Physical and mechanical properties of pultruded composites containing fillers and low profile additives

This article deals with the effect of fillers and additives content on the physical and mechanical properties of unidirectional pultruded glass/polyester composites. The physical characterization consisted of determining the void volume fraction (Vv), density, shrinkage ratio, coefficient of thermal expansion (CTE), and dynamic mechanical properties. The mechanical tests consisted of three-point-bending tests under static, impact, and fatigue loading. The low profile additive (LPA) has been found to compensate the cure shrinkage by microvoid formation. Dynamic mechanical analysis measurements show that the LPA slightly lowers the glass transition temperature Tg and increases the internal damping Tan delta. The transverse coefficient of thermal expansion was found to be sensitive to the LPA content. Three-point bending tests show that the interlaminar shear strength (ILSS) is slightly sensitive to the fillers and LPA content, but the flexural strength is not affected. Impact test results on short beam shear and flexural specimens show the same behavior as in the static tests except that the LPA content has a detrimental effect on the flexural impact properties. The fatigue tests performed show that the effect of fillers is not significant, while the LPA effect is mixed. It seems that there is an LPA content for which the fatigue resistance is maximized. Finally, the wide range of behaviors and span-to-depth ratios investigated suggest that the ILSS as measured according to the ASTM 2344 recommendations can be largely misleading because of the unavoidable compressive yielding under the loading nose. For the materials investigated, higher span-to-depth ratio are more representative of the ILSS.