Adhesive physics and adhesive performance testing (on)

First, the physical and chemical properties of the adhesive test

1. Appearance: Determine the homogeneity, status, color, and impurities of the glue.

2. Density: The density of the liquid adhesive is determined using a density bottle.

3. Viscosity: Tested with a Tu-4 viscometer (sec) and a rotational viscometer (Pa.S).

4. Curing speed: important data for studying adhesive curing conditions.

Second, the determination of adhesive performance

Adhesive strength is related to many factors:

A. The structure, properties, and formulation of the main material of the adhesive;

B, the nature of the adherend and surface treatment;

C, glue, glue and curing process related;

D. The form, geometry and processing quality of the rubber joints;

E. Strength test environment such as temperature, pressure, etc.;

F, external force loading speed, direction and mode.

(A) Shear and tensile strength:

1. Shear strength: The rubber joint can withstand the maximum load parallel to the cemented surface in unit area. Divided according to the manner of stress: tensile shear, compression shear, twist shear and bending shear.

2, the shear strength test method:

A. Single Lap Tensile Shear Strength Test Method: This method is the most commonly used aluminum sheet single-sided lap joint method, the standard size: The test piece should be not less than 5 pairs in the determination, take the arithmetic average and observe Specimen destruction characteristics.

B. Compressive Shear Strength Test Method: This method is used to test the bonding strength of thick non-metallic sheets.

3, the plastic joints shear strength factor.

A. Stress concentration of the adhesive: Due to the uneven distribution of the stress of the rubber joints, stress is concentrated on the ends of the lap joints in the shear load test, gradually causing damage.

B. Influence of adherends and adhesives: The greater the modulus E and thickness of the adherend, the smaller the stress concentration factor and the greater the shear strength of the rubber joint. The high modulus of the adhesive, the severe stress concentration, and the lower the shear strength of the rubber joint.

C, the impact of the thickness of the adhesive layer: According to the stress distribution: the thicker the adhesive layer, the smaller the stress concentration factor of the joint, the greater the shear strength. However, the thicker the adhesive layer, the lower the shear strength. This is because the thicker the adhesive layer is, the more the internal defects increase exponentially, and the cohesive strength of the adhesive layer decreases. The thicker the adhesive layer is, the greater the shrinkage stress and thermal stress caused by the temperature change, resulting in the loss of cohesive strength. This does not mean that the gel layer is the better the book, the glue layer is too easy to cause the lack of glue, resulting in decreased adhesive strength. Therefore, a uniform thickness of the gel layer is preferably controlled within 0.03-0.15 mm.

D. The influence of the lap length is known from the stress distribution. The stress concentration factor increases with the increase of the lap length, and the shear strength of the joint decreases. Therefore, the best lap test must be determined.

4, the tensile strength test

4.1. Tensile strength refers to the maximum load that the glued joint can withstand perpendicular to the cemented surface per unit area.

4.2 Factors Influencing Tensile Strength: According to the stress distribution, the stress of the joint concentrates on the edge of the glue. When the edge stress concentration reaches a critical value or above, the glue layer in the edge area cracks, and the crack instantly expands to the entire bond surface.

(to be continued)