The tensile properties of the

The tensile properties of the two alloys at a wide range of strain rates have been investigated [16]. The tensile tests of the two alloys at low strain rate were performed on a standard tensile test machine. A split-Hopkinson tension bar (SHPT) was used for the tensile test at high strain rate. The typical engineering stress–engineering strain curves of 2024-T4 and 7075-T6 aluminum alloys at four different strain rates are shown in Figs. 2 and 3, respectively. By comparing Figs. 2 and 3, it is observed that the yield stress of 7075-T6 alloy is higher than that of 2024-T4 alloy. However, 2024-T4 alloy exhibits a moderate strain hardening rate and a strain-rate sensitivity, while 7075-T6 alloy exhibits an insignificant strain hardening rate and a strain-rate sensitivity. Their fracture properties could be strongly affected by strain hardening rate and yield stress [10].
Dynamic three-point bending test The extruded aluminum alloy Mitiglinide Calcium are machined into rectangular specimens with 15 mm in width, 7.5 mm in thickness and 75 mm in length for the dynamic fracture test. The direction of length is consistent with the direction of extrusion deformation. An edge notch with 0.25 mm in width and 4 mm in depth is made at the center of the specimen by using a wire electrical discharge machine. Subsequently, the specimens are fatigued in a three-point bending configuration in order to develop a sharp fatigue crack extending from the end of notch. The length of the fatigue crack is typically about 1 mm, resulting in a total initial crack length, a ∼ 5 mm, such that a/W ∼ 0.33. A dynamic three-point bending test set-up is shown in Fig. 4, which consists of a drop tower for impact loading, a notched specimen and two anvils. The 5.08 kg drop tower is equipped with an instrumented hemispherical tup. The specimen is placed on two anvils which have a span of 60 mm between them. The impact load profile of specimen is measured by using a dynamic force measurement transducer with the frequency response of 8 kHz. The initial impact velocity is measured by an electro-optical device. For each test, the load signals are recorded as a function of time. Then the displacement, xdis, of drop tower can be estimated using Newton\'s second law by successive integration of load signalwhere v0 is the measured initial impact velocity, m is the mass of drop tower (m = 5.08 kg), and F(τ) is the impact load measured at the tup. Finally, the absorbed energy can be calculated by successive integration of force–displacement curve.
Experimental results and discussions
Fractography
Conclusions
Acknowledgments This research was supported by the NatiS100onal Science Foundation of China under Grant No. 11072119, the Defense Industrial Technology Development Program under Grant No. B1520110003, the K.C. Wong Magna Foundation of Ningbo University, China, and a grant from the Department of Education of Zhejiang Province through the Impact and Safety of Costal Engineering Initiative, a COE Program at Ningbo University.
Introduction Detonation is an efficient way of combustion heat release, which has many advantages of high thermodynamic cycle efficiency and high energy release rate. It has been highly concerned in aerospace propulsion field. Currently, there are two engines adopting the detonation combustion mode: pulse detonation engine (PDE) and continuous rotating detonation engine (CRDE). Compared with PDE, CRDE can produce stable continuous rotating detonation wave just with single ignition. It has higher average fuel flow and higher thrust because of continuous fuel filling. It can also gain the characteristic of stable propagation, which reduces vibration and noise. As a result of the advantages of CRDE, it has obvious superiorities in performance, structure size, engine structure, thermal protection and other aspects [1,2]. Bykovskii et al. [3–5] studied the continuous rotating detonation. The different detonating modes, fuel–oxidant mixture and variety of engine structures were used in test. It was found that the gaseous fuel can produce continuous detonation. However, if the liquid fuel is used, it can not produce continuous detonation unless extra oxygen is added to improve the activity of mixture. Besides, they did research on many factors, such as outlet pressure, pressure losses of oxidizer and fuel, total mass flow rate, premixed injection structure, and put forward the design criteria of key parameters of continuous rotating detonation engine.