Some Observations Regarding Stochasticity of Dynamic Response of 2D Disordered Brittle Lattices

International Journal of Damage Mechanics

2016

The focus of the present article is on the size effect of a transition region from the damaged to the fragmented phase in impact-induced breakup of a slender projectile. Molecular dynamics simulations of the classic ballistic Taylor test are performed with a simple generic model to explore an extended low-energy range. In the simulation setup, flat-ended, monocrystalline, nanoscale projectiles, with a fixed aspect ratio but 10 different diameters, collide perpendicularly with a rough rigid wall. With gradually increasing impact energy, a non-negligible projectile disintegration eventually takes place and is identified with the damage-fragmentation phase transition. These atomistic simulations offer an indispensable tool to gain an insight into damage evolution in the neighborhood of the damage-fragmentation transition resulting in the occurrence of fragmentation at the critical point. A finite size scaling analysis of the average fragment mass is carried out to determine critical exponents and dependence of the critical striking velocity upon the slender projectile’s diameter.

Section: Observations and Discussionsupporting

confidence: 77%

Section: Size Effect Of the Damage-fragmentation Transition Thresholdsupporting

confidence: 76%

Damage-fragmentation transition: Size effect and scaling behavior for impact fragmentation of slender projectiles

International Journal of Damage Mechanics

2016

“…The remarkable hardening of the brittle response with the rate increase, discussed previously by Mastilovic et al (2008) and Mastilovic (2010), is illustrated in Figure 1. The solid circle represents the mean strength obtained from 30 different statistical realizations at the five selected strain rates.…”

Section: Rate Effects On Mean Tensile Strengthmentioning

confidence: 89%

“…The rate-dependent evolution and pattern of damage accumulation are closely related to the shape of stressstrain curve and the damage energetics Mastilovic, 2010).…”

Section: Damage Patterns and Stochastic Effects On Damage Growthmentioning

confidence: 99%

Further Remarks on Stochastic Damage Evolution of Brittle Solids Under Dynamic Tensile Loading

International Journal of Damage Mechanics

2010

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This article illuminates some general features and provides elementary interpretations of the deformation, damage, and failure of brittle solids characterized by very low fracture energy. The dynamic response of these materials is determined to a large extent by stochastic and random factors. The investigation emphasis is on the moderate-to-extremely high rate range (10 s À1 , 1 Â 10 9 s À1 ), explored under practically identical in-plane stress conditions. The statistical approach is based on repeated particle dynamics simulations for different physical realizations of micromechanical disorder of a 2D brittle discrete system. The proposed strategy is computationally intensive, which necessitates simplicity of the laws governing the interparticular interaction. Based on the simulation results, an expression is proposed to model the mean tensile strength dependence on the strain rate. The linearity of the rate dependence of the stress-peak macroscopic response parameters is observed and discussed.KEY WORDS: brittle systems, dynamic strength, damage energy rate, time to failure, disorder.

“…Nonetheless, based on the simulation data, this fragment mass reduction due to the thermal equilibration is well within the inherent randomness of the initial fragmentation evident from Table 1 (compare, as an example, the striking velocities 0.357 km/s and 0.360 km/s.). Stochasticity of the maximum fragment masses in the phase transition region is expected based on the well-known aleatory variability inherent to low-energy fracture events (e.g., Mastilovic, 2011). The ratio of mmax0 values for the two orientations is-under the circumstances-reasonably close to the value Ctg 60°/Ctg 30° = 3 predicted by Eq.…”

Section: Latín American Journal Of Solids and Structures 14 (2017) 15mentioning

confidence: 78%

Phenomenology of the Maximum Fragment Mass Dependence Upon Ballistic Impact Parameters

Lat. Am. j. solids struct.

2017

Molecular dynamics simulations of the ballistic Taylor test are used to explore correlation between the largest fragment mass and the impact energy of a projectile as well as a set of selected state variables. Flat-ended, monocrystalline, nanoscale bars collide with a rigid wall with striking velocities ranging from 0.27 km/s to 60 km/s. The investigation emphasis is on two border regions of the emerging nonlinear phenomenological model identified with two transitions: the damage-fragmentation transition and the shattering transition. In between these two nonlinear regions, the maximum fragment mass is largely inversely proportional to the impact energy, and the maximum values of the pressure, temperature, and the square of the effective strain. A reverse-sigmoid phenomenological model is proposed to capture the unifying features of this nonlinear and saturable dependence. A crystallographic orientation dependence of the damage-fragmentation transition parameters is investigated.