Mechanical properties of pentaerythritol tetranitrate(PETN) single crystals from nano‐indentation: Depth dependent response at the nano meter scale

Abstract

The current work presents the results from an investigation of the mechanical behavior of single crystals of the energetic material pentaerythritol tetranitrate (PETN) using a nano‐indentation technique. The indentation tests have been performed on the maximum growth habit face (110) of the PETN, using a spherical, Berkovich and an anisometric (wedge‐shaped) tip. The load displacement curves along with analysis have been used to extract the mechanical properties and identify the anisotropic indentation modulus for the PETN. The indentation moduli of the PETN single crystal were found to decrease as indentation depth increases and become independent of indentation depth for depths greater than 200 nm for the spherical indenter and 300 nm for the anisometric wedge indenter and Berkovich tip. The indentation modulus obtained from spherical tip indentation is compared with the results calculated by using literature values of the elastic constants. The wedge indenter measurements and Berkovich indentation at various tip orientations are different due to the anisotropy of the PETN. The yield behaviors of the PETN single crystal were also explored using both spherical and wedge tip indentation and the differences are discussed.

A Thermal and Nanomechanical Study of Molecular Crystals as Versatile Mocks for Pentaerythritol Tetranitrate

“…Other studies on PETN powder have shown similar trends with properties such as surface area coarsening, where newly synthesized PETN initially coarsens at a very high rate but the rates soon become much more gradual, if not completely stable [33,34]. [18], showing a dramatic depth dependence for elastic modulus. Their results showed that PETN appeared to be stiffer (i.e., higher modulus) at the surface, with a significantly decreasing stiffness as a function of depth (indenter penetration) into the material.…”

“…Load-depth data from several such indents per material were analyzed using the method described by Oliver and Pharr [22] to obtain elastic modulus and hardness values, averages for which are reported for each material in Table 3. Nanoindentation results for PETN were previously published by Zhai and McKenna [18], showing a dramatic depth dependence for elastic modulus. Their results showed that PETN appeared to be stiffer (i.e., higher modulus) at the surface, with a significantly decreasing stiffness as a function of depth (indenter penetration) into the material.…”

“…Nanoindentation has previously been used for the purpose of characterizing explosives such as cyclotetramethylene-tetranitramine (HMX), cyclotrimethylenetrinitramine (RDX), triaminotrinitrobenzene (TATB), and others [13][14][15][16][17]. PETN had previously been characterized via nanoindentation but some unusual properties were discovered, such as extreme depth dependence of the elastic modulus [18], which merited a re-examination for this present work.…”

Surface Studies of β-1,3,5,7-Tetranitro-1,3,5,7-Tetrazoctane and Pentaerythritol Tetranitrate from Density Functional Tight-Binding Calculations and Implications on Crystal Shape

“…(b) is reprinted from ref , Copyright (2007), with permission from Springer Nature. (c) is reprinted from ref , Copyright (2010), and (e) is reprinted from ref , Copyright (2016), with permissions from John Wiley & Sons.…”

The mechanical response of micron-sized molecular crystals

“…The understanding of mechanical deformation and fracture in molecular crystals remains less mature than in other classes of materials [7]. While indentation-based methods have proven valuable for investigating strength and elasticity [8][9][10][11][12][13][14][15][16][17], such approaches provide less insight into constitutive stress-strain response, fracture, and extrinsic length scale-or shape-dependent changes in deformation behavior. Indentation fracture methods [18] have been utilized successfully in some cases, but high degrees of anisotropy generally lead to difficulties in applying these approaches to molecular crystals [16].…”