Double Notch Shear test

In-plane and interlaminar shear strength of composites have been measured by the double-notch shear test method at a displacement rate of 2 x 10 mm/s. Results for a unidirectional Hi-Nicalon/BN/SiC/BS AS composite containing 42 volume % of fibers from room temperature to 1200°C are shown [38-39] in Fig. 13. The interlaminar shear strength... 

O. Unal and N. P. Bansal, Interlaminar Shear Strength of a Unidirectional Fiber-Reinforced Celsian Composite by Short-Beam and Double-Notched Shear Tests, Ceram. Eng. Sci. Proc., 22 [3] 585 95 (2001). 

Shear Properties - Double notch shear testing is preferred to short-beam shear, because of the multiple stress condition for the short beam shear geometry. In the double notch shear (DNS) test, the compression load translates into an interlaminar shear stress along the midplane connecting the two notches in the composite (See Figure 3). Table 3 lists the ultimate double notch shear strengths for the two sets of composite test bars. 

The shear strengths of the composites were measured in a double notch shear geometry, loaded in compression with an anti-buckling fixture. Compression testing was done on test coupons with dimensions as shown in Figure 3, using an anti-buckling fixture. 

In addition, a specific tests for composites ASTM 2733 [35] uses the double notched specimens (c.f single lap joint) to assess the shear strength at elevated temperatures. An extension of this test is in an internal aerospace test [36]. which uses thermal spiking to assess performance. In this test a sample is conditioned at the aerospace standard 70 C 85%RH for two weeks prior to a rapid excursion for a maximum of one minute to a higher service temperature. The specimen is then conditioned under the standard conditions for a further two weeks prior to the evaluation of the weight gain. 

For this reason there are also test methods for double lap shear such as ASTM D 3528 (for generic substrates), and for off set notched lap shear such as ASTM D 5656 (for metals) and D 3163, D 3164 and D 3165 (for generic substrates). Refer to Fig. 32. 

ASTM C-1135 can be used to determine the tensile adhesion strength of a sealant bond. Although no ASTM standards that specifically address the measurement of the adhesion or bond strength of sealants loaded in shear, the standards in place for adhesive bonds can be used (single lap shear - ASTM D-1002, notched lap shear - ASTM D-3165, and double lap shear - ASTM D-3528). Much of the adhesion testing that is performed in the industry is testing to determine the effects of environmental and chemical exposure on sealant adhesion. This exposure can be either static or cyclic (Gutowski and Cerra 2009). 

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