Comportamiento en fatiga de poliamidas reforzadas con fibra de vidrio corta

Resumen

The work shows the existence of three states in the fatigue behaviour of short fibre-glass reinforced polyamide up to the moment of failure. In the state I creep transient deformation processes are produced. If temperature, associated to the dynamic process, stabilises, the material is able to withstand an unlimited number of cycles. On the other hand, if temperature grows continuously the material takes a critical strain for which a transition to the state II is reached. This new state shows a constant material´s deformation rate and a homogeneous nucleation of crazing phenomena. The hysteresis energy per cycle grows in a constant way and the material´s temperature increases. These conditions lead to the final instability that starts when the material´s deformation reaches a new critical value for which a second transition to the state III takes place. Under these circumstances local instabilities precede material´s final fracture. This is due to the quantity of crazes and their sizes, which are important enough to origin high concentration of mechanical effects to produce a material´s accelerated growth deformation to obtain its fracture