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Two latent bugs in the elastic-plastic (eps) peridynamic model are corrected. 1. Yield norm. compute_DeviatoricForceStateNorm() built the trial deviatoric force state with an extra dilatation factor theta (omega*theta/wvolume) that the force loop's deviatoric force state (omega/wvolume) does not have, so the yield surface was evaluated against a different, theta-inflated force state and the material yielded much later than intended. The norm now uses the same intensive deviatoric force state the model applies. 2. Plastic extension update. The per-bond plastic deviatoric extension was updated as edpNp1 + rkNew*deltalambda, which reduces (uniform case) to a gain of ~2/r0 on (e_dev - edp) and overshoots/diverges under sustained plastic flow. It now uses the dimensionally consistent radial return edpNp1 + (deviatoric_extension - edpNp1)*(1 - sqrt(2*psi)/tdnorm). With both fixes an elastic-perfectly-plastic uniaxial test yields at the intended stress and the deviatoric stress plateaus stably instead of diverging. The existing PairPeri unit test still passes; results for peri/eps runs that reach the plastic regime will differ from earlier versions (documented with a versionchanged note). Found while re-implementing the PERI models on the BPM framework, where the corrected forms are used. Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
…request) Per the PR #5046 review discussion, recast correction 2 (the per-bond plastic deviatoric extension update) as a minimal correction of the literal Mitchell 2011 (SAND2011-3166) Eq. 45 transcription, rather than switching the model to the closest-point ("radial") return. The original "edp += rkNew*deltalambda" is dimensionally inconsistent in LAMMPS's discrete force-state convention: because the influence function is omega = 1/r0 (units 1/length), the increment is dimensionless while the plastic extension is a length, injecting a spurious gain of order 2/r0 that diverges under sustained plastic flow. The update now restores the missing length factor (0.5*r0), which removes the runaway and, in the equal-weighted-volume interior, coincides with the radial return that lands the deviatoric force state on the yield surface. The dimensionally exact, per-bond radial-return form (also exact at free surfaces) is documented in a source comment and the doc page as a deferred refinement for review by a peridynamics expert, since it would change results near boundaries. Correction 1 (removal of the spurious dilatation factor in the yield norm) is unchanged. No behavior change for purely elastic runs. Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_019nii2NLXtpCD2oqS4rrYAX
…otes Wire the deferred-refinement tracking issue (#5064, adopting the exact per-bond radial-return plastic update at free surfaces) into the peri/eps versionchanged note in doc/src/pair_peri.rst and the source comment in pair_peri_eps.cpp, so the TODO is discoverable from both the docs and the code. Comment/doc only. Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_019nii2NLXtpCD2oqS4rrYAX
PERI: fix peri/eps yield norm and plastic return mapping
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