Fractographic Analysis of Very Small Theta Specimens

Abstract

The theta test specimen is a versatile tool for evaluating the strength of extremely small structures. Round and hexagonal rings are compressed vertically on their ends creating a uniform tension stress in the middle gauge section. The simple compression loading scheme eliminates the need for special grips. A conventional nanoindentation hardness machine with a flat indenter applied load, monitored displacement, and recorded fracture loads. Prototype miniature specimens with web sections as thin as 7.5 m were fabricated by deep reactive ion etching (DRIE) of single crystal silicon wafers. The strength limiting flaws were 200 nm to 500 nm deep surface etch pits.