چكيده به لاتين
The main purpose of this study was to investigate the interlaminar mode I fracture toughness of polymeric laminated composite exposed to the acid-thermal aging condition. To achieve this goal, unidirectional E-glass/vinylester composites manufactured by the hand lay-up method were immersed in 20 wt.% sulfuric acid soluble at 23℃ and 70℃. After exposure to mentioned condition for a period of 0 to 10 weeks, samples were tested according to the ASTM standards. In this study the double cantilever beam (DCB) ([0_9 ]_s), pure resin (tensile specimen), pure fiber, three-point bending (3PB) composite specimens (with [0_9 ]_T and [〖90〗_9 ]_T stacking sequences) were tested and their microscopic appearance were assessed.
In this research, one of the available models for prediction of polymeric composites immersed in a solution was improved using the weight gain of specimens. Also, a new model was presented to predict a normalized value for mechanical properties of composite specimens. In this model, if the data are presented in a normalized form, all properties are collapsed in a single curve, which means each property can be calculated using the trend of degradation in a property and the virgin value of each property. The results of both models were compared with experimental results and showed a high agreement with them.
Experimental results showed a stability of mechanical properties (tensile strength, tensile modulus and hardness) of pure resin specimens but a degradation of 3PB (flexural strength, flexural modulus and hardness) composite specimens. Degradation of mechanical properties at 70 ℃ had a higher rate than that of the 23 ℃. The results represent different trends for the initiation and propagation of the interlaminar fracture toughness at both mentioned conditions. Investigations on fiber samples in the acidic solution and the samples of the solubles at 70℃ condition indicate that the damage in fiber and interphase were the main reasons of degradation in composite materials.
