Prior Thermal Spikes and Thermal Shocks on Mechanical Behavior of Glass Fiber-Epoxy Composites

Abstract

Fiber-reinforced glass-epoxy composites with and without prior thermal history are subjected to hygrothermal conditioning for different exposure times. The prior thermal history is given in the form of thermal shocks and thermal spikes at three different temperatures. The effects of exposure time and prior thermal history on the moisture absorption kinetics are studied. The effects of prior conditioning parameters are also investigated. The variation of mechanical properties as a function of exposure time and prior conditioning parameters are assessed by the three-point short beam shear bend test. It has been observed that there is an initial improvement in the mechanical properties followed by a steady deterioration. Mechanical tests performed at different crosshead velocities show increasing brittleness of the composites and that is found to be a function of cross-head velocity.

Effect of Hygrothermal Shock Cycles on Interlaminar Shear Strength of Hybrid Composites

“…The desorption cycle, therefore, serves to reduce the moisture absorption rate in the initial regime than it would otherwise be for composite specimens aged in a constant high-humidity environment. The results obtained in the present set of experiments are in agreement with the results of a recent study, where the hygrothermal response of glass fiber reinforced epoxy composites were studied under constant humidity conditions [4]. It has been shown [2] that during absorption the outer plies of the composite try to swell, but are resisted by the inner plies.…”

Temperature and anisotropy effects in the application of the hindered diffusion model to composite laminates

“…The spatial moisture concentration and analytical solution are presented in equations (7) and (8). The hindrance coefficient, l, is described in equation (9). Given the dimensions of the specimens used in this study, limiting the investigation to the one-dimensional version of this model is prudent.…”

“…thermal aging following immersion and immersion following thermal analysis. [9][10][11][12] Additionally, mathematical modeling of diffusion in polymer composite systems is of critical importance in order to predict the extent of degradation as a result of moisture ingress and to identify diffusion mechanisms. The direct correlation between property loss and moisture content has driven numerous researchers to develop and test various predictive models of moisture absorption, including the previous and related work on "hindered' diffusion models by Grace et al [13][14][15][16][17][18] and other models reviewed by Wang et al 8 Accurate prediction of moisture content within a polymer composite at a specified time is a prerequisite to estimating structural integrity over time and limits on the safe lifespan of a structure in a given environment.…”

Impact of the ambiance on GFRP composites and role of some inherent factors: A review report

“…It is estimated that voids or empty spaces or free volumes in a polymer material caused due to imperfect curing/cross linking of the polymer, occupy about 1/40 of the total volume of the polymer at/bellow the glass transition temperature. 17 The T g value is lowered resulting in a lowering of the safe working range of temperature of a composite when the extent of free volume/voids is increased. The absorbed moisture acts as a plasticiser increasing the free volume by an action of hygro-elastic-swelling stress.…”

“…The absorbed moisture injures the polymer-chain structure of the matrix, thus lowering the thermo-physical, mechanical and chemical characteristic properties of the composite by way of swelling, plasticisation and hydrolysis. 17,25–28 Moisture is also capable of initiating a thermo-oxidative degradation of the composite weakening the fibre–matrix interface and resulting in the lowering of the shear strength of the material. 29…”