Curing Induced Shrinkage: Measurement and Effect of Micro-/Nano-Modified Resins on Tensile Strengths

Abstract

Fiber reinforced composites are widely used in automotive, aerospace and marine applications because of their light weight, low costs and excellent chemical resistance properties. Physical and chemical behavior of these composites is dependent on their matrix properties. The curing process of resins/matrix can introduce considerable shrinkage, which based on the component and its boundary conditions can detriment the strength of these materials and resulting components. One way to control the curing-induced effects is reinforcement of the resins with micro- and nano-fillers. In this work, the effect of various micro- and nano-fillers (3M™ Glass Bubbles iM16K and Cloisite® 30B nanoclay) in epoxy resin (SC-15) on curing-induced shrinkage and resulting tensile strengths was evaluated. Additionally, volumetric shrinkage (un-restrained) and curing-induced strains (ASTM D638 tensile tests) were measured by AccuPyc™ II 1340 pycnometer and fiber Bragg-grating (FBG) sensors respectively. A special technique was developed to correct the pycnometer measurement technique and make them independent on the testing chamber temperature. Results revealed that the morphology of the fillers (platelets/spherical) and their concentration significantly influence the curing-induced strains and associated shrinkage. Although such observations were expected, detailed quantification on the volumetric shrinkage and its effect on structural components made of such resins are not well documented. Overall, the study uses a novel technique to correct the pycnometer measurement technique and provides the groundwork for understanding the influence of the type and content of the fillers on the curing-induced shrinkage process. This will provide improved dimensional stability and reduce curing-induced residual stresses on resulting composites.