Methods and systems are provided for condition-based maintenance of a structural component exhibiting a physical defect. One exemplary system comprises a measurement system to obtain a current measurement of a defect in a structure, a monitoring system, and a maintenance system. The monitoring system determines a probabilistic representation of degradation development data for the defect using the current measurement, determines a reference remaining usage life metric for the structure based on the probabilistic representation and a target probability value, and determines one or more remaining usage life bounds based at least in part on the reference remaining usage life metric. The maintenance system determines maintenance schedule or other remedial action(s) for the structure in a manner that is influenced by the reference remaining usage life metric and the one or more remaining usage life bounds.
Please help me write a proper abstract based on the patent claims. CLAIM: 1. A system comprising: a measurement system to obtain a current measurement of a defect in a structure; a monitoring system coupled to the measurement system to determine a probabilistic representation of degradation development data for the defect based at least in part on the current measurement, a threshold value, and one or more stress intensity factors, determine a reference remaining usage life metric for the structure based on the probabilistic representation and a target probability value, and determine one or more remaining usage life limits based at least in part on the reference remaining usage life metric; and a maintenance system coupled to the monitoring system to determine an action for the structure in a manner that is influenced by the reference remaining usage life metric and the one or more remaining usage life limits. 2. The system of claim 1, further comprising a user interface coupled to the monitoring system, wherein the monitoring system receives the target probability value via the user interface. 3. The system of claim 2, wherein the monitoring system receives a confidence level via the user interface and determines the one or more remaining usage life limits based on the confidence level and the reference remaining usage life metric. 4. The system of claim 1, wherein the one or more stress intensity factors are influenced by geometric characteristics of the structure and loading data for the structure. 5. The system of claim 4, further comprising a user interface coupled to the monitoring system, wherein the monitoring system receives indicia of the geometric characteristics via the user interface. 6. The system of claim 1, wherein the probabilistic representation of degradation development data comprises a probabilistic representation of a plurality of degradation development data sets representative of predicted developments of the defect obtained by varying one or more of the current measurement and the one or more stress intensity factors. 7. The system of claim 1, wherein the monitoring system determines minimum and maximum fuzzy number limits based on the reference remaining usage life metric and a future loading uncertainty factor and determines the one or more remaining usage life limits based at least in part on the reference remaining usage life metric and the minimum and maximum fuzzy number limits. 8. The system of claim 1, wherein the structure comprises a structural component of an aircraft. 9. A method of monitoring a component having a physical defect, the method comprising: determining degradation development data for the physical defect based at least in part on a current measurement of the physical defect; determining a probabilistic representation of the degradation development data based at least in part on a threshold value associated with the physical defect and uncertainty associated with the current measurement; determining a remaining usage life value for the component based on an input probability value and the probabilistic representation; determining one or more confidence limit values associated with the remaining usage life value; and providing the remaining usage life value and the one or more confidence limit values to a maintenance system. 10. The method of claim 9, wherein determining degradation development data comprise predicting development of the physical defect based at least in part on the current measurement and one or more stress intensity factors associated with the component. 11. The method of claim 10, further comprising determining the one or more stress intensity factors based on geometric characteristics of the component and loading data associated with the component. 12. The method of claim 11, further comprising: determining a stress distribution function based on the loading data; determining a weighting function based on the geometric characteristics; and determining the one or more stress intensity factors as an integral of a product of the stress distribution function and the weighting function over the current measurement. 13. The method of claim 9, further comprising determining rivet forces on the component based at least in part on the current measurement, wherein determining the degradation development data comprises predicting development of the physical defect based at least in part on the current measurement, the one or more stress intensity factors, and the rivet forces. 14. The method of claim 9, wherein determining the probabilistic representation of the degradation development data comprises determining a plurality of degradation development data sets based on the uncertainty associated with the current measurement. 15. The method of claim 14, further comprising receiving the input probability value via a user interface, wherein the remaining usage life value comprises a value of the probabilistic representation at the input probability value. 16. The method of claim 9, wherein determining the one or more confidence limit values comprises: determining fuzzy number bounds based on the remaining usage life value and a future uncertainty adjustment factor; performing probability assignments based on the fuzzy number bounds; and determining the one or more confidence limit values as minimum and maximum remaining usage life values for a confidence level based on the probability assignments. 17. The method of claim 9, further comprising receiving the current measurement of the physical defect from a measurement system, wherein the measurement system includes one or more measurement devices configured to analyze the component obtain the current measurement of the physical defect. 18. A computer-readable medium having computer-executable instructions stored thereon that, when executed by a processing system, cause the processing system to perform the method of claim 9. 19. A method of monitoring an aircraft component, the method comprising: obtaining, from a measurement system, a current measurement of a crack in the aircraft component; determining one or more stress intensity factors associated with the aircraft component based at least in part on a geometry of the aircraft component; determining a crack growth data set based on the current measurement and the one or more stress intensity factors; determining a probabilistic representation of the crack growth data set based at least in part on the crack growth data set, a maintenance threshold for the crack, and uncertainty associated with at least one of the current measurement and the one or more stress intensity factors; determining a remaining usage life value for an input probability value based on the probabilistic representation; determining one or more future uncertainty confidence limits for the remaining usage life value based at least in part on a future uncertainty adjustment factor and the remaining usage life value; and providing the remaining usage life value and the one or more future uncertainty confidence limits to a condition based maintenance system, wherein a maintenance schedule for the aircraft component is influenced by the remaining usage life value and the one or more future uncertainty confidence limits. 20. The method of claim 19, further comprising receiving the input probability value and an input confidence level via a user interface, wherein: determining the one or more stress intensity factors comprises: determining a stress distribution function based on loading data associated with the aircraft component; determining a weighting function based on the geometry of the aircraft component; and integrating a product of the stress distribution function and the weighting function over the current measurement to obtain the one or more stress intensity factors; determining the probabilistic representation comprises: determining a plurality of crack growth data sets across a joint distribution of the current measurement and the one or more stress intensity factors; and determining the probabilistic representation based on the plurality of crack growth data sets and the maintenance threshold; the remaining usage life value comprises a value of the probabilistic representation at the input probability value; and determining the one or more future uncertainty confidence limits comprises: determining fuzzy number bounds based on the remaining usage life value and the future uncertainty adjustment factor; performing probability assignments based on the fuzzy number bounds; and determining minimum and maximum remaining usage life values associated with the input confidence level based on the probability assignments.