# A Model to Study the Creep Behavior of Carbon Fiber/Epoxy Resin Composites Under Temperature
## 4 Results  
### Material and Specimens  
The fiber-reinforced materials under investigation were composites that were sold commercially. The material (resin) used for experiment was a Fibredux 6376 (known as HexPly(r) 6376). This is a high-performance epoxy resin matrix (Hexcel Corporation, Stamford, CT, USA) used mainly for manufacturing primary aircraft structures. The material has a lot of useful properties, such as excellent toughness, damage tolerance, and strong suitability for high-temperature engineering applications. Another property that recommends the use of the material is the high impact resistance, enhancing the durability of the composite structure. This resin maintains good properties up to 150 \({}^{\circ}\)C. Other useful mechanical properties of this material are presented in Table 1.  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Nr.** & **Property** & **Value** \\ \hline
1 & Tensile Strength & 105 MPa \\ \hline
2 & Tensile Modulus & 3.60 GPa \\ \hline
3 & Flexural Strength & 144 MPa \\ \hline
4 & Flexural Modulus & 4.4 GPa \\ \hline
5 & Toughness (GIC) & 432 J/ m \\ \hline \hline \end{tabular}
\end{table}
Table 1: Mechanical properties of the material.  
So, a hardened epoxy resin with a glass transition temperature of roughly 180 \({}^{\circ}\)C serves as the prepreg system's matrix. The laminates were produced using conventional procedures. The epoxy system's laminates were autoclaved for an hour at 180 \({}^{\circ}\)C to cure them, and then they were postcured for six hours at 190 \({}^{\circ}\)C. The cast panels quality was controlled with the aid of ultrasonic scanning. The fiber volume content was 60% \(\pm\) 3%. The fiber-reinforced specimens had nominal measurements of 150 mm in length, 10 mm in width, and 1 mm in thickness. It should be mentioned that the specimens were stored in chambers filled with desiccant after they were made. During storage before testing, the specimens had to be shielded from unnecessary moisture absorption. It was discovered that the rooms' relative humidity was about 35%.  
As mentioned before, both normal and increased temperatures (23 \({}^{\circ}\)C) were used for isothermal creep studies. Each CREEP test took ten hours to load. The experiments were conducted at temperatures below the glass transition temperatures. The highest test temperature was roughly 20 \({}^{\circ}\)C lower than epoxy resin's glass transition temperature. For the reinforced material, the epoxy resin was tested at 23 \({}^{\circ}\)C, 80 \({}^{\circ}\)C, 120 \({}^{\circ}\)C, and 140 \({}^{\circ}\)C. At room temperature, four stress levels ranging from 10% to 70% of the ultimate tensile stress were applied. To guarantee consistent temperature distribution in the sample and the chamber, tests were started an hour after the goal test temperature was obtained in the chamber. Temperature, load, and creep stresses were recorded at suitable intervals throughout the experiment. As required by current standards, these samples must be maintained in a temperature-controlled room for twenty minutes prior to testing in order to ensure that the experimental temperature is reached.