Abstract
Understanding the stability limit of crystalline materials under variable tensile stress conditions is of capital interest for technological applications. In this study, we present results from first-principles density functional theory calculations that quantitatively account for the response of selected covalent and layered materials to general stress conditions. In particular, we have evaluated the ideal strength along the main crystallographic directions of 3C and 2H polytypes of SiC, hexagonal ABA stacking of graphite and 2H-MoS. Transverse superimposed stress on the tensile stress was taken into account in order to evaluate how the critical strength is affected by these multi-load conditions. In general, increasing transverse stress from negative to positive values leads to the expected decreasing of the critical strength. Few exceptions found in the compressive stress region correlate with the trends in the density of bonds along the directions with the unexpected behavior. In addition, we propose a modified spinodal equation of state able to accurately describe the calculated stress–strain curves. This analytical function is of general use and can also be applied to experimental data anticipating critical strengths and strain values, and for providing information on the energy stored in tensile stress processes.
Highlights
A clear understanding of the cohesive and mechanical properties of technological materials is of capital importance especially when applications are demanded in environments with hostile thermal, stress, and chemical conditions
The authors define a linear bulk modulus, or equivalently a directional Young modulus (YI, I specifies the direction), and applied the universal relation of Equation (3). Considering both the physical significance and the directional behaviour of this spinodal-like equation of state, in this article we introduce a 1D-spinodal equation of state (SEOS) to analytically describe the stress–strain curves associated with tensile stress phenomena
The critical strength of 3C- and 2H-silicon carbide (SiC), graphite, and 2H-MoS2 were evaluated by means of first principles quantum-mechanical methodologies based on the density functional theory (DFT) approximation
Summary
A clear understanding of the cohesive and mechanical properties of technological materials is of capital importance especially when applications are demanded in environments with hostile thermal, stress, and chemical conditions. To the best of our knowledge, none of these studies have addressed the description of the observed or calculated stress–strain data by means of analytical functions as normally happens in high-pressure and related fields Such equations of state would open the possibility of anticipating critical values for the strength and strain of materials without reaching the instability condition. We are interested in general analytical functions able to represent the behavior of different types of compounds under these tensile conditions and to reproduce the critical parameters To this end, we propose a new SEOS form that uses the critical strain as the reference state, and that can be used to fit both the experimental and calculated stress–strain data. The paper ends with a summary of our main findings
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