PSI - Issue 20

Victor Petrov et al. / Procedia Structural Integrity 20 (2019) 87–92 Victor Petrov et al. / Structural Integrity Procedia 00 (2019) 000–000

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5

Physical meaning of coefficients, thus, it consists in the loading area and the volume of the material involved in the deformation process. However, this model gives a good agreement with experimental data only on during the first and second zones of destruction and it has a discrepancy in the third zone - at the stage of crack propagation with a constant mean speed due to the prevalence of “break through” mechanisms in conditions of stress reduction and strain relaxation by molecular structure polymer's (see Fig. 3). In comparison with the known numerical solutions described by Ayatollahi (2015) the model is simple, while maintaining a deep physical meaning. Later, the model obtained on the basis of the energy approach was used to assess the crack resistance under load by a wedging impact on the surface statically loaded sample by Petrov (2011). As the main parameter used is critical energy flow value corresponding to the critical crack length:   * crack cr G G   (5) Solid lines on Fig. 3 show the calculated values of the energy flow modulus at different ambient temperatures (- 90°, -40° and 20° C), calculated on the basis of the proposed model (5), and points – the data obtained from the experiment. The loading conditions of the sample correspond to striker energy W =135 J and tensile load P=981 N.

Fig. 3. The crack tip energy low modulus dependence versus crack length at diferent environment temperatures (calculated by model shown by curves and experimental results by points): green – -90°C, red – -40° С , blue – 20° С

Conclusions

Thus, the developed model of brittle crack growth, based on physical representations of the fluctuation nature of the fracture process, makes it possible to make a transition from discrete experimental data under combined loading of a sample from a viscoelastic material with a heterogeneous hierarchy of molecular structures to a set of continuous numerical data necessary to calculate the values of the energy flow entering the crack tip in a wide range of external influences, including low temperatures. The further research would be includes the studies of the much wider range of loading conditions and other materials such as metals and composites. The theoretical part also would be modified for building the numerical model on the base of statistical and quantum theories to completely understand the nature of dynamic fracture.