New Aspects in the Mechanical Behavior of a Polycarbonate Found by an Experimental Study

Alfredo Alán Rey Calderón,Alberto Díaz Díaz

doi:10.1155/2018/1540919

Alfredo Alán Rey Calderón, Alberto Díaz Díaz

Open Access

https://doi.org/10.1155/2018/1540919

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Abstract

The aim of this paper was to analyze in detail the mechanical behavior of a polycarbonate by means of uniaxial tensile and compressive tests and to reveal new key aspects that must be taken into account in any predictive model. Uniaxial monotonic and creep-recovery tests were carried out at a variety of temperatures, stress levels, and load rates to get a complete description of the material response. Prior to mechanical testing, the material was subjected to a thermal rejuvenation in order to eliminate any previous aging and to obtain reliable and useful results. In every test, a complete determination of the strain state was assured by measuring axial and transverse strains with strain gauges. During the tests, significant asymmetry effects and viscous phenomena already reported by other authors were confirmed. The newest finding is that a nonlinear master transverse strain/axial strain curve matches perfectly with the experimental curves. This master curve is temperature- and rate-independent. Another originality of this paper is the disclosure of an instantaneous, hypoelastic-like behavior at high strain rates. The experimental observations presented in this study should be incorporated by a theoretical model whose aim is to accurately predict the mechanical behavior of polycarbonate subjected to any 3D stress state.

Highlights

A good mechanical design must offer a reliable performance which requires an extensive knowledge about how the material behaves
It is well known that mechanical behavior in polymers is complex: there is a dependency on strain rate [1,2,3,4,5]; temperature impacts the mechanical response [6,7,8,9]; hydrostatic stress affects mechanical behavior [10]
McKenna and his coworkers [12, 13] studied the nonlinear viscoelastic behavior of specimens of some glassy polymers subjected to torsional tests in which the distance between the grips was fixed, in such a manner that a normal axial force was provoked. e derivatives of the strain energy density with respect to first and second invariants of the deformation tensor were obtained in an attempt to have a better understanding of the material behavior

Summary

Introduction

A good mechanical design must offer a reliable performance which requires an extensive knowledge about how the material behaves. The mechanical behavior of polymers has been studied under uniaxial stress states with a unique sign: tension or compression. Several types of independent experiments, for example, compression, shear, and hydrostatic pressure, must be done in order to obtain a more complete characterization of materials. Compressive tests that generate a quasiuniform uniaxial stress state may be hard to perform because of potential buckling and Advances in Materials Science and Engineering barreling effects, for large strains. For this reason, Ravi-Chandar and Ma [16, 17] proposed original compressive tests with confined specimens in order to remove the aforementioned effects

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