composite material including a discontinuous reinforcing fiber aggregate of a discontinuous reinforcing fiber having a number average fiber length of 3 to 100 mm and a matrix resin, the discontinuous reinforcing fiber aggregate including a plurality of discontinuous reinforcing fiber bundles having a predetermined number of unidirectionally-bundled single yarns of the discontinuous reinforcing fiber, wherein the discontinuous reinforcing fiber bundle has a cut surface inclined at a predetermined angle with respect to an orientation direction of the single yarn of the discontinuous reinforcing fiber bundle and has different fiber bundle lengths defined as a distance between both ends along the orientation direction of the single yarn of the discontinuous reinforcing fiber bundle, and the longer the fiber bundle length of the discontinuous reinforcing fiber bundle is, the smaller a tip angle defined as an acute angle at an end of a two-dimensional plane projection of the discontinuous reinforcing fiber bundle is.

A discontinuous fiber-reinforced composite material including a discontinuous reinforcing fiber aggregate of a discontinuous reinforcing fiber having a number average fiber length of 3 to 100 mm and a matrix resin, the discontinuous reinforcing fiber aggregate including a plurality of discontinuous reinforcing fiber bundles having a predetermined number of unidirectionally-bundled single yarns of the discontinuous reinforcing fiber, wherein the discontinuous reinforcing fiber bundle has a cut surface inclined at a predetermined angle with respect to an orientation direction of the single yarn of the discontinuous reinforcing fiber bundle and has different fiber bundle lengths defined as a distance between both ends along the orientation direction of the single yarn of the discontinuous reinforcing fiber bundle, and the longer the fiber bundle length of the discontinuous reinforcing fiber bundle is, the smaller a tip angle defined as an acute angle at an end of a two-dimensional plane projection of the discontinuous reinforcing fiber bundle is.

A molded article of a fiber-reinforced resin contains at least a bundled aggregate [A] of discontinuous reinforcing fibers and a matrix resin [M], wherein the average layer thickness h in the molded article of the fiber-reinforced resin is 100 μm or less and the CV value of the average layer thickness h is 40% or less; and a compression molding method therefor. It is possible to reliably and greatly reduce the occurrence of stress concentration in the molded article and to thereby achieve higher mechanical properties and further reduce variation in the mechanical properties.

A molded article of a fiber-reinforced resin contains at least a bundled aggregate [A] of discontinuous reinforcing fibers and a matrix resin [M], wherein the average layer thickness h in the molded article of the fiber-reinforced resin is 100 μm or less and the CV value of the average layer thickness h is 40% or less; and a compression molding method therefor. It is possible to reliably and greatly reduce the occurrence of stress concentration in the molded article and to thereby achieve higher mechanical properties and further reduce variation in the mechanical properties.

In one embodiment, a method for making a high density structural composite includes depositing a plurality of fibrous materials on or adjacent a first plate or surface. A polymer liquid is deposited onto the plurality of fibrous materials to form a composite mixture. A first cyclic pressure is applied onto the composite mixture to compress the composite mixture. In some embodiments, the cyclic pressure may then be reduced to a valley pressure to complete a pressurization cycle. In some instances, the valley pressure may be below atmospheric pressure to induce trapped air and volatile gases to escape from the composite mixture before curing. The pressurization cycle may be repeated. A second pressure, which may be a constant pressure in some embodiments, may be applied to the composite mixture using, in some embodiments, a second plate until the polymer liquid has at least partially cured or partially solidified.

In one embodiment, a method for making a high density structural composite includes depositing a plurality of fibrous materials on or adjacent a first plate or surface. A polymer liquid is deposited onto the plurality of fibrous materials to form a composite mixture. A first cyclic pressure is applied onto the composite mixture to compress the composite mixture. In some embodiments, the cyclic pressure may then be reduced to a valley pressure to complete a pressurization cycle. In some instances, the valley pressure may be below atmospheric pressure to induce trapped air and volatile gases to escape from the composite mixture before curing. The pressurization cycle may be repeated. A second pressure, which may be a constant pressure in some embodiments, may be applied to the composite mixture using, in some embodiments, a second plate until the polymer liquid has at least partially cured or partially solidified.

A composite structure includes a structure that contains first reinforced fibers and first resin and a laminate that is disposed on at least one surface of the structure and has a plurality of layers containing second reinforced fibers and second resin, with the structure and the laminate integrated, the first reinforced fibers being discontinuous fibers and having a thickness-wise average fiber orientation angle in a range of 5 to 60°, the second reinforced fibers being discontinuous fibers and having a thickness-wise average fiber orientation angle in a range of 0 to 5°, the structure having a density in a range of 0.01 to 1 g/cm.sup.3, the laminate having a variation in volume content of the second reinforced fibers in a range of 0 to 10%, and the composite structure having a protruding portion on a laminate's surface opposite from a laminate's surface in contact with the structure.

A composite structure includes a structure that contains first reinforced fibers and first resin and a laminate that is disposed on at least one surface of the structure and has a plurality of layers containing second reinforced fibers and second resin, with the structure and the laminate integrated, the first reinforced fibers being discontinuous fibers and having a thickness-wise average fiber orientation angle in a range of 5 to 60°, the second reinforced fibers being discontinuous fibers and having a thickness-wise average fiber orientation angle in a range of 0 to 5°, the structure having a density in a range of 0.01 to 1 g/cm.sup.3, the laminate having a variation in volume content of the second reinforced fibers in a range of 0 to 10%, and the composite structure having a protruding portion on a laminate's surface opposite from a laminate's surface in contact with the structure.

A method for producing a three-dimensional object, the method including: disposing powder; disposing fibers; and applying liquid for binding the powder and the fibers to at least one selected from the group consisting of the powder and the fibers.