Given the similarity of unconsolidated Granular Materials (GMs) to fibrous materials in airborne attenuation, it is important to study their sound absorption properties and their particle-based distinct relationships. Quantifying absorption using equivalent fluid models is challenging due to the need to estimate several geometric parameters of the porous media. This work presents experimental and modelling insights into the Sound Absorption Coefficient (SAC) spectrum of irregularly shaped granules in unconsolidated granular materials with particle sizes ranging from 100 mu m to 15 mm. Experimentally, impedance tube measurements were taken for the granular material beds with a thickness of 50 mm, and their airflow resistivities were determined using a new sieve arrangement. Absorption models were developed based on the measured flow resistivity and other non-acoustical parameters of GMs, obtained through established empirical and numerical relationships, using three reported porous media models. It was found that the granule size-dependent relationship models the SAC spectrum into three dominant phases (Regions) based on the mean particle diameter (D-e) of the GMs: Region 1 (D-e > 2 mm), Region 2 ( D-e< 2 mm), and Region 3 (D-e <= 100 m). Modelling of these regions showed that the Johnson-Champoux-Allard (JCA)-based model provides a good estimate for the high-frequency absorption peak (>1 kHz) found in Region 1 GMs. Empirical models, such as the Delaney and Bazley and Miki-based sound absorption models, provide better estimates for the frequency-independent plateau absorption in Region 2. For Region 3, a new coupled fluid-solid characteristic impedance model is developed to explain the frame resonance-enhanced attenuation in powders with D-e < 100 m.

Granular Materials (GM) employed within particle dampers attenuate vibration energy due to interparticle and particle-wall interactions. Estimating their kinetic energy losses is usually performed using the Discrete Element (DE) method assuming that particles of uniform size (monodisperse) are excited at anti-resonance conditions. However, the GM found in nature and industrial by-products exhibit size distributions within specific ranges. Estimating their energy losses is important in the presence of structural resonance conditions to obtain the associated damping. This study numerically investigates both monodisperse and mixtures of GM integrated within vibrating structures using a coupled Finite Element-Discrete Element approach. The model developed simulates the oscillation of a small-scale suspended panel system integrated with a 6 mm thick granular layer with a cubic packing arrangement. Various monodisperse and mixed spherical particles ranging from 1 to 6 mm occupy the packing space. Damping characteristics of various spherical particle arrangements were quantified by the panel system's damping loss factor, determined through the logarithmic decrement method. The results showed that mixtures of larger particles of 2-4 mm diameter develop higher damping compared to smaller monodisperse particles and mixtures of smaller sizes (with diameters of 3 mm or less) for the same mass. It is concluded that the damping of these particle sets (with diameters of 3 mm or less) can be assessed using a new geometric parameter developed in this study that characterizes the particles' bed. Additionally, the segregation effect in the 2-4 mm mixture with large porosity results in higher tangential velocities that increase interparticle losses.

The Sound Absorption Coefficient (SAC) of unconsolidated Granular Material (GM) is usually characterized by utilizing empirical models based on airflow resistivity correlations or more comprehensive models like Johnson–Champoux–Allard (JCA). These models rely on porous media geometrical parameters, which are obtained through inverse characterization methods using SAC experimental results. This presents challenges when GM’s SAC estimates are required in the absence of experimental results. Therefore, this paper reports a sound absorption model for GMs based on three porous media absorption models. Each model corresponds to GMs with a mean particle diameter (De) range, related to a specific SAC frequency profile that transitions through three stages, influenced by particle size changes, up to 2 kHz. Model parameters were determined based on granular frame geometrical properties as a function of airflow resistivity and porosity of packed polydisperse Discrete-Element spherical particles. SAC estimates for various GMs were validated against impedance tube measurements. JCA-based absorption model was found suitable for larger-particle GMs (De > 2 mm), exhibiting absorption peaks at frequencies above 1 kHz (Stage 1). Meanwhile, empirical-based absorption model characterized the frequency-independent SAC plateau observed in GMs with De < 2 mm (Stage 2). A newly developed coupled fluid-solid powders absorption model characterized SAC for 100-micron-sized particles (Stage 3).

Granular Materials (GM) employed within the mechanism of particle dampers attenuate the vibration energy due to their interparticle and particle-wall interactions. Estimating their damping effect using the analytical equivalent single mass approach overlooked the particles' individual losses that are built into the total damping. Alternatively, the numerical techniques (e.g., Discrete Element) are time-inefficient and computationally demanding. Therefore, this study explores the implementation of Machine learning (ML) algorithms to estimate the damping effect of GM. The ML model in this study will rely on a Data-Driven Modeling approach (DDM) incorporating the ensemble tress nonlinear regressor method. The models' training and testing data were obtained from an experimental setup of an acrylic beam internally integrated with Stainless Steel (SS) and glass spheres undergoing low excitation amplitude (RMS <1N). The main aim was to map between seven input features (e.g. filling ratio) and one targeted output: the beam's damped frequency response. Three ensemble trees' algorithms were used to create the DDM; Decision Tree, Random Forest, and XGBoost. The hyperparameter combination based on the Gridsearch CV function increases the prediction accuracy of each model. The developed ML models provided high accuracy (86-93%) in predicting the damping effect of the granular materials spheres.

In the context of a wider research project investigating the use of Granular Material (GM) within floor and wall structures to increase their sound insulation, this study presents the sound absorption coefficient (SAC) measurements of different thicknesses for a range of GM. A primary aim has been to extend the understanding of the behaviour of GM layers in absorbing the propagated incident sound wave. Equally important has been an assessment of what GM could be sourced from waste and be acceptable for use in buildings from the point of view of fire insulation, handleability, economy, etc. Samples of GM were placed in an 88mm diameter vertical impedance tube and SACs measured up to 2kHz. The results show the effect GM's different structure (size and shape), bulk volume, and mechanical characteristics have on the range and value of the SAC. These determine the extent to which GM could be a replacement for traditional sound absorption materials.

Modern structures incorporating lightweight, low-stiffness floors face challenges for low-frequency impact noise transmission. Using spring isolators or resilient layers (e.g., floating floors) to improve isolation in light weight floor can introduce variability over time and increase structural complexity, making the system more sensitive to construction errors. An alternative approach is reviewed in this work, using internal floor cavities that contain Granular Materials (GM). Previous studies describe GM particle dampers in different applications where large movements between particles result in significant energy losses. However, a review of the experimental methods used in those studies is needed to be able to quantify the energy losses in relation to the type and degree of impact excitation. Modelling approaches are reviewed comparing their computational demand and which properties of GM are included, motion regimes and container properties. These studies span both destructive and non-destructive testing methods and give some pointers to both the geometrical and mechanical properties of granules which influence dissipation. This review goes beyond structural damping to include airborne sound absorption provided by a granular bed. This additional attenuation can be significant over a wide frequency range. A small number of practical studies of GM integrated with light weight floors show improvement in impact sound insulation. However, the lack of more detailed knowledge of GM damping mechanisms and a better understanding of GM bed interactions with containers prevents optimization of their use for insulating floors against sound transmission. This review proposes a general framework for future GM research to guide the selection of appropriate GM and addresses what is needed for optimizing lightweight floor impact sound insulation.

This work was aimed at examining the overall contributions to displacement of panels of compressed boxes, such as panel compression strain and flap and crease displacements. 3D digital image correlation (DIC) was used to analyse motion of side panels of corrugated fiberboard regular slotted containers. The vertical displacement and the vertical component of strain of the panel face during box compression test were examined. Measuring displacements of the whole compressed box with DIC enables measurement of the in‐plane compression of a panel in isolation from the horizontal fold or crease zone displacement, without having to test tube sections of the box to infer or extract the in‐plane panel compression behaviour. Detailed study of two box designs in three representative test cases was presented, which in future could be extended to other box designs. At peak load, the in‐plane compression of the panels, calculated from the average vertical component of the strain along the right edge of the long panel of the box, was 3% to 6% of total crosshead displacement for the test cases. At peak load, the portion of the box compression associated with bottom box flaps or crease zone crushing was 48% to 59% of total crosshead displacement for the different cases. The analysis showed that the majority of the vertical displacement of the box occurred in the top and bottom creased folds and that these folds are responsible for the low apparent in‐plane stiffness of a box.

To maximize utilization of our forest resources, detailed knowledge of wood property variation and the impacts this has on end-product performance is required at multiple scales (within and among trees, regionally). As many wood properties are difficult and time-consuming to measure our knowledge regarding their variation is often inadequate as is our understanding of their responses to genetic and silvicultural manipulation. The emergence of many non-destructive evaluation (NDE) methodologies offers the potential to greatly enhance our understanding of the forest resource; however, it is critical to recognize that any technique has its limitations and it is important to select the appropriate technique for a given application. In this review, we will discuss the following technologies for assessing wood properties both in the field: acoustics, Pilodyn, Resistograph and Rigidimeter and the lab: computer tomography (CT) scanning, DiscBot, near infrared (NIR) spectroscopy, radial sample acoustics and SilviScan. We will discuss these techniques, explore their utilization, and list applications that best suit each methodology. As an end goal, NDE technologies will help researchers worldwide characterize wood properties, develop accurate models for prediction, and utilize field equipment that can validate the predictions. The continued advancement of NDE technologies will also allow researchers to better understand the impact on wood properties on product performance.

This work is aimed at examining the overall contributions to displacement of a compressed box panel, such as panel compression strain and flap and crease displacements. 3D Digital Image Correlation (DIC) was used to analyse motion of a side panel of a corrugated fibreboard regular slotted container (RSC). The vertical displacement and the vertical component of strain of the panel face during box compression test are examined. Measuring displacements of the whole compressed box with DIC enables measurement of the in-plane compression of a panel in isolation from the horizontal fold or crease zone displacement, without having to test tube sections of the box to infer or extract the in-plane panel compression behaviour. Detailed study of one box design is presented, which in future could be extended to other box designs. Although the crosshead displacement during box compression testing was 10.6 mm at peak load, the in-plane compression of the panel, calculated from the average vertical component of the strain along the right edge of the long panel of the box, was 0.68 mm. At peak load, the portion of the box compression associated with bottom box flaps or crease zone crushing was 6.25 mm. The analysis shows that the majority of the vertical displacement of the box occurred in the top and bottom creased folds and that these folds are responsible for the low apparent in-plane stiffness of the box. The implications of these findings for box design are discussed.

Air-coupled ultrasonic (ACU) is a contactless ultrasonic measurement method which has become increasingly popular for material characterization. This is due to a growing number of advanced materials which cannot be contaminated during the testing processes by coupling agents utilized in conventional ultrasonic testing. This paper provides a review of the applications of ACU to wood and wood products. The ACU fundamentals, including principles, working modes and commercial transducers used for this purpose, is briefly described. The emphasis of this paper is on approaches of inspection and characterization. The applications of ACU to wood characterization with reference to wood quality aspects are summarized. Correlations between the ACU parameters (i. e. amplitude, velocity, and spectrum) and the wood properties (i.e. density, moisture content, strength, and stiffness) as well as the wood defects (i. e. knots, cracks, decay, insect damage, and delamination) are dealt with in detail. Finally, a discussion of apparent future research directions completes this review.

The trade-off between the elastic modulus and damping capacity as a function of fibre composition in carbon–flax hybrid composite laminates was investigated. Hybrid composite laminates with varying carbon–flax fibre–epoxy content were prepared using a combination of compression moulding and vacuum bagging. The elastic modulus and damping loss coefficients were determined by free-vibration in longitudinal and flexural modes, and modelled using a rule of hybrid mixtures (ROHM) and laminate theory. The models were in close agreement with the experimental data for both the longitudinal and flexural modes and thus appeared to be a feasible method of predicting the stiffness–damping relationship in this system of hybrid composite laminates. The experimental data of the tensile strength was found to also follow the ROHM. However, the experimental data of the flexural strength deviated negatively from the theoretical prediction, exhibiting lower values than the predicted ones.

This paper shows how to use a mathematical model to predict the vibration of lightweight timber-framed floor/ceiling systems (LTFSs) caused by mechanical excitation. The LTFS considered here is made up of an upper floor layer, a cavity space with timber joists and a ceiling. These components are joined by timber battens, ceiling furring channels and ceiling clips. The vibration in the structure is caused by a localized excitation on the top surface and the resulting vibration level of the ceiling surface will be analysed. The cavity space is filled with fibre infill for damping the sound transmitting through the cavity. A unique feature of the design and the model is the sand-sawdust mixture in the upper layer. The theoretical model and the experimental measurements show that the sand-sawdust dampens the vibration in the frequency range between 10 and 200 Hz. The damping by the sand-sawdust and the fibre infill are found by comparing the numerical simulations against the experimental measurements. We show that the simple linear frequency dependent loss factors can be used to predict the low-frequency vibrations of LTFSs.

Abstract In order to determine more accurate indicators of wood structure obtained by microwave sensing and improve our understanding of plane wave propagation through this complex material, we have undertaken a permittivity survey and experimentally investigated scattering of a plane wave, measuring its transmission over two non-parallel surfaces of a rectangular lumber sample. This novel non-destructive testing techn-ique offers results which may significantly contribute in a more accurate propagation modeling and industrial wood quality testing.

Abstract In order to determine more accurate indicators of wood structure obtained by microwave sensing and improve our understanding of plane wave propagation through this complex material, we have undertaken a permittivity survey and experimentally investigated scattering of a plane wave, measuring its transmission over two non-parallel surfaces of a rectangular lumber sample. This novel non-destructive testing technique offers results which may significantly contribute in a more accurate propagation modeling and industrial wood quality testing.

The sound speed of wood is related to important wood quality properties such as the microfibril angle of the S 2 layer in the cell wall, stiffness, and shrinkage propensity. Measuring the sound speed of seedling stems has benefits to the forestry industry, potentially enabling early selection of trees that yield better quality wood. A nondamaging longitudinal-wave time-of-flight (LWToF) acoustic technique was used to determine the sound speed of 10 cm long sections of 2-year-old Pinus radiata D. Don seedlings. The measured sections were harvested and acoustic resonance used to determine the sound speed of the sections before and after the bark was removed and after the remaining xylem was dried. A linear relationship between the acoustic resonance sound speed of the dry xylem and the LWToF sound speed of the seedling stem was found (R 2 = 0.89). To demonstrate a potential application using the LWToF acoustic technique, it was used as a tool for investigating the effect of various applied stresses on wood properties of a clone of P. radiata. The LWToF sound speed measurements of phytohormone stressed stems were significantly lower than the control stems, indicating the negative impact on stiffness and shrinkage propensity imposed by this treatment.

A cross-correlation time-of-flight method for measuring the sound speed in a seedling in a non-destructive and non-damaging way is described. The method uses two miniature accelerometers coupled to the bark of a growing seedling stem to record the acoustic signals and a small striker to generate an acoustic pulse. The two acoustic signals are then time-windowed and cross-correlated in order to calculate the speed of the acoustic pulse. The method measures the sound speed of the seedling stem as a whole and does not selectively measure the fastest path. The method was tested on 1- and 2-year-old Pinus radiata clones. A comparison of the results of the method with a destructive acoustic resonance test showed that the sound speed results are unbiased. Repeatability tests give a standard deviation of the sound speed of less than 2%. The method shows good promise as a rapid and cost-effective tool for early screening of wood quality in clonal trials.

A microwave-focused beam transmission measurement is identified as a good candidate for fast, accurate, and affordable industrial wood testing. In this paper, the transmission measurement setup, in its various forms, is used to study wood's properties, considering the wood as anisotropic heterogeneous and multiphase dielectric. The depolarization of a linearly polarized plane wave in an anisotropic media is considered first. It is used for grain angle detection for arbitrary grain inclination in 3-D space. A good correlation with visually inspected grain angle values is obtained. A scattering experiment is performed, measuring the transmission through the wood when the transmitting and the receiving antenna axes are at the right angle. The results indicate that the annual ring arrangement strongly influences scattering in the sideways direction, while other investigated parameters (defects, gradual density variation, and bulk density) show poor correlation with the measured scattering coefficient.

Contrary to common belief, a relatively simple and practical lightweight timber based floor/ceiling can have impact sound insulation superior to that of concrete slab based systems. This paper presents examples of such systems that include vibration isolation/damping features, such as rubber ceiling batten clips, glass fibre wool, and a sand-sawdust mixture layer. We give enough details to reproduce our experiments and build the proposed lightweight systems.