Fatigue Fuse

The FATIGUE FUSE (FF) is a highly calibrated metal analog sensor designed to measure accumulated fatigue damage in its host structure. While relatively simple in appearance, consisting of a series of parallel metal strips (fingers) connected to a common base (hand), each finger is precisely designed to fracture after a known cycle count or damage accumulation, which can be easily observed by the human eye. The FF is mechanically attached or bonded to a structural element of interest, such that the Fuse undergoes the same strain sequence as the structure, and thereby experiences an analogous state of fatigue. Design of these fingers requires a complex understanding of fracture mechanics, fatigue life, and knowledge of the types of dynamic loading that a host structure is likely to undergo. By combining finite element modeling, real-world loading data, and laboratory validation in an iterative development scheme, MFS has developed an easy to use and inspect sensor which can determine whether critical mechanical components are operating safely and within the bounds of their designed limits.

FATIGUE FUSES have been primarily utilized in military applications, such as rapid deployable bridges, where conventional Structural Health Monitoring (SHM) systems are impractical due to access and power restrictions. For these same reasons, FF’s are an ideal addition to numerous civil, structural, and mechanical assets. The elegance and ease-of-use provide asset owners immediate peace-of-mind as to the fatigue status of their structures without requiring complex and time consuming data collection and analysis.

The material, geometry, and notch characteristics of each finger are selected to achieve the highest possible precision. Materials ranging from aluminum alloys, structural steels, and stainless variants have been characterized to match host structures in a myriad of applications from civil infrastructure, to military, to mechanical, and automotive use. Fuse Geometries are precisely customized to application specific constraints, such as attachment envelopes and predicted loading configurations, and can accommodate environmental isolation with a windowed cover system. Notch characteristics, such as width, depth, and shape, have been developed for a wide range of application derived stress concentration factors and tested in sufficient numbers for statistical significance.

The FATIGUE FUSE is ideal for new structures where transport loading and/or construction loading contribute significantly to the overall performance of the structure. It is also well suited for structures that have hard to inspect fatigue sensitive details where the FATIGUE FUSE can be calibrated and translated to an easier to inspect area. Additionally, the FATIGUE FUSE can be utilized on existing structures to compare actual loading conditions to predicted values and used to estimate the remaining fatigue life based on live-use benchmarks.

FATIGUE FUSES can be designed for nearly any combination of load magnitude and effective fatigue life. For a new structure, this can translate into fingers which fracture at known increments of the total designed life such that maintenance plans can transition from purely duration based schemes to use driven ones. For pre-existing or retrofitted structural assets, fingers could also be designed for a number of incrementally increasing load levels and the same fatigue life duration so that individual structural members can be confirmed as operating within their designed performance limits. Finally, each testing condition continues to expand MFS’s knowledge base of design parameters and specific binning processes and tolerances can be custom developed to client specifications.

Hannah SmallThe Fatigue Fuse (FF™) new