Increasing Defect Size Research Articles

Dynamic Modeling of Angular Contact Ball Bearing with Local Defects under EHL Considering Impact Force

In order to analyze the operating status of angular contact ball bearings(ACBBs) with local defects in more detail, a dynamic model of ACBB with local defects considering impact force under elastohydrodynamic lubrication conditions is proposed. Firstly, an elastohydrodynamic lubrication model for defective bearings considering spin is established, the film thickness and film stiffness of the defective bearings are calculated, and then time-varying displacement excitation model and time-varying stiffness model for local defects in angular contact ball bearings is presented. Based on this, an instantaneous impact force function related to defect size and bearing speed is established. Secondly, based on Hertz contact theory and impact force function, a dynamic calculation method for ACBBs with local defects on the outer ring is proposed. Finally, the vibration characteristics of ball bearings with faults are investigated, and the influence of different parameters on the dynamic response of the bearings is analyzed. The calculation results show that under lubrication conditions, the impact force on the vibration of the bearing is significantly weakened. With the increase of defect size and load, the frequency of bearing fault characteristics remain unchanged, but its amplitude increases. As the bearing speed increases, the characteristic frequency and amplitude of bearing faults increase.

Lesion Size Location Dependency on Maximum Pressure in Osteochondral Defects: Experiments and Finite-Element Analysis.

Osteochondral defects (OCDs) in the knee joint have significant clinical implications, particularly regarding contact pressures and pressure distribution. Understanding how these factors are influenced by defect size and location is crucial for developing effective therapeutic strategies. The purpose of this study was to investigate the impact of defect size and location on contact pressures and pressure distribution in the knee joint. It was hypothesized that an increase in defect size would result in elevated contact pressures and alterations in pressure distribution, with specific variations related to defect location. Descriptive laboratory study. The study utilized 6 cadaveric knees, including the patella and fibula, subjected to controlled compressive loading for measuring contact pressures. Simultaneously, computed tomography-based models were created for finite-element analysis (FEA) to investigate the impact of varying defect sizes and locations on contact pressures and pressure distribution in the knee joint, excluding the patellofemoral joint. The study employed analysis of variance to assess contact pressure and defect size association. Comparison between medial and lateral femoral condyles at full extension and 30° flexion angle was performed, followed by post hoc testing. Fisher exact test analyzed peak pressure point location and defect size, categorizing them into medial and lateral. An increase in defect size corresponded with heightened contact pressures on both medial and lateral femoral condyles at full extension (P = .013 for medial and P = .024 for lateral). However, this correlation did not yield significant differences at 30° of flexion (P = .674 for medial and P = .333 for lateral). During mechanical testing, the highest pressures occurred near 5 mm defect dimensions. FEAs showed a significant increase in pressure and circumferential-edge stress with 7-mm defects. Peak contact pressure points shifted laterally with more significant defects. Our study demonstrated the impact of defect size, location, and alignment on knee joint contact pressures. Intervening promptly with defects exceeding 3 mm is crucial, as significant stress levels manifest beyond this threshold. Significant increases in contact pressures were noted with larger defect sizes, particularly between 3 and 10 mm at full extension. Peak pressure points shifted with defect size increments, and alignment variations showed minimal stress variation at 30° compared with 0°. FEA validated increasing contact pressures up to 7 mm defect size, beyond which pressures stabilized or slightly decreased. A concentrated pressure distribution on the medial side was observed. These findings inform our understanding of the biomechanical implications of OCDs. In the field of sports medicine, this research offers valuable insights to clinicians and researchers, elucidating key factors influencing knee joint health and the potential consequences of OCDs.

Effect of monovacancy defects on anisotropic mechanical behavior of monolayer graphene: A molecular dynamics study

The mechanical properties of monolayer graphene were studied using molecular dynamics (MD) simulation. The simulation results show that the tensile stress in the [010] crystal direction is greater than that in the [110] and [100] directions under uniaxial tensile. This confirms that graphene exhibits anisotropic behavior when subjected to external loading, resulting in changes in the Young's modulus in different directions. The calculated Young's modulus were 764.68 GPa, 532.50 GPa and 697.83 GPa for the [010], [110] and [100] directions, respectively. On this basis, the effect of defects on the mechanical properties was also considered. When there are vacancy defects, the stress concentration is linearly distributed along the Zigzag direction on both sides of the atomic vacancy defects. The effect of crack defects on the mechanical properties of graphene [010] crystal direction is the most significant. With the increase of crack size, the difference in fracture strength and fracture toughness calculated by MD simulation and the Griffith model decreases gradually. The potential energy of the non-defect model was found to be the highest, with the potential energy decreasing as the defect size increases. In addition, it was found that the strain rate also affects the stress-strain behavior of the monolayer graphene. However, when the crack size is large, the difference in the effect of strain rate on the anisotropic tensile fracture stress can be ignored.

The benefits of preoperative smoking cessation on abdominal wall reconstruction outcomes: An examination of abstinent versus never smokers

IntroductionActive smoking is related to wound and respiratory complications following abdominal wall reconstruction (AWR), but no AWR studies directly compare outcomes of abstinent-smokers (AS), fulfilling four-weeks of smoking cessation, to non-smokers (NS). MethodsProspectively maintained institutional database was queried for all AWR between 2012 and 2019. AS and NS were included. Primary outcomes were wound and respiratory complications; secondary outcome was recurrence. Standard statistical analyses were performed. ResultsEvaluation included 1088 patients, 305 AS and 783 NS. AS had a lower BMI (31.3 vs 32.7 ​kg/m2; P ​= ​0.004) but increased ASA Class III (51.5% vs 34.5 ​%, P ​= ​0.009), COPD (8.9% vs 4.0 ​%, P ​= ​0.001), comorbidities (6.3 vs 4.7, P < 0.001), and wound class (Class III/IV: 25.3% vs 15.8 ​%, P ​= ​0.003). AS had increased defect size (229 vs 209.1 ​cm2; P ​= ​0.023), use of component separation (CST) (52.5% vs 43.8 ​%; P ​= ​0.010) and hospital stay (6.6 vs 6.2 days, P ​= ​0.015). Postoperative wound, mesh, and pulmonary infection, respiratory failure, and recurrence were similar.On multivariable regression, wound class and complications predicted recurrence. BMI, panniculectomy and CST predicted wound complications. BMI, CST, and wound class predicted respiratory complications. ConclusionDespite greater patient and hernia complexity, smoking cessation appears to result in similar outcomes to never-smokers in this AWR population.

Oxidation and mechanical properties of SiC fibers after high temperature exposure in air and steam

SiC fibers are widely used in composites exposed to high temperature oxidizing environments. The present study compares the oxidation behavior of SiC fibers and the associated changes in tensile strength upon their exposure to dry air and steam for up to 50 hours at temperatures from 950°C to 1350°C. In both cases, the scale thickness and oxide microstructure were analyzed by scanning electron microscopy. When the SiC fibers were oxidized in air, a crack-free amorphous oxide layer formed at temperatures up to 1200°C, whereas a cracked, crystallized oxide layer was found at 1350°C. By contrast under steam environment, a crystalline oxide forms at 950°C for oxidation times longer than 30 h. In both environments, the fiber strength decreased with increasing exposure time and temperature, the degradation being faster after oxidation in steam compared to dry air. This appears to relate to residual stress in the oxide scale and a reduction in the cross section of the load-bearing unoxidized SiC. An increase in defect size may also contribute to the loss of strength. The oxide scale follows parabolic growth kinetics in both dry air and in steam from 950°C to 1350°C, except at 1350°C for over 30 hours. The oxidation rate in steam is faster than that in dry air, with activation energies of 79.8±1.4 kJ/mol in steam and 153.6±3.4 kJ/mol in dry air, respectively. This work is relevant to the application of SiC fibers and SiC fiber reinforced composites in air and steam environments at high temperature.

Mechanical responses and stress distribution of rock-like specimen containing a spherical defect under uniaxial compression

Spherical defect is often seen in rock material, and the size and position of the defect seriously affect the stability of rock mass. In this study, a locating device for preparing spherical defects was designed. A series of uniaxial compression tests and simulations were conducted to study the influence of the defect size and location on the mechanical, micro-cracking, failure characteristics, and stress distribution of the sample containing a spherical defect. The results indicate that the uniaxial compressive strength (UCS) and Young’s modulus both decrease with increasing defect size. The location variation of the same-sized spherical defect has a significant influence on the UCS but hardly influences Young’s modulus. The closer the defect is to the boundary, the lower the UCS is. The acoustic emission (AE) monitoring results indicate that the damage point aggregates and expands around the defect, forming a failure surface in the later stage of specimen loading. The failure modes of the specimen are divided into tensile failure, shear failure, and tensile-shear failure. Laboratory test results match well with the numerical simulation results obtained through the PFC3D program. The numerical stress monitoring results indicate that there is significant stress concentration near the defect. And the concentrated stress at the defect boundary drops before the the model reaches its peak stress, which can be used to predict the failure of the defected rock mass. The research findings could supply a certain reference for stability analysis and control of rock material containing similar types of defects.

Umblikal Hernili Hastaların Değerlendirilmesi: 6 Yıllık Deneyim

Objective: Umbilical hernia is a common anterior abdominal wall defect in childhood. Although the defect is present at birth, unlike other hernias of childhood, it may close spontaneously over time without the need for surgery. However, when these hernias do not close spontaneously, complications can develop that require emergency surgery. The aim of this study was to determine the incidence of spontaneous closure in patients diagnosed with umbilical hernia and the factors that influence this incidence, the complications that may develop during follow-up, the indications for surgery and the issues to consider when planning the follow-up of patients. Material and Methods: Between January 2006 and December 2011, 1928 patients diagnosed with umbilical hernia and followed up and treated in our clinic were included in the study. In this retrospective cohort study the current size of umbilical hernia, comorbidities and demographic characteristics of the patients were analysed. Operative data, complications and postoperative follow-up of the operated patients were evaluated. Results: The spontaneous closure rate of umbilical hernia was found to be 60%. The rate of spontaneous closure of umbilical hernia was higher in boys and the rate of operation was higher in girls. The risk of incarceration was higher in girls than in boys. The rate of spontaneous closure decreased with increasing defect size. It was found that comorbidities did not affect spontaneous closure of umbilical hernias. The rate of emergency surgery for incarceration was low (2%). Strangulation was noted in 1% of patients. All patients with incarceration were in Lassaletta group 2 (defect diameter 0.5-1.5 cm). Conclusion: Conservative management is still the most accepted and safest method in the treatment of umbilical hernia. Incarceration and strangulation are very rare in umbilical hernias. Even if the umbilical hernia is complicated, surgical treatment is possible and peri- and post-operative complication rates are very low. Long-term morbidity and mortality due to incarceration have not been reported in the literature.

Effect of pore size on the flexural strength of porous silicon carbide ceramics

Porous silicon carbide (SiC) ceramics with three different pore sizes (∼7, ∼45, and ∼98 μm) and three different porosities (∼40 %, ∼54 %, and ∼63 %) were prepared from mixtures of SiC, polysiloxane, boron carbide, phenolic resin, and polymer microbeads to investigate the effect of the pore size of porous SiC ceramics on their flexural strength. As the pore size increased from ∼7 to ∼98 μm, the flexural strength decreased from 116.3 to 80.8 MPa at a constant porosity of 40 %, owing to the increased defect size. The typical flexural strengths of porous SiC ceramics fabricated using ∼8 and ∼100 μm templates were 84.9 and 60.6 MPa respectively, at 54 % porosity; the flexural strengths were 58.7 and 43.9 MPa, respectively, at 63 % porosity. These results suggest that depending on the application, the mechanical properties of porous SiC ceramics can be successfully tuned by adjusting their pore size and porosity.

Effect of defects on flux expulsion of pure niobium superconducting radio frequency cavities via spatial temperature gradient

Since flux vortices are easily pinned by defects in superconducting radio frequency (SRF) cavities, trapped magnetic flux increases the surface resistance of the SRF cavity. It has been experimentally demonstrated that trapped magnetic flux can be expelled by cooling down a superconducting cavity under a large spatial temperature gradient. In this paper, we use the time-dependent Ginzburg–Landau (TDGL) theory to theoretically investigate the effect of defects on the flux expulsion ability of pure niobium superconducting cavities with an applied spatial temperature gradient. It is shown that the residual flux vortex density displays a notable stepwise decreasing trend with increasing temperature gradient at smaller residual fields, while it shows a stepwise rising with increasing defect size. Both larger defect number and size make vortices difficult to be expelled. Moreover, long cooling time is beneficial for vortices to be expelled, and the cooling time has nearly no significant effect on flux expulsion under conditions of large cooling times. The results in this paper provide some theoretical guidelines for improving the performance of superconducting cavities in practical situations.

Comparison of effective regurgitant orifice area by the PISA method and tricuspid coaptation gap measurement to identify very severe tricuspid regurgitation and stratify mortality risk

Abstract Background Various definitions of very severe (VS) tricuspid regurgitation (TR) have been proposed based on the effective regurgitant orifice area (EROA) or tricuspid coaptation gap (TCG). Because of the inherent limitations associated with the EROA, we hypothesized that the TCG would be more suitable for defining VSTR and predicting outcomes. Purpose To compare EROA and TCG for outcome prediction in patients with severe TR. Methods In this French multicentre retrospective study, we included 606 patients with ≥ moderate-to-severe isolated TR (without structural valve disease or an overt cardiac cause) according to the recommendations of the European Association of Cardiovascular Imaging. Patients were further stratified into VSTR according to the EROA (≥60 mm²) and then according to the TCG (≥10 mm). The primary endpoint was all-cause mortality and the secondary endpoint was cardiovascular mortality. Results The relationship between the EROA and TCG was poor (R²=0.21), especially when the size of the defect was large. Four-year survival was comparable between patients with an EROA &amp;lt;60 mm² vs. ≥ 60 mm² (67±3% vs. 64±4%, p=0.64), even after adjustment, for all-cause (p=0.72) and cardiovascular mortality (p=0.18). A TCG ≥10 mm was associated with lower four-year survival than a TCG &amp;lt;10 mm (53±7% vs. 69±3%, p&amp;lt;0.001). After adjustment for covariates, including age, comorbidity, right heart failure, dose of diuretics, and right ventricular dysfunction, a TCG ≥10 mm remained independently associated with higher all-cause mortality (adjusted HR[95%CI]=1.46[1.15-2.18], p=0.015) and cardiovascular mortality (adjusted HR[95%CI]=1.95[1.22-3.14], p &amp;lt;0.001), whereas an EROA ≥60 mm² was not associated with all-cause or cardiovascular mortality (adjusted HR[95%CI]:1.07[0.75-1.51], p=0.720, and adjusted HR[95%CI]:1.35[0.87-2.09], p=0.176, respectively). Conclusion The correlation between the TCG and EROA is weak and decreases with increasing defect size. A TCG ≥10mm is associated with increased all-cause and cardiovascular mortality and should be used to define VSTR in isolated TR.Correlation between EROA and TCGEvent free survival curves

A Dynamic Model of Outer Race Defective Bearing Considering the Unbalanced Shaft-Bearing System With Experimental Simulation

Abstract In this study, the effects of the evolution of bearing outer race defect size and increase in speed on the vibration characteristics of a shaft-bearing system under unbalanced conditions are simulated and analyzed. A two degrees-of-freedom mathematical model is presented for a ball bearing used in an unbalanced shaft-bearing system. The contact stiffness between the races and the balls is considered as a series of springs is incorporated in the model. Hertzian contact deformation theory is used to obtain the contact stiffness. This model considers the contact deformation between the balls and the races, the additional displacement between the balls and the inner race due to radial clearance and due to defect geometry. The maximum possible radial displacement of the ball into the defect is calculated analytically using the groove radius, ball radius, and defect diameter. The rectangular function is used for modeling the defect. matlab codes are developed for modeling the bearing and for solving the differential equations of motion using the Runge–Kutta method. The vibration responses (peak and root-mean-square (RMS) values) obtained by modeling and by experimentation show similar vibration characteristics. The investigation shows that the values of statistical parameters initially increase with the increase in defect size and then decrease with a further increase in defect size. While peak and RMS increase with the increase in speed, crest factor and kurtosis decrease with the increase in speed. Peak is more sensitive for diagnosing spalls on outer race and its evolution. This study helps as an effective diagnosis of antifriction bearings having spalls on the outer race under unbalanced conditions.

An analytic solution of an arbitrary location through-crack emanating from a nano-circular hole in one-dimensional hexagonal piezoelectric quasicrystals

The mode III fracture performance of an arbitrary location through-crack at the edge of a nano-circular hole in one-dimensional hexagonal quasicrystals is studied. Based on the G-M elasticity theory, the piezoelectric quasicrystal theory and the boundary value problems theory, the phonon, phason and electric fields of the nano-defects (nano-hole and nano-cracks) are obtained, and the analytic expressions of the field intensity factors at both ends of through-crack are present. The present solution can be degenerated into the existing results. The relationship between the field intensity factors with the nano-defects related parameters, far-field loads and piezoelectric quasicrystal coupling coefficient are discussed. The field intensity factors have obvious size effects when the defects size is at nanoscale and the surface effect is considered. The field intensity factors tend to be classical theory with the increase in defect size. The field intensity factors show different changes with the increase in crack location angle and relative size between cracks. The size effect of the field intensity factors is significantly affected by the crack location. The far-field mechanical-electric loads and the piezoelectric quasicrystal coupling coefficient have obvious influence on the field intensity factors.

Effects of surface defects on rolling contact fatigue of M50 steel with consideration to both the transgranular and intergranular damage

Surface-initiated pitting and subsurface-initiated spalling of M50 bearing steel were investigated, considering transgranular and intergranular damage. The damage initiation and propagation for contact surface with defects produced by different size particles were analyzed using integrated model combined continuum damage method (CDM) and cohesive zone method (CZM). Pitting and spalling mechanism, and defect size effect on damage evolution were discussed. The results indicated both pitting and spalling include intergranular and transgranular damage evolution. As the defect size increases, the RCF mode change from spalling to pitting. Damage evolution mode of spalling and pitting is the plastic deformation and damage accumulation mode, respectively. Moreover, the prediction accuracy for the damage evolution of the integrated model is higher than single-CDM and single-CZM models.

Technique for Introducing Internal Defects with Arbitrary Sizes and Locations in Metals via Additive Manufacturing and Evaluation of Fatigue Properties

Mechanical component failure is usually caused by metal fatigue originating from small defects in metallic materials. Thus, it is important to precisely capture the fatigue properties of materials containing small defects. Fatigue tests of materials with artificial surface defects introduced by drilling have been conducted. Using the resulting data, an equation for predicting the material fatigue limit has been proposed on the basis of the √area parameter model, and its effectiveness has been confirmed for various materials. However, for additive manufactured (AM) materials that contain internal defects resulting in failure, controlling the size of the defect where the fracture originates is extremely difficult. Therefore, verification of the predictive ability of the √area parameter model for AM materials is impossible, in contrast with other materials that fail because of surface defects. In this context, developing a technique to intentionally introduce internal defects with arbitrary sizes at arbitrary locations can provide insights that help predict the fatigue limit of AM materials. This study aimed to establish a technology for quantitatively evaluating the effect of internal defects on the fatigue properties of AM materials by introducing internal defects with arbitrary sizes at arbitrary locations via AM. Specimens with different defect sizes and locations were prepared. Prior to the fatigue tests, the defect sizes and locations were measured non-destructively via X-ray computed tomography (CT). The fatigue tests were conducted in air at room temperature. All the specimens failed because of the intentionally introduced internal defects, and the fatigue lives became shorter with increasing defect sizes, except for the specimens with defects adjacent to the surface. In those cases, fatigue cracks easily reached the surface; therefore, the fatigue lives were speculated to be shorter than those of the specimens with the same defect sizes. Moreover, the defect sizes determined from the fracture surfaces by scanning electron microscopy were nearly consistent with those determined by X-ray CT.

Matched-Pair Analysis: Large-Sized Defects in Surgery of Lower Limb Nonunions.

The treatment of large-sized bone defects remains a major challenge in trauma and orthopaedic surgery. Although there are many treatment options, there is still no clear guidance on surgical management, and the influence of defect size on radiological and clinical outcome remains unclear due to the small number of affected patients. The aim of the present study was to determine the influence of defect size on the outcome of atrophic and infected nonunions of the tibia or the femur based on the diamond concept in order to provide recommendations for treatment guidance. All medical records, surgical reports, laboratory data and radiological images of patients treated surgically for atrophic or infected nonunions of the lower limbs (femur or tibia) between 1 January 2010 and 31 December 2020 were examined. Patients with proximal, diaphyseal or distal nonunions of the femur or tibia who were surgically treated at our institution according to the "diamond concept" and attended our standardised follow-up program were included in a database. Surgical treatment was performed as a one- or two-step procedure, depending on the type of nonunion. Patients with a segmental bone defect ≥5 cm were matched with patients suffering a bone defect <5 cm based on five established criteria. According to our inclusion and exclusion criteria, 70 patients with a bone defect ≥5 cm were suitable for analysis. Two groups were formed by matching: the study group (bone defect ≥5 cm; n = 39) and control group (bone defect <5 cm; n = 39). The study was approved by the local ethics committee (S-262/2017). The mean defect size was 7.13 cm in the study and 2.09 cm in the control group. The chi-square test showed equal consolidation rates between the groups (SG: 53.8%; CG: 66.7%). However, the Kaplan-Meier curve and log-rank test showed a significant difference regarding the mean duration until consolidation was achieved, with an average of 15.95 months in the study and 9.24 months in the control group (α = 0.05, p = 0.001). Linear regression showed a significant increase in consolidation duration with increasing defect size (R2 = 0.121, p = 0.021). Logistic regression modelling showed a significant negative correlation between consolidation rate and revision performance, as well as an increasing number of revisions, prior surgeries and total number of surgeries performed on the limb. Clinical outcomes showed equal full weight bearing of the lower extremity after 5.54 months in the study vs. 4.86 months in the control group (p = 0.267). Surprisingly, defect size does not seem to have a significant effect on the consolidation rate and should not be seen as a risk factor. However, for the treatment of large-sized nonunions, the follow-up period should be prolonged up to 24 months, due to the extended time until consolidation will be achieved. This period should also pass before a premature revision with new bone augmentation is performed. In addition, it should be kept in mind that as the number of previous surgeries and revisions increases, the prospects for consolidation decrease and a change in therapeutic approach may be required.

Comparison of effective regurgitant orifice area by the PISA method and tricuspid coaptation gap measurement to identify very severe tricuspid regurgitation and stratify mortality risk

Various definitions of very severe (VS) tricuspid regurgitation (TR) have been proposed based on the effective regurgitant orifice area (EROA) or tricuspid coaptation gap (TCG). Because of the inherent limitations associated with the EROA, we hypothesized that the TCG would be more suitable for defining VSTR and predicting outcomes. In this French multicentre retrospective study, we included 606 patients with ≥ moderate-to-severe isolated functional TR (without structural valve disease or an overt cardiac cause) according to the recommendations of the European Association of Cardiovascular Imaging. Patients were further stratified into VSTR according to the EROA (≥ 60 mm2) and then according to the TCG (≥ 10 mm). The primary endpoint was all-cause mortality and the secondary endpoint was cardiovascular mortality. The relationship between the EROA and TCG was poor (R2 = 0.22), especially when the size of the defect was large. Four-year survival was comparable between patients with an EROA < 60 mm2 vs. ≥ 60 mm2 (68 ± 3% vs. 64 ± 5%, P = 0.89). A TCG ≥ 10 mm was associated with lower four-year survival than a TCG < 10 mm (53 ± 7% vs. 69 ± 3%, P < 0.001). After adjustment for covariates, including comorbidity, symptoms, dose of diuretics, and right ventricular dilatation and dysfunction, a TCG ≥ 10 mm remained independently associated with higher all-cause mortality (adjusted HR [95%CI] = 1.47 [1.13–2.21], P = 0.019) and cardiovascular mortality (adjusted HR [95%CI] = 2.12 [1.33–3.25], P = 0.001), whereas an EROA ≥ 60 mm2 was not associated with all-cause or cardiovascular mortality (adjusted HR [95%CI]: 1.16 [0.81–1.64], P = 0.416, and adjusted HR [95%CI]: 1.07 [0.68–1.68], P = 0.784, respectively). The correlation between the TCG and EROA is weak and decreases with increasing defect size. A TCG ≥ 10 mm is associated with increased all-cause and cardiovascular mortality and should be used to define VSTR in isolated functional TR (Fig. 1).

OSTEOCHONDRAL GLENOID LOSS: REMAINING GLENOID DEPTH AND CONCAVITY ARE STRONGER PREDICTIVE PARAMETERS FOR SHOULDER INSTABILITY THAN DEFECT SIZE

Osteochondral glenoid loss is associated with recurrent shoulder instability. The critical threshold for surgical stabilization is multidimensional and conclusively unknown. The aim of this work was to provide a well- measurable surrogate parameter of an unstable shoulder joint for the frequent anterior-inferior dislocation direction.The shoulder stability ratio (SSR) of 10 paired human cadaveric glenoids was determined in anterior-inferior dislocation direction. Osteochondral defects were simulated by gradually removing osteochondral structures in 5%-stages up to 20% of the intact diameter. The glenoid morphological parameters glenoid depth, concavity gradient, and defect radius were measured at each stage by means of optical motion tracking. Based on these parameters, the osteochondral stability ratio (OSSR) was calculated. Correlation analyses between SSR and all morphological parameters, as well as OSSR were performed.The loss of SSR, concavity gradient, depth and OSSR with increasing defect size was significant (all p&lt;0.001). The loss of SSR strongly correlated with the losses of concavity gradient (PCC = 0.918), of depth (PCC = 0.899), and of OSSR (PCC = 0.949). In contrast, the percentage loss based on intact diameter (defect size) correlated weaker with SSR (PCC=0.687). Small osteochondral defects (≤10%) led to significantly higher SSR decrease in small glenoids (diameter &lt;25mm) compared to large (≥ 25mm) ones (p ≤ 0.009).From a biomechanical perspective, the losses of concavity gradient, glenoid depth and OSSR correlate strong with the loss of SSR. Therefore, especially the loss of glenoidal depth may be considered as a valid and reliable alternative parameter to describe shoulder instability. Furthermore, smaller glenoids are more vulnerable to become unstable in case of small osteochondral loosening. On the other hand, the standardly used percentage defect size based on intact diameter correlates weaker with the magnitude of instability and may therefore not be a valid parameter for judgement of shoulder instability.

A deep context learning based PCB defect detection model with anomalous trend alarming system

The quality of a printed circuit board (PCB) is paramount towards ensuring proper functionality of electronic products. To achieve the required quality standards, substantial research and development efforts were invested to automate PCB inspection for defect detection, primarily using computer vision techniques. Despite these advancements, the accuracy of such techniques is often susceptible towards varying board and component size. Efforts to increase its accuracy especially for small or tiny defects on a PCB often lead to a tradeoff with reduced real-time performance, which in turn limits its applicability in the manufacturing industry. Hence, this paper puts forward an enhanced deep learning network which addresses the difficulty in inferring tiny or varying defects on a PCB in real-time. Our proposed enhancements consist of i) A novel multi-scale feature pyramid network to enhance tiny defect detection through context information inclusion; and ii) A refined complete intersection over union loss function to precisely encapsulate tiny defects. Experimental results on a publicly available PCB defects dataset demonstrate that our model achieves 99.17% mean-average precision, while maintaining real-time inferencing speed at 90 frames per second. In addition, we introduce three trend detection algorithms which alert an operator when abnormal development of defect characteristics is detected. Each algorithm is responsible for localizing defect buildups, increasing defect size and increasing defect occurrences, respectively. As a whole, the proposed model is capable of performing accurate and reliable real-time PCB inspection with the aid of an automated alert capability. The dataset and trained models are available at: https://github.com/JiaLim98/YOLO-PCB.

Prediction of corrosion defect critical size and corrosion failure assessment study of SGTs

Alloy 690 is a common material for heat transfer tubes of steam generators (SGTs), and its corrosive properties affect service life. In this paper, a corrosion failure assessment diagram (CFAD) of SGTs is proposed for the first time based on the flow stress model and the "mechanical-electrochemical" (M-E) coupled model, and the critical value of defects for the failure of SGTs is predicted. The results show that the electrochemical reaction at both sides of the corrosion interface transforms from anodic to cathodic with increasing a/t, and the corrosion interface undergoes a transition from elastic deformation to plastic deformation. When a/t > 0.6, the SGTs undergo plastic deformation, the corrosion rate at the corrosion defect becomes more uniform with increasing b/t, and the "M-E" synergistic effect decreases. The critical size of the defect affected by the "M-E" coupling is a/t = 0.676, and the failure mode is transformed from electrochemical to "M-E" coupling failure mode. The anode current density at the corrosion defect was 400 times higher than that at the nondefective site. The "M-E" coupling resulted in a 9.03% increase in defect size for SGT failure. Plastic damage occurs when the depth of cracking under stress reaches 62% of the wall thickness. Corrosion is introduced into the structural integrity assessment of SGTs for the first time, which has a leading role in the prediction of the remaining life of different SGT materials under normal operating/accident conditions.

Dynamic Modeling and Simulation Analysis of Inter-Shaft Bearings with Local Defects Considering Elasto-Hydrodynamic Lubrication

As an important component of large engines, inter-shaft bearing is easily damaged due to its poor working conditions. By analyzing the time–frequency distribution rules of fault signals and the evolution law of micro-faults, the bearing failure mechanism can be revealed, and the bearing failure can be monitored in real time and prevented in advance. For the purpose of studying the mechanism of inter-shaft bearing faults, a 4-DOF (degree of freedom) dynamic model of inter-shaft bearing with local defects considering elasto-hydrodynamic lubrication (EHL) is proposed. Based on the established dynamic model, the impact characteristics and distribution rules of the fault signals of the bearing are accurately simulated, and the evolution law of the micro-faults is also analyzed. The effects of different speeds, loads and defect widths on maximum value (MV), absolute mean value (AMV), effective value (EV), amplitude of square root (AST), kurtosis factor (KF), impulse factor (IF), peak factor (PF) and shape factor (SF) are obtained. The findings show that the vibration amplitude of the bearing increases with the increase in defect size, and the faults are easier to diagnose accordingly. At the same time, PF, KF and IF are very sensitive to the initial failure of bearings. With the development of faults, the overall trend of AMV, AST and EV are relatively stable. The PF is sensitive to the change of rotating speeds and defect widths. The SF is insensitive to the change of rotating speeds, loads and defect widths. This lays a foundation for the research of monitoring and diagnosis methods of aeroengine inter-shaft bearing fault.