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Predictive simulation capabilities for modeling fracture evolution provide further insight into quantities of interest in comparison to experimental testing. Based on the variational approach to fracture, the advent of phase-field modeling achieves the goal to robustly model fracture for brittle materials and captures complex crack topologies in three dimensions.
Brittle material failure in high consequence systems can appear random and unpredictable at subcritical stresses. Gaps in our understanding of how structural flaws and environmental factors (humidity, temperature) impact fracture propagation need to be addressed to circumvent this issue. A combined experimental and computational approach composed of molecular dynamics (MD) simulations, numerical modeling, and atomic force microscopy (AFM) has been undertaken to identify mechanisms of slow crack growth in silicate glasses. AFM characterization of crack growth as slow as 10 -13 m/s was observed, with some stepwise crack growth. MD simulations have identified the critical role of inelastic relaxation in crack propagation, including evolution of the structure during relaxation. A numerical model for the existence of a stress intensity threshold, a stress intensity below which a fracture will not propagate, was developed. This transferrable model for predicting slow crack growth is being incorporated into mission-based programs.
Brittle behavior of metal alloys is often critical to modeling ballistic impact and penetration. The ALEGRA multiphysics finite element software incorporates calibrated models for the equation of state, elasticity, yield stress, plasticity and fracture, but simulations do not always capture expected metal fracture. Here we report concerted efforts to do so for one important case where experiments clearly show shear fractures: a tungsten sphere impacting a steel plate at various angles. Our best simulations show fractures that are qualitatively similar to experiments, but there are significant differences in quantitative metrics. Specifically, velocities of tracers used to quantify simulated plug parameters consistently fall short of measured plug velocities. Also, simulated plugs break apart more than expected from experimental evidence. We attribute these shortfalls to the lack of an explicit shear fracture mechanism in the material models, leading to over-estimated resistance to plug formation and movement.
Extension tube captive nut with a standard bolt joins assemblies with an inaccessible nut location. This fastener is excellent for joining brittle materials.
Damage to brittle materials by impact with high velocity projectiles into glass and Lucite
Friction loading device gives axial symmetry to test specimen of brittle materials during tensile testing. This axial alignment prevents bending stresses which hinder measurement of tensile strength.
Application of nonlinear bending theory to prestressed and segmented brittle structures
Effect of cooling rate on ductile-brittle bend-transition temperature of chromium wire
Effect of quenching on ductile-brittle bend transition temperature of chromium wire
Effect of quenching on ductile-brittle bend transition temperature of Cr-35Re wire
Yielding and brittle cracking of orthotropic strip, using Wiener-Hopf technique and asymptotic method for isotropic case
Reinforcing aluminum, aluminum alloys, and ductile epoxies with short, brittle fibers and high modulus filaments, and boron carbide whisker growth
Boron carbide whiskers for reinforcing brittle fibers of aluminum, aluminum alloys, or ductile epoxies
Factors affecting tensile strength of ductile metals reinforced with short, brittle fibers
Yielding and brittle cracking of orthotropic strip, using Wiener hopf technique and asymptotic method for isotropic case
Reinforcement of ductile aluminum and epoxies with brittle high modulus filaments
Reactor irradiation effects on ductile brittle transition and stress-strain behavior of tungsten
Technique requires radio frequency induction power source, induction furnace and good vacuum system to induce brittle material thermal shock testing.