Struct Friction 

pub struct Friction {
    pub normal_dof: usize,
    pub shear_dof: usize,
    pub mu: f64,
    pub k0: f64,
    pub b: f64,
    /* private fields */
}

Couples one “shear” DOF to a different DOF’s own material — the normal direction’s current force — via a bilinear-kinematic-hardening Coulomb return map: sticks (stiffness k0) until |V| reaches mu * yield-eligible normal force, then slides with post-slip tangent b*k0 (see the b field doc comment for why b is required, not optional).

This is deliberately not a Material variant: Material::evaluate is a pure function of one scalar strain (every call site — Truss, ZeroLength, Fiber, the Parallel/Series/MinMax composites — depends on that signature), and friction’s yield force needs a second DOF’s current force, which a single Material has no way to see. So the coupling lives here, in the element, not the material catalog.

Sign convention: this codebase is compression-negative (see Material::Ent/Gap — strain <= 0.0 is the compression/engaged branch). Friction is mobilized only when the normal direction is in compression: yield force is mu * (-normal_force).max(0.0).

The return map: trial = k0*(shear_relative - slip) is the elastic predictor (same shape as ElasticPP’s trial_stress = e*(strain - ep), elastic_like.rs). Inside the yield surface, force = trial. Past it, this is standard 1D linear-kinematic-hardening plasticity with (fixed, for one call) yield force yield_force and hardening modulus chosen so the post-yield tangent is exactly b*k0: force = b*trial + (1-b)*yield_force*sign(trial), which by construction satisfies k0*(shear_relative - next_slip) == force — so, exactly like ElasticPP’s next_ep = strain - stress/e, next_slip = shear_relative - force/k0.

Fields

normal_dof: usize

shear_dof: usize

mu: f64

k0: f64

b: f64

Post-slip hardening ratio (fraction of k0) — required at construction, not defaulted, so callers make an active choice. A small nonzero value (recommended starting range 1e-3-1e-4) keeps the post-slip tangent away from exactly zero: while sliding, this DOF is commonly the only stiffness path on its shear direction, so an exactly-zero tangent risks a structurally singular row/column in the global system (AnalysisError::SingularSystem) — the same reasoning behind Material::MinMax’s nonzero failed-state tangent floor, except here b is part of the actual force law (rounding the stick/slip corner, reducing Newton bouncing at the transition), not a tangent-only fudge. Set to 0.0 for an exact textbook Coulomb comparison and accept the singularity risk that comes back with it.

Implementations

impl Friction

pub fn new( normal_dof: usize, shear_dof: usize, mu: f64, k0: f64, b: f64, ) -> Self

Trait Implementations

impl Clone for Friction

fn clone(&self) -> Friction

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Copy for Friction

impl Debug for Friction

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.