Wrinkle Reduction in Formed Composite Laminates

Abstract

Wrinkling of a contoured composite laminate part during forming to contour is reduced by using laminate plies having off-angle reinforcing fibers that provide the part with primary axial strength along a major axis of loading.

What is claimed is: 
     
         1 . A composite laminate stiffener contoured along a major axis of loading, comprising:
 a plurality of laminated plies of unidirectional reinforcing fibers held in a plastic matrix, wherein all of the plies have fiber orientations at off-angles relative to the major axis of loading.   
     
     
         2 . The composite laminate stiffener of  claim 1 , wherein the plies have fiber orientations relative to the major axis of loading of θ1, θ2, θ3, and 0<θ1<θ2≤θ3≤90°. 
     
     
         3 . The composite laminate stiffener of  claim 2 , wherein θ1 is between approximately 5° and 30°. 
     
     
         4 . The composite laminate stiffener of  claim 2 , wherein the plies have fiber orientations relative to the major axis of loading of −θ1, −θ2, −θ3, and 0<−θ1<−θ2≤−θ3≤90°. 
     
     
         5 . The composite laminate stiffener of  claim 4 , wherein −θ1 is between approximately −5° and −30°. 
     
     
         6 . The composite laminate stiffener of  claim 1 , wherein the plurality of the plies vary in number along the major axis of loading and define zones along the composite laminate stiffener respectively having different stiffness properties. 
     
     
         7 . The composite laminate stiffener of  claim 1 , wherein:
 some of the plies are continuous and other of the plies are discontinuous along the major axis of loading, and   the off-angles include balanced pairs of + and − angles.   
     
     
         8 . A contoured composite laminate part, comprising:
 a plurality of laminated plies of reinforcing fibers held in a plastic matrix, wherein all of the plies have fiber orientations at off-angles relative to the major axis of loading, wherein the part comprises a number of different zones, wherein each zone comprises a different stiffness property, and wherein the different stiffness properties are achieved by varying at least one of the ply orientations and the number of plies of a given orientation in each of the zones.   
     
     
         9 . The contoured composite laminate part of  claim 8 , wherein in a first zone of the number of zones the plies have fiber orientations relative to the major axis of loading of θ1, θ2, θ3, and 0<θ1<θ2≤θ3≤90°. 
     
     
         10 . The contoured composite laminate part of  claim 9 , wherein 81 is between approximately 5° and 30°. 
     
     
         11 . The contoured composite laminate part of  claim 9 , wherein the plies have fiber orientations relative to the major axis of loading of −θ1, −θ2, −θ3, and 0<−θ1<−θ2≤−θ3≤90°. 
     
     
         12 . The contoured composite laminate part of  claim 11 , wherein −θ1 is between approximately −5° and −30°. 
     
     
         13 . The contoured composite laminate part of  claim 9 , wherein some of the plies are continuous and other of the plies are discontinuous along the major axis of loading. 
     
     
         14 . The contoured composite laminate part of  claim 13 , wherein the off-angles include balanced pairs of + and − angles. 
     
     
         15 . A composite laminate stiffener contoured along a major axis of loading, comprising:
 a plurality of laminated plies of unidirectional reinforcing fibers held in a plastic matrix, wherein all of the plies have fiber orientations at off-angles relative to the major axis of loading, wherein the plies have fiber orientations relative to the major axis of loading of θ1, θ2, θ3, and 0<θ1<θ2≤θ3≤90°, and wherein the plurality of the plies vary in number along the major axis of loading and define zones along the composite laminate stiffener respectively having different stiffness properties.   
     
     
         16 . The composite laminate stiffener of  claim 15 , wherein θ1 is between approximately 5° and 30°. 
     
     
         17 . The composite laminate stiffener of  claim 15 , wherein the plies have fiber orientations relative to the major axis of loading of −θ1, −θ2, −θ3, and 0<−θ1<−θ2≤−θ3≤90°. 
     
     
         18 . The composite laminate stiffener of  claim 17 , wherein −θ1 is between approximately −5° and −30°. 
     
     
         19 . The composite laminate stiffener of  claim 15 , wherein some of the plies are continuous and other of the plies are discontinuous along the major axis of loading. 
     
     
         20 . The composite laminate stiffener of  claim 19 , wherein the off-angles include balanced pairs of + and − angles.