Isolating Micro-Machined Accelerometer Zero-G Bias Shifts under Static Thermal Cycles
Static thermal zero-g bias shifts in MEMS accelerometers are isolated by enforcing prolonged thermal dwell periods to decouple stress creep from thermal gradients.
Structural Yield Strength
Material Limit
The maximum stress that a material can withstand without undergoing permanent, non-reversible plastic deformation is a fundamental parameter for mechanical design and sensor housing construction. This threshold, termed structural yield strength, defines the boundary between the elastic region, where the material returns to its original shape, and the plastic region, where it remains permanently deformed. Housing materials and internal support structures must operate well below this limit to ensure that the sensor does not experience permanent shifts in its geometry.
This mechanical stability is essential for maintaining the alignment of internal optical or capacitive components.
Testing Procedure
Standardized tensile testing represents the primary method used to determine this property by stretching a sample of the material until it yields. The force applied to the sample is measured by a calibrated load cell, and the resulting strain is tracked using an extensometer. This data is plotted on a stress-strain curve, and the yield point is identified either by a distinct knee in the curve or by applying a zero point two percent offset line.
This offset method is used for materials that do not exhibit a sharp transition from elastic to plastic behavior.
Metrological Verification
Calibration of the tensile testing machine must be verified against traceable standards to ensure the accuracy of the measured force and displacement. The load cell must be calibrated using reference weights, and the extensometer must be checked against a certified micrometric displacement standard. These steps are necessary to ensure that the measured yield strength of the material is accurate and can be trusted for design calculations.
This verification is performed annually to comply with quality assurance standards.
Design Margin
Engineering designs utilize a safety factor to ensure that the actual stress on a component remains well below the yield limit under all expected operating conditions. This safety margin accounts for variations in material properties and unexpected load spikes.