Damage Pits Research Articles

Characterizing Hypervelocity Impact (HVI)-Induced Pitting Damage Using Active Guided Ultrasonic Waves: From Linear to Nonlinear.

Hypervelocity impact (HVI), ubiquitous in low Earth orbit with an impacting velocity in excess of 1 km/s, poses an immense threat to the safety of orbiting spacecraft. Upon penetration of the outer shielding layer of a typical two-layer shielding system, the shattered projectile, together with the jetted materials of the outer shielding material, subsequently impinge the inner shielding layer, to which pitting damage is introduced. The pitting damage includes numerous craters and cracks disorderedly scattered over a wide region. Targeting the quantitative evaluation of this sort of damage (multitudinous damage within a singular inspection region), a characterization strategy, associating linear with nonlinear features of guided ultrasonic waves, is developed. Linear-wise, changes in the signal features in the time domain (e.g., time-of-flight and energy dissipation) are extracted, for detecting gross damage whose characteristic dimensions are comparable to the wavelength of the probing wave; nonlinear-wise, changes in the signal features in the frequency domain (e.g., second harmonic generation), which are proven to be more sensitive than their linear counterparts to small-scale damage, are explored to characterize HVI-induced pitting damage scattered in the inner layer. A numerical simulation, supplemented with experimental validation, quantitatively reveals the accumulation of nonlinearity of the guided waves when the waves traverse the pitting damage, based on which linear and nonlinear damage indices are proposed. A path-based rapid imaging algorithm, in conjunction with the use of the developed linear and nonlinear indices, is developed, whereby the HVI-induced pitting damage is characterized in images in terms of the probability of occurrence.

Varied laser induced damage phenomena of gold coated gratings for pulse compression

In this paper, gold-coated gratings for pulse compression have been prepared and their laser damage experiments have been performed. Varied laser damage morphologies have been observed: when a 60fs-pulsed laser with energy density slightly higher than the damage threshold was used, damage morphology with a characteristic of discrete distribution of small pits was appeared. These damage pits are linearly distributed at the junction of ridges and grooves. If the laser energy density is much higher than the damage threshold, the gold films was overall ablated and the grating structure disappeared. Besides, if the gold film has poor adhesion, it was peeled off. When a 450ps-pulsed laser with energy density slightly higher than the damage threshold was used, part of grating ridges will be ablated and an obvious line exists between the ablated area and the unchanged area. In theory, the laser induced temperature field and stress field in gold-coated gratings were calculated based on the electromagnetic field using the finite element method. It is demonstrated that the temperature and thermal stress distribution characteristics are affected by the laser heating rate and the heat diffusion time (the calculated diffusion time ranges from 6fs to 450ps), which determines the laser damage characteristics. The possible damage drivers have electron hydrodynamic pressure, thermal ablation and thermal stress.

Evaluation of induced pitting damage of late season cherries ‘Regina’ and ‘Sweetheart’ using an impact energy method

Evaluation of induced pitting damage of late season cherries ‘Regina’ and ‘Sweetheart’ using an impact energy method

Genotypic differences in sweet cherries are associated with the susceptibility to mechanical damage

The rheological properties and structure of the flesh tissue at harvest-ripe fruit of the sweet cherry Prunus avium L. cultivars Bing, Lapins, Regina, Santina, Sweetheart and Van were measured using a textural analyzer equipment and described by light microscopy, respectively. The rheological measurements inflicted reproducible levels of mechanical damage (pitting). The structural and rheological properties of the mesocarp and epidermis correlate with their susceptibility to mechanical damage. Epidermal cell width and area of external mesocarp cells were negatively associated with susceptibility to mechanical damage while cell number, quantified in 1mm2 of external mesocarp, was positively associated. Fruit of Bing and Regina are the least susceptible to mechanical damage among the cultivars under study. The least sensitivity of Regina fruit was associated with its wide epidermal cells and high value of modulus of elasticity, while in Bing with its low number of cells as well as high values of stress and strain at bioyield point. The high susceptibility to mechanical damage of Sweetheart and Lapins fruit was associated with their large number of cells in the external mesocarp tissue and with the lowest values of strain at bioyield point, therefore with the lowest deformation capacity of the tissue.

Thermodynamic damage mechanism of Ni/Cr film on neutral density filter by 1064-nm pulsed laser

We investigate the damage characteristics and mechanism of neutral density filters consisting of metal film on K9 glass substrate by 1064-nm pulsed laser. The damage morphologies present marked differences with different laser pulse energies. Specifically, with the increase of laser fluence, the damage pits density increase as well, and at the same time, the cracks appear around the pits and interconnect, which lead to the abscission of film. The damage mechanism has been studied from the viewpoint of embedded impurities in the film. The theoretical results show that the difference between the thermodynamic properties of impurities and film can lead to thermos-elastic stress, which plays important roles in deformation of film, nucleation and propagation of cracks. Last, methods have been proposed to improve the laser damage resistance by controlling the size distribution of impurity particles and increasing the film tensile strength.

A Subscale Experimental Investigation on the Influence of Sanding on Adhesion and Rolling Contact Fatigue of Wheel/Rail Under Water Condition

With a subscale rolling-sliding apparatus, the objective of this study is to explore the adhesion and rolling contact fatigue characteristics of wheel/rail rollers with sanding under water condition. Sanding improves adhesion coefficient but aggravates the surface damage of wheel and rail materials. With the particle diameter and feed rate increasing, the adhesion coefficient is further improved. However, the surface damage (spalling and pits) becomes severer as well as the surface roughness. Note that pitting is a special damage type when sanding is used to improve the adhesion. Big pits and fatigue cracks appear on subsurface under larger particle diameter and feed rate conditions. Severe cracks initiate from big pits and develop into material to a depth, which results in bulk material breaking.

Effects of different kinds of mitigated pits on transport of laser beam

According to the different kinds of morphology features, 3D grid models of mitigated pits were built, and effects of different kinds of mitigated pits models on transport of laser beam (351 nm) was studied by using scalar diffraction theory and Fast Fourier Transform (FFT) methods. The results indicate that the off-axis downstream intensification of different kinds of mitigated pits, including conic, parabolic and Gaussian, pits, mainly relies on the depth of the mitigated pit. For the off-axis intensification, the maximum intensity increases with deepening depth, and the location of the maximum intensity approaches the output surface of optics with increasing pit depth, and is far away from the output surface of optics with the increasing diameter of mitigated pits. In addition, when the depth and diameter of different kinds of mitigation pits are equal, the parabolic mitigated pits can be the best choice for mitigated morphology. The results of this research indicate that the downstream intensification, which is induced by the mitigated damage pits, can be suppressed by controlling the morphology features of mitigated pits.

Origin of the plasma scalds in dielectric coatings induced by 1ω laser

The plasma scalds initiated by a 1053 nm (1ω) nanosecond laser are separated from the defect-induced damage pits, which is verified as a result of the ionization wavefront with the subnanosecond laser. Considering the beam reflection from solid-state absorption fronts during the damage process, a theoretical scalding threshold about 6.84 J/cm2 (12 ns) based on the energy required to start an air avalanche is evaluated and agrees well with the experimental scalding threshold. The occurrence order of the initial explosion and subsequent ionization wavefront is verified to explain most of the damage morphologies caused by the 1ω laser. In addition to the significance in laser conditioning or cleaning for a high-power laser system, the results also indicate that through the occurrence of plasma scalds it is possible to mark the onset time of air plasma during laser-coating interaction.

The Effect of a Complex Planktonic and Biofilm Bacterial Consortia on Marine Corrosion of 1020 Carbon STEEL

In aquatic environments, the presence of microorganisms often leads to severe deterioration of metallic materials. While sessile cell (biofilm)-driven microbiologically-influenced corrosion (MIC), or biocorrosion, is recognized as a contributor to metal failures in marine systems, uncertainty still exists whether and to what extent products resulting from metabolic activity of the planktonic cells impact corrosion. Electrochemical measurements, molecular ecology techniques, comparative untargeted metabolomics, light and electron microscopy and surface analyses were employed to determine whether there is a difference in corrosion of 1020 carbon steel electrodes exposed to a native North Pacific seawater bacterial population that was either allowed to or prevented from developing a biofilm on the electrode surface. Laboratory studies were carried out using batch reactors. The investigation re-addressed the following issues (a) whether physical contact between cells and the metal surface is essential to enhance corrosion of 1020 carbon steel; (b) what, if any, is the impact of metabolic products secreted by cells kept in the planktonic phase, through confinement within a dialysis tube, on the severity of 1020 carbon steel deterioration; (c) are there any differences between the mineralogy of corrosion products formed on biofilm–free and biofilmed electrodes and (d) whether and to what extent does the biofilm population differ from that of the initial planktonic inoculum and the implication of this difference for diagnosing and mitigating MIC. Increased corrosion rates and extensive pitting damage were observed on the surface of biofilmed electrode (BE) compared to the biofilm-free (BFE) electrode which served as a “sterile” control. Corrosion products recovered from the BE surface had a significantly higher content (% w/w) of CaCO3 (aragonite) than those recovered from BFE surface (24.6% and 1.3% respectively). A reverse trend was observed for goethite (α-FeOOH); the latter dominated the BFE surface (43.8 wt %) and was relatively scarce (6.4 wt %) on BE surface. A vast disparity, mainly in putative lipids content, was found between metabolomes of the bacterial population allowed to form a biofilm and the same population kept in planktonic phase. DNA profiles of planktonic and biofilm bacterial populations, obtained through Illumina sequencing, were also considerably different. Extracellular DNA (e-DNA) comprising 16S rRNA sequences (up to 590 OTU), some of which were characteristic of bacteria implicated in MIC, was observed in the corrosion products recovered from the BFE surface. These results confirmed other reports that, in an oxygenated marine environment, the physical presence of an actively metabolizing bacterial biofilm leads to a pronounced pitting damage and increases corrosion rates of carbon steel. The study revealed that when cells are prevented from interacting with the surface, i.e. confined within a planktonic phase, their metabolic products released into the planktonic phase do not cause significant pitting corrosion. The corrosion in this case, is similar to that measured in filter sterilized seawater. Importantly, the investigation demonstrated that DNA profile of a biofilm differed significantly from that of planktonic seawater population, thus confirming that MIC risk assessment should not be carried out using sampling of planktonic cells alone. The presence of eDNA within corrosion products recovered from the biofilm-free electrode showed that identifying biocorrosion exclusively based on DNA profiling can be misleading and should not be used as a sole MIC diagnostic method.

Effect of Optimizing PID Parameters and Spindle Speeds on Processing Performance of KDP Micro-Defect Mitigation Machine Tool

PID parameters of machine tool for micro-defect mitigation of KDP crystal had been optimized, after which the velocity fluctuation frequency and amplitude variation of motion axis under different spindle speeds were studied. It is evident that the stability and following errors of the system run better under the velocity&acceleration feed forward PID control algorithm and Notch filters. The velocity fluctuation frequency of motion axis varies with spindle speeds significantly when the tool system is stable, while the fluctuation amplitude variation is slightly changed. To be conclude, the optimal working spindle speed is verified to be 4.78×104 rpm based on comparative experiments, at which damage pits can be mitigated by micro-machining successfully with roughness value of 34.4nm.

Study of downstream light intensity modulation induced by mitigated damage pits of fused silica using numerical simulation and experimental measurements

For high-power UV laser facilities, one of the key problems limiting the maximum light influence and safe routine operation is that the UV laser induces damage to fused silica optics. The most effective mitigation protocol of the damaged optics is the CO2 laser processing that leads to make locally melt or evaporate the damage. While the mitigated damage sites possess particular morphology, which may modulate the passing laser beam and induce the downstream intensification that will ruin the neighbor optics. In this work, the morphology features of the mitigated damage pits of fused silica optics are systematically investigated. According to the measured morphology features, a 3D grid model of mitigated pit is built, and the downstream light intensity distribution of the mitigated pit model under incident 351 nm laser is studied by scalar diffraction theory and fast fourier transform (FFT) methods. Results indicate that there are two kinds of downstream intensification: off-axis and on-axis intensifications. In the former intensification, the maximum intensity is located near the output surface of the optics and comes mainly from the depth of the mitigated pit; it increases with the depth. In the alter intensification, the maximum intensity is located far from the output surface of the optics and is mainly dependent on the height of the rim structure at the fringe of the mitigated damage pit; so it increase with increasing height. In addition, it is found that the location of the maximum off-axis or on-axis intensity can approach the output surface of the optics with increasing maximum intensity. For comparison, experimental measurements of downstream intensification induced by the mitigated pits are carried out, and the experimental results are almost consistent with the numerical simulation, implying the validity of the numerical simulation of the mitigated pit model. Results of this research indicate that the downstream intensification of mitigated pits can be suppressed by controlling the morphology features of mitigated pits. this is significant for the development and improvement of the mitigated techniques of damage optics.

Study on braking tribological behaviors of brake shoe material under the wet condition

The objective of this study is to investigate the influence of water on tribological braking behavior of brake shoe material using a sub-scale frictional braking machine. The results indicate that the friction coefficient of braking interface has a close relationship with the braking velocity and the pressure under the wet condition. The friction coefficient shows a reduction by 30% compared with the dry condition at low braking speed. With an increase in braking velocity, more water is thrown off from the braking interface. This makes the water film becomes thinner and the surfaces becomes closer, which results in more contact and more wear. Therefore, more friction heat is produced and more water is evaporated, which makes the water film thinner and the interface more similar to the dry. The water sealed up in the cracks leads to partial high pressure point on the surface resulting in serious pitting damage of brake shoe. Both the stability of friction coefficient and the wear loss under wet condition are worse than those under dry condition.

Optimum inductively coupled plasma etching of fused silica to remove subsurface damage layer

In this work, we introduce an optimum ICP etching technique that successfully removes the subsurface damage (SSD) layer of fused silica without causing plasma induced surface damage (PISD) or lateral etching of SSD. As one of the commonest PISD initiators, metal contamination from reactor chamber is prevented by employing a simple isolation device. Based on this device, a unique low-density pitting damage is discovered and subsequently eliminated by optimizing the etching parameters. Meanwhile etching anisotropy also improves a lot, thus preventing the lateral etching of SSD. Using this proposed technique, SSD layer of fused silica is successfully removed with a surface roughness of 0.23nm.

Elucidating trends in revision reverse total shoulder arthroplasty procedures: a retrieval study evaluating clinical, radiographic, and functional outcomes data

The purpose of this study was to explore relationships between damage modes in explanted reverse total shoulder arthroplasty (RTSA) components, patient and radiographic risk factors, and functional data to elucidate trends in RTSA failure. Fifty RTSA systems, retrieved from 44 patients, with 50 polyethylene (PE) liners, 30 glenospheres, 21 glenoid baseplates, 13 modular humeral metaphases, and 17 humeral stems, were examined for damage modes, including abrasion, burnishing, dishing, embedding, scratching, and pitting. PE liners were also analyzed for delamination and edge deformation. Charts were reviewed for patient, surgical, and functional data. Pre-revision radiographs were analyzed for scapular notching and loosening. Average term of implantation was 20 months (range, 0-81 months). Metallic components exhibited abrasion, burnishing, dishing, pitting, and scratching. PE liners displayed all damage modes. Damage was exhibited on 93% of glenospheres and 100% of PE liners. Of 29 aseptic shoulders, 13 showed evidence of scapular notching and 5 of humeral loosening. There was a moderate correlation between radiographically observed implant failure or dissociation and PE embedding (r = 0.496; P < .001). There were weak and moderate correlations between scapular notching severity and PE dishing (r = 0.496; P = .006), embedding (r = 0.468; P = .010), and delamination (r = 0.384; P = .040). To date, this is the largest series of retrieved RTSA components and the first to relate damage modes to radiographic and clinical data. Most damage was observed on the PE liners, on both the articular surface and rim, and glenosphere components. Correlation of retrieval findings with radiographic and clinical data may help establish predictors of prostheses at risk for failure.

Managing Bitter Pit in ‘Honeycrisp’ Apples Grown in the Mid-Atlantic United States with Foliar-applied Calcium Chloride and Some Alternatives

Three separate experiments were conducted to test standard calcium chloride salt (CaCl2) rates and several new formulations of calcium (Ca) for amelioration of bitter pit, a Ca-related physiological disorder that affects fruit of many apple (Malus ×domestica) cultivars, including the popular cultivar Honeycrisp. Even small amounts of bitter pit damage make apples unmarketable. We evaluated various formulations of Ca to compare their effectiveness in controlling bitter pit, including proprietary Ca products (InCa™, Sysstem-Cal™, Vigor-Cal™, XD10, and XD505) with and without antitranspirant. Calcium chloride is the most common Ca product used to reduce bitter pit incidence, but it has negative impacts, such as phytotoxicity and corrosiveness. Of the products that were tested in 2011, XD10 at the high rate and XD505 are candidates for future study. In 2012, both the CaCl2 and XD10 treatments had lower bitter pit severity than the nontreated control, but only the CaCl2 treatments had a lower total percentage of fruit with bitter pit compared with the control. The antitranspirant reduced bitter pit incidence in one of three treatments. Full season Ca treatments and higher rates (up to 23.5 lb/acre per season of elemental Ca) are needed to significantly reduce bitter pit incidence in ‘Honeycrisp’ apples in the mid-Atlantic United States.

Corrosion pitting damage detection of rolling bearings using data mining techniques

Detection of rolling bearings is very crucial for the reliable operation in the process of condition monitoring of rotating machinery. In this paper, a novel monitoring method using support vector data description (SVDD) with principal component analysis (PCA) for fault diagnosis of corrosion pitting on the raceways and balls in rolling bearings is proposed to improve diagnostic accuracy based on feature extraction dataset of vibration signals. The feasibility and validity of the proposed monitoring scheme are investigated through case study. Experiment results show that the proposed method can achieve 92.85% accuracy, 93.11% sensitivity, and 90.47% specificity based on an imbalanced dataset.

Potential role of the lectin pathway of complement in the pathogenesis and disease manifestations of systemic sclerosis: a case-control and cohort study.

IntroductionRepetitive episodes of ischemia and reperfusion (I/R) are a cardinal feature of the pathogenesis of systemic sclerosis (SSc), which precedes tissue fibrosis. The complement system is a key mediator of tissue damage after I/R, primarily by activation of the lectin pathway. This study investigated whether serum levels and polymorphisms of mannose-binding lectin (MBL) and ficolin-2 (FCN2), two pattern recognition receptors of the lectin pathway, are associated with the predisposition to and clinical features of SSc.MethodsA case-control study was undertaken involving 90 patients with SSc from a single SSc outpatient clinic and 90 age- and sex-matched blood donors. MBL and FCN2 levels and polymorphisms were measured in both groups, and in cases correlated with clinical data.ResultsMBL levels and genotypes were equally distributed in cases and controls while there were some significant differences in FCN2 polymorphisms. Median MBL levels were higher in SSc cases with diffuse disease compared with controls (2.6 versus 1.0 μg/ml, P <0.001).In cases, higher MBL levels were associated with the presence of clinical findings associated with vascular dysfunction and local tissue damage (digital ulcers, calcinosis and pitting). Moreover, MBL levels were associated with fibrotic disease manifestations as evidenced by the presence of diffuse disease (median 2.6 versus 0.8 μg/ml, P = 0.002), the modified Rodnan skin score (r = 0.39, P <0.001), and interstitial lung disease as measured by forced vital capacity (r = −0.33, P = 0.001). Importantly, MBL levels also correlated with the Scleroderma Health Assessment Questionnaire scores (r = 0.33, P = 0.002). The results for FCN2 levels were less striking. Phenotypic MBL results were largely confirmed by analysis of MBL polymorphisms. MBL levels were not associated with the presence of autoantibodies or hypocomplementaemia.ConclusionsOverall, predisposition to SSc was not influenced by the lectin pathway of complement in our matched case-control study. However, our preliminary data suggest that MBL, and to a lesser extent FCN2, may modulate disease manifestations of SSc, particularly in diffuse cutaneous disease.Electronic supplementary materialThe online version of this article (doi:10.1186/s13075-014-0480-6) contains supplementary material, which is available to authorized users.

Electrochemical behaviour of TiO 2 reinforced Al 7075 composite

Microstructures of sintered Al 7075 alloy and Al 7075 alloy reinforced with varying TiO2 composites exhibited uniform distribution of TiO2 particles, but clustering and porosity have increased with TiO2 content. TEM micrographs of the Al 7075 alloy and Al 7075 + TiO2 composite of peak aged T6 (PA) temper showed some coarse and numerous very fine η′ (MgZn2) precipitates, and equilibrium η (MgZn2) precipitates along the grain boundaries. Potentiodynamic electrochemical polarisation studies on the Al 7075 alloy of different tempers and Al 7075 + TiO2 composites in 3.5 wt.% NaCl solution showed that the corrosion potentials (Ecorr) have shifted towards noble direction with the addition of TiO2, and there is an increase of corrosion current density (icorr) beyond 10 vol.% TiO2 in the composites. This is attributed to the increase in particle-matrix interface areas enhancing pitting corrosion. Optical micrographs of the corroded surface of 30% TiO2 composites exhibited maximum pitting damage.

Pitting detection in worm gearboxes with vibration analysis

Diagnostics of worm gearboxes are challenged by lack of research in this field; vibration analysis is rarely employed for the condition evaluation of worm gears due to the inherent challenges involved. However, these gears are commonly used in many applications such as escalators, mills and conveyors and significant cost may arise from their maintenance. This paper aims to apply various vibration analysis techniques to identify faults within worm gearboxes. The conditions of three different worm gearboxes were assessed. Various vibration signal analysis techniques including FM4*, and spectral kurtosis and enveloping were employed to identify the presence of defects within the worm gearboxes. The analysis techniques applied were able to present fault features which indicated high levels of scratching-induced vibration, confirming profile damage (pitting) of Gearbox A worm wheel teeth. Among the employed techniques; FM4* shows high response to the worm gears pitting. In addition the results show sensitivity to the direction of vibration measurement.

PRELIMINARY INQUIRY TO FORECAST APPLE STORAGE ABILITY ON THE BASE OF FRUIT CALCIUM CONTENT

The storage ability of apple fruit is determined by a number of biochemical and physiological processes (respiration, ethylene production, metabolism process of pectins, etc.). Besides these processes there is also the quality and quantity of calcium content. To determine the correlation between calcium content and storage ability of apples 4 apple cultivars were investigated – ‘Golden Spur’, ‘Golden Smooth’, ‘Reinette du Canada’ and ‘Liberty’. During the experiment the content of calcium - total content, in pectin’s and proteins, free and in solution, as well pH, weight and titrate acids of fruits were analyzed. It was determined that weight of fruits and calcium content had negative correlations r=-0.95±0,1. Regression has the following line y=13-0.05x for ‘Reinette du Canada’. Also, in the case of bitter pit damage of storage diseases calcium content in the damaged area is 5.5 mg/100 g while in the not-damaged area this is only 2.3 mg/100 g in the cultivar ‘Liberti’. According to research it was established that by calcium content in apple fruits at the beginning of storage it is possible to determine a proposed evidence of bitter pit damage – this content differs for cultivars and should be determined by experimental way according to cultivars.