Resonances in 1-3 piezocomposite rings

Lead zirconate titanate (PZT)/epoxy 1–3 composite rings with PZT volume fractions ø ranging from 0.82 to 0.94 are fabricated, and their resonance characteristics are studied. These composite rings have sufficiently small epoxy width (∼ 77 μm) and can be treated as effective homogeneous media in which stopband resonances are not observed in the frequency band of interest (< 4 MHz). A mode coupling theory is applied to predict the longitudinal-thickness fH and lateral fL mode resonances of PZT elements inside the rings. By thinning the rings and by measuring the resonance peaks using an impedance analyzer, fH is observed to increase linearly with the decrease in element height while fL remains constant. When the height and width of the elements become comparable, mode coupling occurs. To avoid spurious modes being coupled to fH , the rings cannot be too thin in order to keep fH smaller than fL . In the lower frequency regime, they cannot be too thick to avoid coupling of fH with the wall-thickness fW and radial fR mode resonances. fW and fR are found to be independent of ring thickness but increase as Ø increases.

Milling operations are very common in manufacturing. Often it represents the last operation, determining the final product quality. Then an accurate mathematical model is important in order to design the cutting process, in terms of cutting process, and the geometry of the insert, for tool manufacturers. The finite element modeling (FEM) simulation permits the prediction of the cutting forces, stresses, and temperatures of the cutting process. The 2D FEM can be a reasonable approximation, where the deformation can be considered plain. For the milling operations, this assumption can be suitable if the depth of cut is much bigger than nose radius. But in the normal situation the insert has a complex geometry and the bidimensional model of the milling operation is not appropriate. The 3D FEM involves different element formulations, different remeshing algorithm, and different boundary conditions, so an independent approach is necessary. The approach followed in this paper is to model three-dimensionally the milling operation, considering the real geometry of the insert. The FEM simulation is carried out with a commercial code (3D DEFORM™). First the rheological model has been calibrated using OXCUT software, developed at the ERC/NSM, and a sensitivity analysis about friction model has been performed. Milling tests are conducted and the measured cutting forces are compared to finite element modeling results. The results show an acceptable agreement with experimental results in the range of cutting speed and feed rate considered.

P 221. Subject specific finite element models predict cortical excitation volumes generated by transcranial magnetic stimulation

The biomechanical properties of the cornea have a profound influence on its health and function. Rose bengal/green light corneal collagen cross-linking (RGX) has been proposed as an alternative to UV-A Riboflavin collagen cross-linking (UV-CXL) for treatment of keratoconus. However, the effects of RGX on the biomechanical properties of the cornea are not as well understood as UV-CXL. In this work, we demonstrate the feasibility of quantifying the viscoelasticity of the rabbit cornea before and after RGX using a noncontact method of phase-stabilized swept source optical coherence elastography (PhS-SSOCE) and finite element modeling (FEM). Viscoelastic FE models of the corneas were constructed to simulate the elastic wave propagation based on the OCE measurements. In addition, the effect of the fluid-structure interface (FSI) between the corneal posterior surface and aqueous humor on the elastic wave group velocity was also investigated. The effect of the FSI was first validated by OCE measurements and FEM simulations on contact lenses, and the OCE and FEM results were in good agreement. The Young’s modulus of the rabbit cornea before RGX was assessed as E=80 kPa, and the shear viscosity was η=0.40 Pa•s at an intraocular pressure (IOP) of 15 mmHg. After RGX, the Young’s modulus increased to E=112 kPa and shear viscosity decreased to η=0.37 Pa•s. Both the corneal OCE experiments and the FE simulations also demonstrated that the FSI significantly reduced the group velocity of the elastic wave, and thus, the FSI should be considered when determining the biomechanical properties of the cornea.

In this paper, two novel approaches, gradient-based and direct strain estimation techniques, are proposed for high-quality average strain imaging incorporating a cost function maximization. Stiffness typically is a continuous function. Consequently, stiffness of proximal tissues is very close to that of the tissue corresponding to a given data window. Hence, a cost function is defined from exponentially weighted neighboring pre- and post-compression RF echo normalized cross-correlation peaks in the lateral (for displacement estimation) or in both the axial and the lateral (for direct strain estimation) directions. This enforces a controlled continuity in displacement/strain and average displacement/strain is calculated from the corresponding maximized cost function. Axial stress causes lateral shift in the tissue. Therefore, a 1-D post-compression echo segment is selected by incorporating Poisson's ratio. Two stretching factors are considered simultaneously in gradient-based strain estimation that allow imaging the lesions properly. The proposed time-domain gradient-based and direct-strain-estimation-based algorithms demonstrate significantly better performance in terms of elastographic signal-to-noise ratio (SNRe), elastographic contrast-to-noise ratio (CNRe), peak signal-to-noise ratio (PSNR), and mean structural similarity (MSSIM) than the other reported time-domain gradient-based and direct-strain-estimation techniques in finite element modeling (FEM) simulation and phantom experiments. For example, in FEM simulation, it has been found that the proposed direct strain estimation method can improve up to approximately 2.49 to 8.71, 2.2 to 6.63, 1.5 to 5, and 1.59 to 2.45 dB in the SNRe, CNRe, PSNR, and MSSIM compared with the traditional direct strain estimation method, respectively, and the proposed gradient-based algorithm demonstrates 2.99 to 16.26, 18.74 to 23.88, 3 to 9.5, and 0.6 to 5.36 dB improvement in the SNRe, CNRe, PSNR, and MSSIM, respectively, compared with a recently reported time-domain gradient-based technique. The range of improvement as noted above is for low to high applied strains. In addition, the comparative results using the in vivo breast data (including malignant or benign masses) also show that the lesion size is better defined by the proposed gradient-based average strain estimation technique.

Mould correction for sheet-metal multi-step incremental air-bending forming based on close-loop control and FEM simulation

Bridge inspections typically involve complex measurement criteria and take a long time. This study proposes a simpler inspection method that assesses the performance of reinforced concrete bridge girder beams. The method relies on crack length correlation with beam performance using theoretical approaches, Finite Element Model (FEM) simulations, and experimental testing. A reinforced concrete beam model is used to simulate similar flexural behavior to that of actual bridge girders. The results show that cracks form when concrete stress exceeds rupture stress, usually at 8%-12% of the ultimate capacity. Cracks grow until the steel reinforcement yields, which happens around 80%-90% of the ultimate capacity. Experimental crack length data at ultimate capacity align closely with FEM simulations, with a ratio of 0.92. In contrast, the results differ significantly from the theoretical predictions, with a ratio of 1.54. The study introduces six performance levels for reinforced concrete beams, linking crack length to beam performance. These parameters will help estimate bridge girder performance through visual crack assessments.

Measurement of FRFs of coupled geared rotor system and the development of an accurate finite element model

Biomechanical modeling of the lateral decubitus posture during corrective scoliosis surgery

The swelling behavior of clay-sulfate rocks poses significant challenges in geotechnical engineering due to complex hydro-mechanical and chemical interactions. This study introduces a hybrid framework combining finite element modeling (FEM) with machine learning (ML) to efficiently analyze and predict the nonlinear behavior of swelling processes. We generated synthetic datasets representing swelling phenomena at the Staufen site, Germany, using a coupled hydro-mechanical FEM simulation in OpenGeoSys. A parametric analysis was conducted to systematically vary critical parameters, including Young's modulus, permeability, maximum swelling pressure, and air entry pressure, to capture the inherent uncertainty and variability of swelling processes. A constrained CatBoost ML model was trained on the FEM outputs to predict porosity, saturation, and displacement under varying hydro-mechanical conditions. Results demonstrate strong alignment between the ML surrogate and FEM simulations, achieving high accuracy while significantly reducing computational demands. Sensitivity analysis indicated the dominance of swelling pressure and Young's modulus in influencing swelling-induced deformation, while Monte Carlo simulations quantified prediction uncertainties. This contribution discusses the potential of integrating FEM with ML for site-specific risk assessment and mitigation planning in geotechnical engineering.

Finite element (FE) models are very efficient tools to study internal stresses in human structures that induce severe pressure sores. Unfortunately, methods currently used to generate FE models are not suitable for clinical application involving wheelchair users. A clinical-oriented method, based on calibrated-biplanar radiographs, was therefore developed to generate a subject-specific FE model of the buttocks in a non-weighted sitting position. The model was then used to analyze the stress distribution within the buttocks and compare two wheelchair seat cushions designs. Additional radiographs and pressure measurements in a weighted sitting position were acquired to validate the FE model experimentally. Results from the FE model were in good agreement with experimental data and related literature. An internal peak pressure of 45.3 kPa was observed while seated on a flat foam cushion, corresponding to an interface pressure of 23.6 kPa. Both pressures occurred underneath the ischial tuberosities. When compared to the flat foam cushion, the contoured foam cushion reduced internal and interface peak pressures by 18% and 33%, respectively. The method developed in this study has a great potential for clinical use. The FE model, by predicting realistic stress distributions, allows for the selection of a convenient wheelchair seat cushion.

Electrical impedance myography (EIM) is a recent technology to assess muscle health. As of today, the clinical application of EIM has been applied only to evaluate muscle condition using non-invasive surface electrodes in contact with the skin; however, intermediate tissues at the recording site introduce confounding artifacts which reduce the technique's performance as a biomarker of neuromuscular disorders (NMD). Here, we develop and test in humans a new approach using two concentric needles for intramuscular EIM recordings. First, we study the recording characteristics of dual concentric needle EIM via analytical models and finite element models (FEMs). Next, the validity of the models is verified by performing experiments on saline and agar phantoms. Finally, 8 subjects with various neuromuscular diseases were studied measuring tibialis anterior, biceps, deltoid, adductor pollicis brevis, first dorsal interosseous and flexor carpi radialis muscles. Analytical and FEM simulations are in good agreement with a maximum experimental discrepancy 8% and 9% using gauge needles 26 and 30, respectively. The inter-session reproducibility, as measured by the intraclass correlation coefficients for all muscles studied, was 0.926, which is comparable or exceeds the reproducibility of other well-established electrophysiological tests to assess muscle health. The reproducibility of the technique support future clinical validation of needle EIM for assessment of disease status, either as part of standard patient care or as biomarker measure in clinical trials. Needle EIM has the potential of becoming a valuable diagnostic tool to evaluate NMD in adult population.

The present study discusses the finite element modeling and simulation strategy of projectile impact on thin ductile target like aluminum. Ogive nose projectile was chosen to impact on aluminum target normally by velocities at and above the ballistic limit of the plate. Abaqus/Explicit finite element code was used to model the problem. To define the thermo-viscoplastic behavior of the metal target, Johnson-Cook flow stress was used in conjunction with damage initiation criterion to predict the complete perforation process. Further, Hillerborg’s damage evolution proposal, based on stress-displacement response, was followed to observe the damage response after the failure has initiated in the material. Various parameters, like choice of element size, hourglassing, aspect ratio of elements, etc. which plays an important role in the simulation, have been studied. The result obtained with the presented model is compared with the results from the literature, and good agreement between them was found.

The development of the plastic electronics industry has drawn great interest and inspired technology innovations in a broad area. This has stimulated the rapid development of flexible circuitry manufacturing technologies, including advances in conductive inks, printing technology and most importantly the novel curing technology - laser based curing (or Laser Direct Write). This has the ability to replace the conventional environmentally damaging and time consuming chemical etching method in current Printed Circuit Board (PCB) manufacturing.This work presented in this paper is an investigation into the Nd:YAG laser curing process at the wavelength of 532 nm of particulate silver inks. A mathematical approximation of key physical properties has been developed based on the presented experimental research for use in a finite element model (FEM) simulation. 532 nm has shown benefits in protecting the flexible substrate used from thermal damage, owing to the high transparency of the wavelength through the substrate material. In this paper, liquid-phase particulate silver ink tracks deposited on flexible substrates were irradiated by laser along the track geometry. Repetition of the laser beam scanning was found to produce a smooth and fully cured sample and further reduced the track’s electrical resistivity.The development of the plastic electronics industry has drawn great interest and inspired technology innovations in a broad area. This has stimulated the rapid development of flexible circuitry manufacturing technologies, including advances in conductive inks, printing technology and most importantly the novel curing technology - laser based curing (or Laser Direct Write). This has the ability to replace the conventional environmentally damaging and time consuming chemical etching method in current Printed Circuit Board (PCB) manufacturing.This work presented in this paper is an investigation into the Nd:YAG laser curing process at the wavelength of 532 nm of particulate silver inks. A mathematical approximation of key physical properties has been developed based on the presented experimental research for use in a finite element model (FEM) simulation. 532 nm has shown benefits in protecting the flexible substrate used from thermal damage, owing to the high transparency of the wavelength through the subst...

This study is to develop a methodology and model to analyze the built-in speakers induced structural acoustic vibration of hard disk drive (HDD) in Notebook PC. First, a structural finite element (FE) model is built for the notebook PC to be analyzed using ANSYS. This FE model is subsequently verified by experiments. Second, the effects of acoustically transmitted and structurally transmitted oscillating forces, induced by the speakers, acting on the HDD, are investigated by acoustic FE model (SYSNOISE) and structural FE model. The acoustic transmission effect on the vibration of HDD is also investigated by experiment, which shows that the simulation results have a good agreement with experimental results. Finally, the effects of stiffness and damping ratio of the HDD supporters on the vibration of HDD are analyzed by the verified FE model.