Lightweight structures which consist to a large extent of carbon fiber reinforced plastics (CFRP), often lack sufficient damping behavior. This also applies to hybrid laminates such as fiber metal laminates made of CFRP and aluminum. Since they are usually prone to vibrations due to their high stiffness and low mass, additional damping material is required to meet noise, vibration and harshness comfort demands in automotive or aviation industry. In the present study, hybrid carbon fiber elastomer metal laminates (HyCEML) are investigated which are intended to influence the damping behavior of the laminates by an elastomer interlayer between the CFRP ply and the aluminum sheets. The damping behavior is based on the principle of constrained layer damping. To characterize the damping behavior, dynamic mechanical analyses (DMA) are performed under tension on the elastomer and the CFRP, and under three point bending on the hybrid laminate. Different laminate lay-ups, with and without elastomer, and two different elastomer types are examined. The temperature and frequency dependent damping behavior is related to the bending stiffness and master curves are generated by using the time temperature superposition to analyze the damping behavior at higher frequencies. A numerical model is built up on the basis of DMA experiments on the constituents and micro mechanical studies. Subsequently, three point bending DMA experiments on hybrids are simulated and the results are compared with the experimental investigations. In addition, a parameter study on different lay-ups is done numerically. Increasing vibration damping is correlated to increasing elastomer content and decreasing elastomer modulus in the laminate. A rule of mixture is used to estimate the laminate loss factor for varying elastomer content.

The investigated hybrid carbon fiber reinforced plastics-elastomer-metal laminates (HyCEML) offer the potential of tailored structural materials with adaptable damping properties. Conventional fiber metal laminates, like glass laminate aluminum reinforced epoxy are already widely spread in the aviation industry owing to their outstanding fatigue behavior. By integrating an elastomeric interlayer, the glass fibers can be substituted by carbon fibers and damping properties of these laminates can be adjusted. The viscoelastic interlayer dissipates energy within the laminate by inducing shear strain during bending, which is commonly known as constrained layer damping. The aim of this paper is the description of the vibration and damping behavior of HyCEML over a wide temperature and frequency range by using different test methods. Dynamic mechanical analysis is used for the individual polymeric constituents and coupon specimens and modal analysis is used with different specimen geometries up to a component sized panel. In addition, analytical and numerical approaches complement the experiments and lead to a deeper understanding of the vibration and damping behavior. Owing to the high damping, already at frequencies of 5 kHz only running waves can be detected for the investigated panel size. The discussion of different test methods helps to identify material and wavelength dependent effects, but also possible adverse effects of certain methods.

. In technical applications components are often exposed to vibrations with a broad range of frequencies. To ensure structural integrity and a convenient usage for the customer, materials with good damping characteristics are desirable. Especially stiff and lightweight structures tend to be prone to vibrations. Fibre metal laminates (FML) offer great potential for lightweight design applications due to their good fatigue behavior. By using carbon fiber reinforced plastics (CFRP) as part of the laminates very good strength and stiffness to weight ratios can be obtained. To improve the damping characteristics of this hybrid material an additional layer of elastomer can be added between the CFRP and the metal, generating a fiber-metal-elastomer laminate (FMEL). In this present study the damping behavior of different layups of FMEL was examined. Two different metal sheets and two types of elastomer were used, also the layup of the constituents was variated. Vibrations were induced with a frequency range from 100 Hz to 20 kHz by mounting the laminates onto a speaker. The vibration response was measured with a piezoelectric accelerometer. Eventually the different laminate layups were compared with each other to determine the influence of the individual constituents regarding the damping characteristics. The different elastomer types and prepreg layups affected the damping of vibrations, whereas the use of different metal sheet materials showed only little influence.