Lucas Van Belle

Vibro-acoustic metamaterials recently emerged as promising lightweight and compact solutions with favourable noise insulation properties. Although they are appealing for band-limited and tonal noise level reduction, sound perception also impacts our well-being and health. However, the unconventional frequency content changes caused by these metamaterials was recently found to possibly lead to more annoyance than conventional solutions. Therefore, in this work, a filter-based auralization approach is used to efficiently predict and evaluate the impact of metamaterial partitions. Using analytical model-based filters of metamaterial partitions, the impact of metamaterial tuning on sound quality metrics and annoyance is assessed, as well as optimized.

The development of traction motors with easily recyclable rare-earth permanent magnets (PMs) is studied. The primary objective is to find means and technologies that enable the reuse of the PMs without extracting their elements. Both the motor design and PM assembly need to be aligned with this target. Especially, we are focusing on metallic encapsulation of the PMs to make them strong enough to tolerate the disassembly forces. First, we discuss the design, addressing the positioning of the encapsulated PMs to balance between the mechanical and electromagnetic requirements. Second, we present the first results on the encapsulation of the PMs for intact disassembly, elaborating on the materials, manufacturing via direct energy deposition, and visual inspection of the results. We aim to contribute to the emergence of the next generation less rare-earth-element-dependent, compact, and energy-efficient electric traction motors.

Locally resonant metamaterials (LRMs) have recently emerged in the search for lightweight noise and vibration solutions. These materials have the ability to create stop bands, which arise from the sub-wavelength addition of identical resonators to a host structure and result in strong vibration attenuation. However, their manufacturing inevitably introduces variability such that the system as-manufacture d often deviates significantly from the original as-designed . This can reduce attenuation performance, but may also broaden the attenuation band. This work focuses on the impact of variability within tolerance ranges in resonator properties on the vibration attenuation in metamaterial beams. Following a qualitative pre-study, two non-intrusive uncertainty propagation approaches are applied to find the upper and lower bounds of three performance metrics, by evaluating deterministic metamaterial models with uncertain parameters defined as interval variables. A global search approach is used and compared with a machine learning (ML)-based uncertainty propagation approach which significantly reduces the required number of simulations. Variability in resonator stiffnesses and masses is found to have the highest impact. Variability in the resonator positions only has a comparable impact for less deep sub-wavelength designs. The broadening potential of varying resonator properties is exploited in broadband optimization and the robustness of the optimized metamaterial is assessed. This article is part of the theme issue ‘Current developments in elastic and acoustic metamaterials science (Part 2)’.

In the field of noise and vibration control, locally resonant metamaterials have come forth as promising lightweight and compact noise and vibration solutions. In the field of noise and vibration control, locally resonant metamaterials have come forth as promising lightweight and compact noise and vibration solutions.

In the past decades, an increasing trend towards the structural combination of lightweight materials and traditional metals has been observed. For these multi-material interfaces, traditional joining technologies such as bolting and welding have to be re-thought and adhesive bonds can be a valid alternative. The substitution of the joints has an impact on the stiffness, damping, and mass distribution of the entire assembly and should be taken into account while designing for NVH, durability, and performance. The aim of this work is to experimentally compare the effect of bolts and adhesive bonding on the vibrational response of the assembly, in terms of modal frequency, shape, and damping. Plate-to-plate single lap joints are tested under transverse vibration. In particular, we compare one M4 bolted connection and three adhesive connections, respectively, realized with stiff epoxy, flexible foam tape, and toughened acrylic. Results show that, in a low-mid frequency region between 0 and 250 Hz, the substitution of bolts with adhesives has a limited influence on mode shapes but can lead up to a 6-fold increase of the modal damping values and 10% increase of the modal frequencies.