The bonding strength of the adhesive is introduced

The bonding strength of adhesive is one of the important indicators to evaluate the quality of adhesive. Bonding strength is usually divided into shear strength, stretch strength, peeling strength and impact strength according to the force condition in adhesive use.
1, bonding strength definition
bonding strength refers to the external force, so that the adhesive in the adhesive and the adhesive interface or its adjacent damage required stress, bonding strength is also known as bonding strength .
Bonding strength is the stress required when the adhesive system is destroyed, the size of which depends not only on the adhesive force, the mechanical properties of the adhesive, the nature of the adhesive, the bonding process, but also related to the joint form, the force condition (type, size, direction, frequency), environmental factors (temperature, humidity, pressure, medium) and test conditions, experimental techniques, etc. Thus, adhesion is only one of the important factors that determine bonding strength, so bonding strength and bonding force are two completely different concepts and must not be confused.
2, the force form of the bonding joint
the force of the glue layer under the external force of the bonding joint can be summarized as shearing, stretching, uneven tearing and stripping of 4 forms.
A, cut.
the size of the external force, opposite direction, basically parallel to the bonding surface, and evenly distributed throughout the bonding surface.
B, stretch.
also known as uniform tearing, by the opposite direction of the pull force, perpendicular to the bonding surface, and evenly distributed throughout the bonding surface.
C, uneven tearing.
is also called split, the direction of external force action, although also perpendicular to the bonding surface, but uneven distribution.
D, peel.
the direction of external force action and bonding surface into a certain angle, basically distributed in a straight line on the bonding surface of the above four forces, in the same adhesive system is likely to have several forces at the same time, but what is the main problem.
3, bonding strength classification
According to the bonding joint force situation is different, bonding strength can be divided into shear strength, stretch strength, uneven tearing strength, peeling strength, compression strength, impact strength, bending strength, torsion strength, fatigue strength, anti-creep strength and so on.
A, Shear Strength
Shear strength refers to the shear force that a unit bonding surface can withstand when a bond is broken, expressed in megapa (MPa). Shear strength is divided into stretch shear, compression shear, torsional shear and bending shear strength according to the force mode of testing.
different properties of the adhesive, shear strength is also different, in general, tough adhesive than flexible adhesive shear strength. A large number of experiments show that the thinner the thickness of the glue layer, the higher the shear strength.
the most affected test conditions are the ambient temperature and test speed, as the temperature increases shear strength decreases, as the test speed slows down shear strength decreases, which shows that the temperature and speed have an equivalent relationship, that is, to increase the test temperature is equivalent to reducing the loading speed.
B, stretch strength
extrusion strength, also known as uniform tearing strength, positive pull strength, refers to the adhesion force damage, the unit area of the stretch force, the unit is expressed in megapa (MPa). Because the extrusion is much more uniform than the shear force, the general adhesive stretch strength is much higher than the shear strength. In the actual determination, the test piece under the external force, because the deformation of the adhesive than the viscous, plus the different axial effect of the force, it is likely to produce shearing, there will also be lateral compression, therefore, in the tearing may occur at the same time break. If the length of the test can be increased and the bonding area can be reduced, the effect of stripping can be reduced, so that the stress effect distribution is more uniform. The effect of elastic mod, layer thickness, test temperature and loading speed on stretch strength is basically similar to shear strength.
C, peeling strength
peeling strength is the maximum load that can be sustained per unit width under specified peeling conditions, so that the bonding part is separated, expressed in kN/m units. Stripping takes many forms and can generally be divided into L-type peel, U-type peel, T-type peel and surface peel.
the peeling angle changes, so do the peeling forms. L-type peeling when the peeling angle is less than or equal to 90 degrees, and U-type peeling is greater than 90 degrees or equal to 180 degrees. These two forms are suitable for the peeling of rigid and flexible material bonding. T-type peeling is used for stripping when bonding two flexible materials. Peeling strength is affected by factors such as the width and thickness of the test piece, the thickness of the glue layer, the peeling strength, and the peeling angle.
D, uneven tearing strength
uneven tearing strength indicates the maximum load that the bonding joint can withstand when it is subjected to uneven tearing force, because the load is concentrated on two or one edge of the glue layer, so it is the unit length rather than the unit area force, the unit is kN/m2.
E, impact strength
impact strength means that when the bonding part is damaged by the impact load, the maximum amount of work consumed per bonding area is kJ/m2. According to the different form of joint and the mode of force, the impact intensity is divided into bending shock, compression shear shock, stretch shear shock, twisting shear shock and T-type peeling shock strength.
impact strength is affected by adhesive toughness, adhesive thickness, viscous species, test case size, impact angle, ambient humidity, test temperature, etc. The better the toughness of the adhesive, the higher the impact strength. When the mod of the adhesive is low, the impact strength increases with the increase of the thickness of the adhesive layer.
F, Persistence Strength
Persistence strength is the maximum load that a unit bonding area can withstand after a long period of static load, expressed in megapa (MPa). Long-lasting strength is affected by load stress and test temperature, and decreases with load stress and temperature increase.
G, fatigue strength
fatigue intensity refers to the bonding joint repeatedly applied a certain load to the specified number of times does not cause damage to the maximum stress. Fatigue intensity at 10 times is generally referred to as the fatigue intensity limit. Generally speaking, the shear strength of high adhesive, its peeling, bending, impact and other strength is always low; The peeling strength of the adhesive, its impact, bending strength is higher. Different types of adhesives, different strength characteristics also vary greatly.