Behavior of glass fibers under load
Glass fibers are elastic until failure and exhibit negligible creep under controlled dry conditions. Generally, it is agreed that the modulus of elasticity of mono-filament E-glass is approximately 73 GPa.
The ultimate fracture strain is in the range of 2.5 to 3.5 percent.
The stress-strain characteristics of strands have been thoroughly investigated.
The fracture of the actual strand is a cumulative process in which the weakest fiber fails first and the load is then transferred to the remaining stronger fibers, which fail in succession.
Glass fibers are much stronger than a comparable glass formulation in bulk form such as window glass, or bottle glass.
The strength of glass fibers is well retained if the fibers are protected from moisture and air-borne or
When glass fibers are held under a constant load at stresses below the instantaneous static strength, they will fail at some point as long as the stress is maintained above a
This is called “creep rupture.” Atmospheric conditions play a role, with water vapor being most deleterious.
It has been theorized that the surface of glass contains submicroscopic voids that act as stress concentrations.
Moist air can contain weakly acidic carbon dioxide.
The corrosive effect of such exposure can affect the stress in the void regions for glass fiber filaments until failure occurs.
In addition, exposure to high pH environments may cause aging or a rupture associated with time.
These potential problems were recognized in the early years of glass fiber manufacture and have been the object of continuing development of protective treatments. Such treatments are universally applied at the fiber-forming stage of manufacture.
A number of special organo-silane functional treatments have been developed for this purpose.
Both multifunctional and environmental-specific chemistries have been developed for the classes of matrix materials in current use.