Carbon Fiber Reinforced Polymers (CFRP) are widely applied in lightweight applications like in e.g. aerospace because of their high strength to weight ratio compared to metal structures. However, due to the polymer matrix, CFRP show a limited thermal stability. Examples for thermal stress scenarios are hot engine gases impinging on the outer shell of an aircraft or overheating of electronic components. Due to the one-sided thermal loading, there is a temperature gradient through the material, which leads to an inhomogeneous damage distribution. To ensure a safe application, knowledge about the degradation phenomena and the quantification of the thermal damage is mandatory. However, for a detailed characterization of the damage distribution inside the CFRP, depth-resolved investigations are required. Therefore, chemical, physical and mechanical properties are determined for CFRP samples with varying thickness of the commercially available HexPly® 8552/IM7, which were thermally loaded at different heat fluxes and varying irradiation time. Special attention is paid to matrix degradation, loss of fiber-matrix-adhesion like e.g. occurring delaminations and the decrease of strength. Embedded thermocouples allow the determination of the temperature distribution inside the CFRP. Non-destructive ATR-FTIR spectroscopy is used to investigate the degradation of the polymer matrix. IR spectroscopy along a ground inclined plane allows a depth-resolved analysis of the matrix degradation. Structural changes in the CFRP like delaminations are investigated by using microfocused X-ray computed tomography (µCT). For the determination of the residual strength, tensile, compression and interlaminar shear strength testing are applied. The data shows that matrix degradation and delaminations occur after exceeding a threshold temperature. The delaminations develop only after a certain degree of matrix degradation and are identified as the dominant damage phenomenon, which is responsible for the thermally induced loss of strength. With a view to the correlation between matrix degradation and the formation of delaminations, it is therefore possible to draw conclusions about strength via matrix degradation. Because of the relationship between matrix degradation, the formation of delaminations and the residual strength, IR spectroscopy can be used to predict delaminations and the remaining strengths. The application of multivariate data analysis helps in processing large amounts of data such as those generated by spectroscopic analyses. Principal component analysis (PCA) is applied to show which wavenumber areas in the spectra are affected by thermal stress. Linear discriminant analysis (LDA) is performed to predict the presence or absence of delaminations. In addition, by combining spectra from different depths of the CFRP, partial least squares regression (PLS) models are created to predict strength and delamination depth. The models allow an accurate prediction of strength despite the inhomogeneous distribution of the damage inside the CFRP. Therefore, a contribution to increase the application safety of CFRP structures in aviation is provided.    «

Carbon Fiber Reinforced Polymers (CFRP) are widely applied in lightweight applications like in e.g. aerospace because of their high strength to weight ratio compared to metal structures. However, due to the polymer matrix, CFRP show a limited thermal stability. Examples for thermal stress scenarios are hot engine gases impinging on the outer shell of an aircraft or overheating of electronic components. Due to the one-sided thermal loading, there is a temperature gradient through the material, wh...    »