An Estimation of Longitudinal Strength Reduction of Unidirectional E-glass/Epoxy Composite Exposed to Sulfuric Acid Using a Micromechanics Model

A new model is proposed in this research to calculate the longitudinal strength
of unidirectional E-glass reinforced polymer composites exposed to sulfuric
acid environment, using a micromechanics model. In the proposed method,
it is assumed that the residual strength of the degraded composites under acidic environment can be calculated by knowing the degraded strength properties of the constituent materials. In order to measure the properties of the degraded epoxy resins and E-glass fibers, corrosion tests are performed on them when exposed to 5% sulfuric acid for different immersion times. Acid penetration in composites is a time consuming phenomenon. Thus, before the acid reaches to inside region of composites, the degraded composites cross-section can be divided to two regions, namely intact and degraded regions. In this stage, a simple model is suggested to estimate the acid penetration depth in the degraded composites. Based on the corrosion mechanisms of glass fibers, the energy dispersive x-ray microanalysis (EDX) results of different points of composites cross-section are used to estimate the acid penetration depth in composites. Both the acid penetration depth model and micromechanics model are used to calculate the longitudinal strength of intact and degraded regions for different immersion times. Thus, the longitudinal strength of degraded composites can be calculated. Moreover, some similar unidirectional E-glass/ epoxy composites exposed to sulfuric acid for different immersion times are tested to measure the longitudinal strength of them. The theoretical results are in good agreements with those experimentally measured.