The aim of this article is to share with the educational and scientific community, the usefulness of the new program called Matrix Calculator. That program has been used since the academic year 2011-2012, mainly in teaching Linear Algebra, in the first year of the different degrees of Tecnun, School of Engineering. (University of Navarra, in San Sebastian, Spain). It has been found that meets all expectations for student learning, while providing a great attraction for the study of Linear Algebra, mainly in its practical side. The application has been developed using MATLAB (R). The Matrix Calculator consists of a separate set of more than 150 functions. These functions and the main program are accompanied by a simple pdf file with the user's instructions and a set of solved examples.

Recent biaxial experiments on clear-spruce wood allow to have a more complete understanding of fracture behavior of wood. An elliptic failure surface, like that of Tsai¿Wu, has been previously proposed as a failure surface. Previous works in this area have shown the need for further developments. In this study a new failure model that accounts for existing different couplings and interactions in the longitudinal compressive and tensional domains is presented. The model is based on the fracture behavior of clear spruce wood and related experimental works. The model is more accurate compared to existing phenomenological models.

Many different phenomenological failure criteria have been proposed. These type of criteria do not explain the mechanism of failure itself. They merely identify failure (yes or no) and are usually regarded in practice as a simple and reliable tool for design. Most of them were developed for composite materials, but are extensively applied for wood. In this study, existing phenomenological strength criteria for orthotropic materials were applied to clear wood data. Instead of fitting the criteria to available experimental data, the criteria were used to predict failure of biaxial tests based on uniaxial strength. This procedure is closer to practice, and hence an answer to the question "is there any reliable failure criterion for wood?" Predictability of the criteria was assessed using normalisation procedure, and statistical significance of the difference of the means analysed. Based on the results, it can be concluded that a general criterion cannot be applied to predict failure, but should be chosen according to the biaxial stress state.

En la primera parte de este trabajo se realiza una revisión de los distintos modelos de fallo de la madera en estados de carga multiaxial propuestos hasta el momento. A continuación se hace un análisis estadístico del ajuste de dichos criterios a resultados experimentales, encontrados en la literatura, de ensayos realizados en madera de abeto blanco bajo distintas condiciones de carga. Finalmente se propone un nuevo criterio de fallo no continuo con el cual, sin aumentar el número de parámetros requeridos por otros criterios, se obtiene un mejor ajuste a los datos experimentales.