## 3 Results and Discussion
### Acoustic Emission along Grain Angle Direction in High/Low Tree Ring Density of Scots Pine
#### 3.2.4 Content of Publication
[19] who demonstrated in their experiments that the AE count rate lower than 175 kHz of fresh, never dried sapwood beams appeared to be much higher than that of once or twice pre-dried sapwoods. Sometimes the AE parameters were also related to the RH condition of the environment in which the tests took place. [PERSON] et al. [14] carried out an investigation where the AE signals were recorded during two stages of an experimental procedure that occurred in a climate chamber at two different relative humidity levels and it was noted that the AE activity was concentrated over the first days after the hygric change and successively, as the sample equilibrated with the new environmental conditions in the chamber, it suddenly decreased. Some publications include a theoretical approach aimed to perform numerical simulation and modelling of wooden fracture behaviour, by using Finite Element Analysis through different software such as the Abaqus CAE 2019 software [23], the AutoCAD 2012 software [36], the Adina v. 8.4 Finite Element Method (FEM) program [33] and the ANSYS software package [13]. In a work by [PERSON] et al. [30] Linear Elastic 2D Finite Element Simulations of wood specimens were performed to obtain some insight on the most probable source region of AE signals. [PERSON] et al. [37] used a 2D statistical lattice model based on morphological simulations of microscopic damage evolution in wood. In some cases, comparison between experimental analysis conducted by AE and numerical modelling are presented, for example to show the capability of AE technique to monitor the crack tip growth within wood material [38]. Other works propose mathematical formulations for example as model to express the relationships between surface roughness and chip thickness [25], to compare experimental data to the theoretical ones [16], or to define the location algorithm used for the burst source location in wood specimens [30]. In [PERSON] et al. [39] a theoretical approach was presented in the study of the fractal theory applied to examine the fracture surfaces of five types of woods. In [PERSON] et al. [22], based on thermodynamic approach, a theoretical model for predicting crack instability was established and the model was verified by double cantilever beam (DCB) tests. Although the multi-techniques approach used in these documents appears to be lacking in microscopic observations, they have proved to be effective in the fracture surface analysis. In addition, their efficacy when coupled with AE system was demonstrated in a work by [PERSON] et al. [33], where a scanning photography technique made it possible to distinguish fracture patterns at different magnification, both in radial-longitudinal(RL) and tangential-longitudinal (TL) orientations; or in [PERSON] et al. [32] who used a stereomicroscope to study the fracture characteristics of different wood products. In other works, the scanning electron microscopy system was adopted [13; 18; 39; 40; 41], as in the case of [PERSON] et al. [39] who used it to identify different modes of wood fracture during three-point bending tests of samples. A few documents investigated the influence of the grain angle on the AE activity monitored on wood samples [25; 29]. [PERSON] et al. [25] in their studies identified changes in cutting conditions and surface quality of Scots pine samples. It was assessed that the effect of changing the slope of grain was reflected by a significant variation in the acoustic emission signals. The failure process of red Iauan and Sitka spruce specimens under static and fatigue torsional loading with different grain angle rotations was monitored by [PERSON] et al. [29] and important differences in AE counts for hardwood and softwood were found. It was assessed that the test-piece grain angle influences the total AE counts, up to the fracture. As a result, AE counts decrease as the grain angle increases from 0 to 45 degrees and increase as the grain angle increases from 45 to 90 degrees.