Tue, 2013-04-16 11:26 | 
The objective of this Doctoral Dissertation is an in-depth study of size effect phenomena for concrete and other semi-brittle materials. Size effect is a term used to describe the influence of the dimensions of a structural member and its microstructure to its mechanical response. Classical mechanics theories fail to explain this phenomenon, which has been observed experimentally for a range of materials. All materials in nature can be seen as composites, i.e. consisting of two or more different materials assumed homogeneous. In most cases, the error introduced in the calculations by assuming that the material is homogeneous is relatively low. However, as the scale reduces, the error increases and when the scale of a structure becomes comparable with the scale of the material microstructure itself, the predictions of classical mechanics become unreliable.
The study includes the development of a gradient theory predicting such size effect phenomena, the proposition of a methodology for estimating an additional parameter and the formulation of analytical solutions to certain problems within the framework of gradient elasticity and plasticity. This theory will be verified through experiments on plain and fiber-reinforced concrete beams of various sizes under 4-point bending.
Gradient elasticity theories differ from the classical elasticity theories in the number of material constants they use. These theories assume an additional constant: an internal length. In this way, a measure of inhomogeneity of the material is introduced in the constitutive laws which govern their response. In other words, the scale becomes part of the analysis and hence it can be included in the solution and visa versa. The main difficulty with these theories is that for most materials this additional constant has not been measured and a methodology for estimating this parameter does not exist. Although the specific case of semi-brittle materials will be examined, the proposed model should apply to other heterogeneous materials, as well.
Ph.D Candidate:
Triantafyllou Antonios
Department:
Department of Civil Engineering
School:
School of Engineering
Supervisor:
Prof. Philip Perdikaris (filperd@civ.uth.gr)
Supervising Committee:
(1) P. C. Perdikaris (2) A.E. Giannakopoulos (3) M. Moretti Παραδοτέα έργου δημοσίως προσβάσιμα:
