Structural design based on strength of materials principles or the theory of elasticity requires knowledge of the mechanical properties of the structural components, including adhesives. By the nature of their use, the most important adhesive properties are shear modulus and shear strength. A torsion test, such as described in Test Method E 229, is theoretically the most accurate method for measuring adhesive shear properties. It is, however, impractical in many situations. For example, certain materials of construction are not readily adaptable to fabricating the thin-walled cylinders used as adherends in the torsion test. The modified-rail test does not have this disadvantage.

Two undesirable conditions occur in the modified-rail test specimens that do not occur in butt-joined cylinders; nonuniform shear-stress distribution along the joint, and the addition of some undefined combination of tension and compression stresses to the shear stress at a given location in the joint. The modified-rail shear tool minimizes but does not eliminate these undesirable effects.

Shear modulus, strength, and other properties are measured by the modified-rail method.

1.1 This test method describes equipment and procedures to measure the shear modulus and shear strength of adhesive layers between rigid adherends. The equipment may also be used for determining the adhesive's shear creep compliance, the effects of strain history such as cyclic loading upon shear properties, and a failure criteria for biaxial stress conditions such as shear plus tension and shear plus compression.

1.2 High-density wood shall be the preferred substrate. The practical upper limit on the shear modulus that can be measured is determined by the shear modulus of the adherends and by the strain measuring device. Thus, the practical limit of adhesive shear modulus that can be measured using high-density wood adherends is about 690 MPa (1 10 ⁵ psi).

Note 1—Wood-base composites, metal, plastic, reinforced plastics, and other common construction materials may also be used for adherends.

1.3 The range of specimen dimensions that can be tested are: width 1.59 to 12.70 mm (0.0625 to 0.500 in.), length 102 to 203 mm (4 to 8 in.), and adherend thickness 13 to 25 mm (0.50 to 1.00 in.). The standard specimen dimensions shall be: width 3.18 mm (0.125 in.), length 203 mm (8 in.), and adherend thickness 19 mm (0.75 in.). Bondline thicknesses from 0.15 to 3.18 mm (0.006 to 0.125 in.) may be tested.

1.4 The values stated in SI units are to be regarded as the standard. The values given in parentheses are for information only.

1.5 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.