smart-composites

name	smart-composites
description	Smart composites — embedded sensors/actuators, SHM with Lamb waves, piezoelectric PZT/MFC, shape memory alloy actuation, embedded fiber optic (FBG), self-healing composites, electro-active polymers.
metadata	{"priority":7,"promptSignals":{"phrases":["smart composite","smart material","embedded sensor composite","piezoelectric composite","structural health monitoring composite","self-healing composite","MFC actuator"],"minScore":3}}

Smart Composites — Complete Skill

Smart Material Taxonomy

Sensing: converts mechanical/thermal/chemical input → electrical output Actuation: converts electrical/thermal input → mechanical output Multifunctional: both sensing and actuation simultaneously

Piezoelectric Materials in Composites

PZT (Lead Zirconate Titanate) — PZT-4, PZT-5A, PZT-5H

d₃₁ piezo coefficient: strain/field in direction perpendicular to poling d₃₃: strain/field parallel to poling Typical PZT-5H: d₃₃ = 593 pm/V; d₃₁ = -274 pm/V; coupling k₃₁ = 0.39; k₃₃ = 0.75

Actuation force and displacement: δ = d₃₁ × L × E_field [m; L = actuator length] F_block = d₃₁ × E_field × E_pzt × A_pzt [N; blocking force at zero displacement]

Sensing: V_open = g₃₁ × σ × t [V; g₃₁ = voltage output coefficient = d₃₁/(ε₃₃ ε₀); t = PZT thickness]

Embedding in CFRP: Wafer PZT (0.2–0.5 mm thick) embedded between prepreg plies Electrical leads brought out through ply edges Cure temperature: PZT-5H T_Curie = 195°C → limits cure to < 180°C (below Curie) PZT-5A: T_Curie = 365°C → compatible with 120°C cure, marginal at 180°C epoxy cure

MFC (Macro Fiber Composite) — Smart Material Corp.

Structure: rectangular PZT fibers in epoxy matrix + interdigitated electrode Advantage: flexible; conformable to curved surfaces; can be bonded to outside of composite structure d₃₃ mode: fibers poled along fiber axis; high actuation strain in fiber direction Strain output: ε_free ≈ 0.1–0.2% (600 V actuation at full field)

PVDF (Polyvinylidene Fluoride) Piezoelectric Film

Very thin (9–110 μm); flexible; used as sensor d₃₁ = 23 pm/V; g₃₁ = 216 × 10⁻³ V·m/N (high voltage output → good sensor) Used for: impact detection, vibration sensing, acoustic emission pickup Disadvantage: low actuation force; brittle (depoling under large strains)

Shape Memory Alloy (SMA) Actuators in Composites

NiTi (Nitinol) Wires in Composites

Shape memory effect: low T → martensite → deformed; high T → austenite → recovers to trained shape One-way SMA: actuates on heating; bias spring/stressed composite resets Two-way SMA: actuates both ways (requires training)

Key parameters: M_f, M_s, A_s, A_f = transformation temperatures (finish/start martensite/austenite) Design: A_f < operating temperature < M_s (to ensure full recovery)

Recovery stress: σ_recovery = 100–400 MPa (significant)

Embedding NiTi wires: 0.1–0.5 mm diameter wires in laminate; heated by Joule heating (resistance wire) Used for: morphing structures, vibration control, shape adaptation

Bias composite: SMA wire contracts on heating; compressed laminate straightens Effective stiffness change ΔK: 10–50% with SMA activation → tunes structural frequency

Fiber Optic Sensors (FBG) in Composites

Fiber Bragg Grating (FBG)

Grating written into single-mode optical fiber; reflects narrow wavelength band Bragg wavelength: λ_B = 2 n_eff Λ [n_eff = effective refractive index; Λ = grating period]

Strain sensing: Δλ_B / λ_B = (1 - p_e) × ε_axial [p_e = photoelastic constant ≈ 0.22 for silica; ε = mechanical strain] Typical sensitivity: 1.2 pm/με at 1550 nm wavelength

Temperature sensing: Δλ_B / λ_B = (α_Λ + ξ) × ΔT [α_Λ + ξ ≈ 6.7 × 10⁻⁶ /°C for silica at 1550 nm] Sensitivity: ~10 pm/°C

Simultaneous T and ε: use two FBGs at different wavelengths + deconvolution matrix

Embedding in CFRP: Fiber (125 μm OD) between plies; coating stripped in embedded section; routed to edge for connection Integration with WDM (wavelength division multiplexing) → 50+ sensors on one fiber

Distributed sensing (BOTDR/BOTDA): Brillouin scattering along entire fiber length → temperature/strain profile at 1 m spatial resolution 100–10,000 m sensing range; structural monitoring of bridges, wind turbines, pipelines

Lamb Wave SHM in Composites

Lamb waves: guided waves in plate structures; S₀ (symmetric) and A₀ (antisymmetric) modes Generation and sensing: PZT wafer actuators/sensors in pitch-catch or pulse-echo modes

Damage detection: Baseline subtracted signal: DI (damage index) = ∫|u_damage - u_baseline|dt / ∫|u_baseline|dt Damage imaging: delay-and-sum beamforming → localization

Design of SHM system: PZT spacing: < λ_min/2 (Nyquist spatial sampling; λ = 10–50 mm for 100–500 kHz in CFRP) Actuation frequency: 100–500 kHz typical for CFRP SHM Coverage: overlap at 3 dB level from each actuator

Mode selection: S₀ at low frequency: near non-dispersive; good for long-range A₀: higher sensitivity to surface damage; more dispersive

Self-Healing Composites

Microencapsulated Healing Agents (White-Sottos, 2001)

Dicyclopentadiene (DCPD) microcapsules (50–300 μm) + Grubbs catalyst dispersed in matrix On crack: capsules rupture → monomer released → catalyst contact → polymerization → healing

Healing efficiency: η_heal = K_IC_healed / K_IC_virgin × 100% [fracture toughness recovery] Reported: 75–90% for first heal cycle; decreasing for repeated healing

Vascular Networks

3D-printed or sacrificial fiber vascular channels in composite Healing agent pumped on demand or by capillary action Advantage: multiple healing cycles (external reservoir); controllable delivery Challenge: network must not compromise structural performance

Ionomers (Self-Healing Polymers)

Poly(ethylene-co-methacrylic acid) → ionic crosslinks reform after damage Limited to low-level damage (not fiber fracture) Used for: ballistic impact self-sealing (NASA JSC, US Army programs)

Electro-Active Polymers (EAP)

Dielectric Elastomers (DEA): Soft polymer sandwiched between compliant electrodes Applied voltage → Maxwell stress → in-plane expansion, thickness reduction Actuation strain: 10–300% (very large!); force limited Applications: soft robotics, haptics, artificial muscle

Ionic EAP (IPMC): Nafion + Pt electrodes; bending on low voltage (< 5V) from ion migration Low blocking force; fast response; requires moisture Applications: underwater robots, biomedical actuators

Output

Provide: smart material type (PZT/MFC/SMA/FBG/self-healing), actuation output (δ [μm], F_block [N], ε_free [%]), sensing output (voltage sensitivity [mV/με] or wavelength shift [pm/με]), embedding method (prepreg ply, surface bond, channel), SHM system design (PZT spacing, frequency [kHz], mode, DI threshold for damage alert), healing efficiency η_heal [%] and healing agent type, operational temperature range [°C], and power/voltage requirements for actuation (V_actuation, current/power [W]).