The aerospace industry and other composite material applications have long relied on visual, acoustic, ultrasonic, and radiographic inspection methods for surface size inspection. According to time, cost, product complexity and required degree of safety, non-destructive testing (NDT) technology is increasingly playing an important role.
Since many composite products (whether consumer products, sports products, automotive products or aerospace products) have broken through the limits of lightweight and performance, deep internal part inspection is essential for end-use safety, risk avoidance and business sustainability become more and more important.
The role of computed tomography
Computed tomography (CT) and related data analysis and visualization are ideal for today's complex products. In recent years, X-ray tomography, high-performance computing, software algorithms, and user interfaces have made great strides in communicating complex data. The uniqueness of CT technology is that it can penetrate most of the complex layers of metals and composite materials under a 360-degree viewing angle. Then, this raw data will be processed by the most advanced software to create millions of voxels ( A single 3D element, similar to a 2D pixel), is a precise 3D volumetric image (Figure 1).
Orientation analysis on glass fiber reinforced sheet molding compound (SMC). Each direction is coded by a certain color. The orientation data can be used to obtain the fiber orientation distribution throughout the thickness to verify the flow simulation and provide reliable data for the structure simulation.
Both the digital output and color-coded 3D images created by this software provide details of the composite's microstructure, enabling comparisons by design and by manufacturing. A series of dedicated digital tools can be used to analyze the material density, the orientation of the reinforcing fiber, and also can analyze the internal defects from design and manufacturing defects or overloads, and the strain pattern calculated through multiple scans of different states of the sample.
Today, CT scan data analysis can capture any structure and characterize it according to its design intent. Templates can be created to quickly and repeatedly analyze part features and problems automatically. This includes porosity analysis, such as: pore volume and distance from the surface; fiber and resin analysis to understand local fiber, fabric and roving orientation; and orientation histogram or orientation tensor, fiber volume fraction, porosity in the resin, etc. All data can be exported to FEA tools and used to improve material modeling and structural simulation, so that comparative models can be established for R&D purposes and component design.
Classic composite materials and analysis
The most common commercial composite materials are polymer-based compounds, including carbon fiber and glass fiber reinforced plastics (CFRP and GFRP). Ceramic-based composite materials (CMC) made of ceramic fibers have high crack resistance and thermal performance in high-temperature applications. And fracture toughness shows significant advantages.
These composite materials and even CMC can benefit from the same CT scan analysis technology to determine defects, performance and quality specification status. Depending on the material used, there are inspection solutions for each fiber structure (short, long and continuous), web pattern (unidirectional or with a specified angle for each layer) and bonding material (resin, fabric, silicon, etc.). In addition, the analysis itself can be captured and automated.
A CT scan can be used to visualize and quantify porosity and fiber orientation. Both results can be mapped to the finite element grid (bottom center) to be used locally as input to the structural analysis material model, or to verify the process simulation.