Composite structural panel with undulated body

Abstract

An uncured, thermoset resin sheet is reinforced with oriented fibers and is slit to define a desired length for the fibers. A series of the sheets are cut and stacked to form integrated layers of the composite material for a structural panel. The panel has two outer layers that sandwich two shorter layers on each end, and syntactic or foamed resin layer in between. Each of the composite layers is formed from the same materials and by the same process, but may vary in the directional orientation of their fibers. The uncured panel is assembled into a flexible, substantially flat configuration is heated and formed to the contours of a tool having a undulated surface geometry. The panel is further heated to cure the combined composite and syntactic resins into a series of undulations that permeate each of its layers. In one embodiment, the undulations are in a smooth, sine wave-like pattern that allow the panel to maintain a planar configuration. Although the fibers themselves do not stretch, the short lengths of the fibers enable stretching of the material in the fiber direction so that deformation of the composite is possible in all directions. The panel is stiffened both by spacing its outer layers apart with the syntactic layer, and by its undulated surface.

What is claimed is:  
     
         1 . A structural panel, comprising: 
 a pair of outer layers, each formed from a laminate of composite material sheets of fiber-reinforced, thermoset resin;    an inner layer located between the outer layers such that the panel has a generally planar configuration that defines a coordinate system with x, y, and z-directions;    a series of undulations formed in each layer of the panel substantially across the y-direction of the panel and generally transverse to the x-direction of the panel, the undulations alternating in the z-direction for stiffening the panel; and wherein    the fibers in the composite material sheets have lengths that are less than a length of a period of the undulations.    
     
     
         2 . The structural panel of  claim 1  wherein the inner layer is a syntactic material.  
     
     
         3 . The structural panel of  claim 1  wherein the inner layer is a foamed resin material.  
     
     
         4 . The structural panel of  claim 1  wherein the inner layer has a pair of x-ends and an x-dimension that is shorter than an x-dimension of the outer layers, and further comprising an additional laminate of composite material sheets on each x-end of the inner layer located between the outer layers to form panel edges.  
     
     
         5 . The structural panel of  claim 1  wherein a flange is formed along an edge of the panel and extends generally out of plane relative to the panel.  
     
     
         6 . The structural panel of  claim 1  wherein the undulations form a sine wave pattern.  
     
     
         7 . The structural panel of  claim 1  wherein the undulations are beads having y-dimensions that are less than a y-dimension of the panel to define generally flat side edges on the panel.  
     
     
         8 . The structural panel of  claim 1  wherein a y-dimension of the panel is tapered in the x-direction.  
     
     
         9 . The structural panel of  claim 1  wherein the fibers in each layer of the laminate are oriented in a layer-specific direction.  
     
     
         10 . The structural panel of  claim 1  wherein each of the composite material sheets of the laminate have slits in the fibers.  
     
     
         11 . The structural panel of  claim 1  wherein the fibers are collimated.  
     
     
         12 . The structural panel of  claim 1  wherein the undulations comprise inclined portions with a series of generally planar peaks and valleys that are substantially parallel to the generally planar configuration of the panel.  
     
     
         13 . The structural panel of  claim 12  wherein the inclined portions are formed of homogenous materials.  
     
     
         14 . A structural panel, comprising: 
 a pair of outer layers having a generally planar configuration that defines a coordinate system with x, y, and z-directions, each of the outer layers being formed from a laminate of composite material sheets of fiber-reinforced, thermoset resin and having a longitudinal x-dimension, wherein each of the composite material sheets of the laminate have slits in the fibers, and the fibers in each layer of the laminate are oriented in a layer-specific direction;    an inner layer selected from a group consisting of syntactic and foamed resin material, the inner layer being located between the outer layers and having an x-dimension with longitudinal ends that is shorter than the x-dimension of the outer layers;    a series of uniform undulations formed in each layer of the panel substantially across the y-direction of the panel and generally transverse to the x-direction of the panel, the undulations alternating in the z-direction for stiffening the panel; and wherein    the fibers in the composite material sheets have lengths that are less than a length of a period of the undulations.    
     
     
         15 . The structural panel of  claim 14 , further comprising an additional laminate of composite material sheets located between the outer layers and adjacent to each of the longitudinal ends of the inner layer.  
     
     
         16 . The structural panel of  claim 14 , further comprising a flange formed along an edge of the panel, the flange extending generally out of plane relative to the panel.  
     
     
         17 . The structural panel of  claim 14  wherein the undulations form a sine wave pattern.  
     
     
         18 . The structural panel of  claim 14  wherein the undulations are beads having y-dimensions that are less than a y-dimension of the panel to define generally flat side edges on the panel.  
     
     
         19 . The structural panel of  claim 14  wherein a y-dimension of the panel is tapered in the x-direction.  
     
     
         20 . The structural panel of  claim 14  wherein the fibers are collimated.  
     
     
         21 . The structural panel of  claim 14  wherein the undulations comprise inclined portions with a series of generally planar peaks and valleys that are substantially parallel to the generally planar configuration of the panel.  
     
     
         22 . The structural panel of  claim 21  wherein the inclined portions are formed of homogenous materials.  
     
     
         23 . A method for fabricating a structural panel, comprising the steps of: 
 (a) providing an uncured laminate of composite material sheets of fiber-reinforced, thermoset resin, and an uncured material selected from a group consisting of syntactic and foamed resin;    (b) assembling an uncured panel with outer layers of the laminate and an inner layer of the uncured material, such that the panel has a generally planar configuration that defines a coordinate system with x, y, and z-directions;    (c) heating the uncured panel and forming a series of undulations in each layer of the panel such that the undulations have a period that is greater than a length of the fibers in the composite material sheets, the undulations extending substantially across the y-direction of the panel and generally transverse to the x-direction of the panel, the undulations alternating in the z-direction for stiffening the panel; and then    (d) further heating the panel of step (c) to cure the inner and outer layers.    
     
     
         24 . The method of  claim 23  wherein step (b) further comprises assembling an additional laminate of composite material sheets between the outer layers.  
     
     
         25 . The method of  claim 23 , further comprising the step of forming a flange along an edge of the panel.  
     
     
         26 . The method of  claim 23  wherein step (c) comprises forming the undulations in a sine wave pattern.  
     
     
         27 . The method of  claim 23  wherein step (c) comprises forming the undulations as beads having y-dimensions that are less than a y-dimension of the panel to define generally flat side edges on the panel.  
     
     
         28 . The method of  claim 23 , further comprising the step of tapering a y-dimension of the panel in the x-direction.  
     
     
         29 . The method of  claim 23  wherein step (c) comprises forming the undulations with inclined portions having a series of generally planar peaks and valleys that are substantially parallel to the generally planar configuration of the panel.