Adhesive bond strength tests alignment

There was previously a separate ISO standard for adhesion in shear but this was withdrawn in favour of extending the standard for shear modulus to allow the test to be continued to the failure point, i.e. the two methods have been combined. The composite method is contained in ISO 182715 and uses the same quadruple element test piece as did the separate adhesion standard. The double sandwich construction is intended to provide a very stiff test piece which will remain in alignment under high stresses. The present standard quadruple test piece uses rubber elements 4 1 mm thick and 20 5 mm long and these tolerances are much less tight than previously. The measured adhesion strength in shear is less affected by the test piece shape factor then tension tests8 and the wider tolerances should be perfectly satisfactory. The test piece is strained at a rate of 50 mm/min, in line with the speed for most other adhesion to metal tests, and the result expressed as the maximum force divided by the total bonded area of one of the double sandwiches. The British equivalent BS 903 Part A 1416 is identical. 

The effect of silanes on the bond strength of two epoxide adhesives to glass is shown in Table 13. The test mode was that of Sandwich Butt Tensile in which a glass disc was bonded between two aluminium specimens in the form of a sandwich, and the resulting composite specimen broken on an Instron Universal Test Machine. Clearly in such a composite test specimen, alignment is important and there are many potential sites and modes of failure. 

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