The increased use of fiber composites and the systematic optimization of components presuppose a precise knowledge of the load situation. In many applications, sensor integration is the only way to meet the demand for modern lightweight structures with regard to production control, load monitoring, damage analysis and control signal generation. HBM’s new LI66 strain gages are directly embedded in the structure during the fiber composite production process. This allows measurements at spots that are no longer accessible after production. The most obvious feature of the LI66 strain gage are the two vertically attached contact pins, for contacting the strain gage embedded in the material.

The measuring leads are only connected to the gold-plated pins after manufacture, outside the structure, which makes all the handling easier. The special design of the LI66 strain gage allows you to decide whether the pins should be contacted inside the structure or on its outside. Thus, for example, with sandwich structures, the measuring leads or customized electronics can be introduced into the foam core. The special strain gage layout is designed in such a way that the measuring grid is outside the fibers running round the pin. Furthermore, special strain relief of the solder terminals prevents the forces working on the pin from being transferred to the measuring grid.

When the strain gage is integrated, it is cemented to the material via the matrix resin. The point of the pin concept is that it is then not necessary to also embed the measuring leads in the fiber composite. The measurement performance of integrated strain gages has been verified in countless investigations. Results show that the high level of measurement accuracy that you get from strain gages is retained in full by this integration concept. Secondary, damage analysis investigations indicate that the strain gage is sufficiently sensitive to detect when there are cracks in the resin and delaminations in the fiber composite component.

Key Feature(s)

• Individual adaptation of the strain level through the embedding depth of the strain gage in the composite material
• Measurement between glued joints
• Installation during the manufacturing process
• Strain gage protection in the material
• Flow profiles are not affected by the measuring point
• Measurement at spots that are no longer accessible after production