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

Abstract

The shear strength of a 4-ply unidirectional composite laminate consisting of carbon fibers (T650-35) and a polyimide matrix (HFPE-II-52) was measured over a temperature range of 25 to 315 C. The tests were performed using a Iosipescu test sample, modified to provide a more uniform shear stress distribution across the gauge section and loaded with an Arcan type test fixture. The test specimen design is based on the results of an extensive finite element study. Shear strength tests were performed on dry, 50% RH and 100% RH moisture saturated samples. Results of the experiment show that shear strength decreases from approximately 120 MPa at 25 C to 60 MPa at 315 C and that moisture saturated samples have a 5-10 MPa lower shear strength than dry samples.

Modeling the diffusion of a fluid through viscoelastic polyimides

“…The material parameters were assumed to be: χ = 0.425, β 1 = 1.3, β 2 = 0.018,μ ⋆ p = 0.1,μ ⋆ G = 0.1, γ ⋆ = 20. The characteristic time chosen was 2800 s. Even in this case the numerical results and experimental data taken from (Bhargava (2007)) match well (see Fig. (4)).…”

“…Several materials in the areas of of polymer mechanics, asphalt mechanics, and biomechanics that show non-linear viscoelastic behavior swell in the presence of a fluid. For instance, polyimides which are known to show viscoelastic solid-like response (see Bhargava (2007), Falcone and Ruggles-Wrenn (2009)) are used in the aerospace industry due to their good performance at high temperatures (also see Ghosh and Mittal (1996)); these materials in their service environment are known to swell in the presence of moisture. In addition, asphalt based materials (that are well know to show non-linear viscoelastic fluid-like behavior) degrade in the presence of moisture (Kim et al (2004)).…”

Modeling the non-linear viscoelastic response of high temperature polyimides

“…Hence, there is need for a good understanding of the various degradation mechanisms that are operational when such materials are subject to hostile environment. Recent experimental evidence shows that the response of polyimide resins is solid-like viscoelastic response (see Bhargava (2007), Falcone and Ruggles-Wrenn (2009)). Moreover, the response of such bodies is non-linear (For a detailed description concerning how to differentiate between viscoelastic solid-like and fluid-like response we refer the reader to Wineman and Rajagopal (2000), Málek and Rajagopal (2006)).…”

“…Recently, Falcone and Ruggles-Wrenn performed experiments on PMR-15 at the service temperature of an aircraft, 288 • C, and compared the predictions of Schapery's model for the problem of creep with experimental data. Bhargava (2007) has also used Schapery's model to predict the behavior of HFPE-II-52. More recently, Hall (2008) developed a thermodynamic framework for finite anisotropic viscoplastic models to study the response of polymers subject to extreme thermal environment.…”

“…This model is shown to predict the viscoelastic response of polyimide resin. Experimental data for PMR-15 polyimide resin from Falcone and Ruggles-Wrenn (2009), and for HFPE-II-52 from Bhargava (2007) are used to evaluate the efficacy of the model.…”