## 1 Introduction
Various methods have been proposed for the identification of damage in glass fiber reinforced epoxies (GFREs) [8; 19], but there is still not a straightforward method identified for measuring the continuous damage sequence in CFREs. For this reason, a combined nondestructive testing (NDT) methodology is proposed to qualitatively and quantitatively estimate the damage of the CFRE laminates. Taking advantage of the fact that flat laminates allow free edge damage monitoring during testing [20; 21], in situ microscopy was used to monitor the through-thickness physical damage of the laminates throughout testing, and to correlate this damage with the developed stresses. As it has been proven in this study, the initiation and propagation of damage is not necessarily the same for every laminate configuration, and it strongly depends on the developed stresses, with the damage onset mode (i.e., transverse matrix cracking or delamination) being different depending on the dominant stress state in the composite laminate. At the same time, the acoustic emission (AE) technique was applied to monitor the acoustic response of the laminates throughout the tests. AE is a NDT method that has been used in several applications for the damage characterization of composites and other engineering materials [22; 23; 24; 25; 26], either as a self-standing technique, or in combination with other NDT methodologies [27; 28; 29]. However, no direct correlation of the AE activity to multiaxial stresses developed in composite materials is found in the literature. In this work, it is proven that dissimilar multiaxiality in the same composite material can lead to different AE responses and dissimilar AE wave features from early loading stages. Identifying the different acoustic responses of the same material under different stress states can be used for structural health monitoring in real composite structures. At the same time, AE can be used as a predictive tool for the final material failure, based on the detection of early stage damage. As a supporting tool, the digital image correlation (DIC) technique was used during testing. Through the DIC analyses, strain measurements and damage indications were obtained, which enhanced the results obtained during the microscopic analysis and the AE acquisition. The final aim of this research is the establishment of a NDT methodology in order to physically estimate and measure the static tensile damage, and to correlate its sequence with the different multiaxial stress states acting in the flat CFRE specimens. Moreover, the characterization of the different AE responses related to dissimilar multiaxial stress states in CFRE specimens is a target of this research. Ongoing research is performed for the full damage characterization of the same CFRE material under different multiaxial stress states and under fatigue loads at the same time. Therefore, the data presented in this manuscript is used as an input for the fatigue damage characterization of angle-ply CFRE laminates, and it can serve as an addition to the available datasheets in the literature, in order to contribute to the development and validation of damage criteria and models.