Evaluation Of Stiffness Research Articles

Evaluation of Longitudinal Equivalent Bending Stiffness of Shield Tunnel with Residual Jacking Force

Existing tunnels are often subject to longitudinal bending when undercrossing tunnelling. It is of significance to more accurately evaluate the longitudinal equivalent bending stiffness (LEBS) of the existing tunnel within the influential zone. A new analytical method is proposed for the LEBS of tunnel segmental lining joints with consideration of incorporating combined action of residual jacking force and bending moment. The solution can degenerate into a special case with no residual jacking force, which agrees well with other classical solutions and validates the model and solutions. Sensitivity analyses are carried out for the bending moment, tunnel geometry, tensile stiffness of bolts and concrete grade on the LEBS, and effective ratio of the LEBS considering residual jacking force. The LEBS and the effective ratio of LEBS increase nonlinearly as an S-curve with the residual jacking force and decrease with an increasing bending moment. The results show that the LEBS of the shield tunnel is variable stiffness, which exhibits a significant nonlinearity. The maximum increment of the LEBS reaches 80.3% as the ring width increases from 1 m to 2 m, and the LEBS of the shield tunnel increases by approximately 1.3 × 107 kN·m2 for every 4-bolt added. The influential order on the LEBS of shield tunnels is the tunnel diameter > lining thickness > bolts diameter > ring width > the number of bolts > elastic modulus of bolts. When the effective ratio of LEBS is more than 0.85, it does not change with the ring width, lining thickness, tensile stiffness of bolts, and concrete grade. The response characteristics of the tunnel parameters on the LEBS, considering the residual jacking force, could provide a theoretical basis for the design and deformation control of shield tunnels when undercrossing tunnelling.

Ultrasound stiffness and perfusion markers correlate with tumor volume responses to immunotherapy

Immunotherapy has revolutionized the treatment of dozens of cancers and became a standard of care for some tumor types. However, the majority of patients do not benefit from current immunotherapeutics and many develop severe toxicities. Therefore, the identification of biomarkers to classify patients as likely responders or non-responders to immunotherapy is a timely task. Here, we test ultrasound imaging markers of tumor stiffness and perfusion. Ultrasound imaging is non-invasive and clinically available and can be used both for stiffness and perfusion evaluation. In this study, we employed syngeneic orthotopic models of two breast cancers, a fibrosarcoma and a melanoma, to demonstrate that ultrasound-derived measures of tumor stiffness and perfusion (i.e., blood volume) correlate with the efficacy of immune checkpoint inhibition (ICI) in terms of changes in primary tumor volume. To modulate tumor stiffness and perfusion and thus, get a range of therapeutic outcomes, we employed the mechanotherapeutic tranilast. Mechanotherapeutics combined with ICI are advancing through clinical trials, but biomarkers of response have not been tested until now. We found the existence of linear correlations between tumor stiffness and perfusion imaging biomarkers as well as strong linear correlations between the stiffness and perfusion markers with ICI efficacy on primary tumor growth rates. Our findings set the basis for ultrasound biomarkers predictive of ICI therapy in combination with mechanotherapeutics. Statement of significanceHypothesis: Monitoring Tumor Microenvironment (TME) mechanical abnormalities can predict the efficacy of immune checkpoint inhibition and provide biomarkers predictive of response. Tumor stiffening and solid stress elevation are hallmarks of tumor patho-physiology in desmoplastic tumors. They induce hypo-perfusion and hypoxia by compressing tumor vessels, posing major barriers to immunotherapy. Mechanotherapeutics is a new class of drugs that target the TME to reduce stiffness and improve perfusion and oxygenation. In this study, we show that measures of stiffness and perfusion derived from ultrasound shear wave elastography and contrast enhanced ultrasound can provide biomarkers of tumor response.

The association between brachial-ankle pulse-wave velocity and adverse cardiovascular events in 5719 community participants a prospective cohort study.

The brachial-ankle pulse-wave velocity (baPWV) is regarded as the gold standard in the evaluation of arterial stiffness. Its prognostic significance for major adverse cardiovascular events (MACE) has been demonstrated. However, the factors influencing the association between baPWV and MACE risk have not been determined. In this study, we investigated the association of baPWV and MACE risk and whether it is affected by the risk factors for different cardiovascular diseases (CVDs). This was a prospective cohort study that initially enrolled 6850 participants from 12 communities in Beijing. The participants were divided into three subgroups according to their baPWV values. The primary outcome was the first occurrence of MACE, defined as hospitalization from cardiovascular diseases, first occurrence of a nonfatal myocardial infarction, or nonfatal stroke. Cox proportional hazards regression and restricted cubic spline analyses were used to examine the association between baPWV and MACE. The effect of CVD risk factors on the relationship between baPWV and MACE was explored in subgroup analyses. The final study population consisted of 5719 participants. During a median follow-up of 34.73 months, MACE occurred in 169 participants. The restricted cubic spline analysis indicated a positive linear relationship between baPWV and MACE risk. After adjustment for cardiovascular risk factors, the hazard ratio (HR) for MACE risk per SD increase in baPWV was 1.272 [95% confidence interval (CI): 1.149-1.407, P < 0.001], and the HR for MACE in the high-baPWV vs. the low-baPWV group was 1.965 (95% CI: 1.296-2.979, P = 0.001). Adding baPWV to the conventional cardiovascular risk factors significantly improved the model's prediction performance and the net reclassification (NRI) [NRI: 0.379 (95% CI: 0.072-0.710), P = 0.025] in MACE discrimination. However, in the subgroup analysis, two CVD risk factors, stable coronary heart disease and hypertension, showed significant interaction effects (Pinteraction both < 0.05). This result indicated that the effect of CVD risk factors must be taken into account when assessing the relationship between baPWV and MACE. baPWV is a potential marker to improve the identification of MACE risk in the general population. A positive linear correlation was firstly determined between baPWV and MACE risk, but it may not be valid in participants with stable coronary heart disease and hypertension.

Practical Method to Evaluate the Stiffness of Fractured Radius.

Distal radius fractures (DRFs) are one of the most common fractures of the upper extremity system. To evaluate the performance of DRF treatments, the construct (i.e., a DRF fixed by an implant) was compressed at the distal radius in the axial direction to evaluate the compressive stiffness. In previous studies, various constructs of both cadaveric and synthetic radii have been proposed for biomechanical testing for DRF. Unfortunately, high deviations of the measured stiffness have been reported across the literature, which may relate to the inconsistency of applied mechanical actions (i.e., the tested radii may under various combinations including compression, bending, and shear). In the present study, a biomechanical apparatus and an experimental procedure were proposed for the biomechanical testing of radii under pure compression. After the biomechanical tests of synthetic radii, it was found that the standard deviation of stiffness was significantly lower than that in previous studies. Thus, the biomechanical apparatus and the experimental procedure were proven to be a practical method for the evaluation of radii stiffness.

“The impact of statins addind to the fixed combination antihypertensive therapy on the arterial stiffness in patients with moderate and severe hypertension"

AimThe objective of this study was the evaluation of the arterial stiffness, which changed after adding statins to the guidelines recommended dual or triple fixed combination antihypertensive therapy in patients with moderate to severe arterial hypertension. Materials and methodsIt was included 99 patients in total being diagnosed with moderate and severe arterial hypertension (2nd and 3rd stages of arterial hypertension) without diabetes. Those patients were divided into 2 groups. The first group (n = 59) was assigned to the dual or triple fixed combination antihypertensive therapy plus including statins.Patients in the second group (n = 40) received only the dual or triple fixed combination antihypertensive treatment following the recommended guidelines without any statins. The CAVI index was performed in order to measure in all participants before and at the end of the follow-up period. Furthermore, the Office (Clinic BP) Blood Pressure (BP) was monitored in assigned participants as well as the Ambulatory Blood Pressure Monitoring (ABPM). The laboratory investigations also took place such as the standard blood test, the urine and biochemistry analysis and the estimated Carotid Intima-Media Thicknesses with Ultrasound. The study-duration was 6 months. ResultsOffice BP and ABPM had decreased significantly and equally in both treatment groups. The total cholesterol (TC) and LDL cholesterol had decreased significantly in the statin group on 1,76 mmol/l (30%, p < 0,05) and 1,51 mmol/l (41%, p < 0,05) respectively. In the group without statin therapy, there was no changes in the level of TC and LDL cholesterol. In the group without statins, it was noted a significant decrease in the level of BP, however, the CAVI index level was shown the growth to +0,9 units on the right side and +1,0 units on the left.In the group without statin's treatment, the CAVI index was changed from 7.73 ± 0.17/7.62 ± 0.19 units to 8.63 ± 0.22/8.62 ± 0.12 units on the right/left site after treatment (p < 0,05). It means there was an increase in the stiffness of the arterial wall in terms of cardio-vascular index CAVI in the group without added statin after 6 months of the therapy. In the group with added statin after 6 months of the therapy, the CAVI had not have any changes. It can be seen from the observed figures: the CAVI on the right/left site was 8.32 ± 0.16/8.33 ± 0.19 initially and 8.44 ± 0.16/8.24 ± 0.15 units treatment (p > 0,05) afterwards.We did not note any impact of statin therapy on the BP level. However, a significant correlations was found between the CAVI index with age and the serum level of blood Triglycerides before treatment, including LDL Cholesterol and HDL Cholesterol, duration of hypertension, the blood glucose level, the Potassium level and the Maximum Thickness of Intima-Media of Carotid Arteries in the statins group. ConclusionThe adding of the statin to the current fixed dual or triple combination of the antihypertensive therapy could prevent the progression of arterial stiffness in patients with 2nd and 3rd stages of arterial hypertension.

Study on the Crush Injury Model of the Sciatic Nerve in Rabbits by Conventional Ultrasound and Elastography.

The crush injury model of the sciatic nerve in rabbits is a common nerve injury model, but there is little literature on the evaluation of nerve stiffness by ultrasound elastography. To explore the value of ultrasound elastography in diagnosing crush injury of the sciatic nerve in rabbits. Forty cases of crush injury model of the sciatic nerve in rabbits were examined by conventional ultrasound and elastography. The sonographic manifestations and stiffness of the model were analyzed, and the regularity of nerve injury with time was summarized. Ultrasound could clearly show the location, range, and thickness of the injured nerve in this model. The thickness of the injured area reached a peak in the 2nd week and returned to normal thickness in the 8th week. The nerve stiffness of the injured area increased gradually with time. Conventional ultrasound combined with elastography can comprehensively and quantitatively evaluate the morphological changes and mechanical properties of the injured sciatic nerve in rabbits, which may be of great significance to the repair and rehabilitation of peripheral nerve crush injuries.

LONG TERM EFFECT OF RENAL DENERVATION ON 24 HOUR ABPM AND BLOOD PRESSURE LOAD IS LARGELY DEPENDENT OF BASELINE ARTERIAL STIFFNESS

Objective: The aim of the study was to evaluate the long term effect of renal sympathetic denervation (RSD) on 24h ambulatory blood pressure measurement (ABPM) and blood pressure load (BP load) in patients with resistant hypertension depending of the baseline arterial stiffness status. Design and method: Consecutive patients with resistant hypertension who underwent RSD workout at the University Hospital Saint Anna, Sofia, ESH Excellence center of hypertension, were included. RSD was performed on the grounds of resistant hypertension defined as mean daytime systolic BP &gt;135 mmHg or diastolic BP &gt;85 mmHg in 24-hr ambulatory blood pressure measurement (ABPM) despite the intake of at least three antihypertensive agents, including a diuretic. Cardio ankle vascular index (CAVI) was measured using the VaSera system (Fukuda Denshi Co, Japan). RSD was performed with the Symplicity Flex™ catheter (Medtronic, Minneapolis, MN, USA) according to a standardized protocol. Results: The study included 32 patients with treatment-resistant hypertension and performed successful RSD. CAVI was measured before the intervention and the results of the procedure on 24h daytime, nighttime and 24 blood pressure and systolic and diastolic BP load were evaluated by serial ABPM measurements. A long-term effect of the RSD, reported as a reduction in 24-hour systolic blood pressure above 10 mmHg at month 12, was found in 22 patients (68.8%). Despite similar baseline out-of-office and office blood pressure and concomitant antihypertensive therapy, patients with lower arterial stiffness had a more significant blood pressure effect of renal denervation, a result that persisted within 12 months of follow-up. Along with reduction of all ABPM parameters more profound and clinically meaningful change of BP load during daytime, nighttime and 24h period was also noticed in this group of patients. (Table 1) Conclusions: The long term effect of renal denervation on 24h ABPM and BP load is largely dependent of baseline arterial stiffness. The results of the present study justify the incorporation of arterial stiffness evaluation in clinical decision workout of the procedure.

Structural stiffness evaluation of suspension bridge based on monitoring data

For long-span suspension bridges, the structural deformation is significantly influenced by the environment. Therefore, evaluating the structural stiffness of suspension bridges is crucial. This paper takes a certain long-span suspension bridge over the sea as an example to discuss different methods for evaluating the structural stiffness of suspension bridges. A three-dimensional finite element model is established, and influential lines at key locations are extracted. The fitting accuracy of vertical deformation and environmental temperature data under different time windows is analyzed based on GPS deformation monitoring data. Furthermore, the spatial distribution of the maximum and minimum values of bridge deformation caused by vehicle loads is statistically analyzed. The results indicate that the displacement extreme value coefficient at the mid-span of the suspension bridge is relatively large compared to other locations. The measured displacement envelope curves are within the theoretical envelope curves, demonstrating good overall stiffness performance of the bridge. The research methodology in this paper accurately evaluates the overall structural stiffness of the suspension bridge, providing strong support for ensuring the safe operation of the bridge.

Stiffness evaluation of Forta Fibre Reinforced Asphalt Concrete (FRAC) mixture under different pulse repetition load

Pavement structure can be designed either as a flexible or a rigid pavement based on its structural behaviour, with flexible pavements being frequently favored due to its advantages. One of the major problems that normally occurred in road construction was pavement distresses due to the quality of the materials. Numerous studies were carried out to explore sustainable ways to improve the pavement performance especially on modification of the asphaltic concrete in construction phases. This paper investigates the effect of Forta-Fi fiber on stiffness performance of hot mix asphalt mixture (HMA). In this respect, conventional asphalt binder grade 60/70 and Nominal Maximum Aggregate Size (NMAS) 12.5mm were used in the preparation of asphalt mixture specimens as specified in Superpave mix design method. Performance of modified samples incorporating 0.3, 0.5 and 0.7% of total mixture were evaluated for resilient modulus accordance to ASTM D4123 using Universal Testing Machine (UTM). The samples were tested at 25°C and 40°C with pulse repetition period 1000ms, 2000ms and 3000ms to simulate low, medium and high volume of traffic. As a result, the resilient modulus values of modified asphalt mixture improved 38% with 0.3% additive of Forta-Fi at 25°C with 3000ms pulse repetition period, while at 40°C with 3000ms pulse repetition period improved 23% with 0.5% additive of Forta-Fi. Based on these studies, the addition of fibers reinforcement into the asphalt mixture has a significant effect on resilient modulus of fibers reinforced asphalt mixture.

Stiffness evaluation of UHPC-filled socket column-foundation joints: Numerical investigation and analytical model

Socket connections are widely used to connect precast columns to the foundation and the initial stiffness of the socket joints is of great significance for seismic design. The connection efficiency of precast socket column has an important influence on its initial stiffness. Therefore, based on the previous experiment research on socket column by authors’ team, a finite element model (FEM) of ultra-high performance concrete (UHPC)-filled socket precast bridge column-foundation joints was established and verified by the local damages, failure mode and hysteresis curves. The key parameters that influencing the initial stiffness of socket joints were studied by numerical analysis, and a simplified calculation formula of initial stiffness was proposed. In addition, based on the theory of elastic foundation beam, an analysis model for predicting the initial stiffness of socket joints considering rotating stiffness of the connection was developed. The theoretical results are verified by the proposed simplified equations and experiments results in the literature. The method presented in this paper can conveniently predict the initial stiffness of RC socket column-foundation joints with reasonable accuracy.

Numerical evaluation of stiffness and toughness in bio-inspired composite materials

La naturaleza ha servido de inspiración para múltiples áreas del conocimiento y de desarrollo de la humanidad, en el caso de los materiales su proceso evolutivo de millones de años ha logrado obtener una buena compatibilidad entre las propiedades mecánicas de rigidez y tenacidad, algo que es complicado en los materiales de ingeniería convencionales, debido a que estas propiedades presentan un comportamiento inversamente proporcional entre sí. Se ha establecido que una de las características que la naturaleza utiliza es la formación de estructuras jerárquicas, que pueden ir desde la escala micrométrica hasta la macro escala, con este tipo de organización ha logrado mejorar diversas propiedades, dependiendo de la necesidad a resolver, del medio ambiente en que se encuentre y los materiales disponibles. Uno de estos tipos de estructuras son las helicoidales, presentes en escamas de peces, conchas de moluscos, exoesqueletos, etc., la cual provee protección y buenas propiedades de resistencia mecánica, resistencia a la penetración, al impacto y la fractura. Por tal motivo se pretende realizar un estudio numérico de materiales compuestos por fibras continúas empleando diferentes modelos constitutivos (lineales y plásticos bilineales) para la matriz (suave) y las fibras (rígidas) y observar como la variación del modelo empleado y el ángulo de rotación de las fibras afectan la rigidez general y la tenacidad del material.

Analysis and Optimization of Motion Coupling for the Coordinated Operation of Flexible Multi-Arm Space Robots

This paper presents a novel approach for analyzing and optimizing motion coupling in the coordinated operation tasks of flexible space multi-arm robots (FMSRs). The method integrates motion coupling between multiple arms and system stiffness to improve the motion and force accuracy of FMSRs by optimizing the configuration. First, a comprehensive model of an FMSR is established using the hypothetical modal method. Then, the motion coupling relationship among multiple arms is analyzed, and a motion coupling degree evaluation index is developed. Furthermore, the constraint relationship of coordinated operation is analyzed, and an equivalent stiffness model for the coordinated operation of the FMSR is formulated along with a stiffness evaluation index. Based on these analyses, the motion trajectory of the FMSR is optimized by comprehensively considering both the motion coupling degree and the equivalent stiffness factors. Finally, numerical simulation experiments are conducted to validate the proposed method, and the results show that the accuracy of the FMSR can be improved by 40% using this approach.

Endoscopic Ultrasound (EUS) Guided Elastography.

Endoscopic ultrasound (EUS) is an essential technique for the management of several diseases. Over the years, new technologies have been developed to improve and overcome certain limitations related to EUS-guided tissue acquisition. Among these new methods, EUS-guided elastography, which is a real-time method for the evaluation of tissue stiffness, has arisen as one of the most widely recognized and available. At present, there are available two different systems to perform an elastographic evaluation: strain elastography and shear wave elastography. Strain elastography is based on the knowledge that certain diseases lead to a change in tissue hardness while shear wave elastography monitored shear-wave propagation and measures its velocity. EUS-guided elastography has shown in several studies high accuracy in differentiating benign from malignant lesions from many different locations, mostly in the pancreas and lymph nodes. Therefore, nowadays, there are well-established indications for this technology, mainly for supporting the management of pancreatic diseases (diagnosis of chronic pancreatitis and differential diagnosis of solid pancreatic tumors) and characterization of different diseases. However, there are more data on new potential indications for the near future. In this review, we will present the theoretical bases of this technology and we will discuss the scientific evidence to support its use.

Management of the stiff elbow: a literature review.

The elbow is prone to stiffness due to its unique anatomy and profound capsular reaction to inflammation. The resulting movement impairment may significantly interfere with a patient's activities of daily living. Trauma (including surgery for trauma), posttraumatic arthritis, and heterotopic ossification (HO) are the most common causes of elbow stiffness. In stiffness caused by soft tissue contractures, initial conservative treatment with physiotherapy (PT) and splinting is advised. In cases in which osseous deformities limit range of motion (e.g. malunion, osseous impingement, or HO), early surgical intervention is recommended. Open and arthroscopic arthrolysis are the primary surgical options. Arthroscopic arthrolysis has a lower complication and revision rate but has narrower indications. Early active mobilization using PT after surgery is recommended in postoperative rehabilitation and may be complemented by splinting or continuous passive motion therapy. Most results are gained within the first few months but can continue to improve until 12 months. This paper reviews the current literature and provides state-of-the-art guidance on the management regarding prevention, evaluation, and treatment of elbow stiffness.

Evaluation of liver stiffness in a population of client owned healthy dogs using two-dimensional shear wave elastography: intraobserver reliability

Sonoelastographic techniques can complement conventional grey-scale and Doppler ultrasonography by evaluating tissue elasticity, which has the prospect to provide differentiation between malignant and benign conditions. Both technical and patient-related confounding factors are known to influence the reliability and reproducibility of elastographic methods. Therefore, the study was designed to assess liver stiffness in a diverse population of client-owned healthy dogs, evaluate the effect of patient characteristics on the elastography measurements and to assess intraobserver reliability. A total of forty dogs underwent two-dimensional shear wave elastography (2D SWE) twice, performed by the same operator, one to six days apart. The average, median and maximum 2D SWE velocities for the linear probe were 2.50 +/- 0.067 m/s; 2.46 +/- 0.067 m/s; 3.58 +/- 0.13 m/s, respectively, and for the convex probe 0.99 +/- 0.11 m/s; 0.98 +/- 0.12 m/s and 1.34 +/- 0.21 m/s, respectively. No statistically significant effect (P&gt; 0.05) on the 2D SWVs was seen of the dog-related characteristics sex, age, body weight and body condition score. The intraobserver agreement of 2D SWE was moderate with the intraclass correlation coefficient (ICC) for the average, median and maximum 2D SWE being 0.69; 0.71 and 0.74, respectively. The moderate ICC and discrepant results obtained with different probes mandates standardization of patient-related and technical factors to overcome excessive variability in measurements in order to implement this technique in clinical practice.

Intravascular ultrasound imaging in evaluation of aortic stiffness: A proof-of-concept study.

Aortic stiffness is a well-known cardio-vascular risk factor. For years, different methods have been studied in the assessment of aortic elastic properties and large arterial stiffness for risk stratification. Herein is an assessment of the role of intravascular ultrasound (IVUS) imaging for the evaluation of aortic elastic properties. Intravascular ultrasound imaging of the aorta was performed in 12 patients with transthoracic echocardiography (TTE) and computed tomography (CT) evidence for enlargement of the ascending aorta - diameter ≥ 40.0 mm. Mechanical properties of the aorta were derived from the measured diameters and intra-aortic pressure. Paired samples T-test analyses were performed to determine differences between measurements derived by TTE, CT and IVUS. Mean values of the calculated elastic properties via IVUS of the ascending aorta were as follows: compliance 0.021 ± 0.02; strain 205 ± 4.3; aortic stiffness index 4.3 ± 0.75; elastic modulus 0.31 ± 0.05. On paired T-test analysis maximum ascending aortic diameter measured by CT aortography and IVUS did not differ significantly (t = -0.19, p = 0.985), but a significant difference between IVUS measurements and TTE derived diameters was found (t = 13.118, p = 0.034). On average, IVUS diameters were 2.3 mm larger than the results acquired by TTE (95% confidence interval: 14.21-17.13). Intravascular ultrasound examination of the ascending aorta provided larger diameters than the ones collected by means of TTE. However, IVUS measurements did not differ significantly from diameters derived by CT aortography.

In-Service Performance Evaluation of Flexible Pavement with Lightweight Cellular Concrete Subbase

The objective of engineers to improve the long-term performance of road infrastructure in changing global climate has led to the development of alternate materials for pavement construction. Lightweight cellular concrete (LCC) is a viable option for colder climates where pavements undergo several freeze-thaw cycles each year, resulting in faster deterioration of pavements. This is due to LCCs’ excellent freeze-thaw resistance, ease of placement, and potential sustainability benefits such as reduced use of virgin material and industrial by-products. However, there is a need to quantify these benefits and develop unified specifications for using LCC in the pavement structure. Therefore, this study examined the performance of flexible pavement sections that included a subbase layer, unbound granular materials for the control section, and three LCC densities (400, 475, and 600 kg/m3) for the LCC sections. Post-construction evaluation of pavement stiffness and roughness were evaluated using a Lightweight deflectometer and SurPro equipment. The results showed that LCC subbase thickness ≥ 250 mm produced over 22% smoother riding surfaces than unbound granular pavements while increasing pavement stiffness by up to 21%. Finally, this study recommends that LCC subbase thickness should not be thinner than 250 mm when using densities below 475 kg/m3 over weak subgrades.

A fault diagnosis method based on stiffness evaluation model for full ceramic ball bearings containing subsurface cracks

Most of the surface macroscopic faults of ceramic bearings are caused by the extended evolution of early subsurface cracks in mesoscopic and microscopic levels. Because of the greater contact stiffness and brittle failure mechanism of ceramic materials, the dynamic response becomes more sensitive, especially in the early failure stage with subsurface cracks. To evaluate the non-negligible effect for the cumulative expansion of subsurface cracks on the contact stiffness, this paper proposes a stiffness evaluation method based on the combination of theory and experiment. Combined with fracture mechanics, the quantified weakening effect of subsurface cracks on stiffness is substituted into the dynamics model to establish the stiffness evaluation model. Then the mapping relationship between the subsurface crack groups and the dynamic response is obtained. The results show that the different degrees of early subsurface crack failures in different directions have a significant effect on the magnitude of contact stiffness and the area of action. The model not only effectively evaluates the weakening effect on the contact stiffness of ceramic bearings when early subsurface failures occur, but also promotes the stiffness evaluation models of key components using ceramic materials.

In Situ Evaluation of Cellular Spheroid Stiffness by Pinching Device Composed of Piezoactuator and Strain Gauge

Mechanical characterization of cells is important for understanding their behavior. This paper reports on an in situ evaluation of the stiffness of cellular spheroids using a pinching device. The pinching device is integrated with a bimorph piezoactuator and strain gauge. It can pinch an object by combining a piezo bimorph actuator and a thin Si structure and can detect the reaction force from an elastic object using a strain gauge integrated into the thin Si structure. The strain gauge can detect the bending deformation of the device and estimate the reaction force by considering actuation. This paper presents the design of the pinching device and experimental results when used for the in situ evaluation of the stiffness of cellular spheroids. © 2023 Institute of Electrical Engineers of Japan. Published by Wiley Periodicals LLC.

A spalling evolution model for time-varying mesh stiffness evaluation and service life prediction of gears

Spalling is one of the most common contact fatigue failure modes on gear face. Although there are some prediction models for spalling formation, few prediction models have previously addressed the evolution from initial defects to spalling cavities. In this paper, a damage-connectivity spalling model (DCSM) is proposed to describe the formation and evolution of multiple irregular spalling cavities on the tooth face deriving from the initial defects. Subsequently, a type of TVMS-based indicator is established to represent the evolutionary severity of irregular spalling cavities. Finally, a service life prediction method is developed based on the proposed indicators. The correctness of the proposed DCSM model is verified by comparison with the extant gear spalling experiments. The effects of working load, depth ratio and quantify ratio of initial defect groups on the service life are discussed, which contributes to the service life improvements of gear pairs in the design stage.