## 4 Conclusions  
In the present work, two angle-ply CFRE laminates, [0\({}^{\circ}\)/30\({}^{\circ}\)]\({}_{\text{2s}}\) and [0\({}^{\circ}\)/60\({}^{\circ}\)]\({}_{\text{2s}}\), were tested under quasi-static tension in order to qualitatively and quantitatively assess their damage development using different NDT techniques. By using an in situ microscope, mounted on the frame of the test bench, through-thickness free edge damage monitoring of the laminates was feasible. Through this monitoring, it was proven that when different multiaxial stresses are developed in the same material, significantly different damage sequences occur, even if similar mechanical properties are obtained, with noteworthy findings that can be used for further fatigue studies and for the development and/or validation of damage criteria. Specifically, when shear stresses were dominant, interlaminar delaminations had a greater potential to occur earlier in the test, even prior to matrix cracking, resulting from the developing intralaminar shear debondings and shear friction due to the increasing shear stresses. On the other hand, when the transverse stresses were the dominant ones, matrix cracks occurred early in the test, but delaminations only appeared closer to the final failure of the material. Significant differences were also evident regarding the damage magnitude when the stress state was dissimilar. In the presence of extensive shear, higher delamination lengths were measured until the ultimate failure. At the same time, it was proven that different experimentally measured parameters can be used as damage indicators for the CFRE laminates. As an example, the Poisson's ratio showed decreasing trends when matrix cracking or delaminations occurred. When the shear was dominant, higher values of the Poisson's ratio were recorded and an increasing trend was noticed. The \(\sigma\) parameter of the DIC also proved to be a successful damage indicator, at least in a qualitative manner. In the presence of delaminations, a sudden change in the pattern of the \(\sigma\) parameter was evident. Last but not least, different multiaxial stresses led to different AE activity. The internal shear damage led to more intense AE activity, even at early loading stages. It was proven that the AE activity was recorded prior to any monitored physical damage, stipulating that it can be successfully used for the estimation of early stage damage and the prediction of macrodamage concurrently. At the same time, the signal rise time seems to strongly depend on the stress state in the composite laminate,with greater values and increasing trends being recorded when the shear was dominant. In the appearance of delaminations, increasing rise time values were measured. Conceptualization, K.-A.K., D.V.H., and L.P.; data curation, K.-A.K. ; formal analysis, K.-A.K. ; investigation, K.-A.K. ; methodology, K.-A.K., B.R.M., E.T., D.G.A., D.V.H., and L.P.; supervision, D.V.H. and L.P.; writing (original draft), K.-A.K. ; writing (review and editing), B.R.M., E.T., D.G.A., and L.P. This research was funded by the Fonds Wetenschappelijk Onderzoek (FWO) research funding program \"Multi-scale modelling and characterization of fatigue damage in unidirectionally reinforced polymer composites under multiaxial and variable-amplitude loading\" (G.0090.15). The work leading to this publication has been funded by the SBO project \"M3 Strength\", which fits in the MacroModelMat (M3) research program, coordinated by Siemens (Siemens PLM software, Leuven, Belgium) and funded by SIM (Strategic Initiative Materials in Flanders) and VLAIO (Flanders Innovation and Entrepreneurship Agency) (Flanders, Belgium). The authors gratefully acknowledge the material suppliers Mitsubishi Chemical Corporation (Tokyo, Japan) and Honda R & D Co., Ltd. (Tochigi, Japan). The authors declare no conflict of interest. The funding sponsors had no role in the design of the study; in the collection, analyses, or interpretation of data; and in the writing of the manuscript.