Determination Of Strain Rate Sensitivity Research Articles

Determination of Strain Rate Sensitivity of Micro-struts Manufactured Using the Selective Laser Melting Method

Micro-lattice structures manufactured using the selective laser melting (SLM) process provides the opportunity to realize optimal cellular materials for impact energy absorption. In this paper, strain rate-dependent material properties are measured for stainless steel 316L SLM micro-lattice struts in the strain rate range of 10−3 to 6000 s−1. At high strain rates, a novel version of the split Hopkinson Bar has been developed. Strain rate-dependent materials data have been used in Cowper–Symonds material model, and the scope and limit of this model in the context of SLM struts have been discussed. Strain rate material data and the Cowper–Symonds model have been applied to the finite element analysis of a micro-lattice block subjected to drop weight impact loading. The model output has been compared to experimental results, and it has been shown that the increase in crush stress due to impact loading is mainly the result of strain rate material behavior. Hence, a systematic methodology has been developed to investigate the impact energy absorption of a micro-lattice structure manufactured using additive layer manufacture (SLM). This methodology can be extended to other micro-lattice materials and configurations, and to other impact conditions.

Mathematical description of indentation creep and its application for the determination of strain rate sensitivity

The creep process during the holding stage of nanoindentation test has been analyzed mathematically. It is shown analytically for the first time that the corresponding indentation depth–time relationship can be described by a power-law function, suggesting a direct application of nanoindentation for the determination of the strain rate sensitivity.

Determination of superplastic constitutive equations and strain rate sensitivities for aerospace alloys

Constitutive equations for the superplastic behaviour of titanium and aluminium aerospace alloys have been presented and computational procedures developed for the determination of the material parameters arising in the equations. The equations include a description of grain growth kinetics with deformation enabling the influence of microstructure on superplastic deformation behaviour to be modelled. Three predictive methods have been developed for the determination of strain rate sensitivity. The models represent the dependence of the strain rate sensitivity on strain, strain rate, and grain growth, and therefore, provide useful information for process design and optimization. The models are validated by comparison of predictions with experimental data reported in the literature and obtained in this work. Finally, two conventional experimental testing methods for the determination of strain rate sensitivity, namely the constant strain rate and strain rate jump methods are appraised using the methods developed.