Comparison of Embedded and Conventional Strain Gauges on Glass Fiber-Reinforced Coupons

The coupons were measured under the following test conditions:

• Coupon no. 1 with LY21 strain gauge on surface + embedded LI66 strain gauge
• Coupon no. 2 with LY21 strain gauge only, installed on the surface
• Coupon no. 3 without any strain gauges (tested with extensometer)

The coupons were tested with an uniaxial tensile test until failure at a velocity of 2mm/min and a preload of 50N. The testing conditions were 23°C with 50% relative humidity.

• The strain gauges give very similar results for the stress/strain measurements. Embedding the LI66 strain gauge into the composite material has no measurable impact on the test coupon. The LY21 strain gauge installed on the composite material does not show any measurable effect or delamination.
• The crack position of the coupon is at the same area for all tested coupons.
• The graphs present the stress/strain behavior until failure of strain gauges (signal lost). Ultimate failure of composite is around 400MPa for the three coupons. The test coupon with the embedded strain gauge shows a quicker failure since connection between the pins and the wires was lost.

IPC (Centre Technique Industriel de la Plasturgie et des Composites) is the industrial technical center whose expertise is dedicated to plastic and composite innovation in France. Since 2016, the profession has thus new means to support all companies, especially small and medium-sized businesses, whatever the process used, thanks to a contribution instituted to finance R&D, innovation, transfer of technologies and skills.