APPLICATION OF ESPI-TECHNIQUE FOR THE ASSESSMENT OF MINERAL BUILDING MATERIALS

Abstract eng:
Most of the mineral building materials are quasi-brittle. In deformation controlled axial tensile tests of e.g. concrete prisms, one observes a gradual softening after reaching the maximum load. The reason for this softening is primarily caused by the heterogenity of concrete. In contrast to linear elastic fracture mechanics, the tensile fracture of concrete is not combined with a discrete crack but with a fracture process zone (FPZ), a densely microcracked volume. If one is interested in debonding of CFK-lamellas or sheets, the heterogenity of concrete makes the analytical assessment of the debonding very complicated. Therefore experimental work is necessary. In the paper, the recording of the deformation and post-peak strain distributions of plain concrete are carried out by means of the high sensitive laser speckle interferometry. The Electronic Speckle Pattern Interferometry (ESPI) is a contactless, continuous and repercussionless whole-field measurement technique with a high resolution. The in-plane displacement components of the specimen’s surface are measured and are transformed into isostrain-fields. The width of the FPZ in the post-peak tensile response of concrete is determined from these strain fields. ESPI is also used to measure debonding lengths of concrete elements on which FRP-lamellas have been glued.

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