Strength and Fractography of Glass Wool Fibres

 

Glass wool fibres (GWFs) are produced using the cascade spinning process. The lengths of the fibers range from 1 to 4 cm, whereas the diameters range from 4 and 10 mm. GWFs are widely used as insulation material due to their excellent heat and sound isolation effect, chemical durability, and high strength. In spite of those advantages, GWFs show a certain degree of brittleness, which limits the mechanical performance of GWFs during both transportation and application. Therefore, a reduction in the brittleness of GWFs is an inevitable task for us. To do so, it is important to look into the fracture behaviour and its connection to the mechanical strength. Here we report a detailed study of fracture behaviour of GWFs by means of uniaxial tensile strength and SEM micrographs of fractured surfaces.

The tensile strength data of GWFs are evaluated by Weibull statistics. The Weibull model does not take the failure mechanism into account. But the Weibull modulus (m) gives the spread of the data, and may indicate one or more types of failures. For the cascade spun GWFs m is low (between 2 and 3), hence fracture characteristics of the failed fibres will strengthen the argumentation and conclusions on the mechanical performance of GWFs. The observed fracture surfaces are classified in three categories: 1) surfaces including fracture mirror, mist and hackle; 2) bend fracture surfaces; and 3) surfaces including pores. The first is by far the most common. The second illustrates that some times the failure does not appear in uniaxial tensile stress. The last category is rarely observed. From the characteristics of the fracture surfaces within the first category, it is seen that the strongest fibres have the smallest ratio between the area of the fracture mirror and the fibre cross section. The classical relation between fracture strength (s_f) and mirror radius (r), i.e., s_f = A*r, is confirmed for all the GWFs studied. The materials constant, A, (mirror constant) is found to be 2.4 ~ 2.7 MPam^½ for basaltic wool and 2.0 MPam^½ for E-glass wool, which is similar to the value reported in the literature for different silicate glasses.