Dynamic Stiffness Measurements Research Articles

Relationship between morphometric and mechanical properties of superficial lumbosacral soft tissue layers in healthy young adults.

Introduction: It is commonly considered that myotonometry is a non-invasive method capable of quantifying linear elastic and viscoelastic properties of the myofascial tissue through the application of a weak mechanical impulse to the surface of the skin. However, before the impulse can reach the myofascial tissue, it must cross more superficial tissues such as the skin and subcutaneous tissue (ST). All these superficial tissues have different distributions and organizations of structural components. Therefore, the study aimed to examine the potential relationships between the mechanical and morphometric properties of various superficial soft tissues surrounding the lumbar multifidus muscle (LM). Methods: Myotonometric measurements of dynamic stiffness, logarithmic decrement, and creep, and ultrasonographic measurements of thickness and echogenicity of cutaneous, subcutaneous, perimuscular tissue, and LM were obtained from 50 healthy individuals in the resting prone position and during contralateral arm lift. Results: The most important findings were that in both the relaxed and contracted LM state, the dynamic stiffness strongly negatively (r = -0.69; p < 0.001 in relaxation, r = -0.83; p < 0.001 in contraction) and creep strongly positively (r = 0.79; p < 0.001 in relaxation, r = 0.85; p < 0.001 in contraction) correlated with the thicknesses of the ST. Similar but weaker correlations were noticed between both these measures and the perimuscular tissue thickness. Elasticity was uncorrelated to the thicknesses of the tissues. With LM contraction (change from the relaxed to contracted state), the relative increase in dynamic stiffness was correlated with the relative decrease in dermis (r = -0.51; p < 0.001) and ST (r = -0.47; p = 0.001) thickness, and with the relative increase in LM (r = 0.36; p = 0.010) thickness. Moreover, the relative decrease (thinning) in the ST thickness was correlated with the relative increase in logarithmic decrement (i.e., decrease in soft tissue elasticity, r = -0.37, p = 0.011). The mechanical properties of the soft tissues were not related to their echogenicity. Discussion: In conclusion, the thicker the subcutaneous and perimuscular layers, the lesser the stiffness and the greater the time-dependent deformation to the external force of the tissues surrounding the LM during its relaxation and isometric contraction. Moreover, the greater the thinning of the ST and the thickening of the LM during its contraction, the higher the increase in lumbosacral tissue stiffness and the decrease in elasticity. Therefore, one should consider the thickness of the ST before planning or analyzing the outcomes of myotonometric or other external biomechanical measurements to avoid drawing the wrong conclusions about the mechanical properties of the myofascial tissue.

Feasibility investigation of sinusoidal radial excitation force loading of high-speed motors

Permanent magnet generators have been found most suitable for sustainable energy conversion owing to their relatively simple design, compact structure and high efficiency. To utilize high power density of permanent magnets, this paper integrates a novel function in the permanent magnet generators. Continuous monitoring dynamic stiffness of high-speed rotors and safeguarding the rotor from failure is made possible through a compact double winding stator. In this way, the reliability and maintainability of the generator can be improved and the maintenance costs can be reduced. First, models of the double-winding generator as well as the rotor system are established. Second, the needed radial force for dynamic stiffness measurement is investigated, including rotation force vector and constant direction excitation force. Two control methods without rotor angle position feedback, double frequency current injection and sensorless loading method, are discussed. Then, loading capacity of the loading methods and error of dynamic stiffness at different operating frequencies is analyzed. Finally, experiments at different rotation speeds and loading force frequencies are performed. The results verify the feasibility of the loading methods, the prototype can effectively produce a wide frequency range (0.02–2.5 kHz) of radial force while operating at high-speed (up to 60krpm).

Characterization and Modelling of Mounts for Electric Powertrains

&lt;div class="section abstract"&gt;&lt;div class="htmlview paragraph"&gt;The topic of this paper is to deal with the filtering of medium and high frequency excitations generated by electrified powertrains. It is now recognized that the whining noise generated by the electromagnetic forces and/or the meshing process of the transmission can propagate to the car-body through the rubber mounts. In the design phase, the prediction of the structure borne contribution requires a good knowledge of the dynamic behavior of the rubber mounts. The main issue is the stiffness of the mounts which cannot be modeled as pure springs. In fact, the dynamic behavior of a mount is governed by the material rheology and its internal resonances. The work presented in this paper proposes a simulation workflow for the rubber mounts dynamic model and a methodology for the dynamic stiffness measurement including the sensitivity with the preload and with the amplitude of the excitation. Finally, experimental and digital data are compared to assess the simulation method.&lt;/div&gt;&lt;/div&gt;

Development of a miniature dynamic stiffness measurement prototype toward structural health monitoring of space inflatable structures

Inflatable structures are increasingly used in aerospace engineering. However, the space survivability and durability of such structures are of particular concern due to material aging in space environment and unexpected external impact threats. Thus, it is very urgent to in-situ monitor and assess structural health condition for space inflatable structures. Since inflatable structures are often lightweight, large-sized and flexible, their low-frequency vibration response contains much information about structural health condition. To facilitate in-situ structural health monitoring of space inflatable structures, this paper developed a miniature low-frequency dynamic stiffness measurement prototype. The prototype is capable of generating two channels of swept-sine excitation signals, and concurrently acquiring six channels of response signals. Recorded data is communicated and downlinked from the host spacecraft to the ground, and then the dynamic stiffness is derived to determine structural health condition. To validate the developed prototype, two simulated inflatable space structures are fabricated and tested, including an inflatable boom and an inflatable torus, and then Macro-Fiber Composite transducers are attached on two specimens as actuators and sensors in tests. Experimental studies show that the prototype functions well and the outputted results are consistent with that measured by large-bulked commercial ground devices. Additionally, the multi-channel functionality of the prototype is verified by carrying out the multi-input multi-output test. In summary, the prototype features small size, light weight, and low power consumption, which has the potential for future space applications.

Dynamic indentation measurements on amorphous materials

Abstract An alternative indentation method to study materials that present a time-dependent behaviour (e. g. viscoelasticity) is the dynamic stiffness measurement technique, which provides fast and accurate values of the elastic properties through the calculation of the storage modulus (related to the elastic recovery of the material), and the loss modulus (related to the damping), using indentation cycles with oscillating load or displacement. We have made dynamic measurements on four amorphous materials (CNx, amorphous carbon, fused silica and polypropylene). Such materials have a relatively low density compared to crystalline materials of similar composition and atoms are able to move into internal free space during deformation. The results suggest that all the amorphous materials have a similar time-dependant behaviour associated with the restrictions to movement of atoms (or chains) by neighbouring atoms in the amorphous structure.

Advanced Characterisation of Soft Polymers under Cyclic Loading in Context of Engine Mounts.

The experimental investigation of viscoelastic behavior of cyclically loaded elastomeric components with respect to the time and the frequency domain is critical for industrial applications. Moreover, the validation of this behavior through numerical simulations as part of the concept of virtual prototypes is equally important. Experiments, combined measurements and test setups for samples as well as for rubber-metal components are presented and evaluated with regard to their industrial application. For application in electric vehicles with relevant excitation frequencies substantially higher than by conventional drive trains, high-frequency dynamic stiffness measurements are performed up to 3000 Hz on a newly developed test bench for elastomeric samples and components. The new test bench is compared with the standard dynamic measurement method for characterization of soft polymers. A significant difference between the measured dynamic stiffness values, caused by internal resonance of the bushing, is presented. This effect has a direct impact on the acoustic behavior of the vehicle and goes undetected by conventional measurement methods due to their lower frequency range. Furthermore, for application in vehicles with internal combustion engine, where the mechanical excitation amplitudes are significantly larger than by vehicles with electric engines, a new concept for the identification of viscoelastic material parameters that is suitable for the representation of large periodic deformations under consideration of energy dissipation is described. This dissipated energy causes self-heating of the polymer and leads to the precocious aging and failure of the elastomeric component. The validation of this concept is carried out thermally and mechanically on specimen and component level. Using the approaches developed in this work, the behavior of cyclically loaded elastomeric engine mounts in different applications can be simulated to reduce the time spent and save on the costs necessary for the production of prototypes.

Analysis and experimental study on servo dynamic stiffness of electromagnetic linear actuator

The electromagnetic linear actuator has been widely used in new energy vehicles, aerospace, and intelligent robots in recent years. However, its application especially in high-precision servo control system is limited due to the disadvantage of insufficient dynamic stiffness. In this paper, a theoretical model of servo dynamic stiffness of electromagnetic linear actuator was established through analyzing the definition of servo dynamic stiffness. And the influence of system parameters of the electromagnetic linear actuator on servo dynamic stiffness was studied based on the frequency analysis of the Bode diagram and the mathematical simulation of MATLAB/Simulink. In addition, an innovative servo dynamic stiffness measurement method for electromagnetic linear actuators was established in this paper. The experimental and simulation results showed that the larger the coil resistance and the mover’s mass, the smaller the servo dynamic stiffness and the worse the anti-disturbance ability of the system; the greater the coil inductance and force-current constant, the greater the servo dynamic stiffness, and the better the system's anti-disturbance ability. The experimental results were consistent with the theoretical analysis results. This study provides a reference for improving the dynamic characteristics of electromagnetic linear actuator and paves the way for its practical application in the high precision systems.

Dynamic Stiffness Analysis and Experimental Verification of Axial Magnetic Bearing Based on Air Gap Flux Variation in Magnetically Suspended Molecular Pump

Current and displacement stiffness are important parameters of axial magnetic bearing (AMB) and are usually considered as constants for the control system. However, in actual dynamic work situations, time-varying force leads to time-varying currents and air gap with a specific frequency, which makes the stiffness of appear decrease and even worsens control performance for the whole system. In this paper, an AMB dynamic stiffness model considering the flux variation across the air gap due to frequency is established to obtain the accurate dynamic stiffness. The dynamic stiffness characteristics are analyzed by means of the dynamic equivalent magnetic circuit method. The analytical results show that the amplitude of current and displacement stiffness decreases with frequency increasing. Moreover, compared with the stiffness model without considering the variation of flux density across the air gap, the improved dynamic stiffness results are closer to the actual results. Through the dynamic stiffness measurement method of AMB, experiments of AMB in magnetically suspended molecular pump (MSMP) are carried out and the experimental results are consistent with theoretical analysis results. This paper proposes the dynamic stiffness model of axial magnetic bearing considering the variation of flux density across the air gap, which improves the accuracy of the AMB stiffness analysis.

Stress−strain curves and derived mechanical parameters of P91 steel from spherical nanoindentation at a range of temperatures

This work compares different measurement and analysis protocols of spherical nanoindentation tests performed at different temperatures on a ferritic/martensitic P91 grade steel, in order to derive meaningful indentation stress−strain curves (ISSC) and estimate material parameters such as indentation modulus, yield strength, work hardening exponent and ultimate tensile strength. Quasi-static multi-cycle and dynamic continuous stiffness measurement indentation using a spherical indenter with a tip radius of 20 μm has been carried out from room temperature to 600 °C in vacuum in a set-up where thermal drift has been minimised by an active surface referencing system and accurate temperature stabilization in the contact area. The methodology used to determine the contact radius is critical to achieve consistent results. The application of different combinations of definitions of contact radius and indentation-induced strain to nanoindentation data obtained by the quasi-static and dynamic measurements reveals that Tabor's approach combined with a geometrically determined contact radius best represents the ISSC relationship for the P91 characterized. This method is then extended to predict the high temperature tensile properties of the steel from nanoindentation results.

Fracture toughness testing at the micro-scale − The effect of the unloading compliance method

Fracture mechanical testing of micro-sized cantilevers was conducted in order to quantify the fracture toughness and behaviour of the (1 0 0)[0 1¯ 1] crack system in α-iron at 37.5 K, 133 K and room temperature. The cantilevers are outside the range of validity for linear-elastic fracture mechanics due to the small sample size, rendering the cantilevers out of bounds in relation to linear-elastic fracture mechanics and classical fracture mechanics. Elastic-plastic fracture mechanics has therefore been applied to determine the conditional fracture parameters KQC and JQC. A comparison between cantilevers continuously loaded with corrected dynamic stiffness measurements and another data set of cantilevers tested with the unloading compliance method has been made. A distinct difference in determined fracture toughness and crack behaviour was identified, indicating potential concerns when applying the unloading compliance method at the micro-scale on ductile materials.

Accuracy of genomic prediction of shell quality in a White Leghorn line

Several genomic methods were applied for predicting shell quality traits recorded at 4 different hen ages in a White Leghorn line. The accuracies of genomic prediction of single-step GBLUP and single-trait Bayes B were compared with predictions of breeding values based on pedigree-BLUP under single-trait or multitrait models. Breaking strength (BS) and dynamic stiffness (Kdyn) measurements were collected on 18,524 birds from 3 consecutive generations, of which 4,164 animals also had genotypes from an Affymetrix 50K panel containing 49,591 SNPs after quality control edits. All traits had low to moderate heritability, ranging from 0.17 for BS to 0.34 for Kdyn. The highest accuracies of prediction were obtained for the multitrait single-step model. The use of marker information resulted in higher prediction accuracies than pedigree-based models for almost all traits. A genome-wide association study based on a Bayes B model was conducted to detect regions explaining the largest proportion of genetic variance. Across all 8 shell quality traits analyzed, 7 regions each explaining over 2% of genetic variance and 54 regions each explaining over 1% of genetic variance were identified. The windows explaining a large proportion of genetic variance overlapped with several potential candidate genes with biological functions linked to shell formation. A multitrait repeatability model using a single-step method is recommended for genomic evaluation of shell quality in layer chickens.

Dynamic Stiffness Analysis and Measurement of Radial Active Magnetic Bearing in Magnetically Suspended Molecular Pump

Current stiffness and displacement stiffness are two important parameters of radial active magnetic bearing (RAMB) that are generally considered as constants in a control system. However, such presumption may lead to the probable degradation of the control performance of the RAMB system when the perspective that the current and displacement stiffness should be variable due to variations in the speed. On this regard, a structure analysis and stiffness measurement method based on non-variable stiffness would not be feasible for RAMB under high-speed conditions. This paper presented an analysis of the dynamic stiffness characteristics of RAMB by means of a dynamic equivalent magnetic circuit method and laid out a comparison between the results of the theoretical analysis and the simulation results of finite element method. In particular, a novel dynamic stiffness measurement method of RAMB under high-rotation frequency was introduced. Results of experiments on the dynamic stiffness of RAMB demonstrated an excellent agreement with the theoretical research and the finite element analysis results, thereby verifying the rationality of the discussed dynamic stiffness characteristics. Practically, the proposed measurement method of RAMB dynamic stiffness provides an accurate analysis for the dynamic stiffness and contributes inspiring research significance for the dynamic properties of RAMB.

Measurements of the high frequency dynamic stiffness of railway ballast and subgrade

Conventional railway tracks are laid in a layer of crushed stone known as ballast which contributes to the resilience of the track support. Beneath it is the subgrade which also has a considerable influence on the track support stiffness. Although quasi-static measurements of track stiffness are reasonably common, the dynamic stiffness at higher frequencies is required for noise and vibration modelling. Here, a distinction is made between the dynamic stiffness of the ballast layer itself and the dynamic support stiffness which includes the underlying ground. The dynamic transfer stiffness of a ballast layer is required for ground vibration and bridge noise predictions. Two different methods for measuring this are presented, one in the laboratory and the other in the field. The laboratory method is limited to a maximum frequency of about 600 Hz due to limitations of the test rig. The field measurement, which relies on identifying the wavespeed within the medium, gives results up to 2 kHz. These methods give broadly consistent results, with a stiffness per rail seat for a 300 mm thick ballast layer of approximately 300–500 MN/m, increasing in proportion to the square root of the preload, and a damping loss factor in the range 0.15–0.3. The corresponding Young's modulus is between 200 and 700 MPa, depending on the preload. The dynamic stiffness increases above about 300 Hz with a first peak due to standing wave effects occurring at about 700 Hz. The dynamic support stiffness beneath the sleeper, on the other hand, is required for rolling noise modelling. This has been measured using two methods: a direct method for frequencies 50–500 Hz and an indirect method based on a modal analysis of a sleeper embedded in the ballast. A clear shift in natural frequencies is seen which is associated with the support stiffness. This support stiffness is strongly frequency-dependent, with the value per rail seat increasing from about 100 to 200 MN/m at 100 Hz to 2000 MN/m at 1 kHz. The support damping corresponds to a loss factor of around 1 for frequencies above 200 Hz, or a damping coefficient of 100–200 kN/m per rail seat. This damping is due to the radiation of energy into the ground rather than internal losses in the ballast. It strongly affects the modal damping of the sleeper and thus its radiated noise. The dynamic support stiffness increases roughly in proportion to the cube root of the preload. Comparison with a finite element model indicates that the underlying ground is responsible for the support stiffness and damping at low frequencies. However, above about 500 Hz it is independent of the ground and is only affected by the ballast layer. The results from the finite element model imply behaviour similar to a viscous damper. The sleeper vibration obtained using either a viscous damping or a constant loss factor is similar.

Non-invasive Measurement of Dynamic Myocardial Stiffness Using Acoustic Radiation Force Impulse Imaging

Myocardial stiffness exhibits cyclic variations over the course of the cardiac cycle. These trends are closely tied to the electromechanical and hemodynamic changes in the heart. Characterization of dynamic myocardialstiffness can provide insights into the functional state of the myocardium, as well as allow for differentiation between the underlying physiologic mechanisms that lead to congestive heart failure. Previous work has revealed the potential of acoustic radiation force impulse (ARFI) imaging to capture temporal trends in myocardial stiffness in experimental preparations such as the Langendorff heart, as well as on animals in open-chest and intracardiac settings. This study was aimed at investigating the potential of ARFI to measure dynamic myocardial stiffness in human subjects, in a non-invasive manner through transthoracic imaging windows. ARFI imaging was performed on 12 healthy volunteers to track stiffness changes within the interventricular septum in parasternal long-axis and short-axis views. Myocardial stiffness dynamics over the cardiac cycle was quantified using five indices: stiffness ratio, rates of relaxation and contraction and time constants of relaxation and contraction. The yield of ARFI acquisitions was evaluated based on metrics of signal strength and tracking fidelity such as displacement signal-to-noise ratio, signal-to-clutter level, temporal coherence of speckle and spatial similarity within the region of excitation. These were quantified using the mean ARF-induced displacements over the cardiac cycle, the contrast between the myocardium and the cardiac chambers, the minimum correlation coefficients of radiofrequency signals and the correlation between displacement traces across simultaneously acquired azimuthal beams, respectively. Forty-one percent of ARFI acquisitions were determined to be “successful” using a mean ARF-induced displacement threshold of 1.5 μm. “Successful” acquisitions were found to have higher (i) signal-to-clutter levels, (ii) temporal coherence and (iii) spatial similarity compared with “unsuccessful” acquisitions. Median values of these three metrics, between the two groups, were measured to be 13.42dB versus 5.42dB, 0.988 versus 0.976 and 0.984 versus 0.849, respectively. Signal-to-clutter level, temporal coherence and spatial similarity were also found to correlate with each other. Across the cohort of healthy volunteers, the stiffness ratio measured was 2.74 ± 0.86; the rate of relaxation, 7.82 ± 4.69/s; and the rate of contraction, –7.31±3.79 /s. The time constant of relaxation was 35.90 ± 20.04ms, and that of contraction was 37.24 ± 19.85ms. ARFI-derived indices of myocardial stiffness were found to be similar in both views. These results indicate the feasibility of using ARFI to measure dynamic myocardial stiffness trends in a non-invasive manner and also highlightthe technical challenges of implementing this method in the transthoracic imaging environment.

Efficacy of high-performance ceiling systems

A current approach to try to solve a low frequency impact-induced structure-borne noise issue in lightweight woodframe buildings has been the application of a resilient ceiling suspended by one-inch deflection spring hangers. While this system has been lab tested it was only compared to an assembly with no isolation in which the gypsum board was directly attached to the bottom of the joists. The authors have repeated the testing of one-inch deflection ceiling hangers in the same lab but this time they compared it to the same isolators with the springs removed, standard resilient sound clips and other ceiling isolation systems. Relative performance differences of the isolation systems will be presented along with transmissibility, static stiffness, dynamic stiffness and damping measurements of each isolation element. A few theories as to why the systems behave the way they do will also be presented.

Potential of microwave scanning for determining density and tension strength of four European hardwood species

As an effect of changing forest management—away from softwood monocultures to more robust mixed stands—the availability of hardwood on the European timber market increases. Thus, a more diversified spectrum of hardwood products is required between the established uses in furniture and energy production. Glued timber products are a promising option in this respect. One important prerequisite for efficiently producing glued hardwood products is to establish hardwood strength grading. To this end, the current paper explored the potential of microwave scanning, stand-alone or combined with the measurement of dynamic stiffness, to estimate the tension strength of ash, beech, sweet chestnut and oak lamellas. In this preliminary study, combining microwave and dynamic stiffness measurement showed much potential for hardwood strength grading for all four species; for beech and sweet chestnut, coefficients of determination ( $${r}^{2}$$ ) beyond 60% could be achieved, which is on a level with established softwood grading principles. For ash and oak, $${r}^{2}\approx 45\%$$ was observed, which is acceptable for machine strength grading. The paper also considered measuring density using microwaves. Such a density measurement was found to be as accurate for hardwoods as for softwoods.

Static and dynamic stiffness measurements with Opalinus Clay

ABSTRACTIn this work, an experimental study was carried out with the aim of reconciling static and dynamic stiffness of Opalinus Clay. The static and dynamic stiffness of core plugs from a shaly and a sandy facies of Opalinus Clay were characterized at two different stress states. The measurements included undrained quasi‐static loading–unloading cycles from which the static stiffness was derived, dynamic stiffness measurement at seismic frequencies (0.5–150 Hz) and ultrasonic velocity measurements (500 kHz) probing the dynamic stiffness at ultrasonic frequencies. The experiments were carried out in a special triaxial low‐frequency cell. The obtained results demonstrate that the difference between static and dynamic stiffness is due to both dispersion and non‐elastic effects: Both sandy and shaly facies of Opalinus Clay exhibit large dispersion, that is, a large frequency dependence of dynamic stiffness and acoustic velocities. Especially dynamic Young's moduli exhibit very high dispersion; between seismic and ultrasonic frequencies they may change by more than a factor 2. P‐wave velocities perpendicular to bedding are by more than 200 m/s higher at ultrasonic frequencies than at seismic frequencies. The static undrained stiffness of both sandy and shaly facies is strongly influenced by non‐elastic effects, resulting in significant softening during both loading and unloading with increasing stress amplitude. The zero‐stress extrapolated static undrained stiffness, however, reflects the purely elastic response and agrees well with the dynamic stiffness at seismic frequency.

Optimization of Servo Parameters for Enhanced Dynamic Behavior of Direct Feed System with Hybrid FEM and PLS Regression

Optimal servo dynamics of a direct feed system driven by linear motor play an important role in improvement of its dynamic behavior and the precision of its processing products. An optimization method for enhancement of the dynamics of the drive system is proposed with hybrid FEM and PLS regression. Dynamic stiffness spectrogram of the servo system, also as optimization performance evaluation, is applied to obtain its resonance frequency. A force pulse excitation-based dynamic stiffness measurement scheme is introduced to acquire the spectrum diagram. For simulation of the stiffness characteristic, a FE model of the drive mechanism is developed with dynamic conjunctions, which parameters are considered to be related to the servo parameters. A relationship model between the stiffness variables of the conjunctions and the servo parameters is established with PLS regression. Based on the regression equation, the optimization model is constructed for the dynamics enhancement. To validate the feasibility of the scheme, an experiment was conducted on a domestic test rig. The results show that the method can effectively extend non-resonant frequency and improve the dynamics with 10.4 Hz higher in first-order modal frequency and 6.7 Hz higher in second-order than the corresponding results of the samples in the mean value from random tests.

Real-time shear wave elastography (SWE) assessment of short- and long-term treatment outcome in Budd-Chiari syndrome: A pilot study.

PurposeThe first aim of this study was to analyze the relationships between liver stiffness measurement, hepatic venous pressure and liver fibrosis. The second aim was to demonstrate the utility of real-time shear wave elastography for evaluation of Budd-Chiari syndrome patients before and after balloon hepatic venous angioplasty.Materials and methodsA total of 32 patients with Budd-Chiari syndrome slated for successful balloon angioplasty met the inclusion and exclusion criteria. Shear wave elastography was used to generate dynamic liver stiffness measurement 2 days before angioplasty and 2 days, 3 months, and 6 months after angioplasty. Hepatic venous pressures were measured during balloon angioplasty. Correlations among liver stiffness, hepatic venous pressure, and fibrosis were assessed.ResultMean liver stiffness was 35.17 ± 10.60 kPa, 20.15 ± 5.47 kPa, 15.36 ± 4.34 kPa and 15.68 ± 5.58 kPa at baseline and 2 days, 3 months, and 6 months after angioplasty, respectively. Liver stiffness measured at 2 days and 3 months after angioplasty was significantly decreased (P < 0.001); liver stiffness measured at 6 months after angioplasty was not significantly different from that measured at 3 months after angioplasty (P = 0.636). Analysis of liver stiffness measurement and hepatic venous pressure before balloon angioplasty yielded a coefficient of correlation r = 0.701 (P < 0.001). Before and 2d after angioplasty, liver stiffness measurement did not correlated with fibrosis (r = − 0.170, P = 0.22), (r = 0.223, P = 0.220), respectively, while the LSM difference before and 2 days after angioplasty negatively correlated with stiffness severity (r = − 0.502, P = 0.003). Liver stiffness measured at 2 days and 3 months after angioplasty was significantly decreased (P < 0.001), remaining stable at 3 months, though still in the cirrhotic range.ConclusionsThe liver stiffness of Budd-Chiari syndrome patients, measured by shear wave elastography, decreased considerably after hepatic venous recanalization, and significantly correlated with hepatic venous pressure though not with degree of fibrosis. Shear wave elastography may be effective in monitoring short- and long-term treatment outcomes in Budd-Chiari syndrome.

Measurement of the spindle system dynamic stiffness of a machine tool using a biaxial non-contact loading device

Measurement of the spindle system dynamic stiffness of a machine tool using a biaxial non-contact loading device