Identifying and Quantifying Maritime-Induced Surface Damage on Cessna 172 Seaplane Brake Calipers via SEM and Image Analysis

Abstract

Seaplane brake components are repeatedly exposed to salt-laden moisture, wet–dry cycles, and surface deposits, while also enduring landing impacts, mechanical vibrations, and braking heat. Despite routine periodic maintenance, these combined stresses still trigger micro-scale damage that escapes visual inspection. This study identifies and quantifies surface damage on a dual-piston Cast Aluminum Alloy A356-T6 brake caliper from a Cessna 172 seaplane using scanning electron microscopy (SEM) and digital image analysis. The specimen is a Parker Cleveland caliper (P/N 091-04400, system 30-75, 8.14 × 7.85 × 3.61 inches, 1.95 lbs), examined specifically on the flat surface between the lower piston bore edge and lower guide pin. Secondary electron images at 300×, 500×, 800×, and 1000× (10 kV) were processed through background correction, adaptive segmentation, object measurement, elongated-feature detection, and fractal analysis, alongside operational records from January 2022–July 2026 (3,891.9 flight hours, 3,442 landings, 1,224 water landings). Results show that the segmented damaged surface area fraction within the SEM field of view ranges from 35.60–39.70% (cross-scale mean: 36.78 ± 1.95%). Pit density reaches 4.01×10⁴–1.33×10⁵ pits/mm², while the mean equivalent diameter decreases from 1.08 µm (300×) to 0.41 µm (1000×). Based on segmented area profiles, object shapes, and fractal contours, the damage morphology matches pitting, deposit-related attack, exfoliation-like damage, and microcracking. This study provides a quantitative early-detection method to evaluate component serviceability and optimize periodic maintenance, which future research can complement with SEM-EDX elemental verification and mass-loss or electrochemical corrosion-rate testing.