forked from 1b-agent/fieldcraft-upstream
Theory cases for the nonlinear solver, each frozen as a fixture: uniaxial stretch of a neo-Hookean block to twice its length (closed form), the nonlinear patch test on a distorted hex8 mesh, a quarter turn of the same mesh (objectivity: zero stress), the elastica of a hex20 cantilever at P L²/(E I) = 1, 2, 5, 10 against Bisshopp–Drucker (0.2–0.5 %), and the inflation of a thick neo-Hookean tube by a follower pressure against Rivlin's closed form (0.08 % at the bore). A finite-strain Cook's membrane is pending its transcribed reference. docs/fem.md describes the formulation, the material point interface, the follower-pressure choice and what nonlinear steps refuse; the literature, parity and roadmap pages follow. Co-Authored-By: Claude Opus 5.5 <[email protected]> Claude-Session: https://claude.ai/code/session_01NmAttHhUZTokgPeEJia8sm
200 lines
4.8 KiB
JSON
200 lines
4.8 KiB
JSON
{
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"title": "Large-deflection cantilever under a dead tip load against the elastica (solids)",
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"kind": "theory",
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"source": "The elastica of a cantilever under a vertical end load: K. E. Bisshopp, D. C. Drucker, Large deflection of cantilever beams, Quarterly of Applied Mathematics 3(3):272–275, 1945 (elliptic-integral solution); values computed by integrating θ″ = −(P/EI) cos θ by shooting (our own RK4, 20000 steps), agreeing with the table of K. Mattiasson, Numerical results from large deflection beam and frame problems analysed by means of elliptic integrals, IJNME 17(1):145–153, 1981, to all six digits",
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"quantities": [
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{
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"id": "v1",
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"quantity": "tip deflection δ_v/L at P L²/(E I) = 1",
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"measure": {
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"command": "solve.probe",
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"params": {
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"step": "K1",
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"at": [
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"pointer": "/nodes/0/displacement/2",
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"scale": -0.1
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"value": 0.301721,
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"tolerance": {
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"relative": 0.01
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},
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"reason": "hex20, 40 × 2 through the depth, L/h = 20: shear deformation (0.6 (h/L)² ≈ 0.15 % of the deflection) and the clamp's local restraint, both absent from the elastica"
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},
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{
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"id": "u1",
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"quantity": "tip shortening δ_h/L at P L²/(E I) = 1",
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"measure": {
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"command": "solve.probe",
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"params": {
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"step": "K1",
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"at": [
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"value": 0.056433,
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"tolerance": {
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"relative": 0.02
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},
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"reason": "as δ_v; the shortening is the smaller, second-order quantity, so its relative error is about twice the deflection's"
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},
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{
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"id": "v2",
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"quantity": "tip deflection δ_v/L at P L²/(E I) = 2",
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"measure": {
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"command": "solve.probe",
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"params": {
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"step": "K2",
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"scale": -0.1
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"value": 0.493457,
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"tolerance": {
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"relative": 0.01
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"reason": "hex20, 40 × 2 through the depth, L/h = 20: shear deformation (0.6 (h/L)² ≈ 0.15 % of the deflection) and the clamp's local restraint, both absent from the elastica"
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},
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{
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"id": "u2",
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"quantity": "tip shortening δ_h/L at P L²/(E I) = 2",
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"measure": {
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"command": "solve.probe",
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"pointer": "/nodes/0/displacement/0",
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"scale": -0.1
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"value": 0.160642,
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"tolerance": {
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"relative": 0.02
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"reason": "as δ_v; the shortening is the smaller, second-order quantity, so its relative error is about twice the deflection's"
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},
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{
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"id": "v5",
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"quantity": "tip deflection δ_v/L at P L²/(E I) = 5",
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"measure": {
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"command": "solve.probe",
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"params": {
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"pointer": "/nodes/0/displacement/2",
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"scale": -0.1
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"value": 0.713792,
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"tolerance": {
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"relative": 0.01
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"reason": "hex20, 40 × 2 through the depth, L/h = 20: shear deformation (0.6 (h/L)² ≈ 0.15 % of the deflection) and the clamp's local restraint, both absent from the elastica"
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},
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{
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"id": "u5",
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"quantity": "tip shortening δ_h/L at P L²/(E I) = 5",
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"measure": {
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"command": "solve.probe",
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"params": {
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"pointer": "/nodes/0/displacement/0",
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"scale": -0.1
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"value": 0.387628,
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"tolerance": {
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"relative": 0.02
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},
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"reason": "as δ_v; the shortening is the smaller, second-order quantity, so its relative error is about twice the deflection's"
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},
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{
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"id": "v10",
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"quantity": "tip deflection δ_v/L at P L²/(E I) = 10",
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"measure": {
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"command": "solve.probe",
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"params": {
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"step": "K10",
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"pointer": "/nodes/0/displacement/2",
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"scale": -0.1
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},
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"value": 0.810609,
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"tolerance": {
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"relative": 0.01
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},
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"reason": "hex20, 40 × 2 through the depth, L/h = 20: shear deformation (0.6 (h/L)² ≈ 0.15 % of the deflection) and the clamp's local restraint, both absent from the elastica"
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},
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{
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"id": "u10",
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"quantity": "tip shortening δ_h/L at P L²/(E I) = 10",
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"measure": {
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"command": "solve.probe",
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"params": {
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"step": "K10",
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"at": [
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]
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},
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"pointer": "/nodes/0/displacement/0",
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"scale": -0.1
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},
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"value": 0.554996,
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"tolerance": {
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"relative": 0.02
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},
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"reason": "as δ_v; the shortening is the smaller, second-order quantity, so its relative error is about twice the deflection's"
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}
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]
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}
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