forked from 1b-agent/fieldcraft-upstream
jyvikoandClaude Opus 5.5
a30d0b5c5b
Segment-to-segment penalty contact between element faces: each secondary face and each main face facing it are projected onto the secondary face's plane, split into triangles, clipped (Sutherland–Hodgman) and integrated with a three-point rule per sub-triangle (Puso–Laursen segmentation, the penalty at the integration points as Fischer–Wriggers), so a uniform pressure gives the consistent nodal forces on both meshes and the contact patch test passes on non-matching meshes. Every contact runs both ways at half the penalty: pairs with each surface as the secondary, general and self contact face against face. A bucket grid of face boxes every increment, faces integrated in parallel and their forces added in face order: the same numbers on any thread count. The penalty per area ε = s γ min(m/A)/Δt² comes from the lumped masses, each node's directional area and the stable increment, bounded by Gershgorin's row sums so contact never shortens the increment. Coulomb friction with exponential decay by a regularised return map at the secondary nodes; rigid walls take Coulomb impulses. Contact work and friction dissipation join the energy balance; each contact reports its peak force, first and last contact, deepest penetration, friction and the nodes adjusted at the start (initial penetrations adjusted strain-free or refused with the node, face and depth); a cap on contact faces. Verified (crates/explicit/tests/contact.rs, tests/oracle/explicit-*): colliding bars (2L/c +1.2%, ρcAv₀/2, KE kept to 0.005%, contact energy back to 8e-5 of it), blocks sliding to a stop on a rigid wall and on a plate under constant and decaying friction (0.005–0.2%), the patch test (σ_zz uniform to 0.06%), two spheres colliding against Hertz (peak +2.3%, duration −0.4%; the oracle case waits for a graded sphere mesher), a free body untouched by general contact, determinism across threads. Oracle measures gain `over` (ratios). Existing fixtures do not move. Co-Authored-By: Claude Opus 5.5 <[email protected]> Claude-Session: https://claude.ai/code/session_01NmAttHhUZTokgPeEJia8sm
176 lines
4.4 KiB
JSON
176 lines
4.4 KiB
JSON
{
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"title": "Contact patch test: two blocks with non-matching meshes in uniaxial compression (explicit contact)",
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"kind": "theory",
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"source": "The contact patch test: a contact discretisation must transmit a uniform pressure across a non-matching interface exactly; Taylor & Papadopoulos, On a patch test for contact problems in two dimensions, Nonlinear Computational Mechanics, Springer 1991, 690–702; Crisfield, Re-visiting the contact patch test, IJNME 48:435–449, 2000. Uniaxial stress between frictionless symmetry planes is uniform in both blocks",
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"quantities": [
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{
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"id": "lower_corner",
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"quantity": "σ_zz of the lower block's corner element under the interface (element 10) over that of the upper block's corner element over it (element 19)",
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"measure": {
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"command": "solve.probe",
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"params": {
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"step": "Squeeze",
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"elements": [
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10
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]
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},
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"pointer": "/elements/0/stress/2",
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"over": {
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"command": "solve.probe",
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"params": {
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"step": "Squeeze",
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"elements": [
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19
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]
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},
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"pointer": "/elements/0/stress/2"
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}
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},
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"value": 1.0,
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"tolerance": {
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"relative": 0.005
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},
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"reason": "a uniform stress is an equilibrium of the discrete system (the integrated contact forces are the consistent nodal forces of a uniform pressure on both meshes); what is left is the ringing of the loading, a hundred wave transits slow"
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},
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{
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"id": "lower_centre",
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"quantity": "σ_zz of the lower block's centre element under the interface (element 14) over that of element 19",
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"measure": {
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"command": "solve.probe",
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"params": {
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"step": "Squeeze",
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"elements": [
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14
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]
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},
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"pointer": "/elements/0/stress/2",
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"over": {
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"command": "solve.probe",
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"params": {
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"step": "Squeeze",
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"elements": [
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19
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]
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},
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"pointer": "/elements/0/stress/2"
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}
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},
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"value": 1.0,
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"tolerance": {
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"relative": 0.005
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},
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"reason": "as for the corner element"
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},
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{
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"id": "lower_base",
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"quantity": "σ_zz of the lower block's bottom corner element (element 1) over that of element 19",
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"measure": {
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"command": "solve.probe",
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"params": {
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"step": "Squeeze",
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"elements": [
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1
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]
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},
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"pointer": "/elements/0/stress/2",
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"over": {
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"command": "solve.probe",
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"params": {
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"step": "Squeeze",
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"elements": [
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19
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]
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},
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"pointer": "/elements/0/stress/2"
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}
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},
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"value": 1.0,
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"tolerance": {
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"relative": 0.005
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},
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"reason": "as for the corner element"
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},
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{
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"id": "upper_top",
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"quantity": "σ_zz of the upper block's top far corner element (element 26) over that of element 19",
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"measure": {
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"command": "solve.probe",
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"params": {
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"step": "Squeeze",
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"elements": [
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26
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]
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},
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"pointer": "/elements/0/stress/2",
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"over": {
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"command": "solve.probe",
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"params": {
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"step": "Squeeze",
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"elements": [
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19
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]
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},
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"pointer": "/elements/0/stress/2"
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}
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},
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"value": 1.0,
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"tolerance": {
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"relative": 0.005
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},
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"reason": "as for the corner element"
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},
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{
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"id": "force",
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"quantity": "the force across the interface over −σ_zz A (A = 1)",
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"measure": {
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"from": "solve",
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"pointer": "/contacts/0/peak_force",
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"over": {
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"command": "solve.probe",
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"params": {
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"step": "Squeeze",
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"elements": [
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19
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]
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},
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"pointer": "/elements/0/stress/2",
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"scale": -1.0
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}
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},
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"value": 1.0,
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"tolerance": {
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"relative": 0.01
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},
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"reason": "the integrated contact pressure carries the whole load; the largest force of the run is the final one in a slow squeeze, up to the ringing"
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},
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{
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"id": "lateral",
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"quantity": "σ_xx of element 14 over its σ_zz (uniaxial stress: 0)",
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"measure": {
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"command": "solve.probe",
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"params": {
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"step": "Squeeze",
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"elements": [
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14
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]
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},
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"pointer": "/elements/0/stress/0",
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"over": {
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"command": "solve.probe",
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"params": {
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"step": "Squeeze",
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"elements": [
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14
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]
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},
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"pointer": "/elements/0/stress/2"
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}
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},
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"value": 0.0,
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"tolerance": {
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"absolute": 0.005
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},
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"reason": "frictionless symmetry planes and a frictionless interface leave the blocks free to expand sideways; the non-matching interface must not hold them"
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}
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]
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} |