Pull the crystal and watch the stress rise, peak and drop as bonds break. Heat it to make failure easier. Blue atoms have 6 neighbours; red ones sit next to a crack or void.
The science
Pair potential. Atoms interact through U(r) = 4ε[(σ/r)12 - (σ/r)6] with a minimum -ε at r = 21/6σ. Force is F = -dU/dr; the curve is cut and shifted at 2.5σ.
Dynamics. 168 atoms in a periodic box obey Newton's equations, integrated by velocity Verlet with a weak Berendsen thermostat. Units are reduced (σ = ε = m = 1).
Stress. The virial formula gives the tensile stress σxx = -(Σ m vx2 + Σ xij Fx,ij)/A. Stretching the box in x produces the stress-strain curve: a linear elastic region whose slope is the modulus, a peak, then plastic flow or fracture.
Simplifications. Two dimensions, a perfect triangular crystal with a periodic box (so no free surface), small system, a strain rate far faster than any real test, and reduced units rather than a specific metal. Failure strength is therefore overestimated compared with real materials.