Characterization of the Mechanical Behavior of a Lead Alloy, from Quasi-Static to Dynamic Loading for a Wide Range of Temperatures

Abstract

The current needs in terms of ballistic protection for armed forces require an almost constant improvement in performance to face the constantly evolving threats and scenarios. Ballistic tests are conventionally carried out in order to assess and validate the levels of protection. The challenge is to be able to set up a digital protocol and only carry out final validation tests. Indeed, the advantage of digital simulation lies in the possibility of being able to evaluate a wide variety of configurations. In order to obtain reliable results, it is necessary to use sufficiently precise material behavior models to transcribe the phenomena observed during the impact. Our study focuses on the behavior of a small caliber ammunition with a ductile core impacting personal protection. More particularly on the mechanical behavior of the lead alloy core. Thus, compression tests have been carried out on a wide range of deformation rates, from quasi-static behavior to dynamic regime, at different temperatures. The study in dynamic conditions was carried out using split Hopkinson pressure bars. Due to the material properties, the experimental device had to be adapted in order to optimize the propagation of the waves allowing to measure signals (elastic waves). These tests demonstrate the dependency of the stress with strain rate and temperature. Dynamic restoration and recrystallization phenomena, characteristic of a material deformed in its hot working area, have also been identified. The associated oscillations due to Pochhammer–Chree effect, observable on the stress–strain curves, constitute the major problem for the implementation of behavioral models. Finally, a constitutive model sensitive to strain rate and temperature is investigated for ballistic purposes.

Dynamic testing and simulation of 9 mm full metal jacket ammunition

“…The cylindrical sample is presented on the Fig 1 .b. The constitutive model of the lead alloy core is a custom perfect plasticity model taking into account the temperature and strain rate dependencies presented in [6] defined by equations, (3) and Table 1. The material was tested up to dynamic deformation ranges for different temperatures with an adapted SHPB setup.…”

“…This is why the geometry of the samples is kept as close as possible to the geometry of the ammunition (see Fig 1 .b and c). It is composed of the same lead core studied in [6] and the steel jacket, studied separately in an internal project. The dimensions of the final sample are 9.0 mm in diameter and 5.7 mm height.…”

“…By neglecting the geometry of the ammunition, which has undergone multiple stages of forming, behavioural differences are induced and can result in an incorrect modelling. In the preceding study, the mechanical behaviour of the lead alloy core has been examined in order to identify a constitutive model [6][7]. Concurrently, the steel jacket material surrounding the lead core has also been investigated, leading to the identification of the Johnson-Cook model parameters [8].…”