Catálogo de publicaciones - libros

The paper investigates the response of glass fibre reinforced plastics subjected to repeated low velocity impact loading. The loading condition of repeated impacts is of particular relevance for industrial applications, especially when intended for motor vehicle or naval applications. Recently few papers addressed the problem [ 1 – 3 ].

It is well known that nonhomogeneous materials (such as composites), under cyclic loadings, change their properties because of damage accumulation.

The term ‘Ageing aircraft’ indicates an aircraft structure that is about to reach its original design goal. At this stage, the light alloy structures used in commercial aircraft are susceptible to Widespread Fatigue Damage (WFD) and possibly other deteriorating effects, such as corrosion damage. One typical form of WFD is Multiple Site Damage (MSD), which refers to the simultaneous existence of multiple interacting fatigue cracks at different sites of the same structural component (Fig.1). In the presence of MSD, critical crack sizes are greatly reduced, thus decreasing the residual strength of the structure below critical levels [ 1 , 2 ] and leading to catastrophic failures due to the sudden cohesion of such interacting cracks [e.g. 3 ].

It is unlikely that any engineering component is entirely free from residual stress because of the material processing, fabrication and service load history. Residual stresses originate from the elastic accommodation of misfits between different regions in a structure. The interaction between the misfit and the restraint of the surrounding material and structure determines the magnitude of the resultant residual stress and its length scale. In order to assess the influence of residual stress on fracture, it is essential to quantify the residual stress field over the length scales of concern. This paper identifies the residual stress length scales that must be considered in fracture mechanics analyses for welded joints in engineering structures and proposes a new approach for the treatment of short length scale stresses. The findings are illustrated by results from recent weld residual stress finite element simulations and measurement studies.

The major problems due to welding effects are the residual stresses and deformations of which the levels affect more or less the resistance and lifetime of welded structure.

Composites are complex materials which comprise of multiple phases (components) of different thermal and mechanical properties. By combining such components, especially metals, ceramics, glasses, and polymers, one can produce new functional and construction materials with superior properties which could be tailored for the specific applications. However, due to mismatch in to the properties of their constituents, composite are prone to build-up of residual stresses. This is in particular true to the thermal stresses arising due to mismatch in thermal expansion coefficients. These thermal stresses might be generated either during manufacturing process, more precisely during the cooling from fabrication temperature, or due to thermal cycling in in-service conditions. They, in general, can improve the properties of the composites [ 1 ]. However, they can also have detrimental effect on their performance. This calls for their control over manufacturing and inservice conditions.

The paper studies well published results of direct tensile tests on dog-bone specimens with rotating boundary conditions performed by van Vliet and van Mier [ 1 , 2 , 3 , 4 , 5 , 6 , 7 ]. In particular we are interested in the series of dry concrete specimens A to F (dimension D varying from 50 to 1600 mm, see Fig. 1); a series accompanied by verification tensile splitting tests. The paper attempts at explaining of the complex size effect on mean and variance of nominal strength by combination of random field simulation of local material properties, “weak boundary” effects and a nonlinear fracture mechanics software based on a cohesive crack model.

Rapid development of nanotechnologies in the last decades demands thorough analysis of mechanical properties of the objects at the nanosize scale level. Natural discreteness of the nanoobjects requires new methods involving consideration of their properties from both discrete and continuum points of view. In this work we apply this approach to analysis of mechanical behaviour of close-packed nanocrystals having finite number of atomic layers in some directions and infinite in others (2D nanostripes, 3D nanoplates and nanobars). In the current talk we will focus on elastic and strength properties of nanocrystals being studied using both static and dynamic theories. The scale effect (dependence of the properties on the number of atomic layers) is one of the main topics of interest for this investigation.

Cracking in soils due to water loss is a problem not much studied from a mechanical point of view, despite its environmental implications. For instance, if a clayey soil is used as an impervious barrier in open waste sites, an intense drought may origin cracks and therefore preferential flow paths for polluted water. Cracks produced by environmental agents also reduce the bearing capacity of the soil and increases its propensity to erosion. Previous works have studied the problem either from a Fracture Mechanics perspective (Vallejo [ 1 ], Prat et al. [ 2 ], Ávila [ 3 ], Harison et al. [ 4 ], [ 5 ], Hallet and Newson [ 6 ]), analysing the conditions for crack propagation, or from a classical Soil Mechanics approach (Kodikara et al. [ 7 ], Abu-Hejleh and Znidarcic [ 8 ], Konrad and Ayad [ 9 ], Morris et al. [ 10 ], Lloret et al. [ 11 ], using the effective stress principle. In this case it has been observed that cracks initiate when soil is still close to saturation.

By means of physical mesomechanics three scale levels of plastic flow localization in LiF single crystals under compression were revealed: fine slip at micrometer range, kink bands at a millimeter range and localization of macroshear-bands accompanied by extremely pronounced effects of shear — bending — torsion. In a zone of macro shear-bands localization a crack of longitudinal delaminating nucleates whose development is completed by specimen fracture. Scale levels of shear stability loss of ionic LiF crystals under compression are qualitatively similar to those under tension of metal materials. It testifies the universality of a principle of the physical mesomechanics that the plastic deformation and fracture of solid is related to its shear stability loss at micro-, meso- and macroscale levels.