PSI - Issue 6

Ivan Smirnov et al. / Procedia Structural Integrity 6 (2017) 34–39 Ivan Smirnov et al. / Structural Integrity Procedia 00 (2017) 000 – 000

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5

According to the experimental data, the limiting stresses for both test methods increase with increasing strain (stress) rate. Moreover, it is clearly visible the effect of changing the comparative strength of materials. For example, Fig. 3a shows that limestone is less stable than granite or CARDIFRC under quasi-static loading, but at strain rates in excess of 100 1/s its limit stresses exceed the limit stresses of the fiber-reinforced concrete and close to the limit stresses of the granite. Particular attention should be paid to the tests with different material states (Fig. 3b and 4b). Under quasi-static loads, the frozen materials show the greatest strength, and the saturated materials show the least strength. Under dynamic tests, the reverse trend is observed. The observed effects are well modeled by the failure incubation time criterion approach. Parameter τ was selected in such a way that theoretical curve calculated by (1) fits the experimental points with a minimal deviation. The parameters used in the calculations are presented in Table 1. Thus, following the terminology of the failure incubation time criterion, materials having large stresses at static loads (quasi-static strength) can have smaller failure incubation times under dynamic loads (dynamic strength)

Table 1. The parameters of the tested materials. σ c t is the static tensile strength; τ c is the incubation time of failure at compression; τ t is the incubation time of failure at splitting. Material σ c с [MPa] σ c t [MPa] τ c [ µ s] τ t [ µ s] Gabbro-diabase 189 27.4 13 17 Granite 125 4.8 40 42 Marble 37 2.9 69 51 Limestone 74 6.3 68 65 Limestone saturated 39 5.1 109 54 Limestone frozen 83 7.8 63 34 Concrete CARDIFRC 95 23 15 15 Concrete 22 2.5 27 28 Concrete saturated 12 2.3 65 39 Concrete frozen 33 8.9 59 21 с is the static compressive strength; σ c

5. Conclusions

The dynamic tests of rocks and concrete in compression and splitting by the SHPB setup were carried out. The analysis of the experimental results shows an increase in the limiting stress while reducing the impact duration. Also, the substitution effect of load-carrying capacity of materials at quasi-static and dynamic loads is observed for some rocks and states of concrete and limestone. Both temporal effects can be predicted by the structural-temporal approach. On this basis, it is assumed that dynamic strength can be characterized by a parameter with a time dimension.

Acknowledgements

The studies of the effects of dynamic loading of rocks and concrete on the basis of the structural-temporal approach are financially supported by the Russian Science Foundation (Grant № 15 -19-10032). The studies of the influence of water saturation on the dynamic strength of porous media were carried out within the framework of the state task of the Ministry of Education and Science of the Russian Federation (№9.6109.2017/6.7) .

References

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