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Jukka Aho
13b6c67597
Introduce explicit creep strain increment updates with elastic tangent returns. - Wire `CreepStrain` state requirements and trait classification.
72 lines
2.6 KiB
Julia
72 lines
2.6 KiB
Julia
# SPDX-FileCopyrightText: 2015-2026 Jukka Aho
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# SPDX-License-Identifier: MIT
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"""
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Norton deviatoric creep strain `ε_c` with linear elastic unloading:
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`σ = 𝔻 : (ε − ε_c)`, `Δε_c = (3/2) Δt A σ_vm^{n−1} s / σ_vm`.
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Optional irradiation-like **volumetric swelling** increment
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`Δε_sw = β \\, \\dot{\\phi} \\, Δt` added isotropically to `ε_c` when `β` and
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`phi_dot` are set.
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Elastic tangent only (ignores creep Jacobian); suited to explicit creep
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sub-stepping inside an implicit displacement solve.
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"""
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using Tensors
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struct NortonCreepElastic <: AbstractMaterial
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elastic::LinearElastic
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A::Float64
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n::Float64
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β_swelling::Float64
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phi_dot::Float64
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function NortonCreepElastic(elastic::LinearElastic, A::Float64, n::Float64, β::Float64, ϕdot::Float64)
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A ≥ 0 || throw(ArgumentError("Norton coefficient A must be non-negative"))
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β ≥ 0 || throw(ArgumentError("swelling coefficient β must be non-negative"))
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ϕdot ≥ 0 || throw(ArgumentError("phi_dot must be non-negative"))
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new(elastic, A, n, β, ϕdot)
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end
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end
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function NortonCreepElastic(; E::Real, ν::Real, A::Real, n::Real, β_swelling::Real = 0.0, phi_dot::Real = 0.0)
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NortonCreepElastic(LinearElastic(E = E, ν = ν), Float64(A), Float64(n), Float64(β_swelling), Float64(phi_dot))
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end
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material_behavior(::NortonCreepElastic) = StatefulStrainDependent()
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supported_physics(::NortonCreepElastic) = (Elasticity{3}(),)
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required_state_variables(::NortonCreepElastic) = (CreepStrain,)
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function compute_stress(mat::NortonCreepElastic, ε::SymmetricTensor{2,3}, ::Nothing, Δt::Float64)
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return compute_stress(mat, ε, NamedTuple(), Δt)
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end
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function compute_stress(mat::NortonCreepElastic, ε::SymmetricTensor{2,3}, state_old::NamedTuple, Δt::Float64)
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ε_c_old = get(state_old, :ε_c, zero(SymmetricTensor{2,3}))
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σ_el, _, _ = compute_stress(mat.elastic, ε - ε_c_old, NamedTuple(), 0.0)
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s = dev(σ_el)
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norm2 = s ⊡ s
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seq = √(3.0 / 2.0 * norm2)
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Δε_vol = zero(SymmetricTensor{2,3})
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if mat.β_swelling > 0 && mat.phi_dot > 0 && Δt > 0
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ev = mat.β_swelling * mat.phi_dot * Δt
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Δε_vol = (ev / 3.0) * one(SymmetricTensor{2,3,Float64,6})
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end
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Δε_creep = zero(SymmetricTensor{2,3})
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if mat.A > 0 && Δt > 0 && seq > 1e-14
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η = Δt * mat.A * seq^(mat.n - 1)
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Δε_creep = (1.5 * η / seq) * s
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end
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ε_c_new = ε_c_old + Δε_creep + Δε_vol
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σ_new, _, _ = compute_stress(mat.elastic, ε - ε_c_new, NamedTuple(), 0.0)
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𝔻 = elasticity_tensor(mat.elastic)
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return σ_new, 𝔻, (ε_c=ε_c_new,)
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end
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