Numerical Analysis of Mode I Fracture Toughness for Plain Concrete Beams.

Document Type : Research Studies

Authors

1 Professor and Head of Engineering Material department, faculty of Engineering Zagazig University, Zagazig, Egypt

2 MSc student, Materials Engineering Dept.,faculty of Engineering Zagazig University, Zagazig, Egypt

Abstract

Fracture mechanics is based on the assumption that all engineering materials contain cracks from which failure starts. Structures have sizeable existing cracks that might or might not grow, depending on the load level. when a material has an existing crack, that lead to high stresses near the crack tip. Stress field type in the region of the crack tip can be defined of mode I, where two fracture surfaces are displaced perpendicular to each other in opposite direction where crack growth takes place. The crack tip stress and displacement field can be uniquely characterized by the stress intensity factor, SIF, It is neither the magnitude of stress nor strain, but it is a unique parameter that describes the effect of loading at the crack tip region and the resistance of the material. Stress intensity filed is valid for a small region around the crack tip. It depends on both the values of stress and crack size. In the present work, numerical models were designed to study the effect of specimen thickness, crack-depth ratios and concrete compressive strengths on the behavior of SIF for concrete beams. Nine beams were idealized with dimensions of 1500 mm length, 400 mm depth and different thickness 120, 250 and 400 mm. The crack-depth ratios were 0.1, 0.2 and 0.3 and the concrete compressive strengths were 25, 40 and 55 MPa. The results proved that there is a decrease in SIF with increase in specimen thickness. On the other hand; there is an increase in SIF values with increase in concrete compressive strength and crack-depth ratio.

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