High Temperature Shear Strength of T650-35/HFPE-II-52 Polyimide Matrix Unidirectional Composite
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.
Time and temperature dependent mechanical behavior of HFPE-II-52 polyimide at high temperature
Abstract Motivated by demanding, high temperature applications of polyimides and polyimide matrix composites, this study characterizes the high temperature, time and temperature dependent mechanical behavior of HFPE-II-52 polyimide. Three types of experiments: creep recovery, multistep relaxation and fixed strain rate tension tests were performed at temperatures from 285 °C to 315 °C. A constitutive model combining linear viscoelasticity with viscoplasticity was developed. The viscoplastic part of the model uses a power law flow potential with state variable evolution to model strain hardening and softening. The full model was fit to the experimental data and is shown to capture the key features of the material behavior. The constitutive model was also generalized to 3D and implemented as an ABAQUS user material. Plane-stress finite element simulations of a high temperature tension test and 3D simulations of a unidirectional laminate under axial shear loading were performed as example applications of the model.
Self-assembly of pyridinium-tailored anthracene amphiphiles into supramolecular hydrogels.
The mixing of a polyacid cross-linker with a pyridinium-functionalized anthracene amphiphile afforded a supramolecular hydrogel through a self-assembly process that was primarily driven by π-stacking and electrostatic interactions.