Explosion and impact behavior of fiber-metal laminates

Air-transportable protected vehicles such as the WS Dingo and Wiesel must have adequate protection against fragments and small arms ammunition, as well as protection against blast. Blast represents a comparatively complex load because of the overall impact of pressure waves on the structure. At the same time, blast damage depends on various factors such as the energy transfer and momentum of the charge. In addition, the distance and spatial orientation of the target to the charge can also alter the predominant damage mechanism of the material, so this situation leads to significant design challenges and potentially significant additional weight of the protective structure when conventional materials are used as armor.

Fiber-metal laminates (FMLs) have been used as structural materials in aircraft construction for several years and have demonstrated their potential for explosion protection. The BIFiMela project aims to use FML as an innovative and promising way to reduce the weight of blast-resistant structures. The main objective of the study is to investigate the basic mechanical properties and to analyze, describe and model the properties of different FML under impact and blast loading. This will be achieved by analytical and numerical methods (i.e., virtual simulations) and complemented and validated by physical tests. As a secondary objective, knowledge of the influence of individual material combinations (i.e., different fibers, matrices, and their combinations with different superstructures) and manufacturing parameters on performance under blast loading will be sought, while maintaining a very low structural weight.

Preparation of a review study

• Recent developments and use of FMLs as tailored protective materials against blast loads.
• Definition of the target application as well as product specification for the use of FMLs as materials for lightweight protected land vehicles
• Design, process and material selection

Procurement of the starting materials for manufacturing trials as well as procurement of commercially available FMLs

• Materials necessary for manufacturing tests, such as prepregs, metal sheets, etc., as well as the necessary processing materials will be procured. Commercially available FMLs are researched for comparative studies. A reference material is e.g. GLARE 5, 0.4 mm (Al 2024-T3, S2 glass with EP matrix).
• To ensure product quality, all commercially sourced reference materials will be non-destructively tested.

Performance of manufacturing tests

• Influence of the different Influence of starting materials (e.g. choice of fiber, matrix and metal material, laminate structure, possible combinations of different fiber materials, fiber/resin/metal content, etc.)
• Influence of manufacturing parameters (e.g. surface treatment, temperature / pressure / vacuum control during manufacturing, etc.)
• Characterization of manufacturing quality via non-destructive and destructive testing methods.

Determination of basic mechanical properties

• Both commercially procured and self-manufactured FMLs are subjected to determination of the basic mechanical characteristic values
• Tensile tests
• Compression tests
• Roller peel tests
• Shear tests
• Three-point bending (short beam test)
• Three-point bending or four-point bending

Impact experiments / impact tests

• Coordination of the necessary measurement equipment to characterize the experiments (high-speed recordings, strain measurements, pressure curve measurements, etc.)
• Perform experiments at the Institute's drop tower for various impact energy levels.

Shock tube experiments / blast tests

• Coordination of the necessary measurement equipment for characterization of the experiments (high-speed recordings, strain measurements, pressure course measurements, etc.)
• Design, procurement of the basic material and fabrication of all necessary parts or components to perform the blast experiments.

Characterization of the damage mechanisms

• Non-destructive and destructive testing of the FMLs will be performed. Here, a fundamental understanding of the micromechanical damage or energy dissipation mechanisms is to be developed.
• The knowledge gained will also be used to derive initial parameters and characteristics for computer simulations to support the evaluation.

Computer simulations to support the evaluation

• A computational model will be built to gain a better understanding of the damage or energy dissipation mechanisms and mechanical properties.

Fabrication and testing of optimized FMLs

• At least three optimized laminate structures for FMLs will be derived and fabricated from the knowledge gained.
• Basic mechanical properties are determined for optimized fabricated FMLs
• Impact tests and blast tests are performed
• Characterization of damage mechanisms will be investigated and analyzed.
• Further development of numerical calculation models will be revised for better prediction of expected damage. The aim is to use a suitable model to predict the blowing process and the structural damage as precisely as possible within the framework of the numerical approximations for different material combinations and laminate structures.

The BIFIMeLa project aims to understand the failure mechanisms of fiber-metal laminates subjected to impact and explosion loading. A data base will be created to identify improvement opportunities by using numerous physical test series as a basis for numerical simulations and theoretical models. In addition, the know-how of this project is focused on the production of FMLs. This represents a breakthrough for the institute in the fabrication of complex laminated structures and increases its technical competitiveness.

In a further step of the project, this knowledge will be used for the optimization of FMLs, where the selection of base materials, fiber orientation, layer thicknesses and stacking order play an essential role. In addition to optimal material modeling, it is also possible to implement new geometries or concepts that enhance the protective effect of FMLs for energy absorption or dissipation.

With the knowledge gained in this project on the use of FMLs as protective plates, an important precedent can be set for the use of composite-based armor plates, not only for official use on military vehicles, but also for passive protection of civilian vehicles as lightweight armor to enable low weight and cost.

The BIFiMeLa project is being conducted to investigate the properties of different FMLs for potential use as structural and protective materials for light protected land vehicles.

Project duration: January 2021 to March 2024

Funding volume for the University of the Bundeswehr: 240,000€.

The project is commissioned by the Wehrwissenschaftliches Institut für Werk- und Betriebsstoffe (Institute of Defense Science for Materials and Operations)