Delamination in composite material

Delamination Decoded: How New Tech Protects Your Composites

Nico Varela in Tech & Innovation September 2025 • 5 min read.

"Explore the groundbreaking use of finite element analysis and LS-DYNA software in enhancing the durability and lifespan of composite materials, ensuring safer, more reliable structures for the future."

Delamination, the separation of layers in composite materials under stress, poses a significant threat to the integrity and lifespan of various structures. Imagine a bridge, an aircraft wing, or even a high-performance sports car – all relying on the uncompromised strength of their composite components. When delamination occurs, it severely weakens these structures, potentially leading to catastrophic failures. The challenge lies in predicting and preventing this insidious form of damage.

Traditional methods of assessing structural integrity often fall short when dealing with composites, as they struggle to capture the complex interactions at the layer interfaces. This is where cohesive interface models and advanced finite element techniques step in, offering a more detailed and accurate way to simulate and understand these interactions. These methods allow engineers and scientists to peek inside the material, observing how stresses distribute and how damage initiates and grows.

This article explores the latest advancements in using LS-DYNA, a powerful simulation software, along with innovative cohesive elements, to analyze and combat delamination. We'll delve into the formulations and implementations that promise to stabilize simulations and overcome the numerical instabilities that have long plagued this field. By understanding these cutting-edge techniques, we can pave the way for safer, more durable composite structures that underpin our modern world.

The Science of Separation: Understanding Delamination Growth

Delamination happens when laminated composite materials are under stress, particularly from loads hitting them sideways. This can seriously cut down how much weight a structure can handle. To tackle this, engineers use 'cohesive elements'—think of them as tiny, super-smart connectors in computer models. These elements help predict and figure out how damage behaves between the layers of different materials. There are many types of models, like ones that act perfectly plastic, soften in a straight line, soften gradually, or even soften backward.

Some models also factor in how quickly the stress is applied, known as 'rate-dependent models.' One of the earliest was by Glennie, who made the traction in the cohesive zone depend on how fast the crack opens. Xu and others improved this by adding a damage law that decreases linearly. Each model uses a 'viscosity parameter' to change how much the rate affects things. Kubair and his team thoroughly looked at these models and figured out how to solve problems like steady crack growth and spontaneous propagation.

Here are some key advantages of using cohesive elements:

They can predict when and where delamination starts without needing to know the crack's location beforehand.
They can also forecast how the crack will spread.
However, simulating damage this way has two main issues: it can be numerically unstable, and it's hard to get accurate results.
The instability often happens right after the stress peaks, especially in materials with high strength and stiffness. This becomes more noticeable with coarser meshes, which are less precise.

To fix this, engineers traditionally use direct methods, like making the mesh finer (but this costs more computing power) or lowering the interface strength and stiffness (which can skew the loading history).

The Adaptive Advantage: Stabilizing Simulations for Accuracy

To combat these issues, a new approach called the adaptive cohesive model (ACM) is emerging, designed for stable and accurate simulations of delamination in composites under transverse loads. This model introduces a 'pre-softening zone' ahead of the existing softening zone, where the initial stiffness and interface strengths are gradually reduced as effective relative displacements increase. This helps to smooth out the transition and avoid abrupt changes that can lead to instability. The critical energy release rate, which determines the final displacement for complete decohesion, remains constant, ensuring the material's fundamental properties are respected. The adaptive cohesive model holds significant promise for advancing the field and ensuring more reliable predictions.

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Everything You Need To Know

What is delamination in composite materials, and how do engineers use cohesive elements to address it?

Delamination in composite materials happens when the layers separate due to stresses, such as transverse loads. This reduces the structure's load-bearing capacity. Engineers address this by using cohesive elements in computer models. Cohesive elements help predict damage behavior between material layers. Different models exist, including perfectly plastic, linearly softening, gradually softening, and backward softening models. Some models also consider how quickly stress is applied using rate-dependent models, like Glennie's model, which makes the traction in the cohesive zone dependent on how fast the crack opens.

What are the key advantages and limitations of using cohesive elements in simulating damage in composite materials?

The key advantages of cohesive elements are their ability to predict when and where delamination starts without prior knowledge of the crack's location and forecast crack spread. However, simulating damage this way can be numerically unstable and hard to get accurate results, especially after the stress peaks, mainly in stiff materials. This issue becomes more apparent with coarser meshes. Engineers have traditionally used direct methods, like refining the mesh or reducing the interface strength and stiffness to fix this. Reducing the interface strength and stiffness can skew the loading history.

How does the adaptive cohesive model (ACM) work to stabilize simulations and improve accuracy in predicting delamination?

The adaptive cohesive model (ACM) introduces a pre-softening zone ahead of the existing softening zone, gradually reducing initial stiffness and interface strengths as effective relative displacements increase. This smoothes the transition and avoids abrupt changes that cause instability. The critical energy release rate remains constant, ensuring the material's fundamental properties are respected. The adaptive cohesive model (ACM) aims to create stable and accurate simulations of delamination in composites under transverse loads.

What role does LS-DYNA play in analyzing and preventing delamination in composite materials, and why is it important?

LS-DYNA is a powerful simulation software used with cohesive elements to analyze and combat delamination in composite materials. It helps in understanding how stresses distribute and how damage initiates and grows within the material. Traditional methods often fall short in capturing the complex interactions at the layer interfaces in composites. LS-DYNA, along with cohesive elements, provides a detailed and accurate way to simulate these interactions. This involves formulations and implementations that stabilize simulations and overcome numerical instabilities. These methods allow engineers to observe how stresses distribute and how damage initiates and grows.

Why does numerical instability occur in delamination simulations, and what are the traditional and emerging methods to address it?

The numerical instability often happens right after the stress peaks, especially in materials with high strength and stiffness. This becomes more noticeable with coarser meshes, which are less precise. To fix this, engineers traditionally use direct methods, like making the mesh finer (but this costs more computing power) or lowering the interface strength and stiffness (which can skew the loading history). The Adaptive Cohesive Model is emerging, designed for stable and accurate simulations of delamination in composites under transverse loads. This model introduces a 'pre-softening zone' ahead of the existing softening zone, where the initial stiffness and interface strengths are gradually reduced as effective relative displacements increase. This helps to smooth out the transition and avoid abrupt changes that can lead to instability.