IMR Materials Testing Technical Blog
5 Aerospace Composite Materials Testing Methods
For over four decades, the aerospace industry has increasingly incorporated composite materials into aircraft production, transitioning from secondary components to critical primary structures like fuselages and wings—now comprising nearly 50% of modern aircraft such as the Boeing 787. This expanded use underscores the paramount importance of rigorous quality testing throughout the entire manufacturing process, from initial design to the final product. Such testing is crucial not only for ensuring structural integrity and compliance with stringent industry standards but also for verifying proper curing and identifying potential defects like air bubbles or improper layering that could lead to catastrophic failures. The consequences of overlooking flaws in composite materials extend beyond mere reputational damage, posing significant risks to equipment, personnel, and passenger safety, especially given the extreme reliability demands and the constant drive for increased strength and reduced weight in aerospace engineering. Material property characterization for Finite Element Analysis and basic quality checks like tensile strength and short beam shear are integral to this process, often conducted across a wide temperature spectrum from -320°F to 1800°F to reflect the demanding operational environments of aerospace materials.
AREAL WEIGHT TESTING
Areal weight (Af) calculates the mass of a part per unit area. In aerospace applications, air resistance depends on a part’s area, while gravitational force depends on mass. Therefore, determining a composite’s areal weight helps manufacturers find its material suitability for a specific application. Calculating the Af in composites can be especially challenging due to the measurement variance caused by laminated layers, which is based on both the radius of the fiber in a cross section and the fiber’s density.
BEND TESTING
A key step in material selection and component analysis, bend testing assesses composites for ductility, strength, fracture resistance, and fracture strength when bent at differing angles. This form of testing helps assess the efficacy of area welds, ensuring that proper fusion has been achieved.
COMPRESSIVE PROPERTIES VIA MULTIPLE SPECIFICATIONS
Aerospace components will often be exposed to extreme stresses and pressures. Compressive property testing analyzes the capacity of a material or structure to withstand loads that may crush, compact, or squeeze a material or part. This testing series assesses the composite’s compression and shearing properties, and it also provides compressive modulus, and compressive strength data.
Our compressive property testing complies with ASTM D6641 testing methodology for measuring combined loads on a material sample.
CONSTITUENT CONTENT BY VOLUME OR MASS (RESIN, FIBER, AND VOID)
This test provides an in-depth statistical model of a composite’s material properties along with how their intended application will affect them. This test evaluates the fabrication processes of composite materials, and it also helps us assess the quality of the finished material upon completion. Test results confirm a composite’s fatigue resistance, susceptibility to moisture penetration, and ability to withstand exposure to extreme environments, temperatures, and other conditions.
DYNAMIC MECHANICAL ANALYSIS (DMA)
Given the broad spectrum of conditional tolerances required by most aerospace components, DMA testing characterizes a material’s properties, such as stiffness, as a function of temperature, time, frequency, stress, or atmosphere.
FATIGUE TESTING
Fatigue testing uses cyclic loading to predict the life of parts under repeated loads. Fatigue tests are performed at multiple stages of fabrication, ranging from R & D to finished parts. Providing an accurate accounting or the material properties at each stage ultimately prevents catastrophic part failure and costly recalls.
FILLED-HOLE TENSION/COMPRESSION TESTING
Using a machined hole in a composite laminate, filled-hole testing simulates damage that might result from impacts or fabrication/design defects. In this process, engineers insert a fastener into the hole and expose it to a range of tension and compression factors to determine the materials durability and how it handles strain in a damaged state.
FLEXURAL PROPERTIES
Most composites fail under tensile stress before they will fail under compressive stress. Measuring the maximum amount of tensile stress a beam, rod, or other part will withstand before failure will provide the flexural strength rating of that material or part.
IN-PLANE SHEAR RESPONSE
The in-plane shear response of polymer matrix composites reinforced by high-modulus fibers can be determined by calculating the shear modulus and shear strength of the materials. Strength and stiffness values of a composite under shearing force will differ from that of strength and stiffness values under tension or compressive forces.
OPEN-HOLE TENSION/COMPRESSION
Similar to filled-hole testing, open-hole tension/compression testing involves applying specific loads on an artificially damaged test material to determine the material’s ability to carry an applied load. Open-hole testing compares toughness in composite materials and may be used to calibrate progressive damage model parameters for use in subsequent FEA and composite structures.
PEEL PROPERTIES
Peel strength usually refers to the bond between a material and a coating or adhesive. Accurately measuring peel strength helps designers assess whether a material can withstand physical, chemical, or microbial damage. Specific to aerospace manufacturing, this test typically examines the adhesive properties of sealants used in manufacturing under various stresses.
RESIN PENETRATION TESTING
Aerospace manufacturers typically seal laminate layers of composite materials with resin, and then they cure it using a catalyst such as heat and/or pressure depending on the composite design. Resin penetration tests measure resin flow levels during the curing process at varying temperatures or pressures to compare different resins and determine the optimal curing conditions.
PIN BEARING STRENGTH
This test relies on open- and close-hole tension/compression testing to determine the effectiveness and bearing strength of a pin or bolt should an unexpected hole form in the material. Static pin bearing strength tests apply stress risers to the specimen, helping designers and engineers to measure the point at which a material becomes unsafe.
SHEAR PROPERTIES
This test applies a lateral shear force to the test sample until failure. To determine a material’s shear strength, the test must assess the maximum shear stress that a material can sustain before it fails. This test is commonly used to test adhesive efficacy.
TENSILE PROPERTIES (−100°F TO 660°F)
Engineers can determine the tensile properties of a material by applying stretching forces to the test sample and monitoring its effectiveness and behavior under these forces. A wide variety of materials used in spacecraft require tensile testing before they’re cleared for deployment, including paper, elastic materials, composites, and fabrics.
This list is not complete, there are several other materials testing methods for composites. If you’d like a more comprehensive guide, click here to download our eBook “Composites Testing for the Aerospace Industry”.
If you’d like to find out more about IMR’s capabilities, email us or request a quote.
