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Temperature effects are predominantly ignored when computing the dynamic response of structures. Yet, in applications where large changes in temperature occur, the dynamic response can drastically change. This is particularly true for polymers. While the temperature effects on modulus and loss factor are often available for most polymers, this change is not addressed or corrected for. Meanwhile, the recent research on additively manufactured polymer metastructures has yet to consider the effects of temperature change on their ability to suppress vibrations. In order to fill this gap, the study presented in this paper focuses on the effects of temperature change on additively manufactured structures.

This paper presents the dynamic mechanical and thermal analyses of the inkjet 3D printed materials of the Objet Connex 500 printer by Stratasys. The Objet Connex printer uses different ratios of distinct base materials to produce materials with homogeneous bulk properties using an inkjet process. Small dots of the liquidized polymer base materials are deposited on the print bed and cured with ultraviolet light. This paper examines the materials produced using the base materials TangoPlus (FLX930) and VeroWhitePlus (RGD835), which provide materials with varying levels of rubber-like characteristics. These materials are increasingly used to create prototypes of vibration suppression systems. To better understand the damping properties of these materials, it is necessary to characterize their viscoelastic properties. In this work, the viscoelastic properties are characterized by measuring the frequency and temperature dependent complex modulus. A dynamic mechanical analyzer is used to measure the complex moduli of four materials for a range of frequencies and temperatures. The time-frequency equivalence is used to determine a relationship between frequency and temperature; producing a master curve of the complex moduli over a wide range of frequencies and a single reference temperature. The effects of using tensile versus cantilever testing configurations and the effects of print direction are also discussed.

This work examines the distribution of vibration absorber mass for a lumped mass metastructure model designed to suppress vibrations in the axial direction. Metastructures, a metamaterial inspired concept, are structures with distributed vibration absorbers. In automotive and aerospace industries, it is critical to have low levels of vibrations while also using lightweight materials. Previous work has shown that this design can effectively reduce vibrations by comparing the response of the metastructure to a structure with no vibration absorbers but with equal mass. Previous work constrained the vibration absorber masses to be the same throughout the structure. This work looks at the added performance that can be realized by allowing these masses to varying throughout the length of the metastructure. Additionally, the performance of the metastructure is also compared a host structure with a single tuned mass damper to show how this new technology differs from traditional vibration suppression methods.

3D printing technologies have made creating prototypes with complex geometries relatively simple thus it has become an increasingly popular method for creating prototypes in a research setting. Therefore, it is crucial to understand the properties of the materials being used. This paper examines the effects of printing direction and testing method type on the complex modulus of viscoelastic materials printed using the Objet Connex 3D Printer from Stratasys. Because of its ability to print multiple materials in a single print job, this printer is a popular choice to create models. Throughout these tests the sample material will be kept constant to isolate the effects of print direction and test performed. DM 8430 is produced by mixing VeroWhitePlus™ and TangoPlus™ in a specific ratio. Since the 3D printer threads and smooths the sample uniaxially, the print direction of the sample can be manipulated by changing the orientation at which the sample is placed on the printer. Two different print directions, that are perpendicular with respect to each other, will be examined. The two test methods that will be used to determine the complex modulus are the Dynamic Mechanical Analysis (DMA) test, which examines the tensile behavior of the material, and the vibrating beam test, which examines the bending behavior. The goal is to gain greater insight into the uncertainty in the complex modulus that results from changing the test and printing direction used to determine this value. This will be done by performing a total of four tests. For each testing method, DMA and vibrating beam, the complex modulus will be found for two samples of different print direction, vertical and horizontal. These results will permit a greater understanding of the amount of variability produced by print direction.

The article examines the effectiveness of metastructures for vibration suppression from a weight standpoint. Metastructures, a metamaterial inspired concept, are structures with distributed vibration absorbers. In automotive and aerospace industries, it is critical to have low levels of vibrations while also using lightweight materials. Previous work has shown that metastructures are effective at mitigating vibrations, but do not consider the effects of mass. This work takes mass into consideration by comparing a structure with vibration absorbers to a structure of equal mass with no absorbers. These structures are modeled as one-dimensional lumped mass models, chosen for simplicity. Results compare both the steady-state and the transient responses. As a quantitative performance measure, the H 2 norm, which is related to the area under the frequency response function, is calculated and compared for both the metastructure and the baseline structure. These results show that it is possible to obtain a favorable vibration response without adding additional mass to the structure. Additionally, the performance measure is utilized to optimize the geometry of the structure, determine the optimal ratio of mass in the absorber to mass of the host structure, and determine the frequencies of the absorbers. The dynamic response of this model is verified using a finite element analysis.

This work addresses two issues in lightweight structural composites suitable for aerospace systems. The first is to add additional functionality to multifunctional composites and the second is to provide damping in structures that cover a wide range of frequencies and temperatures. Passive damping in all materials suffer from failing at certain temperature and in certain frequency ranges. The extreme environments often seen by aerospace structures provide high temperature, which is exactly where damping levels in structures reduce causing unacceptable vibrations. In addition, as loading frequencies decrease damping levels fall off, and many loads experienced by aerospace structures are low frequency. This work looks at the implementation of a control system to a longitudinal metastructure bar. A metastructure is a structure which has distributed vibration absorbers which provide passive damping to the system. The active control system will be implemented by adding piezoelectric materials to one of the absorbers to make the absorber active. The structure with the active vibration absorber will be compared to a structure of equal weight with no active components. Since the two comparison structures are of equal weight, the performance improvements are strictly due to the control system and not at the cost of additional weight.

This work looks at the effectiveness of constant weight metastructures for vibration suppression. A metastructure is a structure with distributed vibration absorbers. The metastructures are compared to a baseline structure of equal mass. The equal mass constraint shows that any increase in performance is due to the addition of the vibration absorbers and not due to adding additional mass to the structure. In this paper, two different metastructure designs are compared. These structures are designed to suppress longitudinal vibrations traveling along the length of the bar. The metastructures have ten vibration absorbers distributed on the length of the bar and the ratio of mass of the absorbers to mass of the host structure is 0.26. One metastructure has all the absorbers tuned to the natural frequency of the host structure and the other metastructure uses absorbers that are tuned to frequencies that have linearly varying natural frequencies. These structures were modeled using two different methods, a one-dimensional (1D) finite element method with lumped mass vibration absorbers and a fully three-dimensional (3D) finite element model. The results show that the metastructure with linearly varying natural frequencies outperforms that metastructure with vibration absorbers tuned to a single natural frequency.

The research presented here explores a finite element model of metastructure with distributed vibration absorbers experiencing unidirectional axial vibrations. This work builds off of previous work using a lumped mass model. The proposed model is compared to a baseline model where both models have equal mass. First, it is verified that the finite element formulation produces similar trends as the lumped mass model, specifically, that using vibration absorbers of linearly varying natural frequencies leads to a larger bandgap of reduced vibrations. Second, the two comparison models generated using the finite element formulation have different effective stiffnesses and the effects of this is examined. The results show that a small number of vibration absorbers, less than three, leads to a significant change in stiffness which in turn results in a larger dynamic response of the structure.

This paper examines the damping properties of digital materials from the Objet Connex 3D Printer from Stratsys. The Objet Connex printer is a unique 3D printer because in a single print job, ten different materials with different stiffness can be utilized. The printer utilizes two base materials and mixes them in different ratios to obtain varying stiffness levels. The first base material, VeroWhitePlusTM is a rigid opaque plastic and the second base material, TangoPlusTM is a rubbery translucent material. This 3D printer has a variety of applications including the development of metastructures for vibration suppression. It has been demonstrated that both the VeroWhitePlusTM and TangoPlusTM materials exhibit viscoelastic behavior but extensive studies have not be carried out to determine the Young’s Modulus and loss factor data in terms of frequency. This paper is the first step towards that goal. The paper begins by going into more detail about the properties of the printer and examines some previous work on determining the material properties. Next, the test method used it outlined and lastly the experimental set-up is described. In order to obtain data for a high range of frequencies, the material must be tested at various temperatures.