Portable Device for Indirect Assessment of Strength in Tension of Building Materials and Problem of Boundary Condition

Abstract

A sensitive determination of mechanical properties of brittle building materials of existing buildings, requires gathering of samples by core drilling. Due to the fact, that the material samples may change their properties during transportion, it is preferred to test samples on site. Development of portable machine for Split test was therefore the first choice. The specimen is compressed with diametrically opposite symmetric line loads. The main goal of this paper is to document fine-tuning of experimental setup of the device to provide consistent and reproducible measurement. Therefore the paper concentrates on the biggest problem which is the boundary conditions of the test. For this reason, different types of contacts were studied. For boundary condition analysis was used photoelasticity. Set of experiments was performed in order to fulfill the condition of crack initiating in the middle of the specimen. Location of crack initiation was determined by the Digital Image Correlation - DIC. Various materials for contact were evaluated and it was found that the lead bar and grips with radius are best.