Understand Material Properties Better Thanks To Multiphysical Simulation

2023 Author : Hannah Pearcy | [email protected] . Last modified: 2023-06-01 01:49

A composite is a heterogeneous material that consists of at least two integrated components to improve structural performance. Multi-physics simulation enables combined mechanical, thermal and electromagnetic analyzes of composite materials . Depending on the application, interactions of a composite with, for example, currents or acoustics are also possible. Decisive for the efficiency and feasibility of such analyzes is the numerical implementation, which must be tailored to the different size scales and length ratios of composite materials.

Seminar tip

The seminar on lightweight materials in construction teaches methods, design principles and construction methods for lightweight structures. The participants get an overview of different lightweight materials, learn about criteria for the selection of materials and learn about the advantages, disadvantages and risks of the different materials.

Macroscopic properties from microscopic unit cells

Due to the characteristic structure of the laminates from fiber and matrix materials, the homogenized macroscopic properties depend on the microscopic properties and the respective volume fractions. Micromechanical analyzes are used to model individual layers or representative unit cells made of fiber and matrix, with the aim of determining the macroscopic properties and using them for the actual modeling .

Two approaches for the simulation of layered composites

The multi-physics simulation of entire components that consist of many thin layers is only highly efficient if the layer structures do not have to be explicitly resolved and networked ; because this would lead to extremely fine and computationally complex network structures. In practice, more resource-efficient approaches are needed:

• The equivalent single layer approach is one such approach. It is based on first-order shear deformation theory, a class of equivalent single-layer theory in which all layers are combined into an equivalent material. The results include complete 3D stress and strain distributions so that, for example, stress fluctuations within each layer can be examined.
• The Layerwise Approach is an approach based on the layered theory for a more precise analysis of composite laminates. Boundary conditions can be placed on individual layers as well as on individual interfaces between the layers. The materials in the individual layers can be non-linear. The results include complete 3D stress and strain distributions so that, for example, interlaminar stresses can be calculated and stress fluctuations within each layer can be examined.

Example of use: Analysis of a wind turbine blade

Wind turbines were the most important alternative power source in Germany in 2019, so the design, analysis and manufacture of wind turbines are extremely important for the energy industry. The rotor blades are critical components of a wind turbine ; When generating electrical energy by rotation, they have to withstand various types of loads such as wind, gravitational and centrifugal loads, while being as efficient and quiet as possible. The sheer size of a rotor blade requires light and strong materials, and composite materials are well suited for this.

This example shows how to analyze a rotor blade composed of a mixture of carbon epoxy, glass vinyl ester and PVC foam . The rotor blade is constructed as a sandwich structure, in which the PVC foam core is embedded between carbon epoxy and glass vinyl ester.

• First, a tension analysis of the blade is performed, in which it is exposed to a combination of gravitational and centrifugal loads that correspond to the real operating conditions. The deformation of the blade tip, the maximum stress values and the layer-resolved stress distribution at a certain point on the blade are calculated for different load cases .
• A prestressed natural frequency analysis is then carried out for a typical range of operating speeds. In this way you get the variation of the natural frequencies with the speed , which is very important information for the safe operation of wind turbines. This variation can be clearly represented in a Campbell diagram (Figure 2).

Seminar tip

The systematic material selection seminar teaches the relationship between material production, material structure and the resulting material properties. The aim is to present a holistic representation of the material selection process, starting from the creation of a requirement profile, the pre-selection up to the fine selection and risk assessment.

Multi-physics extends the application possibilities

Composite parts are often designed according to purely structural mechanical requirements, but there are some cases where other physical phenomena have to be taken into account. In such cases, multiphysics links between mechanics and these other phenomena must be established and calculated. We distinguish two fundamentally different types of interaction between the mechanics in the composite and these other phenomena:

• Interactions within the composite layers and
• those that occur on the outer composite edges.

The physical processes that take place within a laminate include thermal and electrical interactions . It is important to consider the simultaneous effect of these effects when designing the laminate. Both of the layer theories mentioned can be coupled with the thermal and electrical modeling of composite materials.

Examples of coupled processes

A typical application example of such coupled processes is Joule heating and the resulting thermal expansion of a composite material. The latter can also be caused by other heat sources, such as laser radiation

Another example of multiphysical couplings is the analysis of piezoelectric layers embedded in composite laminates

• In other physical processes, the laminate acts as a boundary to a 3D area in which crucial processes occur. For example, it is possible to couple the composite laminate with the flow of a surrounding fluid and thus to calculate the force transmission between the laminate and the flow around a fluid. This coupling would be required, for example, to take the aerodynamic forces into account in the wind turbine blade.
• Another coupling is obvious for a piezo element: The sound propagation due to the piezoelectric vibration of a sound transducer , or vice versa, the vibration of a sound sensor excited by acoustic waves can be simulated by coupling layered composites and acoustic sound waves.

* Dr. Phillip Oberdorfer and Maria Iuga Römer, Comsol Multiphysics GmbH