XY and RY strain gauges for determining residual stress
HBM offers you strain gauges for analysis of residual stress and for the ring-core method as well as the hole drilling method.
A common feature of both methods is that, after installation of the strain gauge rosettes onto the work piece, the residual stress condition is disturbed by a suitable action. In the case of the ring-core method this is done by cutting a circular groove around the strain gauge rosette. In case of the hole drilling method, a hole is drilled into the center of the rosette.
Following this action, residual stresses cause strains on the surface of the workpiece, which are detected by the strain gauge and then used to calculate the residual stress state. The HBM product line gives you a choice between three different methods for determining residual stress.
Ring-core method: XY51 rosettes (for residual stresses with known principal direction) and RY51 rosettes (for residual stresses with unknown principal direction) are specifically designed for the ring-core method. This method provides high-precision measurements and the residual stresses are represented depending on the drilling depth.
As these strain gauges are covered by a print plate, they can be used on level or slightly curved surfaces only.
- XY51: For residual stresses with known principal direction
- RY51: For residual stresses with unknown principal direction
Hole-drilling method based on the integral method: RY21 and RY61SG rosettes together with the corresponding drilling equipment can be used to determine residual stresses according to the integral method.
The result is the integral average of the residual stresses over the entire drilling depth.
- RY21: Especially easy to handle. Temperature response optimized for steel.
- RY61: Drill hole rosette. Covered by a print plate and can therefore only be used on level or slightly curved surfaces.
Hole drilling method with high-speed drilling: Drill hole rosettes RY61S, RY61R, RY61K, VY61S and RY61M are specially designed for the requirements of high-speed drilling. This method works with a special drilling technique with the cutter operating at a speed of about 500,000 rpm. This prevents new residual stresses from occurring during the machining process. This method produces extremely precise measurement results that make it possible to represent residual stresses depending on drilling depth very precisely.
- RY61M: Patented structure with six measuring grids. The signals of opposite SGs are determined, which reduces measurement errors, depending on possible eccentricity of the drill hole, by a factor of 5.
No additional connection work because the measuring grids have already been wired on the carrier foil.
Tips for selecting strain gauges
The right measuring grid length: The measuring grid length depends on the aim of measurement, since the result of a measurement with strain gauges (SGs) will be determined as the average of strains. In general, measuring grid lengths of 3 to 6 mm represent a good solution.
Long measuring grids are recommended where there is an inhomogeneous material such as e.g. concrete or wood. A long strain gauge will bridge the inhomogeneities of the workpiece and return the strain underneath the measuring grid as the measurement result.
Short measuring grids are suitable for detecting a local strain state. They are therefore suitable for determining strain gradients (strain gauge chains), the maximum point of notch stresses and similar stresses.
The right resistance: The selection of the resistance depends on the constraints of the measurement task. 120-ohm strain gauges are relatively insensitive to fluctuations in the insulation resistance, for example due to the effects of moisture.
The advantage of higher impedance strain gauges is that they produce less specific heat due to the lower measuring current. In addition they are less sensitive to resistances in the connecting cables to the measuring amplifier. There is also a disadvantage that higher impedance strain gauges may be more sensitive if noise pulses are received.
Customer-specific strain gauges
Do you have special requirements that are not adequately covered by any of the strain gauges in our standard program? Are you looking for an equivalent strain gauge for the product you are current using? Have you designed your own strain gauge? Contact us, we will produce customized strain gauges according to your requirements! From quantities of 20 packages and up.
Get a quote for XY / RY strain gauges
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