干/湿状态下HFRP搭接接头的剪切蠕变试验及分数阶导数流变模型

搭接是纤维增强复合材料(FRP)的重要连接方式,长期性能是该技术实际工程应用的关键.对不同恒定应力和湿度状态下混杂FRP(HFRP)双搭接接头的剪切蠕变性能进行了试验研究.试验观测到了明显的蠕变变形,测定了蠕变与恒定应力及湿度的关系.进一步采用分数阶导数流变模型对试件的蠕变进行模拟.根据模型所包含的Mittag-Leffler函数的性质采用了改进的Powell优化算法,并确定了合理的初值,结合试验曲线拟合得到模型各参数值.根据搭接接头蠕变的特点,在经典分数阶流变模型中引入了表征应力水平对搭接接头非线性蠕变特性影响的函数,提出了一种改进的分数阶蠕变柔量计算公式.研究结果表明,该流变模型能够采用简单的表达形式和较少的参数对试件的非线性蠕变行为进行拟合,在30%~70%恒定应力范围内准确模拟了双剪搭接接头的蠕变曲线.

Experiment and fractional derivative rheological modeling of the shear creep of HFRP overlap joints under dry and moist environments

The long-term performance of overlap adhesion, one of the major joint technologies of FRP, is key to its practical engi-neering application. Experiments on the creep behaviors of the double lap joint of a hybrid FRP ( HFRP) were conducted. Obvious creeps were observed and measured under various environments reflecting different levels of shear stress and humidity. Then, a frac-tional derivative rheological model was proposed to characterize the creep deformation of the overlap joints. By applying the Mittag-Leffler function to the proposed model, an improved Powell optimization algorithm with an initial-value calculation method was utilized to determine the values of the fitting parameters on the basis of the experimental data obtained. By introducing stress influence func-tions to the conventional fractional calculus, a modified formula of fractional creep compliance was considered to reflect the influence of stress level on the creep property of the overlap joint. Results indicate that the model is capable of predicting the creep behavior of o-verlap joints up to a sustained stress level of 30%-70% of the shear strength with relative simple mathematical expressions and only a few fitting parameters.