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The response of cementitious materials is highly time dependent. On the one hand, it can lead to delayed collapse of structures fabricated of such materials. On the other hand, the time dependence is associated with the relaxation of peak stresses, which avoids, or postpones damage. A finite element formulation is presented for the analysis of the time-dependent cracking of cementitious materials. The constitutive law incorporates continuum plasticity and linear visco-elasticity. The former accounts for crack initiation and propagation, while the latter describes the bulk creep via an aging Maxwell chain. The cracking velocity dependence, which considers the additional viscous effect in the fracture process zone, is also included. This contribution to the cracking resistance regularises the localisation process and also introduces the correct time scale. The simple framework of the model allows the inclusion of other important phenomena in cementitious materials, such as stress-dependent hygral and thermal shrinkage.

The mechanisms causing long term changes of materials at mild operating conditions, i.e. relatively low temperatures and loads, has not received as much attention as that for high temperature operating conditions because small strains are involved. Nevertheless the thermo-mechanical loading response of materials used for high precision engineering parts such as ball-bearings is to a large extent determining the service life time of the application. This thesis focuses on the identification of the (microscopic) mechanisms controlling the (macroscopic) deformation of hardened and tempered iron-carbon based alloys when imposing a compressive load. The time-dependent deformation that occurs at mild operating conditions is generally attributed to dislocations movement. This research shows that also phase transformations and diffusion of interstitial atoms significantly contribute to the thermo-mechanical behaviour. Different deformation mechanisms occur for different tempering conditions of the iron-carbon-based alloys. The various mechanisms are implemented in a model so that the dimensional changes can be predicted.

The investigation was undertaken to support innovations in the field of asphalt pavement design and material selection, and to be able to evaluate or judge the risk of failure and cost-effectiveness of newly developed paving materials in order to justify their application. To be able to determine the risk of failure and cost-effectiveness, information is needed about the quality of the pavement. In order to define the quality of the pavement, it is necessary to know the behaviour of the applied materials. In order to know the behaviour of the materials it is necessary to know the properties that are relevant for the behaviour of the material in the pavement. The following aspects of the mechanical behaviour of asphalt mixture were investigated, because it is known based on experience that these are the important phenomena: the viscoelastic and viscoplastic stress strain behaviour, and the crack-growth behaviour. Both analytical and numerical approaches were followed. Test methods were developed that are suitable for use in a practical context for the determination of the stiffness modulus, the resistance to permanent deformation, and the resistance to fatigue and crack-growth. It is concluded that the following tests are suitable for the characterisation of the mechanical behaviour of asphalt mixtures in a practical context: a four point bending frequency sweep test, to characterise the linear dynamic viscoelastic stress strain behaviour, a dynamic triaxial creep test, to characterise the nonlinear dynamic elasto-viscoplastic stress strain behaviour, a tensile test, to characterise the resistance to crack-growth, and a fracture toughness test, to characterise the resistance to fracture. Those properties are important to the functionality of the pavement structure that is defined in terms of bearing capacity, surface characteristics, and long-term behaviour. It is concluded that it is possible, based on the tests mentioned, to develop a set of performance related specifications, which will allow newly developed asphalt mixtures to be tested for applicability relative to standardised asphalt mixtures for which the behaviour is known. Analytical methods will allow one to determine useful improvements to paving materials faster than empirical methods, and to obtain the information required to judge a newly developed and non-standardised paving material for its risk of failure and cost-effectiveness. Therefore, the use of analytical methods will facilitate the acceptation for application of innovative, non-standardised, paving materials.

A creep analysis has been performed on nailed, toothed-plates and split-ring joints in a varying uncontrolled climate. The load levels varied between 30% and 50% of the average ultimate short term strength of these joints, tested in accordance with ISO 6891. The climate in which the tests were performed varied between about 40% and 90% relative humidity, which coincides with Service classes 1 and 2 of Eurocode 5 for timber structures. A large scatter in creep factors was found with the highest average creep values for the 30% load levels. In order to analyse the influence of moisture variations, a creep model was developed containing the effects of mechanical creep, the influence of yearly shrinking and swelling as well as mechano-sorptive creep. Furthermore, a method has been presented in order to be able to derive creep factors to be applied in design calculations, based on the creep factors determined in laboratory creep tests, taking into account the design stiffness values for these joint types.

The new North/South metro line in Amsterdam contains several stations, some of which with an excavation depth of 30 m below surface. The design of these station boxes is very much determined by the adjacent historic buildings, high water table and the relatively soft soil. A lot of effort is put into minimising the settlements of buildings with shallow pile foundations. For this purpose, the walls of the station boxes consist of 45 m deep stiff diaphragm-walls. Apart from steel struts, an extra measure was taken to prevent wall deformation: a jet grout strut. The uncertainties of material properties and construction tolerances demand extra attention in the design stage. In order to deal with these uncertainties, the observational method was adopted. This paper addresses the process of the design, monitoring and evaluation of the jet grout strut of the Ceintuurbaan station.

A deeper understanding of the deformation and failure mechanisms in polycrystals is of utmost importance for their reliable use as engineering materials. These mechanisms are strongly influenced by the geometry of the granular arrangement. In this work, two-dimensional intergranular quasi-static crack propagation in brittle polycrystals and grain boundary sliding in creeping polycrystals have been numerically investigated with the aid of a Generalized Finite Element Method. The role of the parameters defining the cohesion of the grain boundaries in intergranular crack propagation has been investigated. It is shown that under certain circumstances crack paths are not affected by variations of cohesive law parameters. Moreover, beyond a certain brittleness threshold, the load-displacement curves can be mutually scaled and obtained from each other using simple linear elastic fracture mechanics relations. The insensitivity of crack paths to variations of cohesive law parameters and the mutual scaling of load-displacement curves can be exploited to avoid computationally expensive simulations. The uniqueness of the crack path with respect to cohesive law parameters has also enabled the study of the scaling properties of crack profiles in brittle polycrystals. The results of this study shed light on the roughening mechanism in 2D brittle solids. Finally, it has been shown that microstructural randomness has a strong influence on the response of creeping polycrystals with free grain boundary sliding. This study provides an understanding of the role of microstructural geometry in polycrystalline materials undergoing intergranular fracture and grain boundary sliding.

Dit rapport maakt deel uit van het onderzoek naar omgevingsbeïnvloeding bij ophogingen en wegverbredingen in het kader van het DelftCluster programma Blijvend Vlakke Wegen. Binnen dit onderzoek wordt onderzoek gedaan naar de voorspellende waarde met betrekking tot de zettingen en horizontale vervormingen bij ophogingen/wegverbredingen en de correlatie tussen horizontale en verticale volumes van de methode De Leeuw (horizontaal), het MSettle isotachen model (verticaal) en de Plaxis modellen Soft Soil Creep (SSC), Soft Soil (SS) en Hardening Soil (HS) (verticaal en horizontaal), tijdens de bouw-, consolidatie- en kruipfase. Op basis van deze case wordt het volgende advies gegeven voor het maken van een prognose van horizontale gronddeformaties door een ophoging: Voor het maken van een eerste inschatting van de horizontale gronddeformaties in de teen van een ophoging kan de methode Bourges en Mieussens worden gebruikt. Als de grond kruipgevoelig is kunnen de horizontale gronddeformaties het beste met het Soft Soil Creep-model worden bepaald. Bij niet-kruipgevoelige grond of als het verloop van de deformaties in de tijd minder belangrijk is, is het Hardening Soil-model ook bruikbaar. Gezien de achtergrond en de uitgangspunten van het Soft Soil Creep-model en de berekeningsresultaten, kunnen de parameters K0 nc en M het beste worden bepaald uit K0- CRS-proeven. De hoek van inwendige wrijving moet zo worden gekozen dat tan M. Uit numerieke overwegingen wordt voor de cohesie c’ een zeer kleine waarde aangehouden. Op basis van de resultaten van deze case wordt aanbevolen om in het ontwerpstadium dat nog geen resultaten van laboratoriumproeven beschikbaar zijn, de volgende waarden voor K0 nc te hanteren: o Veen: 0,3 ≤K0 nc ≤ 0,35 o Klei: 0,35 ≤ K0 nc ≤ 0,45 o Zandige klei: K0 nc ≥ 0,5.