# US 9,518,907 B2 · Methods and apparatus to determine integrity of composite structures > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 9,518,907 B2 - Document ID: US9518907B2 - Status: Granted - Kind: B2 - Application number: 14/157,211 - Filed: 2014-01-16 - Published: 2015-07-16 - Granted: 2016-12-13 - Earliest claimed: 2014-01-16 - Assignees: The Boeing Company - Applicants: The Boeing Company - Inventors: Eugene A. Dan-Jumbo - Web page: https://patentgrep.com/patent/US9518907B2 ## CPC - G01N 13/02: Investigating surface tension of liquids - B64C 1/12: Construction or attachment of skin panels - B64C 3/26: Construction, shape, or attachment of separate skins, e.g. panels - G01M 5/0016: {of aircraft wings or blades} - B64C 2001/0072: {from composite materials} - G01N 2013/0208: {by measuring contact angle} - G01N: INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES (measuring or testing apparatus or processes other than immunoassay, involving enzymes or microorganisms C12M, C12Q) - B64C: AEROPLANES; HELICOPTERS - G01M: TESTING STATIC OR DYNAMIC BALANCE OF MACHINES OR STRUCTURES; TESTING OF STRUCTURES OR APPARATUS, NOT OTHERWISE PROVIDED FOR ## Abstract Apparatus and methods to determine structural integrity of composites are described herein. One described example method for determining sufficiency of structural integration of a composite structure for an aircraft includes applying a fluid droplet to a surface of the composite structure, determining a three-dimensional contact angle between the surface and a portion of the droplet, comparing the three-dimensional contact angle to a threshold angle, and determining whether the structural integration of the composite structure is sufficient based on the comparison. ## Claims ### Claim 1 A method for determining a bond strength of a composite structure for an aircraft, the method comprising: applying a fluid droplet to a surface of the composite structure; determining a three-dimensional contact angle between the surface and a portion of the droplet; comparing the three-dimensional contact angle to a threshold angle; and determining whether the bond strength is sufficient based on the comparison, wherein a value of the three-dimensional contact angle of less than a predetermined threshold angle of about 10 degrees between the surface of the composite structure and the portion of the fluid droplet is indicative of the composite structure having sufficient bond strength to provide a pre-predetermined load bearing capacity. ### Claim 2 (depends on 1) The method as defined in claim 1, further comprising selecting the composite structure for integration into an assembly when the bond strength is sufficient. ### Claim 3 (depends on 1) The method as defined in claim 1, further comprising approving the composite structure when the bond strength is sufficient after integration of the composite structure into an assembly. ### Claim 4 (depends on 1) The method as defined in claim 1, wherein the three-dimensional contact angle being less than the threshold angle indicates sufficient bond strength of the composite structure. ### Claim 5 (depends on 1) The method as defined in claim 1, wherein the three-dimensional contact angle being greater than the threshold angle indicates insufficient bond strength of the composite structure. ### Claim 6 (depends on 1) The method as defined in claim 1, wherein determining the three-dimensional contact angle further comprises measuring a diameter and volume of the droplet. ### Claim 7 (depends on 1) The method as defined in claim 1, wherein the portion of the droplet comprises a head or a tail of the droplet. ### Claim 8 (depends on 7) The method as defined claim 7, wherein the composite structure comprises bismaleimide, epoxy, polyamide, or thermoplastic. ### Claim 9 (depends on 1) The method as defined in claim 1, wherein the threshold angle is calculated based on a pre-determined load bearing capacity. ### Claim 10 (depends on 9) The method as defined in claim 9, wherein the threshold angle calculation is calculated using an equation including a component of the surface tension of the surface due to vapor gaseous phase of the droplet in equilibrium. ### Claim 11 (depends on 1) The method as defined in claim 1, wherein applying the fluid droplet comprises use of a pipette or ballistic deposition. ### Claim 12 An aircraft component that requires fewer fasteners, comprising: an external skin having a bonded composite structure, defining a skin surface area of an aircraft; a support frame; and an adhesive applied to the composite structure to attach the external skin to the support frame, wherein the composite structure has sufficient bond strength to enable adhesive attachment of the external skin to the support frame with less than 0.50 fasteners to couple the skin and the support frame per square-foot of the skin surface area, where a three-dimensional contact angle between the composite structure and a portion of a fluid droplet applied to the surface of the composite structure is less than a pre-determined threshold angle of about 10 degrees is indicative of sufficient bond strength. ### Claim 13 (depends on 12) The apparatus as defined in claim 12, wherein the composite structure is outboard of an aircraft. ### Claim 14 (depends on 12) The apparatus as defined in claim 12, wherein the portion of the fluid droplet defining the three-dimensional contact angle from the composite structure comprises one or more of a head, a tail, or a mid-section of a loft of the droplet. ### Claim 15 A tangible machine readable medium having instructions stored thereon, which when executed, cause a machine to: determine a three-dimensional contact angle of a droplet placed onto a surface of a composite structure based on a measured diameter and volume of the droplet; compare the three-dimensional contact angle to a threshold angle of about 10 degrees, wherein the three-dimensional contact angle being less than the threshold angle indicates sufficient bond strength of the composite structure, and wherein the three-dimensional contact angle being greater than the threshold angle indicates insufficient bond strength of the composite structure; and output whether the composite structure has sufficient bond strength. ### Claim 16 (depends on 15) The machine readable medium as defined in claim 15, which when executed, further cause a machine to measure the volume and the diameter of the droplet. ### Claim 17 (depends on 15) The machine readable medium as defined in claim 15, which when executed, further cause a machine to calculate an intermolecular surface tension of the composite structure. ### Claim 18 (depends on 17) The machine readable medium as defined in claim 17, wherein the calculated intermolecular surface tension is determined using an equation including a component of the surface tension of the surface due to vapor gaseous phase of the droplet in equilibrium. ### Claim 19 (depends on 17) The machine readable medium as defined in claim 17, which when executed, further cause a machine to output one or more of the intermolecular surface tension and a factor of safety based on the intermolecular surface tension. ### Claim 20 (depends on 15) The machine readable medium as defined in claim 15, which when executed, further cause a machine to generate structural specifications for approval when the three-dimensional contact angle indicates sufficient bond strength.