Spherical Defects Research Articles

Simulation Research for the Effect of KDP Crystal Defect and Initial Internal Stress on Sawing Stress

KDP (KH2PO4) crystal is a kind of excellent nonlinear optical crystals, which has been widely used in nonlinear optical and Inertial Confinement Fusion (ICF) engineering. KDP crystal with the characteristics of low hardness, high brittleness, easy deliquescence and temperature-sensitive is easy to crack during the crystal growth, taken out from crystallizer, and the process of slicing. Stress concentration caused by the initial internal stress redistribution and the growth defect in KDP crystal is an important reason of KDP crystal cracking during sawing process. The numerical simulation model of the KDP crystal containing spherical cavity defect and sawing with fixed abrasive wire saw is established by finite element method in this paper. The effects of initial internal stress, spherical cavity defect on sawing stress are investigated. The maximum tensile stress near the defect during the sawing process is simulated and analyzed. The results show that sawing stress changes smoothly during sawing process, and the fixed abrasive wire saw slicing belongs to low stress cutting way. The sawing stress at sawing kerf is increased obviously. The crystal defect leads to local stress concentration during sawing process. The coupling effect of sawing stress with initial internal stress and the effect of stress concentration are enhanced when the sawing kerf approaches to the defect.

Defects evaluation system for spherical optical surfaces based on microscopic scattering dark-field imaging method.

In the field of automatic optical inspection, it is imperative to measure the defects on spherical optical surfaces. So a novel spherical surface defect evaluation system is established in this paper to evaluate defects on optical spheres. In order to ensure the microscopic scattering dark-field imaging of optical spheres with different surface shape and radius of curvature, illumination with variable aperture angle is employed. In addition, the scanning path of subapertures along the parallels and meridians is planned to detect the large optical spheres. Since analysis shows that the spherical defect information could be lost in the optical imaging, the three-dimensional correction based on a pin-hole model is proposed to recover the actual spherical defects from the captured two-dimensional images. Given the difficulty of subaperture stitching and defect feature extraction in three-dimensional (3D) space after the correction, the 3D subapertures are transformed into a plane to be spliced through geometric projection. Then, methods of the surface integral and calibration are applied to quantitatively evaluate the spherical defects. Furthermore, the 3D panorama of defect distribution on the spherical optical components can be displayed through the inverse projective reconstruction. Finally, the evaluation results are compared with the OLYMPUS microscope, testifying to the micrometer resolution, and the detection error is less than 5%.

State evaluation of a corroded pipeline

ABSTRACTA submarine pipeline is mainly used to transfer liquid or gas between two land masses and may thus suffer corrosion from the severe subsea environment. Hence, the safety of a corroded pipeline must be evaluated by professionals. In this study, stress analysis of a corroded pipeline is conducted for three situations (i.e. simple defect, complex surface, and interacting defects). A simple defect is modelled using the 3D drawing software CATIA, and ANSYS simulates the stress of the corrosion defect; the effects of the defect were determined using different defect widths and depths. A complex surface involves the use of AUTOCAD VBA to establish the 3D surface based on random data and to generate an Initial Graphics Exchange Specification file. CATIA is used for file opening and geometric modelling and is finally keyed into ANSYS for analysis. ANSYS then is used for the stress analysis. The analysis covers a single rectangular defect, a spherical defect, and interacting effects of both types of defects. Finally, the stress analysis results are explored.

Effect of defects on the burst failure of butt fusion welded polyethylene pipes

With the increasing demand of Medium density polyethylene (MDPE) pipes for gas transmission, the safety concern related with welding defects is becoming a serious matter. In this paper, experimental burst tests and finite element analyses were employed to study butt fusion welded MDPE pipe joints with spherical and planar defects of various sizes. These defects were used to simulate lack of bonding during the welding. Test results showed that in all pipe test cases, the failure location originated from pipe substrates, even though the defect size was increased to 45% of the pipe’s wall thickness. The burst pressure could be estimated by the expression employed in the ASME BPVC, and in the burst pressure, the hoop stress was 20.28 MPa. Simulation results showed that the failure position was not only affected by the defect size, but also by the welding bead. It can be argued that a single welding defect whose maximum size is smaller than 15% of the thickness can be used without failure during short-term usage, even when there is no welding bead in the welded joint.

Prediction of pathological fracture of the femoral shaft with an osteolytic lesion using a computed tomography-based nonlinear three-dimensional finite element method.

Physicians radiologically estimate the reduction in bone strength based on the size or location of bone tumors. The goal of this study was to clarify the relationship between the size or location of a bony defect and its mechanical strength using a computed tomography-based three-dimensional finite element method. Computed tomography data of the right femur from two volunteers (one healthy male and one female patient with primary osteoporosis) were used for the present study. A spherical defect of various sizes and locations at the level of the isthmus of the femoral shaft was created on the three-dimensional finite element models to simulate the osteolytic bone tumor. We classified these defects into three types: inner erosion, cortical disruption, and outer erosion. Two types of mechanical testing were performed: axial compression and torsion. In the axial compression testing of the healthy male subject, the correlation coefficients between the defect rate and the failure load in the cortical disruption type, inner erosion type, and outer erosion type were-0.916,-0.358, and-0.106, respectively. In the torsion testing, they were-0.8744,-0.9001, and-0.8907, respectively. In the axial compression testing of the osteoporotic female subject, the correlation coefficients in the cortical disruption type, inner erosion type, and outer erosion type were-0.754,-0.621, and-0.158, respectively. In the torsion testing, they were-0.9199,-0.5098, and-0.8363, respectively. In both tests, the defect rate of the cortex increased and the bone strength decreased, especially in the cortical disruption type. The results of the present study demonstrate that osteolytic bone tumors can weaken the bone strength, particularly when perforation of the cortex occurs via tumor invasion. These results may be useful for risk assessment of pathological fractures due to primary and metastatic osteolytic bone tumors in clinical practice.

Transurethral enucleation of large benign prostatic hyperplasia in sodium chloride solution

Background . Transurethral resection is a generally recognized treatment for small to medium-sized benign prostatic hyperplasia (BPH). Numerous original tools are proposed for surgery of large BPH. These include laser (holmium laser enucleation of the prostate) and transurethral (transurethral enucleation with bipolar (TUEB)) enucleation in 0.9 % NaCl solution, which are accompanied by removal of the maximum adenoma tissue volume, short-term recovery, and a substantially fewer early and late complications. Objective : to evaluate the safety and efficiency of TUEB in patients with large BPH. Subjects and methods . TUEB was carried out in 58 patients with large BPH. Their mean age was 64 years. The gland size was ≥ 102 сm3. The residual urine volume in all the patients was more than 100 ml. One year later, the results of treatment were analyzed using the International Prostate Symptom Score (IPSS), Quality of Life (QoL) Questionnaire, as well as from residual urine volume and remaining prostate tissue. Results. The mean time of surgery and enucleation was 90 and 55 min, respectively. The mean volume of removed adenoma tissue was 99 ml. By the end of month 2 following TUEB, there was a progressive reduction in the total IPSS and QoL scores from 35 to 7 and from 5 to 1, respectively, which preserved this trend by the end of a 1-year follow-up. study. The residual urine amount was less than 30 ml. The mean volume of the prostate tissue left was 8.5 сm3 and less than 11.0 сm3. The ultrasound anatomy of the prostatic urethra (transformation of thin-walled spherical TUR defect that is characteristic slit-like one resembles the inverted letter Y) eventually formed by the end of the 1-year follow-up. Stricture of the urethra and contracture of the bladder neck were noted in none of the cases. Conclusion . TUEB is an alternative to open surgery in patients with the enlarged prostate. The use of isotonic NaCl solution as washing fluid allows one to plan longer surgical intervention without fearing water intoxication.

Effects of Defect Size on Crush Test Load of Butt Fusion Welded MDPE Pipes

It is expected that the size of welding defect affects the mechanical performance of welded medium density polyethylene (MDPE) pipe joints. In this study, butt fusion welded MDPE pipe joints with a single spherical or planar defect of various sizes were studied using experimental crush testing and also by finite element method. The crush test showed that the mechanical performance of crush was not affected by the size and geometry of a single welding defect when the defect size was increased to 45% of the pipe's wall thickness. The simulation results indicated that the effect of the single welding defect on the Von Mises stress distribution near the defect explained the reason of the test results.

Study of the relationship between myopia and personality

ObjectiveTo study the correlation between the myopic refractive error and certain personality traits, and to determine whether there is a correlation between the degree of myopia and an increased frequency in personality disorders. MethodsCross-sectional observational multicenter study conducted on 82 subjects (26 men, 56 women) age over 18 years with myopia (spherical defect≤−0.5D), with 30 subjects having high myopia (<−6D). Data collected: age and gender, academic level, result in the Neo PI-R personality test, autorefractometry, myopic pathology, and ophthalmological treatment. ResultsCorrelation (Spearman's) between the magnitude of the spherical defect and the 5 personality traits studied in the total sample was not statistically significant: neuroticism (−0.057; p=.610), extroversion (−0.020; p=.857), openness (−0.032; p=.774), kindness (−0.060; p=.592), and responsibility (−0.034; p=.765). By dividing them into subgroups of low and high significance (t-test), a significant (p=.002) upward trend of the myopic defect with increasing scores on extraversion was found.When comparing high myopic subjects to the non-high myopic ones, there were significant differences between the 2 groups in terms of the associated pathology (p=.001), received treatment (p=.001) and the level of studies (p=.013). There were no differences in the variables of personality: neuroticism (p=.852), extroversion (p=.199), openness (p=.560), kindness (p=.584), and responsibility (p=.722). ConclusionsA low correlation was found between myopia and personality. There was no difference in the degree of myopia between the groups with different education levels. Subjects with more severe ocular pathology associated with myopia had higher scores in neuroticism, without finding any significant association.

Bubble-wall Casimir interaction in fermionic environments

We consider the Casimir interaction mediated by massless fermions, between a spherical defect and a flat potential barrier, assuming hard (bag-type) boundary conditions at both the barrier and the surface of the sphere. The computation of the quantum interaction energy is carried out using the multiple scattering approach adapted here to the setup in question. We find an exact integral formula for the energy, from which we extract both the large- and short-distance asymptotic behavior. At large distance the fermionic contribution is found to scale as ${L}^{\ensuremath{-}3}$, in contrast to that of electromagnetic vacuum fluctuations that, assuming perfectly conducting boundaries, scale as ${L}^{\ensuremath{-}4}$. At short distance, we compute the leading and subleading contribution to the vacuum energy. The leading one coincides with what it is expected from the proximity force approximation, while the subleading term gives, contrary to the electromagnetic case, a positive correction to the proximity force result.

Aberraciones corneales anteriores y posteriores medidas mediante imágenes de Scheimpflug en el queratocono en niños

ObjectiveIdentify utility of anterior and posterior aberrations in children to differentiate healthy and keratoconus corneas by Scheimpflug imaging with the Oculus Pentacam®. MethodA retrospective comparative observational study of children between 5 and 15 years was conducted. A group with healthy corneas and another group with keratoconus stage 1 and 2. All patients were examined including Scheimpflug's images. Were studied the following variables: spherical refractive defect, cylindrical defect, BCVA, keratometry maximum, Minimum and medium, topographic astigmatism and anterior and posterior aberrations. Student t-test and unpaired Mann-Whitney test was used. ResultsAlmost all aberrations of the anterior surface except the primary and secondary horizontal coma were founded that significant differences between the groups exists. Primary vertical coma, primary spherical aberration, coma and coma-like RMS: posterior corneal surface significant differences between groups were found. In children with healthy corneas was found that in back surface vertical coma, spherical aberration, coma and coma-like RMS frequently. In the keratoconus between the anterior and posterior corneal surface exits significant differences in vertical coma, coma-RMS and coma-like RMS. ConclusionsThe measurements of the aberrations of the anterior surface Sheimpflug imaging measures are useful in early detection of keratoconus in children. The posterior corneal surface aberrations are not useful since they are not in accordance with the optical properties of the cornea.

Effects of defect size on failure of butt fusion welded MDPE pipe under tension

Since medium density polyethylene (MDPE) pipes are increasingly used in the gas industry, welding defects are becoming a safety concern. In this study, butt fusion welded MDPE pipe joints with spherical and planar defects of various sizes were studied by experimental tensile tests and finite element analysis. These defects were considered for simulating lack of bonding during the welding. The tensile test results showed that pipe strength was not reduced by defects that were up to 15% of the pipe’s thickness in size. On the other hand, when the size of the defect was increased to 30% and 45% of the thickness, the failure strain decreased considerably. Finite element analysis verified that the effects of steel defects inserted intentionally before welding are comparable to those of air defects, which are close to actual weld defect conditions. Hence, the experimental results obtained in this study can represent the actual situation. It is argued that a single welding defect with a maximum size smaller than 15% of the pipe’s thickness can be accepted without compromising the structural integrity of the pipe during short term of usage not considering long term creep or slow crack growth.

Numerical investigation of creep crack initiation in P92 steel pipes with embedded spherical defects under internal pressure at 650 °C

Creep crack initiation position and incubation time of P92 steel pipes with embedded spherical defects at 650°C were investigated with finite element method. The function for the relationship between creep crack initiation position and the geometric parameters was obtained by fitting methods. The average equivalent stress was proposed to characterize the stress variation throughout the creep process and the mathematical relationships between it and the geometric parameters, internal pressures, creep crack incubation time were established through nonlinear regression. Finally, the proposed assessment function for creep crack incubation time was deduced from the above functions.

Estudio de la relación entre miopía y personalidad

ObjectiveTo study the correlation between the myopic refractive error and certain personality traits, and to determine whether there is a correlation between the degree of myopia and an increased frequency in personality disorders. MethodsCross-sectional observational multicenter study conducted on 82 subjects (26 men, 56 women) age over 18 years with myopia (spherical defect ≤ −0.5 D), with 30 subjects having high myopia (<−6 D). Data collected: age and gender, academic level, result in the Neo PI-R personality test, autorefractometry, myopic pathology, and ophthalmological treatment. ResultsCorrelation (Spearman's) between the magnitude of the spherical defect and the 5 personality traits studied in the total sample was not statistically significant: neuroticism (−0.057; P=.610), extroversion (−0.020; P=.857), openness (−0.032; P=.774), kindness (−0.060; P=.592), and responsibility (−0.034; P=.765). By dividing them into subgroups of low and high significance (t-test), a significant (P=.002) upward trend of the myopic defect with increasing scores on extraversion was found.When comparing high myopic subjects to the non-high myopic ones, there were significant differences between the 2 groups in terms of the associated pathology (P=.001), received treatment (P=.001) and the level of studies (P=.013). There were no differences in the variables of personality: neuroticism (P=.852), extroversion (P=.199), openness (P=.560), kindness (P=.584), and responsibility (P=.722). ConclusionsA low correlation was found between myopia and personality. There was no difference in the degree of myopia between the groups with different education levels. Subjects with more severe ocular pathology associated with myopia had higher scores in neuroticism, without finding any significant association.

Micromechanically-motivated phenomenological Hosford–Coulomb model for predicting ductile fracture initiation at low stress triaxialities

A phenomenological ductile fracture initiation model for metals is developed for predicting ductile fracture in industrial practice. Its formulation is based on the assumption that the onset of fracture is imminent with the formation of a primary or secondary band of localization. The results from a unit cell analysis on a Levy–von Mises material with spherical defects revealed that a Mohr–Coulomb type of model is suitable for predicting the onset of shear and normal localization. To improve the agreement of the model predictions with experimental results, an extended Mohr–Coulomb criterion is proposed which makes use of the Hosford equivalent stress in combination with the normal stress acting on the plane of maximum shear. A fracture initiation model is obtained by transforming the localization criterion from stress space to the space of equivalent plastic strain, stress triaxiality and Lode angle parameter using the material’s isotropic hardening law. Experimental results are presented for three different advanced high strength steels. For each material, the onset of fracture is characterized for five distinct stress states including butterfly shear, notched tension, tension with a central hole and punch experiments. The comparison of model predictions with the experimental results demonstrates that the proposed Hosford–Coulomb model can predict the instant of ductile fracture initiation in advanced high strength steels with good accuracy.

Influence of Geometrical Features of Meso-Defects on Damage Evolution of Metal Structure

To study the failure process of metal structure with meso-defects, RVE (representative volume element) with various initial meso-defects were analyzed by using ABAQUS software, the parameter f (void volume fraction) of GTN damage model was regarded as the criterion of structural damage. The result shows that f increased more obvious with volume of defects for spherical defects with the same shape but different size. When the radius of defects is less than 0.15mm, the influence of defects’ volume on increases of f is clear enough. When the radius is greater than 0.15mm, the effects is diminishing. For ellipsoidal defects with the same volume but different aspect ratio, when the long axis perpendicular to the direction of load, the increased trend of f according to plastic deformation more obvious along with aspect ratio of defects. Apparently, as aspect ratio approaches infinity, f would have the fastest growth. Consequently, the bigger defect volume and aspect ratio, the more conducive for damage evolution of the metal structure.

Theoretical evaluation of wall teichoic acids in the cavitation-mediated pores formation in Gram-positive bacteria subjected to an electric field

BackgroundElectroporation is a method of choice to transform living cells. The ability of electroporation to transfer small or large chemicals across the lipid bilayer membrane of eukaryotic cells or Gram-negative bacteria relies on the formation of transient pores across the membrane. To exist, these pores rely on an insulator (the bilayer membrane) and the presence of a potential difference on either side of the membrane mediated by an external electric field. In Gram-positive bacteria, however, the wall is not an insulator but pores can still form when an electric field is applied. Past works have shown that the electrostatic charge of teichoic acids, a major wall component; sensitizes the wall to pore formation when an external electric field is applied. These results suggest that teichoic acids mediate the formation of defects in the wall of Gram-positive bacteria. MethodsWe model the electrostatic repulsion between teichoic acids embedded in the bacterial wall composed of peptidoglycan when an electric field is applied. The repulsion between teichoic acids gives rise to a stress pressure that is able to rupture the wall when a threshold value has been reached. The size of such small defects can diverge leading to the formation of pores. ResultsIt is demonstrated herein that for a bonding energy of about ~1−10kBT between peptidoglycan monomers an intra-wall pressure of about ~5−120kBT/nm3 generates spherical defects of radius ~0.1−1nm diverging in size to create pores. ConclusionThe electrostatic cavitation of the bacterial wall theory has the potential to highlight the role of teichoic acids in the formation pores, providing a new step in the understanding of electroporation in Gram-positive bacteria without requiring the use of an insulator.

Evaluation of polychromatic X-ray radiography defect detection limits in a sample fabricated from Hastelloy X by selective laser melting

Selective laser melting is a rapidly maturing additive manufacturing technology ideally suited to the net-shape fabrication of high value metallic components with complex shapes. However, if the processing conditions are poorly controlled, internal defects such as cracks or pores filled with metal powder may be present and impair the properties. As a result, a non-destructive defect detection method needs to be found that is suited to this application. In this work, a staircase sample was designed and fabricated from Hastelloy X by selective laser melting with step thicknesses ranging from 0.8mm to 10mm and with each step containing the same series of custom-made spherical, rod-shaped and coin-shaped defects arranged in different orientations and ranging from 0.2mm up to 2mm in size. The sample was exposed to various X-ray radiography testing and analysis methods. In particular, a theoretical and experimental evaluation of defect detection limits by polychromatic X-ray absorption radiography was performed based on the measurable contrast, which depends on both defect size and shape and slab thickness. The experimental data suggest that the minimum detectable contrast is about 1–2% when using X-rays with a very broad spectrum. This equates to a minimum detectable defect size of about 0.2mm for a Hastelloy X slab thickness of <2mm. The experimental findings are in good agreement with theoretical expectations. The theoretical framework provides a criterion for estimating contrast, which is useful for optimising the experimental conditions. Polychromatic X-ray absorption radiography represents a simple and effective non-destructive investigation technique. Methods for further improving the defect detection limits are also discussed and examples relative to computed tomography are reported.

Influence of casting defects on fatigue strength of an investment cast Ti-6Al-4V alloy

The influence of casting defects on fatigue strength of an investment cast Ti-6Al-4V alloy is investigated. The most common of these defects are: pinhole, linear defect and inclusion. Each of them is currently defined by its size, morphology and position from the surface but is different from each other for a same type. An experimental campaign is defined with different types of defect. The first part of the campaign is focused on the influence of an artificial and spherical defect, considering two different surface conditions. It is shown that fatigue behaviour of this alloy is very sensitive to the surface condition of this artificial defect despite stress concentrations at the tip of the defect. The second part of the campaign is focused on casting defects: reduction of fatigue life is quantified and it is shown that an electro-discharge machined defect cannot be representative of pinhole.

Defects-Induced Hot Spots in TATB

We investigate the interaction between the laser and energetic materials with different defects. The three-dimensional models of triaminotrinitrobenzene (TATB) explosives containing spherical pores, craters, and cracks are established, respectively. The laser ignition process of TATB is simulated with three-dimensional finite difference time domain (3D-FDTD) method to study the electromagnetic field distribution surrounding these defects with 355 nm laser incidence. It indicates that the larger defects in the TATB energetic materials have the stronger electric field modulations to initial incident laser for all the three defects, which is easier to lead to the generation of hot spots. Furthermore, TATB materials with spherical pore defects and crater defects are easier to form hot spots than those with narrow crack defects.

Fatigue damage accumulation and lifetime prediction of defective C35 steel subjected to block loading

This paper deals with the influence of both defect and loading sequence on fatigue damage accumulation of C35 steel containing artificial defects. Tests were carried out using fatigue samples with artificial spherical defects introduced at the surface. Tests were performed using two blocks loading under increasing and decreasing magnitude. The experimental results were compared to the damage calculated by the Miner rule. In the case of defective material; it is shown in both cases a minor influence of sequence’s effect. A lifetime prediction method is then developed to assess the residual lifetime of damaged defective material. The method is based on a multiaxial endurance criterion used to calculate the equivalent local stress distribution around the defect and to inject it in an uniaxial damage cumulative rule. Finally a comparison between experimental and theoretical results is performed. It is observed that the Mesmacque sequential law gives the most accurate lifetime prediction of defective specimens.