Modeling the effect of composition and thermal quenching on the fracture behavior of borosilicate glass Le-Hai Kieu a , Jean-Marc Delaye a, ⁎, Claude Stolz b a Service d'Études et Comportement des Matériaux de Conditionnement, DEN/DTCD/SECM, CEA Marcoule, BP 17171, 30207 Bagnols sur Cèze cedex, France b Laboratoire de Mécanique des Solides, CNRS UMR7649, École Polytechnique, 91128 Palaiseau cedex, France abstract article info Article history: Received 10 May 2012 Received in revised form 26 June 2012 Available online 4 October 2012 Keywords: Failure analysis; Fracture; Silicate; Nuclear applications; Molecular dynamics This article describes the fracture processes simulated by classical molecular dynamics in three alkali borosilicate glasses of different compositions. Applying an external tensile load results in glass fracturing through processes of nucleation, growth, and coalescence of cavities. The cavity nucleation processes begin during the elastic phase and differ depending on the glass composition and especially on the [Na 2 O]/[B 2 O 3 ] ratio. The cavity growth and coalescence phases are associated with the plastic phase. The concentration of BO 3 entities has a strong influence on the cavity growth rate because these entities limit the accumulation of local stresses. Glass specimens with the same compositions but disordered by the application of a higher quenching rate were also fractured. These glasses are considered as models of irradiated structures and analyzing their fracture behaviors gives interesting information as to the understanding on why the fracture toughness evolves under irradiation. © 2012 Elsevier B.V. All rights reserved. 1. Introduction Silicate glasses are increasingly used for applications including con- struction, optics, or nuclear waste disposal, both alone and in associa- tion with other materials to modify their properties. Determining the fracture behavior of this type of glass is a major issue for such applica- tions. Fracturing of silicate glasses has been addressed by numerous studies at macroscopic and nanoscopic scale implementing techniques such as indentation or Chevron notch testing [1–3], AFM analysis [4–6] or simulation by classical molecular dynamics [7–10] (by a hybrid method [11] or by the finite element method [12]). The nanoscopic mechanisms responsible for glass fracturing are still debated [13]. Although glass is historically considered as a brittle mate- rial, which breaks without prior plastic deformation [14], recent studies suggest the existence of plastic deformation mechanisms in areas of stress concentration at the tip of the crack to account for crack propaga- tion in the glass. The appearance of cavities preceding the crack front that allows gradual opening of the material has been demonstrated experimentally by applying slow cracking techniques in humid atmo- sphere together with analysis by AFM [15]. This conclusion must be placed in perspective, however, as some authors have pointed out that the observed cavities could be experimental artifacts, and have pro- vided evidence that glass fracturing could be attributable to purely elas- tic mechanisms [12]. Atomistic modeling methods, especially by classical molecular dy- namics, have been used in recent years to address the problem of glass fracturing at a small scale [9,10,16–18]. Although they are still limited to small dimensions and relatively short time spans, molecular modeling methods are capable of simulating the response of a glassy structure to the application of external shear or tensile stresses. These simulations were performed for pure silica glass and for more complex silica-based glasses containing alkalis or other network formers [19]. It was observed that silica and more complex silicate glasses were frac- tured by nucleation and coalescence of cavities. The formation of cavities is specific to the amorphous nature of the material; in a cristobalite crys- tal the fracture progresses by successively breaking the chemical bonds closest to the crack front [16]. In addition, differences are observed be- tween the fracture behavior of silica and more complex silicate glasses. The cavities tend to be more concentrated at the center of the simulation cell in the case of silica, and more scattered in the case of more complex silicate glasses [20]. Nuclear glasses are complex materials for which satisfactory surro- gates exist in the form of simplified compositions containing SiO 2 ,B 2 O 3 and Na 2 O [21]. Under irradiation by heavy ions, these simplified glasses reproduce the same qualitative behavior as actual nuclear glasses doped with short-lived actinides. When subjected to irradiation, both the actual glass and the simplified glasses tend to swell and their hardness dimin- ishes [22–24]. The fracture toughness of the actual glass increases under irradiation, and recent unpublished results show that this parameter also increases in a simplified glass [25,26]. Moreover, Young's modulus di- minishes in both actual and simplified glass specimens subjected to irra- diation. A comparison of irradiation by heavy ions and by electron beam showed that ballistic effects were responsible for the changes in the mac- roscopic properties of this type of glass [23]. Irradiation by heavy ions alters the glass structure by increasing the degree of disorder and diminishing the degree of polymerization Journal of Non-Crystalline Solids 358 (2012) 3268–3279 ⁎ Corresponding author at: CEA Marcoule, BP 17171, 30207 Bagnols sur Cèze cedex, France. Tel.: +33 4 66 79 17 94; fax: +33 4 66 79 77 08. E-mail address: jean-marc.delaye@cea.fr (J.-M. Delaye). 0022-3093/$ – see front matter © 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.jnoncrysol.2012.07.037 Contents lists available at SciVerse ScienceDirect Journal of Non-Crystalline Solids journal homepage: www.elsevier.com/ locate/ jnoncrysol