Biography:

One of their most recent publications is Influence of aggregate size and volume fraction on shrinkage induced micro-cracking of concrete and mortar. Which was published in journal Cement and Concrete Research.

More information about Peter Grassl research including statistics on their citations can be found on their Copernicus Academic profile page.

Peter Grassl's Articles: (5)

Influence of aggregate size and volume fraction on shrinkage induced micro-cracking of concrete and mortar

AbstractIn this paper, the influence of aggregate size and volume fraction on shrinkage induced micro-cracking and permeability of concrete and mortar was investigated. Nonlinear finite element analyses of model concrete and mortar specimens with regular and random aggregate arrangements were performed. The aggregate diameter was varied between 2 and 16 mm. Furthermore, a range of volume fractions between 0.1 and 0.5 was studied. The nonlinear analyses were based on a 2D lattice approach in which aggregates were simplified as monosized cylindrical inclusions. The analysis results were interpreted by means of crack length, crack width and change of permeability. The results show that increasing aggregate diameter (at equal volume fraction) and decreasing volume fraction (at equal aggregate diameter) increase crack width and consequently greatly increases permeability.

A damage-plasticity interface approach to the meso-scale modelling of concrete subjected to cyclic compressive loading

AbstractConcrete is characterised by stiff inclusions in a soft matrix separated by weak interfacial transition zones (ITZs). Subjected to cyclic loading, this material exhibits a strongly nonlinear response, which is characterised by the occurrence of hysteresis loops. Furthermore, for cyclic loading, failure may occur before the equivalent strength for monotonic loading is reached. The present work investigates, whether the occurrence of permanent displacements in different phases of the meso-structure of quasi-brittle heterogeneous materials, such as concrete, leads to damage evolution during repeated loading.A new three-dimensional interface model based on a combination of damage mechanics and the theory of plasticity is proposed, which allows one to control the ratio of permanent and total inelastic displacements. The model is based on only a few material parameters, which can be directly determined by experiments.The interface model is applied to the plane-stress analysis of an idealised heterogeneous material with cylindrical inclusions and ITZs subjected to cyclic compressive stresses.

Meso-scale approach to modelling the fracture process zone of concrete subjected to uniaxial tension

AbstractA meso-scale analysis is performed to determine the fracture process zone of concrete subjected to uniaxial tension. The meso-structure of concrete is idealised as stiff aggregates embedded in a soft matrix and separated by weak interfaces. The mechanical response of the matrix, the inclusions and the interface between the matrix and the inclusions is modelled by a discrete lattice approach. The inelastic response of the lattice elements is described by a damage approach, which corresponds to a continuous reduction of the stiffness of the springs. The fracture process in uniaxial tension is approximated by an analysis of a two-dimensional cell with periodic boundary conditions. The spatial distribution of dissipated energy density at the meso-scale of concrete is determined. The size and shape of the deterministic FPZ is obtained as the average of random meso-scale analyses. Additionally, periodicity of the discretisation is prescribed to avoid influences of the boundaries of the periodic cell on fracture patterns. The results of these analyses are then used to calibrate an integral-type nonlocal model.

3D network modelling of fracture processes in fibre-reinforced geomaterials

AbstractThe width of fracture process zones in geomaterials is commonly assumed to depend on the type of heterogeneity of the material. Still, very few techniques exist, which link the type of heterogeneity to the width of the fracture process zone. Here, fracture processes in geomaterials are numerically investigated with structural network approaches, whereby the heterogeneity in the form of large aggregates and low volume fibres is modelled geometrically as poly-dispersed ellipsoids and mono-dispersed line segments, respectively. The influence of aggregates, fibres and combinations of both on fracture processes in direct tensile tests of periodic cells is investigated. For all studied heterogeneities, the fracture process zone localises at the start of the softening regime into a rough fracture. For aggregates, the width of the fracture process zone is greater than for analyses without aggregates. Fibres also increase the initial width of the fracture process zone and, in addition, result in a widening of this zone due to fibre pull out.

Initiation of fluid-induced fracture in a thick-walled hollow permeable sphere

Highlights•A model for predicting the deformation and fracture of a thick-walled hollow sphere subjected to radial fluid flow is presented.•Based on radial symmetry and on assumed fracture patterns representing the initial stage of fracture, the problem is reduced to a nonlinear ODE.•The influence of Biot's coefficient and of the sphere size on strength is investigated.•An original closed-form solution of the linear ordinary differential equation in the elastic range is derived.

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