Preparation of Isotropic Carbon Fibers from Kerosene-Purified Coal Tar Pitch by Co-Carbonization with Pyrolysis Fuel Oil

An inexpensive and general-purpose carbon fiber was prepared using coal tar pitch. In contrast to the solvent extraction process employing expensive solvents, a low-cost centrifugal separation method facilitated the reduction of loss due to the pitch purification and an overall yield increase. The coal tar pitch purified by centrifugation and subsequently co-carbonized with pyrolysis fuel oil improved in spinnability. Moreover, the resulting spinnable pitch had a softening point of 250 °C. The obtained carbon fibers were heat-treated at 1000 °C for 5 min, resulting in a tensile strength of approximately 1000 MPa and an average diameter of 9 μm. In this study, we present an effective method for obtaining low-cost general-purpose isotropic carbon fibers.

The effects of edge quality on the measured compression strength of quasi-isoptropic composite specimens and its practical implication to the development of allowables

This manuscript presents results from an experimental study that examined the effect of quality of edge finish of test coupons on the measured compression strength of quasi-isotropic carbon fiber laminates using test standard ASTM D6641. Different cutting and grinding tools were used to machine specimens to get them within the required dimensional tolerances, all of which caused microscopic damage to the specimen edge, mainly in the form of fiber pull-out. Results of compression strength testing showed that the fiber pull-out, despite being only on the order of 0.008 mm in depth, caused a significant reduction in measured compression strength. Upon polishing of the specimen edges to remove the microscopic “gouges” of fiber pull-out, the measured compression strength of the specimens increased. It was also found that open hole compression (OHC) and compression after impact (CAI) strength test results were not affected by fiber pull-out on the edges of specimens. The implications of these results on the development of pristine strength allowables is discussed and a more practical starting point at which to develop allowables is presented.

Estimation of the Dissipative Heat Sources Related to the Total Energy Input of a CFRP Composite by Using the Second Amplitude Harmonic of the Thermal Signal

Theories for predicting the fatigue behaviour of composite laminates often make strong assumptions on the damage mechanisms that strongly depend on the designed laminate lay-up. In this regard, several physical and empirical models were proposed in the literature that generally require experimental validations. The experimental techniques, such as thermography, also provide useful tools for monitoring the behaviour of the specific material so, that they can be used to support the study of the damage mechanisms of materials. In this research, the second amplitude harmonic of the thermal signal has been investigated and used to assess the relationship with the total energy input in order to estimate the fatigue strength of the material. A thermal index was assessed by monitoring the constant amplitude tests (S/N curve) that were performed on a quasi-isotropic carbon fibre reinforced polymer (CFRP) laminate obtained by the automated fibre placement process. The obtained results demonstrated the capability of the second amplitude harmonic of the thermal signal to describe and monitor the fatigue damage.