Strain rate and temperature dependent strain localization of dynamically stretched lightweight bars: from metal to polymer

Longhui Zhang,Nik Petrinic,F Gálvez Díaz-Rubio,David Townsend,Antonio Pellegrino,D.A Cendón Franco

doi:10.1051/epjconf/202125005001

Abstract

This work studies the dynamic strain localization and constitutive relationship of a Ti3Al2.5V alloy in jet engine containment system and a transparent polycarbonate conceived for aircraft canopy application by Digital Image Correlation (DIC) technique from quasi-static condition to high strain rates at different temperatures. The responses of two materials show significant strain rate and temperature sensitivities. Observations of Ti3Al2.5V alloy show that the dynamic local strain rate can reach values up to 1000 % of the nominal strain rate in the necking zone. However, dynamic local strain rate of polycarbonate soars up during strain softening then decreases rapidly with necking propagation, and eventually becomes 20 % of the nominal strain rate until fracture. Appropriate viscoplastic constitutive models are determined for both materials, which are incorporated in finite element simulations to reveal the trend of dynamic local strain rate evolution in dynamic tensile tests. The present work shows two different kinds of strain localization in typical lightweight materials, which should be addressed carefully from Split Hopkinson Tension Bar (SHTB) tests.

Highlights

Split Hopkinson Tension Bar (SHTB) technique has been widely proposed for the characterization of the tensile response of materials at high strain rates since Harding et al [1]
The engineering strain of the specimen was directly measured from the gauge section via Digital Image Correlation (DIC) analysis using commercial software Lavision Davis
The ultimate engineering stress of Ti3Al2.5V alloy is 703 MPa under quasi-static condition, beyond which the engineering stress decreases due to necking localization with the failure engineering strain of 0.29

Summary

Introduction

SHTB technique has been widely proposed for the characterization of the tensile response of materials at high strain rates since Harding et al [1]. The analysis of SHTB test is subjected to non-uniform deformation such as the necking localization. Lightweight metals and polymers have been increasingly applied in aerospace engineering, which would be subjected to high-speed deformation in service. It’s important to understand the high rate constitutive response and the strain localization in the materials. Quasi-static to high strain rate tensile tests, with the assistance of DIC technique to accurately measure the strain history, are carried out to investigate the dynamic strain localization in a Ti3Al2.5V alloy and a polycarbonate (PC). The sensitivities of strain rate and temperature on the constitutive response and failure are studied, in order to guide the design of aerospace components

Experimental protocol

Experimental results

Numerical Simulations

Conclusion