MTS3000 Automatically Determines Residual Stress Using Strain Gauges
The strength behavior of components is influenced by their existing residual stresses without showing any visible signs. Therefore, the aim is to determine the mechanical stresses in the components. With the hole-drilling method for determining residual stresses, a small hole of 1.6mm diameter is drilled into the workpiece, and strain gauges are used to measure the resulting strain.
SINT Technology and HBM offer both the MTS3000 system and the required amplifier QuantumX which enable this process to be implemented easily. The system uses a stepping motor that permits drilling at 350,000 rpm. The strain changes arising due to the step-by-step drilling of the hole into the workpiece will be detected by strain gauge rosettes specifically designed for this process.
Signal processing is performed digitally. In addition to system control functions, the software package comprises four different evaluation algorithms that enable the mechanical stresses to be computed from the measured strain. The entire measurement process is PC-controlled, ensuring a high degree of measurement reliability and optimum reproducibility.
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Residual Stress: Measuring Internal Forces
Residual stresses can arise in material due to the effects of internal forces without any external forces acting. For example, residual stresses arise by non-uniform cooling of cast components, by welding or forging of the parts, or by mechanical processing.
Two strain gauge-based technologies are often used for determining residual stresses: the ring core method and the hole drilling method.
The common feature of both methods is that after installation of the strain gauge rosette on the workpiece, the residual stress state is changed due to the mechanical process of drilling/coring. During this process, the residual stresses relax and release strains that are measured with strain gauges, and later are used for calculating the residual stress state.
With the ring core method, a ring-shaped groove is extracted around the respective strain gauge. For the hole drilling method SINT Technology offers the MTS3000 system. A milling cutter rotating at about 350,000 rpm and advanced by a stepper motor is used for hole drilling. The strain changes arising due to the step-by-step drilling of the hole into the workpiece are detected by a strain gauge rosette designed specifically for this method.
Both the MTS3000 system and the calculation of the residual stress results are compliant to the ASTM E837 standard version 2013, the only complete standard on residual stresses available in the world.