Abstract
Creep behavior and fatigue life are important performance indexes that affect the long-term stability of resistive strain gauges. The resistive strain gauges, fabricated with wet etching and resistance trimming, present micro-morphology such as textures and uneven edges on the surface and side-wall profile of sensitive grids. This paper observed the micro-morphology of the sensitive grids by microscope and analyzed its range of geometric dimensions. A sine function was used to establish equivalent geometric models for the surface textures and side-wall profile. Based on time hardening theory and the S–N curve, the dependence of micro-morphology of metal resistive strain gauges on creep behavior and fatigue life was studied. The results indicate that the roughness of micro-morphology has an influence on creep behavior and fatigue life. The surface textures and side-wall profile lead to the increase of creep strain and the decrease of fatigue life in varying degrees. When 60% of the ultimate stress of the strain gauges is loaded, the average creep strain in steady-state calculated by the maximum roughness of the side-wall profile reaches up to 6.95 times that of the perfect flat surface. Under the condition of loading 70% of the ultimate stress and the same roughness, the fatigue life led by side-wall profile could be reduced to 1/25 of the textured surface. The obtained achievements promote an understanding for optimizing the fabrication process of resistive strain gauges as well as developing high-precision and long-life force sensors.
Highlights
Both wet etching and resistance trimming are critical procedures in the fabrication process of foil-type strain gauges
By using Norton–Bailey time-hardening theory and S–N curve, we analyzed these models and summarized the dependence of the micro-morphology caused by wet etching and resistance trimming on creep behavior and fatigue life
Creep strain and fatigue life are affected by the roughness of surface textures and side-wall profile
Summary
Both wet etching and resistance trimming are critical procedures in the fabrication process of foil-type strain gauges. Two methods are generally used in resistance trimming, one is chemical corrosion and the other is mechanical polishing. The former uses ferric chloride to corrode sensitive grids surface to reduce the thickness of strain gauges, while the latter uses abrasives to polish the surface directly [1]. Both will leave uneven textures on the surface
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