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A characteristic of the glass is its fragility and the scatter of the experimental mechanical strength due to the presence of defects that appear in the process of manufacturing or handling. Accordingly, investigations on this material were priorly conducted to improve the processes of manufacturing and to establish design methodologies based on probabilistic approaches. The influence of mode II of loading was traditionally ignored or considered as ratio of mode II. Recent studies have shown that when a shear-loaded crack becomes unstable a new compressive stress concentration field builds up in the notch formed between the original crack and the branch crack. This stress field affects the energy balance and also the beginning of crack extension. A procedure to design glass elements was developed jointly with CIDA of Cristalería Española, S.A. The aim of this work is to improve the model by the consideration of a mixed mode loading and its experimental contrast.Una de las características del vidrio es su fragilidad y la gran dispersión de sus valores de resistencia mecánica, motivado fundamentalmente por la presencia de defectos procedentes de su fabricación o de su manipulación. Como consecuencia, las investigaciones en este material se han dirigido preferentemente a la mejora de los procesos de fabricación y al establecimiento de metodologías de diseño basadas en modelos probabilísticos. Tradicionalmente, en el análisis de la rotura se ha despreciado la influencia del modo II o se ha representado como un porcentaje del modo I. Recientes estudios demuestran la aparición de un nuevo campo de tensiones de compresión cuando una fisura crece bajo una carga en modo II puro situado en el codo que se forma entre la fisura original y su ramificación. Este campo de compresión influye en el equilibrio energético y, en consecuencia, en la predicción de la rotura. En colaboración con el CIDA de Cristalería Española, S.A. se ha desarrollado un procedimiento para el dimensionamiento probabilista de elementos de vidrio plano para edificación. En este artículo se propone ahora una mejora del modelo, considerando la existencia de un modo mixto de carga y procediendo posteriormente a su contraste experimental.

The surface morphology of the ablation craters generated in LiNbO3 by 130 fs laser pulses at 800 nm has been investigated by AFM/SNOM microscopy. The single pulse fluence corresponding to the ablation threshold has been estimated to be ≈1.8 J/cm2. A complex structure including random cone-shaped protrusions is observed inside the ablated crater. The scale of the protrusion spacing is in the submicron range and the heights are typically of a few tens of nanometers. At and outside the crater rim a novel quasi-periodic wave-like topography pattern is observed in both types of microscopy techniques. The average wavelength, that is slightly dependent on pulse fluence, is (500-800 nm) comparable to the light wavelength. This novel topography feature keeps a close similarity with a Fresnel diffraction pattern by an absorbing circular obstacle or impact wave pattern produced by a combination of heat and shock wave (resemble that of impact crater). It is proposed that the obstacle is associated to the strongly nonlinear multiphoton absorption at the peak of the pulse profile. The energy deposited by nonlinear absorption of such profile causes ablation of both the crater and the rippled structure. © 2008., This work has been partially supported by the Spanish Ministerio de Ciencia y Tecnología (proyect MAT2005-05950 MOISES) and by the Comunidad Autónoma de Madrid (project S-0505-TIC-0191 MICROSERES).