Study On The Damages Of Short Fiber Composites Subjected To Repeated Low Velocity Impact

In the beginning of this papef, random short-glass-fibrereinforced Unsaturated Polyester Resin was used to study themechanical behavior and damage character of short-fibre compositesunder unidirectional low velocity impact and repeated low velocityimpact, by means of Material Test System (MTS) to simulate lowvelocity impact loading. Next, according to experimenta1 data andwith the help of Mechanics of Viscoelasticity Micromechanics ofshort-fibre composites and Theory of Eshelby Equivalent Inclusion,the reinforcement coefficient formula (shown as formula (3.2-l7,l4,22)) of random short-fibre was deduced when E^m0₀/E^f>>(d_f/l_f)²;one-dimensional rate-dependence constitutive equation (shown asformula (3.3-3)) of random short-fibre composites adapting to smallstrain, quasi-static and low velocity impact loading was built up.Subsequently, Classical Thermodynamics, ContinuumThermodynamics and Theory of Prigogine dissipation structure wereused to verify the principle of least energy consumption adaPting toany course of energy consumption; to deduce the general formula oftota1 dissipation energy (shown as formula (4.2-ll)) of continuumthermodynamics system in a irreversible process with the time of t; toanalyze the thermodynamics energy consumption process ofcomposites under repeated impact loading. Using the one-dimensional rate-dependence constitutive equation of short-fibrecomposites and principle of least energy consumption built up in thispaper, calculation formula of dissipation energy (formula (4.3-5)),fOrmula of damage variable (fOrmula (4.3--l3)) and evolutionary' equation of damage (formula (4.3--l4)) of random short-fibrecomposites were deduced under uniaxial repeated 1ow velocity impact.Finally, according to secant-module declining law obtained fromexperiment and the evolutionary equation of damage deduced in thispaper, life prediction fOrmula (shown as fOrmula (5.2--4)) of randomshort-fibre comPosites under uniaxial repeated low velocity imPactloading was given; using experimentaI data, detail life predictionmethod was introduced and the life prediction result was discussed.