# US 6,532,825 B1 · Fatigue damage detection sensor for structural materials and mounting method thereof > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 6,532,825 B1 - Document ID: US6532825B1 - Status: Granted - Kind: B1 - Application number: 09/581,323 - Filed: 2000-07-24 - Granted: 2003-03-18 - Earliest claimed: 1998-09-28 - Assignees: Bmc Co., Ltd. - Inventors: Makoto Abe - Web page: https://patentgrep.com/patent/US6532825B1 ## CPC - G01M 5/0033: {by determining damage, crack or wear} - G01M 5/0075: {by means of external apparatus, e.g. test benches or portable test systems (G01M5/005 takes precedence)} - G01N 2203/0073: Fatigue - G01N 2203/0664: using witness specimens - G01M: TESTING STATIC OR DYNAMIC BALANCE OF MACHINES OR STRUCTURES; TESTING OF STRUCTURES OR APPARATUS, NOT OTHERWISE PROVIDED FOR - 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) ## Abstract Focusing on the application of a predetermined relationship between the length of a fatigue damage detection sensor having a width of a specified shape and a required sensitivity or sensing accuracy (crack propagation rate), the present invention provides a fatigue damage detection sensor for structural materials and mounting method thereof, wherein when the length between a pair of fixing portions for fixing to a surface of a structural material M, both ends of a sensor body (2) sandwiching a notched portion (5) is defined as 2H, the length of a crack C that can propagate from a tip (5A) of the notched portion (5) is defined as (a), the number of times that a working load acts on the material is defined as N, and the crack propagation rate is defined as da/dN, the length 2H between said fixing portions is set so as to obtain a required sensitivity with which da/dN is proportional to H0.5m (m is a constant determined by a material). According to this fatigue damage detection sensor for structural materials and mounting method thereof, the sensor can provide a high sensing performance to stably and reliably determine the level of fatigue damage caused to a structural material, based on the rate and amount of crack propagation. ## Claims ### Claim 1 A fatigue damage detection sensor for sensing the level of fatigue damage caused to a structural material that is subjected to a working load, the sensor comprising: a rectangularly configured, panel-shaped sensor body having a specified width and a pre-determined length, the sensor body including at least one notched portion which is disposed therein and defines a tip; a pair of fixing portions for mounting the sensor body to the structural material, the sensor body having a length 2H between the fixing portions when mounted to the structural material thereby; and a means for crack detection disposed on the sensor body adjacent the tip of the notched portion; the length 2H being set so as to cause a crack propagation rate d(a)/dN to be proportional to H0.5m, (a) being the length of a crack that propagates from the tip of the notched portion, N being the number of times that the working load acts on the structural material, H being one-half the length 2H, and m being a constant determined by the structural material. ### Claim 2 (depends on 1) The fatigue damage detection sensor of claim 1 wherein the sensor body includes a fatigue pre-crack formed therein at the tip of the notched portion. ### Claim 3 (depends on 1) The fatigue damage detection sensor of claim 1 wherein each of the fixing portions is fabricated from an adhesive. ### Claim 4 A method of mounting a fatigue damage detection sensor to a structural material for sensing the level of fatigue damage caused to the structural material when the structural material is subjected to an external stress, the method comprising the steps of: (a) providing a rectangularly configured, panel-shaped sensor body having a specified width and a predetermined length; (b) forming a notched portion which defines a tip in the sensor body; (c) forming a fatigue pre-crack in the sensor body at the tip of the notched portion; (d) relieving a residual stress from the sensor body resulting from the formation of the fatigue pre-crack in step (c), the relief of the residual stress increasing a mean stress of the sensor body; and (e) mounting the sensor body to the structural material. ### Claim 5 (depends on 4) The method of claim 4 wherein step (e) further comprises the step of heating the sensor body prior to the mounting thereof on the structural material. ### Claim 6 (depends on 4) The method of claim 4 wherein step (e) comprises linearly heating the sensor body prior to the mounting thereof on the structural material. ### Claim 7 (depends on 4) The method of claim 4 wherein step (e) is accomplished through the use of an adhesive. ### Claim 8 A method for mounting a fatigue damage detection sensor to a structural material for sensing the level of fatigue damage caused to the structural material when the structural material is subjected to an external stress, the method comprising the steps of: (a) providing a rectangularly configured, panel-shaped sensor body having a specified width and a predetermined length; (b) forming at least one notched portion which defines a tip in the sensor body; (c) positioning a means for crack detection on the sensor body adjacent the tip of the notched portion; and (d) mounting the sensor body to the structural material via a spaced pair of fixing portions such that the sensor body has a length 2H between the fixing portions, with the length 2H being set so as to cause a crack propagation rate d(a)/dN to be proportional to H0.5m, (a) being the length of a crack that propagates from the tip of the notched portion, N being the number of times that the external stress acts on the structural material, H being one-half the length 2H, and m being a constant determined by the structural material. ### Claim 9 (depends on 8) The method of claim 8 wherein step (d) comprises heating the sensor body prior to the mounting thereof on the structural material. ### Claim 10 (depends on 8) The method of claim 8 wherein step (d) comprises linearly heating the sensor body prior to the mounting thereof on the structural material. ### Claim 11 (depends on 8) The method of claim 8 wherein step (d) further comprises forming a fatigue pre-crack in the sensor body at the tip of the notched portion to relieve a residual stress in the sensor body and increase a mean stress therein.