Nonlinear elastic response of thermally damaged consolidated granular media

The mechanical properties of consolidated granular media are strongly affected by large temperature changes which induce the development and localization of stresses, leading in turn to damage, e.g., cracking. In this work, we study the evolution of linear and nonlinear elasticity parameters when increasing the temperature of the thermal loading process. We prove the existence of a link between linear and nonlinear elasticity properties. We show that the change of the nonlinear elasticity parameters with the increase in the thermal loading is larger at the lower temperatures than the corresponding change for the linear parameters, suggesting that nonlinear elasticity can be exploited for early thermal damage detection and characterization in consolidated granular media. We finally show the influence of grain size upon the thermal damage evolution with the loading temperature and how this evolution is mirrored by the nonlinear elasticity parameter

Potential effects of optical solar sail degredation on trajectory design

The optical properties of the thin metalized polymer films that are projected for solar sails are assumed to be affected by the erosive effects of the space environment. Their degradation behavior in the real space environment, however, is to a considerable degree indefinite, because initial ground test results are controversial and relevant inspace tests have not been made so far. The standard optical solar sail models that are currently used for trajectory design do not take optical degradation into account, hence its potential effects on trajectory design have not been investigated so far. Nevertheless, optical degradation is important for high-fidelity solar sail mission design, because it decreases both the magnitude of the solar radiation pressure force acting on the sail and also the sail control authority. Therefore, we propose a simple parametric optical solar sail degradation model that describes the variation of the sail film's optical coefficients with time, depending on the sail film's environmental history, i.e., the radiation dose. The primary intention of our model is not to describe the exact behavior of specific film-coating combinations in the real space environment, but to provide a more general parametric framework for describing the general optical degradation behavior of solar sails. Using our model, the effects of different optical degradation behaviors on trajectory design are investigated for various exemplary missions

Environmental assessment of radical innovation in concrete structures

In the building sector, the contribution of concrete structure to the overall emissions of greenhouse gases is significant. Switzerland is engaged in a 2050 energy strategy where the reduction of the embodied energy of buildings is a key aspect. In this study, we assess the environmental impact of different low energy concrete solutions. The study focuses on technologies that use cement with very high substitution rate (up to 65%) and other tensile resistant materials than steel in order to keep high durability targets. Hybrid wood-concrete structure, low carbon high performance concrete prestressed with carbon fiber reinforced polymer, and ultra-high performance fiber reinforced concrete with synthetic fiber reinforcement are among the studied options. The environmental assessment is done through life cycle analysis using Ecoinvent database for Switzerland and SimaPro software. Results of initial environmental assessment of production of the new technologies present huge energy and emission savings potential for the energy turnaround

3D finite-element modelling of splitting crack propagation

Although many experimental results on bond strength are available and splitting is commonly recognised as an important aspect of bond strength, only a few studies on splitting crack development have been published so far. Although, splitting is a 3D phenomenon, the only measurement easily taken in a lest is the splitting crack width on the specimen surface. As a result, the crack development inside the specimen is unmonitored. Such being the limits of testing, finite-element (FE) analysis can be a valuable alternative for the study of splitting crack 3D nature and for a better understanding of bond behaviour. However, FE studies are limited by the intrinsic difficulty in correctly modelling the bond. In fact, the models proposed so far are either too complex or too limited for describing actual anchorages and for studying splitting development. The main purpose of this research work is to develop a 3D FE model in which bond is modelled by a simple kinematic interface. The model developed is useful for establishing rational design criteria for anchorages and splices. Such a model is validated by simulating a series of pull-out tests concerning the interaction between a bar and a stirrup, when the concrete cover is split and the stirrup crosses the splitting plane. The comparison between experimental and numerical results shows that the proposed model describes quite well the behaviour of an anchored bar in terms of both bond-slip response and splitting crack width. In spite of its simplicity, the proposed model can be easily expanded to cover more complex structural cases and to develop more rational criteria for the design of anchorages and splices in RC members