Abstract: An improved synthesis for PMR-type polyimides, including first preparing a dimer of 5-norbornene-2,3-dicarboxylic acid, or acid ester or anhydride and 4,4'methylenedianiline. This dimer is then reacted with the reaction product of the dimethyl ester (or dianhydride) of 3,3', 4,4'-benzophenonetetracarboxylic acid and 4,4'-methylenedianiline. The resulting polyimide prepolymer exhibits superior physical properties and is substantially free of the undesired trimer of 5-norbornene-2,3-dicarboxylic acid, or acid ester or anhydride and 4,4'-methylenedianiline. When this dimer is reacted with 3,3', 4,4'-benzophenonetetracarboxylic acid dianhydride methylenedianiline amic acid mixture, the resulting polyimide prepolymer exhibits superior physical properties.

Abstract: An improved synthesis for PMR-type polyimides, including first preparing a dimer of 5-norbornene-2,3-dicarboxylic acid, or acid ester or anhydride and 4,4'methylene dianiline. This dimer is then reacted with one of the following:1. the reaction product of a primary aromatic diamine and an aromatic dianhydride.2. an aromatic dianhydride.3. a mixture of a primary aromatic diamine and an aromatic dianhydride, or an ester of an aromatic tetraacid or an aromatic tetraacid.The resulting polyimide prepolymer exhibits superior physical properties and is substantially free of undesired impurities and unreacted 4,4'-methylene dianiline.

Abstract: An improved synthesis for PMR-type polyimides, including first preparing a dimer of 5-norbornene-2,3-dicarboxylic acid, or acid ester or anhydride and 4,4'-methylenedianiline. This dimer is then reacted with the dimethyl ester of 3,3',4,4'-benzophenonetetracarboxylic acid and 4,4'-methylenedianiline. The resulting polyimide prepolymer exhibits superior physical properties and is substantially free of the undesired trimer of 5-norbornene-2,3-dicarboxylic acid, or acid ester or anhydride and 4,4'-methylenedianiline.

Abstract: A method of laminating a porous overlay material to a perforated plate with a dry film adhesive which does not block perforations or pores in the two components. A lay-up is preferably prepared by assembling in order on a vacuum platen a porous peel ply sheet, a sheet of dry film adhesive, a perforated plate, a sheet of microporous material to be bonded to the perforated plate and an air permeable sheet. A vacuum is drawn through holes in the vacuum platen contiguous to the bottom surface of the porous peel ply sheet while the assembly is heated to the softening temperature of the adhesive film. The vacuum is directly applied through the perforation, drawing the film down through the perforations and into contact with the peel ply sheet. As heating continues the film softens sufficiently to adhesively bond the microporous material to the perforated sheet.

Abstract: A noise suppression panel having a first cellular core positioned between and bonded to an imperforate facing sheet on one surface thereof and a first sheet of microporous material on the other surface. A second core is bonded between the other surface of the first sheet of microporous material and a perforated sheet. The other surface of the perforated sheet has a second sheet of microporous material bonded thereto. The cells of the two cores are preferably substantially aligned when maximum core-to-core bonding strength therebetween is required. A method of manufacturing is disclosed which includes flow-through resistance testing of the subassemblies.

Abstract: Broad band noise attenuation sandwich panels utilizing a cellular core positioned between and bonded to two facing sheets by an adhesive bonding system. One facing sheet is perforated and the other imperforate. A thin sheet of porous fibrous felt or fabric is bonded to the outer surface of the perforate sheet. The adhesive layer, at least between the perforate sheet and the porous fibrous material, is sufficiently thick to isolate the two components and form a funnel shaped opening necked down at the entrance to each perforation.

Abstract: A noise suppression panel having a first cellular core positioned between and bonded to an imperforate facing sheet on one surface thereof and a first sheet of microporous material on the other surface. A second core is bonded between the other surface of the first sheet of microporous material and a perforated sheet. The other surface of the perforated sheet has a second sheet of microporous material bonded thereto. The cells of the two cores are preferably substantially aligned when maximum core-to-core bonding strength therebetween is required. A method of manufacturing is disclosed which includes flow-through resistance testing of the subassemblies.

Abstract: A layer of non-metallic open weave fabric sandwiched between the perforate sheet and an outer thin sheet of microporous fabric of a broad band noise attenuation panel comprising a cellular core adhesively bonded between a pair of metal facing sheets, one perforate and the other imperforate in order to provide enhanced durability in a severe environment. The microporous fabric is constructed from a metal different from at least the perforated sheet and is adhered to the perforated sheet. A method of manufacture of such panel is disclosed.

Abstract: A method of manufacturing a double degree acoustic attenuation sandwich panel having a plurality of stacked components adhered together to form a unitary sandwich structure. The structure comprising an impervious facing of thin sheet material, a first honeycomb core with end wise directed cells, a first perforate facing of thin sheet material, a first thin layer of porous fibrous material, a second perforated facing of thin sheet material, a second honeycomb core with end wise directed cells, a third perforate facing of thin sheet material, the second perforated facing sheet having substantially larger perforations than the first and third sheets, and a second layer of porous fibrous material. The resulting sandwich panel has a pre-determined flow through resistance between the outer surface of the first and second layers of porous fibrous material and the cells of the first and second honeycomb cores.

Abstract: Honeycomb noise attenuation sandwich panels and method of construction having a cellular core positioned between and bonded to two facing sheets. One facing sheet is perforated and the other imperforate. A thin sheet of porous fibrous felt or fabric is bonded to the perforated sheet. The core cells communicate with the atmosphere through the perforated sheet and the pores of the fibrous sheet.

Abstract: Honeycomb noise attenuation sandwich panels and method of construction having a cellular core positioned between and bonded to two facing sheets. One facing sheet is perforated and the other imperforate. A thin sheet of porous fibrous felt or fabric is bonded to the perforated sheet. The core cells communicate with the atmosphere through the perforated sheet and the pores of the fibrous sheet.

Abstract: A double degree acoustic attenuation sandwich panel having a plurality of stacked components adhered together to form a unitary sandwich structure. The structure comprising an impervious facing of thin sheet material, a first honeycomb core with end wise directed cells, a first perforate facing of thin sheet material, a first thin layer of porous fibrous material, a second honeycomb core with end wise directed cells, a second perforate facing of thin sheet material and a second layer of porous fibrous material. The resulting sandwich panel has a predetermined flow through resistance between the outer surface of the first and second layers of porous fibrous material and the cells of the first and second honeycomb cores. The cell of the first and second honeycomb cores may be of equal or different volume cells and may be constructed of similar or dissimilar materials.

Abstract: A double degree acoustic attenuation sandwich panel having a plurality of stacked components adhered together to form a unitary sandwich structure. The structure comprising an impervious facing of thin sheet material, a first honeycomb core with end wise directed cells, a first perforate facing of thin sheet material, a first thin layer of porous fibrous material, a second perforated facing of thin sheet material, a second honeycomb core with end wise directed cells, a third perforate facing of thin sheet material, the second perforated facing sheet having substantially larger perforations than the first and third sheets, and a second layer of porous fibrous material. The resulting sandwich panel has a pre-determined flow through resistance between the outer surface of the first and second layers of porous fibrous material and the cells of the first and second honeycomb cores.

Abstract: Method of manufacturing broad band noise attenuation sandwich panels utilizing a cellular core positioned between and bonded to two facing sheets by an adhesive bonding system. One facing sheet is perforated and the other imperforate. A thin sheet of porous fibrous felt or fabric is bonded to the outer surface of the perforate sheet. The adhesive layer, at least between the perforate sheet and the porous fibrous material, is sufficiently thick to isolate the two components and form a funnel shaped opening necked down at the entrance to each perforation. In one embodiment a thin layer of non-metallic cloth is positioned between the perforated and porous fibrous material in those areas where cutting, trimming or drilling of the completed structure is required to maintain isolation.

Abstract: A method of manufacturing a perforate material from wire mesh for honeycomb noise attenuation and the resulting material therefrom comprising the steps of selecting a sheet of wire mesh, constructed from a material that can be readily diffusion bonded; cleaning the selected wire mesh to remove all grease therefrom, suspending the sheet of selected wire mesh within a furnace, evacuating the oven to about 10..sup.5 torr, elevating and maintaining the furnace temperature to facilitate diffusion bonding of the contacting cross-over areas of the strands of the wire mesh; reducing the furnace temperature, removing the sheet of diffused wire mesh from the oven when its temperature is below its oxidation level. The furnace may additionally be charged with an inert gas to decrease the cooling time. In some instances a heat dispersing member is inserted between the sheet of wire mesh and the source of the elevating temperature.