Linear viscoelastic properties of HFPE‐II‐52 polyimide

Abstract

ABSTRACT:The polyimide HFPE-II-52 was developed at NASA Glenn Research Center for use as a matrix in high temperature composite materials. The unique properties of such composites stem largely from the performance of the matrix at high temperature. Thus, as part of a larger effort to study high temperature composite materials, the linear viscoelastic properties of HFPE are measured and a mathematical model of the properties is developed. In particular, storage, loss, and stress relaxation moduli were obtained from cyclic and transient loading experiments. A Prony series was fit to the relaxation modulus data. As a cross check, the fit to the relaxation modulus was converted to storage and loss moduli and compared with those measured directly. Effects of postcuring and of moisture on the properties are investigated as well. These results provide researchers with a constitutive model for HFPE-II-52 and provide some insight into the performance of HFPE matrix composites at high temperatures.

Moisture diffusion properties of HFPE‐II‐52 polyimide

“…12 The moisture diffusion properties were found by performing weight gain and weight loss experiments over a wide range of temperature and relative humidity conditions. Diffusivity below 1008C was found by performing weight gain and weight loss experiments using standard methods.…”

A comparison of nonlinear integral-based viscoelastic models through compression tests on filled rubber

“…The number N of exponential terms in (4) is generally selected to increase the accuracy of the fitting model. In the literature, up to N = 20 relaxation times are used (Antonakakis et al, 2006;Knauss and Zhao, 2007); however a large value of N could lead to ill-conditioned identification problems and, therefore, the parameters identified are highly sensitive to errors in the experimental data. Beside differential viscoelasticity, taken into account with a discontinuous kernel, the constitutive relation (1) can also include fractional differential models.…”

High Temperature Shear Strength of T650-35/HFPE-II-52 Polyimide Matrix Unidirectional Composite

“…Linear viscoelastic properties of the matrix, moisture swelling and thermal expansion of the HFPE-II-52 polyimide matrix are given in [14,15]. The coefficient of thermal expansion of HFPE-II-52 measured using TMA (TA Instruments Q400EM Thermomechanical Analyzer) is 35: Â 10 À6 = C averaged over 50 C to 300 C. The T g of the laminate, measured using DMA (TA Instruments 2980 Dynamic Mechanical Analyzer) with three-point bending samples, is approximately 370 C. This is somewhat higher than T g % 358 C measured for the post-cured neat resin [14].…”

“…To check that the sample design still provides uniform stress at high temperatures, the computations were repeated with composite elastic properties estimated based on the temperature-dependent modulus of the HFPE-II-52 matrix [14]. In addition, two other cases were checked, isotropic material and a material with fibers in the vertical direction.…”

“…This study focuses on composites made from T650-35 graphite fibers with HFPE-II-52 matrix, a polyimide developed for use in composite materials [12]. The limited published data available on HFPE-II-52 and its composites include [12][13][14][15].…”