KGR-2 extensometer

A fully detailed design and accuracy report on the KGR-1 extensometer, designed to fulfill the above requirements, can be found elsewhere.(2)... 

FIGURE 3. KGR-1 extensometer mounted on a thick adherend lap shear specimen. 

FIGURE 4. Shear stress-strain curve produced by the KGR-1 extensometer. 

With the advent of accurate adhesive strain data via the KGR-1 extensometer, it became possible to verify the skin-doubler equations in Figure 1. To do this another extensometer was needed to measure the adhesive shear strain at the doubler tip. This measured value could then be compared to the calculated value. The second extensometer is identified as the KGR-2 and is shown in Figure 5. As before, the adhesive shear movement, Aa, at the doubler tip is made to move the core of an LVDT. The voltage change is fed to a recorder, which plots a curve of load vs. adhesive strain at the doubler tip. Tests were run on a skin-doubler specimen and the... 

Fig. 14. Thick-adhcrend lest coupon and Kreiger KGR-1 extensometer.

Thick adherend lap shear tests (TALST) were not based on any standard. However, standard practice used in the tests was followed. The displacement rate used was 0.3 mm/min. The adhesive layer displacement was measured using two in-house built KGR-1 type extensometers. 

The TALST system and the KGR-1 type extensometers were used for the first time at HUT/LLS in actual testing. The system did not function correctly in every respect. The tests were performed in two sets. The second set of tests was performed about four months after the first one to fill the gaps and to verify the results of the first set. 

KGR-1, AN EXTENSOMETER FOR MEASURING ADHESIVE SHEAR STRAIN VERSUS STRESS... 

Calculated values from formulas in Fig. 1 Q Measured value using KGR-2 extensometer O Measured scribemark offset ... 

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