Composite structure and method of manufacturing it

A composite panel structure having acoustical absorbing properties, comprising:

• a core having wall means forming cells open to a first side and a second side thereof;
• an acoustically semi-transparent first facing of fibrous material and a binder formed to provide a relatively hard outer surface of partially bonded fibers with interstices therebetween, the first facing being bonded to said first side of the core;
• and
• an acoustically semi-transparent second facing of fibrous material and a binder formed to provide a relatively hard outer surface of partially bonded fibers with interstices therebetween, the second facing being bonded to said second side of the core, the facings having portions extending upwardly into the adjacent open cells of the core a depth sufficient to increase the strength of the structure in resisting shear forces adjacent the facings, the facings being non-homogeneous, said portions extending into the cells being relatively soft and of less density than the portions adjacent said cell wall means.

A composite panel structure having acoustical absorbing properties, comprising:

• a first core having wall means forming cells;
• a second core having wall means forming cells;
• a septum of non-porous material interposed between and bonded to the first and second cores such that the first and second cores have cells open to a first side and a second side, respectively, for service as a barrier to reduce the transmission of acoustic energy from one of the cores to the other;
• an acoustically semi-transparent first facing of fibrous material and a binder formed to provide a relatively hard outer surface of partially bonded fibers with interstices therebetween, the facing being bonded to said first side;
• and
• an acoustically semi-transparent second facing of fibrous material and a binder formed to provide a relatively hard outer surface of partially bonded fibers with interstices therebetween, the facing being bonded to said second side, the first and second facings having relatively soft portions extending inward into the adjacent open cells of the first and second cores to a depth sufficient to provide a mechanical interlock between the facings and the cores and to enhance absorption of acoustic energy.

A method of making a composite panel structure having acoustical absorbing properties comprising:

• providing a fibrous facing including an uncured binder and having a relatively uniform thickness and density;
• providing a core having a structure defining cells open to at least one side thereof;
• positioning the fibrous facing against the side of the core in communication with the open cells thereof;
• compressing the fibrous facing against the core such that a portion of the fibrous facing enters the cells of the core to a depth sufficient to provide a mechanical interlock between the facing and the core to increase the strength of the structure in resisting shear forces adjacent the facing, said portions of the facing being soft relative to other portions of the facing and partially filling the adjacent open cells of the core to enhance absorption of acoustic energy directed upon the facing;
• and
• heating the surface of the facing opposite the core to a sufficient temperature to cure the binder to bond the facing to the core and to provide a flat, bonded surface while retaining a substantial amount of interstices between the fibers for absorbing and passing acoustical energy.