Durability of adhesive structure<br>1. Durability of adhesion at bonding interface<br>2. Durability of bonded materials<br>3. Durability of adhesive layer<br>Durability index<br>① Endurance strength<br>The maximum load per unit area of adhesive joint in service time.<br>② Endurance life<br>The failure time of adhesive joint under service load.<br>③ Fatigue failure<br>Under the action of cyclic stress, the strength of adhesive joint decreases until it is destroyed.<br>④ Fatigue strength<br>The maximum stress that does not cause failure at a specified number of cycles.<br>⑤ Fatigue life<br>The failure times of adhesive joint under specified cyclic stress.<br>Environmental impact<br>I function of water<br>Principle of action (effect on bonding interface)<br>Water molecules with small volume and strong polarity are easy to penetrate into the bonding interface along the hydrophilic material, which will destroy the hydrogen bond at the interface, thus weakening the force between the adhesive molecules and the surface of the material to be bonded, resulting in the decrease of bonding strength.<br>Plasticization: water molecules destroy the hydrogen bond and other secondary valence bonds between the adhesive molecules, resulting in plasticization of the adhesive, thus reducing the mechanical and physical properties of the adhesive;<br>Degradation: the chemical bond hydrolysis of adhesive causes the degradation of adhesive.<br>II thermal oxidation<br>1. With the increase of temperature, the thermal oxidation of adhesive is accelerated, and the decrease of bonding strength is accelerated;<br>2. When the bonding surface is exposed to sufficient oxygen, it is easy to degrade and crosslink;<br>3. The thermal stability of adhesive is closely related to the bond energy of chemical bond.<br>III stress action<br>For porous materials, the water absorption or drainage of the adhesive structure will cause expansion or contraction, which will produce stress; in the case of environmental temperature change, thermal stress will also occur. The existence of all these stresses will reduce the durability of the adhesive structure and accelerate the damp heat aging and thermal aging.<br>Adhesive durability, the joint influence of many factors<br>1. Type and composition of adhesive;<br>2. The type and surface state of the material to be bonded;<br>3. Size and shape of bonding part;<br>4. Bonding conditions and methods;<br>5. Stress direction and size of adhesive joint;<br>6. Environmental conditions;<br>7. Whether the glue is directly exposed to air, light and heat for a long time after bonding.<br>-END-<br>
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