Balsa-core sandwich laminate

A structural sandwich laminate formed of thin facing sheets bonded to a core panel, said facings being constituted by aluminum sheets whose surfaces bonded to the core panel are etched whereby the surfaces are free of oxide film, said panel being formed of end-grain balsa having an array of closely spaced clear-through holes punched therein to define a reticulated balsa core of high strength and exceptionally low weight, said end grain balsa being composed of substantially parallel fibers which are at right angles to the faces of core panel whereby the holes punched therein have removed therefrom a phalanx of said fibers without disrupting the surrounding fibers and substantially degrading the strength of the panel, said array of holes being formed by alternative rows of equi-spaced holes in staggered relation, the holes having their centers at the apexes of a diamond, making possible a high concentration of holes with an adequate separation therebetween,

• said aluminum sheets being bonded to said panel by a heat-curable exoxy resin which cures at a relatively high temperature causing volatilization of moisture, and said balsa panel has a moisture content of about 2 to 3% whereby vapors will not be produced to interfere with curing.