The study investigates the effects of salt concentration on some mechanical properties of thermoset polyester resin without reinforce and polyester resin reinforced with random fiber glass mat. The volume fraction of the composite material varies in (15%, 25%, 35% and 45%). The two types of material were immersed for (40) days in different salt concentrations ratio (15%, 35% and 55%). The environment consists of salt 99.9% and 0.008% magnesium carbonate and potassium iodide. The study depends on the experimental results of impact test and tensile test to describe the mechanical properties of polyester resin and composite material. It is found that the fracture toughness of composite material increases at approximate ratio of (2.9%) while the polyester resin increases at approximate of (2.25%) due to increasing the salt concentration in water with ratio (40%), so that the fracture toughness increases with approximate ratio (3%) due to increase in the volume fraction ratio from (15%) to (45%). The elastic modulus of composite material increases with ratio of (14.9%) and (90.29%) for polyester due to increase in the salt concentration ratio in the water at approximate ratio of (40%).
The elastic modulus increases at ratio of (13.73%) , the yield stress of polyester increase at ratio (50.32%) and yield stress of composite material increases at ratio (55%) as a results of increase in the volume fraction ratio from (15%) to (45%).