When it comes to thermoset composite laminate materials, bond strength—particularly interlaminar bond strength—is a key factor in determining whether a material will stand the test of time or fall apart.
What is Interlaminar Bond Strength?
Interlaminar bond strength refers to the adhesive force between adjacent layers within a composite material. It’s a critical property that directly influences a material’s ability to resist delamination, which is the separation of layers under stress. Delamination is a common mode of failure in composites, leading to reduced load-carrying capacity, decreased fatigue life, and an increased risk of damage—particularly in high-performance applications where the material is subjected to extreme conditions.
Why is Interlaminar Bond Strength Important?
Maintaining high interlaminar bond strength is essential for the structural integrity of composite materials. Weak bonds can lead to layer separation under load, causing localized stress concentrations that compromise the material’s overall mechanical properties, including flexural strength and hardness. In demanding applications, such as aerospace or automotive components, low interlaminar bond strength can be catastrophic, reducing the reliability and durability of the material.
Factors Influencing Bond Strength
The bond strength of thermoset composites is influenced by a variety of factors:
Material and Resin Composition: The choice of base materials and resins significantly impacts bond strength. Different combinations can yield varying adhesion properties. For example, Atlas Fibre’s G7 and G10 grades exhibit different bond strengths due to their distinct material and resin compositions.
Processing Conditions: Proper curing is essential to fully develop the resin’s mechanical properties. Incomplete polymerization due to improper curing can result in weak bonds. Additionally, the presence of internal voids or volatiles, if not properly removed during the laminating process, can create weak spots that lead to delamination.
Environmental Conditions: The environment in which the composite is used can also affect bond strength. For instance, low temperatures can increase the brittleness of adhesives, making the composite more prone to delamination.
Testing Interlaminar Bond Strength
To ensure that thermoset composites will perform as expected, rigorous testing is essential. Several methods exist to evaluate interlaminar bond strength, with each offering insights into the material’s resistance to delamination:
ASTM D229 Test: This test measures the force required to split a composite specimen under controlled conditions. The results depend on the sample thickness, so comparisons should only be made between samples of the same thickness.
ASTM D6415 Curved Beam Flexure Test: This test indirectly measures interlaminar tensile stress by applying a bending moment to a curved beam specimen. It’s particularly useful for assessing the strength of fiber-reinforced polymer composites.
ASTM D7291 Flatwise Tensile Test: This direct method applies an out-of-plane tensile load to a flat composite specimen to measure its through-thickness tensile strength and elastic modulus.
These testing methods are crucial for determining the durability and performance of composite materials, ensuring that they can withstand the stresses of their intended applications.
Improving Bond Strength in Thermoset Composites
Achieving high interlaminar bond strength requires careful attention to material selection, processing, and environmental factors. By optimizing the resin system, eliminating voids during the laminating process, and ensuring proper curing, manufacturers can produce composites with strong interlaminar bonds that enhance durability and performance.
At Atlas Fibre, we understand the importance of bond strength in thermoset composites. Our expertise in material science and fabrication ensures that our composites meet the highest standards of durability and reliability. Whether you’re a distributor or a manufacturer relying on high-performance materials, you can trust Atlas Fibre to provide the quality and consistency you need.
If the bond won’t stick, it’s not the right pick
Interlaminar bond strength is a critical indicator of the durability and performance of thermoset composite materials. By understanding the factors that influence bond strength and employing rigorous testing methods, manufacturers can ensure that their composites will perform reliably in even the most demanding applications. With the right combination of materials, processing techniques, and testing protocols, strong interlaminar bonds can be achieved, leading to longer-lasting, higher-performing composites.