Vibration damping devices with liquid crystal elastomers

Abstract

Embodiments of the claimed invention are directed to vibration damping devices that comprise at least one LCE layer and their use in reducing vibrations of a substrate by attaching the vibration damping device to the substrate.

Description

Attorney Docket No.: 171320.00019VIBRATION DAMPING DEVICES WITH LIQUID CRYSTAL ELASTOMERSCRQSS-REFERENCE(S) TO RELATED APPLICATIONS

[0001] This patent application claims priority from, and incorporates by reference, the entire disclosure of U.S. Provisional Patent Application No. 63 / 716.239 filed November 4, 2024.TECHNICAL FIELD

[0002] The present disclosure relates generally to vibration damping devices and specifically, vibration damping devices containing liquid crystal elastomers (LCEs) to reduce structure- borne vibrations.BACKGROUND

[0003] This section provides background information to facilitate a better understanding of the various aspects of the disclosure. It should be understood that the statements in this section of this document are to be read in this light, and not as admissions of prior art.

[0004] Vibration control is a critical challenge in engineering disciplines, particularly in aerospace, automotive, and military applications, where excessive oscillations can lead to fatigue failure, noise, and reduced operational efficiency of structures used in these applications. All structures are prone to vibrations which may cause catastrophic failure if those vibrations are not suppressed.

[0005] Various methods exist to mitigate structural vibrations and acoustic noise caused by those vibrations, i.e., vibration damping. One approach is active vibration isolation, which involves installing complex electronic systems to monitor structural vibrations and generate counteracting forces using actuators. However, this method requires continuous power supply, entails high installation and maintenance costs and introduces potential failure mechanisms of the vibration damping solution. A more practical and widely used approach is passive vibration isolation, which relies on damping materials rather than external energy sources. Passive vibration isolation devices usually involve attaching a device to the structure that resists vibrational motion. The attached devices could be frequency specific (e.g. tuned mass damper) or perform at a broad frequency range (e.g. constrained layer damper). Although tuned mass dampers (TMDs) provide enhanced damping performance, their effectiveness is only within a narrow frequency range for vibrations in the base structure.147469434v l 171320 / 00019Attorney Docket No.: 171320.00019TMDs are applied to applications with excitation from a single vibratory source (i.e. motor). TMDs are generally not effective for external excitation which cause excitations over a broad range of frequencies and modes. For these applications a constrained layer damper (CLD) is more appropriate to use for reducing structural vibration.

[0006] CLD is a form of vibration damping that is more effective than unconstrained layer damping at reducing noise and vibration in thin-walled structures. In unconstrained layer damping, sheets of high damping material are attached to a base structure. As the base structure vibrates, the damping material bends and stretches, dissipating some of the vibration energy.

[0007] CLDs contain a viscoelastic material sandwiched between a base structure requiring vibration damping, and a constraining layer. When the base structure vibrates, the viscoelastic material bends with the structure but also interacts with the constraining layer through shear forces allowing it to dissipate vibrational energy. The viscoelastic layer has a lower modulus than both the base material and the constraining layer, creating shear deformation and internal damping, which converts mechanical energy' into heat. The viscoelastic material generally resists bending in the base structure even without a constrained layer. The constraining layer provides additional support for the viscoelastic material to resist more of the bending and increases effectiveness of the shear deformation. The use of a constraining layer can provide the same performance as a single unconstrained layer at a fraction of the thickness. The reduction of thickness and, consequently, weight allows CLD use in applications with restrictive size, weight, and power such as aerospace.

[0008] While both CLD and unconstrained layer damping use a viscoelastic material to extract energy from a vibrating structure, the main difference is how the energy is dissipated: in CLD, the viscoelastic material shears, while in unconstrained layer damping, the viscoelastic material extends.

[0009] CLDs are utilized in various applications, from aircraft fuselage to airducts, to reduce structure-borne noise. Viscoelastic properties and a constraining layer’s modulus are primarily responsible for the composite performance to reduce structure vibrations. Shear modulus and damping of a viscoelastic material are two key parameters. Due to the inherent properties of liquid cry stal elastomers (LCEs) such as anisotropy, rate dependency, and high247469434v l 171320 / 00019Attorney Docket No.: 171320.00019 damping, LCEs are an ideal candidate to replace traditional viscoelastic material, such as rubbers, in vibration damping devices.

[0010] LCEs are elastomers, i.e., elastic polymers with liquid crystal mesogens embedded in the backbone of the elastomer as a main-chain or side-chain. Liquid crystal (LC) mesogens are rigid, rod-like or disc-like, molecules with an ability to exhibit ordered molecular alignment like a crystal while still behaving as a liquid. The combination of rigid mesogens and flexible backbone elastomer gives LCEs its unique viscoelastic non-Newtoman behavior not seen in other ty pe of elastomers or polymers. When LCEs are exposed to heat, vibration, or light, the disruption of mesogen alignment transitions the liquid crystal order from nematic or smectic ordered structure to isotropic disordered structure. This change in order happens as the LCE goes from a low entropy nematic state (more ordered) to high entropy isotropic state (low ordered) by absorbing vibrational energy. Contrary to other polymers or elastomers, LCE converts vibrational energy into a phase transition instead of thermal energy;

[0011] LCEs are composed of many small domains of LC mesogens. Within each domain, the mesogens are aligned in a single direction, forming a nematic state. In polydomain LCEs, these domains are randomly oriented, giving the material an opaque appearance. In monodomain LCEs, the domains are uniformly aligned, resulting in a highly transparent material. While both poly domain and monodomain LCEs are anisotropic at the domain level due to the nematic alignment of the mesogens, the higher degree of domain order in monodomain LCEs imparts additional unique directional properties.

[0012] LCEs also exhibit a broad relaxation spectrum, where viscoelastic elements with different relaxation times contribute to their mechanical energy dissipation due to vibration. Their inherent rate-dependent (non-Newtonian) response and ability7to dissipate mechanical energy effectively makes them a promising candidate to damp structural vibrations. The energy dissipation in poly domain nematic LCEs arises from the reorientation of mesogenic domains under mechanical stress and the viscoelastic relaxation of the polymer network, both of which are strongly dependent on temperature and frequency. Specifically, poly domain nematic LCEs exhibit high energy dissipation under oscillating loading, particularly in the nematic regime, where reversible domain reorientation allows efficient energy absorption. Consequently, LCEs exhibit an exceptionally high loss factor over a broad range of347469434v l 171320 / 00019Attorney Docket No.: 171320.00019 temperatures and frequencies, making them highly effective for dynamic energy dissipation applications.SUMMARY OF THE INVENTION

[0013] An embodiment of the claimed invention is directed to a vibration damping device with a LCE layer.

[0014] A further embodiment of the claimed invention relates to a method of reducing vibrations of a substrate by providing a substrate that is subject to a vibration; and attaching a vibration damping device to the substrate.BRIEF DESCRIPTION OF THE DRAWINGS

[0015] FIG. 1 shows a schematic of a LCE layer attached to a constraining layer with an adhesive on the opposite side of the LCE layer for attachment to a substrate or structure requiring vibration damping;

[0016] FIG. 2 shows a schematic of multiple LCE layers combined with multiple constraining layers in an alternating arrangement;

[0017] FIG. 3 shows master curves of storage shear modulus and loss factor for four representative LCEs as a function of equivalent frequency; and

[0018] FIG. 4 shows the comparison of composite loss factor for the vibration damping device with LCE.DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

[0019] An embodiment of the claimed invention is directed to a vibration damping device comprising a LCE.

[0020] In another embodiment, the vibration damping device comprises at least one LCE layer, which acts as a viscoelastic material, and is attached to a constraining layer (FIG. 1). In an embodiment, the LCE layer is attached along the length of one side of the constraining layer.447469434v l 171320 / 00019Attorney Docket No.: 171320.00019

[0021] In certain embodiments, the vibration damping device comprises multiple layers of LCE. and multiple constraining layers. In some embodiments, the LCE layer and the constraining layer are arranged in an alternating manner, where an LCE layer is flanked by constraining layers, and a constraining layer is flanked by LCE layers (FIG. 2).

[0022] In certain embodiments, the LCE layer has a thickness ranging from 0. 1 mm to 5 mm.

[0023] In certain embodiments, the constraining layer has a thickness ranging from 0. 1 mm to 5 mm.

[0024] In an embodiment, an adhesive layer is used to attach the LCE layer to the constraining layer.

[0025] In some embodiments, an adhesive is used to attach the LCE layer to a substrate. As used herein, the term substrate refers to a structure or a surface of a structure to which the vibration damping device is attached. In certain embodiments, the vibration damping device of the claimed invention comprises at least one LCE layer that is attached on its one side to a constraining layer, and is attached on the opposite side to a substrate, where the attachment between the substrate and the LCE layer is mediated by an adhesive.

[0026] In certain embodiments, the LCE layer is sandwiched between two stiffer structures.

[0027] In certain embodiments, the thickness of the vibration damping device is less than the thickness of the substrate to which the vibration damping device is attached.

[0028] In an embodiment of the vibration damping device, the LCE layer is attached to a constraining layer. An adhesive is included on a side of the LCE layer that is opposite from the side of the LCE layer that is attached to the constraining layer. The adhesive allows the LCE layer to attach to a substrate. In certain embodiments the adhesive that is used to attach the LCE layer to a substrate is a pressure-sensitive adhesive (FIG. 1).

[0029] In certain embodiments, the LCE is applied to the constraining layer as a coating and cured, which causes the LCE to attach to the constraining layer without the need for an adhesive. In these embodiments, the LCE layer is directly bonded to the constraining without the requirement for an adhesive.547469434v l 171320 / 00019Attorney Docket No.: 171320.00019

[0030] In certain embodiments, the constraining layer comprises a material with a high modulus, i.e., a material with high stiffness that resists deformation and bending. High modulus materials used in embodiments of the invention comprise metal, plastic, carbon fiber, glass fiber and / or fiberglass. Examples of metals that are used in embodiments of the invention include, but are not limited to aluminum and steel. Examples of plastics that are used in embodiments of the invention include, but are not limited to thermoplastics such as poly ether ether ketone (PEEK) and / or poly ether ketone (PEK). Examples of high modulus materials that are used in embodiments of the invention include, but are not limited to carbon fiber, glass fiber and / or fiberglass.

[0031] In certain embodiments, the modulus of the constraining layer ranges from 3 GPa - 250 GPa.

[0032] Embodiments of the invention are directed to vibration damping devices comprising LCEs, which have superior vibration damping properties for the reduction of noise, vibration, and harshness (NVH) across a wide range of temperatures and frequencies.

[0033] In certain embodiments, the LCEs are selected from monodomain or poly domain crosslinked LCEs or LCE resins (regular and high temperature) cured via heat or UV.

[0034] In certain embodiments, mesogens within the LCE layer can be aligned along a direction producing anisotropic performance of the vibration damping device leading to a preferred direction of vibration damping while allowing vibration passthrough perpendicular to that direction for a base structure.

[0035] In certain embodiments, noise and vibration properties that are superior to prior art vibration damping devices can be accomplished with the use of a LCE layer of lesser thickness than prior art damper layers. In some embodiments, the thickness of the LCE layer ranges from 0.1 to 5 mm.

[0036] In certain embodiments, the vibration damping device of the claimed invention demonstrates superior damping properties over a wide temperature and frequency range compared to other competing materials. The LCE is highly tunable, allowing its chemistry to be adjusted for various applications requiring vibration damping depending on temperature and frequency requirements. The high damping of LCE makes it particularly valuable for vibration reduction applications. The LCE effectively absorbs and dissipate energy while647469434v l 171320 / 00019Attorney Docket No.: 171320.00019 conforming to surfaces, enhancing its vibration-damping capabilities without adding excessive weight.

[0037] The storage shear modulus (G' ) and loss factor (tan 8 ) of LCE as a function of equivalent frequency are shown in FIG. 3. The storage modulus of all LCEs increase with frequency, demonstrating the characteristic rate-dependent stiffening. At frequencies beyond 105Hz (100 kHz), the storage modulus of all formulations converges to approximately 100 MPa. At this range of frequencies, the mechanical response of the LCE approaches that of its glassy state, as the material has less time to relax and behaves more rigidly. This suggests that while the network architecture influences the modulus at lower frequencies, the short-term relaxation mechanisms become more comparable at high frequencies.

[0038] The modal loss factor of the LCE demonstrates a frequency -dependent shift across the glass transition temperature (Tg). Below Tg, higher-frequency modes exhibit greater loss factors, whereas above Tg, energy dissipation is more pronounced at lower frequencies. This transition arises from the temperature-dependent shear response of the LCE. In the glassy state, i.e., temperature below Tg, the LCE maintains a high shear modulus, enabling efficient energy dissipation at higher frequencies. Above Tg, the LCE softens, increasing its viscoelastic relaxation time and enhancing energy dissipation at lower frequencies. Consequently, the damping behavior shifts across Tg, with peak loss occurring near Tg, where molecular mobility is maximized. These findings indicate the effectiveness of LCE in providing consistent damping behavior across multiple vibrational modes and a range of operating temperatures.

[0039] In certain embodiments, the glass transition temperature of the LCE layer used in the vibration damping devices ranges from -15 to 30°C.

[0040] The composite loss factor of vibration damping devices comprising different LCEs at 200 Hz is shown in FIG. 4. The composite loss factor serves as a key indicator of a vibration damping device’s ability to dissipate vibrational energy by converting mechanical resonance into heat, thereby reducing structural vibrations and structure-bome noise.

[0041] In certain embodiments, the vibration of the substrate is dissipated over a range of temperatures and range of frequencies. The range of temperatures is -10°C to 60°C. The range of frequencies is 30 Hz - 20 kHz.747469434v l 171320 / 00019Attorney Docket No.: 171320.00019

[0042] In certain embodiments, the maximum composite loss factor of the vibration damping devices of the claimed invention ranges from 0.4 to 0.9.

[0043] For reference, the bare steel beam exhibits a loss factor of approximately 0.001 at 200 Hz, indicating negligible damping. The vibration damping device using LCE3 exhibited the highest damping efficiency, maintaining a composite loss factor exceeding 0. 1 across a broad temperature range of -1°C to 48°C, with a peak value of 0.69 at 21°C. This indicates exceptional energy dissipation near room temperature, making it well-suited for applications requiring superior damping in ty pical operating environments.

[0044] The vibration damping device using LCE4 demonstrates a slightly lower peak loss factor of 0.63 at 27°C, with a shifted temperature range of elevated damping (7°C to 54°C). This shift suggests a degree of tunability of the vibration damping device utilizing LCEs for application with varying thermal environments, indicating the potential for optimizing LCEs to achieve peak performance at specific temperature ranges.

[0045] The vibration damping device using LCE1 still provides effective damping, exhibits the lowest peak loss factor of 0.4 at 22°C. However, it maintains an elevated loss factor across a similar temperature range as the vibration damping device with LCE4. indicating consistent performance in applications requiring moderate damping characteristics.

[0046] In certain embodiments, the composite loss factor of the vibration damping devices of the claimed invention is greater than about 0.2 over a temperature range of 5°C to 40 °C.

[0047] The damping results demonstrate that the vibration damping device utilizing LCE layer offers substantial improvements over bare metal structures, achieving loss factors up to two orders of magnitude higher than untreated metal, and the ability to tune its vibration damping performance by changing the LCE layer.

[0048] Based on the results presented herein, it is clear that use of vibration damping devices comprising LCEs exhibit exceptional damping performance across a broad frequency and temperature range, positioning them as strong candidates for advanced vibration control applications. The shear properties of the LCEs and their damping effectiveness demonstrates their viability as high-performance alternatives to conventional vibration damping devices. Further optimization is available by adjusting the high modulus constraining layer to847469434v l 171320 / 00019Attorney Docket No.: 171320.00019 accommodate other application specific requirements for a vibration damping device such as weight and space limitations.

[0049] The ability of the LCEs to sustain high damping performance over wide frequency and temperature ranges underscores their potential for use in automotive, aerospace, and industrial applications where effective vibration mitigation is essential.WORKING EXAMPLES

[0050] LCEs with four different formulations were synthesized in the nematic state through a controlled chemical reaction to achieve the desired material properties.

[0051] The LCE is made using a reactive mesogen (2-methyl-l,4-phenylene bis(4-(3- (acryloyloxy)propoxy)benzoate); RM257), spacer (2,2'-(ethylenedioxy)diethanethiol;EDDET or ethane- 1,2-dithiol or similar dithiols), stabilizer (butylated hydroxytoluene; BHT), 1-5 wt% toluene or similar solvents, and catalyst (dipropylamine; DPA) using a specific ratio to make an LCE oligomer with specific length. The LCEs have a viscosity of 50,000 millipascal seconds (mPa.s) or centipoise (cP) at 100°C or 200,000 mPas or cP at 50°C. The LCE is layered or coated on a constraining layer at temperatures between 50-80°C at a thickness between 0. 1 -5 mm. During the coating process, the LCE is cured wi th UV or heat while it is being coated or applied on the constraining layer. The curing time is between 3-30 seconds.

[0052] For shear testing, two rectangular specimens (10 mm x 10 mm) were prepared for each LCE.

[0053] The vibration damping device was tested using bare beams. The beams were made of oil-hardened, precision-ground cold-rolled steel with dimensions of 0.79 mm x 12.7 mm x 292. 1 mm. The LCE is attached to a constraining layer. During fabrication, the LCE is applied and cured directly on the constraining layer, ensuring a strong bond between the two layers without the need for additional adhesives. In the beam testing, the constraining layer has the same width and length as the LCE, measuring 12.7 mm x 254 mm, with a thickness of 0.165 mm (6.5 mil). The thickness of the LCE layers range from 1.97 mm to 2.57 mm. To secure the assembled vibration damping device (i.e., LCE layer plus the constraining layer) to the bare beam, the LCE surface opposite the constraining layer was coated with a pressure947469434v l 171320 / 00019Attorney Docket No.: 171320.00019 sensitive adhesive, having a thickness of 0.06 mm (2.3 mil), and pressed onto the base beam at room temperature.

[0054] Anon-contacting magnetic exciter, positioned near the root end applied random white noise excitation, and the beam’s response was measured using a piezoelectric crystal sensor located in the same region. A frequency range of 20 Hz to 5000 Hz was monitored. To examine the temperature dependence of the material properties, the test fixture was placed inside an environmental chamber, where measurements were performed over a temperature range of 17.8°C to 93.3°C. To ensure the specimen reached full thermal equilibrium after a temperature change, the test fixture was maintained in the environmental chamber at the testing temperature for a minimum of 30 minutes before conducting measurements.

[0055] Although various embodiments of the present disclosure have been illustrated in the accompanying Drawings and described in the foregoing Detailed Description, it will be understood that the present disclosure is not limited to the embodiments disclosed herein, but is capable of numerous rearrangements, modifications, and substitutions without departing from the spirit of the disclosure as set forth herein.

[0056] The term “substantially” is defined as largely but not necessarily wholly what is specified, as understood by a person of ordinary skill in the art. In any disclosed embodiment, the terms “substantially”, “approximately”, “generally”, and “about” may be substituted with “within [a percentage] of’ what is specified, where the percentage includes 0.1, 1, 5, and 10 percent.

[0057] The foregoing outlines features of several embodiments so that those skilled in the art may better understand the aspects of the disclosure. Those skilled in the art should appreciate that they may readily use the disclosure as a basis for designing or modifying other processes and structures for earn ing out the same purposes and / or achieving the same advantages of the embodiments introduced herein. Those skilled in the art should also realize that such equivalent constructions do not depart from the spirit and scope of the disclosure, and that they may make various changes, substitutions, and alterations herein without departing from the spirit and scope of the disclosure. The scope of the invention should be determined only by the language of the claims that follow. The term “comprising” within the claims is intended to mean “including at least” such that the recited listing of elements in a claim are1047469434v l 171320 / 00019Attorney Docket No.: 171320.00019 an open group. The terms “a”, “an”, and other singular terms are intended to include the plural forms thereof unless specifically excluded.

[0058] Conditional language used herein, such as, among others, “can”, “might”, “may”, “e.g.”, and the like, unless specifically stated otherwise, or otherwise understood within the context as used, is generally intended to convey that certain embodiments include, while other embodiments do not include, certain features, elements and / or states. Thus, such conditional language is not generally intended to imply that features, elements and / or states are in any way required for one or more embodiments or that one or more embodiments necessarily include logic for deciding, with or without author input or prompting, whether these features, elements and / or states are included or are to be performed in any particular embodiment.

[0059] While the above detailed description has shown, described, and pointed out novel features as applied to various embodiments, it will be understood that various omissions, substitutions, and changes in the form and details of the devices or algorithms illustrated can be made w ithout departing from the spirit of the disclosure. As will be recognized, the processes described herein can be embodied within a form that does not provide all of the features and benefits set forth herein, as some features can be used or practiced separately from others. The scope of protection is defined by the appended claims rather than by the foregoing description. All changes which come within the meaning and range of equivalency of the claims are to be embraced within their scope.

[0060] Although various embodiments of the present invention have been illustrated in the accompanying Drawings and described in the foregoing Detailed Description, it will be understood that the invention is not limited to the embodiments disclosed, but is capable of numerous rearrangements, modifications and substitutions without departing from the spirit of the invention as set forth herein.1147469434v l 171320 / 00019

Claims

Attorney Docket No.: 171320.00019CLAIMSWhat is claimed is:

1. A vibration damping device comprising: at least one constraining layer; and at least one LCE layer, wherein the LCE layer is attached along the length of one side of the constraining layer.

2. The vibration damping device of claim 1, wherein the constraining layer comprises a material having a modulus ranging from 3 GPa - 250 GPa.

3. The vibration damping device of claim 1, wherein the constraining layer comprises at least one metal.

4. The vibration damping device of claim 1, wherein the constraining layer comprises at least one plastic.

5. The vibration damping device of claim 1, wherein the composite loss factor of the device ranges from 0.4 to 0.9.

6. The vibration damping device of claim 1, wherein the composite loss factor is greater than about 0.2 over a temperature range of 5°C to 40 °C.

7. The vibration damping device of claim 1, wherein the glass transition temperature of the LCE layer ranges from -15 to 30°C.

8. The vibration damping device of claim 1, wherein the LCE layer is anisotropic.

9. The vibration damping device of claim 1, wherein an adhesive is applied to the opposite side of the LCE layer from the side that is attached to the constraining layer.

10. The vibration damping device of claim 9, wherein the adhesive is a pressure sensitive adhesive.

11. The vibration damping device of claim 1, wherein the LCE layer has a thickness ranging from 0.1 mm - 5 mm.1247469434v l 171320 / 00019Attorney Docket No.: 171320.0001912. The vibration damping device of claim 1, wherein the constraining layer has a thickness ranging between 0. 1 mm to 5 mm.

13. A method of reducing vibrations of a substrate, the method comprising: providing a substrate that is subject to a vibration; and attaching the vibration damping device of claim 1 to the substrate.

14. The method of claim 13. wherein the vibration of the substrate is dissipated over a range of temperatures and range of frequencies.

15. The method of claim 12, wherein the thickness of the vibration damping device of claim 1 is less than the thickness of the substrate.

16. The method of claim 14, wherein the range of temperatures is -10°C to 60°C.

17. The method of claim 14, wherein the range of frequencies ranges from 30 Hz - 20 kHz.1347469434v l 171320 / 00019

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