Carbon Fiber-reinforced Materials Research Articles

Bio-based epoxy vitrimer for recyclable and carbon fiber reinforced materials: Synthesis and structure-property relationship

Recycling or degradation of epoxy resins is difficult because of their covalent cross-linking structures, which causes resource crisis, environmental pollution, and resource waste. To address this challenge, we reported a recyclable and degradable epoxy vitrimer with dynamic ester bonds prepared from tung oil and diglycidyl ether of bisphenol-A via epoxy-acid-anhydride crosslinking system. Owing to the compact rigid six-member ring and the anhydride structure, the epoxy vitrimer shows high thermal stability, and excellent dynamic mechanical, and mechanical properties with tensile strength of 59.21 ± 1.02 MPa and glass transition temperature of 76.73 °C. The vitrimer network can achieve topological rearrangement via dynamic transesterification reactions with the addition of a Zn catalyst. Thus, the contrivable vitrimer exhibits excellent self-healing, shape memory, and physical recycling at elevated temperatures. Moreover, the epoxy vitrimer matrix has high joining strength with carbon fibers and can be used to prepare carbon-fiber-reinforced materials (CFRMs). The carbon fibers can be completely recycled from CFRMs through an ethanol-NaOH mixture solvent. This work can assist in preparation of degradable high-strength CFRMs using a recyclable tung-oil-based vitrimer matrix and provides a strategy for efficient recycling of carbon fibers from CFRMs.

Health Monitoring of TPS Structures by Measuring Their Electrical Resistance

Health Monitoring in aerospace applications becomes an emerging technology leading to the development of systems capable of continuously monitoring structures for damage with minimal human intervention. A promising sensing method to be applied on hot structures and thermal protection systems is the electrical resistance measurement technique, which is barely investigated up to now. This method benefits from the advantageous characteristics of self-monitoring materials, such as carbon fiber-reinforced materials. By measuring the variation of the electrical resistance of these materials information on possibly present mechanical damage can be derived. In order to set up a database on electric properties of relevant materials under relevant conditions and to perform a proof-of-concept for this health monitoring method a facility has been laid out, which allows for the measurement of the electrical resistance of thermal protection system relevant materials at temperatures up to 2000°C. First preliminary measurements of the surface resistance of a graphite sample have been performed and are presented. It has been proven necessary to make some modifications to the setup. Therefore, the remaining measurements with graphite and C/C-SiC samples are subject of further investigation which will be performed in the future.

An approach to achieve progress in spacecraft shielding

Progress in shield design against space debris can be achieved only when a combined approach based on several tools is used. This approach depends on the combined application of advanced numerical methods, specific material models and experimental determination of input parameters for these models. Examples of experimental methods for material characterization are given, covering the range from quasi static to very high strain rates for materials like Nextel and carbon fiber-reinforced materials. Mesh free numerical methods have extraordinary capabilities in the simulation of extreme material behaviour including complete failure with phase changes, combined with shock wave phenomena and the interaction with structural components. In this paper the benefits from combining numerical methods, material modelling and detailed experimental studies for shield design are demonstrated. The following examples are given: (1) Development of a material model for Nextel and Kevlar-Epoxy to enable numerical simulation of hypervelocity impacts on complex heavy protection shields for the International Space Station. (2) The influence of projectile shape on protection performance of Whipple Shields and how experimental problems in accelerating such shapes can be overcome by systematic numerical simulation. (3) The benefits of using metallic foams in “sandwich bumper shields” for spacecraft and how to approach systematic characterization of such materials.