Adhesives and bonding test methods

There are many reasons why adhesives and bonding test methods need to be tested for adhesives and adhesions, some of which are:

( 1 ) Performance comparison (stretching, shearing, peeling, bending, impact and splitting strength; durability, fatigue, environmental resistance and conductivity, etc.).

( 2 ) Perform a quality inspection on each batch of adhesive to determine whether it meets the standard requirements.

( 3 ) Verify the effectiveness of the surface and its treatment.

( 4 ) Determine the useful parameters for the test performance (curing conditions, drying conditions, adhesive layer thickness, etc.).

From the above we know that tests are very important for all aspects of materials science and engineering, especially for adhesives. The test can not only determine the strength of the adhesive itself, but also evaluate the adhesion technology, the effectiveness of surface cleaning and treatment, surface corrosion, adhesive coating, adhesive layer thickness, and curing conditions.

This chapter begins with a general discussion of the various types of adhesive joint testing, including only some of the more important tests, followed by a listing of the relevant ASTM methods and practices in certain disciplines, and the SAE Aerospace Administration's recommended method ( ARP/s ). .

1 stretching

1 ) The simple tensile test is a test in which the load acts perpendicular to the plane of the adhesive layer and passes through the center of the adhesive surface.

2 ) The ASTM D897 Bonded Joint tensile strength test method is one of the oldest methods retained in ASTM for adhesives.

3 ) Attention must be given to the production of test specimens and fixtures. Due to improper design, edge stress will occur during the test, and there will be a great stress concentration. The obtained stress data will be calculated analogously to different bonding areas or different structures. The strength of the joint is likely to be untrue.

4 ) D897 has been replaced by D2095 (Test method for tensile strength of strip and round bar specimens).

5 ) This kind of test piece is made according to the standard of ASTM D2094 (preparation of strip type and round bar test piece in adhesion test), and it is easy to adjust concentricity.

6 ) Tensile test is the most common test for evaluating adhesives. Although it is a joint designed by an experienced person, it cannot guarantee that it is completely in the form of tension when it is charged.

7 ) Most structural materials have higher tensile strength than adhesives. One of the advantages of the tensile test is that it provides the most basic data, such as tensile strain, elastic modulus, and tensile strength.

2 cut

1 ) The simple shear stress is the stress generated parallel to the adhesive surface. A single lap shear test piece does not represent shearing, but it is practical and relatively simple to produce. The measured data has practical value and good repeatability.

2 ) Shear test is a very common test because of its easy preparation of test pieces, and its geometric shape and operating conditions are applicable to many structural adhesives.

3 ) As with the tensile test, the stress distribution of the shear test is also non-uniform. The failure stress is obtained by dividing the load by the bonding area according to conventional methods. The maximum stress in the adhesive layer is much higher than the average stress. The adhesive layer is subject to different stresses than pure shearing.

4 ) The failure mode of the “shearing” joint is related to the thickness of the adhesive layer and the stiffness of the adherend. Sometimes it is dominated by shear failure and sometimes by tensile failure.

5 ) The shear test method currently used, in addition to ASTM D1002 , also has ASTM D3163 , which is almost the same configuration as ASTM D1002 except that the thickness is different.

6 ) This method solves the problem that the adhesive is easily extruded from the edges. ASTM D3165 (Lamination Shear Strength Test Method for Laminated Composite Adhesives) illustrates how to prepare a test piece to determine the tensile shear strength of a sandwich structure.

7 ) The standard for double-lap shear test is ASTM D3528 (Test method for tensile shear strength of double-lap joints). The advantage is that the force is balanced, which reduces the splitting stress in the single-lap joint test. And peel stress. But it also brings new problems. When two or more layers of glue are subjected to stress at the same time, comparative tests may be complicated.

8 ) Compression shear tests are also commonly used. ASTM D2182 (Metal-to-Metal Bonding Compression Shear Strength Measurement Method) describes the similarity between specimens and lap shear and compression shear test equipment.

9 ) ASTM D905 (Test method for compressive shear strength of bonded joints) is a test for measuring the shear strength of wood (hardwood, etc.). ASTM E229 is a test to determine torsional shear strength and torsional shear modulus.

10 ) If the test piece is suitable and the concentricity is good at the time of loading, the stress distribution in the rubber layer is more uniform than that in the lap shear test in E229 .