Influence on strain-rate history effects on the development of necking instabilities under dynamic loading conditions

The present paper is devoted to the analysis of strain-rate history effects on neck formation under dynamic loading. For materials presenting strain-rate history effects, two different strain-rate sensitivities should be distinguished: the instantaneous strain-rate sensitivity and the work-hardening strain-rate sensitivity. We have analysed the relative contributions of these two kinds of strain-rate sensitivities to neck retardation for two different configurations: a bar under impact tension and a dynamically expanding ring. For this purpose, we have developed finite element models and, for the second configuration, an analytical model based on the linear stability analysis. The obtained results show that strain-rate history effects have a significant influence on the onset and development of necking. The reason of thisphenomenon is that, contrary to the instantaneous strain-rate sensitivity, the work-hardening strain-rate sensitivity does not contribute to delay the neck formation.

A new generalized cross-connected switched capacitor multilevel inverter topology with high output voltage gain for single phase solar PV unit

Switched capacitor multilevel inverters are gaining much attention these days due to their merits like voltage boosting and voltage balancing characteristics. A Cross Connected Switched Capacitor Multilevel Inverter (C2SC-MLI) topology is proposed in this work. It can synthesize thirteen levels in the terminal voltage waveform and with a voltage boost ratio of 1:3. The topology is extendable by adding additional “n” modules in series. The number of levels (NLevel) and the voltage gain can be increased up to 4i+9 and 1:(i+2) respectively by connecting ‘i’ such ‘n’ modules. The topology also has inherent voltage balancing ability. To prove the advantage of proposed topology it is compared with recent switched capacitor multilevel inverter topologies and conventional multilevel inverter topologies in terms of number of power electronic components required, cost and voltage gain. The performance of proposed topology is validated using simulation in MATLAB and with an experimental prototype rated 0.1 kW fed by a solar PV emulator under steady state and dynamic loading conditions.

How the Thermomechanical Processing Can Modify the High Strain Rate Mechanical Response of a Microalloyed Steel

The effects of thermomechanical processing (TMP) on the mechanical response of microalloyed steels subjected to dynamic loading conditions were examined. The deformation conditions in the thermomechanical laboratory rolling processes were selected on the basis of dilatometric tests. It allowed (with a constant value of total deformation) us to obtain microstructures with different compositions and morphology of the particular components. Several samples characterized by a particularly complex and unexpected representation of the obtained microstructures were selected for further research. Plastometric tests, i.e., compression and tensile tests, were performed under quasi-static loading with digital image correlation (DIC) analysis, and under dynamic loading on the Split Hopkinson Pressure Bar (SHPB) apparatus with strain rates of 1400 and 2000 s−1. Samples deformed in such conditions were subjected to microstructural analysis and hardness measurements. It has been observed that the use of various combinations of TMP parameters can result in the formation of specific microstructures, which in turn are the source of an attractive mechanical response under dynamic loading conditions. This opens up new possible areas of application for such popular structural materials which are microalloyed steels.

FDEM Modelling of Rock Fracture Process during Three-Point Bending Test under Quasistatic and Dynamic Loading Conditions

A hybrid finite-discrete element method (FDEM) is proposed to model rock fracture initiation and propagation during a three-point bending test under quasistatic and dynamic loading conditions. Three fracture models have been implemented in the FDEM to model the transition from continuum to discontinuum through fracture and fragmentation. The loading rate effect on rock behaviour has been taken into account by the implementation of the relationship between the static and dynamic rock strengths derived from dynamic rock fracture experiments. The Brazilian tensile strength test has been modelled to calibrate the FDEM. The FDEM can well model the stress and fracture propagation and well show the stress distribution along the vertical diameter of the disc during the Brazilian tensile strength test. Then, FDEM is implemented to study the rock fracture process during three-point bending tests under quasistatic and dynamic loading conditions. The FDEM has well modelled the stress and fracture propagation and can obtain reasonable fracture toughness. After that, the effects of the loading rate on the rock strength and rock fracture toughness are discussed, and the mesh size and mesh orientation on the fracture patterns are also discussed. It is concluded that the FDEM can well model the rock fracture process by the implementation of the three fracture models. The FDEM can capture the loading rate effect on rock strength and rock fracture toughness. The FDEM is a valuable tool for studying the rock behaviour on the dynamic loading although the proposed method is sensitive to the mesh size and mesh orientation.