Application Note | Composite Surface Analysis
Carbon Fiber Composite Material Analysis Using 3D Profilometry
Roughness, Isotropy, Weave Size, and Texture of Bidirectional and Unidirectional Carbon Fiber Weaves
Research & Experimental Testing
NANOVEA Laboratory
Visual Design & Editorial
Andrew Shore
Introduction
It is crucial defects are minimized so composite materials are as strong as possible in reinforcement applications. As an anisotropic material, it is critical weave direction is consistent to maintain high performance predictability. Composite materials have one of the highest strength to weight ratios making it stronger than steel in some cases. It is important to limit exposed surface area in composites to minimize chemical vulnerability and thermal expansion effects. Profilometry surface inspection is critical to quality control production of composites to ensure strong performance over a long service time.
Why Non-Contact Profilometry Matters for Composite Materials
NANOVEA’s 3D Non-Contact Profilometer is unlike other surface measurement techniques such as touch probes or interferometry. Our profilometers use axial chromatism to measure nearly any surface and open staging allows for samples of any size with no preparation needed. Nano through macro measurements are obtained during surface profile measurement with zero influence from sample reflectivity or absorption. Our profilometers easily measure any material: transparent, opaque, specular, diffusive, polished, and rough with the advanced ability to measure high surface angles with no software manipulation. The Non-Contact Profilometer technique provides the ideal and user-friendly capability to maximize composite material surface studies; along with the benefits of combined 2D & 3D capability.
ℹ️ Learn more about non-contact profilometry lab services for composites.
Measurement Objective
The NANOVEA HS2000L Profilometer used in this application measured the surface of two weaves of carbon fiber composites. Surface roughness, weave length, isotropy, fractal analysis, and other surface parameters are used to characterize the composites. The area measured was randomly selected and assumed large enough that property values can be compared using NANOVEA’s powerful surface analysis software.
NANOVEA ST500 Large Area
Optical 3D Profilometer
Samples
Results and Discussion
Surface Analysis
Fig. 1: 3D views of the bidirectional (left) and unidirectional (right) carbon fiber samples.
Fig. 2: 2D views of the carbon fiber samples with height parameters.
| Parameter | Bidirectional | Unidirectional |
|---|---|---|
| Sa (µm) | 34.37 | 59.43 |
| Sq (µm) | 42.07 | 80.62 |
| Sp (µm) | 545.6 | 636.8 |
| Sv (µm) | 421.7 | 719.0 |
| Sz (µm) | 967.3 | 1356 |
| Ssk | −0.4699 | −0.36 |
| Sku | 3.229 | 4.377 |
| Spar (mm²) | 85.19 | 96.63 |
Table 1: ISO 25178 height parameters and projected area of the two weaves.
Height parameters determine how rough composite parts will be with a low fiber to matrix ratio. Our results compare different weave types and fabric to determine surface finish post-processing. Surface finish becomes critical in applications where aerodynamics may become involved.
Isotropy
Fig. 3: Isotropy charts of the carbon fiber scans showing directionality of fibers.
| Parameter | Bidirectional | Unidirectional |
|---|---|---|
| Isotropy | 59.96% | 12.83% |
| First direction | 88.24° | 91.24° |
| Second direction | 93.75° | 157.3° |
Table 2: Texture isotropy and directions.
Isotropy shows directionality of the weave to determine expected property values. Our study shows how the bidirectional composite is ~60% isotropic as expected. Meanwhile, the unidirectional composite is ~13% isotropic due to the strong single fiber path direction fiber.
Weave Analysis
Fig. 4: Distance measurement comparison of the samples.
| Parameter | Bidirectional | Unidirectional |
|---|---|---|
| Measured weave distances | 1.880 mm and 1.860 mm | 2.855 mm and 2.540 mm |
Table 3: Weave distances measured on the extracted profiles.
Weave size determines the consistency of packing and width of fibers used in the composite. Our study shows how easily we can measure weave size down to micron accuracy to ensure quality parts.
Texture Analysis
Fig. 5a: Bidirectional composite: texture map and fractal analysis.
Fig. 5b: Unidirectional composite: texture map and fractal analysis.
| Parameter | Bidirectional | Unidirectional |
|---|---|---|
| Dominant wavelength | 0.004247 mm | 0.004247 mm |
| Amplitude | 167.6 µm | 87.90 µm |
| Fractal dimension | 2.519 | 2.519 |
Table 4: Texture and fractal analysis of the weave types.
Texture analysis of the dominant wavelength suggests strand size for both composites are 4.27 microns thick. Fractal dimension analysis of the fiber surface determines smoothness to find how easily fibers will set in a matrix. The fractal dimension of the unidirectional fiber is higher than the bidirectional fiber which may affect the processing of composites.
Conclusion
In this application, we have shown the NANOVEA HS2000L Non-Contact Profilometer precisely characterizes the fibrous surface of composite materials. We distinguished differences between weave types of carbon fiber with height parameters, isotropy, texture analysis, and distance measurements along with much more.
Our profilometer surface measurements precisely and quickly mitigate composite damage which decreases defects in parts, maximizing composite material capability. NANOVEA’s 3D profilometer speed ranges from <1 mm/s to 500 mm/s for suitability in research applications to the needs of high-speed inspection. The NANOVEA profilometer is the solution to any composite measurement need.
Frequently Asked Questions About Composite Surface Analysis
Why inspect the surface of composite materials?
Defects must be minimized so composites are as strong as possible in reinforcement applications. As anisotropic materials, composites need a consistent weave direction for predictable performance, and limiting exposed surface area reduces chemical vulnerability and thermal expansion effects.
What does isotropy show on a carbon fiber weave?
Isotropy shows the directionality of the weave, which determines expected property values. The bidirectional composite was ~60% isotropic (59.96%), while the unidirectional composite was ~13% isotropic (12.83%) due to its strong single fiber direction.
How rough were the two carbon fiber weaves?
The bidirectional weave measured Sa 34.37 µm and Sz 967.3 µm, the unidirectional weave Sa 59.43 µm and Sz 1356 µm. Height parameters indicate how rough composite parts will be with a low fiber to matrix ratio, which matters where aerodynamics are involved.
How is weave size measured?
Distances between weave features are measured on profiles extracted from the 3D scan, down to micron accuracy: about 1.88 and 1.86 mm on the bidirectional weave and 2.855 and 2.540 mm on the unidirectional weave.
What do texture and fractal analysis add?
The dominant wavelength indicates strand size, and the fractal dimension of the fiber surface describes its smoothness, which affects how easily fibers set in a matrix.
Which NANOVEA instrument was used for composite analysis?
The NANOVEA HS2000L non-contact profilometer, with scan speeds from below 1 mm/s to 500 mm/s. Its current large-area counterpart is the NANOVEA ST500.
