Impact damage hides inside composites. This system tells you how bad, and where.

A carbon-fibre sensing system you cure into a composite laminate. Two readings, one set of strips: resistance grades how bad the damage is, capacitance picks up delamination. Built into a glass-fibre plate to catch barely visible impact damage, the kind a visual inspection misses.

89%

Plate area spanned by the sensing grid; damage resolves to 10×10 mm cells

1/4 load

Early detection: damage flagged at 23–27% of the loads that broke the plates

96

Sensing points scanned, each crossing both a resistor and a capacitor

55–68%

Damage signal retained after the load is fully removed: the system remembers

How the plate senses

Resistance

Ω · Damage

Broken fibers can't carry current, so resistance at the damaged crossing rises, and stays risen. At the 6 kN test point the hit channel climbs +41.6 Ω. The size of the resistance increase defines the damage and location.

Resistance in Ω
damage crossing
red = ΔR rising
~0 healthy
Resistance at the 6 kN point · ΔR vs pre-load baseline per crossing, Ω · Plate A · final scan · the animation in the test section shows the full loading

Two layers of carbon-fiber strips cross into an 8×12 grid, laid just below the midline of the laminate.

The grid is sealed inside the composite: no surface sensors, no bonded gauges, no added mass; fully integrated.

Every crossing is both a resistor and a capacitor. One grid, two physical signals, read independently.

Capacitance

pF · delamination

Compressed plies read high, delaminated plies read low, a severed strip reads zero: three damage signatures on one map, and the dead strips cross at the damaged area. This is the second sense, run as its own test with its own signature, so the map below reads a different condition from the resistance scan above.

Reading scale checked against known reference values: results land within +1.32% and +2.85%.

Capacitance · pF
▲ compression
▼ delamination
0.0 severed strip
~30 healthy
Capacitance after total failure, not the 6 kN test · pF · severed strips (drive 5 + sense 6) cross at the hit; the delaminated cells sit beside it · 8×12 map, Plate B

Loaded to barely visible indentation damage

A hemispherical indenter pressed the plate slowly and steadily (quasi-static) to 6 kN while all 96 crossings were scanned continuously: 235 full-grid scans, live reading every cell.

Plate A · the indenter presses to 6 kN while all 96 crossings are scanned live · red box = damage crossing
The modified ASTM rig: hemispherical indenter over the clamped plate, resistance circuit and Arduino Uno logging below
The test rig with electronics
Layer 2 during layup: twelve M46JB carbon strips taped into the grid with Kapton-protected connectors
Carbon fibre strip sensors laid up on the plate
Finished plate after testing: a faint indent mark at the centre of the orange laminate
The mark it left

The data

Plate B: stepped cyclic loading to 6 kN with resistance change per channel, the damaged channel rising far above the rest
Plate B · stepped cycles to 6 kN · The centre strip (S2 CH07) shows the severity of damage
Plate A: monotonic ramp to 6 kN with resistance change per channel, the same hit channel rising above the rest
Plate A · one continuous ramp to 6 kN · a different protocol
CT cross-section through the indented crossing showing delamination and a ply crack near the bottom face
X-ray CT scan at ~55 µm resolution · delamination + ply crack under the indent

The material is the sensor

Structural health monitoring without external sensors: damage from resistance, delamination from capacitance, located to within 12 mm in one laminate.

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