This paper presents the design, analysis and experimental verification of strut-based lattice structures to enhance the mechanical vibration isolation properties of a machine frame, whilst also conserving its structural integrity. In addition, design parameters that correlate lattices, with fixed volume and similar material, to natural frequency and structural integrity are also presented. To achieve high efficiency of vibration isolation and to conserve the structural integrity, a trade-off needs to be made between the frame’s natural frequency and its compressive strength. The total area moment of inertia and the mass (at fixed volume and with similar material) are proposed design parameters to compare and select the lattice structures; these parameters are computationally efficient and straight-forward to compute, as opposed to the use of finite element modelling to estimate both natural frequency and compressive strength. However, to validate the design parameters, finite element modelling has been used to determine the theoretical static and dynamic mechanical properties of the lattice structures. The lattices have been fabricated by laser powder bed fusion and experimentally tested to compare their static and dynamic properties to the theoretical model. Correlations between the proposed design parameters, and the natural frequency and strength of the lattices are presented

Recent advances in additive manufacturing have enabled fabrication of phononic crystals and metamaterials which exhibit spectral gaps, or stopbands, in which the propagation of elastic waves is prohibited by Bragg scattering or local resonance effects. Due to the high level of design freedom available to additive manufacturing, the propagation properties of the elastic waves in metamaterials are tunable through design of the periodic cell. In this paper, we outline a new design approach for metamaterials incorporating internal resonators, and provide numerical and experimental evidence that the stopband exists over the irreducible Brillouin zone of the unit cell of the metamaterial (i.e. is a three-dimensional stopband). The targeted stopband covers a much lower frequency range than what can be realised through Bragg scattering alone. Metamaterials have the ability to provide (a) lower frequency stopbands than Bragg-type phononic crystals within the same design volume, and/or (b) comparable stopband frequencies with reduced unit cell dimensions. We also demonstrate that the stopband frequency range of the metamaterial can be tuned through modification of the metamaterial design. Applications for such metamaterials include aerospace and transport components, as well as precision engineering components such as vibration-suppressing platforms, supports for rotary components, machine tool mounts and metrology frames.

We report on numerical modelling of three-dimensional lattice structures designed to provide phononic bandgaps. The examined lattice structures rely on two distinct mechanisms for bandgap formation: the destructive interference of elastic waves and internal resonance. Further to the effect of lattice type on the development of phononic bandgaps, we also present the effect of volume fraction, which enables the designer to control the frequency range over which the bandgaps exist. The bandgaps were identified from dispersion curves obtained using a finite element wave propagation modelling technique that provides high computational efficiency and high wave modelling accuracy. We show that lattice structures employing internal resonance can provide transmissibility reduction of longitudinal waves of up to −103 dB. Paired with the manufacturing freedom and material choice of additive manufacturing, the examined lattice structures can be tailored for use in wide-ranging applications including machine design, isolation and support platforms, metrology frames, aerospace and automobile applications, and biomedical devices.

566The performance of a precision machine depends on the attenuation of the environmental disturbances acting upon it, and considerable time and expense is invariably expended to isolate external and internal noise sources. The magnitude of these disturbances also influences the design of process controls (see Chapter 14). This chapter discusses the shock, vibration, thermal and acoustic isolation needed to protect precision machines. Vibration arises from dynamic machine motion, can be generated within the machine itself, transmitted through the floor, coupled in with direct linkages, or might be a result of vibrations and impacts in one machine generating acoustical noise that is absorbed by another. The attenuation of the impact of these perturbations on the machine can be achieved either by isolation or energy dissipation. Isolation refers to the process where the excitation magnitude is prevented from transmitting to the structure of the precision machine, while energy dissipation attenuates the excitation magnitude by dissipating the energy through heat or friction. In this chapter, an understanding of external excitations is first developed by reviewing and classifying different excitation sources. The impact of these excitations on the dynamic behaviour of a precision machine is investigated. Following the dynamic section, the focus is shifted to thermal isolation, where passive and active thermal isolation methods are introduced. In closing, the chapter outlines approaches to acoustic isolation. Different techniques and methods are discussed throughout the chapter to design appropriate isolation systems that ensure the minimisation of external impact on the application of precision machines.