Определение трещиностойкости образцов с шевронным надрезом с использованием трехточечного изгиба

A method is proposed for the experimental determination of the specific fracture energy of a material under loading by a 3-point bending of a rectangular specimen with a chevron notch. It is shown that at the initial stages of crack propagation in the chevron notch zone, a linear dependence of the specimen compliance on the crack length is observed. This makes it possible to calculate the specific fracture energy of the material without using the phenomenological equations used under standard test conditions. The calculations were carried out for technical titanium VT1-0.

Non-traditional Approach to the Evaluation of the Freeze-thaw Resistance of Concrete based on the Fracture Tests

The paper deals with a pilot study focused on the freeze-thaw (F-T) resistance of concrete. A non-traditional approach to the evaluation of the F-T resistance of concrete based on the determination of the fracture parameters is presented in the paper. Three types of specimens were used in the experimental program – prisms with edge and Chevron notch, and cylinders with the Chevron notch. Three sets of specimens of each shape were tested in total. The reference set was stored in the water until the time of testing. Another two sets of specimens were subjected to 50 and 100 freeze-thaw tests, respectively. One F-T cycle consisted of 4 hours freezing in the air at temperature -18 °C and 2 hours thawing in the water at temperature +20 °C. Based on the results, it can be stated that the values of fracture energy are proportional to the area of the ligament. This finding was observed for all tested sets – non-frost and frost attacked. The values of modulus of elasticity and fracture toughness are influenced more by the geometry and also by the changes of the specimens’ stiffness due to the exposition to the F-T cycles.

Fracture Parameters of Concrete from Drill-Core Specimens from Objects at the Transgas Gas Control Center

This paper presents the results of fracture tests conducted on nine concrete specimens from drill-cores taken from three selected objects located at the former Transgas Gas Control Center in Prague. The specimens were provided with a chevron notch before being tested in three-point bending. The evaluation included arithmetic mean values and basic statistics for the static modulus of elasticity, fracture toughness and specific fracture energy of the assessed concrete specimens.

Mechanical Performance of Glass-Based Geopolymer Matrix Composites Reinforced with Cellulose Fibers

Glass-based geopolymers, incorporating fly ash and borosilicate glass, were processed in conditions of high alkalinity (NaOH 10–13 M). Different formulations (fly ash and borosilicate in mixtures of 70–30 wt% and 30–70 wt%, respectively) and physical conditions (soaking time and relative humidity) were adopted. Flexural strength and fracture toughness were assessed for samples processed in optimized conditions by three-point bending and chevron notch testing, respectively. SEM was used to evaluate the fracture micromechanisms. Results showed that the geopolymerization efficiency is strongly influenced by the SiO2/Al2O3 ratio and the curing conditions, especially the air humidity. The mechanical performances of the geopolymer samples were compared with those of cellulose fiber–geopolymer matrix composites with different fiber contents (1 wt%, 2 wt%, and 3 wt%). The composites exhibited higher strength and fracture resilience, with the maximum effect observed for the fiber content of 2 wt%. A chemical modification of the cellulose fiber surface was also observed.