Impulse Excitation Research Articles

New impulse-based test method for early-age elastic modulus measurement in cementitious materials

Accurate monitoring of the elastic modulus evolution during the early-age fluid-solid transition in cementitious materials is crucial for understanding their mechanical behavior under early stresses. While existing methods, such as EMM-ARM, have proven effective, they are often associated with high costs or complex setups. This study presents the development of a low-cost, easy-to-implement system that employs impulse excitation applied to a composite beam, introducing the EMM-IRM method for the effective assessment of the elastic modulus of cement paste from the earliest stages of hydration. The use of impulse excitation is particularly advantageous in low-cost systems with accelerometers of lower sensitivity, as it enhances signal clarity and reduces interference from background noise, thereby improving measurement reliability. The system was validated through experimental comparisons with conventional EMM-ARM, cyclic compression, and traditional impulse excitation techniques, using Portland cement paste as the test material. The results show that EMM-IRM consistently estimates the elastic modulus, with a maximum deviation of 6.33% from other methods. Moreover, despite its cost-effectiveness, EMM-IRM demonstrates a higher signal-to-noise ratio compared to conventional EMM-ARM. This approach offers a practical solution for early-age characterization of cementitious materials, balancing cost, simplicity, and measurement accuracy.

Multiple solutions and orbit change in energy harvesting system with a flag configuration

AbstractThe aim of this paper is to present a methodology for implementing the high-energy orbits which is still an open problem for nonlinear energy harvesters. To achieve it, this paper presents a new design of system with a flag configuration which potential function is shaped with the use of elastic elements. We have identified the lift force in FEM for wide spectrum of air velocities and used it as excitation in dimensionless mathematical model. On this basis we have conducted simulations of energy harvesting effectiveness. In the second part of the work, we focused on identifying the coexisting solutions. Due to the existence of high-energy orbits and low-energy orbits, we conducted simulations to investigate the possibility of changing the orbit. We used the Impulse Excitation Diagram here, but supplemented it with multi-colored probability distribution maps illustrating the possibility of achieving a stable orbit at given numerical values of the impulse amplitude and duration for various values of air flow velocity. The use of probability distribution maps allow to select the optimal impulse characteristics from the point of view of the energy necessary for its initiation.

The role of annealing and grain boundary controls on the mechanical properties of limestones and marbles

Chemical and mechanical processes are coupled in many geological and geochemical environments. Reactive processes anneal defects and restructure grain boundaries, modifying their elastic properties, levels of internal friction, wave propagation rates and fracture behaviors. The nature of these changes is, however, contingent on the initial state of the rock. In this study, impulse excitation was used to measure changes in mechanical properties as a function of dry and steam heating time at 300 °C for three carbonate rocks: Carrara marble, Carthage marble (Burlington Limestone), and Texas Cream limestone (Edwards limestone), with initial porosities of about 1 %, 3 %, and 27 %, respectively. Frequency-dependent phenomena along with mineral recrystallization were observed. This was coupled with small-angle X-ray and neutron scattering analysis to determine the relationship between changes in bulk mechanical and microstructural properties. An observed decrease in both the Young's and shear moduli in the experimental limestones as a function of heating time reflects and quantifies a reduction in the stiffness of the rock due to annealing. The internal friction of the samples first increases then decreases with reaction time, reflecting defect annealing, but this was balanced against grain boundary dissolution apparently driven by condensation of steam in the confined grain-boundary environment. This suggests an increase in the boiling point under confinement leading to dissolution, increased porosity and widening of the grain boundaries. In addition, comparison of small-angle X-ray and neutron scattering results suggests that it is inappropriate to assume that pores are empty for quantitative analysis of typical small-angle scattering samples.

Automatic shock excitation system for dynamic calibration of six-axis force/torque sensor

The coupling behavior between the six-axis force/torque (F/T) sensor and the mechanical environment introduces variations in the dynamic parameters obtained through different calibration methods and devices, which poses challenges in proposing dynamic performance criteria. This paper presents a comprehensive automatic calibration system for determining the dynamic characteristics of the six-axis F/T sensor. Impulse force generators (IFGs), positioned at various orientations, apply three mutually orthogonal directional force and torque components to the sensor using a cruciform artifact. The system ensures repeatable impulse excitation by maintaining consistent spring compression in the IFG, measured by the displacement control system's grating ruler. The pulse width and frequency response function (FRF) are determined based on the response signal without measuring the input signal. The calibration frequency and the impact force magnitude can be controlled by selecting appropriate system parameters. Compared to manual impulse hammers, IFGs exhibit superior features such as high bandwidth, repeatability, and controllable force amplitude. They provide high-quality impulse excitation with calibration frequencies and forces up to 30 kHz and 2500 N or even higher, respectively. Furthermore, a linear relationship between peak value of impulse excitation and spring compression is studied to ensure effective excitation application. The consistency of dynamic calibration results of the six-axis F/T sensor verifies the effectiveness of this automatic calibration system.

Factors Influencing Measurement of Dynamic Elastic Modulus from Disk-Shaped Concrete Specimen

The decrease in dynamic elastic modulus is a primary indicator of quantitative damage in concrete. To quantitatively assess depth-by-depth damage within a concrete structure, cylindrical specimens obtained through coring can be cut into disk specimens to measure the dynamic elastic modulus of concrete at each depth. To minimize external damage during coring, it is essential to extract cylinders with the smallest possible diameter. In addition, for higher resolution in depth-based damage assessment, creating disk specimens with the smallest possible thickness is necessary. However, there is no information available in the literature on experimental limitation of smallest possible diameter and thickness for dynamic elastic modulus of disk-shaped specimens. This study evaluated whether the dynamic modulus measured from various sizes of concrete disk specimens provided sufficient reliability compared to reference values obtained from cylinders. Moreover, the study examined how the presence of coarse aggregate and variation in the water–cement ratio significantly influenced the dynamic modulus measurement. In addition, test results from impulse excitation technique (IET) and impact resonance (IR) were compared to find a more reliable test method for dynamic elastic modulus of disk specimen. The experimental findings revealed that as the thickness-to-radius ratio of the disk specimens decreased, measured data variation increased. Mortar specimens without coarse aggregates showed less variability compared to concrete specimens, and the variation in dynamic modulus measured by IR was lower than that measured by IET.

Band Relevance Factor (BRF): A novel automatic frequency band selection method based on vibration analysis for rotating machinery

Monitoring rotating machinery has become a fundamental activity in the industry given the high criticality in production processes. Extracting useful information from signals is a key factor for effective monitoring. Several studies in the areas of Informative Frequency Selection bands (IFB) and Feature Extraction/Selection have demonstrated the need to identify the bands of interest in vibration signals. However, typical methods in these areas focus on identifying bands where impulsive excitations are present or analyzing the relevance of features after signal extraction. Therefore, they do not focus on other regions that may be related to changes in the dynamic behavior of machines or faults. Furthermore, the methods generally require parameter adjustments and are not automatic. To overcome these problems, the present study proposes a new approach called Band Relevance Factor (BRF). BRF aims to perform an automatic selection of all relevant frequency bands for a vibration analysis of a rotating machine based on spectral entropy. In other words, automatically identify all frequency bands that are related to changes in the behavior of the machines or faults. The results are presented through a relevance ranking and can be visually analyzed through a heatmap. The effectiveness of the approach is validated on a synthetically dataset and on two real datasets, showing that BRF is capable of automatically identifying bands that present relevant information for the analysis of rotating machinery.

Mechanical Characterisation of Gypsum-Based Passive Fire Protection Mortars with Micro and Nano Silica Particles

Steel structures are vulnerable to fire due to the degradation of their mechanical properties at high temperatures, making it necessary to protect them when exposed to high temperatures. This paper presents the results of an experimental research work to characterise the mechanical properties of gypsum-based fire-resistant mortars with and without nano and micro silica particles by destructive and non-destructive tests at ambient temperature. Five compositions were studied: one commercial composition was used as a reference and four were developed in the laboratory. Two were based on gypsum with perlite or vermiculite, and the other two included nano and micro silica particles. Twenty specimens underwent ultrasonic pulse velocity, flexural, and compression tests, while five specimens were tested by the impulse excitation of vibration. Young’s modulus, shear modulus, and Poisson’s ratio were assessed by non-destructive tests, and the flexural and compression strengths were assessed by destructive tests. Additional tests included density and porosity assessments, thermogravimetric analysis, X-ray diffraction, and scanning electron microscopy. Results indicated that adding nano and micro silica particles posed challenges to the mechanical and physical properties. Despite this, vermiculite compositions showcased superior or similar properties to the commercial composition, while perlite compositions exhibited slightly lower properties.

The sound of porosity: Suitability of the impulse excitation technique (IET) to determine the Young's modulus of 2D macroporous ceramics

The presence of pores in a ceramic leads to a lower Young's modulus compared to dense material. For the development of porous ceramics with tailored elastic properties, an exact determination of the Young's modulus is required, especially for industrial applications. Therefore, we investigated the suitability of the non-destructive impulse excitation technique for measuring the dynamic Young's modulus of two-dimensional ceramics with low porosity (P < 19 %). For rectangular samples it was shown that the measurement results depend on the geometric pore position, as added pores outside the nodal lines of the fundamental flexural vibration had no influence on the result. Pores in the inner part of the sample led to a decrease of the Young's modulus that is in good agreement with empirical and analytical models. For the investigated interval of porosity range, the influence of pore size and geometric position on the reduction of the Young's modulus was determined.

A new method for identifying elastic parameters of isotropic materials based on square specimens

This paper proposes a new impulse excitation technique using a square plate. First, the functional relationship between the modal frequency of the specimen and the geometrical dimensions and mechanical parameters was established by using the finite element method. Then, the continuous functional relationship derived by a homotopy method allowed the frequency ratios to be related to the thickness-to-length ratio and Poisson’s ratio. By measuring the frequency ratios and thickness-to-length ratio, Poisson’s ratio could be calculated using this functional relationship. When the density and Poisson’s ratio were known, Young’s modulus could be identified inversely in conjunction with the finite element analysis. Finally, a comparison test between this method and the traditional impulse excitation technique was designed and implemented, and the results showed that this method has advantages in both testing efficiency and accuracy. The study provides a new idea for system identification, which has important application value and promotion significance.

A variational-based non-smooth contact dynamics approach for the seismic analysis of historical masonry structures

A variational formulation of the non-smooth contact dynamics method is proposed to address the dynamic response of historical masonry structures modeled as systems of 3D rigid blocks and subjected to ground excitation. Upon assuming a unilateral-frictional contact law between the blocks, the equations of motions are formulated in a time-discrete impulse theorem format in the unknown block velocities and contact impulses. The variational structure of the problem to be solved at each time step is proven. On that basis, the numerical method requires at each time step to perform a collision detection that identifies antagonist contact points based on the given structural configuration, to solve a second-order conic programming problem that outputs block velocities and contact impulses, and to update the structural configuration for the solution to advance in time. As a merit of the formulation, large-scale problems can be robustly and efficiently addressed thanks to the convex setting of the time-step optimization problem. Numerical results are presented to test the computational performances of the proposed approach. Benchmark problems provide numerical evidence that the formulation is consistent with event-driven solutions based on the classical Housner impact model. The dynamic response, failure domains, and fragility functions of real-size masonry structures are then explored under ground impulse or earthquake excitation. The obtained results prove the reliability of the present computational method for the dynamic analysis and seismic assessment of historical masonry constructions of engineering interest.

Characterizing dispersion in bovine liver using ARFI-based shear wave rheometry

Background: Dispersion presents both a challenge and a diagnostic opportunity in shear wave elastography (SWE). Shear Wave Rheometry (SWR) is an inversion technique for processing SWE data acquired using an acoustic radiation force impulse (ARFI) excitation. The main advantage of SWR is that it can characterize the shear properties of homogeneous soft media over a wide frequency range. Assumptions associated with SWR include tissue homogeneity, tissue isotropy, and axisymmetry of the ARFI excitation). Objective: Evaluate the validity of the SWR assumptions in ex vivo bovine liver. Approach: SWR was used to measure the shear properties of bovine liver tissue as function of frequency over a large frequency range. Assumptions associated with SWR (tissue homogeneity, tissue isotropy, and axisymmetry of the ARFI excitation) were evaluated through measurements performed at multiple locations and probe orientations. Measurements focused on quantities that would reveal violations of the assumptions. Main results: Measurements of shear properties were obtained over the 25–250 Hz range, and showed a 4-fold increase in shear storage modulus (from 1 to 4 kPa) and over a 10-fold increase in the loss modulus (from 0.2 to 3 kPa) over that decade-wide frequency range. Measurements under different conditions were highly repeatable, and model error was low in all cases. Significance and Conclusion: SWR depends on modeling the ARFI-induced shear wave as a full vector viscoelastic shear wave resulting from an axisymmetric source; it is agnostic to any specific rheological model. Despite this generality, the model makes three main simplifying assumptions. These results show that the modeling assumptions used in SWR are valid in bovine liver over a wide frequency band.

Design and characterization of novel Ti-8Mo-xFe-yCu alloys as implant materials: Evaluation of biocompatibility, mechanical properties, and antibacterial potential

Titanium and its alloys are highly desirable materials for biomedical metallic implants due to their superior specific strength, excellent corrosion resistance, and exceptional biocompatibility. Among these alloys, Ti6Al4V is widely used in practical biomedical applications because it offers an excellent combination of strength, fracture toughness, and corrosion resistance. However, recent research has revealed limitations in its biocompatibility attributed to the presence of toxic elements such as Al and V. In addition, it has been reported that Ti6Al4V is costly due to the addition of Vanadium and has the potential for post-implant inflammation. As a result, researchers have been investigating new biomedical beta-Ti alloys using biocompatible, affordable, and easily accessible beta-stabilizers like Mo, Fe, and Cu, to achieve similar performance as Ti6Al4V alloys. The present study aims to develop a novel biomedical alloy through the arc melting method, to obtain an implant material possessing low elastic moduli, biocompatibility, and antibacterial properties to mitigate the risk of post-implant inflammation. Microstructural analysis was conducted using microscopy and x-ray diffraction, while the mechanical properties were evaluated through micro vickers hardness testing machine and elastic moduli measurement utilizing the impulse excitation technique. Cytotoxicity assessment was performed using the (Cell Counting Kit-8) CCK-8 method, followed by an examination of the alloy's antibacterial properties using the point counting method. β-Ti single phase was obtained in this study with the addition of ≥1% Fe and ≥1% Cu. The Ti-8Mo-2Fe-2Cu alloy was found to have the lowest elastic moduli of 95 GPa. Electrochemical measurements show that the Ti-8Mo- xFe- yCu alloys have a lower corrosion current density of around 0.319–2.317 µA/cm2 compared to Ti6Al4V of 16.543 µA/cm2. The Ti-8Mo-1Fe-3Cu, Ti-8Mo-3Fe-1Cu, and Ti-8Mo-3Fe-3Cu alloys have comparable biocompatibility with Ti6Al4V with the viability of mesenchymal stem cells (MSCs) above 75% and have a positive antibacterial response. Ti-8Mo-3Fe-3Cu alloy demonstrates the most favorable blend of microstructure, mechanical attributes, corrosion resistance, cell viability, and antibacterial properties as an alternate biomaterial for implant applications.

Correcting the orbits of coexisting solutions via a piezoelectric element in energy harvesting systems

This paper aims to present a novel and complex methodology for realizing high-energy orbits in energy harvesting systems. To achieve this, we have designed a new system structure that consists of elastic elements with variable configuration. In the first part of the work, we identified the characteristics of a potential function and performed a sensitivity analysis depending on ten thousand values of parameters defining the geometry and stiffness of the system. Then, for selected characteristics and based on the dimensionless model, we calculated and compared the energy effectiveness for various identified coexisting solutions and chaotic and periodic motion zones, with identification of transient chaos. In the second part of the work, because of the existence of high- and low-energy orbits, we conducted simulations to investigate the possibility of changing it by an impulse applied directly to the piezoelectric element. We used the Impulse Excitation Diagram supplemented by multicolored probability distribution maps illustrating the possibility of achieving a stable orbit at given numerical values of the impulse amplitude and duration. On the basis of such maps, it was possible to optimally select parameters of the impulse to jump to a high-energy orbit.

Thermal cycling damage of silica refractories for high-temperature thermal energy storage (HT-TES) – Can it be healed?

Silica refractories are promising materials for high-temperature thermal energy storage (HT-TES), because they exhibit excellent thermal cycling properties, unless cooled below a critical temperature (usually assumed to be 600 °C). When cooling down to room temperature severe damage can occur, which can be conveniently monitored via the impulse excitation technique (IET). This damage is most severe when the cycling maximum temperature is low. The question is whether this damage can be healed again. In this short contribution we show that severe damage in silica refractories, caused by heating from room temperature to 300 °C and back again to room temperature, can indeed be healed by thermal cycling to 1300 °C. The healed material is actually better than the pristine material.

Effective Young’s modulus of highly porous 3D printed mono-material and coaxial structures

The dynamic elastic response of 3D macroporous scaffolds is crucial to determine their performance under operating conditions. In this work, the elastic behaviour of 3D printed bar-shaped scaffolds of γ-Al2O3 and γ-Al2O3/graphene nanoplatelets (GNP) composites (18 vol%), fabricated by Direct Ink Writing (DIW), is investigated. Dynamic Young’s modulus (E) is studied by the Impulse Excitation Technique (IET) and compared with theoretical results obtained by Finite Element Methods (FEM) and the multi-scale material simulator GeoDict®. In addition, Resonant Ultrasound Spectroscopy (RUS) is used to characterize E of single- and bi-material coaxial struts. While additions of GNP to γ-Al2O3 lead to an increase in E, it decreases in the coaxial struts due to the development of thermal residual stresses at the core/shell interface. The suitability of combining experimental and theoretical methods for the analysis of the elastic properties and the anisotropy associated with the lattice pattern is demonstrated.

Analysis of Water Absorption on the Young’s Modulus and Damping of Sponge Gourd (Luffa cylindrica) Composites

ABSTRACT Composites reinforced with lignocellulosic fibers are attracting attention for use in several applications. This fact is directly linked to the advantages of using renewable lignocellulosic fibers. However, due to their cellulose-based structure, lignocellulosic fibers easily absorb water, which can affect the behavior of the composites. Surface treatments are used to reduce the hydrophilicity of fibers, but common surface treatments use chemicals, compromising the green approach of using lignocellulosic fibers. This work compares the water absorption behavior of sponge gourd-epoxy matrix composites with untreated and surface treated fibers. The effect of these treatments on the variation of the Young’s modulus and damping factor of the composites during the immersion time in distilled and salt water was also evaluated using the nondestructive impulse excitation test. In addition to the commonly used surface treatments (mercerization and acetylation), hornification has also been used to reduce the use of chemicals. The results obtained show that hornification is a competitive approach to reduce the water absorption of composites, being an interesting alternative to chemical surface treatments. A relationship was established between the amount of water absorbed and the variation in Young’s modulus and damping factor. Both properties stabilized when the water absorption saturation value was reached.

Decision fusion based on vibrometric data for increase of reliability of damage detection and indentification for plate-like structures

In the realm of structural health monitoring (SHM) for plate-like structures, the need for accurate and reliable damage detection and identification techniques is paramount. This paper explores the application of decision fusion algorithms to vibrometric data, with a focus on increasing the reliability of damage assessment for such structures. The methodology involves leveraging diverse input data sources, including variations in data processing algorithms, excitation parameters, and multiple measurements. By amalgamating these sources of diversity, we aim to mitigate measurement noise and amplify damage indications, ultimately enhancing the precision of the final diagnostic outcome. The study presents results obtained from laser vibrometry measurements on a 10 mm thick aluminum sample containing flat-bottom holes of varying diameters. A network of 12 PZT transducers was used to excite elastic waves, with impulse and chirp excitation techniques employed. Convolution techniques using OpenCV libraries were applied for data processing and fusion. The outcomes reveal a significant reduction in background noise, demonstrating the effectiveness of the fusion approach. Furthermore, the presentation outlines a roadmap for the future development of this methodology, which includes automating data processing, evaluating the impact of damage indicators, processing parameters and usage of different excitation transducers.

Estimating the elastic modulus of concrete under moderately elevated temperatures via impulse excitation technique

PurposeTo evaluate the temperature-dependency of the Young’s and shear moduli of concrete after exposure to moderately elevated temperatures using the non-destructive impulse excitation technique (IET).Design/methodology/approachThe study involved heating the concrete up to 225 °C and measuring the dynamic Young’s and shear moduli using the non-destructive technique of impulse excitation, which measures the natural vibration frequency from a mechanical impulse received by an acoustic sensor. The effects of temperature on the dynamic Young’s and shear moduli were analysed and the importance of the spatial variability of the measured values was also verified.FindingsThe study found that even moderately elevated temperatures (below 225 °C) resulted in a significant permanent reduction in the Young’s modulus of concrete (reduction in the range of 23%–36% for the maximum temperature considered in this research) as well as a modest and permanent reduction in the shear modulus of around 6%. It was also observed that spatial variability of the mechanical properties of concrete plays an important role in the measured values; higher dispersion of the results was found for the values of the Young’s and shear moduli of concrete measured along the height of the beam. The non-destructive test method used in this study was found to be extremely useful in the investigation of heat-related damage in concrete structures for its ease of use, low time consumption and accuracy. The results were consistent with the published literature.Originality/valueThis study provides important insights into the temperature-dependent behaviour of the dynamic Young’s and shear moduli of concrete and highlights the significance of proper consideration of the spatial variability of the measured values. The use of a non-destructive test method for continuous acoustic testing during heating and cooling proved to be effective, and the findings contribute to the fields of materials science and civil engineering in understanding the effects of elevated temperatures on concrete properties. The findings confirm that IET can be easily used to gather important information in the condition assessment and rehabilitation of concrete structures after a fire event. Further studies to foster the application of this technique to real structures are suggested.

Machine learning-enabled characterization of concrete mechanical strength through correlation of flexural and torsional resonance frequencies

In this study, an assessment of concrete compressive strength was conducted using an impulse excitation data-driven machine learning (ML) framework. The model was constructed upon a deep neural network and aided by the backpropagation method, ensuring a precise training process. In contrast to prior research, which mainly focused on mixture components, a meaningful relationship between physical parameters—resonant frequencies and elastic moduli—and compressive strength was established by our ML model. Remarkable performance was demonstrated, with a root mean square error value of 2.8MPa and a determination factor of 0.97. Through Pearson analysis, correlations between input features and output targets, ranging from −0.29 to 0.90, were revealed. Notably, the strongest correlations with compressive strength were found in Young's and shear moduli, derived from flexural and torsional frequencies, highlighting the pivotal role of dynamic elastic response in concrete's mechanical behavior. Furthermore, the findings indicated slight prediction deviations in cases involving samples with a high Poisson's ratio. This work illuminates the potential for accurate compressive strength prediction by leveraging concrete's dynamic response, particularly flexural and torsional modes, thereby opening avenues for research into concrete compressive strength without direct consideration of sample ingredients.

Non-destructive degradation assessment of GFRP beams subjected to hygrothermal ageing

This work used free vibration tests based on impulse excitation technique and experimental modal analysis using an impact hammer and an accelerometer to assess the local and global effects of the hygrothermal ageing of GFRP specimens exposed to salt-spray environment at 35°C and 60°C over a period of 136 days. Through the change in elastic properties, fifteen natural frequencies and damping ratios, the effects of degradation are associated with reductions in elastic properties and natural frequencies and an increase in damping ratios. In turn, the increase in elastic properties and natural frequencies – associated with a reduction in damping ratios – is mainly attributed to the post-curing effect.