Fiber composites

Application framework for selection and method discussions; not a customer test report.

Purpose

Fiber distribution, matrix and interfaces.

Select the section relative to fiber orientation and the inspection objective. Check matrix sensitivity and document regions and directions.

Distinguish fiber pull-out, interface gaps and polishing relief from original features. Interpret sections using the relevant inspection method.

Cutting → Mounting → Grinding and polishing → appropriate microscopy and testing.

Record sampling position, consumables, actual settings and images. Evaluate using the agreed method.

Typical inspection scenarios

Challenge: Fiber and matrix differ greatly in hardness: carbon fibers pull out and interfaces debond during grinding, and excessive cutting feed immediately causes delamination and burrs; porosity and fiber-orientation analysis require sections free of preparation artifacts.
Preparation & method: Cut with a diamond blade at low speed and low feed, applying protective tape over the cut line to suppress delamination; cold mount in epoxy to reinforce the edges. Grind with SiC papers from P400 to P2000, rotating 90° between steps and rinsing thoroughly so abrasive particles do not embed in the resin; polish with 1 μm diamond and finish with 0.05 μm colloidal silica. Examine unetched under reflected/polarized light for fiber distribution and orientation, and determine porosity by image analysis.
Reference standards: GB/T 3365 Determination of void content and resin content of carbon fiber reinforced plastics; ISO 14127 Carbon-fibre-reinforced composites — Determination of resin, fibre and void contents; ASTM E3 Standard Guide for Preparation of Metallographic Specimens

Challenge: Resin-rich zones and dry, resin-starved zones directly govern laminate strength and fatigue life, so the spatial distribution of resin, fiber and voids must be quantified; glass fibers are hard and brittle while the resin is soft and tough — fiber ends shatter and interfaces debond during grinding, and cutting heat softens and smears the resin, all creating artifacts.
Preparation & method: Cut with a diamond blade at low speed and low feed with protective tape over the cut line to suppress delamination and ample water cooling; cold mount in epoxy to consolidate. Grind with SiC papers from P400 to P2000, rotating 90° between steps and rinsing thoroughly so abrasive and glass debris do not embed in the resin; polish with 1 μm diamond and finish with 0.05 μm colloidal silica. Examine unetched under bright-field/polarized reflected light: resin-rich zones appear as homogeneous resin, resin-starved zones as dry packed fiber, and voids as black spots; use image analysis over multiple fields to determine fiber volume fraction, resin content and porosity, and rate the area fraction of resin-starved zones.
Reference standards: GB/T 2577 Test method for resin content of glass fiber reinforced plastics; ISO 1172 Textile-glass-reinforced plastics — Determination of glass fiber and mineral filler content — Calcination methods; ASTM E3 Standard Guide for Preparation of Metallographic Specimens

Scenarios are method examples, not customer test reports; confirm the process per specimen.